Schuler, P.; Li, Y.; Pittet, P.; Favre, P.; Li, M.-H.; Zhang, Y.-L.; Grossiord, C.

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 CO2 fluxes. We present the obtained dynamics of net CO2 fluxes of several C3 and CAM species, including germinating Quercus robur, over several days, as well as the whole-plant net CO2 flux temperature response of Q. robur seedlings, identifying the temperature thresholds at which they shift from a net CO2 sink to source. We show distinct diel patterns of net CO2 fluxes in C3 plants, likely driven by changes in source and sink activities at the whole-plant level in woody C3 plants. These patterns appear temperature-driven, suggesting a dynamic response of plant\'s sink and source activity to environmental drivers. Overall, our results highlight the importance of whole-plant C balance measurements for understanding plant responses to environmental conditions.