Mas E, Vilagrosa A, Morcillo L, Valladares F, Grossiord C
Plant Ecology Research Laboratory (PERL), School of Architecture, Civil and Environmental Engineering, EPFL, Lausanne, Switzerland.
Community Ecology Unit, Swiss Federal Institute for Forest, Snow and Landscape WSL, Lausanne, Switzerland.
Plant Biol (Stuttg). 2024 Sep 27. doi: 10.1111/plb.13716.
Increasing tree species diversity in Mediterranean forests could reduce drought-induced hydraulic impairments through improved microclimate and reduced competition for water. However, it remains unclear if and how species diversity modulates tree hydraulic functions and how impacts may shift during the growing season. Using unmanaged Mediterranean forest stands composed of one (i.e., monospecific) or four (i.e., multispecific) tree species, we examined the seasonal dynamics of in-situ hydraulic traits (predawn and midday leaf water potential - Ψ and Ψ, xylem- and leaf-specific hydraulic conductivity - K and K, percentage loss of conductivity - PLC, specific leaf area - SLA, and Huber value - HV) in four co-existing Pinus and Quercus species over two years. We mainly observed adverse impacts of species diversity with lower Ψ, Ψ, K, K, and higher PLC in multispecific compared to monospecific stands, especially for the two pines. These impacts were observed all along the growing season but were stronger during the driest periods of the summer. Beneficial impacts of diversity were rare and only occured for oaks (Q. faginea) after prolonged and intense water stress. Our findings reveal that mixing oaks and pines could mainly enhance hydraulic impairments for all species during the dry season, suggesting a potential decline in mixed Mediterranean forests under future climate.
在地中海森林中增加树种多样性，可通过改善小气候和减少对水分的竞争来减轻干旱引发的水力损伤。然而，物种多样性是否以及如何调节树木的水力功能，以及在生长季节这些影响如何变化，仍不明确。我们利用由一种（即单种的）或四种（即多种的）树种组成的未受管理的地中海森林林分，对四种共存的松树和栎树物种的原位水力性状（黎明前和中午叶水势——Ψ和Ψ、木质部和叶比水力导度——K和K、导度损失百分比——PLC、比叶面积——SLA以及胡伯值——HV）的季节动态进行了为期两年的研究。我们主要观察到，与单种林分相比，多种林分中物种多样性产生了不利影响，即Ψ、Ψ、K、K较低，PLC较高，尤其是对于两种松树而言。这些影响在整个生长季节都有观察到，但在夏季最干旱时期更为强烈。多样性的有益影响很少见，仅在长期严重水分胁迫后出现在栎树（法氏栎）身上。我们的研究结果表明，在旱季，栎树和松树混交可能主要会加剧所有物种的水力损伤，这表明在未来气候条件下，地中海混交林可能会衰退。
