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Some effects of simulated acid rain on the growth of barley and radish
EnvironmentalPollution(SeriesA) 22 (1980)69-73
SOME EFFECTS OF SIMULATED ACID RAIN ON THE GROWTH OF BARLEY A N D RADISH
S. A. HARCOURTt & J. F. FARRAR
School o f Plant Biology, University College of North Wales, Memorial Buildings, Bangor, Gwynedd LL57 2UW, Great Britain
ABSTRACT
Radish and barley seedlings were sprayed at intervals of 4-5 days with simulated rain to test the factorial combinations of ( i) the presence or absence of O.1 mmol SO ] dm-3 and (ii) the amounts of H2SO 4 giving pHs ranging from 5.5 to 2.5. In experiments with radishes, leaf and root growth were consistently reduced when acidity was increased from pH 3.5 to 2.5, the effect on roots being accentuated by an interaction with sulphite. In one experiment using pHs restricted to the range 5.5 to 3.5, some aspects of the early growth of barley were reduced by sulphite but not by increasing acidity.
INTRODUCTION
Acid rain in the United Kingdom is characterised by the presence of sulphite as well as its low pH (Martin & Barber, 1978). Whilst the effects of simulated rain acidified with sulphuric acid have been investigated (Wood & Bormann, 1974; Ferenbaugh, 1976), there are no reports of the effects of sulphite at pHs of 2.5 to 5 on higher plants. Work on lichens and bryophytes has shown that sulphite and low pH presented together depress the rate of photosynthesis below that achieved with either alone (Hill, 1971; Inglis & Hill, 1974). An investigation of the effects of sulphite and low pH, presented separately and together, on the growth of barley and radish is the subject of this paper. t Present address: Charles Darwin Research Station, Santa Cruz, Galapagos, Ecuador.
69 Environ. Pollut. Ser. A. 0143-1471/80/0022-0069/$02-25 © Applied Science Publishers Ltd, England, 1980 Printed in Great Britain
70
s.A.
HARCOURT, J . F . FARRAR
MATERIALS AND METHODS
Radish Raphanus sativus (L.) cv. Cherry Belle and barley Hordeum distichum (L.) Lam. cv. Magnum were grown from seed in 15-cm diameter pots in John Innes No. 1 potting compost. They were maintained in a heated glasshouse with artificial lighting extending daylength to 16 h and with a minimum temperature of 13 °C. Pots were arranged in a randomised block design, with six replicates per treatment, and watered daily from below with deionised water. Each pot received seven applications of simulated acid rain over the experimental period; this was applied from all-plastic domestic spraying bottles and allowed to fall on the soil as well as the leaves. During spraying each pot was shielded from its neighbours by a clear polythene guard. Each application was of 100 cm 3 per pot; the total dose for one experiment was thus 700cm3--the equivalent of 4cm of rain. In all experiments, the acid rain was based on glass-distilled water (containing 0.1 mmol d m - 3 sodium sulphite if appropriate) and the correct pH obtained on a pH meter by the addition of analytical grade sulphuric acid. The solutions were prepared immediately before use since sulphite can be rapidly oxidised to sulphate in solution. In two experiments, the simulated rain, acidified as described above, also included other ionic species characteristic of natural rain; the method of Ferguson et al. (1978) was followed, giving final nutrient concentrations (in mg d m - 3) of MgCI 2, 0.833; KCI, 0.223; Ca(NO3) 2, 2-010 and NaH2PO4, 0.050. Data are presented as main effects from a 2 x 3 factorial analysis together with the least significant differences (p = 0.05) for the main effects. The level of significance for an interaction between sulphite and acidity is also given. RESULTS
Radish Two experiments (Nos 1 and 2) on radish were carried out sequentially using identical solutions. They differed only in ambient climatic condition. Root fresh weights were recorded, in addition to dry weights, as these are of economic importance. When treated with distilled water acidified with H2SO 4, radish showed a reduced leaf area and dry weight, and fresh and dry root weights were also depressed, at pH 2.5 but not at pH 3.5. When treated with 0.1 m m o l d m - 3 sulphite acidified with sulphuric acid, the same pattern of reduced growth at low pH was seen, particularly at pH 2.5. The presence of sulphite itself seemed to cause at most a small reduction in root growth and leaf area. In both experiments there was a significant interaction between the effects of pH and sulphite (Table 1). In a third experiment, in which the acid rain was modified by the inclusion of a basic mineral solution resembling uncontaminated rainwater, and in which a less extreme pH range was used, no effect of either sulphite or pH, and no interaction between them, was found (Table 1).
