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Understanding how biotic mechanisms confer stability in variable environments is a fundamental quest in ecology, and one that is becoming increasingly urgent with global change. Several mechanisms, notably a portfolio effect associated with species richness, compensatory dynamics generated by negative species covariance and selection for stable dominant species populations can increase the stability of the overall community. While the importance of these mechanisms is debated, few studies have contrasted their importance in an environmental context. We analyzed nine long-term data sets of grassland species composition to investigate how two key environmental factors, precipitation amount and variability, may directly influence community stability and how they may indirectly influence stability via biotic mechanisms. We found that the importance of stability mechanisms varied along the environmental gradient: strong negative species covariance occurred in sites characterized by high precipitation variability, whereas portfolio effects increased in sites with high mean annual precipitation. Instead of questioning whether compensatory dynamics are important in nature, our findings suggest that debate should widen to include several stability mechanisms and how these mechanisms vary in importance across environmental gradients.

Climate gradients shape spatial variation in the richness and composition of plant communities. Given future predicted changes in climate means and variability, and likely regional variation in the magnitudes of these changes, it is important to determine how temporal variation in climate influences temporal variation in plant community structure. Here, we evaluated how species richness, turnover, and composition of grassland plant communities responded to interannual variation in precipitation by synthesizing long-term data from grasslands across the United States. We found that mean annual precipitation,(MAP) was a positive predictor of species richness across sites, but a positive temporal relationship between annual precipitation and richness was only evident within two sites with low MAP. We also found higher average rates of species turnover in dry sites that in turn had a high proportion of annual species, although interannual rates of species turnover were surprisingly high across all locations. Annual species were less abundant than perennial species at nearly all sites, and our analysis showed that the probability of a species being lost or gained from one year to the next increased with decreasing species abundance. Bray-Curtis dissimilarity from one year to the next, a measure of species composition change that is influenced mainly by abundant species, was insensitive to precipitation at all sites. These results suggest that the richness and turnover patterns we observed were driven primarily by rare species, which comprise the majority of the local species pools at these grassland sites. These findings are consistent with the idea that short-lived and less abundant species are more sensitive to interannual climate variability than longer-lived and more abundant species. We conclude that, among grassland ecosystems, xeric grasslands are likely to exhibit the greatest responsiveness of community composition (richness and turnover) to predicted future increases in interannual precipitation variability. Over the long-term, species composition may shift to reflect spatial patterns of mean precipitation; however, perennial-dominated systems will be buffered against rising interannual variation, while systems that have a large number of rare, annual species will show the greatest temporal variability in species composition in response to rising interannual variability in precipitation.

Understanding soil microbiome responses to different land‐management strategies provides insights into tallgrass prairie restoration. However, few studies have examined these interactions. We addressed this issue by surveying samples from the University of Nebraska at Omaha's Glacier Creek Preserve, where a long‐term burn experiment was established in 1982, with the mow treatments incorporated in 2002. In 2015, we collected 89 soil samples and obtained ~2.3 million bacterial and archaeal 16S rRNA sequence reads and ~2.4 million fungal ITS reads. Analysis of the sequences showed that dominant phyla were Proteobacteria (~30.0%) and Acidobacteria (~22.8%) in bacteria and Ascomycota (~66.2%) in fungi. We found that burning and mowing had a distinct effect on soil bacterial and fungal diversity: soils exposed to the burn treatments possessed a relatively high bacterial diversity but a relatively low fungal diversity. We also observed that burning and mowing had different effects on different microbial groups within bacteria and fungi. The burn treatments led to a relatively high abundance of bacterial groups such as Gemmatimonadetes and Armatimonadetes that prefer dry or warmer soils and arbuscular mycorrhizal (AM) fungi, whereas the mow treatments resulted in increased abundances of Nitrospirae bacteria. Moreover, functional prediction revealed that soil samples from the burn treatments were enriched with AM and plant saprotrophic fungi, and fungal plant pathogens were enriched in the mow samples. Considering soil functional differences between burn and mow treatments and an increased plant production after burning treatments, we speculate that burning could be a better strategy in the tallgrass land restoration, with certain fungal groups as an imperative indicator. Highlights: Understanding soil microbiome responses to different land‐management strategies provides insights into tallgrass prairie restorationWe showed differences in the soil bacterial and fungal communities between burn and mow treatments.Soil fungi were enriched in AM fungi and plant saprotroph functions after burning, but fungi with putative plant pathogens after mowing.The burn treatment is a better strategy for tallgrass prairie land restoration in this study region. [ABSTRACT FROM AUTHOR]