Evidence for a periodic excretion of nitrogen by roots of grass-legume associations

Abstract

Diurnal variation in ion content of the solution bathing roots of two plants growing together in sand culture was analysed for three pairs of grass-legume species (Lolium multiflorum and Trifolium pratense; Zea mays and Glycine hispida; Avena sativa and Vicia sativa) and their monospecific controls. Biomass and nitrogen content of plants were determined.Ion concentration (NO~-, NO{, NH~, and K § and pH of root solutions were measured for LoliumTrifolium plant pairs and controls at 6 hours intervals over 36 h, starting at 8 am within a circadian cycle. Root solutions were regularly depleted in NO; by the grasses (Lolium-Lolium control) throughout the cycle. For associations involving the legume (Lolium-Trifolium and Trifolium-Trifolium), NO; depletion was followed by NO; enrichment at night, from late afternoon to early morning; the enrichment was more marked for the Lolium-Trifolium association. Solutions which did not contain NO2 ions, were enriched by trace amounts of NH2-ions, largely depleted in K § and alkalanized for all associations throughout the cycle.Repeating the experiment with the three pairs of species at the vegetative phase of development confirmed the previous results: NO; enrichment during the night for associations with legumes. When the experiment was repeated with older plants which had almost completed their flowering stage, depletion only was observed and no NO; enrichment.These data suggest that NO~-enrichment results from N excretion from active nodulated roots of the legume, accounting for the increase in both biomass and nitrogen content of the companion grass in grass-legume association. The quantitative importance and periodicity of nitrogen excretion as well as the origin of nitrate enrichment are discussed.

Ecological principles underlying the increase of productivity achieved by cereal-grain legume intercrops in organic farming. A review

“…Khan et al 2002aKhan et al , 2002bMayer et al 2003), have shown the effects of the legume on facilitating the acquisition of nitrogen by the cereal (Stern 1993;Jensen 1996b;Xiao et al 2004;Chalk et al 2014) and the transfer of nitrogen from the legume to the cereal. These exchanges are explained by the production by the legume roots of relatively labile nitrogen-rich exudates in the form of NH 4 + (Brophy and Heichel 1989), NO 3 − (Wacquant et al 1989), amino acids (Paynel et al 2001(Paynel et al , 2008Lesuffleur et al 2013) or decomposing plant parts (Johansen and Jensen 1996;Fustec et al 2010). …”

The role of VAM fungi in nitrogen dynamics in maize-bean intercrops

“…Alternatively, direct transfer of fixed N from the legume to the nonlegume could explain the increased yield of intercrops. This transfer may occur via decomposition and mineralization of legume roots and/or nodules (Burity et al, 1989;Haynes, 1980), legume root exudates (Brophy and Heichel, 1989;Burity et al 1989;Wacquant et al, 1989), or via vesicular arbuscular mycorrhizal (VAM) fungi through interplant hyphal connections (Haystead et al, 1988;van Kessel et al, 1985).…”

Testing simulations of intra‐ and inter‐annual variation in the plant production response to elevated CO2 against measurements from an 11‐year FACE experiment on grazed pasture

“…). Some N fixed by legumes can become available to other species (particularly the C3 grasses in this instance) very rapidly through exudation (Wacquant et al ., ) or through grazing animals, however, much of the N becomes available over time, often many months, as the nodules and plant organs, especially the roots, of the legumes senesce and release N (Broadbent et al ., ; Ledgard, ). The period of greatest legume senescence in the environment of the FACE experiment is at the start of spring when there is maximum decay of both stolons (Brock et al ., ; Hay & Kelly, ) and roots (Newton & Hay, ).…”