Autumn temperature and carbon balance of a boreal Scots pine forest in Southern Finland

[摘要] We analyzed the dynamics of carbon balance components: gross primaryproduction (GPP) and total ecosystem respiration (TER), of a boreal Scotspine forest in Southern Finland. The main focus is on investigations ofenvironmental drivers of GPP and TER and how they affect the inter-annualvariation in the carbon balance in autumn (September–December). We used standardclimate data and CO₂ exchange measurements collected by the eddycovariance (EC) technique over 11 years. EC data revealed that increasingautumn temperature significantly enhances TER: the temperature sensitivitywas 9.5 gC m⁻² °C⁻¹ for the period September–October (earlyautumn when high radiation levels still occur) and 3.8 gC m⁻² °C⁻¹for November–December (late autumn with suppressed radiationlevel). The cumulative GPP was practically independent of the temperature inearly autumn. In late autumn, air temperature could explain part of thevariation in GPP but the temperature sensitivity was very weak, less than 1 gC m⁻² °C⁻¹.Two models, a stand photosynthesis model (COCA)and a global vegetation model (ORCHIDEE), were used for estimating stand GPPand its sensitivity to the temperature. The ORCHIDEE model was testedagainst the observations of GPP derived from EC data. The standphotosynthesis model COCA predicted that under a predescribed 3–6 °Ctemperature increase, the temperature sensitivity of 4–5 gC m⁻² °C⁻¹in GPP may appear in early autumn. The analysis by the ORCHIDEEmodel revealed the model sensitivity to the temporal treatment ofmeteorological forcing. The model predictions were similar to observed oneswhen the site level 1/2-hourly time step was applied, butthe results calculated by using daily meteorological forcing, interpolatedto 1/2-hourly time step, were biased.This is due to the nonlinear relationship between the processes and theenvironmental factors.

[学科分类] 地球化学与岩石