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 approaches such as eddy covariance, portable photosynthesis systems, and chambers provide valuable data at ecosystem, leaf, and mesoscales, respectively. Chamber-based measurements are particularly useful at intermediate scales, as they capture photosynthetic activity of whole plant assemblages while integrating microhabitat and belowground processes. However, conventional chambers typically require the installation of collars, involving cutting and trenching of vegetation that may alter fluxes; this often necessitates a delay period before reliable measurements can begin and reduces the portability and applicability of chamber methods in remote peatlands. In a previous companion study, we introduced the skirt-chamber, a minimally invasive method for greenhouse gas flux measurements. Building on that design, we developed a modulated-light skirt-chamber specifically for PI curve determination. This chamber enables in situ characterization of photosynthetic responses under natural light conditions using adjustable shading screens, while preserving portability and minimizing disturbance. Field tests in a subantarctic Sphagnum bog demonstrated that the generated PI curves fit established models and closely matched eddy covariance measurements. The modulated-light skirt-chamber therefore provides a cost-effective and flexible tool for studying carbon dynamics in low-stature peatland ecosystems, with promising applications in heterogeneous landscapes.