Physiological Mechanism of Photosynthetic, Nutrient, and Yield Responses of Peanut Cultivars with Different Tolerances under Low K Stress

Abstract

Potassium is one of the most important elements for crop growth and development. However, potassium deficiencies are common in the cultivated land of oil crops in the world, which limits the increase in their yields. The photosynthesis, fluorescence, and physiological indexes of peanut plants were affected by low K stress to varying degrees, and finally the yield decreased. However, the effect of low K stress on the photosynthetic physiological mechanism of peanut plants remains unclear. In this study, in order to explore the response mechanism of peanuts to low K stress, NH18 (tolerance to low K) and HY20 (intolerance to low K) were used to explore the effects of different peanut varieties under low K stress on the dry matter accumulation, protective enzyme activities, osmotic regulatory substance accumulation capacity, fluorescence characteristics, nutrient content, grain quality, and yield. The results of the 2-year experiment showed that under the stress of low K, the content of malondialdehyde in peanut leaves increased and the activities of NH18 superoxide dismutase (SOD) and peroxidase (POD) in the low-K-tolerant variety were higher than those in the low-K-intolerant variety HY20. The decrease in osmotic regulation caused by low K was compensated for by an increase in the soluble protein content. As a result, the chlorophyll content decreased significantly, F0 increased under dark adaptation, and Fm, Fv, and Fv/Fm decreased. The photosynthetic and fluorescence physiology of low-K-tolerant NH18 was less affected by low K stress. Furthermore, under low K stress, the dry matter accumulation of NH18 was reduced less, so that the final yield was less affected by low K stress than that of HY20. Under low K stress, the potassium content in the roots, stems, leaves, and fruit needles decreased significantly, and the decreasing range of stems and leaves gradually increased with the growth period, while that of the pod gradually decreased with the growth period. Under low K stress, the sodium content in the root system significantly increased and was significantly higher than that in the stem, leaf, pod, and fruit needle, indicating that the peanut plants actively absorbed more Na+ to replace the K+ function. This study clarified the mechanism of photosynthesis and the physiology of peanut plants under low K stress, which is of great significance for the breeding and cultivation of peanut resistance.