A NEW, GLOBAL ESTIMATE FOR BIOCRUST CARBON AND NITROGEN FLUX IN TERRESTRIAL ECOSYSTEMS

Biocrusts are communities of photoautotrophic organisms, such as cyanobacteria, lichen, and bryophytes, that are found ubiquitously in terrestrial ecosystems and play a vital role in regulating carbon and nitrogen fluxes at a local scale. Despite their importance, the global contributions of biocrusts to carbon and nitrogen fluxes are not well understood and estimates from over a decade ago need to be updated. This study analyzed 362 flux records from 1976 to 2021 to derive updated estimates of carbon and nitrogen uptake by biocrusts. We estimate that biocrusts absorb 3.07 Pg of carbon and 102.33 Tg of nitrogen annually, accounting for 7 percent of terrestrial primary productivity and over 50 percent of biological nitrogen fixation. We used random forest regression analysis and Landsat 8 spectral bands to identify drivers of flux with root mean square error of 4.59% and ERA5 reanalysis to predict flux for forecasted climatologies. Sensitivity analysis indicated that in-situ flux measurements are sensitive to temporal and geospatial scaling factors, with up to 86 percent error in predictions. Our findings dramatically update previous estimates of biocrust contributions to global biogeochemical cycles and highlight the need for future research to sample data from understudied ecosystems.