Studies On The Physiological Characteristics,component Biomass And Leaf Function Traits Of The Endangered Plant Horsfieldia Kingie(Hook.F.) Warb.

Horsfieldia kingie(Hook,f.)Warb.,unique to China’s humid tropical rainforest identification species,is part of Myristicaceae R.Br.familia of Horsfieldia Willd.genus tree.It has been listed as a protected plants of national II level,distributed in Guangxi,Yunnan and Hainan provinces now.Because of the high mortality rate under the influence of the environment and the uneven distribution of seedlings,the population renewal is greatly limited.Therefore,in this study,the photosynthetic characteristics,physiological and biochemical indexes,component biomass and leaf functional traits of Horsfieldia kingie(Hook.f.)Warb.seedlings were studied,aimed to investigate the correlation between seedlings growth and environment,and explore the suitable site conditions of Horsfieldia kingie(Hook.f.)Warb.seedlings.The main conclusions are drawn as the following:(1)The average daily changes of net photosynthetic rate and stomatal conductance of seedlings in spring and winter under three site conditions were unimodal curves,while those of forest gap and forest edge in summer and of forest edge in autumn were bimodal curves.The intercellular CO2 concentration of undergrowth seedlings decreased first and then increased in four seasons.The average daily net photosynthetic rate of seedlings in summer and autumn were significantly higher than that in spring and winter.In spring,summer and winter,the stomatal conductance of forest gap and forest edge was significantly higher than that of understory,while forest gap was significantly higher than forest edge and understory in autumn.The maximum net photosynthetic rate of seedlings was the highest under the condition of forest gap.The light compensation point and light saturation point of seedlings were the highest under the condition of forest edge.The net photosynthetic rate,light compensation point and light saturation point of seedlings were lowest in understory.(2)The content of chlorophyll a,chlorophyll b and chlorophyll a+b of seedlings in summer were significantly higher than that in other seasons under three site conditions.The content of chlorophyll a and chlorophyll a+b of seedlings under different site conditions in four seasons were all determined as forest edge>forest gap>understory.Through four seasons,the membrane permeability of seedling leaves was the largest in summer and autumn under the condition of forest edge.The forest gap was the largest in spring,while in winter it showed as understory>forest gap>forest edge.Under three site conditions,there was a significant difference in the content of malondialdehyde among seedlings in four seasons.The content of malondialdehyde was forest edge>forest gap>understory in spring and summer,forest gap>forest edge>understory in autumn,and understory>forest gap>forest edge in winter.Superoxide dismutase and peroxidase of seedlings in summer and autumn performed consistent,both of which were forest edge>forest gap>understory.In spring and winter,superoxide dismutase showed forest edge>forest gap>understory,and peroxidase showed understory>forest gap>forest edge.(3)The dry biomass,leaf biomass,branch biomass,total biomass,leaf number and leaf water content of four age classes were all higher in forest gap.The root biomass and leaf thickness were higher in forest edge,and specific leaf area was higher in understory.Principal component analysis showed that the central position of seedling trait syndrome was the largest position of the main axis of forest gap,indicating that the seedling component biomass and leaf function were the best indexes.It suggested that the forest gap is the most suitable habitat for Horsfieldia kingie(Hook.f.)Warb.through component biomass and leaf function.