This project tests the hypothesis that global warming alters phosphorus cycling and triggers biological feedback mechanisms in pinyon-juniper ecosystems. The intention is to quantify the consequences of increased soil temperature and decreased moisture on biogeochemical phosphorus cycling and the response of dominant plant species relative to woodland successional development. An initial laboratory study will be conducted with soils incubated under various temperature and moisture treatments. During a one year field study, soil climate will be manipulated in an early successional and a mature pinyon-juniper community of north- central Arizona. A replicated factorial design will be used to test for changes in inorganic, organic, microbial, and plant available phosphorus pools and fluxes. Soil phosphatase activity will be examined as an indicator of organic phosphorus mineralization. Phosphorus reabsorption efficiency in pinyon, juniper, and blue grama will be used as a measurement of plant internal changes in phosphorus cycling in response to a soil warming. This project will identify the inorganic and organic processes mediated by an altered soil climate and the biological activity of plants and microbes that are key to understanding phosphorus dynamics and ecosystem function under conditions of climate change. This research may be viewed as a case study for biogeochemical phosphorus cycling at a regional scale under conditions of global change.
