Environmental filtering mediates grassland community assembly following restoration with soil carbon additions

The application of carbon (C) substrates has been viewed as a promising tool for lowering soil nitrogen (N) availability in grassland restoration. However, experimental evidence shows that C additions can enhance, suppress, or have no effect on native species productivity, making it difficult to predict the effects of C‐additions on plant communities. We used a community assembly approach to test the roles of environmental filtering and competition on community structure after C‐additions. We applied 3 recalcitrant C‐additions (wood chips, shavings, mixed chips + shavings), monitored temporal changes in soil N and P availability and species' abundances, and used phylogenetic tools to examine changes in community structure. All 3 soil C‐additions produced significant reductions in soil N and P fertility that, in turn, were correlated with increases in taxonomic species richness, diversity, and evenness, as well as shifts in community structure. In control and C‐amended plots, however, communities were composed of taxa that were more closely related than expected by chance (phylogenetically clustered); this pattern occurred across all C‐additions and years, and in both plot level and species pair‐wise metrics. In nonamended plots, phylogenetic clustering was correlated with soil N availability, consistent with environmental filtering. In C‐addition plots, biotic (clade specialization in different C additions) and abiotic factors (soil P variability) were important in structuring the community. These findings suggest that C‐additions create a different set of environmental filters and that variations in ecological traits among phylogenetically close species may be important in understanding and predicting the effects of C‐additions.