Water stress and water-use efficiency in field grown wheat: A comparison of its efficiency with that of C4 plants

Agricultural Meteorology, 29 (1983) 159--167 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

159

W A T E R S T R E S S A N D W A T E R - U S E E F F I C I E N C Y IN F I E L D G R O W N W H E A T : A C O M P A R I S O N O F ITS E F F I C I E N C Y W I T H T H A T O F C4 PLANTS P.K AGGARWAL and S.K. SINHA Water Technology Centre, Indian Agricultural Research Institute, New Delhi-11012 (India)

(Received December 2, 1982; revision accepted March 1, 1983) ABSTRACT Aggarwal, P.K, and Sinha, S.K., 1983. Water stress and water-use efficiency in field grown wheat: a comparison of its efficiency with that of Ca plants. Agric. Meteorol., 29: 159--167. Two cultivars of wheat, contrasting in their drought resistance characteristics, were grown under irrigated and non-irrigated conditions in the field for two seasons. The water-use efficiency (WUE) ranged from 0.5 to 13.8g dry matter kg -1 water used depending upon the growth stage, cultivar and water stress. The average WUE for the season was between 3.34 and 4.70g dry matter kg -1 water used. Regression analysis indicated that WUE was a function of dry matter produced and had no direct statistical relationship with the weather parameters. The WUE of plants having the C3 system of photosynthesis, like wheat, need not be poorer than the plants with the C4 system if comparisons are made of plants growing in their respective preferred ecological niches. Various possible reasons for the low values of WUE reported for C3 plants are discussed. INTRODUCTION Breeding for water-use efficiency ( W U E ) is an i m p o r t a n t objective for the i m p r o v e m e n t in grain yield o f crops g r o w n in rain-fed areas (Stone, 1 9 7 4 ; Q u i z e n b e r r y , 1 9 8 2 ) . Water-use efficiency can be i m p r o v e d b y either r e d u c i n g the water use or increasing the dry m a t t e r p r o d u c t i o n . Plants with C4 p a t h w a y for assimilation are c o n s i d e r e d m o r e efficient in water use (3 g d r y m a t t e r kg -1 water used) t h a n the plants with C3 s y s t e m ( 1 . 5 g d r y m a t t e r kg-1 w a t e r used), since t h e y (C4) have a higher net assimilation rate and internal resistance (Downes, 1 9 6 9 ; Slatyer, 1 9 7 0 ; Ting et al., 1 9 7 2 ; Teare et al., 1 9 7 3 ; L u d l o w , 1 9 7 6 ; R a w s o n et al., 1 9 7 7 b ; Fischer and Turner, 1978). Based on these estimates Moss et al. ( 1 9 7 4 ) visualised t h a t incorpora t i o n of C4 m e t a b o l i s m into C3 plants w o u l d i m p r o v e t h e latter's WUE. If these estimates are c o r r e c t t h e n the d r y m a t t e r p r o d u c e d b y a c r o p growing on 20 cm moisture, the n o r m a l l y available limit o f water in rain-fed areas in winter in N o r t h e r n India, should be 30 Q h a - 1 for a C3 s y s t e m and 60 Q h a for a C4 system. However, in a 5 year s t u d y o f 25 g e n o t y p e s belonging to wheat, triticale a n d barley (C3 systems), growing o n 20 cm water, the aboveg r o u n d d r y m a t t e r alone was f o u n d to be b e t w e e n 90 and 1 0 0 Q h a -~ (S.K. Sinha, P.K. Aggarwal and G.S. Chaturvedi, u n p u b l i s h e d data). Obviously,

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© 1983 Elsevier Science Publishers B.V.

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the r ep o r ted values of WUE do not hold good for the field grown plants, at least in C3 systems like wheat, triticale and barley. In this communication, therefore, it has been a t t e m p t e d to present a seasonal analysis of dry matter production, water use and water-use efficiency in two contrasting cultivars of wheat grown in an irrigated and non-irrigated environment in the field. MATERIALS AND METHODS

Plan t material Two cultivars of Triticum aestivum L., Kalyansona and C 306, were used in the present study. The former is a high-yielding wheat with a wide adaptability, whereas C 306 is a specific drought resistant cultivar (Rao, 1978). The plants were grown in a field characterized by sandy-loam soil under two different moisture regimes, non-irrigated and irrigated with 5 cm of water, each time, at the r e c o m m e n d e d growth stages of crown root, jointing, booting, flowering and grain filling. The experiment was conduct ed during 1979--80 and 1981--1982. The cultivars were sown on 15 November in both years, using a randomized block design. Fertiliser at the rate of 7 5 : 6 0 : 4 0 kg NPK ha-I was given as a single basal dose. Both cultivars were replicated three times and seeds were sown in rows 2 0 c m apart in 5 × 5 m plots. After germination, the distance between plants was maintained at 2 cm.

