Abstract: In order to elucidate the effects of low-temperature stress on the photosynthetic and stomatal properties of strawberry leaves during the flowering phase, the perennial strawberry cultivar 'Selva' was selected as the experimental material. The environmental control experiment was designed and conducted at Nanjing University of Information Science and Technology (NUIST) with Venlo greenhouse and artificial climate chamber in 2022. Two low temperature levels (15℃/5℃, 20℃/10℃) were set, and each of them represented day temperature with night temperature. Treatment T1 and T2 were used to distinguish them. The duration of low temperature was set at 3d, 6d, and 9d. The plants grown in the greenhouse with temperature set at 25℃/15℃ were used as the control group (CK). Photosynthetic parameters and stomatal indices were determined for the leaves. The results showed that: (1) low temperature stress significantly inhibited the photosynthesis of strawberry, with the intensification of low temperature, the maximum net photosynthetic rate (Pn_max), light saturation point (LSP), stomatal conductivity (Gs), transpiration rate (Tr) gradually decreased, while light compensation point (LCP), dark respiration rate (Rd), intercellular CO2 concentration (Ci), stomatal limit (Ls) and water use efficiency (WUE) tended to increase. The main cause of the reduced photosynthetic rate was stomatal restriction. (2) Low temperature stress reduced the content of chlorophyll a, chlorophyll b, total chlorophyll content (a+b) and carotenoids in leaves. However, as the duration lengthened, the photosynthetic pigment content increased slightly, although it remained significantly lower than CK. (3) Low temperature stress had a particularly significant effect on leaf stomatal characteristics, i.e. the stomatal length, stomatal width, stomatal open degree, stomatal perimeter, stomatal area and stomatal opening ratio, which all decreased significantly with the decrease of temperature and the increase of the duration. Stomatal density tended to decrease but not significantly. This study showed that low temperatures reduced the stomatal size and the chlorophyll content, inhibiting the photosynthetic capacity of the leaves during the flowering stage.

Key words: Strawberry, Low temperature stress, Photosynthesis, Chlorophyll, Stoma