Data from: Identifying environmental drivers of greenhouse gas emissions under warming and reduced rainfall in boreal-temperate forests

1.Atmospheric concentrations of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) are predicted to increase as a consequence of fossil fuel emissions and the impact on biosphere-atmosphere interactions. Forest ecosystems in general, and forest soils in particular, can be sinks or sources for CO2, CH4, and N2O. Environmental studies traditionally target soil temperature and moisture as the main predictors of soil greenhouse gas (GHG) flux from different ecosystems; however, these emissions are primarily biologically driven. Thus, little is known about the degree of regulation by soil biotic vs. abiotic factors on GHG emissions, particularly under predicted increase in global temperatures, and changes in intensity and frequency of precipitation events.

2.Here we measured net CO2, CH4 and N2O fluxes after 5 years of experimental warming (+3.4°C), and 2 years of ≈45% summer rainfall reduction, in two forest sites in a boreal-temperate ecotone under different habitat conditions (closed or open canopy) in Minnesota, USA. We evaluated the importance of microbial gene abundance and climo-edaphic factors (soil texture, canopy, seasonality, climate and soil physicochemical properties) driving GHG emissions.

3.We found that changes in CO2 fluxes were predominantly determined abiotically by temperature and moisture, after accounting for bacterial abundance. Methane fluxes on the other hand, were determined both abiotically, by gas diffusivity (via soil texture) and microbially, by methanotroph pmoA gene abundance, whereas, N2O emissions showed only a strong biotic regulation via ammonia-oxidizing bacteria amoA gene abundance. Warming did not significantly alter CO2 and CH4 fluxes after 5 years of manipulation, while N2O emissions were greater with warming under open canopy.

4.Our findings provide evidence that soil GHG emissions result from multiple direct and indirect interactions of microbial and abiotic drivers. Overall, this study highlights the need to include both microbial and climo-edaphic properties in predictive models in order to provide improved mechanistic understanding for the development of future mitigation strategies.

1. 大气中二氧化碳（carbon dioxide, CO₂）、甲烷（methane, CH₄）和一氧化二氮（nitrous oxide, N₂O）的浓度预计将因化石燃料排放以及对生物圈-大气相互作用的影响而升高。总体而言，森林生态系统，尤其是森林土壤，可作为CO₂、CH₄和N₂O的汇或源。传统环境研究通常将土壤温度与湿度作为不同生态系统土壤温室气体（greenhouse gas, GHG）通量的主要预测因子，但此类排放主要由生物过程驱动。因此，目前对土壤生物与非生物因子对GHG排放的调控程度尚不清楚，尤其是在全球温度预计升高、降水事件强度与频率发生变化的背景下。
2. 本研究在美国明尼苏达州一处寒温带交错带的两个不同生境（郁闭林冠或开阔林冠）的森林样地中，开展了为期5年的模拟增温（+3.4℃）与2年的夏季降水削减（≈45%）实验，并测定了净CO₂、CH₄与N₂O通量。我们评估了微生物基因丰度与气候-土壤因子（土壤质地、林冠、季节动态、气候及土壤理化性质）对GHG排放的调控作用。
3. 研究发现，在考虑细菌丰度的影响后，CO₂通量的变化主要由温度与湿度等非生物因子决定。而CH₄通量则同时受非生物与生物因子调控：非生物因子为气体扩散能力（通过土壤质地体现），生物因子为甲烷氧化菌pmoA基因丰度；N₂O排放则仅受氨氧化细菌amoA基因丰度介导的强烈生物调控。经过5年的实验处理后，增温并未显著改变CO₂与CH₄通量，但在开阔林冠下，增温会使N₂O排放量升高。
4. 本研究结果表明，土壤GHG排放源于微生物与非生物驱动因子之间的多重直接与间接相互作用。总体而言，本研究强调，为了更深入地解析相关机制以制定未来的温室气体减缓策略，预测模型需同时纳入微生物与气候-土壤因子特征。