Temporal variation and controlling factors of canopy conductance in Artemisia ordosica community

Canopy conductance (g_c) is an important factor influencing plant transpiration and photosynthesis, and it is sensitive to environmental factors. Evapotranspiration and environmental factors of a shrub ecosystem, which was dominated by Artemisia ordosica in northwestern China, were continuously measured using eddy covariance technique in growing season (May-October) in 2015. Meteorological variables including air temperature (T_a), relative humidity (RH), photosynthetic active radiation (PAR), soil volumetric water content (VWC), and precipitation (PP) were also measured. g_c was calculated using the inverted Penman-Monteith equation. Diurnal pattern in g_c revealed a clear seasonal trend, with g_c peaking 2 hours earlier in summer (from May to August) than autumn(from September to October)(10:00, 3-4 hours and 1-2 hours before VPD and PAR). During growing season, g_c increased positively with vapor pressure deficit (VPD) and PAR, respectively, saturating at 1.5 kPa and 1 200 μmol/(m²·s), then decreasing with these variables when greater than their respective threshold.The g_c values had positive relationship with soil volumetric water content at 30 cm depth (VWC_30) under high VWC_30 (≥0.16 m³/m³) during the whole growing season. g_c was more responsive to PAR and VPD when VWC_30 was high. It was concluded that VWC played a critical role in regulating canopy conductance in desert ecosystems. Our results could potentially provide important baseline information towards hydrological model creation of arid and semi-arid ecosystems.