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Responses of Agrostis capillaris to gaseous pollutants and wet nitrogen deposition
Agriculture Ecosystems & Enwronment ELSEVIER
Agriculture. Ecosystems and Environment 66 (1997) 89-99
Responses of Agrostis capillaris to gaseous pollutants and wet nitrogen deposition E.A. K u p c i n s k i e n e b T . W . A s h e n d e n a.* S.A. Bell a, T.G. W i l l i a m s a C.P. E d g e " C.R. Rafarel a " bzstitute of Terrestrial Ecology, Bangor Research Unit, University of Wales, Deiniol Road, Bangor, Gwvnedd LL57 2 UP, UK b Lithuanian Academy of Agriculture, Kaunas-Noreikiskes, 4324, Lithuania Accepted 11 February 1997
Abstract
Agrostis capillaris L. plants were exposed to combinations of gaseous pollutants and wet nitrogen mist in Solardome glasshouses. Gaseous pollution treatments were (a) charcoal-filtered air (control), (b) 10 ppb SO 2 + 10 ppb NO 2, (c) 20 ppb SO 2 + 20 ppb NO~, (d) 40 ppb SO 2 + 40 ppb NO 2. Within each Solardome, four plant blocks were allocated different wet deposition treatments which provided a North Wales maritime rain with the equivalent of 0, 20, 40 or 60 kg N per hectare per year without changes in hydrogen ion concentration. Progressive senescence of leaves in the gaseous pollution treatments correlated well with leaf dry weight data, showing increasing injury with time. Growth analysis was performed after 11, 13 and 15 weeks exposure to pollutants. Gaseous pollution treatments resulted in substantial reductions in leaf areas and dry weights of A. capillaris in both the 20 ppb SO~_+ 20 ppb NO 2 and the 40 ppb SO 2 + 40 ppb NO 2 treatments compared with the plants exposed to charcoal filtered air and the 10 ppb SO 2 + 10 ppb NO 2 treatment. Adverse effects of the gaseous pollution treatments were greater on shoots than roots. Additions of wet nitrogen caused reductions in the numbers of tillers and leaf areas of A. capillaris compared with plants with zero nitrogen application. There were no effects of wet nitrogen treatments on total plant dry weights but all nitrogen additions above zero application resulted in a reduction in root dry weights at the final harvest which was reflected in a decrease in root/shoot ratio in the 60 N treatment. © 1997 Elsevier Science B.V. Keywords." Nitrogen dioxide: Sulphur dioxide; Acidic pollutants; Gaseous pollutants; Wet nitrogen deposition: Ammonium nitrate: Agrostis capillaris; Grasses; Semi-natural vegetation; Growth
1. Introduction For the last 30 yr, wet and dry deposition of NO× and NHy has increased throughout Europe (Skef-
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fington and Wilson, 1988). Wet pollutant deposition may often be in excess of dry deposition in mountain regions such as some parts of Western England, Wales and Scotland. Deposition rates across the mountains of Snowdonia, U.K. are large due to the high annual rainfall, exceeding 4000 mm on the higher peaks (Reynolds et al., 1990). In addition, vegetation in upland areas is often cloaked by mist
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and cloud resulting in additional inputs of pollutants via occult deposition (Dollard et al., 1983). There have been numerous studies on the impacts of wet deposition on crop species but most of these, conducted with realistic (near-ambient) acidities have failed to demonstrate adverse effects on plant growth (Irving, 1983). However, Ashenden and Bell (1987) found 9-17% yield reductions in winter barley in response to the normal ambient pH range of rainfall of 3.5-4.5. Less research has been conducted on native plant species. However, in ecosystems which are naturally very low in nitrogen, wet deposition is considered to be of major importance and may lead to the disappearance of original characteristic species (Ellenberg, 1987; Hanson et al., 1989). Sulphur dioxide (SO 2) and nitrogen oxides (NO x) are the major pollutant gases in urban areas. Both are produced naturally, but present global emissions from human activity are approximately equal to those of natural ones (Logan, 1983; Moiler, 1984). The adoption of more effective dispersion mechanisms and cleaner processes over the past 40 yr has reduced the severity of pollution in urban areas and close to sources but this has led to increases of phytotoxic products in rural areas. Hence, assessments of the potential threat of pollutants to plants should be concentrated on investigations of the subtle effects of long-term exposures to the low concentrations of pollutants that are now typical of rural areas in industrialised countries. The majority of studies carried out world-wide within the field of air pollution research have concentrated on the effects of industrial pollutants on crop plants (e.g., Black and Unsworth, 1979: McLaughlin et al., 1979; Kropff et al., 1989). There have been some studies on the interaction of SO 2 + NO z gases (Ashenden and Mansfield, 1978; Irving et al., 1982; Pande and Mansfield, 1985; Darrall, 1989), NH 3 + NO 2 (Vanhove et al., 1992), SO 2 + 0 3 (McLeod and Skeffington, 1995), and more rarely of S O 2 + NO 2 + 0 3 (Reinert, 1984; Rao et al., 1988; Adaros et al., 1991). However, in many of these studies, plants were exposed to pollutant concentrations which were considerably higher than those expected even in heavily polluted environments or investigations were restricted to short-term (under one month) exposures (Wellburn et al., 1981; Rao et al., 1988; Conway and Pretty, 1991). Much less
information is available on the effects of pollutants on native plant species (see Ashmore et al., 1988), especially high-elevation grassland species which naturally receive large amounts of N mist. Similarly, the interactive impacts of wet and gaseous forms of pollutants on plants are largely unresearched (Ashenden et al., 1995, 1996a). The aim of the current study was to determine dose-response relationships for growth parameters during long-term studies on Agrostis capillaris, a major constituent of semi-natural acid to neutral grassland. The impacts of different concentrations of sulphur dioxide and nitrogen dioxide gases in combination with different quantities of wet nitrogen deposition (ammonium nitrate) were investigated. All wet nitrogen treatments were applied at the same pH to remove any confounding effects of changes in hydrogen ion concentration which has often been a feature of earlier studies on the impacts of wet deposition on vegetation.
2. Materials and methods
2.1. Plant material Seeds of A. capillaris L were sown in trays of John Innes No. 1 compost in mid-December. After 3 weeks, seedlings were transferred to 0.5-1 pots containing a low fertility soil. The soil was comprised of 3 parts of sterilised loam: 1 part grit with 1.54 g 1Vitax Q4 fertilizer (Vitax, Skemersdale, Lancashire). The fertilizer addition was calculated to be one half of that used for a John Innes No. 1 potting compost. 432 pots each containing one A. capillaris seedling were divided randomly into 16 equal groups with each group forming an experimental treatment.
2.2. Experimental exposures The exposure experiments were conducted in four hemispherical 'Solardome 1' glasshouses. The fumigation facilities and an assessment of operating performance have been fully reported elsewhere (Rafarel and Ashenden, 1991). Four groups of plants were placed in blocks in each of the 4 Solardomes. Treatment with gases started when the plants were 3.5 weeks old. Plants were exposed for up to 15 weeks
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to either charcoal-filtered air ( C F ) or C F supplem e n t e d with 3 concentrations o f pollutants - 10, 20, 40 ppb e a c h o f S O 2 and N O 2 (later referred as 00 ppb, 10 ppb, 20 ppb or 40 ppb treatments), respectively. L e v e l s o f pollutants in air s a m p l e d f r o m the d o m e s were m e a s u r e d using M o n i t o r Labs instruments m o d e l 8840 for N O x and a M e l o y S A 285 for S O 2. T h e four treatment blocks within each S o l a r d o m e were r a n d o m l y allocated different wet deposition treatments. T h e s e treatments started f r o m the fifth w e e k o f plant g r o w t h and were applied five days per week. T h e y were set to p r o v i d e a total wet deposition o f 50 m m w e e k t and were applied as mists with one 10-min episode per day using a hand held c o m p r e s s e d air sprayer to ensure e v e n distribution. R e p e a t e d assessments were carried out to ensure e v e n n e s s o f mist applications, using d u m m y blocks
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o f pots. A t weekends, supplementary watering was p r o v i d e d using d e i o n i z e d water. Solutions were m a d e f r o m d e i o n i z e d water by adding salts in quantities characteristic for a North W a l e s m a r i t i m e rain: 0.235 m g 1-~ NH4CI; 0.201 m g 1- l KC1; 3.266 m g 1-~ M g S O 4 . 7 H 2 0 ; 1.380 m g 1-1 CaCI 2 • 6 H 2 0 ; 6.177 m g 1-~ NaC1 and 0.722 m g 1-1 98% H 2 S O 4 (Reynolds et al., 1990). Control mist solution contained only maritime rain c o m p o n e n t s . E x p e r i m e n t a l mist solutions were prepared by adding a m m o n i u m nitrate to m a k e up concentrations corresponding to 20, 40 and 60 kg N h a - J yr -~ , referred to as 20, 40 and 60 N treatments. 2.3. G r o w t h m e a s u r e m e n t s
Plants were assessed for s y m p t o m s o f visual injury at w e e k l y intervals throughout the experiment. Destructive harvests were c o n d u c t e d after 11, 13 and
Table 1 Numbers of tillers of A. capillaris after being exposed for 11, 13 and 15 weeks to different concentrations of SO2 + NO 2 and wet nitrogen applications Nitrogen additions kg ha- ~ y- t
Nitrogen treatment means
ppb SO 2 + NO 2 0
10
20
40
31.7 38.8 29.7 29.1 32.3 (P < 0.05).
