Use of a networked digital camera to estimate net CO2 uptake of a desiccation-tolerant moss

Simple visible- light digital cameras offer a potential for expanded forms of plant ecological research. The moss Tortula princeps undergoes changes in reflected visible light during cycles of drying and hydrating in the field, and the MossCam project has collected digital images of T. princeps at least daily since 2003. Laboratory studies can be used to calibrate these images to indicate field physiological conditions. Drying the moss 6 d in the laboratory resulted in a decrease of net CO2 uptake to near 0; recovery after rewetting occurred within 10 min. The difference in reflectance between hydrated and dry T. princeps was maximal ca. 550 nm, and maximal net CO2 uptake was linearly related to the green : red ratio of laboratory images when net CO2 uptake was positive. Using the green : red ratio of field images and otherwise assuming ideal conditions, the total carbon gain for a 6- d period around a 1.3- mm rain event was ca. 208 mmol CO2 m(-2), equivalent to 69 d of respiration under dry conditions. Using a visible- light digital camera with micrometeorological data and laboratory- based gas exchange measurements, T. princeps can be used as a model species for simple field estimations of photosynthesis, carbon gain, and phenological events.