## 4 Discussion  
Climate change is already ongoing and more change is expected. Climate change mitigation is thus, and will continue to be, a major concern for human beings in the next decades [30; 43]. Several studies have demonstrated the essential role of maintaining and planting trees as a way of tackling climate change [9; 18; 44]. However, there were still debates on whether the benefits of CO\({}_{2}\) fertilizer effects on GPP and NPP were offset by the negative influences of increased temperatures and changes in precipitation, such as heat stress and drought [45; 46; 47]. Elevated temperature reduced soil moisture and triggered stomatal closure due to increases in transpiration, leading to negative impacts on the growth of _Pinus densiflora_, which could be compensated by elevated CO\({}_{2}\), as shown in free air CO\({}_{2}\) enrichment (FACE) studies [16; 48; 49; 50]. In this study, to explore interactions between climate change and forests, we studied separately and in combination the impacts of climate change on the growth of _Pinus densiflora_ for the case of a research forest in South Korea. Our results demonstrated that the stimulated photosynthetic CO\({}_{2}\) fixation and water use efficiency of _Pinus densiflora_ due to elevated CO\({}_{2}\) outweighed temperature  
Figure 7: Projected water use efficiency for the scenario of (**a**) precipitation change alone, (**b**) temperature change alone, (**c**) CO\({}_{2}\) change alone, and (**d**) all together under RCP 2.6 (blue), 4.5 (red), 6.0 (green), and 8.5 (orange) for the 2050s (from 2036 to 2065) compared with baseline. Shaded areas represent the 25 th to 75 th percentile intervals. The variables at baseline are shown in dashed lines. and precipitation-driven decreases in GPP and NPP. We also found that, at the study site, increases in the GPP and NPP of _Pinus densiflora_ were modeled as climate change scenarios became severe. These results indicated that _Pinus densiflora_ could serve as a carbon buffer against climate change. Soil N2O flux and nitrogen leaching have been important concerns associated with climate change [30; 51]. This is mainly because N2O has, on an equivalent mass basis, a greenhouse gas 300 times more potent than CO2, although the concentration of atmospheric N2O is much lower than that of CO2. Nitrogen leaching also causes serious environmental damage, such as infant methemoglobin and eutrophication [30; 52; 53]. Several studies have noted that increases in precipitation and temperature would lead to increases in soil N2O emissions and nitrogen leaching due to enhanced subsurface water flux and organic matter decomposition, respectively [54; 55]. In line with previous studies, our results also showed that soil N2O emission and nitrogen leaching would reduce as the intensity of climate change scenarios increased. Elevated atmospheric CO2 stimulated the growth of _Pinus densiflora_ and thus increased nitrogen uptake, leading to a decrease in soil inorganic nitrogen. Previous studies noted that changes in precipitation and temperature due to climate change resulted in increases in evapotranspiration [56; 57; 58]. Improved soil water availability and molecule kinetic energy due to warming led to an increase in evapotranspiration rates. In line with the findings, our results also showed that elevated atmospheric CO2 decreased evaporation, but increased transpiration. The elevated CO2 stimulated the growth of _Pinus densiflora_, leading to increases in water uptake and thus decreases in soil moisture available for evaporation. Although water loss through evapotranspiration increased under climate change, we found improvements in the water use efficiency of _Pinus densiflora_ induced by elevated CO2-induced stomatal closure. There are still debates on whether planting and maintaining trees will act as a pivotal role in mitigating climate change [18; 23; 24].