Ecosystem nutrition as driver of soil organic matter turnover, a modelling approach

长期的生态系统监测表明，大气CO2的增加和持续的氮(N)沉积可能会使森林生态系统进入磷(P)限制，对森林功能产生重大影响。然而，控制磷的生物有效性的过程及其对土壤发育和风化的依赖还没有被充分了解。在第一阶段，SPP 1685收集了关于获取(即主要受风化影响的磷有效性)和再循环(即主要由有机物驱动的磷有效性)生态系统中磷循环的独特数据集。我们建议开发一个新的基于过程的C、N和P循环的生物地球化学土壤模型，将这些观测与主要生物地球化学过程的数学表示相结合，从而将观测纳入一个一致的框架中。我们假设土壤有机质周转是维持沿磷有效性梯度的生态系统营养的关键。为了更好地了解不同磷素有效性水平下的土壤碳动态，我们将利用14C技术对这些森林土壤中的碳周转进行一些关键的分析。该模型将建立在现有的土壤有机碳在土柱中周转、运输和稳定的模型基础上，代表了有机和无机N、P循环以及植物和微生物不同的养分获取策略。利用该模型，我们将研究不同磷素供应水平的影响，特别是土壤有机质储存和周转对生物磷有效性的影响。在努力保持模型简单的同时，所实施的过程应该能够正确地预测生态系统对计划在SPP 1685第二阶段进行的实验施肥的反应。模型的开发将有助于更好地理解磷获取生态系统和循环生态系统之间转变的根本原因，并为在区域应用这一知识以及研究二氧化碳施肥和氮沉积对森林生态系统的影响提供潜力。

Long-term ecosystem monitoring suggests that increasing atmospheric CO2 and continued nitrogen (N) deposition may drive forest ecosystems into phosphorus (P) limitation, with significant impacts on forest functioning. However, the processes controlling the biological availability of P, and their dependence on soil development and weathering are not sufficiently understood. In its first phase, the SPP 1685 has collected a unique data set on P cycling in acquiring (i.e. predominantly weathering-driven P availability) and recycling (i.e. predominantly organic-matter-driven P availability) ecosystems. We propose to develop a novel process-based, biogeochemical soil model of the C, N, and P cycles to integrate these observations with a mathematical representation of the major biogeochemical processes, and thereby to put the observations into one consistent framework. We hypothesise that soil organic matter turnover is pivotal to maintain ecosystem nutrition along the gradient of P availability. To better understand the soil C dynamics at different levels of P availability, we will add some critical analyses on the C turnover in these forest soils using the 14C technique. The model will be built on an existing model of soil organic C turnover, transport, and stabilisation in the soil column, and represent the organic and inorganic N and P cycle as well as differential nutrient acquisition strategies of plants and microbes. With this model, we will study the effects of different levels of P supply, in particular the role of soil organic matter storage and turnover on biological P availability. While trying to keep the model simple, the processes implemented should be able to correctly predict ecosystem responses to the experimental fertilization planned in the second phase of the SPP 1685. The model development will contribute to a better understanding of the underlying causes for the shift between P acquiring and recycling ecosystems, and offer the potential to apply this knowledge regionally and for the study of CO2 fertilization and N deposition on forest ecosystems.