The coarse-soil fraction is the main living space of fungal hyphae in the BhBs horizon of a Podzol

摘要

In acidified forest soils, the coarse-soil fraction is a potential nutrient source. Plant nutrient uptake from the coarse-soil fraction is aided by ectomycorrhiza. Similarly, (recalcitrant) organic matter (OM) is an important nutrient source largely made plant-available through (symbiotic) microorganisms, especially in the topsoil. We hypothesized that in a podzol profile, fungal hyphae would concentrate in nutrient hotspots, either OM or the coarse-soil fraction. Absolute hyphal length, base saturation, and organic-C content of a Podzol profile were determined in the fine-earth and coarse-soil fractions. In the fine-earth fraction, hyphae were attracted by the organic-C content and relative high base saturation. In the coarse-soil fraction of the BhBs horizon, the absolute hyphal length exceeded the hyphal length in the fine earth by factor 3, yet C content and base saturation were lowest. We could not determine to what fungi the hyphae belonged. Most likely ectomycorrhiza, ericoid mycorrhiza and saprotrophic fungi dominate the upper soil layers of this profile and all utilize OM for nutrition. In the deeper mineral horizons and especially in the coarse-soil fraction, ectomycorrhiza are better adapted than other fungi to harvest nutrients from inorganic sources. Additionally, favorable physical properties may explain the high amount of fungal hyphae in the coarse-soil fraction of the BhBs horizon. Both the coarse-soil fraction and deeper mineral soil horizons may play a more active role in microbial nutrient cycling than previously assumed.