Linking land use intensity, biodiversity, soil microbial processes and organo-mineral interactions for a mechanistic understanding of Nitrogen turnover in grassland ecosystems (BE_BioMON)

土地利用强度的增加是草地生态系统氮素流失、生物多样性和多功能性下降的主要原因。尽管如此，LUI，地上和地下生物多样性和N循环在草地生态系统之间的相互作用缺乏一个机械的理解，这使得有针对性的缓解措施。通过土壤微生物生态学的跨学科整合，植物-土壤-微生物系统中生物氮分配的短期过程，以及长期物理化学土壤有机氮（SON）保留途径，BE_BioMon旨在通过连接测量和建模来填补这一知识空白。我们推测，随着LUI的减少和微生物组的多样化，N分配从硝化/反硝化转变为生物同化。这促进了氮保留通过necromass稳定颗粒和矿物相关的SON取决于总营业额和微尺度土壤结构。此外，我们预计，增加LUI将导致从共生到联合固氮的转变，这将增加N2：N2 O排放比，由于在共生固氮生物中截短的反硝化途径。此外，我们假设土壤δ 15 N是指纹LUI对N循环的影响，因此可以作为一个过程集成基准量的生态系统模型。这有望推进基于建模的时空尺度的LUI草原N循环的影响。为了验证假设，我们将在所有3个生物多样性探索站（BE）（WP 1）的不同LUI的选定地块进行田间15 N肥料示踪试验。在WP 2中，我们将进行围隔实验与15 N2暴露解开LUI对BNF-N的命运的影响。WP 3旨在通过垂直δ 15 N土壤剖面、宏基因组学和SON分级对所有草原EP的BE土壤采样活动中的N循环进行指纹识别。从WP 1 -3的实验工作中获得的知识和已经可用的BExIS数据将用于测试和推进基于过程的生态系统模型LandscapeDNDC的N个例程。该模型，扩展的动态植被模型CoSMo，是用来评估整个BE草原地块（WP 4）的N循环的差异。在WP 5（合成）中，我们将机械地将LUI和生物多样性的影响与测量和模拟的地球化学氮转化，通过有机-无机相互作用的氮保留和从天到年的全氮平衡联系起来。我们预计，这种合成最终允许一个先进的机制和功能的理解生态系统N循环的影响LUI，地上和地下的生物多样性和特定地点的属性。

Increase in land use intensity (LUI) is a strong driver for environmental nitrogen (N) losses and decline of biodiversity and multifunctionality in grassland ecosystems. Still, interactions between LUI, above- and belowground biodiversity and N cycling in grassland ecosystems lack a mechanistic understanding, which prevents targeted mitigation measures. Through an interdisciplinary integration of soil microbial ecology, short-term processes of biotic N partitioning in the plant-soil-microbe system, and long-term physicochemical soil organic nitrogen (SON) retention pathways, BE_BioMon aims to fill this knowledge gap by linking measurements and modelling. We hypothesize that with decreasing LUI and more diverse microbiome, N partitioning shifts from nitrification/denitrification to biotic assimilation. This promotes N retention via necromass stabilization in particulate and mineral-associated SON depending on aggregate turnover and microscale soil architecture. Furthermore, we expect that increasing LUI will result in a shift from symbiotic to associative N fixation, which will increase the N2:N2O emission ratio due to truncated denitrification pathways in symbiotic diazotrophs. Moreover, we hypothesize that soil δ15N is fingerprinting LUI effects on N cycling, and thus can serve as a process integrating benchmark quantity for ecosystem models. This is expected to advance modeling-based spatiotemporal scaling of LUI effects on grassland N cycling. To test the hypotheses, we will perform field 15N fertilizer tracing experiments at selected plots of different LUI at all 3 Biodiversity Exploratories (BE) (WP1). In WP2, we will conduct mesocosm experiments with 15N2 exposure to disentangle LUI effects on the fates of BNF-N. WP3 is designed to fingerprint N cycling within the BE soil sampling campaign at all grassland EPs through vertical δ15N soil profiles, metagenomics, and SON fractionation. The gained knowledge from experimental work of WP1-3 and already available BExIS data will be used for testing and advancing N routines of the process-based ecosystem model LandscapeDNDC. This model, expanded by a dynamic vegetation model CoSMo, is used to evaluate differences in N cycling across the entirety of BE grassland plots (WP4). In WP5 (synthesis) we will mechanistically link effects of LUI and biodiversity with measured and modeled biogeochemical N transformations, N retention through organo-mineral interactions and full N balances at scales from days to years. We expect that this synthesis finally allows for an advanced mechanistic and functional understanding of ecosystem N cycling as influenced by LUI, above- and belowground biodiversity and site-specific properties.