Development of a spectral library of biocrusts and related functional traits

Drylands are characterized by a high spatiotemporal heterogeneity, which complicates the development of remote sensing applications for these regions. Biological soil crusts are among the key phenomena driving this heterogeneity. Biocrusts   are living communities composed of photoautotrophic organisms (cyanobacteria, algae, lichens, and bryophytes) in intimate association with heterotrophic microorganisms and covering the soil surface across global drylands. Biocrusts modify surface reflectance through specific absorption features arising from insulation-protective and photosynthetic pigments. These features have been used to develop local applications for biocrust mapping and monitoring, but their extrapolation, especially to the global scale, remains difficult because the biocrust reflectance interacts with the underlying soil signal. Moreover, the currently available biocrust spectral datasets do not capture the great variety of biocrust communities and their diverse spectral signals. Furthermore, these data are often collected without standardized protocols, which hampers data comparison, transferability and the development of standard procedures for mapping and monitoring.

To overcome this limitation, we developed a standard protocol to build the first consistent biocrust spectral library, which aims to support new biocrust mapping and monitoring efforts. that aims at supporting new biocrust mapping and monitoring actions. Spectra of 354 samples representing different biocrust communities from around the world were recorded in the laboratory under dry and wet conditions under controlled illumination intensity in the lab. The library includes a reflectance spectrum, a continuum removal spectrum, albedo, and a set of narrow- and broad-band spectral indices commonly applied for vegetation, soil, and characterization. We also used associated metadata, including general descriptors of habitats, location and sampling time information, and physicochemical variables related to biocrusts development and functioning. The latter facilitates the quantification of some key functional traits for comparison with remote sensing products (e.g., photosynthetic pigments, organic matter, stability, surface roughness, EPS concentration). Spectra and physicochemical features of the underlying soil are also included, as they are known to significantly influence the response of biocrust organisms. Overall, this spectral library encompasses a wide range of biocrust functional types from global drylands but further input from currently not well-covered geographic regions is still welcome.

Awknoledgment:CRUST R-Forze (PID2021-127631NA-I00) project funded by MICIU/AEI /10.13039/501100011033 and FEDER, UE; Support for Encouraging Research Consolidation (CNS2024-154916) funded by MICIU/AEI /10.13039/501100011033 and UE NextGenerationEU/PRTR. ERC was supported by the Ramon y Cajal Fellowship (RYC2020-030762-I) founded by MICIU/AEI/10.13039/501100011033 and El FSE invierte en tu future.