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 森林土壤是氧化亚氮（N₂O）的排放源，同时通常作为甲烷（CH₄）的汇。本研究针对人工桉树林与原生塞拉多（Cerrado）植被下土壤的甲烷、氧化亚氮通量动态，以及环境因子与通量间的潜在关联展开评估。本研究于巴西联邦特区开展，历时26个月，设置三个试验区域：分别为2011年栽植的尾叶桉×巨桉杂交林分（E1）、2009年栽植的尾叶桉×巨桉杂交林分（E2），以及原生塞拉多植被区（CE）。采用密闭静态箱法开展通量测定，测定时段为2013年10月至2015年11月，并同步监测土壤与气候因子。研究期间，E1、E2与CE的甲烷平均通量分别为-22.48、-8.38与-1.31 μg CH₄·m⁻²·h⁻¹，氧化亚氮平均通量分别为5.45、4.85与3.85 μg N₂O·m⁻²·h⁻¹。季节性变化对试验区域内的人工桉树林产生显著影响。累计甲烷吸收通量经计算可得：第一年为-1.86至-0.63 kg·ha⁻¹·yr⁻¹，第二年为-1.85至-1.34 kg·ha⁻¹·yr⁻¹。三个试验区域的累计氧化亚氮通量均≤0.85 kg·ha⁻¹·yr⁻¹。与原生植被相比，由塞拉多植被改造为人工桉树林的土地利用方式，并未对温室气体（GHG）通量产生显著影响。两种温室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年龄差异，均未对累计年通量产生显著影响。