Water relations and growth of Heterotheca subaxillaris in different soil and watering treatments in the greenhouse

Environmental and Experimental Botany, Vol. 30, No. I, pp. 67 73, 1990

009~8472/90 $3.00 + 0.00 © 1989. Pergamon Press plc

Printed in Great Britain.

W A T E R R E L A T I O N S A N D G R O W T H OF HETEROTHECA SUBAXILLARIS IN D I F F E R E N T SOIL A N D W A T E R I N G T R E A T M E N T S IN THE G R E E N H O U S E B. S. C O L L I N S *

a n d G. R. W E I N *

Savannah River Ecology Laboratory, Drawer E, Aiken, SC 29801, U.S.A.

(Received 1 November 1988; acceptedin revisedform 11 July 1989) COLLINS B. S. and WEIN G. R. Water relations and growth of Heterotheca subaxillaris in different soil and watering treatments in the greenhouse. ENVIRONMENTALAND EXPERIMENTALBOTANY 30, 6773, 1990. The purpose of this greenhouse experiment was to determine if differences in soil fertility or soil moisture recharge capacity could influence water relations or growth of Heterotheca, a common herb in abandoned agricultural fields on the coastal plain of South Carolina. Plants were grown from seed (1) in soil taken from two areas of an old field that differed in fertility and (2) with or without soil moisture recharge capacity from underlying soil. Stomatal conductance and xylem pressure potential did not differ with treatment, either over a daily cycle or during experimental droughts. Shoot biomass of Heterothecawas greater in the more fertile soil and with capacity for soil moisture recharge. Root biomass was greater in lower fertility soil and with soil moisture recharge. These results suggest that variations in soil fertility and moisture may contribute to differences in Heterothecabiomass but do not influence water relations.

INTRODUCTION

MEMBERS of the genus Heterotheca are weeds of old fields, roadsides a n d coastal dunes from the A t l a n tic Coastal States n o r t h w a r d to New York, westw a r d to Illinois, a n d southwest to Mexico and California./12) T h e r e is d i s a g r e e m e n t over w h e t h e r one or two species should be recognized in the genus, in p a r t because of the high m o r p h o l o g i c a l a n d d e v e l o p m e n t a l plasticity observed. !2'3'6/ F o r example, prostrate d u n e plants of H. subaxillaris var. procumbens grown in a c o m m o n g a r d e n in N o r t h C a r o l i n a grew u p to be m o r p h o l o g i c a l l y identical to n o n - p r o s t r a t e plants o f H . subaxillaris taken t~om roadsides. (2! I n addition, onset of flowering in H. subaxiUaris grown in a c o m m o n g a r d e n in Massachusetts varied through time in

response to the p a t t e r n of rainfall experienced in the various locations from which the plants originated./3) O n the coastal plain of South Carolina, Heterotheca subaxillaris m a y be a c o m m o n c o m p o n e n t of herbaceous old fields./6-8'~°~ I n a given field, however, its a b u n d a n c e m a y v a r y seasonally a n d spatially. F o r example, PiNDER(9,u.publisheddata) found that the frequency o f Heterotheca d r o p p e d from 93 to 33%, and m e a n biomass from 42 to 1.88 g/m 2 across a 100 ha old field. T h e objective of the present research was to d e t e r m i n e if the physical e n v i r o n m e n t could influence ecophysiology or g r o w t h of Heterotheca subaxiUaris. Specifically, we asked if soil moisture of fertility, factors that were found to v a r y across an old field, could influence w a t e r relations or

*Present address and address for correspondence: Department of Biology, Memphis State University, Memphis, TN 38152, U.S.A. 67

68

B.S. COLLINS and G. R. WEIN

biomass of Heterotheca grown from seed in the greenhouse. We tested the null hypotheses that soil fertility and soil moisture recharge capacity (i) do not affect leaf stomatal conductance or xylem pressure potential of Heterotheca, either over a day or during prolonged drought, and (ii) do not influence biomass of mature Helerotheca.

