Carbon and water fluxes are the core ecosystem processes, which is linked to diverse ecosystem services (Lian et al. 2021). Therefore, clarifying the variations and controls of ecosystem carbon and water fluxes is an effective approach to clarifying how ecosystem respond to global change in EVAs (Baldocchi 2020). As the only technique can directly measure the carbon, water and energy fluxes between vegetation and atmosphere, eddy covariance technique has been considered as a standard method for flux observations (Chen et al. 2020). By integrating long-term, eddy covariance measurements over time and space, researches are able to assess ecosystem metabolism at different time scales (hours to decades) (Forzieri et al. 2020; Han et al. 2020; Jung et al. 2017). Eddy covariance measurements also produce information on how ecosystem respond to the changes in climate, which is useful for assessing ecosystem carbon sequestration (Hu et al. 2018), water and energy balance (Forzieri et al. 2020), resource use efficiency (Liu et al. 2019) and ecosystem feedback to climate change (Huang et al. 2019; Piao et al. 2020; Yue et al. 2020). Long-term flux measurements are also vital for detecting the responses of ecosystem functions to extreme events, optimizing and validating models on regional and global scales (Baldocchi 2020). Combining with remote sensing and ecosystem modeling techniques, scientists can upscale and evaluate the functional relations between carbon and water fluxes with environmental variables at high resolution and across diverse spatial/temporal scales (Niu et al. 2017; Xia et al. 2020).

With the continual efforts from scientists in the past two decades, diverse observations facilities, especially eddy flux towers have been established to monitor ecosystem functioning in EVAs in China (Yu et al., 2006). With the data accumulated based on these observations, enhancing our knowledge of carbon and water fluxes in ecologically vulnerable areas in China become feasible. The authors of this special issue share their findings and insights on how ecosystem carbon and water fluxes at different spatial and temporal scales in EVAs in China. For example, on ecosystem carbon flux, in the water-limited grasslands in Inner Mongolia, You et al. (2022) found that leaf area index directly and soil water content indirectly affected photosynthetic parameters at the canopy scale. In a Tibetan alpine meadow ecosystem, Xu et al. (2022a) revealed that biotic factors, rather than climatic factors, dominated the interannual variations in carbon fluxes. In saline–alkaline grassland, Diao et al. (2022) found that nitrogen deposition simulated soil respiration and the effect was nitrogen compounds dependent from a 3-year field experiment. In the Bayinbuluk alpine wetland, Yao et al. (2022) used an automatic chamber system d reported that the seasonal variations of ecosystem respiration were controlled by soil temperature and water content. On ecosystem water flux, Xu et al. (2022b) reported that variations of ecosystem evapotranspiration (ET) were dominated by net radiation and air temperature and behaved energy limited in wet peak season. However, variations of ET were regulated by canopy stomatal conductance and leaf area index and were water limited in dry seasons. In a desert steppe, Du et al. (2022) found that gross primary production responded more quickly to the plant water stress than ET, which decreased water use efficiency. The large-scale afforestation should fully consider the cost of water consumption. On extreme climate, Zhang et al. (2022) conducted the Fisher discriminant model, involving soil water content and saturated vapor pressure deficit, and successfully detect drought occurrence. The publications of this special issue will largely enrich our understanding the functioning of ecosystems in vulnerable areas in China.

We are grateful to the editorial team of Journal of Plant Ecology, particularly to Wen-Hao Zhang, Bernhard Schmid and Li-Juan Liu, for giving us the opportunity to organize this special issue. The publication of this special issue would not have been possible without their support. We sincerely hope that this special issue will advance our mechanistic understanding of carbon and water functions in vulnerable ecosystems in China.