Print PageAt the phylum level, the distribution of bacterial diversity in arid ecosystems resembles that of other biomes, but fungal diversity is dominated by Ascomycota. This dominance, in conjunction with abiotic processes, directs the carbon and nitrogen cycles.
Results/Conclusions
Aridland soils have high phenol oxidase and protease potentials. The phenol oxidase potential is inconsistent with the abundance and composition of soil organic matter. We hypothesize that these enzymes are laccases produced by Ascomycota to generate melanin pigments. Edaphic conditions stabilize these laccases, creating an oxidative legacy that limits soil organic matter (SOM) accumulation. Low SOM limits N immobilization and availability, which along with alkaline pH, promotes high proteolytic potentials. The sources of this proteolytic activity are unclear; both bacteria and fungi produce alkaline proteases, including thermostable enzymes. A high ratio of proteolytic to aminohydrolase activities suggests a tight N cycle with limited flows of mineral N to dissimilatory pathways. However, aridity allows nitrate to accumulate creating a reserve that supports denitrification during transient periods of high soil water content. Culture and biocide studies suggest that Ascomycota may be the principal denitrifiers under these conditions. Other studies show that Ascomycota dominate the mycorrhizal networks that translocate carbon and nitrogen between biocrusts and plants, and the endophyte assemblages that confer thermal and drought tolerance to plants. These accumulating observations suggest that Ascomycota are integral to the biogeochemical organization of aridland ecosystems.
