Use of the15N natural abundance technique for the quantification of the contribution of N2 fixation to sugar cane and other grasses

Abstract

This paper originates from an address at the 8th International Symposium on Nitrogen Fixation with Non-Legumes, Sydney, NSW, December 2000 The use of the 15N natural abundance technique to quantify contribution of biological nitrogen fixation (BNF) to any plant is based on the observation that N derived from soil is generally slightly different [usually higher in 15N abundance (δ15N‰)] than that of the air. Plants or micro-organisms growing solely on BNF generally accumulate N with 15N isotopic abundance lower than that of the air (i.e. δ15N‰ is negative), while plants obtaining all N from the soil generally show a positive δ15N‰ signal. The technique is applied by estimating the 15N abundance of the putative ‘N2-fixing’ crop and analysing the 15N abundance of neighbouring non-N2-fixing reference plants. However, often there are such large variations in the N derived from the soil by different non-N2-fixing plants that in natural ecosystems it is often impossible to even distinguish plants that are benefiting form BNF, let alone quantity this contribution. The reasons why soil derived N can vary so widely, especially in natural ecosystems, are briefly discussed and a sampling strategy is described to assess possible BNF inputs to sugar cane plants in commercial plantations in Brazil. The results suggest that in nine of the 11 sites studied, BNF inputs were significant ranging from 25 to 60% of N assimilated.

Acquisition of phosphorus and nitrogen in the rhizosphere and plant growth promotion by microorganisms

“…Similar results were obtained in the case of the associative symbiosis between sugar-cane (Saccharum officinarum L.) and the endophytic diazotroph Acetobacter diazotrophicus (renamed Gluconobacter diazotrophicus) (Sevilla et al 2001). Furthermore, Nbalance, 15 N natural abundance and 15 N dilution studies, performed in either pot experiments or in the field, have provided clear evidence of the ability of endophytic N 2 -fixing bacteria to supply significant inputs of nitrogen to some grasses and cereals (Boddey et al 2001;Oliveira et al 2002).…”

Nitrogen-fixing bacteria associated with leguminous and non-leguminous plants

“…batatais that specifically associates with Azotobacter paspali was reported to fix from 15 to 90 kg N/ha/year (Döbereiner et al 1972). At present, sugar cane is a good example of a crop that can benefit from nitrogen fixation, since certain cultivars can derive more than 150 kg N/ha/year from BNF (Boddey et al 2001). Thus, some crops naturally benefit from the nitrogen fixation capacity of associated bacteria.…”

Improving Sugarcane Growth and Nutrient Uptake by Inoculating Gluconacetobacter diazotrophicus

“…Diazotrophic rhizocoenosis in sugarcane was first shown by Ruschel et al (1975) using 15 N 2 and later by long-term N balance and 15 N 2 isotope dilution technique, some sugarcane varieties have been found to derive up to 70% of their nitrogen requirement through biological nitrogen fixation (Urquiaga et al 1992;Boddey et al 2001). Since than various kinds of bacteria such as Gluconacetobacter diazotrophicus, Herbaspirillum spp., Azospirillum amazonense, Burkholderia spp., capable of fixing nitrogen have been reported to colonize the epidermis of sugarcane stem and roots, of which Gluconacetobacter (earlier Acetobacter diazotrophicus) seems to contribute substantially to nitrogen nutrition of the plant (Patriquin et al 1980;James et al 1994;Do¨bere-iner et al 1995).…”