Potential for Nitrogen Fixation in Tropical Legumes and Grasses

Tight coupling of root-associated nitrogen fixation and plant photosynthesis in the salt marsh grass Spartina alterniflora and carbon dioxide enhancement of nitrogenase activity

“…Field evidence of nitrogen fixation in association with legume and nonlegume plants has been supportive of this hypothesis. In both peanut and rice fields and in subtropical grasses, diurnal changes of ARA indicate a coupling between nitrogenase activity and plant photosynthesis (3,5,6). The stimulation of ARA measured by exposing intact S. alterniflora plants to light (Fig.…”

“…Diurnal rhythms of nitrogenase activity in root-associated N2-fixing systems have been observed for rice (3,26) and several grasses (1,5). In Spartina alterniflora (saltmarsh cordgrass), evidence (9, 19) has also been obtained for the influence of plant photosynthesis on acetylene reduction activity (ARA).…”

“…The degree of coupling between root-associated N2-fixing bacteria and plant photosynthesis has remained largely speculative since the energy source for these microbes has been uncertain (see reviews by van Berkum and Bohlool [25], Vose [27], and Hubbell and Gaskins [12]). Potential sources of energy for N2 fixation are pectin from the plant cell wall (23), lysates from senescing cells, mucigels (2), and plant photosynthate (3,5,17,19). The dependency of symbiotic N2 fixation on photosynthate has long been firmly established (14).…”

Evaluation of nitrogen fixation by bacteria in association with roots of tropical grasses.

“…De-Polli et al (51) suggested that the incorporation of '5N2 into P. notatum and D. decumbens confirmed nitrogen fixation by these two grasses. These data have also been used to suggest that observations of acetylene reduction with other grasses demonstrate that they benefit from nitrogen fixation (58,60,136). Although the incorporation of '"N2 was demonstrated with these two grasses, there was a long time between the collection of samples from the field and experimentation (between 4 and 16 days).…”

Performance of Cowpeas on an Inland Valley Swamp in the Dry Season in Sierra Leone

“…There is some uncertainty about the need for cowpea inoculants in tropical soils. According to Sellschop (1962) and Dobereiner (1977) positive responses to inoculation are unlikely, but Ahmad et al (1981) have recently concluded that because of significant increases in shoot fresh weight 35 days after planting resulting from N fertilization, there is a potential for the use of inoculants. This group have also speculated that the lack of response reported by other field workers with cowpeas may be a result of (i) the unnecessary use of inoculants with cultivars already capable of nodulating well with indigenous strains, (ii) the use of inappropriate strains in the inoculant, and (iii) unknown factors limiting the full expression of symbiotic potential.…”