Ectomycorrhizal associations in the tropics – biogeography, diversity patterns and ecosystem roles

Abstract

Contents Summary 1076 I. Introduction 1076 II. Historical overview 1077 III. Identities and distributions of tropical ectomycorrhizal plants 1077 IV. Dominance of tropical forests by ECM trees 1078 V. Biogeography of tropical ECM fungi 1081 VI. Beta diversity patterns in tropical ECM fungal communities 1082 VII. Conclusions and future research 1086 Acknowledgements 1087 References 1087 SUMMARY: Ectomycorrhizal (ECM) associations were historically considered rare or absent from tropical ecosystems. Although most tropical forests are dominated by arbuscular mycorrhizal (AM) trees, ECM associations are widespread and found in all tropical regions. Here, we highlight emerging patterns of ECM biogeography, diversity and ecosystem functions, identify knowledge gaps, and offer direction for future research. At the continental and regional scales, tropical ECM systems are highly diverse and vary widely in ECM plant and fungal abundance, diversity, composition and phylogenetic affinities. We found strong regional differences among the dominant host plant families, suggesting that biogeographical factors strongly influence tropical ECM symbioses. Both ECM plants and fungi also exhibit strong turnover along altitudinal and soil fertility gradients, suggesting niche differentiation among taxa. Ectomycorrhizal fungi are often more abundant and diverse in sites with nutrient-poor soils, suggesting that ECM associations can optimize plant nutrition and may contribute to the maintenance of tropical monodominant forests. More research is needed to elucidate the diversity patterns of ECM fungi and plants in the tropics and to clarify the role of this symbiosis in nutrient and carbon cycling.

Diverse Mycorrhizal Associations Enhance Terrestrial C Storage in a Global Model

“…Although it was widely distributed, its relative contribution to total N acquisition was greatest in the boreal forest and tropics, areas with low inorganic N availability relative to vegetation N demand (Figures b and S2). While ECM‐associated plants are commonly associated with high latitudes, there are significant observed populations of ECM‐associated trees in tropical forests (Corrales et al, ). Modeled spatial distributions of AM and ECM fungi agreed with previous modeled estimates (Shi et al, ), and corresponded with observationally derived species distribution models (SDMs) with an 88% niche overlap for AM and 85.0% overlap for ECM.…”

Resource acquisition strategies facilitate Gilbertiodendron dewevrei monodominance in African lowland forests

“…In addition to acquiring N directly from organic matter, ectomycorrhizal fungi can synthesize hydrolytic enzymes to release P from organic phosphates (Antibus, Sinsabaugh, & Linkins, ; Leprince & Quiquampoix, ). Higher C:P ratios suggest that ectomycorrhizal associations facilitate access to organic P, again at the expense of arbuscular mycorrhizal fungi associated trees dependent upon inorganic forms of this macronutrient (Corrales et al, ; Herrera, Merida, Stark, & Jordan, ; Newbery, Alexander, & Rother, ). Our results therefore indicate that a similar advantage might apply to P as for N in promoting nutrient limitation in Gilbertiodendron and other ectomycorrhizal forests.…”

Cross‐scale integration of mycorrhizal function

“…Systems with bi‐directional dependencies are characterized by strong feedbacks, implying that mycorrhizal interactions may act to stabilize ecosystems, if negative feedbacks prevail, or to destabilize ecosystems and propel directional changes, if positive feed‐backs are common (e.g. Corrales et al ., ; in this issue of New Phytologist , pp. 1076‐1091).…”