Phoebe bournei,a Chinese endemic species,is one of the valuable building timbers in subtropical evergreen broad-leaved forest.The population of P.bournei declined sharply by 30% in the past three centuries and was listed as a national Class Ⅱ protected plant.Most of P.bournei sparsely distributed in mid-subtropical evergreen broad-leaved forest.The purpose of the present study is to explore the adaptive strategy of light environmental heterogeneity and the natural factors contributed to scattered distribution of P.bournei and the strategy of protection and restoration.Thus,the photosynthetic characteristics,biomass allocation in response to different light regimes(100% of full sunlight,L100;40% of full sunlight,L40;8% of full sunlight,L8) were investigated in P.bournei young trees.Our results showed that: 1) There were statistically significant difference in maximum net photosynthesis rate(Pnmax),apparent quenching efficiency(AQY),light saturation point(LSP),light compensation point(LCP) and dark respiration rate(Rd).Pnmax,LSP,LCP,Rd declined as the light intensity increased while AQY increased with the increase of light intensity,revealing that P.bournei could adapt to dark light condition by lowering LCP and carbon consumption.Furthermore,the largest Pnmax of young trees under L100 indicated the full sunlight was in favour of the accumulation of photosynthetic products by the conversion of solar energy to chemical energy to the largest extent.2) Total biomass,leaf biomass,stem biomass and root biomass were largest under L100.Increase in root biomass,fine root biomass in particular,facilitated to maintain normal water absorption and transpiration and keep high photosynthetic rate while increase in leaf biomass and stem biomass was in favour of light capture and construction of supporting and transportation structure separately.In contrast,root to shoot ratio,leaf biomass ratio,root biomass ratio and stem biomass ratio were of no significant difference under three different light regimes.3) Photosynthetic characteristics and biomass accumulation were regulated to adapt to different light regimes,among which biomass accumulation was confined by the decrease of light intensity.However,the allocation ratio of above-ground biomass and under-ground biomass were not significantly influenced,in which the above-ground biomass occupied more than 65% of the total biomass under three different light conditions.Change in biomass allocation ratio of the P.bournei young trees wasn′t significant under L100,L40 and L8,indicating that extremely low plasticity of biomass allocation resulted in high natural selection pressure,which might be a very important natural disturbing factor in sporadic distribution of P.bournei young trees.4) The growth of the above-ground part of P.bournei young trees was predominant by dry matter accumulated in leaves and stems.With the decrease in sunlight intensity,a conservative strategy was adopted by slow gain of resource and consumption.In contrast,the measure was taken to capture and consume resource more quickly in P.bournei young tree under full sunlight.Therefore,it was suggested that mixture of P.bournei and Phyllostachys pubescens will help to reduce the canopy density and then promote the renewal of P.bournei young trees in forestation.