71
EFFECTS OF SIMULATED ACID RAIN ON PLANT GROWTH
TABLE 1 7-25 DAYS (The acid rain was sodium sulphite (0.1 mmol dm-3) in distilled water (experiments 1 and 2) or a dilute nutrient solution (experiment 3) adjusted to the appropriate pH with H2SO4.) THE EFFECT OF SEVEN APPLICATIONS OF SIMULATED ACID RAIN ON RADISH GROWTH OVER THE AGES OF
2.5 Leaf dry weight (g) Experiment 1 Experiment 2 Experiment 3 Leaf area (em 2) Experiment 1 Experiment 2 Experiment 3 Root dry weight (g) Experiment 1 Experiment 2 Experiment 3 Root fresh weight (g) Experiment 1 Experiment 2 Experiment 3
p H by H z S O 4 additions 3.5 4.5 5.5 L SD
0.37 0'35 -137 127 -0.52 0.41 -9.7 7.1 --
0"41 - 0.40 - 0.34 0.36 175 152 141 0.81 0.57 0.26 16.5 10.4 5'0
---
145 --0-26 --4.8
0.42 0'41 0.36 170 161 148
O"1 m m ol SO 2 - dm 3 Without With L S D
0.04 0.04 0.06
0"42 0-39 0.35
13 14 20
168 150 147
0.81 0.17 0.56 0.06 0.28 0'06 15.5 10.2 5.3
1"5 1.0 1.0
0.78 0.52 0"26 14.9 9.4 4.8
0.38 0.37 0.35 154 142 143 0.64 0.50 0.27 12.8 9.0 5.1
0.03 0"03 0.03 il !1 14
p H x SO 3 interaction P
<0-02 NS NS <0'005 NS NS
0-14 0.03 0"03
<0-005 <0.001 NS
1.2 0.8 0.8
<0-001 <0"005 NS
NS, not significant. LSD, least significant difference.
Barley One experiment was conducted with barley, using a pH range of 3.5 to 5.5 and solutions modified by added nutrients, as for the third experiment with radish. Barley receiving seven applications of acid rain, which included a basic mineral solution, showed no response to the acidity treatments of pH 3.5 and 4.5. However, the addition of 0.1 mmol d m - 3 sulphite caused a reduction in total above-ground weight and leaf weight (Table 2): this effect was not significantly dependent on pH. TABLE 2 19--34 DAYS (The acid rain was a dilute nutrient solution with or without sodium sulphite (0" 1 mmol din- 3) adjusted to the appropriate pH with H2SO4. ) THE EFFECT OF SEVEN APPLICATIONS OF SIMULATED ACID RAIN ON BARLEY GROWTH OVER THE AGES
p H by H2SO 4 additions
3-5 Leaf dry weight (g) Leaf area (cm2) Dry weight of tops (g)
4.5
0-32 0.33 96 99 0.46 0'47
NS, not significant. LSD, least significant difference.
