Previous studies have demonstrated the importance of mycorrhizae in utilizing P from "stable" inorganic pools and implicated CO2 and oxalate in differential use of ortho-P pools. Moreover, the ability of some early colonizing species (e.g. Halogeton glomeratus, Salsola kali) to produce oxalate has led to the hypothesis that interactions of plant or associated fungal exudates with the soil matrix plays a pivotal role in P dynamics in arid ecosystems. The proposed research focuses on two weathering agents, CO2 and oxalate, which act to enhance P release from the inorganic pool. In turn, the induced shift in P partitioning among pools influences succession. The hypotheses will be tested through a series of experiments at theoretical and ecosystem levels. The experiments are a logical progression toward evaluation of the hypotheses. Specifically, the project will determine: 1. The existence of oxalate in archived soils from a past successional study, in lysimeter and in field soils; 2. The effect of oxalate driven Ca-phosphate mineral weathering on succession; 3. The rates of oxalate production in systems of varying P availability; 4. The rate of reaction of CO2 or oxalate with soil minerals involved in P release; 5. The potential rate of oxalate degradation; 6. Models of dynamic and equilibrium conditions for CO2 and oxalate reactions with Ca-phosphate minerals; 7. Laboratory, lysimeter and field tests of P chemistry models. The results of these experiments will provide a mechanistic model of some processes which affect P cycling and early succession in a semiarid ecosystem. The investigators are well qualified to perform this type of research and the facilities are adequate.
