Influence of pre-harvest nitrogen supply on post-harvest behaviour of ornamentals: importance of carbohydrate status, photosynthesis and plant hormones

Summary In this review, the potential role of carbohydrates, photosynthesis and the plant hormones ethylene, abscisic acid and cytokinins in nitrogen-affected post-harvest behaviour of ornamentals is discussed, differentiating between pre-harvest influences of nitrogen amount, nitrogen form and a secondary salt stress. The increasingly proposed function of the root as a sensor continuously monitoring root zone stress conditions is emphasized. Recently found interactions between sugars, cytokinins and light and between ammonium and ethylene in leaf senescence are considered as well as signal effects of nitrate on carbon allocation. Excessive nitrogen supply during cultivation, which also causes secondary salt stress, leads to an unfavourable physiological condition for post-harvest behaviour. Decreased carbohydrate reserves coinciding with a low photo-synthetic capacity may cause post-production carbohydrate deficiency. Increased fluxes of abscisic acid via the xylem and higher concentrations in plant tissues coinciding with opposite reactions of cytokinins and high ethylene production increase the risk of growth inhibition and post-harvest senescence. Whereas a balanced ammonium:nitrate ratio potentially favours post-harvest behaviour via higher cytokinin delivery by the root system, pure ammonium fertilization can cause ammonium toxicity, carbohydrate deprivation and high ethylene production. The relevance of these internal changes to post-harvest life is estimated distinguishing between different ornamental products. Changed hormonal situation and carbohydrate deficiency are probably important factors impairing post-harvest life of potted plants after excessive nitrogen supply. An apparently lower sensitivity of cut flowers can be explained by the disconnection from the stressed root system. The variable response of leafy cuttings to high nitrogen supply is additionally proposed to be attributed to the different swiftness of rooting resulting in hormonal changes and to different contribution of photosynthesis to carbohydrate pools in dependence from plant species and light conditions.