MODELING CONCEPTS FOR THE PHENOTYPIC PLASTICITY OF DRY-MATTER AND NITROGEN PARTITIONING IN RICE

To simulate rice growth and yield accurately, models must integrate gr owth and morphogenetic processes. Widely used models such as ORYZA1 gi ve much consideration to environmental effects on growth (e.g. carbon assimilation) but assume that assimilate partitioning among organs is independent of the environment, thereby allowing for no or little phen otypic plasticity. The present study evaluated the effects of nitrogen (N) nutrition on dry matter and N partitioning, using data from previ ous studies in the Philippines on irrigated transplanted and direct-se eded IR64 rice fertilized with six levels of N in one, and two levels in another study. Nitrogen application reduced dry matter partitioning to roots, particularly in direct-seeded rice. High N resources signif icantly increased dry matter partitioning to leaf blades at the expens e of stems, but did not affect partitioning between panicles and the r est of the plant. Partitioning of dry matter to leaves decreased as th e N concentration in th leaves (LNC) decreased, regardless of the caus e of low LNC: low N rate, high population in direct-seeded rice, or ph enological stage of the crop. Leaf partitioning of absorbed N, compare d to dry matter, was high and varied little during early vegetative gr owth, but varied strongly from panicle initiation onwards, probably du e to competition for N between leaves and the stem and the developing panicle. The possible structure of models that would simulate plastici ty of assimilate and N partitioning is discussed on the basis of organ -specific phenological time axes and interacting supply and demand fun ctions. The underlying assumption is that the observed effects of N nu trition on partitioning are mediated by the size of incremental assimi late pools. Copyright (C) 1996 Elsevier Science Ltd