METHODS

Heterotheca seeds were gathered in October 1986 from two sites separated by ca 200 m in a 34year-old field on the Savannah River Project near Aiken, South Carolina. Previous research (PINDE~, unpublished data) has shown that these areas differ in concentration of Ca 2+ (184 vs 281 ppm), Mg 2+ (16 vs 30 ppm), and Zn + (0.75 vs 1.11 ppm) in the soil. Concentrations of other major ions do not differ significantly between the areas. Soils in both sites are composed of 8 5 - 8 6 % sand, 4-5°/[, silt, and 6% clay; (4'8/pH is ca 5.5. (si The site of lower soil fertility borders a Carolina Bay; depth to the water table is 1.9 in. In the more t~rtile site a clay h a r d p a n at 2030 cm is a barrier to herb root growth, restricts vertical soil water percolation, and should enhance evaporation and soil drying after rains. The tillage pan has been present since agriculture ceased. ODUM(7~ reported that few roots penetrated the pan in the first 3 years of succession and GOLLEY(4) showed that less than 3 g/m 2 roots penetrated this layer 8 years after field abandonment. This site had a mean gravimetric soil moisture at 0-10 cm depth in J u n e of 0.035 g water per g dry soil. In the less fertile site, 0.049 g water per g dry soil was tbund. The two field sites are hereafter termed wet (WF) and dry (DF), respectively to reflect their different fertility and potential for soil moisture recharge. Only the disc achenes of Heterotheca were used in this experiment. Seeds from the field were put on moist filter paper in Petri dishes and placed in a greenhouse until they germinated. After the first true leaves had begun to develop, two seedlings were planted in each of 22 pots filled with heat sterilized (24 hr at 120°C) soil that had been removed (to 20 cm depth) from either the wet (less fertile, WF) or dry (more fertile, DF) field site.

Eleven pots of each soil type were placed in each of two treatments designed to simulate soil moisture recharge differences: (1) a wet treatment (WT) in which pots were set in a 15 cm layer of soil that was kept wet to potentially permit recharge of water in the pots between waterings, or (2) a dry treatment (DT) in which soil moisture recharge from the substrate was prevented by not maintaining the wet subsoil layer between waterings. In these treatments, gravimetric soil moisture of wet soil varied between 0.03 and 0.07 g H 2 0 per g dry soil. Soil water potential could not be measured with available instrumentation, thermocouple psychrometers, because temperature gradients between soil and atmosphere were too steep. M i d - d a y pot soil temperatures ranged between 30.0 and 39.8°C and did not differ a m o n g treatments. Plants were grown in the greenhouse until onset of flowering at 19 weeks. To determine daily water relations, ability to withstand drought, and growth (root and shoot biomass) of plants, the following measurements were made on three-five plants in each soil type under each moisture recharge treatment at weeks 19, 21, 24, and 27. Pre-dawn and hourly water potentials were measured with a Scholander-type pressure chamber. (~1~ To determine if stomata respond to differences in soil moisture and fertility, leaf stomatal conductance was determined with a Licor model LI-1600 steady state porometer. The porometer records stomatal conductance (mmol m - 2 sec- ~) as transpiration per water vapor mole fraction gradient where transpiration is measured as mass flow rate of water per cuvette aperture area and water vapor mole fraction gradient is the water vapor partial pressure gradient with respect to atmospheric pressure. At the end of each set of daily readings, twothree pots in each treatment were given a prolonged drought. In all, four droughts were conducted. Mid-day leaf water potentials and stomatal conductance were measured every 2 days during droughting until plants had turned completely brown and were brittle. Three leaf disks ( 19.6 m m 2) were removed daily from two leaves of each plant for a measure of relative water content. Disks were weighed, floated on distilled water for 24 hr to regain turgor, and reweighed. At the end of each drought, plants were harvested, par-

HETEROTHECA WATER RELATIONS AND GROWTH titioned into shoot and root, dried at 70°C for 36 hr, and weighed.

Data analyses Results that involved repeated measurements on individual plants over time, such as the hourly monitoring of leaf water potential and stomatal conductance over a day and the repeated measures of mid-day plant water relations during the drydown series, were analyzed by repeatedmeasures analysis of variance (ANOVA). ~5/This analysis considers the linear and quadratic (arched) trends of plant response over time as well as treatment (soil type and watering) effects. Because plants age and greenhouse conditions could change markedly between the sets of fullday observations, the effect of sampling date was also considered in this ANOVA. Results that did not entail repeated measures were analyzed by two-factor A N O V A considering the main effects of field (soil) type (DF vs WF) and watering treatment (WT vs DT), as well as their interaction. Homogeneity of variances was confirmed by Box-Cox analysis, iu

