Active communities and growth of soil microorganisms are framed by mean annual precipitation in three California annual grasslands

Earth system models project altered precipitation regimes across much of the globe. In California, the winter wet season is predicted to extend into spring, and the summer dry period to lengthen. How altered precipitation will affect soil carbon (C) persistence is a key knowledge gap. However, we do not have a mechanistic understanding of how altered soil moisture regimes will affect microbial population dynamics. Using quantitative stable isotope probing (qSIP), we compared total and active soil microbial communities across three California annual grassland ecosystems that span a rainfall gradient and have developed upon similar parent material. We also assessed multiple edaphic variables, including available C and the radiocarbon (14C) age of soil C. Samples were assayed in the wet season, when we expected environmental conditions would be most similar across sites. We hypothesized that the long-term legacy of soil water limitation would be reflected in lower community growth capacity at the driest site. We also predicted that actively growing communities would be more compositionally similar across the gradient than the total background microbiome. Across the three sites, edaphic parameters such as pH roughly sorted with mean annual precipitation, and soil carbon age increased with precipitation. Bacterial growth rates increased from the driest site to the intermediate site, and rates were comparable between the intermediate and wettest sites. These differences were persistent across major phyla, including the Actinobacteria, Bacteroidetes, and Proteobacteria. Taxonomic identity was a strong predictor of growth, such that the growth rates of a taxon at one site predicted its growth rates at the others. We think this fact, that taxa that grew quickly at one site tended to grow quickly at the others, is likely a consequence of genetically determined physiological traits, and is consistent with the idea that evolutionary history influences growth rate.

Plant And Soil Microbial Communities Regulate Soil Respiration In Response To Precipitation And Land Use In An Inner Mongolian Grassland

Purpose: Changes in precipitation amount and land use are expected to greatly impact soil respiration (Rs) of grassland ecosystems. However, little is known about whether they can interactively impact Rs and how plant and soil microbial communities regulate the response of Rs. Methods: Here, we investigated the impacts of altered precipitation amount (–50%, ambient and +50%) and land-use regime (fencing, mowing and grazing) on Rs with a field experiment in the Inner Mongolian grassland.Results: We found that altered precipitation amount impacted Rs and its components across the 3-year study period, while land-use regime alone or its interaction with precipitation amount impacted them in certain years. In addition, changed soil microclimate, especially soil moisture, under altered precipitation amount and land-use regime can impact the components of Rs either directly or indirectly via influencing plant and soil microbial communities.Conclusions: Integrating changing precipitation amount and land-use regime within experiment can produce more accurate insights into grassland Rs, and chronically shifted plant and soil microbial communities under these changes may result in distinct long-term impacts on Rs.

Altered precipitation regimes mitigate N2O flux response to nitrogen addition in an alpine steppe

Anthropogenic-driven global change, including changes in atmospheric nitrogen (N) deposition and precipitation patterns, is dramatically altering N cycling in soil. How long-term N deposition, precipitation changes, and their interaction influence nitrous oxide (N2O) emissions remains unknown, especially in the alpine steppes of the Qinghai-Tibetan Plateau (QTP). To fill this knowledge gap, a platform of N addition and altered precipitation experiments was established in an alpine steppe of the QTP in 2013. N addition significantly increased N2O emissions, and alterations in soil NO3-N, pH, temperature, and belowground biomass modulated N2O emissions. In addition to abiotic parameters, ammonia-oxidizing bacteria dominated N2O emissions in nitrification compared with ammonia-oxidizing archaea. Changes in the denitrifying microbial community, namely a high ratio of (nirS+nirK) gene-containing to nosZ gene-containing organisms, were responsible for N2O emissions in denitrification. Altered precipitation did not affect N2O emissions. This unexpected finding, which is inconsistent with the conventional view that N2O emissions are controlled by soil water content, indicates that N2O emissions are particularly susceptible to N deposition in the alpine steppes. Notably, whereas N2O emissions were affected by N addition as a single factor, they were not significantly affected by the combination of precipitation changes and N addition, indicating that altered precipitation patterns may mitigate the positive feedback effect of N addition on N2O emissions. Consequently, our study suggests that the response of N2O emissions to N deposition in future global change scenarios will be affected by precipitation regimes in the alpine steppes.