Petrucco Laura, Nardini Andrea, von Arx Georg, Saurer Matthias, Cherubini Paolo
Dipartimento di Scienze della Vita, Università di Trieste, Via L. Giorgieri 10, I-34127 Trieste, Italy.
Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Zürcherstrasse 111, CH-8903 Birmensdorf, Switzerland.
Tree Physiol. 2017 Apr 1;37(4):523-535. doi: 10.1093/treephys/tpx031.
The 2003 and 2012 summer seasons were among the warmest and driest of the last 200 years over southeastern Europe, and in particular in the Karst region (northeastern Italy). Starting from winter-spring 2013, several black pines (Pinus nigra J.F. Arnold) suffered crown die-back. Declining trees occurred nearby individuals with no signs of die-back, raising hypotheses about the occurrence of individual-specific hydraulic strategies underlying different responses to extreme drought. We investigated possible processes driving black pine decline by dendrochronological and wood anatomical measurements, coupled with analysis of tree-ring carbon (δ13C) and oxygen (δ18O) isotopic composition in healthy trees (H) and trees suffering die-back (D). Die-back trees showed higher growth rates than H trees at the beginning of the last century, but suffered important growth reduction following the dry summers in 2003 and 2012. After the 2012 drought, D trees produced tracheids with larger diameter and greater vulnerability to implosion than H ones. Healthy trees had significantly higher wood δ13C than D trees, reflecting higher water-use efficiency for the surviving trees, i.e., less water transpired per unit carbon gain, which could be related to lower stomatal conductance and a more conservative use of water. Relatively high δ18O for D trees indicates that they were strongly dependent on shallow water sources, or that they sustained higher transpiration rates than H trees. Our results suggest that H trees adopted a more conservative water-use strategy under drought stress compared with D trees. We speculate that this diversity might have a genotypic basis, but other possible explanations, like different rooting depth, cannot be ruled out.
2003年和2012年的夏季是过去200年里东南欧最炎热、最干燥的时期，尤其是在喀斯特地区（意大利东北部）。从2013年冬春季节开始，几株黑松（欧洲黑松）出现树冠枯萎现象。枯萎的树木出现在附近没有枯萎迹象的个体旁边，这引发了关于个体特异性水力策略的假说，这些策略是不同个体对极端干旱产生不同反应的基础。我们通过树木年代学和木材解剖测量，结合对健康树木（H）和枯萎树木（D）的年轮碳（δ13C）和氧（δ18O）同位素组成的分析，研究了导致黑松枯萎的可能过程。在上个世纪初，枯萎树木的生长速度比H树木快，但在2003年和2012年的干旱夏季之后，生长显著减少。2012年干旱之后，D树木产生的管胞直径更大，比H树木更容易发生内爆。健康树木的木材δ13C显著高于D树木，这反映了存活树木更高的水分利用效率，即每单位碳增益的水分蒸发量更少，这可能与较低的气孔导度和更保守的水分利用有关。D树木相对较高的δ18O表明它们强烈依赖浅层水源，或者它们的蒸腾速率比H树木更高。我们的结果表明，与D树木相比，H树木在干旱胁迫下采取了更保守的水分利用策略。我们推测这种差异可能有基因型基础，但其他可能的解释，如不同的根系深度，也不能排除。
