Response of root morphology, leaf physiology and yield of stay-green and presenility types of peanut to foliar phosphorus application

Objectives Spraying phosphorus (P) fertilizer is an important supplement for P nutrition of crops. The effect of foliar fertilization is influenced by cultivar type and spraying concentration. The study was to explore the differences of root morphology, leaf antioxidase activity, nutrient uptake and pod yield of different peanut cultivars to deepen understanding the relationship between varietal characteristics and foliar P fertilizer effect.

Methods A sand pot experiment with a two-factorial design was conducted in greenhouse. Two peanut cultivars of Huayu 39 (stay-green type) and Huayu 20 (presenility type) were chosen and three P₂O₅ spraying levels of 0, 0.1% and 0.2% were applied (CK, P_0.1 and P_0.2). P was sprayed on the 5th and 15th day after initial flowering of peanut. In early stage of podding and mature stage (70th and 100th day after sowing), the third leaves from the top were collected for investigating malondialdehyde (MDA) contents and antioxidase activities, fresh roots were collected for measuring morphological indexes and the whole plant was divided into nutritive organ (root, stem and leaf), peg and pod for studying N, P content and dry matter weight.

Results In early stage of podding, P_0.1 treatment significantly increased length, volume and surface area of roots, enhanced the activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), and decreased MDA contents in leaves, while the increments of above indexes decreased in P_0.2 treatment, and had no significant differences in most cases, compared to CK. In mature stage, both P_0.1 and P_0.2 treatments had little effect on leaf and root of stay-green cultivar. While they decreased root length, surface area and volume, increased membrane lipid peroxidation and accelerated plant aging of presenility cultivar, P_0.2 had a greater negative influence than P_0.1. Spraying P fertilizer significantly increased N, P accumulation of different organs and whole plant for both two cultivars, and larger N and P accumulation of pod in P_0.2 treatment than in P_0.1 for stay-green cultivar, and opposite in presenility cultivar. Spraying P fertilizer greatly improved the dry weight of different organs and pod yields of the two cultivars. The dry weight of whole plant in P_0.2 treatment were lower than those of P_0.1 and pod yield in P_0.2 treatment was higher than that of P_0.1 for stay-green cultivar, while the pod yield in P_0.2 treatment was lower than that in P_0.1 for presenility cultivar.

Conclusions In early stage of podding, spraying P fertilizer could promote the root development and increase leaf antioxidase activities of both two cultivars. The effect of 0.1% P₂O₅ is better than that of 0.2% P₂O₅. In mature stage, the responses of root and leaf of stay-green cultivar to foliar P fertilizer are not sensitive. However, N and P accumulation of pod and pod yield in P_0.2 treatment are larger than those in P_0.1 treatment for stay-green cultivar. Therefore, the suitable P fertilizer concentration of this variety is 0.2% P₂O₅. Spraying 0.2% P₂O₅ significantly reduces the root morphological indexes and leaf antioxidase activities of presenility cultivar at mature stage, to a certain extent, it offsets the positive effect of foliar P fertilizer on the early stage of podding, resulting in the increase of plant N, P accumulation and pod yield in P_0.2 treatment is less than that in P_0.1 treatment. Therefore, it is more suitable to apply 0.1% P₂O₅ for presenility cultivar.