Land use intensity as a driver for abundance, diversity and activity of nitrifying microbes in soils from forest ecosystems

土壤微生物群是生态系统健康和大多数相关功能的重要驱动因素。反之，环境条件强烈影响土壤微生物群的结构和功能及其活动模式。因此，生态系统特性和土壤微生物的表现是密切相关的。微生物的高度多样性、动态和遗传灵活性导致了这样的假设，即土壤中的微生物群落在受到抗性、弹性、功能冗余或维持核心微生物群的干扰后确保了过程的稳定性。在这方面，人们对稀有生物圈的作用进行了许多推测，在特定条件下，它可能会成为主导。为了充分了解确保土壤功能的机制，需要将基因的潜在转录和实际转录联系起来。在这方面，氮循环是一个理想的例子，因为具有不同生活方式的微生物（自养、混合养和异养）参与氮的周转，不同群体的功能冗余已经被假设，特别是氨氧化微生物和亚硝酸盐还原微生物，氨或硝酸盐的可用性强烈影响植物的生物多样性。在生物多样性探索框架下获得的数据表明，LUI的增加降低了生物多样性，从而对不同的生态系统服务产生负面影响。因此，在本项目框架内，我们将解决LUI如何影响(i)氮循环基因（有机和无机）的表达，（ii）稀有生物圈的活动和（iii）反硝化基因的遗传组织的问题。为了达到上述目标，宏基因组学和亚转录组学方法将与定量PCR和扩增子测序相结合，比较活性和现有氮循环群落的结构、功能和丰度。为了跟踪活跃群落的变化，将每天和每年从不同的生物多样性探索点采集几次样本，以考虑根系分泌物、光照、温度、湿度等的每日和季节性波动。此外，核心微生物组的存在将通过联合采样活动框架内的大规模调查进行测试。稀有生物圈的作用、功能冗余的机制、恢复力或抗性将在不同的干扰实验中进行研究，这些干扰实验可以操纵植物多样性或土壤中的氧有效性。通过对不同条件下现有和活性氮循环群落的比较，我们希望揭示确保土壤功能的机制。

The soil microbiome is an essential driver for ecosystem health and most related functions. Vice versa environmental conditions strongly influence the structure and function of the soil microbiome as well as its activity pattern. Thus ecosystem properties and the performance of soil microbes are closely interlinked. The high diversity, dynamic and genetic flexibility of microbes lead to the assumption that the microbial community in soil ensures process stability after disturbances by resistance, resilience, functional redundancy or the maintenance of a core microbiome. In this respect much is speculated about the role of the rare biosphere, which might become dominant under specific conditions. To fully understand the mechanisms, which ensure soil functioning, the correlation of potential and actual transcription of genes is needed. In this respect, the nitrogen cycle is an ideal show case, because microbes with different lifestyles (autotroph, mixotroph, and heterotroph) participate in the turnover of nitrogen, functional redundancy has been postulated for different groups especially ammonia oxidising microbes and nitrite reducing microbes and the availability of ammonia or nitrate strongly influences plant biodiversity. Data obtained in frame of the Biodiversity Exploratories indicated that an increase of LUI decreases biodiversity of organisms, which in turn negatively influenced different ecosystem services. Therefore in the frame of this project we will address the question how LUI influences (i) the expression of nitrogen cycle genes (organic and inorganic), (ii) the activity of the rare biosphere and (iii) the genetic organisation of denitrification genes. To reach the described objectives metagenomic and metatranscriptomic approaches will be combined with quantitative PCR and amplicon sequencing to compare the structure, function and abundance of the active and present nitrogen cycle communities. To follow changes in the active community samples will be taken from different Biodiversity Exploratories several times per day and year to take daily and seasonally fluctuations of root exudation, light, temperature, humidity etc. into account. Moreover the existence of a core microbiome will be tested by a large scale survey in frame of the joint sampling campaign. The role of the rare biosphere, mechanisms of functional redundancy, resilience or resistance will be investigated in different disturbance experiments, which manipulate plant diversity or oxygen availability in the soils. By the comparison of the present and active nitrogen cycle community under different conditions we want to uncover mechanisms, which ensure soil functioning.