The proposed study will increase our understanding of ecosystem responses to future drought conditions in grassland ecosystems, particularly the maintenance of soil organic carbon pools critical to ecosystem productivity and the balance of soil carbon storage and loss important for ecosystem feedbacks to atmospheric CO2 pools. By targeting the microbial community responsible for soil carbon transformations, we will also be able to identify mechanisms underlying ecosystem responses and potentially begin to develop novel approaches to habitat management in the face of future climate change.
For example, we may find mycorrhizal fungi that can increase plant resistance to drought and could result in a novel management strategy – “seeding” areas with drought-tolerant mycorrhizas to maintain grasslands under future drought conditions.
We are currently sampling 16 grassland sites across the gradient. These sites are divided into four rainfall zones with four to sites in each zone. We plan to sample in the late spring/early summer annually. We will potentially also sample in the fall, depending on funding.
To address our objectives, we will use two approaches: (1) baseline sampling to describe the sites, and (2) experimental tests of site responses to altered rainfall. Field surveys will include soil sampling (ten soil cores 2 cm wide by 10 cm deep over a 100 m2 area), plant tissue collection (three individuals of the three dominant native grasses at the site, along with samples of any exotic grasses present), and surveying of plant community cover and structure.
Soils will be processed in the lab for total organic carbon, soil microbial biomass carbon, and soil fungal networks. Plant roots will be stained for fungal colonization. Subsamples of soil and roots will be archived in the -80°C freezer for eventual DNA-based analysis of microbial community composition. In subsequent visits, we may examine decomposition rates using mesh litter bags. The mesh will be green, black, or white in color, held down by small stakes, and subsequently retrieved by GPS. Mesh bags will be collected at regular intervals to measure decomposition.
Experimental tests will be carried out to address how altered rainfall will affect plant productivity, the fluxes of carbon (decomposition and respiration), and the microbial drivers of those fluxes. These will include lab incubations and, eventually, reciprocal transplants of soil cores in the field. In the lab, we will address how changes in moisture affect rates of decomposition by exposing soil and litter from each site to the entire range of gradient soil moisture conditions (5 to 35% soil moisture) to characterize the response of each zone to its “home” moisture condition and both drier and wetter habitat conditions.
We will also use greenhouse studies to examine how mycorrhizal fungi from each site affect plant productivity under different levels of drought stress. In the field, we will address the role of the microbial community vs. the environment in driving carbon fluxes and climate change. We will use reciprocal transplants of intact soils in PVC cores among sites to capture the natural variability in moisture and other factors at the same time. Cores will either be “home” soils or soils from wetter or drier sites, with and without mesh litter bags.