Carbon dioxide (CO2) is a critical input for photosynthesis and subsequent plant growth. In controlled environments, CO2 can be enriched above concentrations normally found in the ambient air, which has been shown to accelerate production and increase yields of many crop species. To capitalize on these benefits, broad recommendations have been adopted to enrich CO2 at a concentration of 800-1200 μmol·mol–1. However, these initial benefits may not persist throughout crop production due to prohibitive plant acclimation. The purpose of this study was to determine the timing and severity of CO2 acclimation responses of everbearing strawberry (Fragaria ×ananassa) during the vegetative growth stage. Crown divisions of strawberry ‘Quinault’ were transplanted into 10.7-cm pots and grown for two weeks in walk-in growth chambers under either an ambient (450 μmol·mol–1) or enriched (900 μmol·mol–1) CO2 concentration. Temperature, relative humidity, and photosynthetic photon flux density (PPFD) setpoints were consistent between CO2 treatments at 22/18 °C, 55/65% (day/night), and 320 µmol∙m–2∙s–1 (18-h photoperiod; daily light integral of 21 mol∙m–2∙d–1), respectively. Net photosynthesis (Anet) was surveyed daily for seven days on the same leaf using a portable leaf photosynthesis system, and A in response to internal leaf CO2 concentration (Ci) (A-Ci) curves were collected on day seven. On day 14, Anet and A-Ci curves were collected on the same leaf and on the most recently expanded new leaf, before destructive data (e.g., leaf area, dry mass) were collected. Survey measurements revealed Anet was higher for plants grown under the enriched compared to ambient CO2 concentration across all seven days. However, Anet declined after day 3 for enriched plants compared to relatively stable Anet measurements for ambient plants. After one week of exposure under treatment conditions, maximum rate of photosynthetic electron transport (Jmax) and maximum rate of Rubisco carboxylase (Vcmax) (both indicators of photosynthetic acclimation) were lower under the enriched compared to ambient CO2 concentration. No difference in dry mass between treatments was observed. While the higher Anet observed under the enriched CO2 concentration indicates a potential benefit for production, declining Anet after three days and physiological acclimation within one week pose possible limitations to maximizing the use of this input. Further elucidating the timing of strawberry acclimation to CO2 enrichment will help to improve control strategies for controlled environments to optimize plant yield and quality with fewer resources.