5.5
LSD
0.34 0.05 107 14 0"47 0.06
O. 1 mmol SO~ - dm Without
With
L SD
p H × SO 3 interaction p
0-35 107 0.49
0.31 95 0.43
0.03 12 0.05
NS NS NS
72
S . A . HARCOURT, J . F . FARRAR
DISCUSSION
The pots in these experiments received simulated acid rain equivalent to 4cm of precipitation during the experiment. The wet deposition of sulphur as sulphite, in pots so treated, totalled 0.13 g S m - 2 over about a month, equivalent to an input of 15 kg S ha-1 year-1. The input of S as H2SO 4 varied between treatments, the maximum being equivalent to 154 kg S ha-1 year-1, at pH 2.5 in the presence of sulphite. Garland et al. (1973) calculate an S input from the air of 75 kg ha - 1 year - 1, 20 kg of which is by wet deposition, as a mean for Great Britain. The total dose of S supplied is thus fairly realistic, especially at pH 3.5 and above; what is unrealistic is the pH of 2.5 used in the two experiments on radish. Similarly, the sulphite concentration applied (0.1 mmoldm -a) is of the right order (Martin & Barber, 1978). We tentatively suggest, therefore, that our results show a possibility of plant growth suppression by acid rain in Great Britain. Thus, whilst radish shows a big response to acidity, this is largely due to the application of unrealistically low pH; growth appears as good at pH 3-5 to 4.5 as at pH 5.5. The differences between experiments l and 2 can only be attributed to changed climatic conditions in the glasshouse. Barley is similarly unaffected by pH 3-5. These results accord with data on beans (Ferenbaugh, 1976) and broad-leaf trees (Wood & Bormann, 1974). Sulphite itself has no effects on radish but it does reduce the growth of barley significantly: the effect is seen on both leaf, and total above-ground, dry weight. These effects are striking in view of the short residence time of sulphite in plants (Miller & Xerikos, 1979). It would now seem necessary to examine effects on grain yield in barley. For radish, the effects of sulphite and pH are not simply additive--there is a highly significant interaction between them which is seen as an increased sensitivity to sulphite at low pH. It will be noticed that as pH is lowered using sulphuric acid, the dose of sulphur applied to the plants increases both as pH falls and with sulphite application; it is unlikely to be the dose of sulphur that brings about growth reduction, however, since there can be shown to be no significant correlation (at p = 0.05) between sulphur dose and growth reduction in these experiments. These data indicate that it is not sufficient to simulate acid rain with sulphuric acid alone--both the presence of sulphite, and the possible interaction between sulphite and pH, need to be included in experimental designs. The contribution of other ionic species should also be considered.
ACKNOWLEDGEMENTS
We should like to thank Lynne Jones and Stephen Williams for assistance with one experiment and J. N. B. Bell for his criticism of an early draft of this paper.
EFFECTS OF SIMULATED ACID RAIN ON PLANT GROWTH
73
REFERENCES FERENBAUGH,R. W. (1976). Effects of simulated acid rain on Phaseolus vulgaris L. Am. J. Bot., 63, 283-8. F~GUSON, P., LEE,J. A. & BELL,J. N. B. (1978). Effects of sulphur pollutants on the growth of Sphagnum species. Environ. Pollut., 16, 151-62. GARLAND,J. A., CLOUOH,W. S. & FOWtY.R,D. (1973). Deposition of sulphur dioxide on grass. Nature, Lond., 242, 256. HILL, D. J. (1971). Experimental study of the effect of sulphite on lichens with reference to atmospheric pollution. New Phytol., 70, 831-6. I~ous, F. & H1LL,D. J. (1974). The effects of sulphite and fluoride on carbon dioxide uptake by mosses in the light. New PhytoL, 73, 1207-13. MARTIN,A. & BARBER,P. R. (1978). Some observations of acidity and sulphur in rainwater from rural sites in England and Wales. Atmos. Environ., 12, 1481-7. MILLER,J. E. & XeRI[COS,P. B. (1979). Residence time of sulphite in sulphur dioxide sensitive and tolerant soybean cultivars. Environ. Poliut., 18, 259-64. WooD, T. & BORMAN~,F. H. (1974). The effects of an artificial acid mist upon the growth of Betula allaghanensis. Environ. Pollut., 7, 259-68.
