Thresholds for leaf damage due to dehydration: declines of hydraulic function, stomatal conductance and cellular integrity precede those for photochemistry

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Abstract
Summary: Given increasing water deficits across numerous ecosystems world‐wide, it is urgent to understand the sequence of failure of leaf function during dehydration. We assessed dehydration‐induced losses of rehydration capacity and maximum quantum yield of the photosystemII(Fv/Fm) in the leaves of 10 diverse angiosperm species, and tested when these occurred relative to turgor loss, declines of stomatal conductancegs, and hydraulic conductanceKleaf, including xylem and outside xylem pathways for the same study plants. We resolved the sequences of relative water content and leaf water potential Ψleafthresholds of functional impairment. On average, losses of leaf rehydration capacity occurred at dehydration beyond 50% declines ofgs,Kleafand turgor loss point. Losses ofFv/Fmoccurred after much stronger dehydration and were not recovered with leaf rehydration. Across species, tissue dehydration thresholds were intercorrelated, suggesting trait co‐selection. Thresholds for each type of functional decline were much less variable across species in terms of relative water content than Ψleaf. The stomatal and leaf hydraulic systems show early functional declines before cell integrity is lost. Substantial damage to the photochemical apparatus occurs at extreme dehydration, after complete stomatal closure, and seems to be irreversible.
Funding Information
  • National Science Foundation (1457279)

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