Effects of Low Temperature Stress and Release on Fluorescence Indexes of Greening Seedlings of Three Tree Species

Fluorescence characteristics of seedlings of Carallia brachiata, Ficus microcarpa and Phoebe zhennan were studied at 6℃ low temperature stress using Artificial Climate Box. After continuous treatments of 0 d, 2 d, 4 d and 6 d and 2 d after low-temperature release, the fluorescence indexes of the seedlings were determined, and their cold-resistance ability was evaluated using principal component analysis. The results showed that with increasing low temperature time, the minimum initial fluorescence of C. brachiata and F. microcarpa seedlings decreased, whereas that of P. zhennan fluctuated; the biggest fluorescent, the largest PSII photochemical efficiency, the PSII actual light quantum yield, the photosynthetic electron transport rate and the non-photochemical quenching of the seedlings of three tree species continuously decreased. Two days after low-temperature release, the minimum initial fluorescence of the seedlings decreased, whereas their biggest fluorescent, the largest PSII photochemical efficiency, the PSII actual light quantum yield, the photosynthetic electron transport rate and the non-photochemical quenching of the seedlings increased. The comprehensive cold-resistance ability of fluorescence indexes of the seedlings of three tree species was evaluated with principal component analysis, which decreased in the order of C. brachiata>P. zhennan>F. microcarpa.