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

在温带气候中，生长季节上层土壤干燥是很常见的。已知土壤干燥会显著降低碳矿化。然而，腐坏真菌的菌丝将水分从土壤的湿润区重新分配到干燥区（水力再分配）可能会减轻C矿化的干燥效应，为腐坏真菌在干燥条件下提供更大的竞争力。在这里，我们将研究腐坏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。中生态系统将由两个腔室组成，由2毫米的气隙隔开，以防止大量水流，只允许水流通过真菌菌丝。两室之间菌丝体连接建立后，将两室干燥至pF 4 - 5的土壤水张力。随后，一个腔室将用氘标记水和荧光标记物重新冲洗。在实验结束时，将对土壤样品以及干燥室的菌丝进行稳定同位素含量分析和荧光标记。在第二组实验中，双15N/13C标记的植物材料将暴露在不灌溉的干燥室中。通过测量CO2演化和13CO2信号，研究水力再分配对成矿作用的影响。利用土壤酶谱仪在高空间分辨率下分析水力再分配对真菌酶活性的影响，并对灌溉室土壤样品中的13C和15N同位素进行分析，以确定再转移N和c的百分比。这些实验将揭示真菌菌丝在干燥土壤条件下矿化的作用。

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.