ABSTRACT
This chapter explores how analyses of stable isotope ratio patterns in arid land soils and plants helps to better understand ecosystem dynamics in response to changes in moisture and nitrogen availability. To facilitate modelling approaches for estimating productivity it would be ideal if all vegetation components responded equally to seasonal variations in resource input. Stable isotopes in xylem water have been particularly useful in quantifying soil layers from which plants extract water, since roots do not fractionate during water uptake. Cryptobiotic crusts are biological soil crusts composed of cyanobacteria, lichens, mosses, green algae, and fungi. They are found in mesic environments, tropical and temperate deserts, and in polar regions, but they reach their best development in arid regions where they are ubiquitous on undisturbed arid and semi-arid soils.
