Effects Of Potassium And Magnesium Application On Plant Growth,Antioxidant Activity And Morphological Characteristics Of Rice Seedlings

Potassium (K) and Magnesium (Mg) are essential nutrient elements for plant growth. Their functional roles in plants have been well-documented in many literatures. It has been accepted that the uptake and translocation of K and Mg in plants behave competitively. However, there is little information available on the interactive effects of K and Mg on the plant morphological and physiological characteristics of field crops. Rice (Oryza sativa L.), one of the most important food crops in the world, is mainly grown in flooded soils in tropical and subtropical areas. Fertilizer K application along with, N and P fertilizers dominated rice culture to maintain and boost its production in Indonesia and other countries in the Southeast Asia. Intensive weathering due to high rainfall and temperature in these areas may result in low available Mg, and particularly K deficiency in most crops. Therefore, it is very important to study relationship between K and Mg in rice production. The objectives of the present investigation is aimed at studying effects of K and Mg application and their interaction on plant growth, nutrient uptake, morphological and physiological characteristics of rice seedlings. Two pot experiments in the green house and one nutrient solution culture experiment in the growth chamber were conducted. Rice cultivar Yangdao6was selected as the test crop. Soil was collected from Guangxi province. In the pot experiment Ⅰ, KCl and MgSO4·7H2O, as sources of K and Mg, were applied to soils at the rate of0,100, and400mg K2O kg-1, and0,80, and200mg Mg kg-1, respectively. K and Mg rates were reduced a half in the pot experiment Ⅱ. Yoshida nutrient solution was used in the nutrient solution experiment and modified as treatments with three levels i.e. low (0.005mM), medium (1.5mM), and high (5.0mM) for Mg, and low (0.01mM), medium (1.0mM), and high (5.0mM) for K. There were9treatment combinations in a completely randomized design with4replicates. The main results and conclusions were summarized as followings:(1) Under high K rates at200and400mg·kg-1K2O, rice seedlings exhibited necrotic spots and death in older leaves and plant biomass significantly reduced. However, low Mg treatment didn’t affect plant growth significantly during the experimental periods. K application at200mg·kg-1K2O inhibited root growth and decreased root length, root surface, root volume, and root diameter. Increasing K2O rate reduced Mg content in the plant and increased ratio of K to Mg in shoots. (2) In the nutrient solution experiment, low K or low Mg supply inhibited plant growth as well as root parameters of rice seedlings and the K or Mg deficiency symptoms appeared on leaves. It was shown that the high K addition (5.0mM) reduced Mg content in plants, especially when plants were exposed to low Mg stress (0.005mM). High K addition might induce Mg deficiency in rice plants.(3) Ca content in the plant was decreased by high rate of Mg (100and200mg·kg-1Mg) and K (200and400mg·kg-1Mg K2O) applied to soils and high Mg (5mM) and K (5mM) added to the nutrient solution. It is suggested that high Mg or K application might cause a decline of plant Ca uptake.(4) Deficiency of Mg or K in the nutrient solution culture resulted in the accumulation of soluble sugar in shoots of rice seedlings. Low Mg stress induced higher activities of Superoxide Dismutase (SOD) and Peroxidase (POD) in shoots when rice seedlings were applied with sufficient K. Low K treatment lowered SOD activity in the rice seedlings if plants were subjected with low Mg or high Mg supplies.(5) Deficiency of K and Mg resulted in leaf cell damage according to the anatomical observation by light microscopy. Mg deficiency or K deficiency caused leaf epidemical and mesophyllic cells shrunk, deformed, and the increased space among cells. The severe symptoms of Mg or K deficiency in leaves were the collapse of cells besides reduction and disruption of bulliform cells. However, under the combined stress of K and Mg deficiency, leaf cells were less destructed and leaf become thick.This study showed that excess potassium fertilizer application would easily lead to magnesium deficiency in rice seedlings, which is of important significance to recommend balanced fertilization of potassium and magnesium for improving rice production.