Drought prolongs leaf life span in the herbaceous desert perennial Cryptantha flava

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Abstract
Summary: Drought‐deciduous leaves are common in habitats with predictable, seasonal drought, and a reduction in transpirational surface area is generally considered an important drought‐response strategy. Yet leaf demographic responses to unpredictable drought events that can occur at any time during the growing season have been little studied in ecological systems. We created drought in a natural population of the herbaceous desert perennial Cryptantha flava (A. Nels.) Payson (Boraginaceae) in north‐eastern Utah, USA, by installing rainout shelters just before and during the early part of the growing season, from 1 March until mid‐June in 1998, and from 1 March until mid‐May in 1999. Droughted plants exhibited water stress through lower rates of midday photosynthesis and conductance, and by producing leaves with a smaller surface area and greater specific mass than plants exposed to ambient precipitation. Under drought, leaf life span increased on flowering stalks and vegetative rosettes and new leaf production decreased, reducing leaf turnover and increasing standing leaf crop in droughted plants. A larger number of leaves under drought conditions compensated in area for their smaller size, which means that transpirational surface area was not reduced. The reduction in photosynthetic rate and the increase in leaf life span are consistent with a more general pattern in response to other low resource conditions, paralleling leaf‐level responses to shortages of nutrients and light. Plants in the drought and ambient precipitation treatments responded to late‐season rainfall with increased leaf production, providing an additional example of developmental plasticity in response to temporal heterogeneity in water availability.

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