Three million years of soil development affect aboveground and belowground processes in semiarid woodlands

Soil nutrient availability, texture, and water holding capacity combine to have a substantial effect on aboveground and belowground processes and their interactions. The Substrate Age Gradient of Arizona (SAGA), a three million year semiarid chronosequence of soil development in northern Arizona, has been shown to have a background gradient of carbon, nitrogen, and phosphorus, and soil texture. This dissertation used the SAGA sites as a naturally occurring gradient to assess the influence of soil nutrients and soil textural changes on aboveground processes such as tree growth and mortality and belowground processes mediated by microbial activity. I found that substrate age had important influences on tree growth and mortality, and belowground processes such as the stability of soil organic matter. In addition, I used the combination of the strong gradient in soil texture and water holding capacity at the SAGA and strong seasonal precipitation dynamics to explore mechanisms and seasonal dynamics of methane oxidation and nitrification in soil. Neither soil texture nor soil water content, which are the two most commonly described mechanisms controlling methane oxidation rates, sufficiently explained the strong seasonal dynamics of methane oxidation I measured. Rather, I found that methane uptake was correlated with dissolved organic carbon (DOC) content, suggesting DOC regulates methane oxidation. Similarly, potential nitrification rates did not respond to seasonal dynamics of nitrogen and water availability as might be expected based on paradigms of nitrogen cycling. This dissertation provides insight about the interactions of aboveground and belowground processes with soil chemical and physical characteristics that change as a result of soil development.