荆条叶性状对野外不同光环境的表型可塑性

光照是影响植物生长和分布的重要环境因子。对生长在野外5种不同光环境下(林外、阔叶林林缘、阔叶林林下、针叶林林窗和针叶林林下)的荆条的叶片进行取样研究,通过对光合作用光响应曲线、叶绿素荧光、叶绿素含量、叶片氮磷含量以及叶片形态的测量,来反映荆条对不同光环境的表型可塑性。研究结果表明,荆条叶片对于野外不同的光环境具有很好的适应机制,叶片功能性状受到结构性状的调节。低光下通过高的比叶面积(SLA)、单位质量叶绿素含量、光系统II最大量子产量,低的暗呼吸速率、光饱和点、光补偿点、叶绿素a,b的比值来提高对光能的利用效率,维持生长;高光下则通过与SLA有关的叶片结构的变化对光合作用进行调节。大多数的叶性状只受到日光照总量的影响,SLA的大小与日最高光强有关,可以对不同日变化模式的光照做出迅速的响应,是适应不同光照的敏感指标。尽管光照是不同光环境下影响荆条叶性状的主要环境因子,土壤养分含量同样会对叶性状产生影响,高土壤养分下的高叶长与叶柄长的比值体现了植物对资源获取和支撑结构之间分配的权衡。

Foliar phenotypic plasticity of a warm-temperate shrub, Vitex negundo var. heterophylla, to different light environments in the field

Light is an important factor affecting plant growth and species distribution. In the field, open forest, forest edge, forest gaps and forest understory are typical light environment for species to survive and growth, in which light intensity are different for 10 times and even more. Plant phenotypic plasticity, which allows plants to adapt to different light environments, plays an important role in how plants adapt to changes in lighting, and leaves play an especially important role. Leaves are the main organs plants use for gas exchange with the environment. Leaves have both structural and functional characteristics. Different species show different sensitivities to irradiance. Vitex negundo Linn. var. heterophylla (Franch.) Rehd. is the dominant shrub of the warm temperate zone in China. It is an important native and pioneer species for vegetation restoration of Shandong Province, because of the high soil and water conservation ability. But up to now, studies related to its adaptation to irradiance are lacking. This study provides information related to this shrub and its use in vegetation restoration in Luzhong Mountains of Shandong Province. We measured leaf photosynthetic light response curves, leaf chlorophyll fluorescence, leaf chlorophyll content, leaf nirtogen (N) and phosphorus (P) content and leaf morphology. We studied the response of V. negundo var. heterophylla to five different light environments in the field: open forest, broad-leaved forest edge broad-leaved forest understory, gaps in needle-leaf forests and needle-leaf forest understory. The results the leaf traits of V. negundo var. heterophylla acclimated well to different habitats. Leaf functional traits were adjusted by leaf structural traits. The species exhibited some shade tolerance based on its ability to modify the characteristics of its leaves. The species improved its light use efficiency and kept growing in low light by increasing its specific leaf area (SLA), its chlorophyll (Chl) content, and the maximal quantum yield of PSII, and by lowering its respiration rate, light saturation point, light compensation point, and Chl a to b ratio. Also, leaf structure, especially SLA, played an important role in the regulation of photosynthesis under high levels of irradiance. Most of the traits were only impacted by the daily total irradiance; however, the variation of SLA and leaf maximal fluorescence in the dark (F_m) was related to the highest irradiance levels. SLA was sensitive to different light conditions, and responded quickly to changes in lighting. Although light is the most important factor affecting the characteristics of V. negundo var. heterophylla leaves in this study, soil nutrient content also played an important role. Plants with higher nutrient levels had a higher ratio of leaf length to petiole length, revealing an investment tradeoff between resource obtaining and supporting structure. Based on the low leaf N to P ratio, Luzhong Mountains is proved to be short of soil N. Adding N during vegetation restoration activities will assure an adequate supply of N. Also, V. negundo var. heterophylla can be planted in a variety of light environments because of its broad irradiance tolerance.