Water use Water-use was estimated gravimetrically by following the change in soil moisture profiles down to 1 5 0 c m depth at regular time intervals from sowing to harvest in different plots. Samples were taken for 0--15, 15- 30, 30--60, 60--90, 90--120 and 1 2 0 - - 1 5 0 c m soil depths. Change in total moisture between two consecutive samplings was taken as the water used during th at period. Rainfall, if any, was included in the water used. There was no significant cont r i but i on of ground water by capillary rise, since the depth of water table was always below 4 m.

Dry matter (DM) Above-ground biomass was harvested at regular intervals from an area of 0.2 m 2 in each plot. T he plants were oven-dried at 80°C for 96 h before t hey were weighed. Change in DM between two consecutive samplings was taken as the DM p r o d u ced during that period.

Water-use efficiency (WUE ) This was calculated for different periods by DM p r o d u c e d / w a t e r used.

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Fig. 1. Average daily mean temperature, solar radiation, relative humidity, pan evaporation and fortnightly rainfall during the crop seasons.

Weather parameters Average daffy mean temperature, solar radiation, relative humidity, pan evaporation and fortnightly rainfall were obtained for the entire crop season from an agro--meteorological laboratory situated adjacent to the experimental plots. RESULTS

Weather parameters Average daily mean temperatures, solar radiation and pan evaporation were generally higher, whereas relative humidity and fortnightly rainfall were lower in 1979--80 than in 1981--82 (Fig. 1). Solar radiation remained constant until 60 days after sowing and then increased. Pan evaporation was also relatively constant for 60 days at 2.5 ram, but later it increased to 5.0 mm (Fig. 1). Average temperature declined for 45 days after sowing, but it later became constant at 14 -+ 1°C until day 90 after which it again increased. Rainfall was scanty (45 mm) in 1979--80 compared to 1981--82 when it was substantial (104 mm) and well distributed (Fig. 1).

162

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Fig. 2. Seasonal change in DM production, water use and WUE in irrigated and nonirrigated wheat in 1979--80. Values are means -+ 1 s.e.m, and vertical bars represent ± 1 s.e.m. Dry matter (DM) D r y m a t t e r p r o d u c t i o n was greater in irrigated plants t h a n in the nonirrigated plants o f b o t h varieties, particularly in 1979---80 w h e n the rainfall was s c a n t y (Figs. 2 and 3). T h e rate o f DM p r o d u c t i o n increased with time until t h e pre-flowering period ( 7 5 - - 9 0 days) and t h e n started declining in all t h e t r e a t m e n t s , e x c e p t for K a l y a n s o n a during 1 9 7 9 - - 8 0 w h e r e m a x i m u m DM was f o r m e d b e t w e e n 105 and 120 days. On average, K a l y a n s o n a prod u c e d m o r e DM t h a n C 306, in b o t h irrigated and non-irrigated t r e a t m e n t s (Table I). Water used In a t r e a t m e n t , w a t e r used during d i f f e r e n t g r o w t h periods was approxim a t e l y equal in 1 9 8 1 - - 8 2 , b u t it varied with time in 1 9 7 9 - - 8 0 (Figs. 2 and 3). T h e cultivar C 306 used m o r e water t h a n K a l y a n s o n a in b o t h irrigated and non-irrigated t r e a t m e n t s during d i f f e r e n t stages (Figs. 2 and 3) which

163 C 30 6~rrigated C306, Non q r r i g a t e d K Sona, lrr,gated -~ ~( SoD(], Non-irrigated

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Fig. 3. Seasonal change in DM production, water use and WUE in irrigated and nonirrigated wheat in 1981--82. Values are means -+1 s.e.m, and vertical bars represent ± 1 s.e.m.

was also reflected in t h e total water used in a crop season (Table I). In all t h e t r e a t m e n t s , water used b e t w e e n 45 and 90 days after s o w i n g was l o w e r than t h e periods b e f o r e and after this period.

