Responses of Pinus massoniana and Pinus taeda to freezing in temperate forests in central China

Masson pine (Pinus massoniana Lamb.), a native species widely distributed in temperate forests in central China, and Loblolly pine (Pinus taeda L.), an exotic tree species introduced to China from southeastern United States, are dominant evergreen conifers that play a pivotal role in maintaining forest structure and functions for the region. We examined the effects of freezing on these species with chlorophyll fluorescence and electrolyte leakage using both field- and laboratory-based experiments in September 2009 and January 2010, respectively. We found that freezing could cause a greater impact on the Loblolly pine than the Masson pine. Although the two species showed similar values of Fv/Fm and electrolyte leakage before freezing, the Masson pine needles showed lower Fv/Fm and higher electrolyte leakage ratios than those of the Loblolly pine when treated in low temperatures (-15 to 0C). We also found that cold-acclimation was crucial for both species to adapt to low temperatures with the Fv/Fm ratio decreased approximately by 80% in the first freezing hour for the non-acclimated needles of both species while the cold-acclimated needles showed little changes in the Fv/Fm ratio. This finding is also supported by our measurements of electrolyte leakage. These results suggest that the Loblolly pine could be more susceptible to freezing damages than the Masson pine in central China. 2012 Copyright Taylor and Francis Group, LLC