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Journal Article

Leaf physiological responses to extreme droughts in Mediterranean Quercus ilex forest

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Misson, L., Limousin, J. M., Rodriguez, R., & Letts, M. G. (2010). Leaf physiological responses to extreme droughts in Mediterranean Quercus ilex forest. Plant, Cell and Environment, 33, 1898-1910. doi:10.1111/j.1365-3040.2010.02193.x.

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Global climate change is expected to result in more frequent and intense droughts in the Mediterranean region.To understand forest response to severe drought, we used a mobile rainfall shelter to examine the impact of spring and autumn rainfall exclusion on stomatal (SL) and nonstomatal (NSL) limitations of photosynthesis in a Quercus ilex ecosystem. Spring rainfall exclusion, carried out during increasing atmospheric demand and leaf development, had a larger impact on photosynthesis than autumn exclusion, conducted at a time of mature foliage and decreasing vapour pressure deficit. The relative importance of NSL increased with drought intensity. SL and NSL were equal once total limitation (TL) reached 60%, but NSL greatly exceeded SL during severe drought, with 76% NSL partitioned equally between mesophyll conductance (MCL) and biochemical (BL) limitations when TL reached 100%. Rainfall exclusion altered the relationship between leaf water potential and photosynthesis. In response to severe midsummer drought stress, An and Vcmax were 75% and 72% lower in the spring exclusion plot than in the control plot at the same pre-dawn leaf water potential. Our results revealed changes in the relationship between photosynthetic parameters and water stress that are not currently included in drought parameterizations for modelling applications.