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ARS Home » Pacific West Area » Davis, California » Crops Pathology and Genetics Research » Research » Publications at this Location » Publication #194894

Title: MICROBIAL UTILIZATION OF NITROGEN FROM VINEYARD COVER CROPS

Author
item Baumgartner, Kendra
item Cheng, Xiaomei

Submitted to: American Society of Enology and Viticulture Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 4/1/2006
Publication Date: 6/29/2006
Citation: Baumgartner, K., Cheng, X. 2006. Microbial utilization of nitrogen from vineyard cover crops. American Society of Enology and Viticulture Annual Meeting Abstracts.

Interpretive Summary: Arbuscular mycorrhizal (AM) fungi are one of few groups of soil microbes that have been shown to benefit grapevine nutrition. Previously, we showed that their fungal filaments (external hyphae) can serve as “bridges” for nitrogen (N) transfer from vineyard cover crops to grapevines. The objectives of this study were to evaluate the contribution of AM fungi to N uptake from a cover crop that is incorporated into the soil, bur medic (Medicago polymorpha), and to characterize the soil microbial response to the decomposing cover crop under the influence of mycorrhizal roots or external hyphae. Grapevines were grown in specially-designed containers, within which a mesh core was inserted. The mesh allowed mycorrhizal roots (roots + hyphae), external hyphae alone, or neither to access ground cover crop shoots (leaves and stems) labeled with a stable isotope of N, 15N, and placed inside the mesh cores. Grapevines and soils were harvested 0, 7, 14, and 28 days after addition of the cover crop, and analyzed for 15N content. External hyphae increased 15N uptake from the litter (62 µg), but their contribution relative to that of the mycorrhizal roots (927 µg) was small. We detected similar peaks in soil microbe populations supported by the hyphae alone (37 nm g-1 soil) and in soil microbe populations supported by mycorrhizal roots (38 nm g-1 soil). Our results suggest that although grapevine roots play a dominant role in the direct uptake of nutrients from tilled cover crops, AM fungi may have a more important role in maintaining soil microbial communities associated with nutrient cycling.

Technical Abstract: Arbuscular mycorrhizal (AM) fungi are one of few groups of soil microbes that have been shown to benefit grapevine nutrition. Previously, we showed that external hyphae of AM fungi can serve as bridges for nitrogen (N) transfer from no-till cover crops to grapevines. The objectives of this study were to evaluate the contribution of AM fungi to N uptake from a tilled cover crop, bur medic (Medicago polymorpha), and to characterize the soil microbial response to the decomposing cover crop under the influence of mycorrhizal roots or external hyphae. Grapevines were grown in specially-designed containers, within which a mesh core was inserted. The mesh allowed mycorrhizal roots (mycorrhizosphere treatment), external hyphae (hyphosphere treatment), or neither to access 15N-labeled cover crop litter placed inside the cores, after 4 months of grapevine growth. Grapevines and soils were harvested 0, 7, 14, and 28 days after addition of the litter. External hyphae increased 15N uptake from the litter (62 µg), but their contribution relative to that of the mycorrhizal roots (927 µg) was small. We detected similar peaks in soil microbial biomass in the hyphosphere (37 nm g-1 soil) and mycorrhizosphere treatments (38 nm g-1 soil) after addition of the litter, despite significantly lower microbial biomass in the hyphosphere treatment initially (10 nm g-1 soil). Our results suggest that although grapevine roots play a dominant role in the direct uptake of nutrients from tilled cover crops, AM fungi may have a more important role in maintaining soil microbial communities associated with nutrient cycling.