Bai Zhen, Xie Hongtu, Kao-Kniffin Jenny, Chen Baodong, Shao Pengshuai, Liang Chao
Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, China.
School of Integrative Plant Science, Cornell University, Ithaca, NY 14853, USA.
FEMS Microbiol Ecol. 2017 May 1;93(5). doi: 10.1093/femsec/fix063.
Understanding soil CO2 flux temperature sensitivity (Q10) is critical for predicting ecosystem-level responses to climate change. Yet, the effects of warming on microbial CO2 respiration still remain poorly understood under current Earth system models, partly as a result of thermal acclimation of organic matter decomposition. We conducted a 117-day incubation experiment under constant and diurnally varying temperature treatments based on four forest soils varying in vegetation stand and soil horizon. Our results showed that Q10 was greater under varying than constant temperature regimes. This distinction was most likely attributed to differences in the depletion of available carbon between constant high and varying high-temperature treatments, resulting in significantly higher rates of heterotrophic respiration in the varying high-temperature regime. Based on 16S rRNA gene sequencing data using Illumina, the varying high-temperature regime harbored higher prokaryotic alpha-diversity, was more dominated by the copiotrophic strategists and sustained a distinct community composition, in comparison to the constant-high treatment. We found a tightly coupled relationship between Q10 and microbial trophic guilds: the copiotrophic prokaryotes responded positively with high Q10 values, while the oligotrophs showed a negative response. Effects of vegetation stand and soil horizon consistently supported that the copiotrophic vs oligotrophic strategists determine the thermal sensitivity of CO2 flux. Our observations suggest that incorporating prokaryotic functional traits, such as shifts between copiotrophy and oligotrophy, is fundamental to our understanding of thermal acclimation of microbially mediated soil organic carbon cycling. Inclusion of microbial functional shifts may provide the potential to improve our projections of responses in microbial community and CO2 efflux to a changing environment in forest ecosystems.
了解土壤二氧化碳通量温度敏感性（Q10）对于预测生态系统对气候变化的响应至关重要。然而，在当前的地球系统模型下，变暖对微生物二氧化碳呼吸的影响仍知之甚少，部分原因是有机质分解的热适应。我们基于四种植被林分和土壤层不同的森林土壤，在恒定温度和昼夜变化温度处理下进行了为期117天的培养实验。我们的结果表明，在变化温度条件下的Q10大于恒定温度条件下的Q10。这种差异很可能归因于恒定高温和变化高温处理之间可用碳消耗的差异，导致在变化高温条件下异养呼吸速率显著更高。基于使用Illumina的16S rRNA基因测序数据，与恒定高温处理相比，变化高温条件下具有更高的原核生物α多样性，更多地由富营养型策略者主导，并维持着独特的群落组成。我们发现Q10与微生物营养类群之间存在紧密的耦合关系：富营养型原核生物对高Q10值有正向响应，而贫营养型原核生物则表现出负向响应。植被林分和土壤层的影响一致支持富营养型与贫营养型策略者决定了二氧化碳通量的热敏感性。我们的观察结果表明，纳入原核生物功能特征，如从富营养型向贫营养型的转变，对于我们理解微生物介导的土壤有机碳循环的热适应至关重要。纳入微生物功能转变可能为改善我们对森林生态系统中微生物群落和二氧化碳排放对变化环境的响应预测提供潜力。
