Effects of environmental factors on evapotranspiration characteristics of Haloxylon ammodendron plantation in the Minqin oasis-desert ectone, Northwest China.

Abstract

This study continuously measured the evapotranspiration (ET) of degraded Haloxylon ammodendron shrub plantation of Minqin oasis-desert ectone using an eddy covariance system for ET, and TDR for soil moisture profile, analyzing ET in relation to the weather conditions and describing the responses of ET to the microclimate variables in different weather from July 2014 to June 2015. Results showed that the hourly ET dynamics had an apparent seasonal trend in the growing season. This trend gradually increased in the beginning of season from the low level of non-growing season, reached its maximum peak value (0.07 mm·h-1) in the most physiologically active period, and decreased to the minimum peak value (0.01 mm·h-1) in December. The diurnal change in ET of the plantation depended on the weather conditions. The ET fluctuated less with a small magnitude in a cloud day, but fluctuated obviously with a greater magnitude after rain if weather was clear. After a strong rainfall (>9 mm·d-1), ET increased sharply to a high level of 28 folds prior to rain, at which it took four clear days to gradually decease to the pre-rain ET level. The yearly ET over H. ammodendron plantation was 108 mm, equivalent to 98% of annual precipitation. Soil moisture was the water source for ET. Therefore, soil moisture was the dominant factor for theET over the plantation. Net radiation, photosynthesis active radiation, air temperature, and vapor pressure deficit were the microclimate variables to drive the transpiration of vegetation and evaporation over the soil surface, being the major factors forET over the plantation. The regression equation of ET to the dominant factor and major factors had a coefficient of multiple determination (R2) over 0.80.