Arbuscular mycorrhizal trees influence the latitudinal beta-diversity gradient of tree communities in forests worldwide

Abstract

Arbuscular mycorrhizal (AM) and ectomycorrhizal (EcM) associations are critical for host-tree performance. However, how mycorrhizal associations correlate with the latitudinal tree beta-diversity remains untested. Using a global dataset of 45 forest plots representing 2,804,270 trees across 3840 species, we test how AM and EcM trees contribute to total beta-diversity and its components (turnover and nestedness) of all trees. We find AM rather than EcM trees predominantly contribute to decreasing total beta-diversity and turnover and increasing nestedness with increasing latitude, probably because wide distributions of EcM trees do not generate strong compositional differences among localities. Environmental variables, especially temperature and precipitation, are strongly correlated with beta-diversity patterns for both AM trees and all trees rather than EcM trees. Results support our hypotheses that latitudinal beta-diversity patterns and environmental effects on these patterns are highly dependent on mycorrhizal types. Our findings highlight the importance of AM-dominated forests for conserving global forest biodiversity.

Global patterns of vascular plant alpha diversity

“…There is evidence that niche processes play a stronger role than neutral processes in determining fine-scale beta diversity at higher latitudes and altitudes [28][29][30] , where species are thought to have broader niches and be less responsive to geographical changes 55 . This is consistent with recent findings that the nestedness of tree communities increases with latitude, possibly due to the high share of ectomycorrhizal species in colder and wetter conditions 52 . Finally, high species richness at fine grains might also depend on plant size, as many small plants can coexist in a given grain size.…”

“…Recent work found a latitudinal increase in niche specialization and marginality of trees towards the equators, which has been attributed to the stable climate and high productivity in the tropics 51 . Alternative explanations include rarity and priority effects related to high productivity 29 , more uniform environmental conditions and stronger dispersal limitation at fine scales 28 , or stronger mycorrhiza-mediated effects of interspecific competition and habitat adaptation 52 in the tropics compared to temperate regions. While the relative contribution of these processes remains a matter of speculation, our work points to the need for an improved understanding of the spatial variation of beta diversity in plant diversity analysis 53 .…”

The latitudinal gradient in plant community assembly processes: A meta‐analysis

“…However, despite the observation of a latitudinal gradient in β‐diversity patterns and the recognition of the general importance of community assembly on β‐diversity, a systematic understanding of how community assembly mechanisms vary with latitude is currently limited (e.g. in plant communities: De Cáceres et al, 2012; Muñoz Mazón et al, 2021; Qian & Ricklefs, 2007; Zhong et al, 2021).…”

Tree biomass allocation differs by mycorrhizal association

“…Two primary groups of mycorrhizal fungi form the vast majority of these associations among trees: arbuscular mycorrhizal (AM) fungi and ectomycorrhizal (ECM) fungi. Recently, functional differences between these two groups of mycorrhizal fungi have been linked to patterns in global carbon stocks (Soudzilovskaia et al, 2019), carbon stabilization on soil minerals (Cotrufo et al, 2019; Craig et al, 2018; Keller et al, 2021), and the global latitudinal diversity gradient (Zhong et al, 2021). Together, these studies suggest that mycorrhizal fungi are critical determinants of global scale ecosystem patterns and processes.…”