Effects of drought on mesophyll conductance and photosynthetic limitations at different tree canopy layers

In recent years, many studies have focused on the limiting role of mesophyll conductance (gm) to photosynthesis (An) under water stress, but no studies have examined the effect of drought on gm through the forest canopy. We investigated limitations to An on leaves at different heights in a mixed adult stand of sessile oak (Quercus petraea) and beech (Fagus sylvatica) trees during a moderately dry summer. Moderate drought decreased An of top and lowest beech canopy leaves much more than in leaves located in the mid canopy; whereas in oak, An of the lower canopy was decreased more than in sunlit leaves. The decrease of An was probably not due to leaf-level biochemistry given that VCmax was generally unaffected by drought. The reduction in An was instead associated with reduction in stomatal and mesophyll conductances. Drought-induced increases in stomatal limitations were largest in leaves from the top canopy, whereas drought-induced increases in mesophyll limitations were largest in leaves from the lowest canopy. Sensitivity analysis highlighted the need to decompose the canopy into different leaf layers and to incorporate the limitation imposed by gm when assessing the impact of drought on the gas exchange of tree canopies. Mesophyll conductance (gm) is now recognised as a key limitation of photosynthesis that should be incorporated into canopy-level models of C exchange. Variation in gm through the canopy of trees has been investigated, but we do not know if water stress affects equally gm of all canopy layers. We investigated limitations to photosynthesis at different heights in a mixed adult stand of Quercus petraea and Fagus sylvatica trees during a moderately dry summer. Drought-induced increases in stomatal limitations were largest in leaves from the top canopy, whereas drought-induced increases in mesophyll limitations were largest in leaves from the lowest canopy. © 2013 John Wiley & Sons Ltd.

Bibliographic Details

Main Authors:	Cano, F. J., Sánchez-Gómez, D., Rodríguez-Calcerrada, J., Warren, C. R., Gil, L., Aranda, I.
Format:	journal article biblioteca
Language:	eng
Published:	2013
Online Access:	http://hdl.handle.net/20.500.12792/5696
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