15N isotope dilution to quantify dinitrogen (N2) fixation associated with Canadian and Brazilian wheat

摘要

Putative dinitrogen (N2) fixation associated with wheat (Triticum aestivumL. emend. Thell) has been studied using acetylene reduction and nonisotopic N-balance techniques. Absolute proof of N2fixation using15N2(gas) or15N isotope dilution procedures has not been reported. This paper presents the first use of the15N isotope dilution technique to determine in wheat the percent plant N derived from associated N2fixation. Although inoculation with eitherBacillus polymyxa(C-11-25) orAzospirillum brasilense(ATCC 29145) resulted in no significant increase in total plant N in nine Canadian and one Brazilian wheat varieties, isotopic N data showed that N2fixation did occur. The amounts of plant N derived from atmosphere, fertilizer, and soil varied. A high degree of plantndash;bacterial specificity existed. In several instances, the substitution of a single chromosome pair in the wheat regulated the amount of N2fixed. The agreement between this15N isotope experiment and two previous nonisotopic experiments suggests that the trait supporting N2fixation in wheat may be consistently expressed in the varietal lines.