Preprints
https://doi.org/10.5194/egusphere-2023-2746
https://doi.org/10.5194/egusphere-2023-2746
30 Nov 2023
 | 30 Nov 2023
Status: this preprint is open for discussion.

The emission of CO from tropical rain forest soils

Hella van Asperen, Thorsten Warneke, Alessandro Carioca de Araújo, Bruce Forsberg, Sávio José Filgueiras Ferreira, Thomas Röckmann, Carina van der Veen, Sipko Bulthuis, Leonardo Ramos de Oliveira, Thiago de Lima Xavier, Jailson da Mata, Marta de Oliveira Sá, Paulo Ricardo Teixeira, Julie Andrews de França e Silva, Susan Trumbore, and Justus Notholt

Abstract. Soil CO fluxes represent a net balance between biological soil CO uptake and abiotic soil and (senescent) plant CO production. Studies largely from temperate and boreal forests indicate that soils serve as a net sink for CO, but to date uncertainty remains about the role of tropical rain forest soils. Here we report the first direct measurements of soil CO fluxes in a tropical rain forest. We compare with estimates of net ecosystem CO fluxes derived from accumulation of CO at night under stable atmospheric conditions. Further, we used laboratory experiments to demonstrate the importance of temperature on net soil CO fluxes. Net soil surface CO fluxes ranged from -0.19 to 3.36 nmol m-2 s-1, averaging ∼1 nmol CO m-2 s-1. Fluxes varied with season and topographic location, with highest fluxes measured in the dry season in a seasonally inundated valley. Ecosystem CO fluxes estimated from nocturnal canopy air profiles, which showed CO mixing ratios that consistently decreased with height, ranged between 0.3 and 2.0 nmol CO m-2 s-1. A canopy layer budget method, using the nocturnal increase in CO, estimated similar flux magnitudes (1.1 to 2.3 nmol CO m-2 s-1). In the wet season, a greater valley ecosystem CO production was observed in comparison to measured soil valley CO fluxes, suggesting a contribution of the valley stream to overall CO emissions. Laboratory incubations demonstrated a clear increase in CO production with temperature that was also observed in field fluxes, though high correlations between soil temperature and moisture limit our ability to interpret the field relationship. At a common temperature (25 °C), expected plateau and valley senescent leaf CO production was small (0.012 and 0.002 nmol CO m-2 s-1) in comparison to expected soil material CO emission (∼0.9 nmol CO m-2 s-1). Based on our field and laboratory observations, we expect that tropical rain forest ecosystems are a net source of CO, with thermal degradation-induced soil emissions likely being the main contributor to ecosystem CO emissions. Extrapolating our first observation-based tropical rain forest soil emission estimate of ∼1 nmol m-2 s-1, a global tropical rain forest soil emission of ∼16.0 Tg CO yr-1 is estimated. Nevertheless, total ecosystem CO emissions might be higher, since valley streams and inundated areas might represent local CO emission hot spots. To further improve tropical forest ecosystem CO emission estimates, more in-situ tropical forest soil and ecosystem CO flux measurements are essential.

Hella van Asperen, Thorsten Warneke, Alessandro Carioca de Araújo, Bruce Forsberg, Sávio José Filgueiras Ferreira, Thomas Röckmann, Carina van der Veen, Sipko Bulthuis, Leonardo Ramos de Oliveira, Thiago de Lima Xavier, Jailson da Mata, Marta de Oliveira Sá, Paulo Ricardo Teixeira, Julie Andrews de França e Silva, Susan Trumbore, and Justus Notholt

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  • RC1: 'Comment on egusphere-2023-2746', Jörg Matschullat, 22 Jan 2024 reply
Hella van Asperen, Thorsten Warneke, Alessandro Carioca de Araújo, Bruce Forsberg, Sávio José Filgueiras Ferreira, Thomas Röckmann, Carina van der Veen, Sipko Bulthuis, Leonardo Ramos de Oliveira, Thiago de Lima Xavier, Jailson da Mata, Marta de Oliveira Sá, Paulo Ricardo Teixeira, Julie Andrews de França e Silva, Susan Trumbore, and Justus Notholt
Hella van Asperen, Thorsten Warneke, Alessandro Carioca de Araújo, Bruce Forsberg, Sávio José Filgueiras Ferreira, Thomas Röckmann, Carina van der Veen, Sipko Bulthuis, Leonardo Ramos de Oliveira, Thiago de Lima Xavier, Jailson da Mata, Marta de Oliveira Sá, Paulo Ricardo Teixeira, Julie Andrews de França e Silva, Susan Trumbore, and Justus Notholt

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Short summary
Carbon monoxide (CO) is considered an important indirect greenhouse gas. Soils can emit as well as take up CO but, until now, uncertainty remains which process dominates in tropical rain forests. We present the first soil CO flux measurements from a tropical rain forest. Based on our observations, we report that tropical rain forest soils are a net source of CO. In addition, we show that valley streams and inundated areas are likely additional hot spots of CO in the ecosystem.