Jansen Kirstin, von Oheimb Goddert, Bruelheide Helge, Härdtle Werner, Fichtner Andreas
Institute of Ecology, Leuphana University of Lüneburg, Universitätsallee 1, 21335 Lüneburg, Germany.
Institute of General Ecology and Environmental Protection, Technische Universität Dresden, Pienner Straße 7, 01737 Tharandt, Germany.
Proc Biol Sci. 2021 Mar 10;288(1946):20203100. doi: 10.1098/rspb.2020.3100. Epub 2021 Mar 3.
Biodiversity is considered to mitigate the adverse effects of changing precipitation patterns. However, our understanding of how tree diversity at the local neighbourhood scale modulates the water use and leaf physiology of individual trees remains unclear. We made use of a large-scale tree diversity experiment in subtropical China to study eight tree species along an experimentally manipulated gradient of local neighbourhood tree species richness. Twig wood carbon isotope composition (C) was used as an indicator for immediate leaf-level responses to water availability in relation to local neighbourhood conditions and a target tree's functional traits. Across species, a target tree's C signatures decreased progressively with increasing neighbourhood species richness, with effects being strongest at high neighbourhood shading intensity. Moreover, the C-shading relationship shifted from positive (thin-leaved species) or neutral (thick-leaved species) in conspecific to negative in heterospecific neighbourhoods, most likely owing to a lower interspecific competition for water and microclimate amelioration. This suggests that promoting tree species richness at the local neighbourhood scale may improve a tree's local water supply with potential effects for an optimized water-use efficiency of tree communities during drought. This assumption, however, requires validation by further studies that focus on mechanisms that regulate the water availability in mixtures.
生物多样性被认为可以减轻降水模式变化带来的不利影响。然而，我们对于局部邻域尺度下树木多样性如何调节单株树木的水分利用和叶片生理的理解仍不明确。我们利用中国亚热带地区的一项大规模树木多样性实验，沿着局部邻域树种丰富度的实验控制梯度研究了八个树种。细枝木材碳同位素组成（C）被用作一个指标，以反映叶片水平对与局部邻域条件和目标树功能性状相关的水分可利用性的即时响应。跨物种来看，目标树的C特征随着邻域物种丰富度的增加而逐渐降低，在高邻域遮荫强度下影响最为强烈。此外，C-遮荫关系从同种邻域中的正相关（薄叶物种）或中性（厚叶物种）转变为异种邻域中的负相关，这很可能是由于种间对水分竞争较低以及微气候改善所致。这表明在局部邻域尺度上促进树种丰富度可能会改善树木局部的水分供应，对干旱期间树木群落优化水分利用效率具有潜在影响。然而，这一假设需要通过进一步聚焦于调节混交林中水分可利用性机制的研究来验证。
