基于茎流-蒸渗仪法的荒漠草原带人工灌丛群落蒸散特征

Characteristics of evapotranspiration in planted shrub communities in desert steppe zone based on sap flow and lysimeter methods

中国西北地区通过大量种植中间锦鸡儿(Caragana liouana)进行生态治理,在荒漠草原带上形成人工灌丛景观,改变了生态系统的结构和功能,影响到地-气水汽循环过程,研究该人工灌丛群落的蒸散特征,对揭示其生态水文效应和指导地方生态治理实践具有重要意义。该文以宁夏盐池荒漠草原带上的人工灌丛群落为例,利用茎流-蒸渗仪法测定了2018年5–8月的灌木蒸腾和丛下蒸散,并分析了环境因子对人工灌丛群落蒸散的影响。结果表明:(1)茎流-蒸渗仪法所测的群落蒸散与水量平衡法、涡度相关法得到的群落蒸散有较好的一致性,茎流-蒸渗仪法能适用于荒漠草原带人工灌丛群落蒸散及其组分结构的测定;(2)观测期内晴天的灌木蒸腾速率和丛下蒸散速率日变化趋势相近,均为单峰曲线,群落蒸散主要发生在日间,但灌丛最大蒸腾速率的出现时间比丛下蒸散最大速率的出现时间晚1 h;(3)5–8月间灌木累积蒸腾为83.6 mm,日平均蒸腾量为0.7mm·d^-1,季节变化呈抛物线状;同期丛下累积蒸散为182.5 mm,日平均蒸散量为1.5 mm·d^-1;丛下蒸散明显大于灌木蒸腾;(4)观测期间人工灌丛群落累积蒸散266.1 mm,而同期的降水量为222.6 mm,陆面水分收支处于亏缺状态;(5)净辐射是影响蒸散最主要、最直接的驱动因素,且能够影响其他因子进而对人工灌丛群落蒸散产生作用。综上,人工灌丛引发荒漠草原地带陆面水分收支亏缺的现象,在生态恢复与重建中须引起注意。

Aims Caragana liouana has been widely planted in northwest China for ecological restoration which has induced the planted shrub landscape in the desert steppe zone and changed the structure and function of the original ecosystem.These plantations would affect the water vapor interactions between land surface and atmosphere eventually.Therefore,studying the evapotranspiration characteristics of the planted shrub communities in the desert steppe zone is significant for us to understand its ecohydrological mechanism and guide local ecological restoration.Methods The transpiration of shrubs and the evapotranspiration under shrub canopy in the desert steppe zone in Yanchi County,Ningxia,were measured by a coupled method of sap flow sensors and lysimeter from May to August in 2018.The effects of environmental factors on the evapotranspiration of the planted shrub communities were analyzed by path analysis.Important findings(1)The evapotranspiration obtained by the coupled method of sap flow sensors and lysimeter was consistent with the estimations based on the water balance method and the eddy covariance method.Thus,the coupled method of sap flow and lysimeter can be used to measure the evapotranspiration and its components of the planted shrub communities in the desert steppe zone.(2)The diurnal variations of transpiration rate of shrubs and the evapotranspiration rate under shrub canopy were consistent with each other,and both presented an obvious single peak at noon.The evapotranspiration of the planted shrub communities mainly occurred in day time.However,the time of the maximum transpiration rate of shrubs was 1 h later than that of the maximum evapotranspiration rate under shrub canopy.(3)The cumulative transpiration of shrubs was 83.6 mm,the daily average transpiration was 0.7 mm·d^-1,and the series curve of daily transpiration had a parabolic shape from May to August.The cumulative evapotranspiration under shrub canopy was 182.5 mm,and the daily average evapotranspiration was 1.5 mm·d^-1 during the same period.The evapotranspiration under shrub canopy was higher than the transpiration of shrubs.It can be concluded that the water consumption in the planted shrub communities is mainly caused by evapotranspiration under shrub canopy.(4)The total evapotranspiration of the planted shrub communities from May to August was 266.1 mm,and the total precipitation in the same period was 222.6 mm.Therefore,the water balance in the planted shrub communities was in deficit.(5)Net radiation is the most important and direct driving factor that affected evapotranspiration of the planted shrub communities,and it coupled other environmental factors to drive the process of evapotranspiration.Therefore,the water deficit in the planted shrub communities encroaching desert steppe zone should be paid attention in ecological restoration and reconstruction.