Water stress reduces net CO 2 assimilation (A) and yield of cotton ( Gossypium hirsutum L.), but our knowledge of the physiology, of water stress on A and assimilation capacity is incomplete. Experiments were conducted in a rain shelter‐lysimeter facility in 1990 and 1991 to determine if the yields of two short‐season cotton cultivars with common ancestry, TAMCOT HQ95 (HQ95) and G&P74 + (GP74), resulted from intrinsic differences in A and assimilation capacity. Water stress was imposed by withholding 0, 50 or 75, and 100% of the depleted soil water after flowering. Results indicated that both stomatal and nonstomatal factors were important in controlling A. HQ95 bad higher A and g than GP74 over leaf water potentials (Ψ L ) ranging from − 1.0 to − 3.2 MPa. Nonstomatal limitations to A were more important than stomatal factors when Ψ L was > − 1.5 MPa. Stomatal factors limited A when Ψ L was < − 1.5 MPa for both cultivars. The initial slope (S i ) and the maximum A at high c i (A max )declined with increasing water stress for both cultivars. The S i was greater for HQ95 than GP74 over the range in Ψ L and suggest that HQ95 had higher ribulose‐l,5‐bisphosphate carboxylase‐oxygenase activity than GP74. Increasing water stress reduced A max equally in both cultivars. This suggests that electron transport processes for ribulose‐l,5‐bisphosphate regeneration of the cultivars did not differ. Therefore, stomatal and nonstomatal CO 2 assimilation processes are important in limiting A of water stressed cotton. Intrinsic differences in these processes enable some cotton cultivars to better tolerate water stress.
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Faver et al. (1996) studied this question.