黄河三角洲白蜡人工林不同冠层光合特征研究

Photosynthetic Characteristics in Different Canopy Layers of Ash Plantation in the Yellow River Delta

本研究以黄河三角洲地区典型白蜡人工林为研究对象,测定了不同冠层叶片的光响应曲线及光合参数的日变化,并对影响不同冠层净光合速率(Pn)的主要生态环境因子进行了分析。结果表明:白蜡人工林不同冠层叶片的光量子效率(α)表现为上冠层(U)>中冠层(M)>下冠层(L),最大光合速率(Pn_(max))、光饱和点(I_(sat))表现出相同的特征,而光补偿点(I_(c))变化相反,说明冠层越往上光适应范围越大;暗呼吸速率表现为冠层U>冠层L>冠层M。冠层U和冠层M的Pn呈双峰曲线变化,有明显的‘光合午休’现象,首峰出现时间均为上午10时,次峰时间分别为14时和16时;冠层L表现为单峰曲线,峰值出现在12时。逐步回归分析和通径分析表明,不同冠层Pn主要受气孔导度(Gs)和胞间二氧化碳浓度(Ci)的影响,分别表现为正向、负向影响,但不同冠层的主要影响因子存在差异,且因子间存在互作效应。总之,黄河三角洲白蜡人工林上冠层具有较高的光合能力和光合效率,这为白蜡人工林经营管理中改善其空间结构提供了参考。

With the representative ash(Fraxinus pennsylvanica)plantation in the Yellow River Delta as research object,the light response curves of leaves in different canopy layers and the diurnal changes of photo⁃synthetic parameters were measured,and the main environmental factors affecting the net photosynthetic rate(Pn)of different canopy layers were analyzed.The results were as follows.The photon quantum efficiency(α)of leaves in different canopy layers of ash plantation showed upper canopy(U)>medium canopy(M)>lower canopy(L),and the maximum photosynthetic rate(Pn_(max))and saturation light intensity(I_(sat))showed the same characteristics,while the photosynthetic compensation point(I_(c))changed oppositely,which indica⁃ted that the higher the canopy was,the larger the light adaptation range was.The dark respiration rate(Rd)ranked as canopy U>L>M.The Pn change of canopy U and M showed bimodal curves with the obvious‘photo⁃synthetic noon⁃break’phenomenon;the first peak appeared at 10 a.m.,and the second peak appeared at 14 and 16 p.m.The Pn change of canopy L exhibited a unimodal curve with the peak at 12 p.m.The stepwise re⁃gression and path analyses showed that the Pn of different canopy layers were mainly affected by stomatal conductance(Gs)positively and intercellular carbon dioxide concentration(Ci)negatively,but the main influ⁃encing factors varied with the change of canopy layer;these factors had a certain interaction effect.In conclu⁃sion,the higher canopy of the ash plantation had higher photosynthetic capacity and photosynthetic efficiency.All these results could provide references for improving the spatial structure of the ash plantation during man⁃agement.