水保所知识产出(1956---)知识库

The timescale dependence of environmental factors’ influence on net ecosystem productivity (NEP), evapo-
transpiration (ET), and the effect of high and cool air temperature (Ta) across multiple timescales need to be
quantified to identify the response mechanisms of forest ecosystems. We analyzed NEP and ET over 11 years in a
subtropical coniferous plantation, and wavelet analysis was used to determine spectrum characteristics of these
fluxes and quantify the time lag between these fluxes and environmental factors from daily to annual timescales.
The NEP and ET had significant daily and annual spectrum variabilities, but ET exhibited a broader significant
spectrum than NEP from days to months timescales. At daily and annual timescales, NEP was significantly
synchronized with, and preceded photosynthetically active radiation (PAR) and Ta by 1. 12 ± 0.6 h and 23.16 ±
17 days, respectively. Meanwhile, ET was significantly synchronized with net radiation (Rn) at both daily and
annual timescales, lagging Rn by 1.15 ± 1.4 h, but preceding it by 5. 73 ± 4.39 days, respectively. From days to
months timescales, with no continuous significant effect, NEP preceded PAR and vapor pressure deficit (VPD),
and lagged soil water content (SW); however, ET only preceded Rn and VPD. In addition, summer high-Ta
enhanced the effect of SW on NEP and ET across multiple timescales. Early spring cool-Ta shortened the time
lag between PAR and NEP at daily and annual timescales, but only shortened it between Ta and ET at a daily
timescale. This study demonstrated the more modulating effect of SW on the dominant influence of solar energy
on NEP than ET, with timescale increased. This study also indicated that NEP and ET were more sensitive to high-
than cool-Ta, and the time lag effects of these Ta events should be considered separately to adequately
acknowledge the response mechanisms of these fluxes.