Response of upland cotton (Gossypium hirsutum L.) leaf chlorophyll content to high heat and low-soil water in the Arizona low desert

CWSI – crop water stress index; DOY – day of year; H – height; L1 – level one; L2 – level two; LAI – leaf area index; NDVI – normalized difference vegetation index; PD – planting dates; RTK – real time kinematic; SEM – structural equation modeling; Ta – ambient temperature; Tc – canopy temperature; TRT – treatment; UTM – universal transverse mercator. Acknowledgments : We would like to thank Matthew McGuire, Paloma Fajardo, Dusti Baker, Scott Machtley, Sharette Rockholt, Kathy Johnson, Suzette Maneely, Pernell Tomasi, Sara Harders, Matthew Hagler, and Melissa Stefanek for assistance with data collections and field management; and Mike Roybal and Bill Luckett for assistance with proximal sensing data handling and management. This work was supported by a Cotton Incorporated Research Grant 13-738 and the United States Department of Agriculture-Agricultural Research Service 2020-2100-013-00D. Conflict of interest : The authors declare that they have no conflict of interest. The sustainable production of upland cotton, an economically important fiber crop, is threatened by changing environmental factors including high temperatures and low-soil water content. Both high heat and low-soil water can reduce net photosynthesis resulting in low fiber yields or poor fiber quality. Leaf chlorophyll content has a direct relationship with photosynthetic rate. Understanding how high heat and low-soil water affect chlorophyll content can identify opportunities for breeding improvement that will lead to sustainable fiber yields. A two-year field trial located in Maricopa Arizona measured leaf chlorophyll content, available soil water, ambient air temperatures, and cotton growth measurements collected by a high-clearance tractor equipped with proximal sensors. The results showed that low-soil water significantly increased leaf chlorophyll content, while high temperatures significantly reduced content. Structured equation modeling revealed that cotton may divert available resources to leaf area and chlorophyll content for the production of photosynthates during periods of high temperatures.