<scp> TinyCO ₂ </scp> : High‐performance, low‐cost <scp> CO ₂ </scp> enrichment for field‐grown plants

Abstract Rising atmospheric CO 2 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 CO 2 (eCO 2 ) 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 eCO 2 research, we designed, built, and tested TinyCO 2 , a low‐cost field experiment for climate change research on plants. TinyCO 2 features sixteen 0.62‐m 2 plot areas, half with ambient and half with elevated (+200 ppm) CO 2 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, TinyCO 2 achieves consistent elevation of [CO 2 ] averaging +196.9 ppm. During testing, 95.1% of measured CO 2 concentrations fell within 20% of the setpoint (ambient CO 2 + 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 CO 2 elevation for significantly reduced cost. We envision the TinyCO 2 design being implemented in a multitude of field‐based eCO 2 studies, perhaps as part of a globally distributed collaborative network experiment.