Performance of the enlarged Rice-FACE system using pure CO₂ installed in Tsukuba, Japan

Abstract

Free-air CO₂ enrichment (FACE) provides a unique platform for testing the response of future ecosystems to higher atmospheric CO₂ concentration ([CO₂]) without disturbing various ecosystemscale interactions. To investigate adaptations to climate change, it is crucial to test the responses of diverse cultivars and management conditions to higher [CO₂]. The older rice-FACE facility at Shizukuishi had an effective area of about 80 m² for [CO₂] treatment in each replicate, which was not large enough to test multiple genotypes and management practices. We report the first-year performance of the Tsukuba rice-FACE system installed at Tsukubamirai, Ibaraki, Japan. The new system was designed to have twice the usable area (>160 m²) of the Shizukuishi system without deteriorating the ability to control [CO₂]. We adopted a pure-CO₂ injection type system to elevate [CO₂] in the FACE ring by 200 μmol mol^-1 above ambient (control) plots. Overall temporal [CO₂] control of the Tsukuba FACE system was slightly better than of the Shizukuishi system; mean [CO₂] in the FACE plots was 584 μmol mol^-1, nearly equal to the target [CO₂] of 586 μmol mol^-1. The one-minute mean [CO₂] deviated by <±10% and <±20% from the target [CO₂] 73.9% and 91.3% of the time, respectively. Spatial distribution of [CO₂] inside the ring strongly depended on wind direction and speed. Relatively uniform [CO₂] was achieved near the ring center and in the northwestern direction, yielding an aerial fraction of 66% that experienced a season-mean [CO₂] within ±20% of the target. These aspects of spatio-temporal performance are comparable to those of other FACE facilities, indicating that the Tsukuba system can serve as a useful and reliable platform on which to test various rice genotypes that may be beneficial under projected high [CO₂] conditions in the future.