Effect of arbuscular mycorrhizas on uptake of nitrogen by Brachiaria arrecta and Sorghum vulgare from soils labelled for several years with ¹⁵N

Abstract

summary A pot experiment was conducted under glasshouse conditions to investigate the effect of the inoculation of arbuscular mycorrhizal (AM) fungi on the growth and N uptake of two graminaceous plants: Brachiaria arrecta (Hack. ex. Th. Dur & Schinz) Stent and Sorghum vulgare (Pers.) growing in four fumigated soils which had been labelled for several years with 15N. The four soils had different chemical characteristics, especially in their P availability. The levels of root colonization by AM fungi were inversely related to the P concentration in these soils. Positive responses to AM fungal inoculation were observed for all the yield parameters except in the soil with the highest P availability (40 μg P g−1 soil, extractant Mehlich‐1). In the other three soils, AM fungal inoculation of both crops increased N accumulation by between 17 and 46%, but the 15N enrichment of the N absorbed was significantly lower in the mycorrhizal plants than in those not colonized by mycorrhizal fungi. This suggests that some of the N absorbed from the soil by the mycorrhizal roots was derived from N sources other than the mineral N.

Glomus intraradices, Pseudomonas alcaligenes, and Bacillus pumilus: effective agents for the control of root-rot disease complex of chickpea (Cicer arietinum L.)

“…The manipulation of crop rhizosphere with PGPR to control plant pathogens has shown considerable promise (Nelson 2004;Siddiqui 2006). In addition, arbuscular mycorrhizal (AM) fungi colonize the roots of many crop plants (Smith and Read 1997;Ozgonen et al 1999) and are of great value in promoting the uptake of phosphorus, minor elements and water (Allen 1996;Ibijbijen et al 1996;Siddiqui et al 2001). They also reduce the severity of several plant diseases (Dehne 1982;Siddiqui and Mahmood 1995;Linderman 2000;Barea et al 2002;Akkopru and Demir 2005).…”

Impact of pea growth and arbuscular mycorrhizal fungi on the decomposition of 15N-labeled maize residues

“…The presence of AMF affects δ 15 N (Handley et al 1993;Wheeler et al 2000) as well as δ 13 C values (Handley et al 1993;Querejeta et al 2003) differently in different plant parts, due to generic differences between autotrophic and heterotrophic organs (Yoneyama et al 2003;Cernusak et al 2009). AMF have been reported to decrease δ 15 N in legumes because mycorrhizal plants take up N from sources that are not or are less available to non-mycorrhizal plants (Ames et al 1984;Ibijbijen et al 1996). The δ 13 C values in plant organic matter reflect net photosynthesis and water use efficiency in C 3 plants (Farquhar et al 1989).…”

Boundaries in Miniature: Two Examples from Soil

“…Thus, the quantity and number of labile C compounds exuded in the rhizosphere have been shown to increase (Schwab et al 1984), decrease (Bansal andMukerji 1994, Marschner et al 1997), and remain the same (Azaizeh et al 1995, Marschner et al 1997) in response to mycorrhizal infection. Mycorrhizal inoculation of roots can also increase rhizosphere N 2 fixation by Rhizobium bacteria and increase nutrient uptake by roots (and therefore increase nutrient flow through the boundary zone) compared with uninoculated controls (Ibijbijen et al 1996). The species composition of BSCs has also been manipulated through various disturbances.…”

“…Fluxes in the rhizosphere are certain to be affected by the interactions of mycorrhizae with roots and other root-associated microorganisms. For example, mycorrhizae have the potential to affect soil C and N cycling in the mycorrhizosphere through changes to plant C exudation (Schwab et al 1984), through enhanced decomposition of complex organic material (Hodge et al 2001), through retention of C and nutrients in recalcitrant fungal tissues (Rillig, et al 2001), and through increased transfer of nutrients to plants (Ibijbijen et al 1996). Mycorrhizal fungi may also indirectly affect soil C and N cycling through impacts on the soil microbial community (Hodge et al 2001).…”