26.3 26.9 23.4 25.2 25.5
29.6 31.8 18.1 29.1 29.7
33.2 28.7 42.0 35.8 34.9
58.8 23.2 33.8 43.7 39.9
51.2 37.1 41.6 41.1 42.7
After l 1 weeks
0 35.8 24.7 20 32.8 28.8 40 29.8 29.7 60 32.1 29.8 Gas treatment means 32.6 28.2 There were no significant differences between gas or nitrogen treatments After 13 weeks
0 20 40 60 Gas treatment means L.S.D. (P _<0.05) between gas treatments
50.9 61.9 42.0 54.3 40.2 50.2 48.7 36.4 45.4 50.7 or nitrogen treatments = 8.7.
After 15 weeks
0 42.0 52.6 45.4 51.7 47.9 20 39.4 39.9 38.8 42.8 40.2 40 41.1 50.6 37.4 41.6 42.7 60 28.4 33.1 37.4 37.3 34.1 Gas treatment means 37.8 44.0 39.8 43.3 41.2 L.S.D. (P _<0.05) between nitrogen treatments = 8.2. There were no significant differences between gas treatments (P < 0.05).
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15 weeks exposure to the different gas × mist treatments. On each occasion, nine replicate individuals of A. capillaris per treatment were taken and washed free of soil. Next, numbers of tillers were counted and plants were separated into roots, leaf blades and stems. The total plant leaf area was measured using a Digital Image Analysis System (DIAS) with conveyor belt. Dry weights of the harvested material were taken after drying for 24 h at 80°C. All of the data obtained were analysed by two-way analysis of variance with gases (levels of SO 2 + NO 2) and nitrogen treatments (wet deposition) as main effects.
3. Results Visual assessments of plant health revealed a general yellowing of A. capillaris leaves in the 20 and 40 ppb SO 2 + NOr treatments during the 12th week of exposure which was not modified in respect
to the different wet nitrogen regimes. There were no significant differences in the numbers of tillers between control and gaseous pollution treatments except for a transitory decrease in tillers in the 20 ppb treatment after 13 weeks ( P < 0 . 0 5 ; Table 1). In contrast, total leaf areas were reduced in the 40 ppb treatment by 27-38%, compared with control plants at all harvests (Table 2) and, in the 20 ppb treatment after 11 and 13 but not after 15 weeks. Wet nitrogen application had significant effects on tillering (Table 1). There were significant reductions ( P < 0.05) in the numbers of tillers for plants exposed to all nitrogen addition treatments after 13 weeks of exposure. However, after 15 weeks, this reduction in the numbers of tillers was only significant ( P < 0.05) for the 60 N treatment. All wet nitrogen additions resulted in decreases in leaf areas compared with plants with no added nitrogen after 15 weeks of exposure to experimental treatments (Table 2), but the effect was not significant for the 60 N treatment.
Table 2 Leaf areas of A. capillaris after being exposed for 11, 13 and 15 weeks to different concentrations of SO 2 + NO 2 and wet nitrogen applications Nitrogen additions kg h a - ~ y - t
Nitrogen treatment means
ppb SO 2 + NO 2
0
10
20
40
After 11 weeks 0 20 40 60 Gas treatment means L.S.D. ( P < 0.05) between gas treatments
90.7 114.4 69.6 91.6 91.6 118.6 104.9 69.7 86.9 95.1 78.2 121.5 77.0 58.4 83.8 118.0 111.0 79.7 53.5 90.6 101.4 113.0 74.0 72.6 90.2 = 21.5. There were no significant differences between nitrogen treatments ( P < 0.05).
After 13 weeks 0 20 40 60 Gas treatment means L.S.D. ( P < 0.05) between gas treatments
229.7 271. l 250.0 176.2 177.0 228.0 262.3 149.4 229.8 206.2 or nitrogen treatments = 31.7.
134.5 160.3 105.4 159.1 139.8
252.8 134.7 87.2 137.0 152.9
222.0 180.3 t 49.4 176.9 182.2
282.9 211.7 168.5 190.6 137.7 255.7 188.3 242.0 194.4 225.0 or nitrogen treatments = 32.0.
201.4 198.8 205.9 180.2 196.6
145.5 102.0 100.9 132.4 120.2
210.4 165.0 175.0 185.7 184.0
After 15 weeks 0 20 40 60 Gas treatment means L.S.D. ( P _< 0.05) between gas treatments
E.A. Kupcinskiene et al. / Agriculture, Ecosystems and Ent,ironment 66 (1997) 89-99 The effects of S O 2 + N O 2 on the dry w e i g h t fractions o f A. capillaris are s h o w n in Tables 3 - 5 . There w e r e significant reductions in the dry weights o f leaves o f A. capillaris of up to 4 8 % for the 40 ppb and 20 ppb pollution treatments c o m p a r e d with control plants. Similar significant ( P < 0.05) reductions ( 3 7 - 5 0 % ) were recorded for stem dry weights under the 40 ppb treatment for all three harvests and under 20 ppb treatment for the first two harvests ( P < 0.05). Reductions in shoot dry weights were a c c o m p a n i e d with significant ( P _< 0.05) reductions ( 1 8 - 3 9 % ) in root dry weights in both the 20 ppb and
93
40 ppb treatments at all harvests. The reductions in dry weights o f the different plant fractions were reflected in reductions in total plant dry weights o f A. capillaris e x p o s e d to both the 20 ppb and 40 ppb treatments c o m p a r e d with controls ( P < 0.05). At the final harvest total plant dry weights were reduced by 20% and 38%, in the 20 ppb and 40 ppb treatments respectively. There were no significant differences in dry w e i g h t fractions for plants e x p o s e d to the 10 ppb treatment c o m p a r e d with controls e x c e p t for transitory reductions in root and stem weights after 11 w e e k s exposure ( P < 0.05) which were not
Table 3 Dry weights (g) of fractions of A. capillaris after being exposed for 11 weeks to different concentrations of SO 2 + NO 2 and wet nitrogen applications Nitrogen additions kg ha- ~ y ~
Nitrogen treatment means
ppb SO2 + NO 2
0
10
20
40
0.26 0.22 0.28 0.28 0.26
0.30 0.28 0.22 0.14 0.24
LeaL,es 0 0.57 0.48 20 0.40 0.37 40 0.33 0.47 60 0.36 0.32 Gas treatment means 0.42 0.41 L.S.D. ( P < 0.05) between gas or nitrogen treatments = 0.09.
0.40 0.32 0.33 0.28
Stems 0 20 40 60 Gas treatment means L.S.D. (P _<0.05) between gas treatments
0.51 0.40 0.52 0.40 0.46 = 0.11. There
0.43 0.21 0.31 0.24 0.37 0.28 0.26 0.21 0.34 0.24 were no significant differences
0.30 0.37 0.34 0.33 0.26 0.36 0.13 0.25 0.26 between nitrogen treatments (P _<0.05).
0.75 0.56 0.64 0.68 0.66 = 0.10. There
0.58 0.43 0.58 0.52 0.55 0.43 0.44 0.53 0.54 0.48 were no significant differences
0.44 0.55 0.53 0.54 0.43 0.51 0.39 0.51 0.45 between nitrogen treatments ( P _<0.05).
1.83 1.37 1.50 1,43 1.53 = 0.26. There
1.49 0.90 1.26 0.98 1.39 0.99 1.02 1.02 1.29 0.97 were no significant differences
1.04 1.32 1.15 1.19 0.91 1.19 0.67 1.03 0.94 between nitrogen treatments (P < 0.05).
Roots 0 20 40 60 Gas treatment means L.S.D. ( P _< 0.05) between gas treatments Total plants 0 20 40 60 Gas treatment means L.S.D. ( P < 0.05) between gas treatments
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Table 4 Dry weights (g) of fractions of A. capillaris after being exposed for 13 weeks to different concentrations of SO z + NO~ and wet nitrogen applications Nitrogen additions kg ha- i y - t
Nitrogen treatment means
ppb SO 2 + NO 2 0
10
20
40
Leaves 0 0.72 20 0.78 40 0.49 60 0.59 Gas treatment means 0.65 L.S.D. ( P < 0.05) between gas treatments = 0.11. There
0.69 0.29 0.55 0.56 0.49 0.38 0.26 0.48 0.64 0.33 0.24 0.43 0.51 0.41 0.42 0.48 0.58 0.35 0.37 were no significant differences between nitrogen treatments P < 0.05).
