The influence of temperature on morphology and growth rate of bean seedlings

Bush bean seedlings were grown at 16 and 25°C and two light intensities. At 25°C the relative growth rate (RGR) was twice that of 16°C and plant development took half the time. This suggests a linear proportionality between relative growth rate and temperature in this range because the minimum temperature for growth and development is about 8°C for bush beans. This relation implies that the relative growth rate has a specific maximum which depends on temperature. Slow extension growth induced by low temperature leads to a high level of carbohydrate reserves under conditions of high light intensity. This explains why at 16°C the dry matter content of seedling leaves rises gradually whereas it remains practically constant at 25 C. This also explains why leaf area per unit leaf dry weight drops at I6°C (fig. 2) so that leaf area ratio (LAR) decreases after reaching a maximum (fig. 1). This, however, does not lead to a drop in relative growth rate which suggests that a compensation through a higher net assimilation rate (NAR) occurs. At 25°C the decline of RGR in low light intensity is relatively strong, probably because of a high respiration level. Light intensity and temperature have little influence on the specific weight of leaves (fig. 4). Furthermore leaf area per unit fresh leaf weight appears to be proportional to the inverse of leaf thickness (fig. 5). These findings suggest that inner leaf structure maintains a certain homogeneity independent of outward conditions. Cotyledons are exhausted by the young seedling at a constant rate which is higher in high temperatures and low light intensities.