光强对两种入侵植物生物量分配、叶片形态和相对生长速率的影响

THE EFFECT OF LIGHT INTENSITY ON BIOMASS ALLOCATION, LEAF MORPHOLOGY AND RELATIVE GROWTH RATE OF TWO INVASIVE PLANTS

比较研究了不同光强下生长的 (透光率分别为 12 .5 %、36 %、5 0 %、10 0 % )两种入侵性不同的外来种———紫茎泽兰 (Eupatoriumadenophorum)和兰花菊三七 (Gynurasp .)的生物量分配、叶片形态和生长特性。结果表明 :1)两种植物叶片形态对光环境的反应相似。弱光下比叶面积 (SLA)、平均单叶面积 (MLS)和叶面积比 (LAR)较大 ,随着光强的升高 ,SLA、MLS、LAR和叶根比 (LARMR)降低。 2 ) 10 0 %光强下紫茎泽兰叶生物量比 (LMR)、叶重分数 (LMF)和叶面积指数高于低光强下的值 ,也高于兰花菊三七 ,支持结构生物量比 (SBR)则相反。强光下紫茎泽兰叶片自遮荫严重 ,这可能是其表现入侵性的重要原因之一 ;兰花菊三七分枝较多 ,避免了叶片自遮荫 ,较多的分枝利于种子形成对其入侵有利。 3)随生长环境光强的升高 ,两种植物的净同化速率 (NAR)、相对生长速率 (RGR)和生长对NAR的响应系数均升高 (但 10 0 %光强下兰花菊三七RGR降低 ) ,平均叶面积比 (LARm)和生长对LARm 的响应系数均降低 ,但不同光强下LARm 对生长的影响始终大于NAR。 4 )随着光强的减弱 ,两种植物都增加高度以截获更多光能 ,但它们的生物量分配策略不同 ,紫茎泽兰根生物量比 (RMR)降低 ,SBR增大 ,而兰花菊三七SBR降低 ,RMR增大。

The high biodiversity and economic costs associated with invasive pla nts have promoted research to identify traits associated with invasiveness. At p resent, most research has been based on comparisons between invasive and native species but, in this paper, two invasive species with different levels of invasi veness, Eupatorium adenophorum and Gynura sp., were studied. Both specie s were g rown under four different relative irradiances (RI 12.5%, 36%, 50%, 100%) fo r 50 days, and we then measured their biomass allocation, leaf morphology and growth properties to compare their light acclimation abilities and growth strategies.The two species exhibited typical leaf morphological responses to different ligh t conditions. At low light levels, plants enhanced light interception by means o f increased biomass allocation to leaves and formation of large, thin leaves wit h high specific leaf area (SLA), leading to a high leaf area ratio (LAR) . At hig h light levels, plants reduced transpiration losses and increased carbon gain by making small-sized, thick leaves with a low SLA, leading to a low LAR a nd leaf area to root mass ratio. Under most light regimes, E. adenophorum was higher in leaf mass ratio (LMR), leaf mass fraction (LMF), LAR, root mass rati o (RMR) and root mass to crown mass ratio (R/C), but lower in supporting organ biomass r atio (SBR), MLA and branch number as compared to Gynura sp. Leaf mass ra tio, LMF, an d leaf area index of E. adenophorum were the highest under 100% irradiance t han unde r other light regimes and higher than for Gynura sp.; however, for SBR, these pa tterns were reversed. Under 100% irradiance, leaves were much more self-shaded i n E. adenophorum than in Gynura sp. This might be an adaptive strategy t hat supp orts the vigorous invasiveness of this species because a high-shaded canopy coul d prevent other plant species from surviving and competing. The number of branch es of Gynura sp. was greater under 100% irradiance than under other light re gime s and significantly more than for E. adenophorum. This might be an adaptive stra tegy for Gynura sp. because a greater number of branches can produce more fl ower s and thus more seeds. For both species, an increase in light intensity resulted in an increase in net assimilation rates (NAR) and growth response coeffici ent of NAR (GRC NAR ), whereas mean leaf area ratio (LAR m) and g rowth response coeffic ient of LAR m (GRC LAR m ) decreased. GRC LAR m was high er than GRC NAR at all times. T he relative growth rate (RGR) of E. adenophorum increased with an increa se in li ght intensity but decreased in Gynura sp. With a decrease in light intensity , bo th E. adenophorum and Gynura sp. grew taller and produced more branches to inte rcept more light energy. The biomass allocation strategy differed between the tw o species: RMR decreased and SBR increased in E. adenophorum, while RMR increase d, and SBR decreased in Gynura sp. All of the results presented above in dicate t hat E. adenophorum was able to acclimate better to different light condition s, e specially to low light regimes, than Gynura sp., and its better ability to acclimate might explain its greater invasiveness.