Characterizing Leaf Gas Exchange Responses of Cotton.

Physiological responses of plants to the environment can be monitored using leaf gas exchange measurements. The objective of this study was to investigate physiological responses of several cotton (Gossypium hirsutum) varieties using leaf gas exchange measurements under different irrigation treatments. Variables of leaf gas exchange, soil moisture (θ), and plant growth parameters were measured. Significant differences were found in leaf net assimilation (An), stomatal conductance (g), transpiration rate (Tr), and water use efficiency (WUE) among irrigation treatments in 2006 while no significant differences were found in these parameters in 2007 due to precipitation in excess amounts of 576 mm during the growing season. Lint yield was strongly correlated to g, Tr, WUE, and θ at 60 cm depth. We also present the feasibility of using normalized An and Tr to quantify plant water deficit. Relative An started to decrease between 0.4 and 0.2 of fraction of transpirable soil water (FTSW) and relative Tr started to decrease at ~ 0.2 of FTSW. The results demonstrate that plant water status under deficit irrigation management can be quantitatively monitored using the measures of leaf gas exchange. These parameters are expected to be developed as decision tools for irrigation management.

Keywords: cotton, leaf net assimilation rate, stomatal conductance, transpiration rate.