175tions occur is affected by temperature (Johnson and Thornley 1985 ). Thus, when
water stress goes below 40 % ASM, available substrate is limited, and hence the
role of the temperature is reduced on the reaction rates in the plant. The reduction
in dry weight of groundnut plants on exposure to water stress was due to severe
decrease in the amount of water available for transpiration (Fig. 8.7), as evapora-
tion was constant irrespective of the water stress treatment.
The increase in SLA value in 40 % ETC treatment of sowing 1 could be attrib-
uted to a decrease in biomass causing a decrease in leaf weight but not in leaf area.
On the other hand, decrease in SLA of 40 % ETC treatment in sowing 2 could be
attributed to decrease in both leaf weight and leaf size. To account for a decrease
in SLA, the transpiration efficiency ( TE) and transpiration ( T) values were derived
from the equations of Wright et al. (1996). The values of TE (Table 8.8) are similar
in response irrespective of water stress treatment and sowing date.
The decrease in SLA in 40 % ETC of sowing 2 can be attributed to the severe
reduction in transpiration, which could cause a decrease in leaf size along with a
decrease in leaf weight. The decrease in leaf weight and biomass due to reduced
transpiration can be attributed to reduced CO 2 assimilation (Hsiao 1973 ). Similar
decrease in dry matter due to reduced photosynthesis under water stress conditions
were reported in groundnuts by Hubick et al. ( 1986 ).
There were differences in the values for T obtained ( Tsla) from SLA in the above
table using the equations (8.4–8.6) and T values ( Tsim) obtained from the simulations
made using the PNUTGRO model. The total ETC during the crop growth from 30
DAS, when 40 % ETC treatment was initiated, Tcalc and Tsim are depicted in Fig. 8.8.
Fig. 8.6 Simulated values of percentage soil moisture in irrigated (● received 100 % ETC) and
water stress (○ received 40 % of ETC from flowering) treatments in sowing 1 from sowing to
harvest
8 Effect of High Temperature and Water Stress on Groundnuts ...