Chin J Plan Ecolo ›› 2018, Vol. 42 ›› Issue (4): 453-465.DOI: 10.17521/cjpe.2017.0214

• Research Articles • Previous Articles     Next Articles

Temporal changes of vegetation water use efficiency and its influencing factors in Northern China

Chao-Yang FENG,He-Song WANG*(),Jian-xin SUN   

  1. College of Forestry, Beijing Forestry University, Beijing 100083, China
  • Online:2018-04-20 Published:2018-06-01

Abstract:

Aims Water use efficiency (WUE) is an important variable for evaluating the growth adaptation of vegetation; it links carbon and water cycles of terrestrial ecosystems. Charactering the spatial and temporal variations in WUE and the driving factors not only can help understand the processes and regulations of ecosystem carbon and water cycles, but also provides scientific basis for formulating sustainable regional development policies and guiding water resources management. This study was conducted to determine the patterns of temporal changes for different vegetation types in northern China.

Methods Flux and meteorological data of nine field observation sites in northern China were used to analyze the changes of WUE under different temporal scales, including half-hourly, daily, 8-day intervals, and monthly. The effects of temperature (Ta), relative humidity (RH), vapor pressure deficit (VPD) and photosynthetically active radiation (PAR) on WUE under different time scales were also examined.

Important findings (1) Diurnal change of WUE displayed an asymmetric “U” shape, with greater values at the sunrise than at the sunset. The seasonality of WUE in the Gobi and desert areas displayed a pattern of “U” shape, while it occurred as a single peak in other regions. The seasonal changes of WUE can be further divided into the types of gross primary production (GPP)-driven and the evapotranspiration (ET)-driven; the significance of either driven type increases with time. (2) Ta, RH, VPD and PAR were the main factors influencing the changes of WUE on a shorter temporal scale (half-hourly and daily). With increasing temporal scale, Ta and RH continue to remain the main factors affecting the changes of WUE, and their correlations with WUE were influenced by the prevailing role of GPP or ET. Moreover, the correlation coefficients became more significant with increasing temporal scales. (3) WUE increased with increases in leaf area index (LAI) until a certain value, beyond which the sensitivity of WUE to LAI decreased at the Changbai Mountain, Haibei and Zhangye stations. The relationship between precipitation and WUE was not significant in all the study areas. (4) Among the vegetation types, WUE ranked in order from high to low as forest, cropland, grassland, wetland and desert.

Key words: water use efficiency, flux measurement, gross primary production, evapotranspiration, meteorological factor