69

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RESULTS AND DISCUSSION

Daily responses Over the day, light and temperature in the greenhouse rose from pre-dawn lows to peak in early afternoon and decline by dusk (Fig. 1). Light (photosynthetically active radiation, PAR) reached a maximum value of 1375 #E m 2 sec-' shortly after noon, as temperature, which never fell below 23°C, peaked at 38°C. Relative humidity fell from early morning highs near 70% to mid-afternoon lows of 48% . In response to the changing greenhouse environment, stomatal conductance of Heterotheca showed a significant drop (linear and quadratic effects, Table 1) from pre-dawn highs >460 mmol m 2 sec-] t o midafternoon lows <350 mmol m -2 sec h, with recovery through the afternoon (Fig. 1). Xylem pressure potential showed a significant drop to < - 1.2 M P a and recovery to > - 0 . 7 M P a (linear and quadratic effects, Table 1; Fig. 1). Date of sampling showed a significant influence on both stomatal conductance and xylem pressure potential (Table 1), presumably because plants aged and conditions in the greenhouse changed over

40~

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. . . . . . . . . . . . . . . .

0500 0700 0900 t100 1300 t500 t700 t900 2t00

u.-

0600 0600 t000 1200 1400 t600 ts00 2000 2200

Time

(hr)

FIG. 1. Stomatal conductances (S.C.) and xylem pressure potentials (X.P.P.), of Heterotheca, as well as light (PAR), temperature, and relative humidity (R.H.), over a daily cycle in the greenhouse.

the course of the study. In addition, there was a significant date by treatment interaction in the linear trend for stomatal conductance (Table 1), which suggests that the rate of stomatal closure from morning to afternoon differed over days between watering treatments. A significant total data by watering treatment effect on xylem pres-

70

B. S. COLLINS and G. R. WEIN

Table 1. ANO VA of stomatal conductance and xylem pressure potential over a day with time (hr) considered a repeated measure dissolved into linear, quadratic, and total effects Linear Source Stomatal conductance Grand mean Soil type Watering trt. Soil type X Watering trt. Date Date X Soil type Date X Watering trt.

Quadratic

Total

df

MS

F

MS

F

MS

F

1 1 l

4.34 x 103 1.05 x 106 1.92 x 106

127.5" 0.31 0.56

1.07 X 10 9 4.62 x 10~ 2.51 x 10~

62.57* 0.03 0.01

2.13 x 105 5.85 x 103

0.21 0.01

1 3

1.01 x 107 3.71 x 10a

2.96 36.33*

1.20 x 108 2.98 x 108

0.75 1.74

1.30 x 103 2.97 x 107

0.0 9.57*

3

2 . 1 5 x 10 7

2.11

2.04x 108

0.40

3.68x 10~

0.12

3

1.10x 108

10.77"

1.65x 108

0.32

4.39x 106

1.41

2.33 x 104 1.04 x 103 1.29 x 10:~

12.68" 0.57 0.70

4.04 x 104 1.41 x 10° 4.81 x 103

17.2" 0.0 2.05

6.08 x 10 ~ 5.70 x 10o

3.17 0.30

1.65 x 10:~ 2.82x 104

0.90 5.11

1.02 x 10:~ 7.27x 103

0.44 1.03

4.49 x 102 1.04x 103

23.59* 54.74*

2.96 x 103

0.54

2.24 x l0 s

0.03

4.38 x 102

7.68

1.06x 104

1.93

1.28 x 103

0.18

6.17 x 102

10.81"

Xylem pressure potential Grand mean 1 Soil type 1 Watering trt. 1 Soil type X Watering trt. 1 Date 3 Date X Soil type 3 Date X Watering trt. 3 * P<0.05.

sure p o t e n t i a l suggests that, over days, a consistently different response of x y l e m pressure p o t e n t i a l relative to soil m o i s t u r e recharge c a p a c i t y was seen. T h e r e was, however, no overall significant difference b e t w e e n soils or w a t e r i n g t r e a t m e n t s in Heterotheca s t o m a t a l c o n d u c t a n c e a n d x y l e m pressure p o t e n t i a l over the d a y (total effect, T a b l e 1).

