Temperature adaptation of Glycine species as expressed by germination, photosynthesis, photosynthate accumulation and growth.

Abstract

The temperature adaptation of five wild Glycine species of diverse geographic origin was compared with that of the cultivated species (G. max) under controlled conditions. The optimum temperature for germination was about 30°C for G. max and G. tomentella, 22°C for G. argyrea and 20°C for G. clandestina, respectively. In all the species examined, net CO2 exchange rate per unit leaf area (NCE) appeared to be maximal at growth temperatures in the range from 18/13 to 30/25°C (8 h / 16 h, 16 h daylength) with little variation over this range. Four of six species exhibited no net CO2 uptake in the light at 9/4°C after being exposed to successively lowered temperature, but G. clandestina retained a considerable net gain at this temperature. Across the species, NCE was correlated negatively with leaf size, but positively with specific leaf weight (SLW) or chlorophyll content. Most of the species revealed optimal temperatures for relative growth rate (RGR) in the range from 30/25 to 33/28°C. Across the species and growth temperatures, RGR was correlated more closely with relative leaf area growth rate (RLAGR) than with net assimilation rate (NAR). G. clandestina and G. latrobeana of cooler habitats adapted to low, temperature more strongly than other species, by increasing root/top ratio, SLW and chlorophyll content while maintaining a stable NCE. In contrast G. max tended, over a wide range of temperature, to express the greatest potential for leaf growth, leading to greater dry matter production at the expense of NCE.