Diel pattern driven by free convection controls leaf-cutter ant nest ventilation and greenhouse gas emissions in a Neotropical rain forest
Diel pattern driven by free convection controls leaf-cutter ant nest ventilation and greenhouse gas emissions in a Neotropical rain forest
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DOI：
10.1007/s00442-020-04602-2
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发表时间：
2020-01-28
期刊：
影响因子：
2.7
通讯作者：
Harmon, Thomas C.
中科院分区：
文献类型：
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作者：
Fernandez-Bou, Angel Santiago;Dierick, Diego;Harmon, Thomas C.
切叶蚁巢穴是生物地球化学热点地区，蚂蚁在此居住并进口植被来生长真菌。如果通风不充分，代谢活动和（在潮湿的热带森林中）流入巢穴的土壤气体通量可能会导致巢穴二氧化碳浓度较高。风驱动的通风可以缓解草原中高浓度的二氧化碳，但对于长期无风条件下森林物种的交换却知之甚少。我们研究了位于哥斯达黎加潮湿的热带雨林中茂密树冠（叶面积指数> 5）下的头螺类巢穴，那里的风事件很少发生。我们用热电偶和流通式二氧化碳传感室对巢进行检测。结果表明，离开切叶蚁巢穴的二氧化碳浓度遵循昼夜模式，夜间浓度较高。我们开发了一个基于压力差的外排模型，通过以下方式评估观察到的二氧化碳昼夜模式：（1）自由对流（温暖、密度较小的空气在夜间更明显地从巢中升起）和（2）偶发的强风对流事件，在白天提供偶尔的补充通风。通过巢穴通风口估算的平均温室气体排放量约为 78 千克 CO(2)eq 巢(-1)年(-1)。在生态系统层面，切叶蚁巢穴排放量占雨林土壤总排放量的 0.2% 至 1%。在潮湿的粘土质热带土壤中，切叶蚁巢穴充当自由对流驱动的管道，通过巢穴周围的根部和土壤微生物排出巢穴内产生的二氧化碳和其他温室气体（真菌和蚂蚁呼吸、垃圾腐烂）。这使得头孢甲螺的巢穴可以在没有可靠风力条件的情况下进行通风。
Leaf-cutter ant nests are biogeochemical hot spots where ants live and import vegetation to grow fungus. Metabolic activity and (in wet tropical forests) soil gas flux to the nest may result in high nest CO2 concentrations if not adequately ventilated. Wind-driven ventilation mitigates high CO2 concentrations in grasslands, but little is known about exchange for forest species faced with prolonged windless conditions. We studied Atta cephalotes nests located under dense canopy (leaf area index > 5) in a wet tropical rainforest in Costa Rica, where wind events are infrequent. We instrumented nests with thermocouples and flow-through CO2 sensing chambers. The results showed that CO2 concentrations exiting leaf-cutter ant nests follow a diel pattern with higher values at night. We developed an efflux model based on pressure differences that evaluated the observed CO2 diel pattern in terms of ventilation by (1) free convection (warm, less dense air rises out the nest more prominently at night) and (2) episodic wind-forced convection events providing occasional supplemental ventilation during daytime. Average greenhouse gas emissions were estimated through nest vents at about 78 kg CO(2)eq nest(-1) year(-1). At the ecosystem level, leaf-cutter ant nest vents accounted for 0.2% to 1% of total rainforest soil emissions. In wet, clayey tropical soils, leaf-cutter ant nests act as free convection-driven conduits for exporting CO2 and other greenhouse gases produced within the nest (fungus and ant respiration, refuse decay), and by roots and soil microbes surrounding the nest. This allows A. cephalotes nests to be ventilated without reliable wind conditions.