遮荫对苦丁茶树叶片特征及光合特性的影响

Effects of shading on the leaves and photosynthetic characteristics of Ligustrum robustum

通过人工遮荫方式研究了4种遮荫强度(全光照、20%、40%和60%遮荫)对苦丁茶树叶片生长和光合特性的影响,从而为苦丁茶合理栽培和抚育管理提供理论依据。结果表明:(1)40%遮荫条件下苦丁茶树叶片宽度、厚度、叶面积和栅栏组织厚度均显著高于其它3个处理(P<0.05),栅栏组织层数为2层,其它3个处理均为1层。遮荫显著提高了苦丁茶树叶片总叶绿素、叶绿素a和叶绿素b含量,且随遮荫程度的增强叶绿素含量呈上升趋势,而叶绿素a/b呈相反趋势。(2)40%遮荫处理显著提高了苦丁茶树叶片净光合速率(P<0.05),而遮荫达到60%时则抑制了其光合速率。20%和40%遮荫处理促进苦丁茶树叶片气孔导度、胞间CO2浓度和蒸腾速率的提高,降低了蒸汽压亏缺,有利于光合作用的进行;全光照和60%遮荫处理下蒸汽压亏缺显著高于其它处理,而气孔导度和胞间CO2浓度等因子极显著降低,从而抑制了苦丁茶树叶片蒸腾作用和光合作用。(3)遮荫处理降低了苦丁茶树叶片光补偿点和暗呼吸速率,40%遮荫处理下表观量子效率和最大净光合速率显著提高。随着遮荫程度的增强,Fv/Fm和Fv/Fo降低,与全光照相比,3种遮荫处理Fv/Fm依次下降了2.71%、4.59%和8.03%,Fv/Fo值依次降低了6.89%、11.99%和19.81%(P<0.01);60%遮荫下各荧光参数值显著低于其它3个处理,过度遮荫使苦丁茶树叶片叶绿素分子捕获激发能的效率及光系统Ⅱ(PSⅡ)潜在活性降低。综上,苦丁茶树在适宜的遮荫强度下,即40%遮荫(日光合有效辐射在273—1222μmol·m-2·s-1范围内)条件下其叶片生长和光合能力会有效提高。

We study the effect of different shading treatments（ 0,20%,40% and 60% shade） on the leaf growth and photosynthetic characteristics of Ligustrum robustum through artificial shade,aiming to provide scientific advices for cultivation and management of the species. The results showed that（ 1） the leaf width,leaf area and leaf thickness at 40%shade of L. robustum were significantly higher than those under other three different treatments, the palisade tissue thickness（ 64. 70 μm） at 40% shade of L. robustum was significantly higher than those under other three different treatments, there were two palisade tissue layers at 40% shading treatment comparing to one layer at the other three different treatments. The contents of total chlorophyll,chlorophyll a and chlorophyll b in leaves under the shading conditions were significant higher than those under the full daylight,and the chlorophyll contents increased with the increasing of shading levels. That L. robustum showed significantly higher leaves growth and the best overall growth anddevelopment at 40% shading treatment,which could be regarded as an appropriate shading intensity for its growth and development of L. robustum.（ 2） The net photosynthetic rate increased at 40% shading treatment but decreased at 60%shading treatment. The stomatal conductance,internal carbon dioxide concentration and transpiration rate increased while the vapor pressure deficit decreased at both 20% and 40% shading treatment,which was helpful for photosynthesis. The vapor pressure deficit was highest while stomatal conductance and internal carbon dioxide concentration lowest at the 0%and 60% shading treatment comparing to other shade treatments,which suppressed net photosynthetic rate and transpiration rate of the plants.（ 3） The dark respiration and light compensation point declined in the shading treatments while the 40%shading treatments resulted in the increases of the apparent quantum efficiency and maximum net photosynthetic rate,which indicated that L. robustum had shade tolerance to some extent. The Fv /Fm and Fv /Fo became smaller as the increase of shading level,the Fv /Fm of 20%,40% and 60% shading treatments were about 2. 71%,4. 59% and 8. 03%significantly lower than that under full day light respectively,and the Fv /Fo of 20%,40% and 60% shading treatments were about 6. 89%,11. 99% and 19. 81% significantly lower than that under full day light respectively. All fluorescence parameters of 40% shading treatment were significantly lower than those under the other three different treatments. Shading significantly depressed the efficiency of chlorophyll molecules capture excitation energy and potential activity of photosystemⅡ（ ΦPSⅡ）. In summary,L. robustum is shade-tolerant plants,and 40% shading treatment（ the daily PAR values within the range of 273—1222 μmol·m-2·s-1） is an appropriate light environment,which could significantly improve leaves growth and photosynthetic capacity.