光照强度对景宁木兰幼苗叶片形态结构、化学计量特征和非结构性碳水化合物的影响

Effects of light intensities on leaf morphological structure,stoichiometry and non⁃structural carbohydrates of Magnolia sinostellata seedlings

为探讨濒危植物景宁木兰(Magnolia sinostellata)对不同光环境的适应机制,以2年生幼苗为研究对象,设置自然光强的100%(I_(100))、40%(I_(40))、10%(I_(10))3种光照处理,测定不同光环境下叶片形态结构、化学计量特征和非结构性碳水化合物(NSC)的变化。结果表明:(1)景宁木兰幼苗叶长、叶宽、叶周长和叶面积均以I_(40)下最高,而叶片含水量和比叶面积随着光照强度的减弱而显著增加。(2)全光照下的气孔密度和气孔器面积百分比显著高于遮荫处理。(3)I_(100)、I_(40)下栅栏组织和叶厚度显著高于I_(10)。I_(40)下单位叶面积内叶肉细胞面向外围空间的表面积(Smes)、单位叶面积内叶绿体面向细胞外围空间的面积(Sc)均显著高于I_(100)、I_(10),单位叶面积内叶绿体个数(nchr)以I_(10)下最大。(4)I_(10)下N含量和N∶P均显著高于I_(100)、I_(40),意味着重度遮荫能提高光合作用的酶活性和叶绿素含量。(5)遮荫下可溶性糖、NSC和可溶性糖淀粉比显著高于全光照。总之,景宁木兰在I_(40)下具有高的叶面积、Smes和Sc,叶片结构更为紧密,对CO_(2)的利用能力增强。遮荫处理具有较高的NSC含量。表明景宁木兰属于耐阴性木本植物,适当遮荫能缓解夏季高温、干旱对幼苗生长的限制,但遮光强度不宜过大,建议在野外保护以及人工栽培中光照强度应保持在自然光强的40%以上。

To provide a theoretical basis for field conservation and scientific cultivation of endangered plant Magno⁃lia sinostellata,we investigated its adaptation mechanism to different light environments.The changes of morpholo⁃gical structures,stoichiometry and non⁃structural carbohydrates in two⁃year⁃old seedlings of M.sinostellata were examined under three light conditions:full light intensity(I_(100)),40%light intensity(I_(40)),and 10%light intensity(I_(10)).The results showed that:(1)Leaf length,leaf width,leaf circumference,and leaf area of M.sinostellata seedlings under I_(40) were the largest,while leaf water content and specific leaf area significantly increased with decreasing light intensities.(2)The stomatal density and stomatal area percentage of M.sinostellata seedlings under I_(100) were significantly higher than those under I_(40) and I_(10).(3)Leaf thickness and palisade tissue of M.sinos⁃tellata seedlings under I_(100) and I_(40) were significantly higher than those under I_(10).Surface area of mesophyll intercel⁃lular space/unit leaf area(Smes)and chloroplast surface area/unit leaf area(Sc)of M.sinostellata seedlings under I_(40) were significantly lower than those under I_(100) and I_(10).Chloroplast number per unit area(nchr)of M.sinostellata seedlings under I_(10) were the largest.(4)The N content and N∶P under I_(10) were significantly higher than those under I_(100) and I_(40),which suggested that heavy shading could increase enzyme activities and chlorophyll content of photosynthesis.(5)Soluble sugar and non⁃structural carbohydrate(NSC)in the shading treatments were significantly higher than those under I_(100).In conclusion,M.sinostellata seedlings had higher leaf area,Smes and Sc,tigh⁃ter leaf structure,and enhanced CO_(2) utilization ability under I_(40).Shading treatment led to higher NSC content.As a shade⁃tolerant woody species,moderate shading can alleviate the limitation of high temperature and drought on seedling growth in summer,but the shading intensity should not be too high.The effective light intensity should be kept above 40%of natural light intensity.