## 3 Results
### GPP and NPP  
We estimated separately and in combination the impacts of precipitation, temperature, and CO\({}_{2}\) concentration under four different RCP scenarios (RCP2.6, RCP4.5, RCP6.0, and RCP8.5) on the GPP and NPP of _Pinus densiflora_ (Figure 3). An increase in precipitation was projected in all seasons, with larger increases in higher greenhouse gas emission scenarios (Table 1). For the scenario of precipitation change alone, our results showed that changes in precipitation did not considerably alter GPP and NPP compared to baseline (Figure 3, first column). The percentage changes of GPP and NPP under climate change scenarios compared to baseline were less than 0.2%. At a first glance, water availability would not be a limiting factor to the rate of _Pinus densiflora_ photosynthesis and soil respiration. However, the small changes in GPP and NPP were indeed caused by the balance between two opposite effects: (i) reduced oxygen in the root zone, which lowered nutrient uptake and thus photosynthesis, and (ii) improved photosynthesis and respiration under well-watered conditions.  
For the scenario of temperature change alone, slight changes in GPP of \(-0.69\%\), \(-0.23\%\), \(-0.48\%\), and \(0.89\%\) under RCP 2.6, 4.5, 6.0, and 8.5, respectively, were modeled compared to baseline (Figure 3, second column). The potential improvement of photosynthesis due to increased kinetic energy under elevated temperature was offset by increased water stress. Warming led to an increase in the energy used to support evaporation, thereby leading to water-limited environments. With the rising temperature, an increase in stomatal conductance decreased the leaf water potential and growth of _Pinus densiflora_. That is, the benefits of elevated temperature for photosynthesis were offset by water stresses. For NPP dynamics under temperature change only, we modeled decreases in NPP of \(-9.89\%\), \(-11.69\%\), \(-9.75\%\), and -13.87% under RCP 2.6, 4.5, 6.0, and 8.5, respectively, compared to baseline. Mean annual temperatures were projected to increase by 1.2, 1.56, 1.29, and 2.14 \({}^{\circ}\)C under RCP 2.6, 4.5, 6.0, and 8.5, respectively, compared to baseline. That is, there was an approximately 7% reduction of NPP per degree celsius increase in temperature. These results were obtained through the positive influence of temperature on plant and microbial respiration, leading to reduced NPP.  
For the scenario of CO\({}_{2}\) change alone, the improvements of GPP and NPP were modeled compared to baseline (Figure 3, third column). There was a positive relationship between CO\({}_{2}\) concentration and photosynthesis rate due to CO\({}_{2}\) fertilizer effects, as expected. However, we noted that elevated CO\({}_{2}\) also stimulated soil respiration from increased litter inputs into the soil (explained in further detail in Section 3.3). The ratios of NPP to GPP were 0.5059, 0.5142, 0.5157, and 0.5205 under RCP 2.6, 4.5, 6.0, and 8.5, respectively.  
When all of the climate variables were considered together, which included changes in precipitation, temperature, and atmospheric CO\({}_{2}\) concentration, increases in GPP of 5.51%, 10.85%, 12.16%, and 19.74% under RCP2.6, 4.5, 6.0, and 8.5, respectively, were modeled compared to baseline (Figure 3, fourth column). We noted that the sums of changes in GPP under the individual climate change scenarios were 4, 7, and 12% smaller than those under all-considered RCP 2.6, 4.5, and 8.5, respectively. The corresponding case for RCP6.0 was not considerably different (due to relatively small changes in precipitation). That is, the beneficial influences of elevated CO\({}_{2}\) on the GPP of _Pinus densiflora_ were not fully restored due to nutrient limitations. Increases in precipitation during growing seasons under climate change scenarios (see Table 1) caused increased nutrient leaching and thus reduced nutrient uptake. Higher NPP was modeled as climate change scenarios become more pronounced in responses to GPP dynamics under climate change.