NITROGEN-FIXATION AND NITRATE METABOLISM FOR GROWTH OF 6 DIVERSE SOYBEAN [GLYCINE MAX. (L.) MERR.] GENOTYPES UNDER LOW-TEMPERATURE STRESS

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 Ameri ca. Low temperature stress inhibits N-2 fixation and NO3 metabolism in soybean. A controlled environment experiment was conducted to test th e effects of low temperature stress (16/9 degrees C day/night versus 2 6/19 degrees C) on N-2 fixation and NO3 metabolism of one American, on e northern Chinese, one Polish, one Swedish and two Canadian soybean c ultivars. The objectives of this work were to measure variability in N -2 fixation, NO3 use, and plant growth under low and optimal temperatu re regimes among these diverse genotypes, and to determine the physiol ogical bases for these differences. The results showed that: (1) the r elative 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 nodu le 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:! fixation or NO, utilization among the cultivars tested. (C ) 1997 Elsevier Science B.V.