极小种群物种滇桐幼苗与幼树光合特性和叶片显微结构的比较研究

Comparison of photosynthetic characteristics and leaf microstructure between seedlings and youngtrees of Craigia yunnanensis, a plant species with extremely small populations

关键词:  滇桐, 极小种群, 光合特性, 叶解剖结构, 叶绿素

Key words:  Craigia yunnanensis, extremely small population, photosynthetic characteristics, leaf anatomical structure, chlorophyll

摘要:

滇桐(Craigia yunnanensis)为我国特有的极小种群物种,被列为国家二级重点保护野生植物。针对滇桐自然种群更新中存在的幼树断档现象,该研究以引种栽培的滇桐为试验材料,研究其幼苗(苗龄6个月)和幼树(树龄8年)的光合特性、光合色素含量、叶表皮特征、叶解剖结构及叶片功能性状差异。结果表明:(1)幼树最大净光合速率(P_max)(12.00 μmol·m^-2·s^-1)和光饱和点(LSP)(1 360.40 μmol·m^-2·s^-1)极显著(P<0.01)高于幼苗(分别为5.69 μmol·m^-2·s^-1和839.61 μmol·m^-2·s^-1),而幼苗的光补偿点(LCP)(11.37 μmol·m^-2·s^-1)更低,表明幼苗耐荫而幼树喜光。(2)幼树叶绿素(Chl)和类胡萝卜素(Car)含量均显著或极显著(P<0.05或P<0.01)高于幼苗,且叶片更厚、栅栏组织更发达、中脉导管直径更大,同时具有更大叶面积,以及更高的比叶重和叶干物质含量。(3)相关性分析显示,P_max与叶片厚度、叶绿素含量、比叶重、叶干物质含量均呈显著(P<0.05)或极显著(P<0.01)正相关。综上所述,幼苗适应林下弱光环境,而幼树需较强光照支撑其高光合能力。自然种群林下光照不足导致滇桐幼苗难以向幼树转化,这可能是其濒危的重要原因。该研究为滇桐的保育和引种驯化提供了科学依据,建议在保育中通过人工疏伐改善光照条件,促进其种群更新。

Abstract:

Craigia yunnanensis, a plant specieswith extremely small populations(PSESP)endemic to China, is listed as a National Class Ⅱ protected wild plant. To clarify the causes of regeneration failure — particularly the lack of sapling recruitment in natural populations — this study compared the photosynthetic characteristics, photosynthetic pigment contents, leaf epidermal traits, leaf anatomical structures, and leaf functional traits between seedlings(6-month-old)and young trees(8-year-old)cultivated in an experimental plantation. The results were as follows:(1)The maximum net photosynthetic rate(P_max)(12.00 μmol·m^-2·s^-1)and light saturation point(LSP)(1 360.40 μmol·m^-2·s^-1)of young trees were extremely significantly higher(P<0.01)than those of seedlings(5.69 μmol·m^-2·s^-1 and 839.61 μmol·m^-2·s^-1, respectively), whereas the light compensation point(LCP)of seedlings was lower(11.37 μmol·m^-2·s^-1), indicating a shade-tolerant strategy in seedlings and a light-demanding strategy in young trees.(2)Chlorophyll(Chl)and carotenoid(Car)contents in young trees were significantly or extremely significantly higher than that in seedlings(P<0.05 or P<0.01), and their leaves were thicker, with more developed palisade tissues, larger midrib vessel diameters, and bigger leaf area, higher specific leaf weight(SLW), and leaf dry matter content(LDMC).(3)Correlation analysis revealed significant or extremely significant positive correlations(P<0.05 or P<0.01)between P_max and leaf thickness, chlorophyll content, SLW, and LDMC. In conclusion, seedlings adapt to low-light understory environments, whereas young trees require higher light availability to sustain their elevated photosynthetic capacity. Insufficient understory light in natural habitats likely hinders the transition from seedlings to young trees, contributing to the species' endangered status. These findings provide essential scientific support for conservation and cultivation practices. It is recommended that thinning or canopy-opening measures be implemented to improve understory light conditions and promote population regeneration.