The Peatland-ES-UK team found that using artificial light can be used as a low-cost, flexible and valuable tool to obtain carbon sink/ source measurements in remote field environments.
Chamber-based carbon flux measurements are frequently used to assess ecosystem carbon sink/source dynamics as part of the net ecosystem exchange (NEE). For manual measurements over vegetated areas, light response curves LRC can be used to determine light compensation points, maximum photosynthetic rates, and dark respiration to varying light conditions. To simulate shade, meshes and covers are used. Light conditions in the field are limited especially in darker seasons, and in upland areas where there are frequent cloudy and foggy conditions. This questions the robustness of shade responses under such low light conditions. Artificial light sources therefore offer a crucial way to assess these potential limitations. Recent advances in LED lights with improved wavelength spectra and intensity are becoming suitable for deployment on flux chambers. The Peatland-ES-UK team thus investigated whether artificial light can be used to safely obtain data on NEE flux measurements.
They tried out the IMALENT SR 16 LED flashlight which is mainly used for search and rescue as a flexible, handheld and low weight option. The team investigated the wavelength spectrum and photosynthetic active radiation (PAR) output under controlled conditions, and tested it under field conditions as part of NEE flux measurements on the heather-dominated UK blanket bog sites under low light conditions. This allowed them to compare the LRC of natural light to those with supplementary PAR.
The light spectrum was mainly in the plant-relevant PAR range and remained stable across the intensity range. Potential PAR output was at least twofold than that of the maximum summer field values. NEE measured carbon uptake benefited from the increased PAR range without affecting chamber temperatures. A comparison of LRC parameters revealed very good agreement between with and without supplementary LED light for most measurements. However, for some measurements, especially with more noise at the maximum natural light levels, the wider PAR range resulted in a better fit with a parameter set more similar to the overall LRC.
Carbon flux measurements obtained with a Perspex chamber in the field on one of the Peatland-ES-UK heather-dominated blanket bog sites in October 2023 with thick cloud cover. The LED flashlight illuminated the NEE flux chamber to increase light levels for photosynthesis. Note the shade mesh (green) and the dark cover (silver) used to alter ambient light conditions to obtain a range of light conditions to allow light response curve modelling. Picture credit: Tom Holmes.
The team showed that the lightweight flashlight can be operated at several PAR intensity settings. The flashlight is also a valuable and flexible tool for enhancing PAR ad hoc when required for manual NEE flux measurements in remote environments. It also prevents the chamber overheating, and heavy, costly, and power intensive cooling systems. A manuscript will shortly be submitted for publication.
