Abstract
Many studies have demonstrated that the cotton in warm environments is vulnerable to water-limitations thus reducing the yield. A number of plant traits have been recommended to ameliorate the effects of water deficits on plant growth and yield. Limitation on maximum transpiration rate (TR) under high vapor pressure deficit (VPD), usually occurs during midday, is often considered as a water conservation trait. The genotypes with this trait are desirable in high VPD environments where water deficits commonly develop in the later part of the growing season. Our objective of the study was to find the genotypic variation for the trait limited TR under high VPD and also to study leaf temperature, water potential, photosynthesis, and stomatal conductance responses. Also, our objective was also to study the structural changes in the stomatal traits when exposed to long term high VPD conditions and involvement in such responses. In the present study, 17 cotton genotypes were studied for their (TR) response to various VPD environments under well irrigated conditions. Out of 17, eight genotypes limited TR after approximately 2 kPa VPD and rest of them increased their TR with increased VPD. Five selected genotypes with different TR response to increasing VPD were further studied for gas exchange and stomatal properties. All genotypes, irrespective of exhibiting limited TR at high VPD, reduced stomatal conductance, photosynthesis and water potential at high VPD of 3.3 kPa. The genotypes with limited TR modified their stomatal traits mostly on the adaxial surface with frequent and small stomata under high VPD. The genotypes with limited TR also exhibited an increase in epidermal cell expansion and stomatal index at contrasting VPD gradients to effectively balance the liquid and vapor phase conductance to limit TR at high VPD.
Highlights
Drought is the major limiting factor for cotton production, affecting growth, productivity, and fiber quality (Parida et al, 2007)
Some genotypes were well characterized by the two-segmental analysis with a break point (BP) (X0), and other genotypes exhibited a linear increase in transpiration rate (TR) for the range of vapor pressure deficit (VPD) tested (Figure 1 and Table 2)
The results showed that the effect on the stomatal index (SI) was different on the adaxial and abaxial surfaces, when VPD significantly increased the SI by 13–51% on the adaxial surface (P < 0.001) but marginal or no increase on the abaxial surface (Figures 4B,C)
Summary
Drought is the major limiting factor for cotton production, affecting growth, productivity, and fiber quality (Parida et al, 2007). One of the strategies is to limit transpiration rate (TR) under high vapor pressure deficit (VPD) environments. VPD, is the difference between the amount of moisture in the air and the moisture air can hold when it is saturated It combines the effect of temperature and RH, has an effect on transpiration of the plants. High VPD, which usually occurs usually in the midday to end of the day, influences the water balance of the plant affecting photosynthesis and growth. Limiting transpiration in this situation will help the plant to conserve water for use later in the crop growing seasons when drought develops. Limited TR in response to high VPD has been observed in several crop species due to genotypic variability (Fletcher et al, 2007; Devi et al, 2010; Gholipoor et al, 2010; Kholová et al, 2010; Schoppach and Sadok, 2013) and found to increase crop yield by 75% in water-limited areas based on simulations in crop models (Sinclair et al, 2005, 2010; Sermons et al, 2012; Drake et al, 2013; Shekoofa et al, 2016)
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