Microbial Resource Limitation and Terrestrial Ecosystem Ecology

Soil microbes function as decomposers in terrestrial ecosystems. They break down the organic matter, which plays a significant role in supplying nutrients to plants, but also in regulating biogeochemical cycling which feeds back to climate change. Like other organisms, soil microbes can be limited by the availability of essential resources, which could consequently affect their ability to decompose organic matter. Besides, climate change events could change the resource regime of an ecosystem, which could alter microbial resource limitation and trigger microbial mining of the limiting resource from organic matter. This PhD aimed to better understand these mechanisms. By using limiting factor assay, I found that microbial growth in both arctic and tropical soil was primarily limited by carbon (C) and secondarily limited by phosphorus (P). I found that climate change events could alter microbial resource limitation. In the Arctic, C enrichment due to arctic greening or shrubification alleviated microbial C limitation. Conversely, nitrogen (N) enrichment in the Arctic due to warming-accelerated decomposition enhanced microbial C limitation, which stimulated microbial use of new plant litter input. In the tropics, elevated atmospheric CO2 (eCO2) increased the C availability of the ecosystem. This enhanced the microbial C limitation, which might be explained by a more active community under eCO2 demanding more C. This enhanced microbial C limitation was found to stimulate microbial use of new plant litter input. In summary, soil microbial growth was primarily limited by C in all studied environments. The microbial C limitation could be altered by climate changes events, and the direction would be determined by both the change of resource availability in the environment and the status of the microbial community.