Characteristics of soil water and salt associated with Tamarix ramosissima communities during normal and dry periods in a semi-arid saline environment

Tamarisk (Tamarix ramosissima) plants are widely distributed in semi-arid regions with saline soils. In these environments, the survival and sustainability of the Tamarisk plants are critically related to the availability and distribution of soil water and salt. In this study, we analyzed the soil water content (SWC) and soil electrical conductivity (EC) to the depth of 60 cm in natural Tamarisk communities, located in a semi-arid saline region of northwestern China, in July 2016 (a normal period) and July 2017 (a dry period). The results showed that SWC varied from 1.91 to 7.82% and soil EC ranged from 9.65 to 25.38 mS/cm in the 0-60 cm soil layer. Despite the deficiency of precipitation in the study period of 2017, the SWC in all plots was higher at the 20-60 cm depth than that of the normal study period in 2016. Compared to 2016, the soil was also less saline in 2017, representatively by lower soil EC values at the 0-40 cm depth. Additionally, the SWC decreased with Tamarisk density, indicating that Tamarisk plants increase water consumption. The SWC and soil EC both revealed "island" distribution, with highest level found inside or underneath the Tamarisk plant canopies. Both the SWC and soil EC presented a strong or moderate spatial dependency, and the spatial dependency in soil EC were significantly affected by community composition. Correlations (Pearson's r) showed that there were positive correlations between SWC and soil EC. The results above indicate that Tamarisk communities can ameliorate the semi-arid high saline soil environment, and that the growth and distribution of Tamarisk plants influence the spatio-temporal variability of SWC and soil EC. In addition, the results also demonstrate that the possible appropriate density in the process of constructing Tamarisk plants should be considered in order to achieve the optimal water condition. The study may provide a scientific basis for the ecological restoration and halophytes establishment in the semi-arid saline region of northwestern China and other areas with similar ecologies.