Water-use efficiency Water-use e f f i c i e n c y changed w i t h t h e g r o w t h stage, variety and irrigation (Figs. 2 and 3). The highest WUE ( 1 3 . 8 g D M k g -1 H 2 0 used) was rec o r d e d in t h e K a l y a n s o n a irrigated t r e a t m e n t during t h e pre-flowering period ( 7 5 - - 9 0 days). Water-use e f f i c i e n c y ranged b e t w e e n 0.5 and 13.8 g D M k g -1 water used. The m e a n WUL' o f the season was higher in the non-irrigated t r e a t m e n t o f b o t h varieties (Table I). K a l y a n s o n a had higher WUE than C 3 0 6 in b o t h irrigated and non-irrigated t r e a t m e n t s . Regression analysis o f WUE p r o d u c e d t h e e q u a t i o n

WUE = 3 . 8 2 + 0 . 0 2 9 D M -- 0 . 0 9 5 WU, (r = 0 . 9 1 ; n

= 68)

(1)

WUE appeared to be d e p e n d e n t o n DM p r o d u c t i o n and to s o m e e x t e n t o n w a t e r use (WU). M e t e o r o l o g i c a l parameters had n o direct significant relationship w i t h WUE.

164 TABLE I Water use, D M p r o d u c t i o n and WUE in w h e a t per crop season (data are the mean o1' two years and values are m e a n s + 1 s.e.m.) Treatment

C 306, irrigated C 306, non-irrigated Kalyansona, irrigated Kalyansona, non-irrigated

Water used ( k g m -2)

DM produced ( g m -2)

WUE (gDMkg

430 + 14

1437 -+ 35

3.34 -+ 0.10

244 -+ 10

991 -+ 90

4.05 +- 0.33

410 +- 19

1578 -+ 46

3.85 +- 0,20

228 +

1073-+81

4.70+- 0.82

7

' water used)

DISCUSSION

Results of these field based experiments indicate that WUE of wheat, a C3 system, ranges between 0.5 g and 13.8 g DM kg- 1 H2 O used depending upon the cultivar, stage and water stress. Seasonal averages of WUE also ranged between 3.34 and 4.70 g DM kg -1 H 2 O used. This clearly shows that C3 plants need not be p~or in WUE when compared to C4 plants as is widely believed (Downes, 1969; Slatyer, 1970; Teare et al., 1973; Ludlow, 1976; Rawson et al., 1977b; Fischer and Turner, 1978). The observed values of WUE in these experiments would be higher still if the weight of roots and loss of water by evaporation were also considered. What then could be the possible reasons for the difference between these observed values and the reported values of WUE in the literature? In a large number of earlier studies, plants were grown either in solution cultures or in pots maintained at field capacity (Downes, 1969; Slatyer, 1970). Under such conditions, in the absence of canopy effects, a greater vapour pressure gradient would be established between the evaporating surfaces (leaves and soil) and the atmosphere resulting in excessive water loss without any concomitant increase in DM production. This is amply proven by the experiments of Rawson et al. (1977a) where stressed wheat plants having better WUE became poor in WUE when the water was made freely available to them. The usefulness of anti-transpirants in improving WUE has been shown to occur only under irrigated conditions (Gale and Hagan, 1966); this further suggests that WUE would obviously be poor if water is freely available as in pots or in solution cultures. Indeed, Ritchie (1974) indicated that WUE would be better if plants experienced moderate water deficits causing root systems to absorb water from deeper layers in the soil. Secondly, it has now been conclusively shown that results of pot experiments cannot be wholly extrapolated to field conditions (Begg and Turner, 1976; Jones and Rawson, 1979).

