University of Bonn, Plant Nutrition in the Tropics and Subtropics, Germany
Rice genotypes subjected to salt-stress can develop several mechanisms to cope with salinity. Atmospheric conditions modify the efficiency of most of those mechanisms. Germplasm improvement programs have to take environmental conditions such as temperature, humidity or day length into account when selecting for salinity resistance. Factors influencing the level of salinity resistance are exclusion of sodium, selective uptake of potassium, high tissue tolerance for sodium, establishment of high K/Na ratios in photosynthetically active tissues, maintaining viable leaves, retention of sodium in physiologically less important tissues and more. Many of these factors depend on the amount of water passing through the plant passively carrying the sodium load into the plant. The amount of water passing through the plant is a function of transpiration and thus stomatal conductance. Stomatal conductance can be directly influenced by the number of stomata per surface and the stomatal aperture, which in turn is directly influenced by, nitrogen concentration in the leaf, VPD, temperature, and the hormonal status of the plant.
In order to avoid enormous field or greenhouse trials to test all possible combinations of mechanisms and their responses to climate, simulation modelling can be employed to create a large number of scenarios. In recent years our group has developed a concept model for sodium and potassium uptake and distribution in rice, which depends mainly on factors influencing transpiration for sodium uptake and distribution and assuming energy consuming active uptake and (re)distribution of potassium. This model has worked well as a static model, however, in order to be used as a tool for genotype development, the model needs to be dynamic and responsive also to salinity influences on growth parameters such as leaf initiation and carbon partitioning. This contribution will summarise the concept as it is now and show some of the underlying principles of the transpiration driven sodium distribution, stress independent simulation of leaf appearance and the influence of the potassium concentration in different tissues on the sodium retention level of these tissues. Problems of up-scaling will be discussed.
Keywords: Rice, germplasm, modelling