Predawn Respiration Rates during Flowering Are Highly Predictive of Yield Response in Gossypium hirsutum When Yield Variability Is Water-Induced.

Respiratory carbon evolution by leaves under abiotic stress is implicated as a major limitation to crop productivity; however, respiration rates of fully expanded leaves are positively associated with plant growth rates. Given the substantial sensitivity of plant growth to drought, it was hypothesized that predawn respiration rates (R_PD) would be 1) more sensitive to drought than photosynthetic processes and 2) highly predictive of water-induced yield variability in Gossypium hirsutum. Two studies (at Tifton and Camilla Georgia) addressed these hypotheses. At Tifton, drought was imposed beginning at the onset of flowering (first flower) and continuing for three weeks (peak bloom) followed by a recovery period, and predawn water potential (Ψ_PD), R_PD, net photosynthesis (A_N) and maximum quantum yield of photosystem II (F_v/F_m) were measured throughout the study period. At Camilla, plants were exposed to five different irrigation regimes throughout the growing season, and average Ψ_PD and R_PD were determined between first flower and peak bloom for all treatments. For both sites, fiber yield was assessed at crop maturity. The relationships between Ψ_PD, R_PD and yield were assessed via non-linear regression, and the interactive effects of Ψ_PD and R_PD on fiber yield was assessed using response-surface analysis. It was concluded for field-grown G. hirsutum that 1) R_PD is exceptionally sensitive to progressive drought (more so than A_N or F_v/F_m), 2) average R_PD from first flower to peak bloom is highly predictive of water-induced yield variability, and 3) average Ψ_PD during flowering alters yield response to R_PD.