Associative N2 fixation and root exudation of organic acids from wheat cultivars of different aluminium tolerance

Abstract

Three wheat cultivars with different tolerances against free aluminium were grown monoxenically in association with Azospirillum brasilense. In situ nitrogen fixation, measured with the acetylene reduction assay, was higher by the aluminium-tolerant cultivars than by the sensitive cultivar. The transfer of fixed nitrogen to the host plant, determined by the 15N dilution technique, was also significantly higher in the aluminium-resistant wheat plants. The total accumulation of fixed nitrogen in the host plants due to an A. brasilense inoculation varied from approximately 13% to 17% of the total nitrogen in the root and 2.9% to 3.9% of the nitrogen in the shoot.The quantity and quality of exudates released in liquid nutrient solution were analysed separately for two of the wheat cultivars, one aluminium-tolerant and one aluminium-sensitive. After 29 days of growth the aluminium-tolerant plants exudated significantly higher total amounts of carbon than aluminium-sensitive plants. No differences between the two cultivars existed in the carbon exudation rate per gram dry root.Much higher concentrations of low molecular dicarboxylic acids i.e. succinic, malic and oxalic acid, were found in the exudates of aluminium-tolerant plants. Dicarboxylic acids are potential chelating compounds for positively charged metals such as aluminium and they may play an important role in protecting the plant against aluminium incorporation. They are also very suitable substrates for Azospirillum spp. It is therefore suggested that these factors may be causing the higher associative nitrogen fixation rates which was found in the aluminium-tolerant wheat cultivars.

Periodic carbon flushing to roots of Quercus rubra saplings affects soil respiration and rhizosphere microbial biomass

“…Researchers have, for example, quantified the carbon "costs" of mycorrhizal infection (Whipps 1990), characterized the flux of organic compounds from roots under the influence of various environmental conditions (e.g. Barber and Martin 1976;Christiansen-Weniger et al 1992;Kraffczyk et al 1984;Smith 1969Smith , 1976, and mapped sugars around roots in non-sterile soil (Bringhurst et al 2001;Jaeger et al 1999). Also, a number of studies have explored whether rhizodeposition (the deposition of organic compounds by roots to soil) stimulates or suppresses microbial breakdown of SOM, and under what conditions (e.g.…”

Breeding for increased nitrogen‐use efficiency: a review for wheat (T. aestivum L.)

“…N-fixing bacteria occur naturally in soils including in the wheat rhizosphere (Nelson andMele 2006, Venieraki et al 2011), and inoculation with N fixers may enhance wheat yield (Kapulnik et al 1987, Hungria et al 2010, Behl et al 2012, Neiverth et al 2014. Their diversity and activity fluctuate with both plant species (Perin et al 2006, Reardon et al 2014) and cultivar (Coelho et al 2009) including in wheat (Christiansen-Weniger et al 1992, Manske et al 2000, Venieraki et al 2011. For example, the N-fixing bacterium Klebsiella pneumonia strain 342 can relieve N deficiency and enhance plant N levels (Iniguez et al 2004) depending on cultivar (Manske et al 2000).…”

Comparison of the effectiveness of wheat roots colonization by Azotobacter chroococcum and Pantoea agglomerans using serological techniques

“…The count of A. chroococcum and P. agglomerans in rhizosphere and bulk soil was 10 4 and 10 5 /g soil in individual treatments, respectively. This might be probably due to the root exudates that help in modification of soil environment and proliferation of bacteria (Parke 1991, Christiansen-Weniger et al 1992, Jiang and Sato 1994, Baldani et al 1997, and improve the wheat growth. Variable quantities and compositions of root exudates of different plant species could be responsible for specific colonizations.…”