This dissertation has three chapters. Chapter 1 examines nutrient resupply patterns during decomposition in forest ecosystems, including tropical, temperate, and boreal, through meta-analysis. The hypothesis tested is that C, N, and P follow different prototypes in mineralization and be affected by the mean annual temperature and precipitation of sites. Results show that P will be preferentially released compared with C in mineralization, while C and N are coupled and released together. And C is more obviously affected by the higher the mean annual temperature (MAT), the higher the mineralization rate. C shows a significant increase in the mineralization rate with increasing temperatures. At the same time, N and P are not as strong as C. Thus, global climate change will aggravate the loss of C, further worsening the greenhouse effect. However, mean annual precipitation (MAP) has no significant effects on it. Chapter 2 analyzes the nutrient (N and P) use efficiency, global fertilizer uses for 2015, and predictions for the year 2050 using models and scenario analysis. Country-level nutrient use efficiency was calculated based on crop yield and total nutrient inputs for each country, and global heterogeneity was studied. Five scenarios were applied for 2050 fertilizer demand prediction: business as usual (BAU), climate change mitigation, nutrient use efficiency improvement, dietary shift, and all methods. Results showed that some countries in Africa and South America have abnormally high nutrient use efficiency, which indicates nutrient mining. Generally, nutrient use efficiency is higher in developed countries and lower in developing countries. For fertilizer use, by the year 2050, even population grows over 30 percent, with all scenarios applied, the fertilizer use can still reduce while feeding the population. Chapter 3 studies technology and management that can increase the nutrient (N and P)use efficiency, and did a meta-analysis and scenario analysis. Meta-analysis results were applied as nutrients use efficiency increasing scenario to fertilizer application in the year 2050. The results show that technologies and management can reduce future fertilizer demand. If combined with the scenarios in Chapter 2, the fertilizer demand in 2050 can be even less than in 2015.