FUNGAL WEATHERING ACROSS A MOISTURE GRADIENT AT THE SANTA CATALINA CRITICAL ZONE OBSERVATORY

Mineral weathering processes serve a fundamental role in transforming bedrock to soils and microorganisms play a critical role in regulating these physical and chemical processes. Mycorrhizal fungi were documented to increase weathering rates and nutrient uptake of their vascular host plants, while the connection between water and nutrient acquisition in water-limited environments is less understood. Climate models have predicted an imminent drying trend in the semiarid Southwest, and the climatologically diverse Santa Catalina Mountains (SCM) exhibits a gradient from desert to mixed forest ecosystems that are equivalent to a latitudinal transect ranging from southern Arizona to southern Canada. Thus, the SCM critical zone observatory provides an ideal location to examine the effects of climatic and biotic factors on soil development and evolution. The goals of this study were to determine 1) the response of fungal aquaporins (water transport proteins) to water limitation, and 2) the proportion of fungal weathering of granite along a moisture gradient. Soil cores were collected from five established zero-order basins in the SCM. Each soil core was dissected into 10 cm increments. Each increment was homogenized and divided in two subsamples. One subsample was analyzed for fungal community structure, abundance, diversity, and aquaporin concentrations and expression using RNA and DNA extractions, ITS sequencing, and quantitative PCR. The other subsample was used for microscopic visualization of the particle surface morphologies, fungal attachment features, mineral transformation products, and documentation of micro- and nano-scale chemical changes induced by fungal weathering of the major minerals in the granite. Chemical weathering rate decreases from mixed forest to desert sites along the moisture gradient, however, the proportion of fungal weathering is expected to increase, indicated by a higher percentage of fungal colonization and fungal sized etching patterns of the soil minerals. The higher fungal weathering proportion may also be linked to increased fungal aquaporin expression/activity at the drier sites. These results can provide information about interactions between water and nutrient acquisition in increasingly water-limited ecosystems of the Southwestern United States.