Microbial interactions and phosphorus mobilization in forest soils - effects of carbon, nitrogen and phosphorus availability

新建立的氮磷肥施用试验将用于测试营养添加是否会改变真菌与真菌的相互作用，使其在森林土壤表面产生强烈的菌丝体生长，从而使腐养真菌的优势地位更高。在养分添加试验中，真菌与真菌的相互作用可能会发生变化，因为在碳有效性不变或略高的情况下（由于植物生长增强），养分增加了，但环带减少了从树木向土壤环境的碳转移。因此，我们将测试来自根沉积的C量的减少是否会降低土壤中外生菌根真菌（EMF）共生P动员的重要性。由于分解高分子有机碳化合物的能力对于微生物获取结合在复杂生物结构（如根和凋落物）中的含氮和含磷化合物是必要的，因此我们希望研究腐坏营养和EMF在有机化合物分解过程中的相对作用。氧化酶与水解酶活性的比值将告诉我们，排除电磁场是否会改变土壤微生物群落在有机物分解过程中的行为，从而改变有机质中养分释放过程中的行为。在我们的土壤生长实验中，对主导EMF的宏基因组分析将证明EMF是否具有分解有机物的遗传潜力。在实验室条件下添加Mn过氧化物酶将证明氧化酶是否可以释放出其他受保护的有机N和P化合物，供随后的微生物分解。我们将继续与SPP内对植物与土壤微生物相互作用感兴趣的其他小组密切合作。

The newly established N x P application experiment will be used to test whether nutrient addition changes fungal-fungal interactions towards higher dominance of saprotrophic fungi due to the resulting intense mycelial growth at the surface of forest soils. Fungal-fungal interactions in the nutrient addition experiment may change due to an increase in nutrients at either constant or slightly higher carbon availability (due to enhanced plant growth), but girdling decreases the C transfer from trees into the soil environment. Therefore, we will test whether a decrease in the amount of C derived from rhizodeposition reduces the importance of symbiotic P mobilization by ectomycorrhizal fungi (EMF) in soils. Since the ability to cleave high molecular organic carbon compounds is necessary for microorganisms to access N and P containing compounds bound up in complex biotic structures like roots and litter, we want to investigate the relative roles of saprotrophic and EMF during decomposition of organic compounds. The ratio of oxidative to hydrolytic enzyme activities will give us an indication whether the exclusion of EMF will modify the behaviour of the soil microbial community during decomposition of organic matter and consequently during the release of nutrients from organic matter. Metagenomic analyses of the dominant EMF in our soil-in-growth experiment will demonstrate whether EMF have the genetic potential to decompose organic matter. The addition of Mn peroxidase under lab conditions will prove whether oxidative enzymes might liberate otherwise protected organic N and P compounds for subsequent microbial decomposition. We will continue our intense collaborations with other groups within the SPP interested in interactions between plants and soil microorganisms.