张振, 辛晓洲, 裔传祥, 彭志晴, 柳钦火. 考虑植被类型的冠层气孔导度模型[J]. 农业工程学报, 2021, 37(3): 164-172. DOI: 10.11975/j.issn.1002-6819.2021.03.020
    引用本文: 张振, 辛晓洲, 裔传祥, 彭志晴, 柳钦火. 考虑植被类型的冠层气孔导度模型[J]. 农业工程学报, 2021, 37(3): 164-172. DOI: 10.11975/j.issn.1002-6819.2021.03.020
    Zhang Zhen, Xin Xiaozhou, Yi Chuanxiang, Peng Zhiqing, Liu Qinhuo. Advanced model of canopy stomatal conductance considering vegetation types[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2021, 37(3): 164-172. DOI: 10.11975/j.issn.1002-6819.2021.03.020
    Citation: Zhang Zhen, Xin Xiaozhou, Yi Chuanxiang, Peng Zhiqing, Liu Qinhuo. Advanced model of canopy stomatal conductance considering vegetation types[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2021, 37(3): 164-172. DOI: 10.11975/j.issn.1002-6819.2021.03.020

    考虑植被类型的冠层气孔导度模型

    Advanced model of canopy stomatal conductance considering vegetation types

    • 摘要: 冠层气孔导度指示着植物的光合和蒸腾作用的强弱,冠层气孔导度的精确估算对于研究蒸散、农业生产和生态系统的功能等具有重要意义。以往冠层气孔导度的模型很少考虑植被类型的影响,而不同植被类型间冠层气孔导度存在较大差异,本研究旨在考虑植被类型,引入气孔长度和密度计算最大气孔导度,建立植被冠层气孔导度模型。使用HJ-1卫星数据反演了2012年7-9月黑河流域植被冠层气孔导度分布,基于地面实测数据对卫星反演的冠层气孔导度进行验证,结果表明,与改进前未区分植被类型的模型相比,决定系数由0.51提高至0.70,均方根误差由4.91 mm/s下降至3.32 mm/s。改进模型可以描述植被类型间冠层气孔导度的差异,如2012年7月27日反演获得的玉米冠层气孔导度均值为15.12 mm/s,而云杉的冠层气孔导度均值则为3.84 mm/s。研究可为地表能量平衡和碳水循环等科学研究及精细农业、水资源管理等应用提供便利。

       

      Abstract: Canopy stomatal conductance indicates the intensity of photosynthesis and respiration of a plant, particularly for the evapotranspiration, agricultural production and ecosystem function. The estimated accuracy of canopy stomatal conductance varies greatly among different vegetation types. However, the influence of vegetation types on canopy stomatal conductance has rarely been considered in most previous studies. This study aims to develop a canopy stomatal conductance model considering vegetation types, thereby to achieve higher accuracy than before. According to a widely-used model of canopy stomatal conductance proposed by Leuning in 2008, two improvements were focused mainly on: 1) Stomatal length and density were introduced into the new model to calculate the maximum stomatal conductance, which differed among vegetation types but usually been calculated via parameter optimizing by minimizing the cost function. 2) Satellite-derived photosynthetically active radiation data was used to calculate the flux density of visible radiation at the top of canopy, instead of the net absorbed radiation minus the soil heat flux in previous studies, where the flux can contain the absorption by non-vegetation component. Ground observations were used to validate the model via the inversion of Penman-Monteith equation, including eddy covariance and automatic meteorological data from 15 sites in the middle reaches of Heihe Basin (100°20′-100°24′ E, 37°45′-42°40′ N) in China. An attempt was made to partition the evapotranspiration into soil evaporation and plant transpiration, where only plant transpiration was selected to derive canopy stomatal conductance, ruling out the influence of soil evaporation. Evaluation indexes included the determination coefficient, Root Mean Square Error (RMSE), and Mean Absolute Error (MAE). The results were as follows: 1) The improved model achieved higher accuracy in the land cover of maize and bell pepper, where the ground observed data was used to validate the models before and after partitioning soil evaporation and plant transpiration by the inversion of Penman-Monteith equation. Specifically, the determination coefficient of maize improved from 0.49 to 0.68 after improvement, while the RMSE reduced from 3.99 to 2.67 mm/s, and the MAE reduced from 3.34 to 2.06 mm/s, after partitioning soil evaporation and plant transpiration. Before that, the determination coefficient of maize improved from 0.38 to 0.46 after improvement, with both RMSE and MAE reduced. 2) The new improved model was applied to the middle reaches of Heihe Basin from July to September 2012 using HJ-1 satellite data, including the leaf area index, photosynthetically active radiation, and land cover data. The model showed a good ability in estimating the canopy stomatal conductance of different vegetation types. The average value for the canopy conductance of maize on July 27 was 15.12 mm/s, while that of spruce was 3.84 mm/s. The determination coefficient improved from 0.51 to 0.70, and the RMSE reduced from 4.91 to 3.32 mm/s, comparing with the model before and after improvement. The commission error was calculated to evaluate whether the new model was sensitive to stomatal characteristics, indicating that there was an obvious difference, only when the vegetation was wrongly classified. It demonstrated that the remote sensing data can be used for the better accuracy of new model in various vegetation types. A better improvement was achieved in estimating canopy stomatal conductance using the new model considering vegetation types, compared with the traditional models without considering that. The finding can bring great convenience to scientific research, such as surface energy balance and carbon-water cycle, as well as the specific practical applications in precision agriculture, water resources management, and ecology.

       

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