Effects of temperature and photoperiod on photosynthesis in everbearing strawberry

There is little knowledge about photosynthesis in everbearing strawberry cultivars. We therefore grew three everbearing strawberry cultivars in daylight phytotron compartments at temperatures of 9, 15, 21 and 27°C and photoperiods of 10 h (SD) and 20 h (LD). After three weeks, the rates of dark respiration and photosynthesis and their acclimation were measured in 'Favouri'. Photosynthesis of plants grown in the various conditions was measured as CO₂-uptake with an infrared gas analyzer at increasing irradiances (50-1000 µmol quanta m^‑2 s^‑1) and temperatures ranging from 9 to 27°C. In the dark, CO₂-production (dark respiration) increased with increasing measuring temperature and was always largest in plants grown at low temperature (9°C) with no significant effect of photoperiod. Photosynthetic CO₂-uptake was lowest at almost all irradiances in plants grown at 9°C, and with no clear effect of growth temperatures in the 15-27°C range. At saturating irradiances (500-1000 µmol), CO₂-uptake increased with increasing measuring temperatures, reaching a plateau at about 21°C for plants grown at 15-27°C in SD and at 21-27°C in LD. For plants grown at 15°C in LD, the maximum CO₂-uptake rate was obtained at 27°C. Light response curves showed that CO₂-uptake increased with increasing irradiance and measuring temperatures and that the irradiance effect was markedly enhanced by increasing growth temperature. Maximum uptake rates were lowest for plants grown at 9°C at both photoperiods and highest for plants grown at 15°C in SD. Comparison of plants of 'Altess', 'Favouri' and 'Murano' at 500 µmol irradiance and 21°C revealed no significant differences in photosynthetic efficiency between the cultivars. Generally, the everbearing strawberry cultivars showed considerable photosynthetic plasticity to temperature within the 9-27°C range, although with an overall optimum at 15-21°C.