Dryland Biocrusts and Functional Diversity

Project title: Mapping Biocrust Community Composition and Functional Diversity Across Global Drylands

Background and Objectives

Biological soil crusts (hereafter, biocrusts), are photosynthetic communities of cyanobacteria, lichens, and/or bryophytes that cover vast expanses of the terrestrial surface and play critical roles in soil stabilization, fertility, water cycling, and carbon exchange with the atmosphere. Biocrusts are found on all of Earth's continents and are ubiquitous and play keystone roles in global dryland ecosystem structure and function. Global estimates of biocrust distribution suggest that these photosynthetic soil communities make up 12% of Earth's land surface roughly equivalent to the total extent of tropical and temperate forests combined. Biocrusts exude an exopolysaccharide glue" that binds mineral soils together and their tissues form an intact crust that dramatically increases soil stability and reduces erosion. Biocrusts also fix significant amounts of CO2, including at times of year when many vascular plants are inactive (e.g., winter), and they are a major source of dryland nitrogen through their ability to fix N2. Despite their global extent and importance, our quantitative understanding and spatially explicit estimates of biocrust community composition, coverage, function, and response to global change remains in their infancy compared to our understanding of vascular plants. In part this relatively poor spatial quantification comes from the fact that we cannot use many of our existing multispectral remote sensing tools for assessing biocrust communities to the same degree we can for vascular plants.

Here, we propose to address this critical knowledge gap by integrating Earth Surface Mineral Dust Source Investigation (EMIT) and other complementary satellite observation records with the larger goal of mapping biocrust community composition and functional diversity across global drylands. The EMIT mission provides full-range (400-2500nm) hyperspectral surface reflectance observations at high spatiotemporal resolution with the first-time potential to reveal the distinct role and function of biocrusts within dryland

ecosystems. We will fully explore this unique opportunity by leveraging multiple unique long-term dryland climate manipulation experiments; assess soil stability and erodibility in the context of plant and biocrust stabilization; and acquire new C flux, stock, and soil

microclimate data from an existing global network of dryland eddy covariance sites. We propose three main objectives: 1) Develop a biocrust hyperspectral library across multiple spatial scales; 2) Quantify critical biocrust functional traits through new measurements at core research sites; 3) Map biocrust community composition and function at the global scale utilizing a global network of dryland eddy covariance sites.

Significance and Relevance to NASA

Our proposed work fulfills a key focal area of the solicitation in representing new hypothesis-driven research and innovative analyses using EMIT data products alone or in combination with data products from other sensors & that advance the understanding of & the carbon cycle, ecosystems and their biodiversity&". We propose an interdisciplinary framework that incorporates multiple key focus areas within NASA's mission in Earth system science including Carbon Cycle and Ecosystems and Climate Variability and Change. Our core sites and high resolution remote sensing measurements will be invaluable for evaluation and calibration purposes, and for broader integrated analysis. Our proposed work is planned to complement and directly integrate data from multiple NASA Earth science data platforms including ECOSTRESS and GEDI. Our integrated data products will also have broad real-world utility including as potential key components of land management decision support frameworks that guide improved management of vulnerable dryland ecosystems.

Project Team

William Smith

University of Arizona