Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2006
Publication Date: 5/11/2006
Citation: Cheng, X., Baumgartner, K. 2006. Effects of mycorrhizal roots and extraradical hyphae on 15N uptake from vineyard cover crop litter and the soil microbial community. Soil Biology and Biochemistry. 38:2665-2675.
Interpretive Summary: The goal of our study was to investigate the roles of arbuscular mycorrhizal (AM) fungi in absorption of nutrients by grapevines, which are known to be dependent on AM fungi for adequate nutrition. To this end, we compared the relative contributions of mycorrhizal roots (the mycorrhizosphere) and extraradical hyphae (the hyphosphere) to nutrient uptake from cover crop litter labeled with a stable isotope of nitrogen, 15N, in specially-designed containers in the greenhouse. In addition, we examined the response of the soil microbial community to the cover crop litter under the influence of the mycorrhizosphere and the hyphosphere, using phospholipid fatty acid (PLFA) analyses. Collectively, both of the methods provided evidence of the important roles of AM fungi in utilizing nutrients from cover crops. AM fungi significantly increased the uptake of 15N in grapevines, relative to our bulk soil treatment, in which neither roots nor hyphae had direct access to the cover crop litter. We also found that the AM fungi supported a soil microbial community that responded similarly to addition of the cover crop litter, as did the soil microbial community supported by the mycorrhizal roots. Our findings demonstrate the significance of AM fungi in supporting other soil microbes, a topic that is of interest to researchers who study mycorrhizal fungi, but of which there is little substantive evidence.
Technical Abstract: The objectives were to quantify the contribution of arbuscular mycorrhizal (AM) fungal hyphae to 15N uptake from vineyard cover crop litter, and to examine the soil microbial community under the influence of the mycorrhizosphere and the hyphosphere. Mycorrhizal grapevines were grown in containers, within which mesh cores were vertically inserted. The mesh allowed mycorrhizal roots (mycorrhizosphere treatment), extraradical hyphae (hyphosphere treatment), or neither (bulk soil treatment) to access 15N-labeled cover crop litter placed inside the cores. Grapevines and soil were harvested 0, 7, 14, and 28 days after addition of the litter. Extraradical hyphae increased 15N uptake from the cover crop litter, but their contribution relative to that of the mycorrhizal roots was small. We detected similar peaks in soil microbial biomass in the hyphosphere and mycorrhizosphere treatments after addition of the cover crop litter, despite significantly lower microbial biomass in the hyphosphere treatment initially. Our results suggest that although grapevine roots play a dominant role in the direct uptake of nutrients from a decomposing cover crop, AM hyphae may have a more important role in maintaining soil microbial communities associated with nutrient cycling.