Spatial cover and carbon fluxes of urbanized Sonoran Desert biological soil crusts.

Biological soil crusts (BSC) are important contributors to nutrient cycling in arid environments such as the Sonoran Desert. BSC at an urban (University Indian Ruins) and at a non-urban site (Santa Rita Experimental Range) were compared to determine if their structure or function was influenced by proximity to an urban environment. The Step Point method was used in the field to determine ground cover; which was found to be similar between sites. However, the spatial distribution of the BSCs was significantly different, such that more BSCs were found under plants at the non-urban site (P < 0.05). Relative gross photosynthesis was measured in the lab by addition of a watering event. Gross photosynthesis was found to be higher in the non-urban BSCs (P < 0.001), indicating lowered productivity in urban BSCs due to effects caused by proximity to urban environments. This study provides evidence that BSCs at urbanized sites are affected functionally, and therefore may be contributing differently to carbon and nitrogen cycling in these ecosystems.