Delimiting important ecological conservation areas is critical for ecological integrity, sustainability of the ecological service function, and management of environmental degradation. However, the process of defining important areas for ecological protection purposes is elusive, especially in the Qinghai Province of China, which is home to unique ecosystems. To address this issue, we selected biodiversity (endangered mammals, birds, and plants), soil retention, water storage, and carbon sequestration to define and delimit important areas for the protection of these ecosystem functions. We found that the important endangered birds of Qinghai Province were mainly distributed in the eastern and southern parts, while important endangered plants were relatively centralized, with relatively high distribution in the Golog of Qinghai Province. The total amounts were 2.245 billion tons, 46.513 billion m³, and 60.91 Tg for soil retention, water storage, and carbon sequestration in Qinghai ecosystems, respectively. Soil retention and carbon sequestration presented a similar trend, with high levels in the eastern and low levels in the western parts of Qinghai, while water storage was higher in the south than in the north. Among various ecosystem types, the grassland ecosystem was the main body of soil retention, water retention, and carbon sequestration; soil retention, water retention, and carbon sequestration were quite small in the desert, town, and city ecosystems. By evaluating the spatial distribution of the service functions of ecosystems, we found that extremely important areas of the ecosystem service function in Qinghai Province totaled 247,200 square kilometers, and the important areas summed to 124,500 square kilometers. Combined extremely important and important areas of the ecosystem service function reached 371,700 square kilometers and accounted for 53.36% of the total area of Qinghai. The ecological protection red line has now become an important national strategy for ecological protection. The demarcation of the ecological protection red line has great significance in safeguarding Qinghai’s ecological security. It is the basic guarantee for sustainable economic and social development in China.

Human activities have increased the imbalance in atmospheric N and P deposition, which changes soil nutrient availability and subsequently affects the structure and function of terrestrial ecosystems. Dioecious plants are important parts of terrestrial ecosystems and are characterized by sex-related differences in their response to the external environment and always exhibit a skewed sex ratio, which makes them more vulnerable to climate change and increases their risk of extinction. However, little attention has been paid to the effects of unbalanced N and P deposition on these plants, especially on their defense traits. In this study, we used dioecious Populus cathayana to investigate the influence of gradient N and P deposition on the correlation between growth and defense traits. The results showed that although the different rates of N and P deposition enhanced biomass accumulation in both sexes to varying degrees, the most substantial biomass increment was noted under a lower-nitrogen and higher-phosphorus (LNHP) treatment regimen, with females showing an approximately 112% increase and males a 47% increase in total biomass. In response to varying levels of simulated N and P deposition, males and females adopt distinct strategies for biomass allocation. Although declines in root biomass were observed in both sexes as nutrient availability increased, the decrement was more marked in males; under the LNHP treatment, it dropped by about 11%, while under a high-nitrogen and high-phosphorus (HNHP) treatment, the decrease was about 35%. Conversely, females demonstrated a heightened propensity to allocate biomass towards leaf development. Furthermore, with increasing N and P deposition, there was a general reduction in the concentrations of physical and chemical defense substances within the leaves of both sexes. Nonetheless, the correlations between defense substances, nutrient element content, non-structural carbohydrate (NSC) content, and dry biomass were more pronounced in males, suggesting a greater sensitivity to defense substance responses in males than in females. Overall, these results indicate that there is sexual dimorphism in the accumulation of chemical substances in male and female P. cathayana under unbalanced N and P deposition and they provide a technical and theoretical basis for predicting the population dynamics of dioecious plants, maintaining the stability of poplar populations, and constructing high-productivity poplar plantations globally in the future.