Key aspects of global change include warming, nitrogen deposition, and increasing precipitation variability. Microbes have important roles in biogeochemical processes that may feedback to influence global change through carbon and nitrogen cycles. We studied the structure and function of surface microbes in drylands under factorial manipulations of global change. Because drylands make critical contributions to interannual carbon flux, it is important to understand how desert microbes respond to predicted conditions. Biocrusts are surface microbial communities that have key roles in dryland nutrient exchanges, including nitrogen fixation and carbon fluxes via photosynthesis and respiration. In this study, we addressed the question, How do simulated future changes in nitrogen deposition, warming, and winter rain affect the function and structure of biocrust bacteria?
Biocrust samples were collected at the Sevilleta Long Term Ecological Research (LTER) site within a full factorial experiment that altered nighttime warming (warmed 1-1.5C), El Niño rainfall (50% of winter amount increased), and nitrogen deposition (2.0 g m-2 y-1 of NH4NO3 added) with five replicates of each combination (WENNDEx). During March 2019-2020, we collected samples monthly for chlorophyll extractions to assess function. In September 2019, samples were sequenced for 16srRNA with Illumina MiSeq to assess changes in the bacterial community.
Results/Conclusions
Biocrust bacterial diversity was resistant to global change manipulations, but biocrust function responded to both nighttime warming and nitrogen fertilization. Bacterial diversity of biocrust was not significantly altered by warming (P = 0.21), nitrogen addition (P = 0.71), the increased El Nino treatment (P = 0.49), or any treatment interactions. However, warming (P= 0.002) and nitrogen fertilizer (P < 0.0001) significantly decreased chlorophyll content of biocrusts, but precipitation and treatment interactions were non-significant. Sample time (P= 0.0037) also significantly affected chlorophyll results, suggesting a potential seasonal component of biocrust activity. Overall, our results demonstrate that while bacterial diversity in biocrusts did not respond to global change manipulations, biocrust activity responded negatively to 2 of the 3 perturbations tested. Future analyses will explore changes in biocrust taxonomic composition. Ultimately, results thus far suggest that increases in nitrogen deposition and warming nighttime temperatures could reduce biocrust photosynthetic activity, thus potentially influencing dryland carbon dynamics in the future.