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Acta Prataculturae Sinica ›› 2023, Vol. 32 ›› Issue (9): 160-172.DOI: 10.11686/cyxb2022401

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Comparison of photosynthetic-CO2 response process and models of Leymus chinensis under differing nitrogen addition and mowing conditions

Si-qi YANG1(), Ya-jing BAO1(), Jia-qi YE1,2, Shuai WU1, Meng ZHANG1, Meng-ran XU1, Yu ZHAO1, Xiao-tao LYU3, Xing-guo HAN4,5   

  1. 1.College of Environment and Bioresources,Dalian Minzu University,Dalian 116600,China
    2.School of Ecology and Environment,Inner Mongolia University,Hohhot 010021,China
    3.Erguna Forest-Steppe Ecotone Research Station,Institute of Applied Ecology,Chinese Academy of Sciences,Shenyang 110016,China
    4.State Key Laboratory of Vegetation and Environmental Change,Institute of Botany,Chinese Academy of Sciences,Beijing 100093,China
    5.University of Chinese Academy of Sciences,Beijing 100049,China
  • Received:2022-10-07 Revised:2022-11-30 Online:2023-09-20 Published:2023-07-12
  • Contact: Ya-jing BAO

Abstract:

Photosynthesis of plants is affected by grassland management practices such as nitrogen addition and mowing. In this research, the photosynthetic-CO2 response process of the dominant species, Leymus chinensis, was determined in a controlled field experiment exploring the interaction between nitrogen addition (0, 2, 5, 10, 20 and 50 g N·m-2·yr-1) and mowing (mown and unmown) in an Inner Mongolian meadow steppe. Leaf photosynthetic-CO2 response curves were fitted using a rectangular hyperbolic model, a non-rectangular hyperbolic model, a modified rectangular hyperbolic model and a Michaelis-Menten model in order to define photosynthetic trait responses of L. chinensis to nitrogen addition and mowing. It was found that the initial carboxylation efficiency and photorespiration rate of the non-rectangular hyperbolic model were closest to the measured values. The modified rectangular hyperbola model provided the best fit for CO2 saturation point, CO2 compensation point and maximum net photosynthetic rate, and the modified rectangular hyperbolic model the highest goodness of fit. Moderate nitrogen addition increased the net photosynthetic rate, water use efficiency, maximum net photosynthetic rate, initial carboxylation efficiency and CO2 saturation point, and decreased the CO2 compensation point, and thereby improved the CO2 use efficiency of L. chinensis. With the increase of CO2 concentration, the net photosynthetic rate of L. chinensis with nitrogen concentration of 20 g N·m-2·yr-1 with mowing increased, and higher maximum net photosynthetic rate, CO2 saturation point and water use efficiency was observed, together with a lower CO2 compensation point. In conclusion, the non-rectangular hyperbolic model and the modified rectangular hyperbolic model were more suitable for fitting L. chinensis CO2 response curves defining responses to nitrogen addition and mowing. In this experiment conducted on an Inner Mongolian steppe, the photosynthetic capacity of L. chinensis was most efficiently increased by applying 20 g N·m-2·yr-1 with mowing. This treatment combination is beneficial to carbon sequestration of the grassland ecosystem.

Key words: Leymus chinensis, nitrogen addition, mowing, photosynthetic-CO2 response curve, fitting model