Mediterranean forests face an intensification of droughts caused by ongoing climate change. To improve our understanding of tree and forest responses to increasing drought, we explored over nine years, the effects of a 30% rainfall exclusion experiment on the water potential, sap velocity and primary and secondary growth of two co-occurring species (Quercus ilex and Pinus halepensis) in a French Mediterranean forest. In addition, native embolism was measured after six and nine years of exclusion onset. Water potentials decreased earlier during summer drought for both species in the rainfall exclusion plot, and to a higher extent during the drought peak for Q. ilex, involving earlier stomatal closure and reduced sap velocity. Sap velocity reduction persisted throughout the years in the exclusion plot. Outside summer the water potential difference between predawn and midday was similar between treatment which indicate that reduced water transport efficiency may be linked to decrease hydraulic conductance. Such differences were neither related to differences in xylem embolism, that remained similar between treatments, nor to change in secondary growth. In contrast primary growth measurements indicate that P. halepensis trees, and Q. ilex to a lesser extent, experienced reduction in total leaf areas in response to the rainfall exclusion. Globally, our results suggest that increase drought lead, for both species, to a decrease in sap velocity not mediated by increase embolism but rather by a reduction in primary growth. So far little conclusion can be drawn regarding the competitive advantage of one species over the other in the context of increasing drought related to climate change.

由于持续的气候变化，地中海森林面临着加剧的干旱。为了加深我们对树木和森林对日益干旱的反应的理解，我们在九年多的时间里探索了 30% 降雨排除实验对两种共生物种（栎属和Pinus halepensis）在法国地中海森林中。此外，在排除性发作 6 年和 9 年后测量了原生栓塞。降雨排除区中两个物种在夏季干旱期间的水势下降较早，而在冬青的干旱高峰期间下降幅度更大，涉及早期气孔关闭和降低的树液速度。在排除图中，树液速度降低持续多年。在夏季以外，黎明前和中午之间的水势差在处理之间是相似的，这表明水传输效率的降低可能与水力传导率的降低有关。这种差异既与木质部栓塞的差异无关，在处理之间保持相似，也与次生生长的变化无关。相比之下，初级生长测量表明P. halepensis树和Q. ilex在较小程度上，由于排除降雨，总叶面积减少。在全球范围内，我们的结果表明，对于这两个物种，干旱的增加会导致树液速度的降低，这不是由栓塞增加引起的，而是由初级生长的减少引起的。到目前为止，在与气候变化相关的干旱加剧的背景下，一种物种相对于另一种物种的竞争优势几乎无法得出结论。