## 1 Introduction
[20] observed an overall increasing trend in WUE across the Loess Plateau over the past 15 years, with intra-annual WUE in different vegetation ecosystems predominantly exhibiting a \"bimodal\" distribution, with peaks observed in April-May and September-October. These findings revealed the spatiotemporal variability of vegetation CUE and WUE across regions, ecosystems, and time scales, shaped by regional climate, vegetation types, and human impacts. Despite advancements in understanding regional dynamics of CUE and WUE, critical knowledge gaps remain. Specifically, there is a lack of comprehensive investigations into the spatiotemporal interactions between CUE and WUE within the same region, particularly across diverse plant functional types. Furthermore,their responses to climate change, including feedback mechanisms and implications for carbon-water coupling, remain insufficiently explored. Prior research indicates that vegetation CUE and WUE exhibit high sensitivity to environmental and climatic variations [15; 17]. [PERSON] et al. [21] revealed that temperature has an inverse relationship with CUE in global carbon utilization, while precipitation shows a direct relationship with CUE. Temperature identified as the primary driving factor of CUE in alpine environments [22]. In contrast, in Heilongjiang, both vegetation CUE and WUE exhibited a positive relationship with temperature and an inverse relationship with precipitation [23]. In high-altitude regions, an increase in both precipitation and temperature enhanced vegetation WUE [24]. However, vegetation WUE exhibits a negative feedback response to temperature and precipitation under arid conditions [25]. Most of these studies are limited to examining the response of a single indicator (CUE or WUE) to climate at a regional scale, with little attention given to the CUE and WUE in the subtropical region of South China and their responses to climate variability. In addition, the carbon dioxide fertilization effect [6], nitrogen deposition [26], and vegetation greening degree [27] may affect the carbon sequestration potential of the ecosystem and the water cycle process, thereby affecting carbon and water utilization efficiency. [PERSON] et al. [28] found that decrease in WUE may be associated with ecosystem degradation, while ecosystem restoration tends to enhance WUE. Prior research has demonstrated the high sensitivity of vegetation CUE and WUE to environmental and climatic variations, highlighting complex and region-specific responses, while underscoring the need for more comprehensive studies in subtropical regions to address knowledge gaps regarding their spatiotemporal dynamics and interactions with climate variability and ecosystem changes. The Nanling Mountains Region (NMR), located in southern China, serves as a critical ecological barrier and biodiversity hotspot, connecting the eastern and western parts of China's subtropical zone. The region is characterized by complex topography, high climatic heterogeneity, and diverse vegetation types. However, the region is highly vulnerable to climate change, with recent decades witnessing increasing temperatures, altered precipitation patterns, and extreme weather events. In recent years, the NMR has undergone varying degrees of degradation, with degraded areas accounting for 31.78% of the total region [29]. Yet, studies on the factors influencing CUE and WUE in degraded mountain ecosystems remain limited, and it is still unclear how the CUE and WUE of various land use types in degraded mountain regions respond to global warming. Compared to previous studies, this study integrates remote sensing data with analytical methods such as linear regression, trend analysis, Hurst exponent analysis, and stability analysis to examine the spatiotemporal dynamics of CUE and WUE in the NMR, focusing on vegetation type differences and their climatic responses.