Abstract: Background, aim, and scope Soil water is the critical matter in crops and plant recovering, thus is has significant value in environment research. In previous study, rain water has been proved that it is one of main sources of soil water and rain water, which can be used to measure the procedure of infiltration, evaporation and mixture of soil water in soil. In recent years, there are many studies which claim that the biomarker δD in geological carrier (such as soil and lake sediment) can be used to reconstruct palaeoenvironment and paleoecology etc., especially it is important for rebuilding the ancient precipitation. In addition, recent studies are mainly focused on the relationship between leaf wax δD and precipitation δD, few of them concern with soil water δD. Soil water δD generally comes from precipitation, nevertheless, it has differences comparing with precipitation δD. Therefore, the research of soil water δD may cause significant influences to the comprehension of the constitution changes of leaf wax hydrogen isotope from terrestrial plants. The propose of this study is to analyze soil δD from precipitation and other factors (such as latitude) by investigating the topsoil water δD from different latitude systematically. Also to provide understanding of environmental effects to the research of leaf wax hydrogen isotope of terrestrial plant in mechanism aspect. Materials and methods We collected 43 topsoil samples from south to northwest parts of China (20°N — 51°N) in the rain season, 2016. Following that, we analyzed the soil samples to obtain the soil water δD. Soil water samples were collected by using vacuum distillation. Stable isotopic composition of liquid water was determined by using a Liquid Water Isotope Analyzer Picarro L2130-I (Picarro, Inc., Sunnyvale, CA, USA). Results (1) Precipitation δD has latitude effects, in comparison, soil water δD also has latitude effect. (2) The soil water δD and precipitation δD in different latitudes have positive correlation (R2 = 0.40, p＜0.01). Discussion (1) Soil water δD and precipitation δD have positive linear correlation (R2 = 0.40). It proves that precipitation is the one of main sources of soil water, which is consistent with previous studies. (2) Previous studies illustrate that soil water δD and altitude have negative correlation. (3) The isotope constitution of soil water has correlation with plant cover and soil water evaporation. (4) It is more effective to rebuild paleoenvironment by comparing plant δD and soil water δD. Conclusions (1) The change of soil water δD can record the signal of precipitation, their δD both have negative correlation with latitude. (2) Precipitation is one of main sources of soil water. Precipitation water δD and soil water δD have good linear fitting but there are also some other factors which affect the data. Our study shows that altitude, evaporation and plant cover are the major influence factors, which is consistent with previous study. There are still some other factors are waiting for further research. (3) It is more effective to rebuild paleoenvironment by comparing plant δD and soil water δD. Recommendations and perspectives (1) Our samples were collected in August and September, which belong to rain season (June to September). Consequently, this result shows the relation between precipitation and soil water in rain season in some extent. In addition, it has shortcomings since we lack of the data from June and July. The characteristic of whole rain season is planning to be completed in the future study. (2) In future research, focusing on the comparison of the δD value of leaf wax and the δD value of soil water will help to reducethe error.
Keywords: hydrogen isotope; soil water; precipitation; latitude