Growth rate-reserve content relationship as influenced by irradiance, CO2 concentration, and temperature

The patterns of the CO2 exchange of single vegetative bean plants were monitored during steady state exchange and after lowering the irradiance, the CO2 concentration, or the temperature. The measured patterns were used to calculate the dynamics of the rate of synthesis of structural dry matter and of the amount of the reserve materials during the experiments. The rate of synthesis of structural dry matter was assumed to be proportional to growth respiration (total minus maintenance). The growth conversion efficiency was assumed to be independent of the treatments. The maintenance respiration coefficient was taken to be dependent only on the temperature. Change in the amounts of reserve materials was calculated as a difference between the net CO2 input and the amount converted into new structural dry matter.During the first day of a low CO2 uptake a substantial depletion of reserve materials took place also during light hours, since the rate of synthesis of structural dry matter lagged behind the decrease of photosynthesis. On the second day the rate of synthesis was adapted to the low CO2 input and there occurred little change in the amount of reserve materials. There was a rapid increase in the amount of reserve materials after the irradiance was increased again or after temperature was lowered.A saturating dependence of the specific growth rate on the content of reserve materials was found to exist irrespective of the mode of changing the content of reserve materials. A hysteresis-like retardation of the specific growth rate took place after the reserve had already been exhausted for some time. During retardation a replenishment of reserve materials took place.It is suggested that adaptation processes tend to keep the content of reserve materials within a certain (probably optimal) range.