SOME EFFECTS OF SIMULATED ACID RAIN ON THE GROWTH OF BARLEY A N D RADISH
S. A. HARCOURTt & J. F. FARRAR
School o f Plant Biology, University College of North Wales, Memorial Buildings, Bangor, Gwynedd LL57 2UW, Great Britain
ABSTRACT
Radish and barley seedlings were sprayed at intervals of 4-5 days with simulated rain to test the factorial combinations of ( i) the presence or absence of O.1 mmol SO ] dm-3 and (ii) the amounts of H2SO 4 giving pHs ranging from 5.5 to 2.5. In experiments with radishes, leaf and root growth were consistently reduced when acidity was increased from pH 3.5 to 2.5, the effect on roots being accentuated by an interaction with sulphite. In one experiment using pHs restricted to the range 5.5 to 3.5, some aspects of the early growth of barley were reduced by sulphite but not by increasing acidity.
INTRODUCTION
Acid rain in the United Kingdom is characterised by the presence of sulphite as well as its low pH (Martin & Barber, 1978). Whilst the effects of simulated rain acidified with sulphuric acid have been investigated (Wood & Bormann, 1974; Ferenbaugh, 1976), there are no reports of the effects of sulphite at pHs of 2.5 to 5 on higher plants. Work on lichens and bryophytes has shown that sulphite and low pH presented together depress the rate of photosynthesis below that achieved with either alone (Hill, 1971; Inglis & Hill, 1974). An investigation of the effects of sulphite and low pH, presented separately and together, on the growth of barley and radish is the subject of this paper. t Present address: Charles Darwin Research Station, Santa Cruz, Galapagos, Ecuador.
69 Environ. Pollut. Ser. A. 0143-1471/80/0022-0069/$02-25 © Applied Science Publishers Ltd, England, 1980 Printed in Great Britain
70
s.A.
HARCOURT, J . F . FARRAR
MATERIALS AND METHODS
Radish Raphanus sativus (L.) cv. Cherry Belle and barley Hordeum distichum (L.) Lam. cv. Magnum were grown from seed in 15-cm diameter pots in John Innes No. 1 potting compost. They were maintained in a heated glasshouse with artificial lighting extending daylength to 16 h and with a minimum temperature of 13 °C. Pots were arranged in a randomised block design, with six replicates per treatment, and watered daily from below with deionised water. Each pot received seven applications of simulated acid rain over the experimental period; this was applied from all-plastic domestic spraying bottles and allowed to fall on the soil as well as the leaves. During spraying each pot was shielded from its neighbours by a clear polythene guard. Each application was of 100 cm 3 per pot; the total dose for one experiment was thus 700cm3--the equivalent of 4cm of rain. In all experiments, the acid rain was based on glass-distilled water (containing 0.1 mmol d m - 3 sodium sulphite if appropriate) and the correct pH obtained on a pH meter by the addition of analytical grade sulphuric acid. The solutions were prepared immediately before use since sulphite can be rapidly oxidised to sulphate in solution. In two experiments, the simulated rain, acidified as described above, also included other ionic species characteristic of natural rain; the method of Ferguson et al. (1978) was followed, giving final nutrient concentrations (in mg d m - 3) of MgCI 2, 0.833; KCI, 0.223; Ca(NO3) 2, 2-010 and NaH2PO4, 0.050. Data are presented as main effects from a 2 x 3 factorial analysis together with the least significant differences (p = 0.05) for the main effects. The level of significance for an interaction between sulphite and acidity is also given. RESULTS
Radish Two experiments (Nos 1 and 2) on radish were carried out sequentially using identical solutions. They differed only in ambient climatic condition. Root fresh weights were recorded, in addition to dry weights, as these are of economic importance. When treated with distilled water acidified with H2SO 4, radish showed a reduced leaf area and dry weight, and fresh and dry root weights were also depressed, at pH 2.5 but not at pH 3.5. When treated with 0.1 m m o l d m - 3 sulphite acidified with sulphuric acid, the same pattern of reduced growth at low pH was seen, particularly at pH 2.5. The presence of sulphite itself seemed to cause at most a small reduction in root growth and leaf area. In both experiments there was a significant interaction between the effects of pH and sulphite (Table 1). In a third experiment, in which the acid rain was modified by the inclusion of a basic mineral solution resembling uncontaminated rainwater, and in which a less extreme pH range was used, no effect of either sulphite or pH, and no interaction between them, was found (Table 1).
