高寒草地甘肃臭草茎-叶性状的坡度差异性

Variations with slope in stem and leaf traits of Melica przewalskyi in alpine grassland

茎与叶的生长形态决定植物与外界环境的物质交换能力,茎叶的异速生长模式对认识植物表型可塑性及其调节机理具有重要意义。在祁连山高寒退化草地,利用Arc GIS建立研究区域的数字高程模型(DEM),并提取样地坡度数据,采用标准化主轴估计(SMA)方法,研究了不同坡度甘肃臭草(Melica przewalskyi)种群茎与叶的生长。结果表明:随着坡度增大,甘肃臭草茎干质量、叶干质量、叶面积均呈逐渐减小趋势,叶片数呈增加趋势;甘肃臭草叶干质量的增长速度显著大于茎干质量的增长速度,叶面积与茎干质量近等速增长;不同坡度间的比较显示,随着坡度变陡甘肃臭草茎干质量与叶干质量异速斜率显著减小(p<0.05),陡坡上的甘肃臭草若要生成与缓坡样地中相同的叶生物量需要投入更多的茎生物量,茎干质量与叶面积的y轴截距显著减小(p<0.05),即相同的茎干质量投入下,较大坡度的甘肃臭草叶面积投入显著降低,趋向于减小叶面积增加叶数量。坡度梯度上甘肃臭草加快了茎的相对生长速率而减小了在叶面积上的投入,体现了不同坡度甘肃臭草茎-叶生物量分配机制及资源利用策略,同时说明高寒草地中小叶更具生境适应性。

Aims The relationship between stem and leaf growth is a strategy that plant canopy enhances photosynthetic efficiency and competitiveness through configuration adjustments; this relationship indicates the ratio between xylem and photosynthetic area in a heterogeneous environment. Our objective was to examine how Melica przewalskyi modulated leaf and stem traits in adaptation to changes in slope. Methods In the alpine grassland of Qilian Mountains, Gansu Province, China, 80 plots were set up along four transects corresponding to contrasting aspects with 20 m distance between adjacent plots. A GPS was used to record latitude, longitude and altitude of each plot and ArcGIS software was used for constructing a digital elevation model （DEM） and extracting information on elevation, aspect, and slope. Community characteristics were inves tigated and 10 random individuals of M. przewalskyi were cut at the soil surface in each plot, and leaf mass, leaf area and stem mass were measured in laboratory. The 80 plots were grouped into 0°-10°, 10°-20°, 200-30° slope gradients. Stem and leaf traits were log-transformed and then standardized major axis （SMA） estimation method was used to examine the allometric relationships of stem mass with leaf area or leaf mass. Important findings The stem mass, leaf mass and leaf area of M. przewalskyi gradually decreased, but the leaf number increased, with slope gradient. An isometric relationship was found between stem mass and leaf area in plots within each slope gradient, whereas an allometric relationship was found between stem mass and leaf mass. Melica przewalskyi grown on steeper slopes tended to have smaller leaf area and greater leaf number at a given stem mass, and leaves with greater stem mass had greater leaf mass. A significant difference in the SMA slope among the three slope gradients of the plots suggested that the slope of the growth site constrained leaf area and leaf mass by stem mass, reflecting plant adaptation to heterogeneous environment.