Drought response D u r i n g the four droughts, m i d - d a y s t o m a t a l c o n d u c t a n c e s o f Heterotheca r e m a i n e d below the m i d - d a y lows observed before d r o u g h t i n i t i a t i o n (Figs 1, 2). T h e r e was a significant rise a n d fall fi'om < 100 m m o l in -2 see -~ to > 2 0 0 m m o l m -2 sec J to < 200 m m o l m - 2 sec- 1 ( q u a d r a t i c effect, T a b l e 2). W e l l - w a t e r e d c o n t r o l p l a n t s also h a d low m i d - d a y s t o m a t a l c o n d u c t a n c e s a n d showed decreasing s t o m a t a l c o n d u c t a n c e s over time. W h e n expressed as a p e r c e n t a g e of control p l a n t

values, s t o m a t a l c o n d u c t a n c e s of p l a n t s in all e x p e r i m e n t a l t r e a t m e n t s a c t u a l l y rose over the d r o u g h t period (Fig. 2), p e r h a p s because g u a r d cells b e c a m e i n c r e a s i n g l y u n a b l e to regulate s t o m a t a l o p e n i n g size as p l a n t s dried. O u r results showed no significant i n d i v i d u a l or i n t e r a c t i v e effect of soil type or w a t e r i n g regime o n s t o m a t a l c o n d u c t a n c e d u r i n g the d r o u g h t s (total effect, T a b l e 2). Both xylem pressure p o t e n t i a l ( X P P ) a n d leaf w a t e r c o n t e n t ( L W C ) d e c l i n e d in d r y i n g Heterotheca (Fig. 2). X P P fell to < - 5 M P a by d a y 10 o f d r o u g h t i n g . T h e r e was no significant difference in X P P d u e to soil type or w a t e r i n g t r e a t m e n t (total effect; T a b l e 3), n o r was there significant t r e a t m e n t i n t e r a c t i o n t h a t m i g h t be expected if c o m b i n e d w a t e r a n d n u t r i e n t stress affected plants d u r i n g droughts. L e a f w a t e r c o n t e n t of d r y i n g plants fell t~om 8 6 % of t u r g i d to o n l y 4 0 6 0 % b y the 8th d a y of d r o u g h t (Fig. 2). At 60°/~,

HETEROTHECA WATER RELATIONS AND GROWTH

pressure potential were chosen randomly, this drying pattern contributed to higher variance in measurements toward the end of the droughts.

80

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7

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r

j

I

~

Plant biomass Dry weights of Heterotheca harvested after droughting were significantly influenced by the experimental growing conditions (Table 3). Shoots of plants grown in soil from the more fertile dry field site (DF) had significantly greater mass than those of plants in the less fertile wet site soil (WF; Table 3). In addition, shoots given soil moisture recharge had greater biomass than those kept dry (Table 3). Roots were significantly affected by watering regimes, but not by soil type (Table 3); and there was a significant interaction effect (F = 8.62, P = 0.006). Root biomass of plants grown in the more fertile dry field soils (DF) varied little between watering treatments; in contrast, root growth of plants grown in soil from the less fertile wet site (WF) was greater when allowed soil moisture recharge (WT; Table

• 4o C.9

~A 20

0 Q.

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3). CONCLUSIONS

iOC

d "~

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60

40

2

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6

8

t0

Days into Drought Fro. 2. Stomatal conductances (S.C.), xylem pressure potentials (X.P.P.), and relative water content of leaves (R.W.C.) of Heterotheca during experimental droughts in the greenhouse•

water content leaves were wilted and had begun to brown. By the end of the droughts, pot gravimetric soil moisture averaged 0.007 g H 2 0 per g dry soil and soil water potential was as low as - 3.6 MPa. Mid-day soil temperatures averaged 35°C. Heterotheca plants tended to dry from the bottom up, and many maintained green, turgid growing tips as late as day 10 of the drought. Because stems tbr measures ofstomatal conductance and xylem

We did not reject the null hypothesis that differences in soil fertility and soil moisture recharge capacity have no effect on water relations oflteterotheca. Throughout the day, and during 12-day droughts, xylem pressure potential and stomatal conductances of greenhouse-grown Heterotheca subaxiUaris were insensitive to differences in soil fertility and soil moisture. In contrast to xylem pressure potential and stomatal conductance, growth (biomass) of" Heterotheca was significantly affected by soil type and watering regime in the greenhouse. The more fertile soil (DF) produced heavier shoots, as did a positive capacity for soil moisture recharge (WT). Root biomass of Heterotheca was less affected than shoot biomass by the experimental treatments. However, roots of plants grown in lower fertility soil (WF) showed a greater response to watering treatment than their counterparts in the more fertile (DF) soil; and a positive capacity for soil moisture recharge produced greater root biomass. These results suggest that differences in biomass of Heterotheca could be partly explained by plant growth response to soil fertility or moisture.

