UC Santa Cruz

Rising atmospheric CO2 levels place terrestrial ecosystems under novel environmental conditions, and research in field settings is key to understanding how real plant communities will respond. Despite decades of progress in elevated CO2 (eCO2) experiments, major gaps persist in our knowledge of plant responses to interacting influences of climate change, especially in areas outside North America and Western Europe. With a goal to expand access to field-based eCO2 research, we designed, built, and tested TinyCO2, a low-cost field experiment for climate change research on plants. TinyCO2 features sixteen 0.62-m² plot areas, half with ambient and half with elevated (+200 ppm) CO2 concentrations, and is suitable for short-stature plants (≤0.5 m in height). Using a proportional-integral control algorithm and constant sampling of air within the plots, TinyCO2 achieves consistent elevation of [CO2] averaging +196.9 ppm. During testing, 95.1% of measured CO2 concentrations fell within 20% of the setpoint (ambient CO2 + 200 ppm). A streamlined design and efficient use of instrumentation reduced the cost of the system to roughly one-fifth of the cost of similar experiments from the past 30 years ($13.68 vs. $64.65 ppm⁻¹ m⁻², adjusted to 2024 USD). Our results demonstrate a system capable of precise and accurate field-based CO2 elevation for significantly reduced cost. We envision the TinyCO2 design being implemented in a multitude of field-based eCO2 studies, perhaps as part of a globally distributed collaborative network experiment.