Impact of seasonally frozen soil on germinability and antioxidant enzyme activity of Picea asperata seeds

In the subalpine zone of the Qinghai–Tibetan Plateau of China, Dragon spruce (Picea asperata Mast.) is commonly used for reforestation. The aim of the present work was to study the effects of seasonally frozen soil on the germination of P. asperata seeds and to investigate whether these effects were associated with resumption of the antioxidant defense system. The nonfrozen treatment resulted in near failure of germination (1%) and was associated with relatively high levels of hydrogen peroxide (H2O2) and low activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxide (APX). Germination of P. asperata seeds at 10 cm under the seasonally frozen soil was higher than that at 5 cm by 26%; this higher germination rate was associated with the recovery of SOD, CAT, and APX activities. The levels of malondialdehyde (MDA) in seeds from seasonally frozen treatments were higher than those in the nonfrozen treatment, implying greater lipid peroxidation and that frozen seeds might have suffered from oxidative stress. The results indicate that seasonally frozen soil facilitated the germination of P. asperata seeds and that germination was closely related to the resumption of antioxidant enzymes activity. Overall, these findings suggest that the disappearance of seasonally frozen ground caused by global warming might result in failure of regeneration of P. asperata.