Poeydebat Charlotte, Jactel Hervé, Moreira Xoaquín, Koricheva Julia, Barsoum Nadia, Bauhus Jürgen, Eisenhauer Nico, Ferlian Olga, Francisco Marta, Gottschall Felix, Gravel Dominique, Mason Bill, Muiruri Evalyne, Muys Bart, Nock Charles, Paquette Alain, Ponette Quentin, Scherer-Lorenzen Michael, Stokes Victoria, Staab Michael, Verheyen Kris, Castagneyrol Bastien
INRAE, UMR 1202 BIOGECO, Cestas, France.
Université de Bordeaux, BIOGECO, UMR 1202, Talence, France.
Funct Ecol. 2021 Jan;35(1):67-81. doi: 10.1111/1365-2435.13700. Epub 2020 Oct 14.
Associational resistance theory predicts that insect herbivory decreases with increasing tree diversity in forest ecosystems. However, the generality of this effect and its underlying mechanisms are still debated, particularly since evidence has accumulated that climate may influence the direction and strength of the relationship between diversity and herbivory.We quantified insect leaf herbivory and leaf chemical defences (phenolic compounds) of silver birch in pure and mixed plots with different tree species composition across 12 tree diversity experiments in different climates. We investigated whether the effects of neighbouring tree species diversity on insect herbivory in birch, that is, associational effects, were dependent on the climatic context, and whether neighbour-induced changes in birch chemical defences were involved in associational resistance to insect herbivory.We showed that herbivory on birch decreased with tree species richness (i.e. associational resistance) in colder environments but that this relationship faded as mean annual temperature increased.Birch leaf chemical defences increased with tree species richness but decreased with the phylogenetic distinctiveness of birch from its neighbours, particularly in warmer and more humid environments.Herbivory was negatively correlated with leaf chemical defences, particularly when birch was associated with closely related species. The interactive effect of tree diversity and climate on herbivory was partially mediated by changes in leaf chemical defences.Our findings confirm that tree species diversity can modify the leaf chemistry of a focal species, hence its quality for herbivores. They further stress that such neighbour-induced changes are dependent on climate and that tree diversity effects on insect herbivory are partially mediated by these neighbour-induced changes in chemical defences.
关联抗性理论预测，在森林生态系统中，昆虫食草作用会随着树木多样性的增加而减少。然而，这种效应的普遍性及其潜在机制仍存在争议，特别是因为已有证据表明气候可能会影响多样性与食草作用之间关系的方向和强度。我们在不同气候条件下的12个树木多样性实验中，对纯林和混交林中白桦的昆虫叶片食草作用和叶片化学防御（酚类化合物）进行了量化。我们研究了相邻树种多样性对白桦昆虫食草作用的影响，即关联效应，是否取决于气候背景，以及相邻树木引起的白桦化学防御变化是否参与了对昆虫食草作用的关联抗性。我们发现，在较寒冷的环境中，白桦上的食草作用随着树种丰富度的增加而降低（即关联抗性），但随着年平均温度的升高，这种关系逐渐减弱。白桦叶片的化学防御随着树种丰富度的增加而增加，但随着白桦与其相邻树种的系统发育差异的增加而降低，特别是在温暖和潮湿的环境中。食草作用与叶片化学防御呈负相关，特别是当白桦与亲缘关系较近的物种相关联时。树木多样性和气候对食草作用的交互效应部分是由叶片化学防御的变化介导的。我们的研究结果证实，树种多样性可以改变目标物种的叶片化学性质，从而改变其对食草动物的质量。它们进一步强调，这种由相邻树木引起的变化取决于气候，并且树木多样性对昆虫食草作用的影响部分是由这些相邻树木引起的化学防御变化介导的。
