| Wetlands play an important role in water cycle and the maintenance of biodiversity. The arid and semi-arid areas contain the large numbers of the world’s rivers and riverine wetlands. However, arid wetlands are mostly facing serious problems such as soil salinization and water resource shortage. Computer model is a powerful tool to optimize the management measures by simulating and predicting soil water and salt dynamics and crop growth. In this study Hydrus-1D model was firstly calibrated and validated with the observed data of 2012 and 2013, and then Chinese tamarisk root distribution, soil water and salt dynamics in the root zone and root water uptake characteristics were evaluated. At the same time, we investigated soil water and salt dynamics and root water uptake of Chinese tamarisk under different scenarios(i.e., combinations of different groundwater levels, groundwater electric conductivities). In addition, we investigated ion content in the three major plants. The main results were listed as follow:(1) Chinese tamarisk root distribution was greatly affected by soil water and salt distribution in the soil profile, with about 73.8% of the roots being distributed in the 20–60 cm layer; soil salinity is the major stress factor on root water uptake, root water uptake accounted for 91.0% of the potential maximal value when water stress was considered, and for 41.6% when both water and salt stress were considered.(2) The modeled soil water and electrical conductivity of soil solution(ECsw) are in good agreement with the observations, as indicated by RMSE values(0.031 and 0.046 cm3 cm-3 for soil water content, 0.037 and 0.035 dS m-1 for ECsw, during the model calibration and validation periods, respectively). The distribution of soil water and salt were a coupled effect of boundary condition and soil physical properties.(3) Precipitation was unable to offer enough water for plant growth and leach salt out of the root zone. Furthermore, rainfall infiltration could dissolve large quantities of soluble salts from the upper layer. Though precipitation in this region is unable to provide sufficient water for plant growth, cumulative upward soil water flux that attribute to groundwater charge reached 216 mm during the growing season of 2012. Further, compared with the infiltration water from the upper boundary, the recharged water from the groundwater has a low salt concentration and can be easily utilized by plant roots. Therefore, the groundwater plays a critical role in the maintenance of Chinese tamarisk growth and water supplements.(4) Root water uptake was most sensitive to the fluctuations of water table levels. Too deep or too shallow a groundwater table was found to severely repress root water uptake. Even though shallow groundwater served as the main water resource of arid wetland, it was found to result in increased soil salinization, especially when the groundwater contains a large amount of salts(high ECsw) or the water table was too shallow.(5) Compared with no irrigation, root water uptake increased 4.5, 40.2, 79.3, 100.6 and 115.4% when the irrigation amounts were 10, 20, 30, 40 and 50 cm, respectively. This mainly due to preseason irrigation has the potential to leach salt out of the root zone and maintain the ECsw at a reduced level during the growing season which would result in increased water uptake. The average root zone ECsw dropped rapidly below 52.5, 27.7, and 13.7 dS m-1 in 15 days when the irrigation quantities were 20, 40, and 60 cm, respectively.(6) The main salts at the study point were Na2SO4 and NaCl, Na+ accounts for 70% of total cations, which led to higher Na+ content in plants caused by transpiration. Na+ accumulated more in leaves and flowers compared with other organs. As K+ is the large number necessary nutrient for plant growth, plants contain higher K+ although the K+ content in the soil is low. |
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