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

了解养分吸收的控制因素对生态系统科学的进步和环境政策的健全形成至关重要。不幸的是，与生态系统的投入、产出和各种地上通量不同，生态系统的养分吸收不能直接测量。估计养分摄入量基本上有两种方法。可以根据某些生态系统通量：凋落物、根周转、叶淋洗和生物量增量，通过物质平衡计算吸收。或者，可以使用养分吸收模型来计算吸收，该模型依赖于已知的根表面积、根吸收动力学和模拟的土壤溶液在根表面的浓度。养分吸收模型提供准确预测的潜力已被它们在大田作物上的成功所证实，但尚未在森林生态系统中得到成功证明。LTER跨地点研究项目的目的是找出我们目前在生态系统规模上对森林养分吸收过程的理解中最重要的差距。该方法涉及养分吸收模型的参数化，以及将结果与各种森林生态系统类型的养分吸收的生态系统收支进行比较。跨地点比较的优势在于，不同的过程在不同的地点可能是重要的。这项研究将解决三个主要问题。第一个问题是，预算与模拟吸收的比较将揭示各种模型假设失效的情况。其次，对参数化模型的分析将确定哪些参数是最重要的，需要准确指定。最后，将提供有关一系列非农业物种和条件下的吸收动力学的新数据。在吸收模型作出有用的预测之前，必须查明和纠正参数值错误和模型假设错误。总体而言，这项研究将首次提供不同森林生态系统中不同树种吸收动力学的详细机械测量

0087263YanaiUnderstanding 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