Nitrogen capture by grapevine roots and arbuscular mycorrhizal fungi from legume cover-crop residues under low rates of mineral fertilization

Abstract

The influence of mineral fertilization on root uptake and arbuscular mycorrhizal fungi-mediated 15 N capture from labeled legume (Medicago polymorpha) residue was examined in winegrapes (Vitis vinifera) in the greenhouse, to evaluate compatibility of fertilization with incorporation of cover-crop residue in winegrape production. Plants grown in marginal vineyard soil were either fertilized with 0.25× Hoagland's solution or not. This low fertilization rate represents the deficit management approach typical of winegrape production. Access to residue in a separate compartment was controlled to allow mycorrhizal roots (roots + hyphae), hyphae (hyphae-intact), or neither (hyphae-rotated) to proliferate in the residue by means of mesh core treatments. Leaves were weekly analyzed for 15 N. On day 42, plants were analyzed for 15 N and biomass; roots were examined for intraradical colonization; and soils were analyzed for 15 N, inorganic N, Olsen-P, X-K, and extraradical colonization. As expected, extraradical colonization of soil outside the cores was unaffected by mesh core treatment, while that inside the cores varied significantly.15 N atom% excess was highest in leaves of roots + hyphae. In comparison, leaf 15 N atom% excess in hyphae-intact was consistently intermediate between roots + hyphae and hyphae-rotated, the latter of which remained unchanged over time. Fertilization stimulated host and fungal growth, based on higher biomass and intraradical colonization of fertilized plants. Fertilization did not affect hyphal or root proliferation in residue but did lower %N derived from residue in leaves and stems by 50%. Our results suggest that even low fertilization rates decrease grapevine N uptake from legume crop residue by both extraradical hyphae and roots.

Arbuscular mycorrhiza symbiosis in viticulture: a review

“…Besides inorganic N uptake, it is well established that AMF can draw substantial amounts of N from decomposing organic materials (Hodge and Fitter 2010). Organic nitrogen represents a large proportion of total soil N. Indeed, in organic vineyards, incorporation of legume crop residue is used as a primary mean of modifying soil fertility (Cheng et al 2008). In the absence of N fertilization only, total N uptake from the residue was significantly enhanced by the fungus: A significant increase in the percentage of N derived from the residue was noted in grapevine leaves in response to hyphal proliferation (Cheng et al 2008).…”

“…Organic nitrogen represents a large proportion of total soil N. Indeed, in organic vineyards, incorporation of legume crop residue is used as a primary mean of modifying soil fertility (Cheng et al 2008). In the absence of N fertilization only, total N uptake from the residue was significantly enhanced by the fungus: A significant increase in the percentage of N derived from the residue was noted in grapevine leaves in response to hyphal proliferation (Cheng et al 2008). However, although the ability of AMF to take up organic N in the form of arginine has been recently reported (Fellbaum et al 2012), direct uptake of organic N might not be the main N uptake pathway, and organic N could be mineralized before it is absorbed by hyphae (Hawkins et al 2000;Smith et al 2011).…”

The symbiotic recapture of nitrogen from dead mycorrhizal and non-mycorrhizal roots of tomato plants

“…The use of isotope-labelled phosphorus has shown that AMF mycelia can transfer nutrients over a distance of as much as 50 cm (Walter et al 1996). The application of 15 N-enrichment technology in the substrates of AMF compartments (accessible to AMF but not to roots) has enabled the quantification of soil-to-plant N transfer via the AMF extra-radical mycelium (ERM) from inorganic as well as organic N sources (Ames et al 1983;Frey and Schüepp 1993;Johansen et al 1992;Johansen et al 1994;Hawkins et al 2000;Hawkins and George 2001;Mäder et al 2000;Hodge et al 2001;Cheng et al 2008). For example, about 30 % of receiver plant N content derived from AMF N transfer (Ames et al 1983;Frey and Schüepp 1993;Mäder et al 2000) suggesting that AMF may have a large potential to improve N nutrition of host plants.…”