Carbon and greenhouse gas balances in an age sequence of temperate pine plantations

[摘要] This study investigated differences in the magnitude and partitioning of thecarbon (C) and greenhouse gas (GHG) balances in an age sequence of four whitepine (Pinus strobus L.) afforestation stands (7, 20, 35 and 70 yearsold as of 2009) in southern Ontario, Canada. The 4-year (2004–2008) meanannual carbon dioxide (CO₂) exchanges, based on biometric and eddycovariance data, were combined with the 2-year means of static chambermeasurements of methane (CH₄) and nitrous oxide (N₂O) fluxes(2006–2007) and dissolved organic carbon (DOC) export below 1 m soil depth(2004–2005). The total ecosystem C pool increased with age from 46 to197 t C ha⁻¹ across the four stands. Rates of organic matter cycling(i.e. litterfall and decomposition) were similar among the three olderstands. In contrast, considerable differences related to stand age and sitequality were observed in the magnitude and partitioning of individualCO₂ fluxes, showing a peak in production and respiration rates in themiddle-age (20-year-old) stand growing on fertile post-agricultural soil. TheDOC export accounted for 10% of net ecosystem production (NEP) at the7-year-old stand but <2% at the three older stands. The GHG balancefrom the combined exchanges of CO₂, CH₄ and N₂O was 2.6, 21.6,13.5 and 4.8 t CO₂ equivalent ha⁻¹ year⁻¹ for the 7-, 20-,35- and 70-year-old stands, respectively. The maximum annual contributionfrom the combined exchanges of CH₄ and N₂O to the GHG balance was13 and 8% in the 7- and 70-year-old stands, respectively, but<1% in the two highly productive middle-age (20- and 35-year-old)stands. Averaged over the entire age sequence, the CO₂ exchange was themain driver of the GHG balance in these forests. The cumulative CO₂sequestration over the 70 years was estimated at 129 t C and297 t C ha⁻¹ year⁻¹ for stands growing on low- andhigh-productivity sites, respectively. This study highlights the importanceof accounting for age and site quality effects on forest C and GHG balances.It further demonstrates a large potential for net C sequestration and climatebenefits gained through afforestation of marginal agricultural and fallowlands in temperate regions.

[学科分类] 地球化学与岩石