Tree mycorrhizal type mediates the responses of foliar stoichiometry and tree growth to functionally dissimilar neighbours in a subtropical forest experiment

Plant nutrient stoichiometry is of critical importance to productivity and nutrient cycling in terrestrial ecosystems. The impacts of tree species diversity on productivity have been well studied at the stand level. However, it is unclear how neighbourhood interactions impact the foliar nutrient stoichiometry of trees at the neighbourhood scale and how plant mycorrhizal associations can mediate such effects. We randomly selected eight tree species from a large‐scale biodiversity experiment with mixtures up to 32 tree species in subtropical China to assess the effects of species richness, phylogenetic and trait dissimilarities and competition on the foliar nutrient stoichiometry of focal trees associated with either arbuscular mycorrhizal (AM) or ectomycorrhizal (EM) fungi. We further investigated whether neighbourhood diversity can alter focal tree growth by regulating C:N:P stoichiometry. Neighbourhood species richness had no significant impact on the foliar C:N, N:P or C:P for both AM and EM trees. Increased neighbourhood phylogenetic dissimilarity significantly decreased the foliar N:P and C:P of AM trees but did not affect those of EM tree species. Foliar C:N, N:P and C:P of AM trees decreased with increasing neighbour trait (specific leaf area, root diameter, wood density dissimilarity, total trait) dissimilarities, while those of EM trees increased or remained unchanged. The increase of the neighbourhood competition index resulted in an increase in the foliar C:N of AM tree species but not EM tree species. The structural equation model analysis revealed that the increase of neighbourhood phylogenetic dissimilarity and functional trait dissimilarity indirectly enhanced tree growth of AM trees by decreasing foliar C:N. Conversely, the increase of neighbourhood‐specific root length and wood density dissimilarity indirectly reduced the growth of EM trees by increasing foliar N:P. Synthesis . Our results indicate that neighbourhood trait dissimilarity regulated tree foliar stoichiometry and growth performance, but the effects depended on the mycorrhizal type of trees. Our findings highlight the importance of tree mycorrhizal associations for better understanding the relationship between plant diversity and ecosystem functions. Read the free Plain Language Summary for this article on the Journal blog.