Leaf gas exchange responses to combined heat and drought stress in wheat genotypes with varied stomatal density

Abstract

Stomata regulate the plant’s gas exchange and water balance, and their density may be a crucial factor in the response to abiotic stresses. The aim of this study was to investigate the response of leaf gas exchange of three spring wheat genotypes with different stomatal density to progressive drought and combined heat and drought stress. The stomatal conductance ( g s ) was the most sensitive parameter that declined with increasing drought stress. This negatively affected transpiration and leaf cooling, and limited photosynthesis ( A ) when g s decreased to < 550 mmol m −2 s −1 . The treatments affected all three genotypes similarly over time irrespective of stomatal density. However, when related to the fraction of transpirable soil water ( FTSW ) in the pot, g s and A of the low and high stomatal density cultivars responded differently when heat was added to the drought stress. The high stomatal density cultivar showed no difference in maximum g s at FTSW > 0.3, and a similar decline of g s and A at FTSW < 0.3 in drought alone and combined drought and heat. The low stomatal density cultivar showed a higher maximum g s and the most severe decline of g s under combined heat and drought s tress and a significantly slower decline of g s under drought alone, which was also reflected in a significantly slower reduction in A under drought compared to the combined stress. Overall, the drought response of stomatal closure dominated the physiological response under simultaneous heat and drought irrespective of stomatal density, and it was only in the combined stress that the maximum photochemical efficiency F v /F m was negatively affected. In conclusion, to elucidate the effect of drought and combined drought and heat on the leaf gas exchange in wheat cultivars with varied stomatal density, it is crucial to relate the parameters to the available soil water, not the duration of the drought. • Stomatal conductance was the most sensitive parameter under drought stress. • Lower stomatal density led to higher maximum conductance under combined stress. • Stomatal closure dominated under combined stress irrespective of stomatal density. • Cultivar differences depended on available soil water, not drought duration.

Topics & Concepts