Clonal and seasonal shifts in communities of saprotrophic microfungi and soil enzyme activities in the mycorrhizosphere of Salix spp.

摘要

The species-specific microbial root and rhizosphere colonization contributes essentially to the plant nutrient supply. The species number and colonization densities of cultivable saprotrophic microfungi and the activities of nutrient-releasing soil enzymes (protease, acid and alkaline phosphatase, arylsulfatase) were investigated in the rhizosphere of one low mycorrhizal (Salix viminalis) and one higher mycorrhizal (S. x dasyclados) willow clone at a Eutric Cambisol in N Germany. After soil washing, in total 32 and 28 saprotrophic microfungal species were isolated and identified microscopically from the rhizosphere of S. viminalis and S. x dasyclados, respectively. The fungal species composition changed within the growing season but the species number was always lower under S. x dasyclados than under S. viminalls. Under both willow clones, the fungal colonization density was largest in spring, and the species number was largest in autumn. Acid-phosphatase activity (p < 0.001) and protease activity (p < 0.003) were significantly affected by the Salix clone, whereas arylsulfatase and alkaline-phosphatase activities did not show clone-specific differences. All enzyme activities reached their maxima in the summer sampling. Rhizosphere colonization with Acremonium butyri, Cladosporium herbarum, and Penicillium janthinellum contributed significantly to explain the activities of acid phosphatase. Rhizosphere colonization with Cylindro-carpon destructans, Penicillium, spinulosum, Plectosphaerella cucumerina, and Trichoderma polysporum contributed significantly to explain the arylsulfatase activities. Effects of the saprotrophic fungal colonization densities on the protease activities in the rhizosphere were low. Acid- and alkaline-phosphatase and arylsulfatase activities in the rhizosphere soil were stronger affected by the composition of the saprotrophic fungal communities than by the Salix clone itself. In conclusion, the colonization density of some saprotrophic microfungi in the rhizosphere contributed to explain shifts in soil-enzyme activities of the P and S cycles under different willow clones.