Daily GHG fluxes from a subtropical rainforest. Mooloolah, Queensland, 2007-2009 [ARC Discovery]

Soil-atmosphere exchange of CO2, CH4 and N2O was measured over two consecutive years from a subtropical rainforest in South-Eastern Queensland, Australia using an automated sampling system. Interannual variation in fluxes of all gases over the 2 years was minimal despite large discrepancies in rainfall, while a pronounced seasonal variation could only be observed for CO2 fluxes. High infiltration, drainage and subsequent high soil aeration under the rainforest limited N2O loss while promoting substantial CH4 uptake. The average annual N2O loss of 0.5 ± 0.1 kg N2O-N ha-1 over the two year measurement period was at the lower end of reported fluxes from rainforest soils. The rainforest soil functioned as a sink for atmospheric CH4 throughout the entire two year period despite periods of substantial rainfall. A clear linear correlation between soil moisture and CH4 uptake was found. Rates of uptake ranged from greater than 15 g CH4-C ha-1 day-1 during extended dry periods to less than 2-5 g CH4-C ha-1 day-1 when soil water content was high. The calculated annual CH4 uptake at the site was 3.65 kg CH4-C ha-1 year-1. This is amongst the highest reported for rainforest systems, reiterating the ability of aerated subtropical rainforests to act as substantial sinks of CH4.
A spatial study involving 30 manual chambers distributed across three remnant rainforest sites with similar vegetation and climatic conditions showed N2O fluxes almost 8 times higher and CH4 uptake reduced by over one third as clay content of the rainforest soil increased from 12% to 23%. An exponential relationship was found between N2O flux and percent clay content (r2 = 0.57) across the 30 chambers. This demonstrates that for some rainforest ecosystems soil texture and related water infiltration and WFPS constraints may play a more important role in controlling fluxes than either vegetation or seasonal variability.

本数据集基于一项野外监测研究：研究人员采用自动采样系统，对澳大利亚昆士兰州东南部一片亚热带雨林的二氧化碳（CO₂）、甲烷（CH₄）与氧化亚氮（N₂O）的土壤-大气交换通量开展了连续两年的监测。尽管两年间降雨量差异显著，但所有气体通量的年际变化均极小；仅二氧化碳通量可观测到显著的季节变化。雨林下较高的水分入渗、排水能力及随之产生的高土壤通气性，抑制了氧化亚氮的排放，同时促进了强烈的甲烷吸收。两年监测期内，该站点的年均氧化亚氮排放量为0.5±0.1 kg N₂O-N·ha⁻¹，处于已报道的雨林土壤通量区间的下限。尽管监测期间出现多段强降雨事件，该雨林土壤在整个两年监测期内始终作为大气甲烷的汇。研究发现土壤湿度与甲烷吸收之间存在显著线性相关关系：甲烷吸收速率在长期干旱期高于15 g CH₄-C·ha⁻¹·d⁻¹，而在土壤含水量较高时则降至2~5 g CH₄-C·ha⁻¹·d⁻¹以下。经计算，该站点的年均甲烷吸收量为3.65 kg CH₄-C·ha⁻¹·a⁻¹，这一数值位列已报道的雨林生态系统甲烷吸收量的较高水平，再次证明通气性良好的亚热带雨林可作为强效大气甲烷汇。

一项空间分布研究在三个植被与气候条件相似的残存雨林样地开展，共布设30个手动采样箱。结果显示，随着雨林土壤黏粒含量从12%升至23%，氧化亚氮通量提升近8倍，而甲烷吸收量降低逾三分之一。30个采样箱的氧化亚氮通量与黏粒百分比之间呈指数相关关系（决定系数r²=0.57）。这表明，在部分雨林生态系统中，土壤质地及相关的水分入渗、充水孔隙度（Water-Filled Pore Space，WFPS）限制因素，对气体通量的调控作用可能较植被或季节变异性更为显著。