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Acta Prataculturae Sinica ›› 2022, Vol. 31 ›› Issue (9): 63-75.DOI: 10.11686/cyxb2021343

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Effect of nitrogen application on photosynthetic daily variation, leaf morphology and dry matter yield of alfalfa at the early flowering growth stage

Yan-liang SUN(), Jun-wei ZHAO, Xuan-shuai LIU, Sheng-yi LI, Chun-hui MA, Xu-zhe WANG(), Qian-bing ZHANG()   

  1. College of Animal Science and Technology,Shihezi University,Shihezi 832003,China
  • Received:2021-09-13 Revised:2022-01-25 Online:2022-09-20 Published:2022-08-12
  • Contact: Xu-zhe WANG,Qian-bing ZHANG

Abstract:

In this research, studies on leaf morphological characteristics and the diurnal changes of photosynthesis in a drip-irrigated alfalfa (Medicago sativa) crop were monitored under different nitrogen levels and the relationships between the daily changes of photosynthesis, leaf morphology, and dry matter yield were analyzed in order to better understand the mechanism of the impact of nitrogen on alfalfa dry matter yield development. The study thus provides a theoretical framework for optimizing the nitrogen management strategy of alfalfa in commercial production. The study used a single factor randomized complete block design with four nitrogen application levels of 0 (CK), 60 (N1), 120 (N2), and 180 kg N·ha-1 (N3). At the early flowering growth stage, daily photosynthetic variation, leaf morphology, leaf nitrogen content, and yield components were of the alfalfa were measured. It was found that the net photosynthetic rate, transpiration rate, and water use efficiency of alfalfa leaves under the nitrogen application treatments were higher than those under the non-nitrogen application treatment, and the intercellular CO2 concentration of alfalfa leaves under the nitrogen application treatments was lower than that under the non-nitrogen application treatment. The environmental factor that had the greatest combined effect on net photosynthetic rate and transpiration rate was photosynthetic effective radiation. The leaf length, leaf width, leaf area, and specific leaf weight of alfalfa, as well as leaf dry weight, stem dry weight, dry matter yield, leaf nitrogen content, starch, and soluble sugar content all showed a pattern of initial increase and then decrease with successive increments of N application. For different nitrogen concentrations, leaf area was the most significant factor affecting leaf morphological structure, followed by leaf specific weight, leaf length, and leaf width. The effects on dry matter yield of alfalfa were, in descending order, leaf nitrogen content>net photosynthetic rate>leaf area>transpiration rate>specific leaf weight. The decrease in photosynthetic rate in the zero-N and high-N treatments was primarily due to the inhibition of photosynthetic activity; This is a non-stomatal factor. Based on a principal component analysis, the highest overall score for dry matter yield, leaf morphology and photosynthesis was obtained in the N2 treatment, followed by N3, N1 and CK treatments. Therefore, nitrogen fertilization promoted the synergistic improvement of photosynthetic rate and photosynthetic area in alfalfa. It facilitated the production of photosynthetic products, thereby increasing alfalfa dry matter yield, especially at the nitrogen application rate of 120 kg·ha-1.

Key words: alfalfa, nitrogen, leaf morphology, diurnal variation of photosynthesis, dry matter yield