Hydraulic acclimation in a Mediterranean oak subjected to permanent throughfall exclusion results in increased stem hydraulic capacitance

Stem water storage capacity and hydraulic capacitance (C-S) play a crucial role in tree survival under drought-stress. To investigate whether C-S adjusts to increasing water deficit, variation in stem water content (StWC) was monitored in vivo for 2 years and related to periodical measurements of tree water potential in Mediterranean Quercus ilex trees subjected either to permanent throughfall exclusion (TE) or to control conditions. Seasonal reductions in StWC were larger in TE trees relative to control ones, resulting in greater seasonal C-S (154 and 80 kg m(-3) MPa-1, respectively), but only during the first phase of the desorption curve, when predawn water potential was above -1.1 MPa. Below this point, C-S decreased substantially and did not differ between treatments (