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

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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.