PANDA: A simple and affordable chamber system for measuring the whole-plant net CO ₂ flux

Summary The carbon (C) balance of plants is the sum of all source and sink processes. However, due to methodological limitations, most studies focus predominantly on measurements of leaf-level assimilation and respiration, with less attention given to these processes in heterotrophic organs or the whole-plant level. As a result, knowledge of the whole-plant net C balance is scarce, limiting our understanding of the dynamics between C source and sink activities. Therefore, we developed an easily reproducible chamber system for continuous measurements of whole-plant net CO 2 fluxes. We present the obtained dynamics of net CO 2 fluxes of several C 3 and CAM species, including germinating Quercus robur , over several days, as well as the whole-plant net CO 2 flux temperature response of Q. robur seedlings, identifying the temperature thresholds at which they shift from a net CO 2 sink to source. We show distinct diel patterns of net CO 2 fluxes in C 3 plants, likely driven by a dynamic diurnal up- and downregulation of sink activities in woody C 3 plants. These patterns appear temperature-driven, suggesting a dynamic response of plant’s sink and source activity to environmental drivers. Our results highlight the importance of whole-plant C balance measurements for understanding plant responses to environmental conditions.