165 An additional major reason responsible for the reported low WUE values for C3 plants is the growth conditions where such comparisons were made. Most of the time the comparisons were made in conditions of relatively high temperature and radiation, which favour C4 systems more than the C3 systems (Downes, 1969; Slatyer, 1970). However, it is a common understanding that the majority of C3 plants are grown in a temperate climate where temperatures and radiation are not very high (Bjorkman, 1971). Therefore, a comparison made for both systems when grown in identical conditions in a growth-room may not be relevant in terms of differences associated with photosynthesis systems or crop productivity under field conditions. The variance of WUE with temperature in wheat has been shown earlier (Warren and Lill, quoted, in Fischer, 1979). Gifford (1974) reviewed the reported data on growth and photosynthetic assimilation of C3 and C4 systems. He could not find any apparent difference between the best examples of both the groups when grown in their own preferred natural environments. However, Monteith (1978) criticised the conclusions of Gifford (1974), but agreed that part of the reported differences between C 3 and C4 may be environmental. It would not, therefore, be surprising if the WUE of C3 and C4 plant systems are not found to be different when comparisons are made between plants growing in their respective ecological niches. Indeed, it has been demonstrated to be so by Caldwell et al. (1977) in a study of shrub plants. The water use efficiency could also be influenced by the growth stage of the plants. Experiments conducted with seedlings would always show poor WUE due to excessive evaporative losses, as was the case in these studies during the initial stages of growth when the crop cover was inadequate. Moreover, the instantaneous values of WUE would be different from daily WUE, and both would be poorer than the seasonal WUE since the canopy, age and environment effects are neglected in the former. Further, the observed values of WUE in wild plants like Atriplex and trees may not be true for annual herbaceous crop plants, because in the latter it is more important to produce substantial dry matter in a short time. Sinclair and de Wit (1975) reported that the DM produced per unit of photosynthesis is less in a legume and in oilseed plants than in a cereal. Recently Sinha et al. (1982) have suggested that the energy output of legumes and oilseeds, when compared with cereals, is not different. Therefore, for this reason, the wide apparent differences in WUE between a C4 system like sorghum and maize, and leguminous C3 systems like soybean, observed by Ludlow and Wilson (1972) and Teare et al. (1973), may not remain so when the DM produced is expressed in terms of energy conservation. It can be deduced from these experiments that WUE is m o s t l y a function of DM produced, and that ago--meteorological parameters have no direct effect. The excess water used in irrigated treatments was not associated with a proportional increase in leaf area (Aggarwal and Sinha, unpublished data)

166 suggesting t h a t a large p a r t o f t h e w a t e r was e v a p o r a t e d d i r e c t l y and n o t t r a n s p i r e d , resulting in a relatively w e a k r e l a t i o n s h i p b e t w e e n w a t e r use a n d WUE. In a s t u d y involving inbreds and h y b r i d s of maize, Mtui et al. ( 1 9 8 1 ) also f o u n d a r e l a t i o n s h i p b e t w e e n WUE and n e t assimilation rate. H e r e , it m a y be i m p o r t a n t to p o i n t o u t t h a t in o u r studies the d a y t e m p e r a t u r e during m o s t o f t h e g r o w t h stage r a n g e d b e t w e e n 20 a n d 25°C, which w o u l d be n e a r o p t i m a l f o r p h o t o s y n t h e s i s ( B j o r k m a n , 1971). The low night t e m p e r a t u r e ( 5 - - 1 0 ° C ) w o u l d s i m u l t a n e o u s l y r e d u c e the r e s p i r a t o r y Losses. C o n s e q u e n t l y , these c o n d i t i o n s w o u l d help in m a i n t a i n i n g a higher net assimilation r a t e , a n d h e n c e , p r o d u c i n g m o r e DM. T h u s , the environmentaL f a c t o r s w o u l d have a direct e f f e c t on p h o t o s y n t h e s i s and n o t on WUE. It is c o n c l u d e d t h a t WUE of w h e a t m a y range f r o m 0.5 to 1 3 . 8 g D M kg -~ w a t e r d e p e n d i n g u p o n g r o w t h stage, cultivar and w a t e r stress. T h e r e p o r t e d d i f f e r e n c e s in WUE b e t w e e n C3 a n d C4 p l a n t s y s t e m s w o u l d be s u b s t a n t i a l l y r e d u c e d if t h e c o m p a r i s o n s are m a d e in their natural p r e f e r r e d e n v i r o n m e n t s . I n c o r p o r a t i o n o f C 4 characteristics in a C3 s y s t e m w o u l d n o t really h e l p in i m p r o v i n g t h e WUE o f t h e latter as has b e e n visualised b y Moss et al. (1974). ACKNOWLEDGEMENTS We are grateful t o Dr~ A.M. Michael, Project D i r e c t o r , Water T e c h n o l o g y Centre, f o r p r o v i d i n g t h e facilities, and to Mr. K a i l a s n a t h a n for t h e w e a t h e r data.

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