Characteristics of water and carbon fluxes during growing season in three typical arid ecosystems in central Asia

Aims The arid region in central Asia, in the hinterland of Eurasia, is characterized by low precipitation and extremely fragile ecological environment. Study of energy and matter exchange between atmosphere and the land surface is essential to understanding the balance of water resources and ecosystem functioning in arid region. The objective of this study was to investigate the characteristics of water and carbon fluxes and responses to environmental factors in a typical ecosystem of central Asia.
Methods Eddy covariance measurements were made at three sites representing desert and grassland ecosystems in the central Asia. We analyzed the responses of evaporation and gross primary productivity to selective environmental factors using the enveloped curve fitting method, which determines the response of a dependent variable to a given independent factor while fixing other factors at their best values.
Important findings During growing season from April to October, the diurnal variations of energy, water vapor, net ecosystem CO₂ exchange and gross primary productivity showed patterns of “single peak curve” at the three sites; whereas ecosystem respiration in the desert ecosystem kept relatively stable. The ratio of latent heat flux to net solar radiation in the grassland ecosystem (76.3%) was greater than in the desert ecosystem (32.7%). The grassland ecosystem occurred as a strong carbon sink, whilst the desert ecosystem showed weak carbon fixation. Evapotranspiration and gross primary productivity in the two types of ecosystems were susceptible to changes in precipitation, net solar radiation or photosynthetically active radiation, vapor pressure deficit and air temperature.