Response of Scots pine (Pinus sylvestris L.) and pubescent oak (Quercus pubescens Willd.) to soil and atmospheric water deficits under Mediterranean mountain climate

The physiological responses to water deficits of Scots pine (Pinus sylvestris L.) and pubescent oak (Quercus pubescens Willd.) were studied under Mediterranean mountain climate. Minimum leaf water potentials were -3.2 MPa for oak and -2.1 MPa for pine, with higher predawn values for pubescent oak. Relative sap flow declined in both species when vapour pressure deficit (D) went above ca. 1.2 kPa, but stomatal control was stronger for pine during the 2003 summer drought. P. sylvestris plant hydraulic conductance on a half-total leaf area basis (k(L,) (s-1)) was 1.2-2.6 times higher than the values shown by Q. pubescens, and it showed a considerably steeper decrease during summer. Leaf-level gas exchange was positively related to k(L, s-1) in both species. Scots pine was more vulnerable to xylem embolism and closed stomata to prevent substantial conductivity losses. The results of this study confirm that pubescent oak is more resistant to extreme drought events.