Redistribution of water via mycelia networks of saprotrophic fungi and its effect on C-mineralization in desiccated soils

在温带气候中，上层土壤在生长季节干燥是很常见的。众所周知，土壤干燥会大大减少碳矿化。然而，腐生真菌菌丝体将水分从湿润地带重新分配到土壤干燥区域(水力再分配)可能会缓解碳矿化干燥的影响，从而为腐生真菌在干旱条件下提供更大的竞争力。在这里，我们将调查腐生真菌的菌丝体网络是否有助于土壤中的水分再分配，以及这如何影响有机质的矿化。将使用由2毫米气隙隔开的两个室组成的中膜，以防止水的大量流动，并仅允许水通过真菌菌丝体流动。在两室之间的菌丝连接建立后，两室都将被干燥到土壤水张力为Pf4-5。随后，其中一室将用标记的水和一个荧光标记物重新灌溉。在实验结束时，将对土壤样本和干燥室的菌丝进行稳定的同位素含量和荧光标记分析。在第二组实验中，双15N/13C标记植物材料将暴露在未灌溉的干燥室中。通过测量CO2释放量和13CO2信号，研究水力再分配对成矿作用的影响。将分析灌水室土壤样品中的13C和15N同位素，以确定N和C再转移的百分比。此外，将利用土壤酶谱在高空间分辨率下分析水力再分配对真菌酶活性的影响。这些实验将为了解干燥土壤条件下真菌菌丝体在矿化中的作用提供新的线索。

Desiccation of the upper soil during the growing season is common in temperate climate. Soil desiccation is known to reduce C mineralization substantially. However, redistribution of water by mycelia of saprotrohic fungi (hydraulic redistribution) from moist to dry zones of the soil might mitigate the effects of desiccation of C mineralization, providing a larger competitiveness of saprotrophic fungi under dry conditions. Here, we will investigate if mycelia networks of saprotrophic fungi contribute to water redistribution in soil and how this influences mineralization of organic matter. Mesocosms will be used comprising two chambers, separated by a 2 mm air gap to prevent bulk flow of water and allowing only water flow via fungal mycelia. After the mycelia connection between both chambers is established, both chambers will be desiccated to a soil water tension of pF 4 - 5. Subsequently, one chamber will be reirrigated with deuterium labelled water and a florescent marker. At the end of the experiment, soil samples as well as hyphae of the desiccated chamber will be analysed for stable isotope content and fluorescent labelling. In a second set of experiments double 15N/13C labelled plant material will be exposed in the non-irrigated desiccated chamber. The effect of hydraulic redistribution on the mineralization will be studied by measuring CO2 evolution and the 13CO2 signal. 13C and 15N isotopes will be analyzed in soil samples of the irrigated chambers to determine the percentage of retransferred N and C. Furthermore, the impact of hydraulic redistribution on fungal enzyme activity will be analyzed at high spatial resolution using soil zymography. These experiments will shed new light on the role of fungal mycelia for mineralization under dry soil conditions.