Tropical Tree Ectomycorrhizae Are Distributed Independently of Soil Nutrients

The Science

This study investigates the distribution of mycorrhizae, plant-fungal partnerships that influence ecosystem function. Researchers traditionally believed climate and decomposition rates determined mycorrhizal distribution, with arbuscular mycorrhizal plants being more prevalent in fertile areas and ectomycorrhizal (EcM) plants in less fertile ones. However, a team of researchers used fine-scale data from lowland tropical forests to challenge this notion, revealing soil fertility is not associated with the distribution of EcM-associated trees. The research underscores the importance of understanding mycorrhizal symbiosis in lowland tropics, refuting assumptions based on temperate and boreal regions, and highlighting historical biogeographies that influence mycorrhizal patterns in tropical forests worldwide.

The Impact

This study challenges understanding of how plants and fungi collaborate in lowland tropical forests and reveals these relationships are more intricate than previously believed. Conventional ideas about nutrient levels and plant partnerships may not always hold true. The study stresses the importance of gaining a deeper understanding of the symbiotic relationships between plants and fungi in tropical regions and cautions against assuming they operate similarly to other areas, like temperate and boreal regions. Overall, the research makes researchers rethink how plants and fungi interact in diverse tropical forests, highlighting the need for more studies to understand these complex partnerships.

Summary

Mycorrhizae mediate vegetation impacts on ecosystem functioning. Climatic effects on decomposition and soil quality are suggested to drive mycorrhizal distributions, with arbuscular mycorrhizal plants prevailing in low-latitude and high-soil-quality areas and EcM plants in high-latitude and low-soil-quality areas. However, these generalizations, based on coarse-resolution data, obscure finer-scale variations and result in high uncertainties in the predicted distributions of mycorrhizal types and their drivers.

Using data from 31 lowland tropical forests, both at a coarse scale (mean-plot-level data) and fine scale (20 × 20 meters from a subset of 16 sites), the study demonstrates the distribution and abundance of EcM-associated trees are independent of soil quality. Resource exchange differences among mycorrhizal partners, stemming from diverse evolutionary origins of mycorrhizal fungi, may decouple soil fertility from the advantage provided by mycorrhizal associations. Additionally, distinct historical biogeographies and diversification patterns have led to differences in forest composition and nutrient-acquisition strategies across three major tropical regions. Notably, Africa and Asia’s lowland tropical forests have abundant EcM trees, but they are relatively scarce in lowland neotropical forests. A greater understanding of the functional biology of mycorrhizal symbiosis is required, especially in the lowland tropics, to overcome biases from assuming similarity to temperate and boreal regions.

Principal Investigator

José A. Medina-Vega
Forest Global Earth Observatory, Smithsonian Tropical Research Institute
[email protected]

Program Manager

Brian Benscoter
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

The study was supported as part of the Next-Generation Ecosystem Experiments Tropics, which is funded by the Biological and Environmental Research program within the U.S. Department of Energy’s Office of Science. Funding for data management, quality control, travel, and consumables was provided by various funding agencies to the principal investigators of the plots used in this study. For detailed information on site-specific funding, please refer to the supporting documents of the manuscript.

References