The function of the hyphosphere in carbon and nutrient partitioning between plants and microorganisms in grassland soils under different land-use intensities

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Processes at the micro-habitat scale in grassland soils may explain changes in ecosystem functions at larger scales. In the last phase we demonstrated that fungi are important transmitters of carbon and nutrients between the mineralosphere and the rhizosphere in grassland soils. In the next phase we want to elucidate the specific importance of the hyphosphere (root-free soil around hyphae) under field conditions using newly developed HYPHOboxes. We will separate the rhizosphere and detritusphere from the hyphosphere. Using two 13C-labelling approaches, one with labelled CO2, the other with labelled plant residues, we will test whether land-use intensity (LUI) influences carbon flow from plants into the rhizo- and hyphospheres, and nutrient flow from the hyphosphere into the rhizosphere, respectively. The question is whether mutualistic arbuscular mycorrhizal (AMF) or free-living saprotrophic fungi will dominate the initial C uptake by processing and rapid channelling of rhizodeposits into the hyphosphere. Hyphosphere microorganisms may also act as carbon and nutrient bridges between the detritusphere and the rhizosphere. The newly established multi-grassland land-use experiments will give us the opportunity to investigate to what degree and how quickly de-intensification of grassland land-use will modify biomass and function of soil microorganisms. The reduction in nutrient supply (reduction of fertilization, direct response of soil microorganisms) or the reduced mowing intensity (changes in plant input into soils, indirect response of soil microorganisms) will allow us to disentangle the two different mechanisms and will improve our mechanistic understanding of the response of grassland agroecosystems to changes in land-use intensity. Long-term monitoring of soil microbial properties in 150 grassland sites (in continuation of 2011, 2014 and 2017) will enable us to disentangle short-term changes (over three years) in land-use intensity from longer-term history of the sites (legacy effects) on the functioning and composition of microbial communities.