# Influences of Extreme Weather Conditions on the Carbon Cycles of Bamboo and Tea Ecosystems
## 3 Results and Discussion
### Influences of Climate and Land Use on the Carbon Cycle  
The substantial differences in annual precipitation between 2015-2017 and drought in August 2016 provided a valuable opportunity to analyze the influences of climate and extremely dry events on the C cycle. The annual precipitation amounts were 1720 and 2251 mm in 2015 and 2016, respectively, and the precipitation in 2017 was 1349 mm. Therefore, 2015 and 2016 were considered to be wet and extremely wet years, respectively, while 2017 was near-normal conditions, considering the multi-year average precipitation of 1157 mm. The modeled annual mean GPP values at the bamboo (tea) plot were 4.80 (5.21), 4.33 (4.71), and 4.57 (5.07) \(\upmu\)mol m\({}^{-2}\) s\({}^{-1}\) in 2015, 2016, and 2017, respectively (Figure 10 and Figure S6). The plentiful rainfall in 2016 (2251 mm) did not increase the GPP compared with 2015 (1720 mm) and 2017 (1349 mm). This may have been due to sufficient water during normal years for plant growth in the study area; therefore, additional water does not substantially stimulate plant growth. Figure 9: Correlations between observed air temperature and soil respiration at bamboo (panels (**a–d**): sites B1–B4) and tea (panels (**e–h**): sites T1–T4) plots. Both air temperature and soil respiration were observed between 9:00–11:00 Dots in squares were soil respirations that were observed during the dry August of 2016. The modeled GPP values at the bamboo (tea) plot were 6.18 (6.48), 3.91 (3.92), and 5.31 (5.65) \(\upmu\)mol m\({}^{-2}\) s\({}^{-1}\) between August-October in 2015, 2016, and 2017, respectively (Figure 10 and Figure S6), indicating that the extremely dry August in 2016 reduced the GPP during August-October, despite high precipitation in September and October in 2016 (717 mm) (Figure 10a). The MODIS GPP product also illustrated the reducing impact of drought on the GPP during August-October (shown in the grey rectangle in Figure 7a). Overall, the results indicated that the modeled GPP was not sensitive to extremely wet weather conditions but was sensitive to short periods (August 2016) of extremely dry weather conditions. The drought in August 2016 caused marked decreases in GPP in August and the following two months (Figure 10a), while the modeled LAI was less affected (Figure S5), consistent with observations from other studies. For example, [PERSON] et al. (2016) reported that extreme drought in Hesse, France,  
Figure 10: Modeled monthly carbon fluxes at the two study plots. (**a**) AR, autotrophic respiration; (**b**) ER, ecosystem respiration; (**c**) GPP, gross primary production; (**d**) NEE, net ecosystem exchange; (**e**) NPP, net primary production. caused a three-year reduction in GPP in a beech forest, even though the state of the forest remained unaltered (i.e., no browning or defoliation occurred). The monthly NEE with an absolute value greater than 0.50 \(\upmu\)mol m\({}^{-2}\) s\({}^{-1}\) was defined as CO\({}_{2}\) emissions or absorption in this study. CO\({}_{2}\) absorption mainly occurred within (2015) or around (2016 and 2017) spring (March-May), and CO\({}_{2}\) emissions mainly occurred in autumn (September-November) and winter (December-February). The tea plot acted as a strong CO\({}_{2}\) emission source during the drought in August 2016 and in the following two months (Figure 10e). Both plots acted as CO\({}_{2}\) sinks (negative NEE) in 2015 and 2017, with a mean annual NEE of \(-\)0.06 (\(-\)0.15) and \(-\)0.13 (\(-\)0.26) \(\upmu\)mol m\({}^{-2}\) s\({}^{-1}\) at the Bamboo (tea) plot, respectively. In contrast, both plots acted as a CO\({}_{2}\) source (positive NEE) in 2016, with a mean annual NEE of 0.18 and 0.29 \(\upmu\)mol m\({}^{-2}\) s\({}^{-1}\), respectively. The increase in C emissions into the atmosphere after the extreme drought in 2016 (positive NEE; Figure 10e) from the modeling results was consistent with the existing understanding that extreme droughts reduce terrestrial C sinks [41].