Soil water potential dynamics and water utilization of typical planted forests in the mountain area of North China

Large scale afforestation alleviates soil erosion effectively in North China. The water cycle has been consequently modified under plant growth and changing precipitation regimes. Soil water dynamics is critical to investigate the water cycle of planted forests under changing environment for plant restoration. In this study, multi-time scale（i.e. half-hourly, daily, monthly, and annual scales） analysis of soil water potential（SWP） was conducted based on long-term measurement of the SWP between 2014 and 2018 under 60 a and 90 a arborvitae（Platycladus orientalis） planted forests as well as weeds as a reference in Chongling catchment in the mountain area of North China. The temporal variations in vertical gradients of SWP and zero flux planes（ZFPs） were analyzed to propose the patterns of soil water movement and plant water utilization for three representative vegetation types. Results showed that the diurnal variation of the SWP appeared as a unimodal curve with a peak occurring between 13:00 and 14:00. Daily variation in the SWP of arborvitae was significantly small compared to that of weeds. Daily changes of SWP decreased with the increase of soil depth, while the declining rate was larger under 90 a arborvitae than that under 60 a arborvitae and weeds. It was evident that the SWP decreased gradually from April to June, reaching a minimum value of-305.3 cm with the standard deviation（SD） of 58.3 cm. Nevertheless, the SWP increased rapidly from July to August（（-215.7±105.9） cm） and then remained high during September to October（（-210.6±51.9） cm）. The responses of SWP at different soil depths to precipitation under arborvitae at monthly and annual scale were greater than those under weeds. There was a significant linear relationship between the annual mean SWP and annual precipitation under 60 a arborvitae（P