Multi-temporal scale analysis of impacts of extreme high temperature on net carbon uptake in subtropical coniferous plantation.

Extreme high temperature is one of important extreme weathers that impact forest ecosystem carbon cycle. In this study, applying CO₂ flux and routine meteorological data measured during 2003-2012, we examined the impacts of extreme high temperature and extreme high temperature event on net carbon uptake of subtropical coniferous plantation in Qianyanzhou. Combining with wavelet analysis, we analyzed environmental controls on net carbon uptake at different temporal scales, when the extreme high temperature and extreme high temperature event happened. The results showed that mean daily cumulative NEE decreased by 51% in the days with daily maximum air temperature range between 35 °C and 40 °C, compared with that in the days with the range between 30 °C and 34 °C. The effects of the extreme high temperature and extreme high temperature event on monthly NEE and annual NEE related to the strength and duration of extreme high temperature event. In 2003, when strong extreme high temperature event happened, the sum of monthly cumulative NEE in July and August was only -11.64 g C ⋅ m^-2 ⋅ (2 month)^-1. The value decreased by 90%, compared with multi-year average value. At the same time, the relative variation of annual NEE reached -6.7%. In July and August, when the extreme high temperature and extreme high temperature event occurred, air temperature (T_a) and vapor press deficit (VPD) were the dominant controller for the daily variation of NEE. The coherency between NEE & T_a and NEE & VPD was 0.97 and 0.95, respectively. At 8-, 16-, and 32-day periods, T_a, VPD, soil water content at 5 cm depth (SWC), and precipitation (P) controlled NEE. The coherency between NEE & SWC and NEE & P was higher than 0.8 at monthly scale. The results indicated that atmospheric water deficit impacted NEE at short temporal scale, when the extreme high temperature and extreme high temperature event occurred, both of atmospheric water deficit and soil drought stress impacted NEE at long temporal scales in this ecosystem. [ABSTRACT FROM AUTHOR]