Stems 0 0.97 0.87 0.36 0.85 0.76 20 1.08 0.72 0.56 0.49 0.71 40 0.67 1.08 0.48 0.35 0.65 60 0.86 0.69 0.65 0.56 0.69 Gas treatment means 0.90 0.84 0.51 0.56 L.S.D. ( P < 0.05) between gas treatments = 0.17. There were no significant differences between nitrogen treatments P < 0.05).
Roots 0 1.14 1.04 0.59 20 1.21 0.78 0.72 40 0.92 1.09 0.51 60 0.89 0.63 0.72 Gas treatment means 1.04 0.89 0.63 L.S.D. ( P < 0.05) between gas treatments = 0.15. There were no significant differences
0.90 0.92 0.59 0.83 0.52 0.76 0.88 0.78 0.72 between nitrogen treatments ( P < 0.05).
Total plants 0 2.83 2.60 1.25 2.29 2.24 20 3.07 1.99 1.65 1.34 2.01 40 2.08 2.82 1.32 1.11 1.83 60 2.34 1.82 1.78 1.86 1.95 Gas treatment means 2.58 2.31 1.50 1.65 L.S.D. ( P < 0.05) between gas treatments = 0.41. There were no significant differences between nitrogen treatments ( P < 0.05).
r e f l e c t e d in s i g n i f i c a n t d i f f e r e n c e s in d r y w e i g h t s o f total plants. G e n e r a l l y , t h e r e w e r e n o s i g n i f i c a n t effects o f w e t n i t r o g e n t r e a t m e n t s o n the d r y w e i g h t f r a c t i o n s o f A. capillaris. T h e o n l y e x c e p t i o n w a s a l o w e r root dry w e i g h t for all n i t r o g e n a d d i t i o n s a b o v e the c o n t r o l ( z e r o a p p l i c a t i o n ) at the final h a r v e s t ( P < 0.05). T h i s w a s n o t r e f l e c t e d in c h a n g e s in total p l a n t d r y w e i g h t s ( T a b l e 5). C a l c u l a t i o n s o f r o o t / s h o o t ratios r e v e a l e d that both SO 2 + NO 2 and wet nitrogen treatments caused shifts in the p a r t i t i o n i n g o f a s s i m i l a t e s ( T a b l e 6). T h e r e w a s a t e n d e n c y for r o o t / s h o o t ratios to inc r e a s e w i t h i n c r e a s i n g c o n c e n t r a t i o n s o f S O 2 + N O 2.
T h i s r e s u l t e d in s i g n i f i c a n t l y ( P < 0 . 0 5 ) higher r o o t / s h o o t ratios in the 4 0 p p b S O 2 + N O 2 treatm e n t in c o m p a r i s o n to c o n t r o l p l a n t s for all h a r v e s t s . F o r w e t n i t r o g e n a p p l i c a t i o n s , t h e r e w a s a n initial i n c r e a s e (11 w e e k s ) a n d t h e n a d e c r e a s e (15 w e e k s ) in r o o t / s h o o t ratios o f A. capillaris in the 60 N t r e a t m e n t c o m p a r e d w i t h p l a n t s w i t h zero n i t r o g e n a p p l i c a t i o n ( P < 0.05).
4. Discussion
It is c l e a r f r o m the data p r e s e n t e d t h a t e x p o s u r e to N O 2 + S O 2 m a y h a v e a d v e r s e e f f e c t s o n the g r o w t h
E.A. Kupcinskiene et al. / Agriculture, Ecosystems and Ent'ironment 66 (1997) 89-99
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Table 5 Dry weights (g) of fractions of A. capillaris after being exposed for 15 weeks to different concentrations of SO, + NO, and wet nitrogen applications Nitrogen additions kg h a - i y I
Nitrogen treatment means
ppb SO_, + NO 2
0
10
20
40
teat~es 0 20 40 60 Gas treatment means L.S.D. (P _< 0.05) between gas treatments
0.69 0.51 0.55 0.65 0.60 = 0.11. There
0.46 0.45 0.55 0.50 0.61 0.48 0.64 0.45 0.56 0.47 were no significant differences
0.40 0.50 0.28 0.46 0.28 0.48 0.27 0.50 0.31 between nitrogen treatments ( P < 0.05).
0 1.73 2.01 1.04 20 1.13 1.47 1.50 40 1.17 1.70 1.34 60 1.58 1.71 1.22 Gas treatment means 1.40 1.72 1.27 L.S.D. (P _< 0.05) between gas treatments = 0.29. There were no significant differences
1.15 1.48 0.73 1.21 0.68 1.22 0.88 1.35 0.86 between nitrogen treatments ( P < 0.05).
Stems
Roots 0 20 40 60 Gas treatment means L.S.D. ( P _< 0.05) between gas or nitrogen
1.62 1.61 1.27 1.09 1.18 1.14 1.07 1.04 1.29 1.22 treatments = 0.21.
0.88 1.04 0.90 0.74 0.89
0.99 0.94 0.64 0.80 0.84
1.28 1.08 0.97 0.91
Total plants 0 4.04 20 2.90 40 2.90 60 3.29 Gas treatment means 3.28 L.S.D. ( P < 0.05) between gas treatments = 0.44. There
4.08 2.37 3.10 3.04 3.45 2.73 3.38 2.41 3.50 2.64 were no significant differences
of A. capillaris. Visible symptoms of injury in the form of chlorosis was recorded in the 20 and 40 ppb gas treatments after the 12th week of exposure. This occurred after growth analysis data had already revealed decline in growth at the harvest after 11 weeks when plants did not have any visible signs of injury. These symptoms of leaf injury were not associated with any reductions in the numbers of tillers except for a transitory decrease in the 20 ppb treatment after the 13 weeks ( P < 0.05). This is in contrast to many earlier studies where reductions in tillering have been reported for crops fumigated with SO 2 (Baker et al., 1987; Wilson and Murray, 1990) and in other grasses exposed to NO 2 + SO 2 treat-
2.54 3.26 1.95 2,75 1.60 2.67 1.95 2.76 2.01 between nitrogen treatments (P < 0.05).
ments (Ashenden and Williams, 1980). Despite no reductions in tillers, there was a decrease in total leaf areas of A. capillaris exposed to the higher (20 and 40 ppb) SO 2 + NO 2 treatments. This would indicate a reduction in the numbers of leaves per tiller or the sizes of individual leaves. Many earlier studies have shown SO 2 + NO 2 to reduce leaf numbers in grasses (e.g., Ashenden and Williams, 1980) and SO 2 exposure to reduce total leaf area without changes in numbers of leaves or tillers (Ashenden and Mansfield, 1977). The reduced leaf areas for plants of A. capillaris exposed to both 20 and 40 ppb SO 2 + N O 2 t r e a t m e n t s were accompanied by reductions in the dry
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Table 6 Root/shoot ratios of A. capillaris after being exposed for l 1, 13 and 15 weeks to different concentrations of SO 2 + NO 2 and wet nitrogen applications Nitrogen additions kg ha-~ y t
Nitrogen treatment means
ppb SO 2 + NO 2 0
10
20
40
0.97 1.20 0.88 1.13 1.04
0.91 0.94 1.01 1.44 1.08
After 11 weeks 0 0.79 0.71 20 0.87 0.94 40 0.94 0.80 60 0.95 0.89 Gas treatment means 0.89 0.84 L.S.D. ( P < 0.05) between gas or nitrogen treatments = 0.16.
0.84 0.99 0.91 1.10
After 13 weeks 0 20 40 60 Gas treatment means L.S.D. ( P < 0.05) between gas treatments
0.73 0.66 0.92 0.76 0.77 0.68 0.75 0.86 0.81 0.77 0.87 0.69 0.67 0.91 0.79 0.67 0.59 0.70 0.93 0.72 0.74 0.67 0.79 0.85 = 0.10. There were no significant differences between nitrogen treatments ( P < 0.05).
After 15 weeks 0 0.74 0.66 20 0.82 0.54 40 0.75 0.51 60 0.50 0.46 Gas treatment means 0.70 0.54 L.S.D. ( P < 0.05) between gas or nitrogen treatments = 0.08.
