Physiological Responses of Cotton Leaves to Shading and Aging

Shading causes early stomatal closure, decreasing gas exchange and photoassimilate production. Additional changes in leaf photosynthetic rates result from its aging. We aimed to show the effects of leaf aging with short and long term shading on cotton physiological response. Cotton plants were grown in 12 L pots in a greenhouse. Measurements were made in 15 and 60 day old leaves. The leaves were preconditioned receiving or not shade for 4 days before measurement (long term shading). Each leaf was shaded or no-shaded at the measurement (short term shading), using a black shade cloth (50%). Long term shading (4 days) decreased leaf net photosynthesis in 15 day old leaves but did not in under the short term shading. Shading in leaves over 60 days old did not affect gas exchange. Stomatal conductance was higher in younger leaves. Stomatal conductance in 60 days old leaves declined while intercellular CO2 concentration increasing. Transpiration rates decreased and vapor pressure deficit based on leaf temperature (VpdL) increased with leaf aging.