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

[87263]了解控制养分吸收的因素对生态系统科学的进步和环境政策的合理制定至关重要。不幸的是，与生态系统的投入、产出和各种地上通量相比，生态系统的营养吸收不能直接测量。基本上有两种估算营养吸收的方法。吸收量可以通过基于某些生态系统通量的质量平衡来计算：凋落物、根系周转、叶面淋失和生物量增量。或者，可以使用养分吸收模型来计算吸收量，该模型依赖于知道根表面积、根吸收动力学和根表面土壤溶液的模拟浓度。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证实，但尚未在森林生态系统中得到成功证明。LTER跨站点研究项目的目的是确定我们目前对生态系统尺度森林养分吸收过程的理解中最重要的空白。该方法包括养分吸收模型的参数化，并将结果与各种森林生态系统类型的养分吸收生态系统预算进行比较。跨站点比较的优势在于，不同的过程在不同的站点可能很重要。这项研究将解决三个主要问题。第一个问题是，预算与模拟摄取的比较将揭示各种模型假设失败的情况。其次，对参数化模型的分析将确定哪些参数是最重要的，以便准确指定。最后，将提供在一系列非农业物种和条件下的吸收动力学的新数据。在吸收模型能够做出有用的预测之前，必须识别和纠正参数值中的错误和模型假设中的错误。总的来说，这项研究将是第一个提供不同森林生态系统中各种树种摄取动力学的详细机制测量

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