Analysis and experimentation on ecosystems

Climate change that we are facing is expected to influence multiple environmental processes, including weathering and soil formation. While temperature and partial pressure of CO2 in the atmosphere are expected to directly influence dissolution, in the soils their effect is compounded by plant response to environmental change. In order to evaluate effect of temperature and CO on rock dissolution, plant growth and nutrient uptake, we conducted mesocosm experiments 2where we exposed three different plants grown in unweathered basalt tephra, as well as unplanted but not sterilized control, to following conditions: two different CO2 levels, 400 ppm and 800 ppm, and two climate regimes, with ambient (21-25°C) and elevated (25-30°C) temperatures. Tight control on the environmental variables was possible by conducting experiments at the ECOTRON Ile-De-France facility, France. Studied plants included velvet mesquite (Prosopis velutina), green spangletop (Leptochloa dubia), and alfalfa (Medicago sativa). Both mesquite and alfalfa were inoculated with the nitrogen-fixing bacteria. Pore water solution and leachates were collected at set intervals and analyzed to determine pH, conductivity, and concentrations of C, N, and lithogenic elements. At the end of the experiment, all plant biomass was collected, dried, weighed, and subsamples digested to determine nutrient uptake by the plants. Soils were also analyzed for changes in organic and inorganic C and total N content. We observed significant increase in solution concentrations for several lithogenic elements, such as Si, Mg, and P with increase in temperature. Concentrations in the biomass were also increased for many elements. However, biomass production was smaller at elevated temperature for alfalfa, resulting in less treatment difference when total uptake by the plants was compared. Fewer effects of elevated CO were measured; 2among them was greater carbonate precipitation in the soil. This study indicates that climate change would affect both abiotic and biotic components of soil formation.