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（LUI）的增加是草地生态系统环境氮(N)流失、生物多样性和多功能性下降的重要驱动因素。然而，草地生态系统中LUI、地上和地下生物多样性与氮循环之间的相互作用缺乏机制理解，这阻碍了有针对性的缓解措施。BE_BioMon通过跨学科整合土壤微生物生态学，植物-土壤-微生物系统中生物N分配的短期过程，以及长期的物理化学土壤有机氮（SON）保留途径，旨在通过连接测量和建模来填补这一知识空白。我们假设，随着LUI的降低和微生物组的多样化，氮分配从硝化/反硝化转变为生物同化。这通过颗粒和矿物相关土壤的坏死团稳定促进了氮的保留，这取决于团聚体周转和微尺度土壤结构。此外，我们预计LUI的增加将导致共生重氮营养体从共生固氮向结合固氮转变，这将增加共生重氮营养体中N2:N2O排放比，因为反硝化途径被截断。此外，我们假设土壤δ15N是LUI对N循环的指纹效应，因此可以作为生态系统模型的基准量。这有望推进基于建模的草地氮素循环效应时空尺度研究。为了验证这一假设，我们将在3个生物多样性探索中心（WP1）的不同LUI地块上进行田间15N肥料示踪试验。在WP2中，我们将进行15N2暴露的中观实验，以了解解缠LUI对BNF-N命运的影响。WP3旨在通过垂直δ15N土壤剖面、宏基因组学和SON分选，在所有草地EPs的BE土壤采样活动中指纹N循环。从WP1-3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landscape ndc的N个例程。该模型在动态植被模型CoSMo的基础上进行扩展，用于评价整个BE草地样地氮循环的差异（WP4）。在WP5（合成）中，我们将把LUI和生物多样性的效应与测量和模拟的生物地球化学氮转化、通过有机-矿物相互作用产生的氮保留以及数天至数年尺度上的全氮平衡机制联系起来。我们期望这种综合最终允许对生态系统氮循环受LUI、地上和地下生物多样性和地点特异性影响的机制和功能有一个先进的理解。

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.