0.60 0.57 0.57 0.46 0.55
0.68 1.01 0.69 0.74 0.78
0.67 0.73 0.63 0.54
weights of all plant fractions. At the final harvest, total plant dry weights compared with control plants were reduced by 20% and 38%, in the 20 ppb and 40 ppb treatments respectively. In contrast, plants in the 10 ppb SO 2 + NO 2 showed a slight stimulation in growth (not significant; P < 0.05) indicating that the threshold concentration for injury (critical level) of SO 2 + NO 2 for this species is between 10 and 20 ppb SO 2 + N O 2. This concentration is substantially lower than in a previous study where exposure to 40 ppb SOa + NO 2 for 22 weeks did not reduce shoot growth in A. capillaris (Ashenden et al., 1996a). However, in this earlier study, plants were grown on a nutrient rich potting compost rather than the relatively nutrient-poor soil used here. It is implied that plant sensitivities to SO 2 + NO 2 may be influenced by soil fertility. Supporting evidence comes from a recent screening study where high concentrations of SO 2 (100-300 ppb) were required to differentiate sensitivities of species growing in sand cultures with
non-limiting nutrient supplies (Ashenden et al., 1996b). Reductions in the dry weights of total plants and their separate parts could be caused by changes in physiological processes (Darrall, 1991; Saxe, 1991). Gaseous pollution treatments have been shown to cause significant reductions of net photosynthesis and stomatal conductance (Freer-Smith, 1985; Vanhove et al., 1992; Schenone et al., 1994). In addition, reduced weights of A. capillaris could be caused by respiratory losses of carbohydrates. In general, respiration has been found to increase in response to fumigation with gaseous pollutants. These changes are likely to reflect both the activity of injury repair and have a direct effect on the rate of maintenance respiration (Darrall, 1989; Saxe, 1991). In contrast to the effects of SO 2 + NO 2 gases, additions of wet nitrogen resulted in a reduction in the numbers of tillers of A. capillaris. Generally, this was reflected in a reduction in total leaf area but
E.A. Kupcinskiene et al. / Agriculture, Ecosystems and Environment 66 (1997) 89-99
no effects on total plant dry weights. In previous studies, wet deposition treatments with high levels of nitrogen have been found to reduce leaf production for a range of species (Irving, 1983; Edge et al., 1994) but these have usually been confounded by changes in hydrogen ion concentrations. Normally, additions of nitrogen as fertilisers for crops increase above ground productivity at the expense of the roots (INDITE, 1994). Nitrogen is a major nutrient, the supply of which is often the growth limiting factor in natural ecosystems (Ellenberg, 1987). In this investigation, nutrient-poor soils were used and, under such conditions, wet nitrogen additions might be expected to have a fertilising effect on growth. Indeed, earlier studies have shown substantial increases in growth for a range of species exposed to highly acidic rain/mist episodes (as low as pH 2.5) which have been attributed to the fertiliser effects of nitrogen and sulphur in treatment solutions (Ashenden et al., 1991; Edge et al., 1994). However, nitrogen demands of species vary considerably and are much lower for semi-natural communities (INDITE, 1994). Also, an increase in nitrogen supply may cause a relative shortage of other nutrients. Jeffrey and Pigott (1973) found no effect of nitrogen alone on grassland, but did find changes in abundance of grasses when nitrogen and phosphorus were added in combination. Similarly, increased inputs of nitrogen have been found to result in shortages of other nutrients and result in the disruption of nutrient relations in trees (Nambiar and Fife, 1987). While dry weights of all plant fractions were depressed in response to the 20 ppb and 40 ppb SO 2 + NO 2 treatments, the effects were greater on shoots than roots. This resulted in an increase in root/shoot ratio for A. capillaris exposed to the 40 ppb treatment. This observation conflicts with the results of many earlier studies where a proportionately greater reduction in root compared with shoot growth in response to gaseous pollutants has been reported for other species (Ashenden and Mansfield, 1978; Lucas, 1990). The reduction in root growth at the expense of shoot growth has been attributed to a reduced translocation of assimilates from leaves of polluted plants (Mansfield, 1988) which clearly did not occur in A. capillaris in this investigation. The effects of wet nitrogen applications on assimilate partitioning in A. capillaris changed with time.
97
Initially, there was an increase in root/shoot ratio for plants exposed to the 60 N compared with the zero N application. However, at the final harvest, the response was reversed with plants at 60 N having a reduced root/shoot ratio compared with controls. Thus it appears that assimilate partitioning in response to wet nitrogen applications alters with age and the stage of plant development. The resulting reduction in the proportion of roots to shoots, if maintained, would make plants more susceptible to drought at later stages of development. A. capillaris is an abundant and widely distributed species throughout Europe. It is the dominant species in large areas of poorer permanent grassland, particularly in upland regions which are characterised by acidic shallow soils and high inputs of pollutant nitrogen in wet deposition. Thus the indication that sensitivity to SO~ + NO~ gases may be increased for plants growing on less fertile soils and that increased deposition of wet nitrogen may reduce leaf canopy development may have important implications for A. capillaris. Both these responses may be expected to alter its competitive ability in mixed swards. Other less sensitive species might gain a competitive advantage. In polluted environments, this could result in changes in the vegetation structure of poorer grasslands.
Acknowledgements This work was partly funded by the UK Department of the Environment ( P E C D 7 / 1 2 / 2 3 ) and the Welsh Office (WEP100/12/1). E.A.K. was funded by a grant from the Central European University, Budapest.
References Adaros, G., Weigel, H.J., £iger, H.J., 1991. Concurrent exposure to SO 2 a n d / o r NO 2 alters growth and yield responses of wheat and barley to low concentrations of O~. New Phytol. 118, 581-591. Ashenden, T.W., Bell, S.A., 1987. Yield reductions in winter barley grown on a range of soil and exposed to simulated rain. Plant and Soil 98, 433-,437.
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Ashenden, T.W., Bell, S.A., Rafarel, C.R., 1991. Exposures of two upland plant species to acidic fogs. Environ. Pollut. 74, 217-225. Ashenden, T.W., Bell, S.A., Rafarel, C.R., 1995. Responses of white clover to gaseous pollutants and acid mist: implications for setting critical levels and loads. New Phytol. 130, 89-90. Ashenden, T.W., Bell, S.A., Rafarel, C.R., 1996a. Interactive effects of gaseous air pollutants and acid mist on two major pasture grasses. Agric. Ecosyst. Environ. 57, 1-8. Ashenden, T.W., Hunt, R., Bell, S.A., Williams, T.G., Mann, A., Booth, R.E., Poorter, L., 1996b. Responses to SO 2 pollution in 41 British herbaceous species. Funct. Ecol. 10, 483-490. Ashenden, T.W., Mansfield, T.A., 1977. Influence of wind speed on the sensitivity of ryegrass to SO 2. J. Exp. Bot. 28, 729-735. Ashenden, T.W., Mansfield, T.A., 1978. Extreme pollution sensitivity of grasses when SO 2 and NO 2 are present in the atmosphere together. Nature, Lond. 273, 142-143. Ashenden, T.W., Williams, I.A.D., 1980. Growth reductions in Lolium multiflorum Lam. and Phleum pratense L. as a result of SO 2 and NO 2 pollution. Environ. Pollut. A21, 131-139. Ashmore, M.R., Bell, J.N.B., Garretty, C., (Eds.) 1988. Acid Rain and Britain's Natural Ecosystems. Imperial College Centre for Environmental Technology, London. Baker, C.K., Fullwood, A.E., Coils, J.J., 1987. Tillering and leaf area of winter barley exposed to sulphur dioxide in the field. New Phytol. 107, 373-385. Black, V.J., Unsworth, M.H., 1979. Effects of low concentrations of sulphur dioxide on net photosynthesis and dark respiration of Viciafaba. J. Exp. Bot. 30, 473-483. Conway, G., Pretty, J.N., 1991. Unwelcome harvest: Agriculture and Pollution. Earthscan, pp. 377-443. Darrall, N.M., 1989. The effect of air pollutants on physiological processes in plants. Plant, Cell Environ. 12, 1-30. Darrall, N.M., 1991. Changes in net photosynthesis, transpiration and dark respiration in winter barley exposed to elevated levels of sulphur-dioxide using an open-air fumigation system. Agric. Ecosyst. Environ. 33, 309-324. Dollard, G.J., Unsworth, M.H., Harvey, M.J., 1983. Pollutant transfer in upland regions by occult precipitation. Nature, Lond. 302, 241-243. Edge, C.P., Bell, S.A., Ashenden, T.W., 1994. Contrasting growth responses of herbaceous species to acidic fogs. Agric. Ecosyst. Environ. 51,293-299. Ellenberg, H., 1987. Floristic changes due to eutrophication. In Ammonia and Acidification, Proc. EUROSAP Symposium, Asman, W.A.H., Diederen, S.M.A., (Eds.), Bilthoven, The Netherlands, pp. 301-305. Freer-Smith, P.H., 1985. The influence of SO 2 and NO~ on the growth development and gas exchange of Betula pendula Roth. New Phytol. 99, 417-430. Hanson, P.J., Rott, K., Taylor, G.E. Jr., Gunderson, C.A., Lindberg, S.E., Ross-Todol, B.M., 1989. NO 2 deposition to elements representative of a forest landscape. Atmos. Environ. 23, 1783-1794. INDITE, 1994. Impacts of Nitrogen Deposition on Terrestrial Ecosystems. United Kingdom Review Group on Impacts of Atmospheric Nitrogen, London,
