A model explaining genotypic and environmental variation in leaf area development of rice based on biomass growth and leaf N accumulation

Leaf area index (LAI) is one of the major determinants of crop photosynthesis. The objectives of this study were to clarify the relationship between LAI development and crop growth in diverse rice genotypes grown under widely different climate conditions and to develop a model explaining genotypic and environmental variation in LAI dynamics based on environmental and plant factors. Cross-locational experiments were conducted with nine different rice genotypes at eight locations in Asia covering a wide climate range under irrigated conditions with sufficient nitrogen application. The LAI observed at the heading stage ranged from 0.85 to 8.77 among the genotypes grown at the eight locations. A fairly stable allometric relationship was observed between LAI development and above-ground biomass growth during the period from transplanting to 2 weeks before heading over all the genotypes, sites and years (r = 0.91). The allometric relationship was, however, under the influence of leaf nitrogen content per unit leaf area (LNC, g m−2 leaf) and air temperature. On the basis of these results, we modeled the LAI development as a function of relative crop growth rate (RGR), LNC and air temperature. The rate of LAI decrease associated with leaf senescence was also described as a function of LNC.The observed genotypic and environmental variations in dynamics of LAI development were well explained (R2 = 0.95) by the model with only one genotype-specific parameter to represent the critical LNC below which leaves start senescing. The genotypic difference in the rate of LAI development was effectively explained by the variation in LNC and RGR under various environments, while that of LAI decrease with leaf senescence was explained by the variation in LNC and a genotype-specific coefficient of the critical LNC. It was suggested that genotypic difference in LNC was derived from the difference in crop N uptake at a given RGR.