Field CO2, CH4, and environmental measurements from leaf-cutter ant (Atta cephalotes) nests, and conceptual fluid dynamics model describing gas emissions ----- supporting for "Diel pattern driven by free convection controls leaf-cutter ant nest ventilation and greenhouse gas emissions in a Neotropical rainforest" in Oecologia ----- DOI: 10.1007/s00442-020-04602-2]

Contents R code and data.zip Data from several leaf-cutter ant nests and R scripts to model convective CO2 emissions. The conceptual model contains equations for forced and free convection. ***For information about how to fabricate the devices to measure CO2, please contact the authors. The R script contains the code to transform CO2 concentrations in time into CO2 emissions assuming that the chamber behaves as a well-mixed volume. The equations (Eq. S1, S2, and S3) are described explained in the supplementary information on http://doi.org/10.1007/s00442-020-04602-2 Temperature Data Excavation.xlsx Fungus and soil temperatures during leaf-cutter ant nest excavation (Atta cephalotes) CH4 and N2O concentration.xlsx Methane (CH4) and Nitrous oxide (N2O) concentrations (ppm in volume) measured from 19 vents 3 nests CO2 data Day vs Night.xlsx Summary of CO2 measurements in 10 leaf-cutter ant nest vents and one control (bare soil) comparing the statistics during the day and night. In all cases, CO2 concentration (ppmv) at night was significantly higher than during daytime, although the standard deviation was almost always greater during the day, suggesting more stability in (higher) nest emissions at night than during the day (more prone to sporadic wind episodes). Abstract 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 CO2eq nest-1 yr‑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. Location Latitude: 10.431200Longitude: -84.003400Minimum Elevation: 35.0 mMaximum Elevation: 135.0 m Resumen en españolLos hormigueros de las cortadoras de hojas son áreas muy activas biogeoquímicamente en donde las hormigas viven y cultivan un hongo a partir de la vegetación que colectan. La actividad metabólica y (en zonas tropicales) el intercambio de gases entre la matriz del suelo y el aire del hormiguero resultan en elevadas concentraciones de CO2 que debe ser ventilado. La ventilación inducida por el viento mitiga este efecto en especies localizadas en campo abierto, pero se desconocen muchos detalles sobre las emisiones de especies típicas de locales sin la influencia del viento. Nuestro estudio se enfocó en hormigueros de Atta cephalotes situados bajo el denso dosel de un bosque tropical lluvioso maduro de Costa Rica, donde episodios de viento son infrecuentes. Instrumentamos hormigueros con termopares y cámaras para detectar CO2 sin inhibir el caudal de aire a través de los orificios. Los resultados muestran que las concentraciones de CO2 provenientes del hormiguero siguen un patrón de 24 horas, con valores más altos por la noche. Creamos un modelo conceptual basado en diferencias de presiones que confirmó que este patrón diario está dominado por convección libre, por la que el aire húmedo y caliente cargado de CO2 sale más eficientemente cuando la temperatura del hormiguero es superior a la exterior. Episodios de viento esporádicos producen convección forzada y proveen ventilación adicional durante el día. Estimamos que la media de emisiones de gases de efecto invernadero es de unos 78 kg CO2eq nest-1 yr‑1. A nivel de ecosistema, los hormigueros de las cortadoras de hojas producen emisiones adicionales entre 0.2% y 1% del CO2eq total emitido por el suelo en este bosque Neotropical lluvioso. En suelos húmedos y arcillosos, estas estructuras actúan como conductos para el aire que es impulsado por convección libre para exportar CO2 producido en el hormiguero (por la respiración del hongo y de las hormigas, y por la descomposición de los residuos) y en el suelo circundante (raíces y microorganismos del suelo). Esto permite a los hormigueros de A. cephalotes mantenerse ventilados sin depender en vientos regulares.