Change with time in potential radiation-use efficiency in field pea

In most crop models, radiation-use efficiency (RUE) is critical to the calculation of yield. Daily biomass production is usually calculated as the product of intercepted solar radiation and RUE which is assumed to be constant. In this work, field experiments were conducted with field pea (Pisum sativum L.) to assess the stability of RUE during the plant growth cycle, in the absence of biotic and abiotic stresses. Two contrasting locations with regard to solar radiation and air temperature were used in France. At each location, various combinations of years, genotypes, sowing dates and densities were studied. The results demonstrated that RUE is not constant during the plant growth cycle but that a consistent sigmoidal pattern can be defined. During vegetative growth, RUE declined from emergence to a low point before flowering. Once in the reproductive stage, RUE increased to reach a maximum level soon after the beginning of seed filling. Thereafter, it declined to zero upon the death of the plant. The level and timing of change in RUE were affected by sowing date, genotype and plant density. However, the sigmoidal pattern was unaffected by these factors and was not related to air temperature. The specific pattern of RUE probably results from the appearance, growth and subsequent senescence of such plant organs as roots, shoots, leaves, pods and seeds and also changes in those meteorological variables which affect photosynthetic plant capacity. Accurate estimation of RUE is important for the quantification of plant productivity in fluctuating environmental conditions and more mechanistic studies on changes in RUE are needed to investigate the causes of these changes and their consequences for plant productivity.