CH4 and N2O fluxes from planted forests and native Cerrado ecosystems in Brazil

ABSTRACT Forest soils are N2O sources and commonly act as CH4 sinks. This study evaluated the dynamics of the CH4 and N2O fluxes of soils under Eucalyptus plantations and native Cerrado vegetation, as well as possible interactions between environmental factors and fluxes. The study was carried out in the Distrito Federal, Brazil, during 26 months, in three areas: in two stands of the hybrid Eucalyptus urophylla × Eucalyptus grandis, planted in 2011 (E1), and in 2009 (E2) and native Cerrado vegetation (CE). Measurements to determine the fluxes in a closed static chamber were carried out from Oct 2013 to Nov 2015. Soil and climate factors were monitored. During the study period, the mean CH4 fluxes were –22.48, –8.38 and –1.31 μg CH4 m–2 h–1 and the mean N2O fluxes 5.45, 4.85 and 3.85 μg N2O m–2 h–1 from E1, E2 and CE, respectively. Seasonality affected plantations in the studied sites. Cumulative CH4 influxes were calculated (year-1: –1.86 to -0.63 kg ha–1 yr–1; year-2: –1.85 to –1.34 kg ha–1 yr–1). Cumulative N2O fluxes in the three sites were ≤ 0.85 kg ha–1 yr–1. The change in land use from Cerrado to Eucalyptus plantations did not significantly changed regarding greenhouse gases (GHG), compared to the native vegetation. Flux rates of both gases (N2O and CH4) were low. Temporal variations in GHG fluxes and different ages of the stands did not cause significant differences in cumulative annual fluxes.

摘要：森林土壤是一氧化二氮（N₂O）的排放源，同时通常充当甲烷（CH₄）的汇。本研究针对桉树（Eucalyptus）人工林与原生塞拉多（Cerrado）植被下土壤的CH₄与N₂O通量动态，以及环境因子与通量间的潜在相互作用展开评估。本研究于巴西联邦特区（Distrito Federal）开展，为期26个月，共设置3个样地：2个分别于2011年（E1）与2009年（E2）栽植的尾叶桉×巨桉（Eucalyptus urophylla × Eucalyptus grandis）杂交桉人工林样地，以及1处原生塞拉多植被样地（CE）。采用静态密闭箱法于2013年10月至2015年11月间开展通量测定，并同步监测土壤与气候因子。研究期内，E1、E2与CE样地的CH₄平均通量分别为–22.48、–8.38与–1.31 μg CH₄·m⁻²·h⁻¹，N₂O平均通量分别为5.45、4.85与3.85 μg N₂O·m⁻²·h⁻¹。季节动态对研究样地内的人工林存在显著影响。研究计算得到年累积CH₄吸收量：第1年为–1.86 ~ –0.63 kg·ha⁻¹·yr⁻¹，第2年为–1.85 ~ –1.34 kg·ha⁻¹·yr⁻¹；3个样地的年累积N₂O通量均≤0.85 kg·ha⁻¹·yr⁻¹。相较于原生植被，由塞拉多植被改造为桉树人工林的土地利用变化，并未对温室气体（GHG, Greenhouse Gas）排放产生显著影响。两种气体的通量速率均处于较低水平。温室气体通量的时间变异与林分树龄差异，均未对年累积通量造成显著影响。