Comparing ET-VPD hysteresis in three agroforestry ecosystems in a subtropical humid karst area.

Understanding evapotranspiration–vapor pressure deficit ( ET - VPD ) hysteresis for different ecosystems can improve our knowledge of vegetation adaptability to a changing environment. However, no previous studies have compared the controlling factors of ET - VPD hysteresis for different agroforestry ecosystems in karst landscapes. Therefore, this study explored ET - VPD hysteresis patterns and the controlling factors for three agroforestry ecosystems, using field observations in a subtropical humid karst catchment from March 12, 2015 to May 26, 2016. The results showed both similarities and differences in ET - VPD hysteresis among the three ecosystems. For example, all three agroforestry ecosystems exhibited noticeable ET - VPD hysteresis, and the hysteric magnitude showed noticeable seasonality with higher values during the growing season. For all three ecosystems, the ET - VPD hysteretic magnitude had no significant relationship with the daily mean environmental factors (e.g. meteorological factors and soil moisture ( θ )), but it was highly ( R 2 > 0.59) correlated to changing rates of meteorological factors (e.g. temperature ( Ta ), relative humidity ( RH ), and vapor pressure deficit ( VPD )) in the morning. The ET - VPD hysteretic magnitude of the forest–grass mixed ecosystem (142.48 ± 74.16 min) was significantly higher than that of the grass ecosystem (104.37 ± 82.93 min). Hysteresis reflected the extent of imbalance between water demand and water supply for ecosystems during a day. Therefore, this study may be helpful in modeling ET and further understanding ecosystem responses to environmental change. [ABSTRACT FROM AUTHOR]