Swiss Federal Research Institute for Forest, Snow and Landscape Research WSL, Zürcherstrasse 111, Birmensdorf, Switzerland.
Plant Biol (Stuttg). 2013 Jan;15 Suppl 1:169-76. doi: 10.1111/j.1438-8677.2012.00625.x. Epub 2012 Jul 9.
Oaks are commonly considered as drought- and heat-tolerant trees that might benefit from a warmer and drier climate. Their tolerance to drought has been frequently studied in the past, whereas studies dealing with elevated temperature or its combination with drought are very limited in number. In this study we investigated seasonal photosynthetic patterns in three European oak species (Quercus robur, Q. petraea, Q. pubescens) exposed in lysimeter-based open-top chambers (OTC) to elevated daytime temperature, drought and their combination. Stomatal and non-stomatal traits of photosynthesis were followed over an entire growing season and related to changes in daytime temperature, soil moisture and pre-dawn leaf water potential (Ψ(PD) ). Elevated daytime temperature enhanced net photosynthesis (P(N) ) in a season-dependent manner, with higher mid-summer rates than in controls exposed to ambient temperature. Drought imposed in early and mid-summer reduced the soil moisture content and caused a gradual decline in Ψ(PD) , stomatal conductance (g(S) ) and P(N) . Drought effects on Ψ(PD) and P(N) were exacerbated when drought was combined with elevated daytime temperature. In general, P(N) tended to be more affected by low soil moisture content or low Ψ(PD) in Q. robur than in Q. petraea and Q. pubescens. Non-stomatal limitations may have contributed to the drought-induced decline of P(N) in Q. robur, as indicated by a down-regulation of PSII photochemistry (F(V) /F(M) ) and decreased chlorophyll content. Taken together, our findings show that European oaks may benefit from elevated temperature, but detrimental effects can be expected when elevated temperature occurs simultaneously with drought.
橡树通常被认为是耐旱和耐热的树种，可能受益于温暖和干燥的气候。过去经常研究它们对干旱的耐受性，而研究高温或高温与干旱结合的研究数量非常有限。在这项研究中，我们在基于根箱的开顶式气室 (OTC) 中研究了三种欧洲橡树物种（Quercus robur、Q. petraea、Q. pubescens）在升高的白天温度、干旱及其组合下的季节性光合作用模式。在整个生长季节中，我们跟踪了光合作用的气孔和非气孔特性，并将其与白天温度、土壤水分和黎明前叶片水势（Ψ（PD））的变化相关联。升高的白天温度以季节依赖的方式增强了净光合作用（P（N）），与对照相比，中夏季的速率更高，对照暴露在环境温度下。在初夏和仲夏施加干旱会降低土壤水分含量，并导致Ψ（PD）、气孔导度（g（S））和 P（N）逐渐下降。当白天温度升高与干旱结合时，干旱对Ψ（PD）和 P（N）的影响会加剧。一般来说，与 Q. petraea 和 Q. pubescens 相比，P（N）更容易受到 Q. robur 土壤水分含量低或 Ψ（PD）低的影响。非气孔限制可能导致 Q. robur 中干旱引起的 P（N）下降，这表明 PSII 光化学（F（V）/F（M））下调和叶绿素含量降低。综上所述，我们的研究结果表明，欧洲橡树可能受益于高温，但当高温与干旱同时发生时，可能会产生不利影响。