Irving, P.M., Miller, J.E., Xerikos, P.B., 1982. The effect of NO 2 and SO 2 alone and in combination on the productivity of field-grown soybeans. In: Air Pollution by Nitrogen Oxides, Schneider, T., Grant, L., (Eds.), pp. 521-531. Elsevier, Amsterdam. Irving, P.M., 1983. Acidic precipitation on crops: a review and analysis of research. J. Environ. Qual. 12, 442-453. Jeffrey, D.W., Pigott, C.D., 1973. The response of grasslands on sugar limestone in Teesdale to application of phosphorus and nitrogen. J. Ecol. 61, 85-92. Kropff, M.J., Mooi, J., Goudriaan, J., Smeets, W., Leeman, A., Kliffen, C., 1989. The effects of long-term open-air fumigation with SO 2 on a field crop of broad bean (Viciafaba L.) II. Effects on growth components, leaf area, development and elemental composition. New Phytol. 113, 345-351. Logan, J.A., 1983. Nitrogen oxides in the troposphere: global and regional budgets. J. Geophys. Res. 88, 785-807. Lucas, P.W., 1990. The effects of prior exposure to sulphur dioxide and nitrogen dioxide on the water relations of Timothy grass (Phleum pratense) under drought conditions. Environ. Pollut. 66, 117-138. Mansfield, T.A., 1988. Factors determining root shoot partitioning. In: Cape, J.N., Mathy, P., (Eds.). Scientific Basis of Forest Decline Symptomatology, Brussels: Report No 15 COST/CEC, pp. 171-181. McLaughlin, S.B., Shriner, D.S., McConathy, R.K., Manning, W.J., 1979. The effects of SO 2 dosage kinetics and exposure frequency on photosynthesis and transpiration of kidney beans (Phaseolus t,ulgaris L.). Environ. Exper. Bot. 19, 183-191. McLeod, A.R., Skeffington, R.A., 1995. The Liphook Forest Fumigation Project: an overview. Plant, Cell Environ. 18, 327-335. Moller, D., 1984. Estimation of the global man-made sulphur emission. Atmos. Environ. 18, 19-27. Nambiar, E.K.S., Fife, D.N., 1987. Growth and nutrition retranslocation in needles of Radiata pine in relation to nitrogen supply. Ann. Bot. 60, 147-156. Pande, P.C., Mansfield, T.A., 1985. Responses of winter barley to SO 2 and NO 2 alone and in combination. Environ. Pollut. 39, 281-291. Rafarel, C.R., Ashenden, T.W., 1991. A facility for the large-scale exposure plants to gaseous atmospheric pollutants. New Phytol. 117, 345-349. Rao, D.N., Agrawal, M., Nandi, P.K., 1988. Air pollutant mixtures and their effects on plants: a review. Perspectives in Environ. Bot. 2, 217-249. Reinert, R.A., 1984. Plant response to air pollutant mixtures. Ann, Rev. Phytopathol. 22, 421-442. Reynolds, B., Williams, T.G., Stevens, P.A., 1990. The chemical composition of bulk precipitation across the mountains of Snowdonia U.K. Sci. Total Environ. 92, 223-234. Saxe, H., 1991. Photosynthesis and stomatal responses to polluted air, and the use of physiological and biochemical responses for early detection and diagnostic tools. Adv. Bot. Res. 18, 2-126. Schenone, G., Fumagalli, I., Mignanego, L., Montinaro, F., Soldatini, G.F., 1994. Effects of ambient air-pollution in open-top chambers on bean (Phaseolus vulgaris L.). 2. Effects on
E.A. Kupcinskiene et al. /Agriculture, Ecosystems and Enl,ironment 66 (1997) 89 99 photosynthesis and stomatal conductance. New Phytol. 126, 309-315 Skeffington, R.A., Wilson, E.J., 1988. Excess Nitrogen Deposition: Issues for Consideration. Environ. Pollut. 54, 159-184. Vanhove, L.W.A., Bossen, M.E., Mensink, M.G.J., Vankooten, O.. 1992. Physiological-effects of a long-term exposure to low concentrations of NH 3, SO, and NO 2 on Douglas-fir (Pseudotsuga menziesii). Physiologia Plant 86, 559-567.
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Wellbum, A.R., Higginson, L., Robinson, D., Walmsley, C., 1981. Biochemical explanations of more than additive levels of SO 2 and NO 2 upon plants. New Phytol. 88, 223-237. Wilson, S.A., Murray, F., 1990. SO2-induced growth reductions and sulphur accumulation in wheat. Environ. Pollut. 66. 179191.
Agriculture. Ecosystems and Environment 66 (1997) 89-99
Responses of Agrostis capillaris to gaseous pollutants and wet nitrogen deposition E.A. K u p c i n s k i e n e b T . W . A s h e n d e n a.* S.A. Bell a, T.G. W i l l i a m s a C.P. E d g e " C.R. Rafarel a " bzstitute of Terrestrial Ecology, Bangor Research Unit, University of Wales, Deiniol Road, Bangor, Gwvnedd LL57 2 UP, UK b Lithuanian Academy of Agriculture, Kaunas-Noreikiskes, 4324, Lithuania Accepted 11 February 1997
Abstract
Agrostis capillaris L. plants were exposed to combinations of gaseous pollutants and wet nitrogen mist in Solardome glasshouses. Gaseous pollution treatments were (a) charcoal-filtered air (control), (b) 10 ppb SO 2 + 10 ppb NO 2, (c) 20 ppb SO 2 + 20 ppb NO~, (d) 40 ppb SO 2 + 40 ppb NO 2. Within each Solardome, four plant blocks were allocated different wet deposition treatments which provided a North Wales maritime rain with the equivalent of 0, 20, 40 or 60 kg N per hectare per year without changes in hydrogen ion concentration. Progressive senescence of leaves in the gaseous pollution treatments correlated well with leaf dry weight data, showing increasing injury with time. Growth analysis was performed after 11, 13 and 15 weeks exposure to pollutants. Gaseous pollution treatments resulted in substantial reductions in leaf areas and dry weights of A. capillaris in both the 20 ppb SO~_+ 20 ppb NO 2 and the 40 ppb SO 2 + 40 ppb NO 2 treatments compared with the plants exposed to charcoal filtered air and the 10 ppb SO 2 + 10 ppb NO 2 treatment. Adverse effects of the gaseous pollution treatments were greater on shoots than roots. Additions of wet nitrogen caused reductions in the numbers of tillers and leaf areas of A. capillaris compared with plants with zero nitrogen application. There were no effects of wet nitrogen treatments on total plant dry weights but all nitrogen additions above zero application resulted in a reduction in root dry weights at the final harvest which was reflected in a decrease in root/shoot ratio in the 60 N treatment. © 1997 Elsevier Science B.V. Keywords." Nitrogen dioxide: Sulphur dioxide; Acidic pollutants; Gaseous pollutants; Wet nitrogen deposition: Ammonium nitrate: Agrostis capillaris; Grasses; Semi-natural vegetation; Growth
1. Introduction For the last 30 yr, wet and dry deposition of NO× and NHy has increased throughout Europe (Skef-
* Corresponding author. Tel.: +44 (0) 1248 370045; Fax: +44 (0) 1248 35565; E-mail: [email protected]
fington and Wilson, 1988). Wet pollutant deposition may often be in excess of dry deposition in mountain regions such as some parts of Western England, Wales and Scotland. Deposition rates across the mountains of Snowdonia, U.K. are large due to the high annual rainfall, exceeding 4000 mm on the higher peaks (Reynolds et al., 1990). In addition, vegetation in upland areas is often cloaked by mist
0167-8809/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PII S01 6 7 - 8 8 0 9 ( 9 7 ) 0 0 0 5 2 - 2
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and cloud resulting in additional inputs of pollutants via occult deposition (Dollard et al., 1983). There have been numerous studies on the impacts of wet deposition on crop species but most of these, conducted with realistic (near-ambient) acidities have failed to demonstrate adverse effects on plant growth (Irving, 1983). However, Ashenden and Bell (1987) found 9-17% yield reductions in winter barley in response to the normal ambient pH range of rainfall of 3.5-4.5. Less research has been conducted on native plant species. However, in ecosystems which are naturally very low in nitrogen, wet deposition is considered to be of major importance and may lead to the disappearance of original characteristic species (Ellenberg, 1987; Hanson et al., 1989). Sulphur dioxide (SO 2) and nitrogen oxides (NO x) are the major pollutant gases in urban areas. Both are produced naturally, but present global emissions from human activity are approximately equal to those of natural ones (Logan, 1983; Moiler, 1984). The adoption of more effective dispersion mechanisms and cleaner processes over the past 40 yr has reduced the severity of pollution in urban areas and close to sources but this has led to increases of phytotoxic products in rural areas. Hence, assessments of the potential threat of pollutants to plants should be concentrated on investigations of the subtle effects of long-term exposures to the low concentrations of pollutants that are now typical of rural areas in industrialised countries. The majority of studies carried out world-wide within the field of air pollution research have concentrated on the effects of industrial pollutants on crop plants (e.g., Black and Unsworth, 1979: McLaughlin et al., 1979; Kropff et al., 1989). There have been some studies on the interaction of SO 2 + NO z gases (Ashenden and Mansfield, 1978; Irving et al., 1982; Pande and Mansfield, 1985; Darrall, 1989), NH 3 + NO 2 (Vanhove et al., 1992), SO 2 + 0 3 (McLeod and Skeffington, 1995), and more rarely of S O 2 + NO 2 + 0 3 (Reinert, 1984; Rao et al., 1988; Adaros et al., 1991). However, in many of these studies, plants were exposed to pollutant concentrations which were considerably higher than those expected even in heavily polluted environments or investigations were restricted to short-term (under one month) exposures (Wellburn et al., 1981; Rao et al., 1988; Conway and Pretty, 1991). Much less
information is available on the effects of pollutants on native plant species (see Ashmore et al., 1988), especially high-elevation grassland species which naturally receive large amounts of N mist. Similarly, the interactive impacts of wet and gaseous forms of pollutants on plants are largely unresearched (Ashenden et al., 1995, 1996a). The aim of the current study was to determine dose-response relationships for growth parameters during long-term studies on Agrostis capillaris, a major constituent of semi-natural acid to neutral grassland. The impacts of different concentrations of sulphur dioxide and nitrogen dioxide gases in combination with different quantities of wet nitrogen deposition (ammonium nitrate) were investigated. All wet nitrogen treatments were applied at the same pH to remove any confounding effects of changes in hydrogen ion concentration which has often been a feature of earlier studies on the impacts of wet deposition on vegetation.
