遮光环境下玉兰幼苗光合日进程特征及其与重要环境因子的关系

Diurnal Photosynthetic Characteristics of Magnolia denudata Seedlings under Shading and Their Relationship with Key Environmental Factors

为了探明夏季遮光对环境因子和玉兰(Magnolia denudata)幼苗光合特征的影响,分析幼苗光合日变化特征和环境因子的关系,通过设置4个遮光处理,分别是全日照(CK)、轻度遮光(遮光度25%,LS)、中度遮光(遮光度55%,MS)和重度遮光(遮光度85%,SS),记录1 d中不同遮光环境下重要条件因子日变化规律,并利用便携式光合测定系统对2年生玉兰幼苗的光合日变化进行测定。结果表明,不同遮光条件下幼苗的净光合速率、蒸腾速率和水分利用效率表现为先升高后降低的单峰型曲线,峰值一般出现在10:00、12:00和14:00,胞间CO2浓度均表现为早晚高中间时段较低的趋势,气孔导度因遮光条件不同而变化,其中CK和SS处理为双峰曲线,峰值出现在10:00和14:00,谷值出现在12:00,LS和MS处理为典型的单峰曲线,12:00达最大值,气孔限制值与气孔导度表现出相反趋势。通过对光合指标的整体分析,不同遮光条件下的光合活性表现为LS>MS>CK>SS。结合与环境因子的相关分析来看,影响幼苗光合活性的环境因子主要包括光合有效辐射、大气温度、大气相对湿度、饱和水汽压差和叶表温度,其中,CK处理的过高光合有效辐射和大气温度引发的其他环境因子变化共同作用限制了叶片气孔导度开放程度,导致净光合速率低于LS和MS处理,造成SS处理净光合速率较低的原因在于过低的光合有效辐射。通过对不同遮光条件下环境因子变化水平和幼苗光合活性分析可知,适度的增加光温条件,降低大气湿度更有利于玉兰幼苗光合活性的提升。

To find out the influence of summer shading on environmental factors and photosynthetic characteristics of Magnolia denudata seedlings,and analyze the relationship between diurnal variation characteristics of photosynthesis and environmental factors. In this study,four shading environments:CK,light shading(25% shading condition,LS),Moderate shading(55% shading condition,MS) and severe shading (85%shading condition,SS)were set up to record the diurnal variation of important environmental factors in different shading environments during the day.The diurnal variation of photosynthesis in two-yearold Magnolia denudata seedlings was measured by portable photosynthetic system.The results showed that the net photosynthetic rate(Pn),transpiration rate(Tr)and water use efficiency(WUE)of seedlings under different shading conditions showed a single peak curve,which first increased and then decreased.The peak values generally appeared at 10:00,12:00 and 14:00.The intercellular CO2 concentration(Ci)was higher in the morning,evening,and lower in the middle.The stomatal conductance(Gs)varied with different shading conditions.CK and SS treatments were double-peak curves,peaks appeared at 10:00 and14:00,valleys appeared at 12:00,LS and MS treatments were typical single-peak curves,and reached the maximum at 12:00,and stomatal limitation values(Ls)showed opposite trends with Gs.According to the overall analysis of photosynthetic index,the photosynthetic activity under different shading conditions was LS>MS>CK>SS.Considering the correlation with environmental factors,the environmental factors affecting photosynthetic activity of seedlings mainly included photosynthetic active radiation(PAR),atmospheric temperature(Ta),atmospheric relative humidity(RH),saturated water vapor pressure deficit(VPD)and leaf surface temperature(Tleaf),among which,under CK treatment.The combination of excessive PARand Tainduced changes in other environmental factors limited the opening of leaves to Gs,resulting in Pnlower than LS and MS.The reason for the lower Pn under SS treatment was that PAR was too low.Through the analysis of the changes of environmental factors and photosynthetic activity of Magnolia denudata seedlings under different shading conditions,it was found that moderately increasing light and temperature conditions and reducing atmospheric humidity were more conducive to the improvement of photosynthetic activity of Magnolia denudata seedlings.