Effect of Changes in Amount and Seasonality of Rainfall on Soil Carbon and Cation Nutrient Composition.

Over the last six years, at the Angelo Reserve climate change experiment (near Mendocino, CA) researchers from several institutions have been studying the effect of changing amount and seasonality of rainfall (in accordance to the projections made for California in the 21^st century by the Canadian/CGCM1 and Hadley/HadCM2 climate models) on several ecosystem variables—including net primary productivity, plant diversity, microbial biomass and diversity, arthropod diversity, and apatite dissolution. After six years, preliminary data has shown that there is significant effect on variables that control biochemical composition of soil organic matter, soil aggregation, and dynamics of iron-bound phosphorous. We are currently investigating the effects of changing amount and seasonality of rainfall on the amount and biochemical composition (molecular architecture determined from ¹³C-NMR) of, and cation nutrient budgets. So far, we have found that addition of more rainfall in the winter rainy season has very little effect on amount of soil organic matter or its humification. However, extension of the rainy season into the summer months results in accumulation up to 50% more carbon (especially in the subsoil horizons) that is less humified. We find that shifts in seasonality of rainfall have created critical change in soil carbon pools and the soil’s acid-base chemistry.