North Carolina State University Raleigh, North Carolina, United States
Background/Question/Methods Legacy effects of historical climate on soil microbial function have the potential to control how ecosystem processes such as carbon cycling respond to environmental change. Previous work has shown that climate legacies in ecosystems with historically variable precipitation can be challenging to overcome in experimental manipulations, but this may be caused by small-scale plots being embedded in the surrounding landscape with its potentially large input of microbial propagules. An El Niño event after a long-term drought across a rainfall gradient in central Texas gave us the opportunity to examine local and regional responses to drought relief. If regional dispersal is the major factor driving these communities, we would expect historically drier regions of the gradient to more closely resemble historically wetter regions with drought relief. If local dormancy/resuscitation dynamics are dominant, we would expect the active fraction of the microbial community to remain relatively unique at the site level. To test this, we sampled soils seasonally during the El Niño event and characterized microbial communities based on either 16S rDNA or rRNA.
Results/Conclusions By repeatedly sampling 14 sites across a rainfall gradient experiencing release from long-term drought, we discovered that active microbial dynamics diverged substantially compared to the DNA-based community at all sites. RNA-based microbial communities were comprised of 55% fewer taxa on average than DNA-based communities, consistent with a subset of the soil microorganisms responding to the change in available water. In addition, as drought was relieved over time, alpha diversity in the RNA pool decreased by 13% while increasing by 30% in the DNA pool. Network structure also differed, with fewer clusters and connections in the RNA- vs. DNA-based microbial communities. Nevertheless, microbial community trajectories through time were largely site-specific in both the RNA and DNA pools. These findings are consistent with local constraints on the active microbial community despite the seemingly increased dispersal and homogenization of the overall community. Such local effects may be responsible for previously observed legacies of historical climate on soil respiration and further support the need to better understand the drivers of historical contingencies that may control future ecosystem function.