Under the more frequent and extreme global drought events, utilizing stable isotopes to quantify soil evaporation losses ( SEL) is of great significance for understanding the water supply capacity from soil to plants. From March 2017 to September 2019, we continuously monitored meteorological factors, soil temperature and humidity, and collected precipitation and soil water stable isotope data. Used the Craig-Gordon (C-G) model and the line-conditioned excess (lc-excess) couple with Rayleigh fractionation (RL) model to quantify SEL in subtropical secondary forests. The results showed: (1) The theoretical Evaporation Line (EL) slope correlated negatively with air temperature ( AT). Water source isotopic values were more positive in autumn and more negative in spring. The aridity index ( AI) and soil evaporation loss ratio ( f) from both models indicated drier conditions from March to September 2018 compared to 2017 and 2019; (2) Comparative analysis showed the C-G model agreed more closely with measured evapotranspiration ( ET0) and water surface evaporation ( E) than the RL model, indicating its better suitability for the study region; (3) Because the “inverse temperature effect” of the precipitation isotopes, the linear fitting method was not suitable for determining the water source in spring, summer, autumn, and on the annual scale, while the EL slope obtained by the fitted slope was consistent with the basic principle of soil evaporation in winter. Thus, the theoretical method was more suitable for determining the EL slope in such regions; (4) because the different fundamentals, the C-G model was positively correlated with air temperature and negatively with relative humidity ( h), while the RL model showed the opposite, indicating different applicability. Meanwhile, SEL is influenced by soil thickness, atmospheric evaporation, and soil water supply capacities. These findings support using stable isotope techniques to quantify SEL and are important for analyzing soil water resources in subtropical secondary forests.

Knowledge about the ecological patterns of abundant and rare bacteria in regulated river ecosystems, especially with respect to their community traits, is an important but poorly investigated subject. In this study, we examined the community assembly of abundant and rare bacteria, as well as their environmental adaptation, across complex environmental gradients in sediments of the Yarlung Tsangpo River on the Tibetan Plateau. Results showed that abundant taxa exhibited broader environmental thresholds and stronger phylogenetic signals for ecological traits than rare taxa. In contrast, rare taxa were more sensitive to environmental changes and showed stronger phylogenetic clustering. Although both subcommunities exhibited significant distance-decay patterns, the abundant subcommunity was governed primarily by dispersal limitation, while the rare subcommunity was strongly driven by heterogeneous selection. The similar distribution patterns but contrasting assembly mechanisms affecting abundant and rare subcommunities resulted from the differences in environmental adaptation. Forest area and total nitrogen were key factors in determining the stochastic and deterministic assembly for abundant and rare subcommunities, respectively. Additionally, rare taxa might play potential roles in maintaining network stability, although they were less connected and located more peripherally within the network. Collectively, our study provides a new perspective for the ecological significance of abundant and rare bacteria in fluvial sediments, and facilitates the prediction of microbial responses to ongoing environmental changes in the Yarlung Tsangpo River.