RAPID: Breaking drought as an opportunity to examine regional vs. local constraints on microbial community responses to environmental change

University Of Texas At Austin, Austin TX

Investigators

Abstract

More than twice the amount of carbon is stored in soils than is found as carbon dioxide in the atmosphere. Microbes consume soil organic material for both carbon and nutrients, and so their activities dictate how much carbon is retained by soils, and how much is released. Current models used to forecast how microbes will affect soil carbon assume that they all behave exactly the same in response to moisture and temperature no matter where they are located. By contrast, recent research by the PI has found that soils from drier regions did not have the same capacity to respond to moisture as soils from wetter sites. These local 'historical contingencies' make it more difficult to accurately predict future soil carbon storage and loss. Also complicating the picture is that the PI's prior studies have taken place during an extended regional drought period, and therefore could reflect a temporary condition created by drought stress. This year, her sample sites in Texas are experiencing excessive rainfall, and even flooding, which could affect both regional immigration and dormancy/resuscitation dynamics that might overcome local historical constraints and allow for soil microbes to better acclimate to a change in moisture. This RAPID award will enable her to test these ideas. Her team will take advantage of this rare wet year in 2015, the first in Texas since 2007. These studies will result in improvements in our understanding of how soil microbial communities function and respond to changes in precipitation, knowledge that is important to agriculture, range land and forestry management. One technician, one graduate student, and several undergraduates will receive training through this project. The undergraduates will be recruited from a class taught by the PI for freshman as part of the Freshman Research Initiative at the University of Texas, Austin, which implements innovative research-based education and targets underrepresented groups in STEM fields. The graduate and undergraduate students also will be encouraged to develop a related independent research projects. The goal of this RAPID project is to determine how the balance of local vs. regional processes affect historical contingencies in microbial responses to environmental change. The current wet year provides an opportunity to separate local vs. regional drivers. This will be addressed by (1) testing for release of historical contingencies on soil respiration responses to moisture, (2) documenting whether community composition shifts occur in parallel in the field, and (3) examining two mechanisms that likely underlie the previous observations of contingencies: dormancy/resuscitation and immigration dynamics. This research will be accomplished using a combination of a steep rainfall gradient where the PI and her lab have worked for 9 years, as well as lab microcosm experiments to generate moisture response curves and manipulate dispersal. Results have the potential to improve how soil biogeochemical processes are forecast in climate change scenarios. If historical contingencies persist despite this wet year, then local spatial variation in process responses may be necessary for accurate forecasting. Alternatively, if regional processes rescue prior historical contingencies and allow soils to acclimate to a new rainfall regime, then models might be improved by incorporating lags in process responses.