Leaf carbon and water status control stomatal and non-stomatal limitations of photosynthesis in trees.

Salmon Y , Lintunen A , Dayet A , Chan T , Dewar R , Vesala T , Hölttä T
The New phytologist
Photosynthetic rate is concurrently limited by stomatal and non-stomatal limitations. However, the controls on non-stomatal limitations to photosynthesis (NSL) and their coordination with stomatal control on different timescales remain poorly understood. According to a recent optimization hypothesis, NSL depends on leaf osmotic or water status, and is coordinated with stomatal control so as to maximize leaf photosynthesis. Drought and notching experiments were conducted on Pinus sylvestris, Picea abies, Betula Pendula, and Populus tremula seedlings in greenhouse conditions to study the dependence of NSL on leaf osmotic and water status, and its coordination with stomatal control, on timescales of minutes and weeks, to test the assumptions and predictions of the optimization hypothesis. Both NSL and stomatal conductance followed power-law functions of leaf osmotic concentration and leaf water potential. Moreover, stomatal conductance was proportional to the square root of soil-to-leaf hydraulic conductance, as predicted by the optimization hypothesis. While the detailed mechanisms underlying the dependence of NSL on leaf osmotic or water status lie outside the scope of this study, our results support the hypothesis that NSL and stomatal control are coordinated to maximize leaf photosynthesis, and allow the effect of NSL to be included in models of tree gas-exchange.

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