2. Materials and methods
2.1. Plant material Seeds of A. capillaris L were sown in trays of John Innes No. 1 compost in mid-December. After 3 weeks, seedlings were transferred to 0.5-1 pots containing a low fertility soil. The soil was comprised of 3 parts of sterilised loam: 1 part grit with 1.54 g 1Vitax Q4 fertilizer (Vitax, Skemersdale, Lancashire). The fertilizer addition was calculated to be one half of that used for a John Innes No. 1 potting compost. 432 pots each containing one A. capillaris seedling were divided randomly into 16 equal groups with each group forming an experimental treatment.
2.2. Experimental exposures The exposure experiments were conducted in four hemispherical 'Solardome 1' glasshouses. The fumigation facilities and an assessment of operating performance have been fully reported elsewhere (Rafarel and Ashenden, 1991). Four groups of plants were placed in blocks in each of the 4 Solardomes. Treatment with gases started when the plants were 3.5 weeks old. Plants were exposed for up to 15 weeks
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to either charcoal-filtered air ( C F ) or C F supplem e n t e d with 3 concentrations o f pollutants - 10, 20, 40 ppb e a c h o f S O 2 and N O 2 (later referred as 00 ppb, 10 ppb, 20 ppb or 40 ppb treatments), respectively. L e v e l s o f pollutants in air s a m p l e d f r o m the d o m e s were m e a s u r e d using M o n i t o r Labs instruments m o d e l 8840 for N O x and a M e l o y S A 285 for S O 2. T h e four treatment blocks within each S o l a r d o m e were r a n d o m l y allocated different wet deposition treatments. T h e s e treatments started f r o m the fifth w e e k o f plant g r o w t h and were applied five days per week. T h e y were set to p r o v i d e a total wet deposition o f 50 m m w e e k t and were applied as mists with one 10-min episode per day using a hand held c o m p r e s s e d air sprayer to ensure e v e n distribution. R e p e a t e d assessments were carried out to ensure e v e n n e s s o f mist applications, using d u m m y blocks
91
o f pots. A t weekends, supplementary watering was p r o v i d e d using d e i o n i z e d water. Solutions were m a d e f r o m d e i o n i z e d water by adding salts in quantities characteristic for a North W a l e s m a r i t i m e rain: 0.235 m g 1-~ NH4CI; 0.201 m g 1- l KC1; 3.266 m g 1-~ M g S O 4 . 7 H 2 0 ; 1.380 m g 1-1 CaCI 2 • 6 H 2 0 ; 6.177 m g 1-~ NaC1 and 0.722 m g 1-1 98% H 2 S O 4 (Reynolds et al., 1990). Control mist solution contained only maritime rain c o m p o n e n t s . E x p e r i m e n t a l mist solutions were prepared by adding a m m o n i u m nitrate to m a k e up concentrations corresponding to 20, 40 and 60 kg N h a - J yr -~ , referred to as 20, 40 and 60 N treatments. 2.3. G r o w t h m e a s u r e m e n t s
Plants were assessed for s y m p t o m s o f visual injury at w e e k l y intervals throughout the experiment. Destructive harvests were c o n d u c t e d after 11, 13 and
Table 1 Numbers of tillers of A. capillaris after being exposed for 11, 13 and 15 weeks to different concentrations of SO2 + NO 2 and wet nitrogen applications Nitrogen additions kg ha- ~ y- t
Nitrogen treatment means
ppb SO 2 + NO 2 0
10
20
40
31.7 38.8 29.7 29.1 32.3 (P < 0.05).
26.3 26.9 23.4 25.2 25.5
29.6 31.8 18.1 29.1 29.7
33.2 28.7 42.0 35.8 34.9
58.8 23.2 33.8 43.7 39.9
51.2 37.1 41.6 41.1 42.7
After l 1 weeks
0 35.8 24.7 20 32.8 28.8 40 29.8 29.7 60 32.1 29.8 Gas treatment means 32.6 28.2 There were no significant differences between gas or nitrogen treatments After 13 weeks
0 20 40 60 Gas treatment means L.S.D. (P _<0.05) between gas treatments
50.9 61.9 42.0 54.3 40.2 50.2 48.7 36.4 45.4 50.7 or nitrogen treatments = 8.7.
After 15 weeks
0 42.0 52.6 45.4 51.7 47.9 20 39.4 39.9 38.8 42.8 40.2 40 41.1 50.6 37.4 41.6 42.7 60 28.4 33.1 37.4 37.3 34.1 Gas treatment means 37.8 44.0 39.8 43.3 41.2 L.S.D. (P _<0.05) between nitrogen treatments = 8.2. There were no significant differences between gas treatments (P < 0.05).
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15 weeks exposure to the different gas × mist treatments. On each occasion, nine replicate individuals of A. capillaris per treatment were taken and washed free of soil. Next, numbers of tillers were counted and plants were separated into roots, leaf blades and stems. The total plant leaf area was measured using a Digital Image Analysis System (DIAS) with conveyor belt. Dry weights of the harvested material were taken after drying for 24 h at 80°C. All of the data obtained were analysed by two-way analysis of variance with gases (levels of SO 2 + NO 2) and nitrogen treatments (wet deposition) as main effects.
3. Results Visual assessments of plant health revealed a general yellowing of A. capillaris leaves in the 20 and 40 ppb SO 2 + NOr treatments during the 12th week of exposure which was not modified in respect
to the different wet nitrogen regimes. There were no significant differences in the numbers of tillers between control and gaseous pollution treatments except for a transitory decrease in tillers in the 20 ppb treatment after 13 weeks ( P < 0 . 0 5 ; Table 1). In contrast, total leaf areas were reduced in the 40 ppb treatment by 27-38%, compared with control plants at all harvests (Table 2) and, in the 20 ppb treatment after 11 and 13 but not after 15 weeks. Wet nitrogen application had significant effects on tillering (Table 1). There were significant reductions ( P < 0.05) in the numbers of tillers for plants exposed to all nitrogen addition treatments after 13 weeks of exposure. However, after 15 weeks, this reduction in the numbers of tillers was only significant ( P < 0.05) for the 60 N treatment. All wet nitrogen additions resulted in decreases in leaf areas compared with plants with no added nitrogen after 15 weeks of exposure to experimental treatments (Table 2), but the effect was not significant for the 60 N treatment.
Table 2 Leaf areas of A. capillaris after being exposed for 11, 13 and 15 weeks to different concentrations of SO 2 + NO 2 and wet nitrogen applications Nitrogen additions kg h a - ~ y - t
Nitrogen treatment means
ppb SO 2 + NO 2
0
10
20
40
After 11 weeks 0 20 40 60 Gas treatment means L.S.D. ( P < 0.05) between gas treatments
90.7 114.4 69.6 91.6 91.6 118.6 104.9 69.7 86.9 95.1 78.2 121.5 77.0 58.4 83.8 118.0 111.0 79.7 53.5 90.6 101.4 113.0 74.0 72.6 90.2 = 21.5. There were no significant differences between nitrogen treatments ( P < 0.05).
After 13 weeks 0 20 40 60 Gas treatment means L.S.D. ( P < 0.05) between gas treatments
229.7 271. l 250.0 176.2 177.0 228.0 262.3 149.4 229.8 206.2 or nitrogen treatments = 31.7.
134.5 160.3 105.4 159.1 139.8
252.8 134.7 87.2 137.0 152.9
222.0 180.3 t 49.4 176.9 182.2
282.9 211.7 168.5 190.6 137.7 255.7 188.3 242.0 194.4 225.0 or nitrogen treatments = 32.0.
