HOW DO WATER AVAILABILITY IMPACT MINERAL WEATHERING BY MYCORRHIZAL FUNGI?

Biological weathering plays a fundamental role in transforming bedrock to soils. Results of laboratory and field experiments support that mycorrhizal fungi increase mineral and rock weathering, facilitate efficient nutrient acquisition, and improve water transport to the host plants. However, the connection between water and nutrient acquisition by fungal assistance in water-limited environments is poorly understood. The Santa Catalina Mountains Critical Zone Observatory (SCM-CZO) exhibits a moisture gradient from desert to mixed forest ecosystems and 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 the response of 1) fungal aquaporins (water transport proteins) to water limitation and 2) fungal weathering of silicate minerals to moisture availability. Soil cores were collected from five established and instrumented zeroth order basins at the SCM-CZO. The cores were divided by horizons and then into two subsamples. One of the subsamples was freeze-dried to determine the physical and chemical characteristics using scanning electron microscopy, electron microprobe, energy-, and wavelength-dispersive spectroscopy. The collected data were compared within the soil profiles and between the sites to assess the effect of the moisture gradient on mineral weathering. The other subsample was kept frozen for DNA analysis. Aquaporin concentrations and expression of specific fungi was determined using bioinformatics and quantitative PCR. Microscopy results confirm the presence of ectomycorrhizal fungi at the mid- and high-elevation sites. Fungal hyphae attached to mineral surfaces, and often embedded in an organo-clay layer. In addition, a high degree of etching is found on feldspar grains at all sites. The estimated elemental ratios of feldspar grains show depletion of sodium and accumulation of potassium from the core to the edge of the mineral grains. Total DNA concentration decreases from top to bottom in each soil profile, and from the wetter toward the drier site. Preliminary data suggest the presence of fungal aquaporins at two sites. This study provides some insights into the potential changes caused by the warming climate and decreasing moisture content of the soils in this already dry region of the US.