71
EFFECTS OF SIMULATED ACID RAIN ON PLANT GROWTH
TABLE 1 7-25 DAYS (The acid rain was sodium sulphite (0.1 mmol dm-3) in distilled water (experiments 1 and 2) or a dilute nutrient solution (experiment 3) adjusted to the appropriate pH with H2SO4.) THE EFFECT OF SEVEN APPLICATIONS OF SIMULATED ACID RAIN ON RADISH GROWTH OVER THE AGES OF
2.5 Leaf dry weight (g) Experiment 1 Experiment 2 Experiment 3 Leaf area (em 2) Experiment 1 Experiment 2 Experiment 3 Root dry weight (g) Experiment 1 Experiment 2 Experiment 3 Root fresh weight (g) Experiment 1 Experiment 2 Experiment 3
p H by H z S O 4 additions 3.5 4.5 5.5 L SD
0.37 0'35 -137 127 -0.52 0.41 -9.7 7.1 --
0"41 - 0.40 - 0.34 0.36 175 152 141 0.81 0.57 0.26 16.5 10.4 5'0
---
145 --0-26 --4.8
0.42 0'41 0.36 170 161 148
O"1 m m ol SO 2 - dm 3 Without With L S D
0.04 0.04 0.06
0"42 0-39 0.35
13 14 20
168 150 147
0.81 0.17 0.56 0.06 0.28 0'06 15.5 10.2 5.3
1"5 1.0 1.0
0.78 0.52 0"26 14.9 9.4 4.8
0.38 0.37 0.35 154 142 143 0.64 0.50 0.27 12.8 9.0 5.1
0.03 0"03 0.03 il !1 14
p H x SO 3 interaction P
<0-02 NS NS <0'005 NS NS
0-14 0.03 0"03
<0-005 <0.001 NS
1.2 0.8 0.8
<0-001 <0"005 NS
NS, not significant. LSD, least significant difference.
Barley One experiment was conducted with barley, using a pH range of 3.5 to 5.5 and solutions modified by added nutrients, as for the third experiment with radish. Barley receiving seven applications of acid rain, which included a basic mineral solution, showed no response to the acidity treatments of pH 3.5 and 4.5. However, the addition of 0.1 mmol d m - 3 sulphite caused a reduction in total above-ground weight and leaf weight (Table 2): this effect was not significantly dependent on pH. TABLE 2 19--34 DAYS (The acid rain was a dilute nutrient solution with or without sodium sulphite (0" 1 mmol din- 3) adjusted to the appropriate pH with H2SO4. ) THE EFFECT OF SEVEN APPLICATIONS OF SIMULATED ACID RAIN ON BARLEY GROWTH OVER THE AGES
p H by H2SO 4 additions
3-5 Leaf dry weight (g) Leaf area (cm2) Dry weight of tops (g)
4.5
0-32 0.33 96 99 0.46 0'47
NS, not significant. LSD, least significant difference.
