LTER Cross-Site: Nutrient Uptake at the Ecosystem Scale - Testing Model Assumptions by Cross-Site Comparisons with Nutrient Budgets

Suny College Of Environmental Science And Forestry, Syracuse NY

Investigators

Abstract

0087263 Yanai Understanding the factors controlling nutrient uptake is essential to the advancement of ecosystem science and to the sound formation of environmental policy. Unfortunately, ecosystem nutrient uptake cannot be measured directly, in contrast to ecosystem inputs, outputs, and various aboveground fluxes. There are basically two approaches to estimating nutrient uptake. Uptake can be calculated by mass balance based on certain ecosystem fluxes: litterfall, root turnover, foliar leaching, and biomass increment. Alternatively, uptake can be calculated using nutrient uptake models, which depend on knowing root surface area, root uptake kinetics and the simulated concentration of the soil solution at the root surface. The potential of nutrient uptake models to provide accurate prediction has been confirmed by their success with field crops, but has yet to be demonstrated successfully in forest ecosystems. The purpose of the LTER Cross-site research project is to identify the most important gaps in our current understanding of nutrient uptake processes in forests at the ecosystem scale. The approach involves the parameterization of a nutrient uptake model and comparison of the results to ecosystem budgets of nutrient uptake across a variety of forest ecosystem types. The strength of the cross-site comparison is that different processes are likely to be important at different sites. This study will address three main issues. The first issue is the comparison of budgeted with simulated uptake will reveal the circumstances under which various model assumptions fail. Second, analysis of parameterized models will identify which parameters are most important to specify accurately. Finally, new data will be provided on uptake kinetics across a range of non-agricultural species and conditions. Both errors in parameter values and errors in model assumptions must be identified and corrected before uptake models can make useful predictions. Overall, this study will be the first to provide detailed mechanistic measurements of uptake kinetics on a variety of tree species in a different forest ecosystems