Imbalance between nitrogen and potassium fertilization influences potassium deficiency symptoms in winter oilseed rape (Brassica napus L.) leaves
Jing Li,
Wenshi Hu,
Zhifeng Lu,
Fanjin Meng,
Rihuan Cong,
Xiaokun Li,
Tao Ren,
Jianwei Lu
Affiliations
Jing Li
College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, Hubei, China; Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Ministry of Agriculture and Rural Affairs, Wuhan 430070, Hubei, China
Wenshi Hu
College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, Hubei, China; Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Ministry of Agriculture and Rural Affairs, Wuhan 430070, Hubei, China
Zhifeng Lu
College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, Hubei, China; Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Ministry of Agriculture and Rural Affairs, Wuhan 430070, Hubei, China
Fanjin Meng
College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, Hubei, China; Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Ministry of Agriculture and Rural Affairs, Wuhan 430070, Hubei, China
Rihuan Cong
College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, Hubei, China; Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Ministry of Agriculture and Rural Affairs, Wuhan 430070, Hubei, China
Xiaokun Li
College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, Hubei, China; Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Ministry of Agriculture and Rural Affairs, Wuhan 430070, Hubei, China
Tao Ren
College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, Hubei, China; Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Ministry of Agriculture and Rural Affairs, Wuhan 430070, Hubei, China; Corresponding author.
Jianwei Lu
College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, Hubei, China; Key Laboratory of Arable Land Conservation (Middle and Lower Reaches of Yangtze River), Ministry of Agriculture and Rural Affairs, Wuhan 430070, Hubei, China
Chlorosis at leaf margins is a typical symptom of potassium (K) deficiency, but inappropriate application of K with other nutrients often masks symptoms of K deficiency. A two-year field experiment was conducted to measure the interactive effects of N and K on leaf photosynthesis and dry matter accumulation and the resulting growth dilution effect on K concentration and leaf K deficiency symptoms. N application aggravated the imbalance of N and K nutrients and further exacerbated K deficiency symptoms under K limitation. Synergistic effects of N and K promoted plant growth, amplified the growth dilution effect, and reduced the critical K concentration in leaves. Using 90% of the maximum shoot biomass as a threshold, the critical K concentration was 0.72% at the recommended N (N180) fertilization level. The critical K concentration increased by 62.5% owing to the reduced biomass under insufficient N (N90) supply. In contrast, high N (N270) reduced the critical K concentration (0.64%), accelerating chlorophyll decomposition and exacerbating K deficiency symptoms. The basis of changing the critical K concentration by magnifying growth dilution effect was the functional synergistic effect of N and K on photosynthetic characteristics. Under insufficient N, the low maximum carboxylation rate (Vcmax) limited the net photosynthetic rate (An) and necessitated more K to maintain high CO2 transmission capacity, to improve the total conductance gtot /Vcmax ratio. High N supply increased gtot and Vcmax, possibly mitigating the effect of K reduction on photosynthesis. In conclusion, it is unwise to judge K status of plants only by K concentration without accounting for crop mass (or dilution effect), critical K concentration and deficiency symptoms are affected by N fertilization, and the synergistic effect of N and K on leaf photosynthesis is the foundation of maximal growth of plants under diverse critical K concentrations.
