摘要:
研究了两个光照梯度和3个土壤氮素水平交互作用对喜旱莲子草(Alternan thera philoxeroides(Mart.)Griseb.)形态特征和生物量分配的影响。结果表明,全光照促进喜旱莲子草总生物量的积累,但在遮荫条件下,喜旱莲子草可以通过增加株高、光合叶面积和改变生物量分配来适应弱光生境。土壤中氮素含量对喜旱莲子草生长有明显影响,总生物量、株高、叶面积、茎生物量比和叶生物量比等随土壤氮素水平增加而增加。光照和氮素的交互作用对总生物量、根生物量比、茎生物量比和叶生物量比也有显著影响。随着氮素水平的增高,遮荫和高光照处理下喜旱莲子草的叶面积、总生物量和叶生物量比之间的差异减小,而株高和根生物量比之间的差异增大。此外,光照强度对茎生物量比的影响具有明显的氮素浓度依赖性,低氮条件下,茎生物量比在高光照处理下显著高于遮荫处理,而在中氮条件下,遮荫处理却显著高于高光照处理,且在高氮处理下其差异进一步加大。这些结果表明喜旱莲子草在高氮素环境下能够通过形态可塑性和生物量分配模式的改变来适应弱光环境所带来的不利影响。研究结果不但可为研究喜旱莲子草对异质生境的入侵机制提供资料,也可为进一步研究喜旱莲子草的入侵和扩散与农业等生态系统中土壤氮素残留的关系提供参考。
Abstract:
Most invasive plants experience highly variable environments during their invasion,spread and establishment,and therefore,it is crucial to understand the factors controlling the success of invasive species.However,few studies have evaluated the interactive effect of both light intensity and soil nitrogen levels on functional response in phenotypic plasticity of invasive plants.The present study examined the main effects of light intensity and soil nitrogen level and their interactions on morphological traits and biomass allocation performance of an alligator weed Alternanthera philoxeroides,a widespread invasive plant in China,by outdoor experiments.Approximately identical size of ramets from one genotype of population were planted separately in plastic pots with combined compost and sand,and grown under the combination of two light intensities(full sunlight and 16.5% of full sunlight) and three soil nitrogen levels(low,midterm and high) treatments.The result indicated that full sunlight enhanced the production accumulation of A.philoxeroides and the plant could allocate more resources to leaf and above-ground stem and less to below-ground root under shade as a response to low light condition.Soil nitrogen level also had a significant effect on plant growth,showing an increase of total biomass,plant height,total leaf area,stem biomass ratio and leaf biomass ratio with the increasing soil nitrogen concentration.Additionally,there was a significant light譶itrogen interaction on total biomass,root biomass ratio,leaf biomass ratio and stem biomass ratio.Differences in leaf area,total biomass and leaf biomass ratio between two light intensities reduced with the increasing soil nitrogen concentration,whereas,those in plant height and leaf biomass ratio showed an opposite trend.In addition,the light effect on stem biomass ratio depended on nitrogen concentration greatly.Under low nitrogen condition,stem biomass ratio was significantly higher in full sunlight treatment compared with that in shade.But it was significantly lower under middle nitrogen condition,and the tendency became even more obvious under high nitrogen condition.Our data further implied that the negative effect caused by shade on plant growth of A.philoxeroides could be altered by phenotypic plasticity in morphology and biomass allocation performance in a response to high nitrogen concentration,which in turn adapts the plant to low light condition.This suggested that the great success of A.philoxeroides over a variety of heterogeneous habitats is probably due to both a high degree of phenotypic plasticity of individuals and compensation of one resource for another.Our study also confirmed the importance of nitrogen in affecting the establishment of invasive A.philoxeroides populations,and therefore,control of A.philoxeroides may be aided by nutrient management.
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