Flooding responses of eight tree species introduced from America.
The present study demonstrates the differences of growth responses and tolerance to flood stress among 8 exotic tree species (including provenances) using 2 native tree species as control. We studied the mortality, the survival rate, collar diameter growth and foliar symptoms of all tested trees and measured the content of chlorophyll in leaves respectively after 21 d and 42 d of flooding treatment. The results showed nearly all the trees tested in this experiment survived during the whole period of flooding except the native tree species Nyssasinensis which showed a relatively high mortality after 49 days of flooding treatment, and there is no significant difference among the mortality of other species (P>0.05). We also found flood stress inhibited the net growth rate of collar diameter of Nyssa sinensis, Betula nigra, LA provenance for Liquidambar styraciflua and Quercus nuttallii, and promoted the net growth rates of collar diameter of the other trees to different extent. The total chlorophyll content and the ratio between chlorophyll a and chlorophyll b of 11 trees were either inhibited or elevated during the whole period of flood. Some of the trees exihibited more powerful tolerant to flooding with the elevation in chlorophyll content at the late stage of flooding. We finally concluded that there are significant differences among the 11 trees according to the tolerance index of net growth rates of collar diameter and the ratio between chlorophyll a and chlorophyll b (P<0.05), and suggested Nyssa sylvatica v. biflora, Nyssa aquatica, Quercus nuttallii, LA provenance for Liquidambar styraciflua and Yixing provenance for Liquidamba formosan Hance as the most suitable trees for wetlands.