亚热带常绿阔叶林冠层附生植物叶片形态结构及生理功能特征的适应性研究

以南亚热带常绿阔叶林林冠层不同部位的4种附生植物:瓜子金(Dischidia chinensis Champ.ex Benth.)、蔓九节(Psychotria serpens L.)、白背瓜馥木(Fissistigma glaucescens (Hance) Merr.)和山萎(Piper hancei Maxim.)为研究对象,比较其叶片解剖结构和光合、蒸腾等生理特性,探讨附生植物叶片形态结构、生理生态功能对冠层不同部位水、热和光资源的适应以及叶片形态结构与生理生态功能的联系.结果表明:着生在冠层上部的两种附生植物瓜子金和蔓九节叶片小而厚(厚度分别为3558±63 μm和217.1±33.1 μm),气孔面积小(分别为185.7±3.7 μm2和225 4±5.2 μm2)且覆盖角质膜,有利于降低蒸腾速率(两者分别为0.17±0.02 mmol H2O和0.34±0.05 mmol H2O),提高水分利用效率WUE(分别为11.35±0.87 μmol CO2/mmolH2O和7.88±1.31 μmol COJmmol H2O),更适应冠层顶部高温、低湿、强光照的生境.这些结构特征却不利于气体交换,会致使瓜子金和蔓九节的光合作用降低(二者最大净光合速率Pmax分别为2.2±0.1 μmol CO2 ·m-2·s-1和3.2±0 4 μmol CO2·m-2·s-1).冠层中下部的白背瓜馥木和山蒌叶片相对较薄(厚度分别为90.8±9.9 μm和114 9±18.2 μm),气孔面积较大(分别为260.6±6.3 μm2和362.5±8.7 μm2),叶肉细胞分化明显,海绵组织排列松散,有利于提高对弱光的利用,增强光合能力(二者Pmax分别为9.5±1.3 μmol CO2·m-2·s-1和7.1±0.8 μmol CO2·m-2·s-1,是瓜子金和蔓九节Pmax的3～4倍),更适应冠层中下部低温、高湿、弱光照环境.这些结构同时会导致白背瓜馥木和山蒌蒸腾速率提高(两者分别为0.67±0.10 mmol H2O和0.74 +0.13 mmol H2O),WUE下降(分别为4.4±1.01μmol CO2/mmol H2O和3.4±0.9 μmol CO2/mmol H2O,仅为瓜子金和蔓九节WUE的30％ -48％).这表明着生在林冠层不同部位的附生植物叶片形态结构特征随着光合有效辐射、温度、湿度等微环境因子的变化表现出显著的差异,并致使各自的生理生态功能发生了相应的适应,是植物适应环境条件的重要表现.

Acclimation in Leaf Morphological and Eco-physiological Characteristics of Different Canopy-dwelling Epiphytes in a Lower Subtropical Evergreen Broad-leaved Forest

Epiphytes have been well characterized in terms of the morphological and eco-physiological traits that permit them to thrive in the complex forest canopy.Our aim was to characterize and analyze the morphological and eco-physiological traits of different canopy-dwelling epiphytes in a lower subtropical evergreen broad-leaved forest in Southern China. Results showed that the differences in morphological and eco-physiological characteristics between the upper and lower canopy-dwelling epiphytes were largely explained by changes in environmental factors such as photosynthetic active radiation（PAR）,temperature,and humidity within the complex forest canopy.Two epiphytes,Dischidia chinensis and Psychotria serpens located in the upper canopy had low Tr（0.17 ± 0.02 mmol H 2 O and 0.34 ± 0.05 mmol H 2 O,respectively） and low P max（2.2 ± 0.1 μmol CO 2.m-2.s-1 and 3.2 ± 0.4 μmol CO 2.m-2.s-1,respectively） associated with thick leaf（558 ± 63 μm and 217.1 ± 33.1 μm,respectively） and small stomata size（185.7 ± 3.7 μm 2 and 225.4 ± 5.2 μm 2,respectively） to adapt to their upper dwelling environments（high temperature,low air humidity and high PAR）.At the same time,the special structures led to high WUE（11.35 ± 0.87 μmol CO 2 /mmol H 2 O and 7.88 ± 1.31 μmol CO 2 /mmol H 2 O,respectively）.However,the lower canopy-dwelling epiphytes Fissistigma glaucescens and Piper hancei had thin leaf（90.8 ± 9.9 μm and 114.9 ± 18.2 μm,respectively） and large stomata size（260.6 ± 6.3 μm 2 and 362.5 ± 8.7 μm 2,respectively）.The ratios of palisade to spongy tissues thickness（P/S）,the thickness of leaf epidermis thickness and other structures also changed with various canopy-dwelling heights.In comparison with Dischidia chinensis and Psychotria serpens located at upper canopy-dwelling conditions,Fissistigma glaucescens and Piper hancei showed high P max（9.5 ± 1.3 μmol CO 2.m-2.s-1 and 7.1 ± 0.8 μmol CO 2.m-2.s-1,respectively）,high Tr（0.67 ± 0.10 mmol H 2 O and 0.74 ± 0.13 mmol H 2 O,respectively）,and low WUE（4.4 ± 1.0 μmol CO 2 /mmol H 2 O and 3.4 ± 0.9 μmol CO 2 /mmol H 2 O,respectively）,which was 1.2-3.3 times（P max）,1.2-2.3 times（Tr）,and 30%-48% higher（WUE）.