Bingran Ma

Rising atmospheric carbon dioxide (CO₂) enhances C₃ photosynthesis and often improves intrinsic water-use efficiency, yet the extent to which this physiological potential translates into durable agronomic and ecological benefits remains uncertain. This review integrates evidence from controlled environments, free-air CO₂ enrichment experiments, field studies, and modelling to evaluate the mechanisms, constraints, and applications of CO₂ fertilization. We synthesize this evidence within a cascade-filtering framework that follows carbon gain from leaf photosynthesis through whole-plant allocation, resource limitation, environmental stress, and belowground processes to realized outcomes. Three major conclusions emerge from this review. First, leaf-level photosynthetic gains are progressively attenuated by photosynthetic acclimation, source–sink limitation, nutrient shortage, and water and heat stress, so biomass and harvestable-yield responses are smaller and more variable. Second, yield gains can coincide with lower protein, iron, and zinc concentrations, making nutrient yield as important as mass yield. Third, greater carbon input belowground does not guarantee persistent soil-carbon storage because allocation, turnover, and rhizosphere priming determine retention. In controlled-environment agriculture, enrichment is most effective when CO₂ supply is coordinated with light, climate, water, nutrients, crop load, energy use, and gas delivery. Future progress requires multi-factor, multi-year, genotype-resolved studies that link physiology with nutritional quality, soil processes, modelling, life-cycle impacts, and economics.

National parks play a crucial role in promoting the achievement of the Sustainable Development Goals (SDGs) and have become one of the key topics of global concern and discussion. However, it is still unclear whether national park development can effectively enhance the level of sustainable development in local communities related to social and economic dimensions of SDGs. In this study, we constructed an evaluation system based on the SDG assessment indicator framework, to evaluate the sustainable development level of local communities within Hunan Nanshan National Park (NSNP), China. We assessed the development level of various SDG indicators through field visits and structured surveys of local communities inside and around HNNP. We used the entropy method to determine the weight of each indicator and calculated the integrated development index of different communities within and around NSNP. The results indicate the following: (1) The integrated development index of communities within NSNP is generally lower than that of the surrounding communities, but it scores higher in the dimensions of SDG1 and SDG10. (2) The integrated development index within NSNP shows the highest in communities within original natural park, but the lowest in communities within original nature reserve. (3) The structured questionnaire surveys reveal that the primary cause of income decline of residents within NSNP is the restriction on land-use and resource exploitation, while ecological compensation and employment opportunities related to national park management can help improve local livelihoods and thereby promote development level of local communities. This study provides a technical framework for assessing the sustainable development of local communities in Chinese national parks and supports regional planning. It also offers a scientific basis for balancing national park conservation with local community development.