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

甲烷（CH4）是第二大温室气体，对全球变暖有重大贡献。于二零二一年，全球已开始政治努力以减少其排放。土壤微生物组是最重要的陆地甲烷汇，但这在很大程度上取决于土地利用管理。当今农业面临的一个主要挑战是调整土地使用强度，以确保生产力，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日益增加的粮食需求。两组根本不同的微生物对CH4循环至关重要。甲烷氧化菌通过氧化大气中的CH4作为生物汇，而产甲烷菌在缺氧区、团聚体和深层土壤中产生甲烷。在上一个项目中，合作伙伴揭示了（1）高土地利用强度对草原土壤中甲烷氧化细菌的负面影响，以及（2）决定草原是CH4源还是汇的高季节性微生物组动态。结果提出了几个问题的规模和动态的土地利用强度对甲烷循环微生物和由此产生的净表面通量的影响。因此，在新的提案MetGrass中，我们将通过促进多地点联合草原实验雷克斯和LUX，研究草原土地利用去集约化对甲烷氧化菌和产甲烷菌的影响。如何减少施肥，割草，放牧将影响生物多样性，活性，丰富和分布在土壤剖面的甲烷氧化菌和产甲烷菌尚未在任何生态系统规模的实验研究。我们将测试四个互补的假设，总体目标是评估（1）去强化如何导致产甲烷和甲烷氧化微生物的物种组成和丰度的变化，（2）这是如何与变化的CH4净表面通量和（3）这些变化有多快。在工作包（WP）1中，我们将研究在去强化后草原土壤中CH4汇功能和甲烷氧化菌的长期恢复效果。WP2评估了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，我们的目标是建立基于微生物的草地土壤CH4通量预测模型。WP4将评估施肥率增加后草原土壤CH4汇功能的临界点，从而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MetGrass团队的跨学科性质。MetGrass将能够（a）解决土地利用去集约化对草原中这些关键土壤微生物的功能多样性和活性的影响的紧迫问题，（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.