Nitrogen fixation and nitrate metabolism for growth of six diverse soybean [ Glycine max. (L.) Merr.] genotypes under low temperature stress

Abstract

Soybean [ Glycine max (L.) Merr] is a subtropical legume that is at the northern limit of its range in the cool temperate zone of North America. Low temperature stress inhibits N 2 fixation and NO 3 metabolism in soybean. A controlled environment experiment was conducted to test the effects of low temperature stress (16/9°C day/night versus 26/19°C) on N 2 fixation and NO 3 metabolism of one American, one northern Chinese, one Polish, one Swedish and two Canadian soybean cultivars. The objectives of this work were to measure variability in N 2 fixation, NO 3 use, and plant growth under low and optimal temperature regimes among these diverse genotypes, and to determine the physiological bases for these differences. The results showed that: (1) the relative ranking of cultivars for growth and accumulation is different between nitrogen sources under optimal or suboptimal temperatures; (2) the cultivars which are better able to fix N 2 usually have more nodule mass; (3) the plants which fix more N 2 allocate less photosynthate to the plant root system, and (4) there was no negative relationship between N 2 fixation or NO 3 utilization among the cultivars tested.