Linking functional traits and spectral responses of biocrust at different scales

Biological soil crusts or biocrusts, are complex communities composed of photoautotrophic organisms (cyanobacteria, algae, lichens, and bryophytes) and heterotrophs living in intimate association with soil surface particles covering most open areas of drylands. These poikilohydric communities play a crucial role in the functioning of dryland ecosystems by regulating water, carbon, and nitrogen cycles, stabilizing soil and preventing erosion. In addition, biocrusts accumulate protective and photosynthetic pigments such as scytonemin, carotenoids, and chlorophyll, which, together with their surface roughness, exert a strong control on surface spectral response.In this study, we aimed at exploring the influence of different biocrust types on surface spectral signal and to explore the relationship between the observed biocrusts spectral traits and related key functional attributes at different spectral and spatial resolutions.As expected, biocrusts showed higher pigment concentration, carbon and nitrogen content, and surface roughness than bare soil, and this effect increases from low-developed cyanobacteria to well-developed lichen- and moss-dominated biocrusts. These functional differences are reflected in their spectral signal, and more developed biocrusts exhibited more pronounced pigment and water absorption peaks and higher values of broadband spectral indices compared to early cyanobacteria or bare soil. Moreover, this effect is accentuated under wet conditions. Finally, we found a clear relationship between spectral signal and functional traits that facilitates the quantification of key functional attributes using the biocrust spectral signal from both field spectra and UAV This linkage facilitates the identification and estimation of functional traits of biocrusts at the ecosystem scale and improves the interpretation of high-resolution remote sensing data in dryland landscapes.