RECENT ADVANCES IN UNDERSTANDING THE ROLE OF POTASSIUM AND MAGNESIUM IN MITIGATING ABIOTIC STRESS IN CROPS

摘要

Potassium (K) and magnesium (Mg) have fundamental roles in plant nutrition and productivity particularly with respect to crop tolerance to diverse abiotic stresses. During the reproductive growth of crops the demand for Mg and K is particularly high as the transport of carbohydrates and other metabolites from source to sink tissues (e.g. into tissues not capable of photosynthesis like seeds, roots and/or tubers) heavily depends on both nutrients. Consequently, typical deficiency symptoms are related to these roles of K and Mg in plant metabolism: chlorosis, starch accumulation in leaves, retarded root growth and wilting and necrosis of leaf margins. Recent results indicate that an adequate and balanced supply of these two nutrients helps to significantly increase the water use efficiency as well as the drought and cold stress tolerance of crop plants. Drought stress is typically associated with high radiation and/or temperatures, coupled with sub-optimal water availability (often appearing during the reproductive growth phase) and has great potential to induce oxidative stress in crops. Therefore, not only to prevent photo-oxidative damage and related disorders but also to maintain root growth under drought stress, an adequate and uninterrupted supply of K and Mg during yield and quality formation is indispensable for maximising economic returns. Hence, in-season foliar application of magnesium and potassium fertilisers can be a useful practice to contribute to better productivity and higher drought stress tolerance. With respect to cold stress tolerance, K in particular is known to reduce the freezing point of the cell sap when accumulated by the crop in high concentrations. In addition, over-winter yield losses caused by plant dehydration during frost (e.g. when the crop is not protected by snow cover) can also be mitigated by ensuring an adequate supply of K and Mg. Both nutrients are involved in the efficient regulation of the plants' water household. Furthermore, root growth is facilitated resulting in greater soil exploration into depths which are less subject to large temperature fluctuations and freezing. In this way, plants are better able to maintain the ability to take up water from the subsoil under severe low temperatures when the topsoil is frequently frozen. Taken together, K and Mg are plant nutrients important for yield security under increasingly challenging environmental conditions.