5.5
LSD
0.34 0.05 107 14 0"47 0.06
O. 1 mmol SO~ - dm Without
With
L SD
p H × SO 3 interaction p
0-35 107 0.49
0.31 95 0.43
0.03 12 0.05
NS NS NS
72
S . A . HARCOURT, J . F . FARRAR
DISCUSSION
The pots in these experiments received simulated acid rain equivalent to 4cm of precipitation during the experiment. The wet deposition of sulphur as sulphite, in pots so treated, totalled 0.13 g S m - 2 over about a month, equivalent to an input of 15 kg S ha-1 year-1. The input of S as H2SO 4 varied between treatments, the maximum being equivalent to 154 kg S ha-1 year-1, at pH 2.5 in the presence of sulphite. Garland et al. (1973) calculate an S input from the air of 75 kg ha - 1 year - 1, 20 kg of which is by wet deposition, as a mean for Great Britain. The total dose of S supplied is thus fairly realistic, especially at pH 3.5 and above; what is unrealistic is the pH of 2.5 used in the two experiments on radish. Similarly, the sulphite concentration applied (0.1 mmoldm -a) is of the right order (Martin & Barber, 1978). We tentatively suggest, therefore, that our results show a possibility of plant growth suppression by acid rain in Great Britain. Thus, whilst radish shows a big response to acidity, this is largely due to the application of unrealistically low pH; growth appears as good at pH 3-5 to 4.5 as at pH 5.5. The differences between experiments l and 2 can only be attributed to changed climatic conditions in the glasshouse. Barley is similarly unaffected by pH 3-5. These results accord with data on beans (Ferenbaugh, 1976) and broad-leaf trees (Wood & Bormann, 1974). Sulphite itself has no effects on radish but it does reduce the growth of barley significantly: the effect is seen on both leaf, and total above-ground, dry weight. These effects are striking in view of the short residence time of sulphite in plants (Miller & Xerikos, 1979). It would now seem necessary to examine effects on grain yield in barley. For radish, the effects of sulphite and pH are not simply additive--there is a highly significant interaction between them which is seen as an increased sensitivity to sulphite at low pH. It will be noticed that as pH is lowered using sulphuric acid, the dose of sulphur applied to the plants increases both as pH falls and with sulphite application; it is unlikely to be the dose of sulphur that brings about growth reduction, however, since there can be shown to be no significant correlation (at p = 0.05) between sulphur dose and growth reduction in these experiments. These data indicate that it is not sufficient to simulate acid rain with sulphuric acid alone--both the presence of sulphite, and the possible interaction between sulphite and pH, need to be included in experimental designs. The contribution of other ionic species should also be considered.
ACKNOWLEDGEMENTS
We should like to thank Lynne Jones and Stephen Williams for assistance with one experiment and J. N. B. Bell for his criticism of an early draft of this paper.
EFFECTS OF SIMULATED ACID RAIN ON PLANT GROWTH
73
REFERENCES FERENBAUGH,R. W. (1976). Effects of simulated acid rain on Phaseolus vulgaris L. Am. J. Bot., 63, 283-8. F~GUSON, P., LEE,J. A. & BELL,J. N. B. (1978). Effects of sulphur pollutants on the growth of Sphagnum species. Environ. Pollut., 16, 151-62. GARLAND,J. A., CLOUOH,W. S. & FOWtY.R,D. (1973). Deposition of sulphur dioxide on grass. Nature, Lond., 242, 256. HILL, D. J. (1971). Experimental study of the effect of sulphite on lichens with reference to atmospheric pollution. New Phytol., 70, 831-6. I~ous, F. & H1LL,D. J. (1974). The effects of sulphite and fluoride on carbon dioxide uptake by mosses in the light. New PhytoL, 73, 1207-13. MARTIN,A. & BARBER,P. R. (1978). Some observations of acidity and sulphur in rainwater from rural sites in England and Wales. Atmos. Environ., 12, 1481-7. MILLER,J. E. & XeRI[COS,P. B. (1979). Residence time of sulphite in sulphur dioxide sensitive and tolerant soybean cultivars. Environ. Poliut., 18, 259-64. WooD, T. & BORMAN~,F. H. (1974). The effects of an artificial acid mist upon the growth of Betula allaghanensis. Environ. Pollut., 7, 259-68.