Evaluation of Effects of Sustained Decadal Precipitation Manipulations on Soil Carbon Stocks

Abstract

Throughout a 13 year period, the Throughfall Displacement Experiment sustained both increased (+33) and decreased (-33%) throughfall into an upland Oak forest in Tennessee. Organic (O) horizon carbon (C) stocks were measured at several occasions before, during and after the experiment and mineral soil C stocks before and after the experiment. In the O horizon, higher litter fall rates and slower decomposition lead to higher C stocks in the dry treatment compared to the ambient and wet. Dry plot accumulation of C in the O horizon was attributable to a combination of enhanced litter inputs and reduced decomposition. Implications of the immobilization of nutrient elements as long-term feedbacks are discussed. No treatment effect on C stocks was found in the mineral soil, but a significant long-term reduction in mineral soil C stocks was found between the start and the end at the experiment from 3.5 to 2.7% C in the 0-15 cm layer and from 0.6 to 0.5% in the 15-30 cm layer. Explanations for this significant trend in C storage were not readily apparent, but are fully discussed in the context of measurement bias, temperature, and primary production.