Design and validation of a low-cost open-top chamber for plant climate change experiments

Rising atmospheric CO2 is a primary driver of ongoing climate change; however, plant responses to elevated CO2 remain highly variable across species and functional traits. Given that CO2 enrichment fundamentally modulates photosynthesis, water-use efficiency, and growth, controlled experiments are essential to quantify these responses under climate-relevant conditions. In this context, open-top chambers (OTCs) provide a practical and standardized approach to simulate elevated CO2 environments in field settings. We describe a reproducible, low-cost OTC system and provide detailed protocols for its design, construction, calibration, and operation to facilitate widespread adoption. Performance validation confirmed that the system significantly elevated CO2 concentrations compared to ambient levels (targeting the RCP4.5 concentration of ~540 ppm), while maintaining consistent temperature and humidity profiles across chambers. As a case study, we compared the physiological responses of the endemic plant Leontopodium leiolepis and the widespread native plant Dendranthema zawadskii var. tenuisectum under ambient and elevated CO2 conditions. Elevated CO2 significantly increased leaf gas-exchange rates in both species, demonstrating that the developed OTC system is effective in inducing distinct physiological shifts in plants. However, morphological growth traits remained unchanged, with neither species showing significant plasticity between ambient and elevated CO2 conditions. Our OTC platform maintains environmental conditions while enabling precise regulation of CO2 concentrations. By simulating realistic future CO2 scenarios, the system effectively induces measurable physiological responses in plants, offering an accessible and reproducible framework for generating standardized trait datasets and empirically grounded sensitivity metrics.