Factors affecting soil acidification under legumes. III. Acid production by N₂‐fixing legumes as influenced by nitrate supply

Abstract

Leaching of nitrate through soil profiles is a major cause of soil acidification. Legume species differ in their ability to take up nitrate (NO $ − ) and in the degree to which soil NO $ − impairs legume nodulation and N # fixation. This pot experiment examined species variation in N # fixation and acid production in grain legumes grown for 6 wk on a sandy soil with Ca(NO $ ) # added at 0-56.7 mg N kg −" soil. The eight legumes studied were Lupinus angustifolius (' Gungurru '), Lupinus albus (' Kiev mutant '), Lupinus luteus (' Teo '), Cicer arietinum (Selection T1587), Pisum sativum (' Dundale ' and ' Wirrega '), Vicia faba (' Fiord ') and Lathyrus sativus (Selection 453). While number of nodules was not significantly affected by treatment with NO $ − , increasing supply of NO $ − decreased nodule mass, with P. sativum ' Wirrega ' being most sensitive and C. arientinum and V. faba least sensitive. The concentrations of nitrogen in plants generally decreased as the supply of NO $ − increased. Increasing supply of NO $ − decreased the percentage of N # fixation, most significantly in L. sativus and least in L. albus. In the absence of added NO $ − , the amounts of H + produced per unit biomass (specific acid production) differed by as much as 2.2-fold among the species, with C. arientinum generating most H + , followed by L. angustifolius, L. luteus, L. albus, V. faba, L. sativus, P. sativum ' Dundale ' and P. sativum ' Wirrega '. This species variation was even greater at higher NO $ − supply. In the presence of NO $ − at up to 14.2 mg N kg −" , acid production by these legumes correlated well with uptake of excess cations but not with the concentration of nitrogen in plants. For all species, release of H + declined with increasing supply of NO $ − , decreasing most in L. sativus and least in C. arientinum. The results suggest that there might be scope for selecting grain legume species in order to minimize soil acidification by decreasing leaching of NO $ − .

Wheat, canola and grain legume access to soil phosphorus fractions differs in soils with contrasting phosphorus dynamics

“…Alternatively, another factor such as soil acidity may have constrained plant growth in the Harvey soil. P-deficient canola and N-fixing legumes typically acidify the rhizosphere (Hoffland et al 1989;); however, all species in our study generally increased rhizosphere pH (except in the highly buffered Harvey soil) presumably due to preferential uptake of NO 3 − as the N source (Tang et al 1999).…”

Dynamics of phosphorus fractions in the rhizosphere of common bean (Phaseolus vulgaris L.) and durum wheat (Triticum turgidum durum L.) grown in monocropping and intercropping systems

“…In a preliminary experiment, we found indeed that proton release of P-deficient common bean decreased by almost 60% when supplying 1 mM nitrate (data not shown). Tang et al (1999) showed similarly that proton release was more or less (from 40 to 100%) decreased upon nitrate supply to a range of grain legume species relying on N 2 -fixation.…”

Genotypic differences in phosphorus acquisition and the rhizosphere properties of Brassica napus in response to low phosphorus stress

“…This may be because rapeseed roots release H + as a result of low P stress as reported by previous studies (Akhtar et al 2008;Ruiz and Arvieu 1990;Moorby et al 1985Moorby et al , 1988). However, a major source of H + fluxes in the rhizosphere was also related to the differential uptake of cations and anions by plant roots (Hinsinger et al 2003;Jaillard et al 2002;Marschner 1995;Tang et al 1999). In the experiment, urea was the only nitrogen source and it was mainly taken up by plants as therefore the rapeseeds receiving NH 4 + maybe release equivalent amounts of H + in the rhizosphere to counterbalance the corresponding excess of positive charges entering the cell, thereby decreased the rhizosphere pH.…”