遮光对红果榆幼苗光合作用及叶片解剖结构的影响

Effects of Shading on Photosynthetic Characteristics and Leaf Anatomical Structure of Ulmus szechuanica Seedlings

为揭示不同光照条件下红果榆幼苗光合生理及叶片结构的变化,推测其耐荫性,设置L_(0)(辐射光强100%)、L1(辐射光强45%)、L_(2)(辐射光强25%)和L_(3)(辐射光强18%)4种不同的光环境,研究了遮光对红果榆幼苗光合作用参数、叶片形态及解剖结构的影响。结果表明:不同遮光处理下P_(n)呈现出不对称的凸型变化。L_(1)处理下P_(n)变幅较大,最大值出现在午时,午后P_(n)开始急剧下降。而遮光处理下光合有效辐射(PAR)显著不足,各时点P_(n)绝对值显著减小,峰值降低。相应地,G_(s)表现出先升高后降低,而G_(i)呈现先降后升的凹形变化。不同遮光条件下P_(n)的日均大小序列为L_(0)>L_(1)>L_(2)>L_(3)。遮光显著影响红果榆幼苗的光响应参数。弱光条件下红果榆幼苗LCP、LSP显著降低,P_(nmax)、R_(d)均明显变小。遮光影响叶片的形态发育。随着遮光强度的加大,单叶面积(SLA)增加,比叶重(LMA)减小,比叶面积(LAM)增大,并与对照相比呈现显著差异(P<0.05)。遮光条件下红果榆叶片厚度变小,表皮细胞(EP)厚度变薄,栅栏组织(PT)和海绵组织(ST)厚度均明显降低。红果榆苗期表现出一定的喜光性,对弱光具有一定的生理调节能力,但是重度郁闭将导致幼苗营养不良。光照条件不足可能是影响红果榆种实成苗、种群更新的重要外因。生产实践中,建议对密度过大的自然林实施适度疏伐,增进通风透光,适度清理林内凋落物,为野生种群的更新繁衍创造条件。

To reveal the changes of photosynthetic physiology and leaf structure of U.szechuanica seedlings under different light conditions and infer its shading tolerance,four different treatments,including L_(0)(100%radiation intensity),L_(1)(45%radiation intensity),L_(2)(25%radiation intensity)and L_(3)(18%radiation intensity),were set up,photosynthesis parameters,leaf morphology and leaf anatomical structure characteristics of seedlings under shading were studied.Results showed that P_(n)showed asymmetric convex linear changes under different shading treatments.The variation of P_(n)under L_(0)treatment was strong,the maximum value of P_(n)appeared at 12:00,it began to decline sharply over it.However,the photosynthetic effective radiation under shading treatment was insufficient,the P_(n)of each time decreased significantly,and the peak value decreased.Correspondingly,the G_(s)basically showed the change of firstly rise and late decline,and G_(i)showed convex shape.The daily average sequence of P_(n)under different light environments was L_(0)>L_(1)>L_(2)>L_(3).Shading had a significant effect on photosynthetic response parameters of U.szechuanica seedlings,which caused a significant decrease of LCP,LSP,and changes of P_(nmax) and R_(d) was so.Shading affected the leaf morphology.With the increase of shading intensity,single leaf area(SLA)increased,single leaf dry weight(SLW d)and lamina mass per unit area(LMA)decreased,and lamina area per unit mass(LAM)increased.There was significant difference between these indexes of seedlings under shading compared with the control.Under shading,leaves of U.szechuanica became thinner,thickness of epidermal cells(EP)decreased significantly,thickness of both palisade tissue(PT)and sponge tissue(ST)reduced.U.szechuanica seedlings like light,which has certain physiological regulation ability to weak light,but strong shading will lead to poor malnutrition.Light conditions might be an important external factor affecting the living and population renewal of seedlings,so it was suggested to carry out moderate thinning of natural forest,reduce canopy density in forest,clean up the litter,and create a favorable condition for propagating of wild population.