Nitrogen fixation and symbiosis-induced accumulation of mineral nutrients by cowpea (Vigna unguiculata L. Walp.)

Abstract

Little information currently exists on the relationship between rhizobial symbiosis and mineral accumulation in nodulated legumes. The aim of this study was to measure fixed nitrogen (N) in whole plants and in young fully expanded trifoliate leaves of cowpea genotypes, and to relate this to mineral accumulation in the leaves. The data revealed marked differences between high and low N2-fixing genotypes, with the former consistently showing greater %N, plant or leaf total N, and amount of N fixed compared with the latter. There was a 2.0–3.8-fold difference in amount of N fixed at whole-plant level between high- and low-fixing cowpea genotypes at Taung, South Africa, and 2.4–4.0-fold at Manga, Ghana. Furthermore, the genotypes with high N2 fixation consistently exhibited greater concentration and content of minerals (e.g. P, K, Mg, S, Na, Fe, Cu, Zn, Mn and B) in their trifoliate leaves, whereas those that recorded low N2 fixation accumulated lesser amounts of mineral nutrients in leaves. In a nodulation assay, we found that rhizobial isolates TUT53b2vu and TUT33b4vu, which exhibited higher symbiotic efficiency (measured here as nodule number, nodule fresh weight, and plant dry matter yield), also elicited greater mineral accumulation in cowpea shoots, while strains with low N2-fixing ability induced limited mineral accumulation. These results, together with a correlation analysis, show that, at least in nodulated cowpea, there is a strong relationship between N2-fixing efficiency and mineral accumulation, two traits that could be exploited in breeding programs for improved human nutrition and health.

Evaluation of Protein and Micronutrient Levels in Edible Cowpea (Vigna Unguiculata L. Walp.) Leaves and Seeds

“…Another factor that seems to define the level of mineral accumulation in nodulated legumes is the symbiotic efficiency of N 2 -fixing bacteria in root nodules. It has been shown that high N 2 -fixing legumes generally tend to accumulate more nutrient elements in shoots than their lowfixing counterparts (Belane et al, 2014). In this study, genotypes such as Apagbaala, Fahari, Iron Gray, Line 2020, Bengsogla and Omondaw, which accumulated significantly high concentrations of trace elements in leaves and seed, were earlier reported to be high N 2 -fixers, and to accumulate large amounts of symbiotic N in their biomass Dakora, 2009, 2010).…”

“…Similarly, at Manga in the Sudano-Sahelian savanna of Ghana, leaf protein levels varied from 24 to 35%, with 12 out of 30 genotypes recording more than 30% protein in their leaves (Figure 3). The leaves of N 2 -fixing legumes such as cowpea are very rich in N due to the species ability to reduce N 2 into NH 3 and subsequently into nitrogenous solutes for plant use (Belane et al, 2014). In plants, N is required for the synthesis of macromolecules such as chlorophyll needed for harvesting light photon energy during photosynthesis and formation of the enzyme ribulose-1,5-bisphosphate carboxylaseoxygenase (Rubisco), which reduces CO 2 during photosynthesis.…”

Nutrient management in African sorghum cropping systems: applying meta-analysis to assess yield and profitability

“…Fertilizer production is an energy intensive process and even in highly mechanized agricultural systems of the US Corn Belt, energy resulting from fertilizer production is >30 % of farm energy use in rain-fed maize systems (Kim et al 2009). Assuming a cowpea seed yield of 820 kg ha −1 (Kaizzi et al 2007) and seed N content of 4 % (Tagoe et al 2010), sale of cowpea seed removes 16.4 kg N ha −1 of the N fixed during the (Belane et al 2014), the remaining root and shoot biomass would provide on the order of 7-75 kg N ha −1 to the field or for use as animal fodder. The benefits of legumes in rotation need to be qualified; however, because they assume that farmers have access to cowpea seeds, can generate a significant return when planting cowpea, and have a place to market cowpea; this may be a large assumption for many farmers in Africa.…”

Plastic Responses Mediated by Identity Recognition in Below-Ground Competition in Cycas micronesica K.D. Hill

“…Recent work with Vigna unguiculata L. Walp. [19] indicated that as root nodule number and weight increased, the expected increase in Rhizobia-fixed nitrogen was associated with a concomitant increase in a majority of other rhizosphere-derived essential mineral elements in the leaf tissue. If this strong relationship between endosymbiont nitrogen-fixation and general mineral accumulation in legumes is similar in cycads, the implications of our results are of critical importance to conservation managers.…”