201.4 198.8 205.9 180.2 196.6
145.5 102.0 100.9 132.4 120.2
210.4 165.0 175.0 185.7 184.0
After 15 weeks 0 20 40 60 Gas treatment means L.S.D. ( P _< 0.05) between gas treatments
E.A. Kupcinskiene et al. / Agriculture, Ecosystems and Ent,ironment 66 (1997) 89-99 The effects of S O 2 + N O 2 on the dry w e i g h t fractions o f A. capillaris are s h o w n in Tables 3 - 5 . There w e r e significant reductions in the dry weights o f leaves o f A. capillaris of up to 4 8 % for the 40 ppb and 20 ppb pollution treatments c o m p a r e d with control plants. Similar significant ( P < 0.05) reductions ( 3 7 - 5 0 % ) were recorded for stem dry weights under the 40 ppb treatment for all three harvests and under 20 ppb treatment for the first two harvests ( P < 0.05). Reductions in shoot dry weights were a c c o m p a n i e d with significant ( P _< 0.05) reductions ( 1 8 - 3 9 % ) in root dry weights in both the 20 ppb and
93
40 ppb treatments at all harvests. The reductions in dry weights o f the different plant fractions were reflected in reductions in total plant dry weights o f A. capillaris e x p o s e d to both the 20 ppb and 40 ppb treatments c o m p a r e d with controls ( P < 0.05). At the final harvest total plant dry weights were reduced by 20% and 38%, in the 20 ppb and 40 ppb treatments respectively. There were no significant differences in dry w e i g h t fractions for plants e x p o s e d to the 10 ppb treatment c o m p a r e d with controls e x c e p t for transitory reductions in root and stem weights after 11 w e e k s exposure ( P < 0.05) which were not
Table 3 Dry weights (g) of fractions of A. capillaris after being exposed for 11 weeks to different concentrations of SO 2 + NO 2 and wet nitrogen applications Nitrogen additions kg ha- ~ y ~
Nitrogen treatment means
ppb SO2 + NO 2
0
10
20
40
0.26 0.22 0.28 0.28 0.26
0.30 0.28 0.22 0.14 0.24
LeaL,es 0 0.57 0.48 20 0.40 0.37 40 0.33 0.47 60 0.36 0.32 Gas treatment means 0.42 0.41 L.S.D. ( P < 0.05) between gas or nitrogen treatments = 0.09.
0.40 0.32 0.33 0.28
Stems 0 20 40 60 Gas treatment means L.S.D. (P _<0.05) between gas treatments
0.51 0.40 0.52 0.40 0.46 = 0.11. There
0.43 0.21 0.31 0.24 0.37 0.28 0.26 0.21 0.34 0.24 were no significant differences
0.30 0.37 0.34 0.33 0.26 0.36 0.13 0.25 0.26 between nitrogen treatments (P _<0.05).
0.75 0.56 0.64 0.68 0.66 = 0.10. There
0.58 0.43 0.58 0.52 0.55 0.43 0.44 0.53 0.54 0.48 were no significant differences
0.44 0.55 0.53 0.54 0.43 0.51 0.39 0.51 0.45 between nitrogen treatments ( P _<0.05).
1.83 1.37 1.50 1,43 1.53 = 0.26. There
1.49 0.90 1.26 0.98 1.39 0.99 1.02 1.02 1.29 0.97 were no significant differences
1.04 1.32 1.15 1.19 0.91 1.19 0.67 1.03 0.94 between nitrogen treatments (P < 0.05).
Roots 0 20 40 60 Gas treatment means L.S.D. ( P _< 0.05) between gas treatments Total plants 0 20 40 60 Gas treatment means L.S.D. ( P < 0.05) between gas treatments
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Table 4 Dry weights (g) of fractions of A. capillaris after being exposed for 13 weeks to different concentrations of SO z + NO~ and wet nitrogen applications Nitrogen additions kg ha- i y - t
Nitrogen treatment means
ppb SO 2 + NO 2 0
10
20
40
Leaves 0 0.72 20 0.78 40 0.49 60 0.59 Gas treatment means 0.65 L.S.D. ( P < 0.05) between gas treatments = 0.11. There
0.69 0.29 0.55 0.56 0.49 0.38 0.26 0.48 0.64 0.33 0.24 0.43 0.51 0.41 0.42 0.48 0.58 0.35 0.37 were no significant differences between nitrogen treatments P < 0.05).
Stems 0 0.97 0.87 0.36 0.85 0.76 20 1.08 0.72 0.56 0.49 0.71 40 0.67 1.08 0.48 0.35 0.65 60 0.86 0.69 0.65 0.56 0.69 Gas treatment means 0.90 0.84 0.51 0.56 L.S.D. ( P < 0.05) between gas treatments = 0.17. There were no significant differences between nitrogen treatments P < 0.05).
Roots 0 1.14 1.04 0.59 20 1.21 0.78 0.72 40 0.92 1.09 0.51 60 0.89 0.63 0.72 Gas treatment means 1.04 0.89 0.63 L.S.D. ( P < 0.05) between gas treatments = 0.15. There were no significant differences
0.90 0.92 0.59 0.83 0.52 0.76 0.88 0.78 0.72 between nitrogen treatments ( P < 0.05).
Total plants 0 2.83 2.60 1.25 2.29 2.24 20 3.07 1.99 1.65 1.34 2.01 40 2.08 2.82 1.32 1.11 1.83 60 2.34 1.82 1.78 1.86 1.95 Gas treatment means 2.58 2.31 1.50 1.65 L.S.D. ( P < 0.05) between gas treatments = 0.41. There were no significant differences between nitrogen treatments ( P < 0.05).
r e f l e c t e d in s i g n i f i c a n t d i f f e r e n c e s in d r y w e i g h t s o f total plants. G e n e r a l l y , t h e r e w e r e n o s i g n i f i c a n t effects o f w e t n i t r o g e n t r e a t m e n t s o n the d r y w e i g h t f r a c t i o n s o f A. capillaris. T h e o n l y e x c e p t i o n w a s a l o w e r root dry w e i g h t for all n i t r o g e n a d d i t i o n s a b o v e the c o n t r o l ( z e r o a p p l i c a t i o n ) at the final h a r v e s t ( P < 0.05). T h i s w a s n o t r e f l e c t e d in c h a n g e s in total p l a n t d r y w e i g h t s ( T a b l e 5). C a l c u l a t i o n s o f r o o t / s h o o t ratios r e v e a l e d that both SO 2 + NO 2 and wet nitrogen treatments caused shifts in the p a r t i t i o n i n g o f a s s i m i l a t e s ( T a b l e 6). T h e r e w a s a t e n d e n c y for r o o t / s h o o t ratios to inc r e a s e w i t h i n c r e a s i n g c o n c e n t r a t i o n s o f S O 2 + N O 2.
T h i s r e s u l t e d in s i g n i f i c a n t l y ( P < 0 . 0 5 ) higher r o o t / s h o o t ratios in the 4 0 p p b S O 2 + N O 2 treatm e n t in c o m p a r i s o n to c o n t r o l p l a n t s for all h a r v e s t s . F o r w e t n i t r o g e n a p p l i c a t i o n s , t h e r e w a s a n initial i n c r e a s e (11 w e e k s ) a n d t h e n a d e c r e a s e (15 w e e k s ) in r o o t / s h o o t ratios o f A. capillaris in the 60 N t r e a t m e n t c o m p a r e d w i t h p l a n t s w i t h zero n i t r o g e n a p p l i c a t i o n ( P < 0.05).
4. Discussion
It is c l e a r f r o m the data p r e s e n t e d t h a t e x p o s u r e to N O 2 + S O 2 m a y h a v e a d v e r s e e f f e c t s o n the g r o w t h
E.A. Kupcinskiene et al. / Agriculture, Ecosystems and Ent'ironment 66 (1997) 89-99
95
Table 5 Dry weights (g) of fractions of A. capillaris after being exposed for 15 weeks to different concentrations of SO, + NO, and wet nitrogen applications Nitrogen additions kg h a - i y I
Nitrogen treatment means
ppb SO_, + NO 2
0
10
20
40
teat~es 0 20 40 60 Gas treatment means L.S.D. (P _< 0.05) between gas treatments
0.69 0.51 0.55 0.65 0.60 = 0.11. There
0.46 0.45 0.55 0.50 0.61 0.48 0.64 0.45 0.56 0.47 were no significant differences
0.40 0.50 0.28 0.46 0.28 0.48 0.27 0.50 0.31 between nitrogen treatments ( P < 0.05).
0 1.73 2.01 1.04 20 1.13 1.47 1.50 40 1.17 1.70 1.34 60 1.58 1.71 1.22 Gas treatment means 1.40 1.72 1.27 L.S.D. (P _< 0.05) between gas treatments = 0.29. There were no significant differences
1.15 1.48 0.73 1.21 0.68 1.22 0.88 1.35 0.86 between nitrogen treatments ( P < 0.05).
