Abstract
Mediterranean forests including Tunisian pine species are threatened by the rising of temperature and decreasing of precipitation. The impact of the increase of aridity differs across species depending on their stomatal and hydraulic responses. In this paper, three pine species: P. halepensis, P. brutia and P. canariensis growing in three different climatic zones: humid, sub-humid and semi-arid, were studied to detect their different responses to drought and guide their selection for reforestation program. Measurements carried out are hydraulic conductivity at point P50, specific conductivity (Ks), midday stem water potential and hydraulic safety margins. Results showed that during summer, vulnerability to embolism, estimated by water potential inducing 50% loss of xylem hydraulic conductivity (P50), is strongly associated with the capacity for drought resistance. Pinus halepensis (P50 = -4.19 MPa) was found to be more resistant to drought than P. brutia and P. canariensis in the semi-arid climate, whereas P. brutia tolerated the humid climate (P50 = -3.7 MPa) and P. canariensis seems more adapted to the sub-humid climate (P50 = -4.08 MPa). Hydraulic safety margins confirmed the conservative behavior of pine species to avoid drought and for maintaining relatively high water potential in dry conditions. These findings help to assess the impact of mid-summer water deficit on pine species in the context of climate change and to select among these species the most resistant for future reforestation programs.
Highlights
Global warming is rapidly changing climatic conditions worldwide, hotter drought periods are inducing tree mortality (Allen et al, 2015) and, by the year 2050, there is likely to be a substantial reorganization of vegetation (McDowell & Allen, 2015)
Three pine species: P. halepensis, P. brutia and P. canariensis growing in three different climatic zones: humid, sub-humid and semi-arid, were studied to detect their different responses to drought and guide their selection for reforestation program
Pinus halepensis (P50 = -4.19 MPa) was found to be more resistant to drought than P. brutia and P. canariensis in the semi-arid climate, whereas P. brutia tolerated the humid climate (P50 = -3.7 MPa) and P. canariensis seems more adapted to the sub-humid climate (P50 = -4.08 MPa)
Summary
Global warming is rapidly changing climatic conditions worldwide, hotter drought periods are inducing tree mortality (Allen et al, 2015) and, by the year 2050, there is likely to be a substantial reorganization of vegetation (McDowell & Allen, 2015). Mediterranean pinewoods are subject to severe droughts (Martinez-vilalta & Pinol, 2002). In this context, the study of variation among and within forest species in terms of cavitation resistance is very important in order to predict the potential of adaptation to climatic change (Choat et al, 2012). P50 is the xylem pressure corresponding to a 50% loss of conductivity, and it is a proxy of cavitation resistance. It is widely used as a comparative index of xylem hydraulic safety, within different parts of the same individual and within species across environmental gradients (Maherali et al, 2004). Reaching P50 indicates that a hydraulic failure has already occurred (Tyree & Sperry, 1988)
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