Effects of Potassium Levels on Waterlogging Resistance and Endogenous Hormone Balance of Rapeseed During Seedling Stage

This study aimed to investigate the effect of potassium (K) on the waterlogging tolerance of rapeseed (Brassica napus L.) and elucidate the physiological regulatory mechanisms involving K in the plant's response to waterlogging stress, to provide a theoretical basis for effective waterlogging management in rapeseed production.

A sand culture pot experiment was conducted with two water treatments: well-watered (CK) and waterlogging (WL), and two potassium levels: 1.0 mmol K₂SO₄·L^-1 (HK) and 0.1 mmol K₂SO₄·L^-1 (LK). Seven-day waterlogging stress was imposed at the seedling stage. Differences in growth, photosynthetic characteristics, antioxidant enzyme activities, and endogenous hormone levels under different K levels were compared.

Rapeseed growth was significantly affected by waterlogging and K level. Biomass, root-shoot ratio, and net photosynthetic rate consistently exhibited the hierarchical pattern: HK_CK＞HK_WL＞LK_CK＞LK_WL. Waterlogging elevated superoxide dismutase (SOD) and catalase (CAT) activity in leaves, while the activities of both enzymes were suppressed in LK treatments (LK_CK and LK_WL) compared to HK treatments (HK_CK and HK_WL). Consequently, the MDA content was significantly higher in the LK treatments than in the HK treatment. Waterlogging and K deficiency profoundly altered the endogenous hormone profiles in rapeseed. Leaf abscisic acid (ABA) cotent progressively increased across treatments: HK_CK＜HK_WL＜LK_CK＜LK_WL. Both waterlogging and potassium deficiency significantly increased the leaf jasmonic acid (JA) content after 7 d of waterlogging stress, peaking at LK_WL treatment. Waterlogging and K deficiency induced salicylic acid (SA) accumulation, with the highest SA content observed in LK_WL treatment. During the recovery stage, both waterlogging and potassium deficiency induced the decrease of indole-3-acetic acid (IAA) content in root and leaf, with the most pronounced depletion occurring in LK treatments (LK_CK and LK_WL).

Waterlogging stress inhibited rapeseed growth and severely restricted root development. Root growth and K⁺ uptake were significantly promoted, and leaf photosynthetic capacity as well as SOD and CAT activities were enhanced by elevated K levels, thereby improving waterlogging tolerance. Waterlogging stress triggered the accumulation of ABA, JA, and SA in leaves. The stress responses induced by ABA and JA accumulation were significantly alleviated by improved K levels and promoted the accumulation of IAA in roots and leaves after stress removal, facilitating the recovery growth of rapeseed.