BIOGEOCHEMISTRY OF EXPERIMENTAL ECOSYSTEMS: HOW DO ROOT-FUNGUS ASSOCIATIONS AFFECT CHEMICAL WEATHERING AND DENUDATION?

Base cation fluxes were measured in experimental ecosystems (sandboxes) at Hubbard Brook Experimental Forest, New Hampshire. Chemical weathering was estimated for 5 and 15-yearintervals, and denudation was monitored for 18 years in large, fully lined sandboxes planted with red pine (Pinus resinosa Ait.) and kept free of vascular vegetation. Mass-balance equations included base cations (Ca, Mg, and K) in precipitation inputs and drainage outputs, and changes of base cation contents in biomass and soil. Scanning Electron Microscopy (SEM) and Environmental-SEM were used for detection of mycorrhizal fungal association of roots and fungal development on mineral surfaces.

In the non-vascular system chemical weathering and denudation fluxes do not change significantly during the monitored period, but denudation rates are 1.3-1.4 times higher than weathering rates. In the vascular ecosystem the chemical weathering flux is 3 and 1.8 times higher than denudation flux over 5 and 15 years, respectively, but both rates decrease over time. In our experiment the pines retard denudation and accelerate weathering relative to the nonvascular system, thereby increasing available nutrient pools. Ecosystems control chemical weathering and denudation budgets via vegetation and successional stages. The weathering products are built into the biomass with the help of ectomycorrhizal fungi in vascular ecosystems. Sandbox observations suggest that this process may also reduce losses to bulk soil water. The sandbox study offers insight into short-term effects of ecosystems (0-15 yrs), but the long-term effects are not predictable from our findings. The long-term magnitude of chemical denudation from ecosystems may depend strongly on frequency and severity of perturbations.