Dynamics of canopy photosynthesis in Pima cotton (Gossypium barbadense L.) as influenced by growth temperature

Abstract

Pima cotton plants (60-day-old) were grown in controlled environment chambers at five day/night temperature regimes (20/12, 24/16, 28/20, 32/24 and 36/28°C) with a 14 h photoperiod in a CO2 concentration of 450μ1 1-1. following complete acclimation to the treated environmental regimes, whole plant CO2 effluxes and influxes were continuously monitored. Pima cotton leaves exhibited extremely high rates of gross photosynthesis (Pg, 6.5 mg CO2 m-2 ground area s-1) under high irradiances (1800μol m-2 s-1). The profile of growth irrandiance and canopy Pg as a function of the time of day indicated a significantly high positive relationship of Pg with photosynthetic photon flux (PPF). Estimates of quantum use efficiency (α) and canopy conductance (l) were very responsive to varying growth temperature. The daily light use efficiency (ratio of daily Pg and the daily incoming solar radiation) qualitatively mimiced the photosynthetic patterns of the canopy with the greatest efficiency from the canopies at 28/20°C (8.35) and the lowest at 20/12°C (5.75). The results indicate that though Pima cotton is an efficient photosynthesizer, the greater carbon sequestering capacity has a pronounced sensitivity to growth temperature.