Symbiotic nitrogen fixation in eight Acacia senegal provenances in dryland clays of the Blue Nile Sudan estimated by the 15N natural abundance method

Abstract

The symbiotic biological N 2 fixation by Acacia senegal was estimated using the 15 N natural abundance (d 15 N) procedure on eight provenances collected from different environments and soil types grown in a clay soil in the Blue Nile region, Sudan. Balanites aegyptiaca (a non-legume) was used as a non-N 2 -fixing reference plant to allow 15 N-based estimates of the proportion of the Acacia N derived from atmospheric N 2 (N dfa ) to be calculated. Results show variation in leaf d 15 N between A. senegal and the reference plant and among years. The relative d 15 N values (&) were higher in B. aegyptiaca than in the N 2 -fixing acacia provenances. Provenances originally collected from clay soils fixed little N in the first year, but the amount fixed increased as the trees aged. All provenances showed a decrease in d 15 N with age. The N dfa varied between 24% (Mazmoom provenance) and 61% (Rahad provenance) 4 years after planting. There was no significant difference in d 15 N between provenance groups based on soil type or rainfall at original growing site. The amount of N dfa increased significantly with age in all provenances. The above-ground contribution of fixed N to foliage growth in a 4-year-old A. senegal was highest in the Rahad sand-soil provenance (46.7 kg N ha )1 ) and lowest in the Mazmoom clay-soil provenance (28.7 kg N ha )1 ). Our study represents the first use of the d 15 N method for estimating the N input by A. senegal to the clay plain soils of the gum belt in the Sudan.

Nitrogen symbiotically fixed by cowpea and gliricidia in traditional and agroforestry systems under semiarid conditions

“…However, the amounts of fixed N vary much, depending on the specificities of the symbiosis and on the environmental characteristics that affect biomass production and SFN. In Kenya, for instance, from 70 to 90% of the N in the biomass of Sesbania sesban and Calliandra calothyrsus was derived from SFN, amounting to 120 to 360 kg ha -1 N (Stahl et al, 2002), whereas in Sudan, 48% of the N in pure stands of Acacia senegal were fixed from the atmosphere (%Ndfa), introducing 36 kg ha -1 N per year to the agrosystem (Raddad et al, 2005). Therefore, SFN may represent relevant N inputs to soil-plant systems, decreasing the need of N fertilizer application, which is frequently the most expensive among commercial fertilizers.…”

Termites create spatial structure and govern ecosystem function by affecting N2 fixation in an East African savanna

“…The widespread success of Acacia trees growing in arid and semi-arid regions of Africa has been attributed to their prowess as N 2 fixers (Ho¨gberg 1986). Although levels of fixation vary amongst species and across topoedaphic and climatic gradients (Schulze et al 1991, Raddad et al 2005, the potential for Acacia trees to obtain large fractions of N from fixation allows them to thrive in N-poor soils (Ho¨gberg 1986). Nitrogen isotope (d 15 N) values measured in plant tissues provide insight into relative contributions of N sources (e.g., fixed N 2 vs. soil N), if the sources are isotopically discreet.…”

“…There is a large literature addressing the assets and liabilities of this approach to estimating N 2 fixation by legumes (Shearer and Kohl 1986, Boddey et al 2000, Spriggs et al 2003, which includes examples of studies where this method worked (Raddad et al 2005), and where it was not effective (Gehring and Vlek 2004 Handley et al 1993, Michelsen et al 1998, Spriggs et al 2003.…”

Nitrogen Fixing Legumes in the Plant Communities

“…If the calculations had been done with B = 0, these values would have increased to 61.5% and 77.0%, respectively. Comparison of these results with those found in literature, were done utilizing B = -2%, a value that is commonly used in tree legume studies (Raddad et al, 2005;Mirzakhani et al, 2009;Ezrin et al, 2010).…”

“…For the N 2 -fixing species, estimates of percentage of plant nitrogen derived from the air (%Ndfa) were made, using the formula recommended by Shearer and Kohl (1986) With the absence of data for the studied species, values of % and -2% were used which are commonly found in studies of tree legumes (Raddad et al, 2005;Akran et al, 2009;Ezrin et al, 2010). The quantities of fixed N (kg/ha/year) were estimated using %Ndfa and %N content results, obtained in this study and the annual production of leaf mass of the fixing species.…”