Environmental filtering controls soil biodiversity in wet tropical ecosystems

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The environmental factors controlling soil biodiversity along resource gradients remain poorly understood in wet tropical ecosystems. Aboveground biodiversity is expected to be driven by changes in nutrient availability in these ecosystems, however, much less is known about the importance of nutrient availability in driving soil biodiversity. Here, we combined a cross-continental soil survey across tropical regions with a three decades' field experiment adding nitrogen (N) and phosphorus (P) (100 kg N ha−1y−1 and 100 kg P ha−1y−1) to Hawai'ian tropical forests with contrasting substrate ages (300 and 4,100,000 years) to investigate the influence of nutrient availability to explain the biodiversity of soil bacteria, fungi, protists, invertebrates and key functional genes. We found that soil biodiversity was driven by soil acidification during long-term pedogenesis and across environmental gradients, rather than by nutrient limitations. In fact, our results showed that experimental N additions caused substantial acidification in soils from Hawai'i. These declines in pH were related to large decreases in soil biodiversity from tropical ecosystems in four continents. Moreover, the microbial activity did not change in response to long-term N and P additions. We concluded that environmental filtering drives the biodiversity of multiple soil organisms, and that the acidification effects associated with N additions can further create substantial undesired net negative effects on overall soil biodiversity in naturally tropical acid soils. This knowledge is integral for the understanding and management of soil biodiversity in tropical ecosystems globally.
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Acknowledgements We are grateful to Dr. Minna Zhang and Dr. Yinong Li from Northeast Normal University, Dr. Xincheng Li from Fudan University, and Dr. Shengen Liu from China Three Gorges University for the valuable feedback and suggestions for the data analysis in the earlier version. M.D-B. is supported by a Ramón y Cajal grant (RYC2018-025483-I), a “Ayuda P.P. 2020. Desarrollo Lineas Investigación Propias (UPO), a project from the Spanish Ministry of Science and Innovation (PID2020-115813RA-I00), and a project PAIDI 2020 from the Junta de Andalucía (P20_00879). H.Y.C. is supported by National Natural Science Foundation of China (32101335), China Postdoctoral Science Foundation (2021M690589), Innovation Project of Young Technological Talents in Changchun City (21QC07), and Fundamental Research Funds for the Central Universities (2412021QD014). J.P.V. is thankful to DST and SERB (Science and Engineering Research Board), India for financial support for plant-microbe interaction research. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
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