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Title:   Author  item
                                            CHENG, XIAOMEI - UC DAVISitem
                                            Baumgartner, Kendra
  Submitted to: Soil Ecology Meeting Abstracts
                                    Publication Type: Abstract Only
                                    Publication Acceptance Date: 3/1/2005
                                    Publication  Date: 5/25/2005
                                    Citation: Cheng, X., Baumgartner, K. 2005. Roles of arbuscular mycorrhizal fungi in nutrient utilization from vineyard cover crops. Soil Ecology Meeting Abstracts.Interpretive Summary: We conducted two greenhouse studies to examine how arbuscular mycorrhizal (AM) fungal networks help grapevines absorb nutrients from vineyard cover crops. The objective of the first study was to determine if nutrients are transferred from no-till cover crops directly to grapevines, via the AM fungal hyphae that connect them. We grew grapevines and cover crops in specially-designed containers that restricted their root systems to separate compartments, but allowed AM fungi to colonize both. Leaves of cover crops, a grass and a legume, were labeled with a stable isotope of Nitrogen, 15N, and grapevine leaves were analyzed for 15N content after labeling. Our results showed evidence of AM fungi-mediated 15N transfer from cover crops to grapevines. More 15N was transferred to grapevine from the grass than from the legume, suggesting that grasses may be better nutrient donors than legumes. The objective of the second study was to evaluate the contribution of AM fungi to nutrient uptake from a tilled cover crop. After growing grapevines in the same specially-designed containers used in the first study, labeled cover crop leaves (litter) were added to a separate core compartment that was surrounded by mesh screens of differing sizes which allowed access of roots or fungal hyphae to the litter. Our results showed that AM fungi did help grapevines absorb 15N from the litter, but their contribution relative to that of the roots was small. The relative contribution of AM fungi to nutrient utilization likely varies depending on nutrient status of the grapevine tissues and soil fertility. Grapevines growing in poor soils, especially P-deficient soils, may rely more heavily on AM fungi than grapevines growing in fertile soils.
                                Technical Abstract: To study the role of arbuscular mycorrhizal (AM) fungal networks in nutrient utilization from vineyard cover crops, we conducted two greenhouse studies. The objective of the first study was to evaluate AM fungi-mediated nutrient transfer from no-till cover crops to grapevines. We grew grapevines and cover crops in specially-designed containers that restricted their root systems to separate compartments, but allowed AM fungi to colonize both. Leaves of cover crops, a grass (Bromus hordeaceus) and a legume (Medicago polymorpha), were labeled with 99 atom% 15N solution and grapevine leaves were analyzed for 15N content after labeling. Our results showed evidence of AM fungi-mediated 15N transfer from cover crops to grapevines. N transfer was significantly greater from the grass than from the legume. Possible reasons for these differences include lower 15N enrichment in legume roots, higher biomass of grass roots, and/or differences in AM fungal community composition. The objective of the second study was to evaluate the contribution of AM fungi to nutrient uptake from a tilled cover crop (Medicago polymorpha). After growing grapevines in the same specially-designed containers used in the first study, dual labeled (15N and 13C) cover crop litter was added to a separate core compartment that was surrounded by a mesh screen of differing sizes which allowed access of roots (1-mm) or hyphae (25μm) to the litter. Our results showed that AM fungi did help grapevines absorb 15N from the litter, but their contribution relative to that of the roots was small. The relative contribution of AM fungi to nutrient utilization likely varies depending on nutrient status of the grapevine tissues and soil fertility. Grapevines growing in marginal soils, especially P-deficient soils, may rely more heavily on AM fungi than grapevines growing in nutrient-sufficient soils.


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