Stems
Roots 0 20 40 60 Gas treatment means L.S.D. ( P _< 0.05) between gas or nitrogen
1.62 1.61 1.27 1.09 1.18 1.14 1.07 1.04 1.29 1.22 treatments = 0.21.
0.88 1.04 0.90 0.74 0.89
0.99 0.94 0.64 0.80 0.84
1.28 1.08 0.97 0.91
Total plants 0 4.04 20 2.90 40 2.90 60 3.29 Gas treatment means 3.28 L.S.D. ( P < 0.05) between gas treatments = 0.44. There
4.08 2.37 3.10 3.04 3.45 2.73 3.38 2.41 3.50 2.64 were no significant differences
of A. capillaris. Visible symptoms of injury in the form of chlorosis was recorded in the 20 and 40 ppb gas treatments after the 12th week of exposure. This occurred after growth analysis data had already revealed decline in growth at the harvest after 11 weeks when plants did not have any visible signs of injury. These symptoms of leaf injury were not associated with any reductions in the numbers of tillers except for a transitory decrease in the 20 ppb treatment after the 13 weeks ( P < 0.05). This is in contrast to many earlier studies where reductions in tillering have been reported for crops fumigated with SO 2 (Baker et al., 1987; Wilson and Murray, 1990) and in other grasses exposed to NO 2 + SO 2 treat-
2.54 3.26 1.95 2,75 1.60 2.67 1.95 2.76 2.01 between nitrogen treatments (P < 0.05).
ments (Ashenden and Williams, 1980). Despite no reductions in tillers, there was a decrease in total leaf areas of A. capillaris exposed to the higher (20 and 40 ppb) SO 2 + NO 2 treatments. This would indicate a reduction in the numbers of leaves per tiller or the sizes of individual leaves. Many earlier studies have shown SO 2 + NO 2 to reduce leaf numbers in grasses (e.g., Ashenden and Williams, 1980) and SO 2 exposure to reduce total leaf area without changes in numbers of leaves or tillers (Ashenden and Mansfield, 1977). The reduced leaf areas for plants of A. capillaris exposed to both 20 and 40 ppb SO 2 + N O 2 t r e a t m e n t s were accompanied by reductions in the dry
96
E.A. Kupcinskiene et al./ Agriculture, Ecosystems and Environment 66 (1997) 89-99
Table 6 Root/shoot ratios of A. capillaris after being exposed for l 1, 13 and 15 weeks to different concentrations of SO 2 + NO 2 and wet nitrogen applications Nitrogen additions kg ha-~ y t
Nitrogen treatment means
ppb SO 2 + NO 2 0
10
20
40
0.97 1.20 0.88 1.13 1.04
0.91 0.94 1.01 1.44 1.08
After 11 weeks 0 0.79 0.71 20 0.87 0.94 40 0.94 0.80 60 0.95 0.89 Gas treatment means 0.89 0.84 L.S.D. ( P < 0.05) between gas or nitrogen treatments = 0.16.
0.84 0.99 0.91 1.10
After 13 weeks 0 20 40 60 Gas treatment means L.S.D. ( P < 0.05) between gas treatments
0.73 0.66 0.92 0.76 0.77 0.68 0.75 0.86 0.81 0.77 0.87 0.69 0.67 0.91 0.79 0.67 0.59 0.70 0.93 0.72 0.74 0.67 0.79 0.85 = 0.10. There were no significant differences between nitrogen treatments ( P < 0.05).
After 15 weeks 0 0.74 0.66 20 0.82 0.54 40 0.75 0.51 60 0.50 0.46 Gas treatment means 0.70 0.54 L.S.D. ( P < 0.05) between gas or nitrogen treatments = 0.08.
0.60 0.57 0.57 0.46 0.55
0.68 1.01 0.69 0.74 0.78
0.67 0.73 0.63 0.54
weights of all plant fractions. At the final harvest, total plant dry weights compared with control plants were reduced by 20% and 38%, in the 20 ppb and 40 ppb treatments respectively. In contrast, plants in the 10 ppb SO 2 + NO 2 showed a slight stimulation in growth (not significant; P < 0.05) indicating that the threshold concentration for injury (critical level) of SO 2 + NO 2 for this species is between 10 and 20 ppb SO 2 + N O 2. This concentration is substantially lower than in a previous study where exposure to 40 ppb SOa + NO 2 for 22 weeks did not reduce shoot growth in A. capillaris (Ashenden et al., 1996a). However, in this earlier study, plants were grown on a nutrient rich potting compost rather than the relatively nutrient-poor soil used here. It is implied that plant sensitivities to SO 2 + NO 2 may be influenced by soil fertility. Supporting evidence comes from a recent screening study where high concentrations of SO 2 (100-300 ppb) were required to differentiate sensitivities of species growing in sand cultures with
non-limiting nutrient supplies (Ashenden et al., 1996b). Reductions in the dry weights of total plants and their separate parts could be caused by changes in physiological processes (Darrall, 1991; Saxe, 1991). Gaseous pollution treatments have been shown to cause significant reductions of net photosynthesis and stomatal conductance (Freer-Smith, 1985; Vanhove et al., 1992; Schenone et al., 1994). In addition, reduced weights of A. capillaris could be caused by respiratory losses of carbohydrates. In general, respiration has been found to increase in response to fumigation with gaseous pollutants. These changes are likely to reflect both the activity of injury repair and have a direct effect on the rate of maintenance respiration (Darrall, 1989; Saxe, 1991). In contrast to the effects of SO 2 + NO 2 gases, additions of wet nitrogen resulted in a reduction in the numbers of tillers of A. capillaris. Generally, this was reflected in a reduction in total leaf area but
E.A. Kupcinskiene et al. / Agriculture, Ecosystems and Environment 66 (1997) 89-99
no effects on total plant dry weights. In previous studies, wet deposition treatments with high levels of nitrogen have been found to reduce leaf production for a range of species (Irving, 1983; Edge et al., 1994) but these have usually been confounded by changes in hydrogen ion concentrations. Normally, additions of nitrogen as fertilisers for crops increase above ground productivity at the expense of the roots (INDITE, 1994). Nitrogen is a major nutrient, the supply of which is often the growth limiting factor in natural ecosystems (Ellenberg, 1987). In this investigation, nutrient-poor soils were used and, under such conditions, wet nitrogen additions might be expected to have a fertilising effect on growth. Indeed, earlier studies have shown substantial increases in growth for a range of species exposed to highly acidic rain/mist episodes (as low as pH 2.5) which have been attributed to the fertiliser effects of nitrogen and sulphur in treatment solutions (Ashenden et al., 1991; Edge et al., 1994). However, nitrogen demands of species vary considerably and are much lower for semi-natural communities (INDITE, 1994). Also, an increase in nitrogen supply may cause a relative shortage of other nutrients. Jeffrey and Pigott (1973) found no effect of nitrogen alone on grassland, but did find changes in abundance of grasses when nitrogen and phosphorus were added in combination. Similarly, increased inputs of nitrogen have been found to result in shortages of other nutrients and result in the disruption of nutrient relations in trees (Nambiar and Fife, 1987). While dry weights of all plant fractions were depressed in response to the 20 ppb and 40 ppb SO 2 + NO 2 treatments, the effects were greater on shoots than roots. This resulted in an increase in root/shoot ratio for A. capillaris exposed to the 40 ppb treatment. This observation conflicts with the results of many earlier studies where a proportionately greater reduction in root compared with shoot growth in response to gaseous pollutants has been reported for other species (Ashenden and Mansfield, 1978; Lucas, 1990). The reduction in root growth at the expense of shoot growth has been attributed to a reduced translocation of assimilates from leaves of polluted plants (Mansfield, 1988) which clearly did not occur in A. capillaris in this investigation. The effects of wet nitrogen applications on assimilate partitioning in A. capillaris changed with time.
97
Initially, there was an increase in root/shoot ratio for plants exposed to the 60 N compared with the zero N application. However, at the final harvest, the response was reversed with plants at 60 N having a reduced root/shoot ratio compared with controls. Thus it appears that assimilate partitioning in response to wet nitrogen applications alters with age and the stage of plant development. The resulting reduction in the proportion of roots to shoots, if maintained, would make plants more susceptible to drought at later stages of development. A. capillaris is an abundant and widely distributed species throughout Europe. It is the dominant species in large areas of poorer permanent grassland, particularly in upland regions which are characterised by acidic shallow soils and high inputs of pollutant nitrogen in wet deposition. Thus the indication that sensitivity to SO~ + NO~ gases may be increased for plants growing on less fertile soils and that increased deposition of wet nitrogen may reduce leaf canopy development may have important implications for A. capillaris. Both these responses may be expected to alter its competitive ability in mixed swards. Other less sensitive species might gain a competitive advantage. In polluted environments, this could result in changes in the vegetation structure of poorer grasslands.
Acknowledgements This work was partly funded by the UK Department of the Environment ( P E C D 7 / 1 2 / 2 3 ) and the Welsh Office (WEP100/12/1). E.A.K. was funded by a grant from the Central European University, Budapest.
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