Linking soil microbes to ecosystem function: How does history inform the present and future?
Per unit volume, soils harbor the greatest diversity on earth. Most of this diversity is microbial. These microbes are responsible for degrading and mineralizing carbon and nutrients that enter the soil system. Thus understanding the links among microbial abundance, diversity and ecosystem function has been a major goal of ecosystem ecology. Traditionally, ecosystem ecologists have taken an indirect or 'shot-gun' approach to exploring how soil communities, and changes within those communities, are linked to function. If microbial abundance or community composition shifted with a shift in function, it was assumed that the changes in communities were related to change in function. Recent technical advances have enabled us to better explore the diversity of microorganisms in soil as well as quantify their functions, however, linking abundance, diversity and function is still rare in ecological studies. Using data from experimental manipulations in the field as well as constructed ecosystems in the lab, we will explore how four different groups are approaching how to link soil microbial communities to ecosystem function.
We use datasets from tropical and temperate systems to make three key points: (1) Individual microbes influence plant traits and ecosystem function, but understanding microbial contributions to ecosystem function across complex communities remains challenging. In a very simple four member bacterial community, we found that the least abundant bacteria shaped plant productivity patterns. While intriguing, it is difficult to scale these results to communities of thousands of microbes. (2) Interactions among soil communities, such as among mycorrhizal fungi and free-living soil organisms, shape soil carbon dynamics, but these interactions are heterogeneous throughout the soil matrix. Interactions between mycorrhizal fungi and the free-living soil community alter soil carbon processes in contrasting ways when they happen near and far from plant roots. (3) Ecological legacies as well as background climate variability shape microbial community stability and function. For example, fluctuating redox environments support a district microbial community compared to more static aerobic or anaerobic soils, even when fluctuating redox environments occur in a complex ecological matrix of well-aerated or poorly drained soils. These fluctuating environments are characterized by district biogeochemical dynamics including higher rates of carbon cycling.