Mutitrophic interactions determine ecosystem functions
Protists are crucial to soil ecosystem functions, occupying unique soil niches with bacteria and fungi at higher trophic levels. Their interactions with soil microbes and impacts on ecosystem functions have not been explored in detail. In global first, we manipulated protist diversity simultaneously with soil bacterial, fungal and plant diversity to examine the impact of protist diversity and their interactions with soil microbes on aboveground and belowground processes under ambient and drought conditions. The experiment included three levels of both microbial and plant diversity manipulation, and regular measurements of biodiversity and ecosystem functions. Over the experiment, 812 soil samples were collected at four stages- before and after plant establishment, during drought, and post-drought recovery, analysed for bacterial, fungal, and protist communities, along with 22 plant and soil traits. Results showed that microbial diversity manipulation had impacted protist/bacterial/fungal community composition more than plant richness and plant diversity, and this effect persisted through both the drought and recovery stages. Protist along with bacterial and fungal diversity positively correlated with ecosystem multifunctionality (EMF) and soil organic matter decomposition, suggesting that a higher microbial diversity enhanced ecosystem functions . Multiple linear regression analyses revealed consistent results of protists supporting EMF. For example, specific soil protist groups like Chlorophyta and Rhizaria showed consistent but group-dependent links to plant and soil traits. Among these, protists most prominently contributed to soil phosphatase production, and drought majorly impacted soil phosphorus. Lastly, the interactions between bacteria, fungi, and protist groups varied greatly, reflecting the diverse influences/links of protists on different microbes and ecosystem functions and highlighting their importance in regulating ecosystem health of all aspects.