B. S. C O L L I N S and G. R. W E I N

72

Table 2. ANO VA of stomatal conductance and xylem pressure potential of Heterotheca during a drydown series. Time (day) was considered a repeated measure dissolved into linear, quadratic and total effects Linear Source Stomatal conductance Grand mean Soil type Watering trt. Soil type X Watering trt.

Quadratic

Total

df

MS

F

MS

F

MS

F

1 1 1

4.82 x 106 1.59 X l 0 4 5.36 X 1 0 4

4.33 0.01 0.05

1.16 X 1 0 6 2.97 X 104 1.85 X 10 :~

29.7* 0.76 0.05

1.59 X 104 5.36 X 104

0.01 0.05

1

1.04

× 10 4

0.01

1.68 X 10:~

0.04

1.04

X 10 4

0.0l

3.71 x 104 7.95 x 102 3.17 x 10 z

1.21 0.03 0.0

5.65 X 1 0 4 7.73 x 102 8.62 x 10:~

2.68 0.04 0.39

5.59 x 10 ~ 5.90 x 103

0.01 0.59

1.15

0.04

7.50 x 102

0.04

3.90 x 103

0.40

Xylem pressure potential Grand mean 1 Soil type 1 Watering trt. 1 Soil type X Watering trt. 1

x 10 3

*P<0.05.

Table 3. Above and below ground biomass (g) of Heterotheca grown in soil from wet, lessfertile ( W F ) and dry, more fertile (DF) sites, with ( W T ) or without ( D T ) soil moisture recharge. Means are given +_ one standard deviation DT

WT

Above ground DF a t WF b

a* 18.2-t-9.3 10.2+_5.1

b 58.9+_22.1 45.7+29.0

Below ground DF a WF a

a 11.9+6.8 9.1 + 6 . 9

b 11.4__+3.9 20.6+_5.9

* Across the table, different letters signify significant differences (P<0.05) between watering treatments in shoot or root biomass. ~ Down the table, different letters signify significant differences between soils in shoot or root biomass.

Acknowledgements

We thank Dr Philip Dixon for statistical advice; Dr J o h n E. Pinder, I I I for use of unpublished data; and two anonymous reviewers for their comments. Support for this project was provided by the U.S. Department of Energy (Contract DE-AC0976SROO-819) through the Savannah River Ecology Laboratory.

REFERENCES 1. Box G. E. and Cox D. R. (1964) An analysis of transtbrmations. Jl R. Statist. Soc., Series B 26, 21 l. 2. BURK C. J. (1961) Environmental variation in Heterotheca subaxiUaris from Texas. Rhodora 63, 243246. 3. BURK C . J . (1966) Rainfall periodicity as a major factor in the formation of flowering races of camphorweed (Heterotheca subaxiUaris). Am. J. Bot. 53, 933-936. 4. GOLLEY F. B. (1965) Structure and function of an old-field broomsedge community. Ecol. Monogr. 35, 113-137. 5. GUREVITCH J. and CHESTER S. T., JR (1986) Analysis of repeated measures experiments. Ecology 67, 251-255. 6. KEEVER C. (1955) Heterotheca latifolia, a new and aggressive exotic dominant in piedmont old-field succession. Ecology 36, 732 739. 7. ODUM E. P. (1960) Organic production and turnover in old-field succession. Ecology 41, 34-49. 8. ODUM E. P., PINDER J. E., I I I and CHRISTIANSEN T. A. (1984) Nutrient losses from sandy soils during old-field succession. Am. Midl. Nat. 111, 148154. 9. PINDERJ. E., I I I (1975) Effects of species removal on an old-field plant community. Ecology 56, 747751. 10. PINDER J. E., I I I (1988) Plant photosynthetic

HETEROTHECA WATER RELATIONS AND GROWTH

pathways and grazing by phytophagous Orthopterans. Am. Midl. Nat. 120, 201-211. SGHOLANDER P. F., HAMMEL H. T., BRADSTREET E. D. and HEMMINGSENE. A. (1965) Sap pressure

73

in vascular plants. Science 148, 339-346. 12. WAGENKNECHTB,L. (1960) Revision of Heterotheca, section Heterotheca (Compositae). Rhodora 62, 61107.