南澳岛光裸地和次生林下6种乡土树幼苗生长与光合特征

Growth and photosynthetic characteristics of six native tree species seedlings grown on bare land and beneath secondary forest in Nan’ao Island

海岛是国土的重要组成部分。对海岛退化生态系统进行恢复和改造具有重要意义。通过系统观测并比较乡土树种重阳木Bischofia javanica、大叶杜英Elaeocarpus balansae、蒲桃Syzygium jambos、鸭脚木Schefflera octophylla、阴香Cinnamomum burmannii及樟树Cinnamomum camphora苗木在南澳岛光裸地和次生林下的存活、生长及其光合特征,探讨两种不同生境对6个树种生长、存活的影响及用乡土树种苗木进行海岛荒坡恢复和人工林林分改造的可行性。结果如下:①从2007年4月栽植到2008年7月,所有苗木在光裸地平均存活率为46%,低于次生林下的78%。光裸地重阳木存活率最高,为85%;鸭脚木存活率最低,只有18%。次生林下重阳木和鸭脚木存活率都较低,约为60%,远低于其它树种。②各树种苗木在光裸地生长量均高于次生林下。光裸地所有树种苗木地径、苗高和冠幅的平均相对增长量分别是次生林下苗木的4.8,1.7和2.0倍。光裸地重阳木生长较快;次生林下阴香生长较快,重阳木、鸭脚木生长较慢。③苗木在光裸地的日均净光合速率、蒸腾速率和气孔导度分别是次生林下的2.3,3.7和2.1倍。同一生境下各树种苗木的日均净光合速率差异不大。④各树种苗木在光裸地的光饱和点(LSP)、光补偿点(LCP)及表观量子效率(AQY)与次生林下同一树种相比均差异显著(P<0.01)。光裸地重阳木、鸭脚木和樟树具有较高的光饱和点和光补偿点,为喜光树种;大叶杜英、蒲桃和阴香具有较高的光饱和点和较低的光补偿点,为喜光耐阴树种。而次生林下各树种均具有较低的光补偿点和较高的表观量子效率,表明在次生林下各树种均具有较好的耐阴性。综合考虑,重阳木适于在光裸地等光照条件好的生境栽植,阴香适于在林下生长,大叶杜英、蒲桃和樟树适应性较好,在强光和弱光下均可生长,而鸭脚木更适于半遮荫环境。这些研究结果可为海岛退化生态系统的植被恢复提供理论参考。

Islands are important parts of a country＇ territory. Restorating degraded island vegetation such as abandoned grass slopes and introduced tree species dominated secondary plantations is of great importance. Whether native tree species can be used to restore the bare lands and structurally retransform the secondary plantations is practically important as well. Six native tree species seedlings such as Bischofia javanica, Elaeocarpus balansae, Syzygium jumbos, Schefflera octophylla, Cinnamomum burmannii and Cinnarnomum carnphora were planted on bare land and beneath secondary forest in Nan＇ao Island in April,2007. Seedling survival rate and growth were measured every three months since then, photosynthetic diurnal course and light-response curve were also measured using LiCor-6400 in August, 2008. The results showed that： ① The average seedling survival rate on bare land （48%） was much lower than that of the secondary forest （78%）. Bischofiajavanica had the highest survival rate （85%） while Schefflera octophylla had the lowest （18%） on the bare land. Beneath the secondary forest, the survival rate of Bischofia javanica and Schefflera octophylla were about 60%, lower than the other four species which were all 70% above; ② The average relative growth of basal diameter, height and canopy diameter of seedlings on bare land were 274%, 243% and 220%, respectively, which were 4.8, 1.7 and 2.0 times higher than those under the secondary forest. Bischofiajavanica grew faster on bare land but slower beneath forest; Cinnamomum burmannii grew faster beneath the secondary forest but Schefflera octophylla grew slower; ③ The daily average net photosynthetic rate, transpiration rate and stomatal conductance of seedlings on bare land were 2.3, 3.7 and 2.1 times of seedlings beneath the secondary forest, respectively. The daily average net photosynthetic rate of seedlings grown at the same sites were not markedly different; ④The average light saturation point（LSP）, light compensation point（LCP）and apparent quantum yield（AQY）of each seedling on bare land and beneath secondary forest were significantly different （P〈0.01）. Bischofiajavanica, Schefflera octophylla and Cinnarnomum camphora grown on bare land were photophilic with high LSP and high LCP whereas Elaeocarpus balansue, Syzygium jambos and Cinnamomum burmannii were both photophilic and shade-tolerant with high LSP and low LCE All seedlings grown beneath secondary forest had lower LCP and higher AQY. In summary, Bischofiajavanica grew better under strong light while Cinnamomum burmannii grew better under weak light. Elaeocarpus balansae, Syzygium jambos and Cinnamomum camphora grew well under both strong and weak light while Schefflera octophylla grew well only under moderate light conditions. These growth and physiological data may be referential in restoring the degraded island vegetation using native tree species.