闽楠幼树光合特性及生物量分配对光环境的响应

The response of photosynthetic characters and biomass allocation of P.bournei young trees to different light regimes

设置100%光环境(L100)、40%光环境(L40)、8%光环境(L8)3种光照梯度,分析万木林闽楠(Phoebe bournei)幼树的光合特性及生物量分配特征对不同光环境的响应。结果表明:(1)闽楠幼树在不同光环境下的最大净光合速率(Pnmax),表观量子效率(AQY),光饱和点(LSP),光补偿点(LCP),暗呼吸速率(Rd)均有显著差异(P<0.05),且随着光照强度的降低,Pnmax,LSP,LCP,Rd随之降低,而AQY却呈现升高的趋势。(2)总生物量、茎生物量、叶生物量、根生物量均表现为L100最大,根冠比、叶生物量比、茎生物量比及根生物量比在3种光环境下无显著差异。(3)闽楠幼树通过改变光合特性,生物量积累来适应光环境的变化,其中光照强度的降低限制了生物量的积累,但并未显著改变生物量地上地下分配比例。闽楠幼树在3种光环境下生物量分配比例并无显著的改变,生物量分配可塑性极低可能是闽楠零散分布的一个重要非人为干扰因素。(4)闽楠幼树所采取的生存策略以地上部分生长为主,光照强度降低时则采取保守策略进行缓慢的资源获取和消耗,全光照条件下采取快速的资源获取和消耗策略。未来造林时可以将闽楠与毛竹(Phyllostachys pubescens)混交来减少郁闭度,促进闽楠幼树的生长。

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.