Root K affinity drivers and photosynthetic characteristics in response to low potassium stress in K high-efficiency vegetable soybean

Abstract

Aims Vegetable soybean is highly demanded on potassium (K) application. Significant variations of K absorption and utilization exist in vegetable soybean. This study aim at exploring mechanisms of K absorption and utilization of high-efficiency in vegetable soybean by studying the characteristics of root K affinity-associated drivers and photosynthesis in vegetable soybean (edamame) (Glycine max (L.) Merr.).Methods Pot and hydroponic experiments were carried out to examine the characteristics of root K affinity-associated drivers and photosynthesis in vegetable soybean genotypes with different K efficiency. Two K high-efficiency vegetable soybean genotypes and two K low-efficiency genotypes were investigated in low K and normal K conditions. Results The root of K high-efficiency genotypes had a higher K+ affinity associated with higher maximum K+ uptake rate (Imax), but lower Michaelis constant for K+ absorption (Km) and lower compensation concentration for K+ uptake (Cmin). Seedlings of K high-efficiency genotypes also had higher root vigor (TTC reduction method) and greater absorbing activity (methylene blue method), especially in the low K condition. Besides, the root bleeding-sap rate per root length and K upward fluxes rate per root length of K high-efficiency genotypes in beginning seed stage were consistently higher than that of K low-efficiency genotypes. The root of K high-efficiency vegetable soybean genotypes exhibits K+ high-affinity and driving advantages. Photosynthetic parameters of K high-efficiency vegetable soybean genotypes were less affected by low K stress. Low K stress decreased the net photosynthetic rate of K high-efficiency genotypes by 6.1~6.9%, while that of K low-efficiency genotypes decreased by 10.9~15.7%. The higher Chl a/b ratio with enhanced relative content of Chl a in response to low K stress might be an adapted mechanism for K high-efficiency genotypes to maintain photosynthetic capacity.Conclusion Stronger root K affinity drivers associated with photosynthetic adaptability to low potassium stress are the key factors in determining the K high-efficiency of vegetable soybeans.