COS 166-6 - Scale dependence in functional equivalence and difference in the soil microbiome

Background/Question/Methods

Climatic history can shape the functioning of soil microbial communities and thus rates of ecosystem processes such as organic matter decomposition. For example, broad spatial scale differences in climatic history, such as contrasting precipitation regimes, have been shown to generate unique microbial functional responses to contemporary moisture conditions. Yet it is an open question as to whether local differences in soil microclimate similarly influence the functional potential of decomposer communities. Here, we use a multi-scale approach within and among two temperate forest field sites to investigate this question. Soils from fifty-four microsites, that vary in their soil moisture climate-regimes, were used as inocula for a common leaf litter (Quercus rubra) in a controlled, laboratory microcosm study. Microcosms were placed under dry, mesic and wet lab-moisture conditions and the rate of carbon (C) mineralization of the litter was measured over 202 days. We have additionally sampled and are analyzing the soil microbial communities via 16s and ITS amplicon sequencing. This data will help explore how microclimate at the local and regional scale shapes these communities and contribute to functioning under lab conditions and field decomposition rates.

Results/Conclusions

Our results from the laboratory experiment reveal differences in decomposition rates under controlled conditions that highlight broad-scale functional differences between the soil communities at each site. Specifically, we found that C mineralization differed by as much as two-fold for soil communities when compared between the sites. Our results also show that functional differences of soil communities are observable within one site but not the other. In the site where local-scale functional legacies were apparent, the historical soil moisture microclimate-regimes generated as much as an 89% change in C mineralization rates of the leaf litter under the same contemporary, lab-imposed moisture conditions. A similar pattern was not observable in the other site; instead, laboratory moisture conditions explained almost all variation in C mineralization. Our findings confirm those from prior studies where regional-scale moisture-regime differences shape microbial function, and extends this prior work by providing evidence that pronounced local-scale differences in soil moisture microclimate-regimes can generate microbial functional legacies.