Recent Advances in Biological Nitrogen Fixation in Agricultural Systems

Abstract

The environmental concerns due to the increasing amount of the reactive forms of nitrogen in atmosphere, originating fro m t h e man u fact u re an d u se o f ch emi cal fert i l i zers h ave resu l t ed i n a re-fo cu s o n t h e i mp o rt an ce o f b i o l o gi cal n i t ro gen fi xat i o n (BNF ), p art i cu l arl y b y l egu mes. Th e wo rl d wi d e co n t ri b u t i o n o f BNF i s est i mat ed at 1 0 5 Tg yr -1 . N i t r o g e n f i x a t i o n is catalysed by the enzyme nitrogenase. Advances have included discovery of alternative nitrogenases, elucidation of more details on the mechanism of action, discovery of novel nitrogenases, existence of nitrogenase siblings in eukaryotes etc. There are fresh efforts to engineer cereal plants to nodulate and fix nitrogen. Discovery of common signalling mechanisms between mycorrhization and nodulation, discovery of cereal endophytes and advances in plastid physiology have given a f r e s h i m p e t u s t o s u c h a p p r o a c h e s . H o w e v e r , t h e c o n t r i b u t i o n o f a g r o n o m i c a l l y s i g n i f i c a n t q u a n t i t i e s o f N t h r o u g h e n d o p h y t e sstill requires more rigorous evidences. Advances in molecular biology have included a greater understanding of the native diversity of rhizobia and together with advances in plant breeding for selection of high nodulating genotypes, presents an attractive opportunity to maximize BNF. Recent advances include the discovery of novel rhizobial species, emphasis on study of climate change and adaptation to various abiotic stresses like high temperature, drought and salinity. This review fo cu ses o n maj o r d evel o p men t s i n BNF i n l ast t wo d ecad es wi t h emp h asi s o n rh i zo b i a. Th e b en efi ci al effect s o f ap p l yi n g organics and of rhizobial inoculation practices are discussed to bring out the strategies to improve the contribution of BNF in agriculture.Key Words: Climate Change; Endosymbiosis; Fertilizer; Nitrogenase; Nodulation; Rhizobium; Salinity; Soybean *Author for Correspondence: E-mail: desiraju.rao@gmail.com; Mob: 09303129740 Proc Indian Natn Sci Acad 80 No. 2 June 2014 Spl. Sec. pp. 359-378 Printed in India. IntroductionNitrogenous fertilizers have revolutionized crop yields and food availability worldwide. Of all the previous century's technological marvels, the HaberBosch process of manufacturing ammonia has made the most difference to our survival and it is considered t h e m o s t v a l u a b l e i n v e n t i o n o f t h e p r e v i o u s millennium [1]. However, this has come at a s u b s t a n t i a l e c o n o m i c a n d e n v i r o n m e n t a l c o s t . I n d u s t r i a l n i t r o g e n f i x a t i o n i s a $ 1 0 0 b i l l i o n p e r y e a r global industry, growing and bringing with it the concomitant environmental nitrogen pollution effects.Intensive cropping with the use of high analysis fertilizers coupled with a concomitant reduction in recycling of organics or other wastes has led to a decline in the organic carbon levels i...

Effect ofRhizobiumsp. BARIRGm901 inoculation on nodulation, nitrogen fixation and yield of soybean (Glycine max) genotypes in gray terrace soil

“…8) The host soybean plant supplies the bacteria with carbohydrates in the form of sugars and related molecules, produced by photosynthesis, which are transferred to the nodules. 9) Thus, the rhizobial bacteria in the nodules receive energy and produce forms of nitrogen that can be assimilated by the host plant. 10) The efficiency of BNF depends on the type and variety of crop, rhizobial strain, and the interactions between bacterial strains and plant varieties, as well as on management practices and environmental factors.…”

Isolation and Proto-cooperation of Pseudomonas putida TS 18 from Water Calyx Fluid of Spathodea campanulata P. Beauv.

“…This is the first study aimed at understanding the role of associative symbiosis of alkalophilic nitrogen fixing bacteria present in water calyx fluid of S. campanulata. Nitrogen fixing is considered to be second most vital process occurring in plants after photosynthesis influencing primary productivity (Rao, 2014). Nitrogen fixing is an important plant growth promoting character exhibited by the plant growth promoting rhizobacteria.…”

Taxonomic Appraisal of Nodulation in the Leguminosae of Pakistan

“…A consolidated account of the results of nodulation surveys carried out in Pakistan are presented in Table 1. Nodulation studies are not only the source of increasing database of nodulating or non-nodulating legumes throughout the world (Allen and Allen, 1981) but they also provide an indirect means of exploring new symbiotic nitrogen fixing associations operating in natural ecosystems (Rao, 2014). As a result, diverse groups of Gram-negative bacteria have been identified that are involved in forming nodules on the roots and sometimes on stems of leguminous plants (Graham, 2008).…”