| Summary: | Water is a crucial factor affecting plant growth and ecosystem processes. In the subtropical region, global climate change leads to frequent seasonal droughts. How plant water strategies and the adaptability of forest ecosystems change is an urgent issue to be discussed. In this study, four sample plots (<i>P. massoniana</i> for Plot 1, <i>C. lanceolata</i> for Plot 2, <i>Q. acutissima</i> for Plot 3, <i>C. funebris</i> and <i>I. corallina</i> for Plot 4) were selected in the Taizishan Mountain area of Hubei, China, including three forest types (coniferous forest, broad-leaved forest and coniferous broad-leaved mixed forest) and five dominant tree species. The <i>δD</i> and <i>δ</i><sup>18</sup><i>O</i> isotope compositions in plant and soil water were analysed, and the water use strategies of dominant species were predicted by using the MixSIAR model. The water absorption depth and proportion of the five species were significantly different in different seasons. In plot 4, <i>I. corallina</i> and <i>C. funebris</i> derived (58.8 ± 14.0% and 55.7 ± 23.4%, respectively) water from 10–40 cm soil in wet season, but <i>C. funebris</i> shifted to derive water from deep soil in dry season. This result indicates that the mixing of <i>C. funebris</i> and <i>I. corallina</i> can effectively prevent water competition in dry season with water deficit. From wet season to dry season, the depth of water utilisation of the <i>P. massoniana</i>, <i>C. lanceolata</i>, <i>Q. acutissima</i> and <i>C. funebris</i> with deep roots converted from shallow to deep soil, suggesting that the four species had significant dimorphic root systems and strong ecological plasticity.
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