羊草草原群落6种植物叶片功能特性对氮素添加的响应

VARIATIONS IN LEAF FUNCTIONAL TRAITS OF SIX SPECIES ALONG A NITROGEN ADDITION GRADIENT IN LEYMUS CHINENSIS STEPPE IN INNER MONGOLIA

该文比较了羊草草原群落中包括建群种和优势种在内的6种植物,羊草(Leymus chinensis)、西伯利亚羽茅(Achnatherum sibiricum)、大针茅(Stipa grandis)、冰草(Agropyron cristatum)、糙隐子草(Cleistogenes squarrosa)和黄囊苔草(Carex korshinskyi)的比叶面积(Specific leaf area,SLA)、叶片含氮量和叶绿素含量等叶片功能特性(Leaf functional trait)对氮素添加的响应,旨在探讨草原生态系统中,不同物种对氮素可利用性改变的响应和适应对策。结果表明:随着氮素添加量的增加,物种对光资源的竞争增强,不同物种在光资源的竞争策略和竞争力间存在着显著的差异。羊草通过提高SLA、单位质量叶片的叶绿素含量和含氮量,使单位面积叶片含氮量和叶绿素含量均呈线性提高,进而增强了其对光的竞争力。西伯利亚羽茅主要通过提高SLA增加光合总面积,来增强自身的光竞争力。冰草在SLA和单位质量叶片的叶绿素和氮含量均有一定的可塑性,但对光的竞争力明显弱于羊草和西伯利亚羽茅。大针茅和黄囊苔草对SLA的调节能力较低,加之大针茅SLA较低,而黄囊苔草处于群落的下层,这两种植物的光竞争力较弱。糙隐子草具有较高的SLA,对单位质量叶片叶绿素和氮含量的调节能力相对较强,其光竞争力高于黄囊苔草。同时,糙隐子草叶片叶绿素a与叶绿素b的比值沿氮素添加梯度显著降低,进一步证实氮素添加改变了群落的光环境。

Aims We conducted a field manipulation experiment to examine the underpinning mechanisms of variation in plant leaf functional traits along a nitrogen addition gradient in a mature typical steppe ecosystem in Inner Mongolia. Methods We selected six dominant and sub-dominant plant species for study： Leymus chinensis, Achnatherum sibiricum, Agropyron cristatum, Stipa grandis, Cleistogenes squarrosa and Carex korshinskyi. Together, they account for 〉 90% of the total community aboveground biomass. We examined the effects of N addition on specific leaf area （ SLA ）, leaf N content, total chlorophyll content, and chlorophyll a/b ratio. Important findings Nitrogen addition lessened the N limitation while strengthening light competition among co-existing plant species. Plant species differed significantly in their responses to increased N addition rates. Leymus chinensis showed high plasticity in S/A, leaf N, and total chlorophyll content. Its area-based leaf N content increased linearly with N addition rate. Achnatherum sibiricum showed the highest plasticity in SL4 and high mass-based leaf N and chlorophyll content to N enrichment, whereas its area-based leaf N content was relative stable. Compared to L. chinensis and A. sibiricum, A. cristatum had low plasticity in the three leaf functional traits investigated. Both S. grandis and C. korshinskyi illustrated low plasticity in SL4 along with low SL4 of S. grand/s and short stature of C. korshinskyi, leading to reduced light competitive ability of the two species under N enrichment. Cleistogenes squarrosa had the highest SL4 among the six species and a rela-tively high plasticity in mass-based leaf chlorophyll and N contents. The chlorophyll a/b ratio of C. squarrosa decreased significantly under N treatment, indicating declining light availability.