Fungal functional diversity: Exploring patterns and processes associated with soil fungal assemblages along an altitudinal gradient in the Chihuahuan Desert

Soil fungi are intimately associated with the maintenance and stability of terrestrial ecosystems through their involvement in the decomposition process. During decomposition, organic carbon is mineralized to CO₂ and bound nutrients are returned to the labile soil nutrient pool for subsequent growth of plants and soil microbes. To better understand the relationship between soil fungal diversity, and factors influencing their functional ability in the decomposition of soil organic matter, this dissertation examined, (1) development of methods to determine soil fungal functional diversity, (2) seasonal trends in fungal function al diversity, and (3) the relation between soil fungal functional abilities and a suite of environmental variables that are important in ecosystem nutrient cycles. The context of this research endeavor focused on assemblages of soil fungi associated with an environmental gradient in the Chihuahuan Desert, specifically, the Pine Canyon Watershed in Big Bend National Park. The Pine Canyon Watershed contains five distinct vegetation zones along an attitudinal gradient and contains the majority of vegetation types that are found in the Chihuahuan Desert. Soil samples were collected within each of these zones over a three-year period. Sampling coincided with seasonal changes in temperature and precipitation. Functional diversity was determined for fungal assemblages from each vegetation zone, using the Soil FungiLog procedure developed from this research. Fungal assemblages from the upper elevation sites responded to season with an enhanced functionality during the summer, whereas functionality of low desert fungi was enhanced in the winter. Regardless of season or elevation, complex and simple carbohydrate carbon compounds were the most frequently utilized by all soil fungal assemblages. At the regional scale, soil moisture, pH and soil nitrogen levels were the primary environmental determinants of soil fungal functional diversity. However, at the local and site scale the response to soil properties was specific to the scale of inference. At the landscape level, soil fungal functional diversity is strongly influenced by seasonal trends in soil moisture and soil temperatures. At scales related to vegetation composition, soil properties exert significant influence on the functional capabilities of the soil fungi by regulating soil organic matter levels and soil nitrogen dynamics.