Development of a Low-Cost, Autonomous Pulse Amplitude Modulated (PAM) Chlorophyll Fluorometer for In Situ Monitoring of Photosystem II Efficiency

The quantum yield efficiency of photosystem II (PhiPSII) is an important parameter for assessing the photosynthetic performance and stress status of plants. Commercial PAM fluorometers can measure this parameter, but they are often expensive, bulky, or lack autonomous operation. This work presents the development of an autonomous PAM fluorometer designed to address these limitations and enable large-scale deployment. It supports high spatio-temporal monitoring of PhiPSII in forest canopies under a wide range of ambient light conditions. The prototype costs approximately 150 EUR, has dimensions of 3 cm x 6 cm x 2 cm, and weighs about 50 g. In side-by-side tests across three plant species, it achieved measurement accuracy comparable to state-of-the-art commercial sensors, with a correlation factor of R^2 = 0.95.