Inter-annual variation of carbon uptake by a plantation oak woodland in south-eastern England

[摘要] The carbon balance of an 80-yr-old deciduous oak plantation in thetemperate oceanic climate of the south-east of Great Britain was measured byeddy covariance over 12 yr (1999–2010). The mean annual net ecosystemproductivity (NEP) was 486 g C m⁻² yr⁻¹ (95% CI of ±73 g C m⁻² yr⁻¹), and this was partitioned into a gross primaryproductivity (GPP) of 2034 ± 145 g C m⁻² yr⁻¹, over a 165 (±6) day growing season, and an annual loss of carbon throughrespiration and decomposition (ecosystem respiration, R_eco) of 1548 ± 122 g C m⁻² yr⁻¹. Although the maximum variation ofNEP between years was large (333 g C m⁻² yr⁻¹), the ratio ofR_eco/GPP remained relatively constant (0.76 ± 0.02 CI). Someanomalies in the annual patterns of the carbon balance could be linked toparticular weather events, such as low summer solar radiation and low soilmoisture content (values below 30% by volume). The European-wideheat wave and drought of 2003 did not reduce the NEP of this woodlandbecause of good water supply from the surface-water gley soil. Theinter-annual variation in estimated intercepted radiation only accounted for~ 47% of the variation in GPP, although a significantrelationship (p < 0.001) was found between peak leaf area index andannual GPP, which modified the efficiency with which incident radiation wasused in net CO₂ uptake. Whilst the spring start and late autumn endof the net CO₂ uptake period varied substantially (range of 24 and 27 days respectively), annual GPP was not related to growing season length.Severe outbreaks of defoliating moth caterpillars, mostly Tortrix viridana L. and Operophtera brumata L., causedconsiderable damage to the forest canopy in 2009 and 2010, resulting inreduced GPP in these two years. Inter-annual variation in the sensitivity ofR_eco to temperature was found to be strongly related to summer soilmoisture content. The eddy covariance estimates of NEP closely matchedmensuration-based estimates, demonstrating that this forest was asubstantial sink of carbon over the 12-yr measurement period.

[学科分类] 地球化学与岩石