Technical note: In situ photosynthesis-irradiance curve determination in peatlands with a modulated-light skirt-chamber

Abstract. Peatlands play a crucial role in the global carbon cycle, and among several key processes, it is essential to characterize photosynthesis-irradiance (PI) curves, which describe the relationship between light availability and carbon assimilation through photosynthetic activity. Traditional methods, such as Eddy Covariance and portable photosynthesis measurement systems, provide valuable data at the ecosystem and leaf scales, respectively. However, these approaches leave a gap in capturing carbon dynamics at intermediate scales, where complex plant assemblages and microhabitat variability influence photosynthetic activity in ways that cannot be fully resolved at broader or finer spatial resolutions. In a previous companion paper, we introduced a skirt-chamber method for measuring greenhouse gas emissions in peatlands. Building on that work, we further developed a second version, specifically designed to determine photosynthetic activity at multiple light intensities. This improved modulated-light skirt-chamber enables in situ characterization of photosynthetic responses under natural light conditions by using adjustable screens to regulate light intensity. The chamber is particularly suited for generating PI curves in peatlands and other low-stature ecosystems with diverse microhabitats. Field tests conducted in a subantarctic peatland bog demonstrated the method’s reliability. The generated PI curves fit well with existing models and closely matched measurements from an EC station at the study site, accurately capturing photosynthetic responses to light. The modulated-light skirt-chamber offers a portable, cost-effective, and flexible solution for studying carbon dynamics at an intermediate scale, bridging leaf-level measurements and ecosystem-scale observations. This method holds significant promise for advancing our understanding of carbon fluxes in complex and heterogeneous ecosystems.