The mycorrhiza-mediated pathway for soil organic matter (SOM) formation and consequences for the SOM turnover under short rotation forestry

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Arbuscular- (AM) and ectomycorrhizal (EM) fungi influence soil organic matter (SOM) quantity and quality using different mechanisms. So far little is known how changes in the dominating mycorrhiza type occurring after land use change from arable crops to short rotation forestry (SRF) affect the quantity, composition and turnover of SOM. Therefore, we will manipulate the dominating mycorrhiza type in field and lab experiments to test the following hypotheses: (1) A change from AM to EM, expected under SRF, results in SOM storage due to mycelium formation and SOM stabilising hydrophobin production; (2) A back-change to AM in crops after SRF stimulates saprotrophs to decompose the previously stored SOM and forms new SOM using aggregating effects of glomalin. Accordingly, we will sample recent and former long term SRF and their corresponding reference sites. We will investigate the mycorrhizal colonisation, the amount and molecular composition of SOM including markers (chitin, hydrophobin, glomalin). The microbial decomposition of SOM in the presence and absence of EM will be investigated using 13C studies in incubation experiments. This will prove the importance and sustainability of mycorrhizal C for SOM formation.