De-intensification Effects on Methane-Cycling Microorganisms and the Methane Sink Function of Grasslands (MetGrass)

甲烷(CH4)是第二大最相关的温室气体，对全球变暖有很大贡献。2021年，全球政治努力已经开始减少其排放。土壤微生物群是最重要的陆地甲烷汇，但这高度依赖于土地利用管理。今天S农业面临的一个主要挑战是调整土地利用强度，以确保高产且同时可持续的草地生产系统，以平衡温室气体排放和不断增长的世界人口对粮食的需求。两组完全不同的微生物对甲烷循环至关重要。甲烷营养细菌通过氧化大气中的甲烷作为生物汇，而产甲烷菌在缺氧区、团聚体和更深层的土壤中产生甲烷。在之前的项目中，合作伙伴揭示了(1)高土地利用强度对草原土壤中甲烷营养细菌的负面影响，以及(2)决定草原是CH4的源还是汇的高季节性微生物群落动态。研究结果提出了几个问题，涉及土地利用强度对CH4循环微生物群和由此产生的净地表通量的影响的大小和动态。在新提议的MetGrass中，我们将通过参与REX和LUX联合多点草原实验，研究草原土地利用非集约化对甲烷氧化菌和产甲烷菌的影响。化肥、割草和放牧的减少将如何影响生物多样性、活性、丰度和土壤中甲烷氧化菌和产甲烷菌的分布，到目前为止还没有在任何生态系统规模的实验中进行过调查。我们将测试四个互补的假设，总的目标是评估(1)不强化如何导致产甲烷和营养甲烷微生物的种类组成和丰度的变化，(2)这与CH4净表面通量的变化有何关系，以及(3)这些变化有多快。在工作包(WP)1中，我们将研究去集约化后草原土壤中CH4汇功能和甲烷氧化菌的长期恢复效果。WP2评估甲烷氧化菌和产甲烷菌对单一管理事件(即施肥和割草)的短期反应。在WP3中，我们的目标是开发基于微生物组的草原土壤CH4通量预测模型。WP4将评估在增加施肥率时草原土壤CH4汇功能的临界点，从而将提供对潜在微生物组动态的机械理解。我们将采用最先进的方法的独特组合，反映出MetGrass团队的跨学科性质。MetGrass将能够(A)解决土地利用非集约化对草原上这些关键土壤微生物的功能多样性和活动的影响的紧迫问题，(B)将为改善草原管理以实现可持续土地利用奠定基础。

Methane (CH4) is the second most relevant greenhouse gas and contributes substantially to global warming. In 2021, global political efforts have been started to mitigate its emission. The soil microbiome is the most important terrestrial methane sink, but this is highly dependent on land use management. A major challenge for today´s agriculture is to adjust land-use intensity to ensure productive and at the same time sustainable grassland production systems to balance greenhouse gas emissions and increasing food demands of a growing world population. Two fundamentally different groups of microbes are crucial for CH4-cycling. Methanotrophic bacteria act as biological sink by oxidizing atmospheric CH4, while methanogens produce methane in anoxic zones, aggregates and deeper soil layers. In the previous project, the partners have revealed (1) the negative impact of high land-use intensity on methanotrophic bacteria in grassland soils, and (2) the high seasonal microbiome dynamics that determine if grasslands are sources or sinks of CH4. The results raise several questions regarding the magnitude and dynamics of land-use intensity effects on CH4-cycling microbiomes and the resulting net surface fluxes. In the new proposal MetGrass, we will thus study the effects of grassland land-use de-intensification on methanotrophs and methanogens, by contributing to the joint multi-site grassland experiments REX and LUX. How a reduction of fertilization, mowing, and grazing will impact biodiversity, activity, abundance and the distribution over the soil profile of methanotrophs and methanogens hast not been investigated in any ecosystem-scale experiment to date. We will test four complementary hypotheses with the overall aim to assess (1) how de-intensification leads to changes of the species composition and abundance of methanogenic and methanotrophic microbes, (2) how this is associated with changed CH4 net surface fluxes and (3) how rapid these changes are. In work package (WP)1, we will study the long-term recovery effects of the CH4 sink function and methanotrophs in grassland soils after de-intensification. WP2 assesses short-term responses of methanotrophs and methanogens to single management events (i.e. fertilization and mowing). In WP3, we aim to develop microbiome-based predictive model of grassland soil CH4 fluxes. WP4 will assess the tipping point of the CH4 sink function of a grassland soil upon increasing rates of fertilization and will thereby provide a mechanistic understanding of underlying microbiome dynamics. We will employ a unique combination of state-of-the-art approaches, reflecting the interdisciplinary nature of the MetGrass team. MetGrass will be able (a) to address pressing questions on the effect of land-use de-intensification on the functional diversity and activity of these key soil microorganisms in grasslands and (b) will deliver the basis for improvement of grassland management towards sustainable land use.