Abstract: From September 2020 to January 2021, take “hongyan”(Fragaria×ananassa Duch “Benihope”) strawberry as test material to carry out low temperature environmental control test in Nanjing University of Information Science and Technology. Four low temperature treatments 21℃ (daily maximum temperature) / 11 ℃ (daily minimum temperature), 18℃/8℃, 15℃/5℃ and 12℃/2℃ were set, and the duration was set at four levels of 3d, 6d, 9d and 12d, with 25℃/15℃ as the control (CK). The chlorophyll content of strawberry leaves and canopy hyperspectral reflectance were measured. The effects of low temperature stress on chlorophyll content and canopy reflectance spectrum of strawberry were studied. The sensitive bands and characteristic parameters of chlorophyll content estimation model were selected. The results show that: (1) Under the same low temperature condition, Chla, Chlb and Chl(a+b) content of strawberry leaves decreased with the extension of stress days. Under the same stress days, the lower the temperature, the lower Chla, Chlb and Chl(a+b) content, that is, the greater the degree of low temperature stress, the greater the decline of chlorophyll content. (2) The changes of canopy spectral reflectance of strawberry seedlings under different temperatures and the same stress days were roughly the same. In the visible region, there are green peaks and red valleys in the reflection spectrum curve of strawberry canopy. In the near-infrared reflection platform, the spectral reflectance increases gradually with the decrease of temperature, that is, the reflection platform increases gradually. (3) The first-order differential spectrum curve of strawberry canopy changed violently, with obvious peaks and valleys, and occasionally double peaks in the red edge range. With the deepening of low temperature stress, the higher the value of the highest peak of the first-order differential spectrum, the near-infrared reflectance of strawberry canopy spectrum increased and the red edge position shifted blue, and then the peak gradually decreased and the red edge position shifted red. (4) The correlation coefficient between Chl(a+b) content and original spectral reflectance of strawberry canopy is negatively correlated. The correlation between Chl(a+b) content and reflectance in near-infrared band is significantly higher than that in visible band. The correlation between Chl(a+b) content and original spectral reflectance is good, reaching a significant level. The correlation coefficient of 737nm band is the largest, so it can be used as a sensitive band to predict chlorophyll content. The correlation between Chl(a+b) content and DVI, MSAVI, PVI, RDVI, SAVI and TSAVI in vegetation index is very significant, which can be selected as a characteristic parameter to predict chlorophyll content.

Key words: Strawberry, Low temperature stress, Chlorophyll, Canopy spectrum, Vegetation index