Print PageModels of primary succession typically describe processes of and controls over vegetation development following initial plant colonization, emphasizing the role of early successional plant species in facilitating the establishment of later successional species. However, in glacial forelands, the earliest stages of succession begin immediately following glacial retreat, as pioneer microorganisms rapidly colonize newly exposed substrates. Thus, microbial communities play a fundamental role in transforming soil substrates and facilitating plant colonization by adding organic matter, mineralizing nutrients, and fixing nitrogen. Previous work from a handful of proglacial sites has shown that developing soil microbial communities undergo rapid structural and functional shifts during early ecosystem development, but the generality of those patterns remains unknown. We performed a soil incubation experiment using samples spanning three proglacial chronosequences to assess whether microbial community succession follows consistent patterns across climatically and geographically disparate sites and to identify whether or not broad patterns exist. We used a catabolic response profiling technique to measure short-term respiration responses to 24 different organic carbon (C) substrates, and we predicted that despite profound phylogenetic differences during early ecosystem development, the functional development of microbial communities would follow similar trajectories across sites.
Results/Conclusions
Microbial C substrate utilization increased with time-since-exposure across all three chronosequences. For example, as succession proceeded, the microbial communities utilized an increasingly diverse array of C compounds. In addition, while C utilization profiles indicated that the initial microbial communities at individual sites were functionally unique, in later successional stages, we observed a convergence in the catabolic profiles of communities between the different glacial sites. The diversity of substrates metabolized was positively correlated with basal respiration for all sites (Pearsons r = >0.75, P < 0.02), though the nature of this relationship was site specific. Additionally, we observed significant increases in available soil nutrients (NH4+-N and NO3--N), total soil C and N, and soil C:N ratios with soil age for all sites. Our results suggest that despite phylogenetic differences in microbial community composition during early succession, functionally, microbial community development may follow a common trajectory. The initial increases in microbial community functional diversity are similar to patterns increases in plant functional traits during primary succession, suggesting interesting similarities between microbial and macrobial ecology. Finally, the generality of these patterns suggests that microbial communities play a consistent and biogeochemically important role in early ecosystem development prior to plant establishment.
