Water deficit in field-grown Gossypium hirsutum primarily limits net photosynthesis by decreasing stomatal conductance,increasing photorespiration,and increasing the ratio of dark respiration to gross photosynthesis |
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| Authors: | Daryl R Chastain John L Snider Guy D Collins Calvin D Perry Jared Whitaker Seth A Byrd |
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| Institution: | 1. Department of Crop and Soil Sciences, University of Georgia, 115 Coastal Way, Tifton, GA 31794, USA;2. College of Agriculture and Environmental Sciences, University of Georgia, 8207 Georgia 37, Camilla, GA 31730, USA;3. Department of Crop and Soil Sciences, University of Georgia, PO Box 8112, GSU Statesboro, GA 30460, USA |
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| Abstract: | Much effort has been expended to improve irrigation efficiency and drought tolerance of agronomic crops; however, a clear understanding of the physiological mechanisms that interact to decrease source strength and drive yield loss has not been attained. To elucidate the underlying mechanisms contributing to inhibition of net carbon assimilation under drought stress, three cultivars of Gossypium hirsutum were grown in the field under contrasting irrigation regimes during the 2012 and 2013 growing season near Camilla, Georgia, USA. Physiological measurements were conducted on three sample dates during each growing season (providing a broad range of plant water status) and included, predawn and midday leaf water potential (ΨPD and ΨMD), gross and net photosynthesis, dark respiration, photorespiration, and chlorophyll a fluorescence. End-of-season lint yield was also determined. ΨPD ranged from −0.31 to −0.95 MPa, and ΨMD ranged from −1.02 to −2.67 MPa, depending upon irrigation regime and sample date. G. hirsutum responded to water deficit by decreasing stomatal conductance, increasing photorespiration, and increasing the ratio of dark respiration to gross photosynthesis, thereby limiting PN and decreasing lint yield (lint yield declines observed during the 2012 growing season only). Conversely, even extreme water deficit, causing a 54% decline in PN, did not negatively affect actual quantum yield, maximum quantum yield, or photosynthetic electron transport. It is concluded that PN is primarily limited in drought-stressed G. hirsutum by decreased stomatal conductance, along with increases in respiratory and photorespiratory carbon losses, not inhibition or down-regulation of electron transport through photosystem II. It is further concluded that ΨPD is a reliable indicator of drought stress and the need for irrigation in field-grown cotton. |
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| Keywords: | CC CO2 concentration at the carboxylation site Ci internal leaf CO2 concentration E leaf transpiration rate ETR electron transport rate through photosystem II F&prime steady state fluorescence of illuminated leaves Fo minimum fluorescence of dark adapted leaves Fm maximum fluorescence of dark-adapted leaves Fm&prime maximum fluorescence of illuminated leaves Fv/Fm maximum quantum yield of photosystem II gs stomatal conductance to water vapor PAR photosynthetically active radiation PG gross photosynthesis PN net photosynthesis PSII photosystem II RD dark respiration Rl photorespiration Rn single-leaf nocturnal respiration rate TL air temperature TA leaf temperature Ψl leaf water potential ΨMD midday leaf water potential ΨPD predawn leaf water potential ΦPSII actual quantum yield of electron transport through PSII |
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