The role of different daily irradiations on shoot growth and root/shoot ratio in lucerne (Medicago sativa L.)

Abstract

The effect of two levels of daily irradiation on shoot growth and root/shoot partitioning was investigated on two lucerne varieties (Medicago sativa L.). Individual plants were studied under constant temperature and optimal water and mineral nutrition conditions.For both lucerne varieties, daily irradiation did not change biomass partitioning between shoots and roots. It can be shown that leaf area expansion occurs independently of daily irradiation and that the process of shoot dry matter production is strictly proportional to daily irradiation, since the ratio leaf area/shoot dry matter is inversely proportional to it.From a model of shoot production of the isolated plant, we show that the relative shoot specific activity is not affected by daily irradiation. A simple model of partitioning leads us to determine why partitioning remains the same for the two at the levels of daily irradiation.Finally, the allocation between shoot and root turns out to be independent of the main stem extension rate, which is faster at the higher daily irradiation. © 1991 Annals of Botany Company.