薇甘菊(Mikania micranth)是世界性的入侵有害植物,对其入侵特性的理解将有助于我们更进一步揭示入侵机理和开展植物入侵的防治工作。叶片的光合作用是入侵植物薇甘菊入侵特性的研究内容之一,但到目前为止,仍没有开展对薇甘菊非同化器官茎的同化特性的研究。该文采取对比的研究方法,使用LICOR-6400气体交换系统和荧光系统对其幼嫩的绿色茎和成熟叶片的气体交换和叶绿素荧光特性进行测定,并对测定结果进行了对比分析,同时应用激光共聚焦显微镜对薇甘菊茎中叶绿体分布进行观察。使用叶绿素荧光系统测量瞬时叶绿素荧光特性表明,茎和叶的电子传输速率(Electron transport rate, ETR)和光系统Ⅱ实际光化学量子产量(Φ_PSⅡ)存在较好的正比例关系,相关系数达到0.97,说明茎中存在和叶中类似的光合结构。但在应用LICOR-6400气体交换系统测量稳定状态下的CO₂的气体交换速率时,观察到叶的气体交换速率稳定性较好,而茎的气体交换速率出现较大的波动,这可能是由于茎的气孔因素引起。综合来看,在相同面积和饱合光强下(光通量密度(Photosynthetic photo flux density, PPFD)=2 000 μmol·m ^-2·s^-1),叶的ETR为42.44 μmol·m ^-2·s^-1,茎的ETR为30.32 μmol·m ^-2·s^-1。在相同面积和低光强(PPFD=10 μmol·m ^-2·s^-1)下,叶的Φ_PSⅡ为0.69;茎的Φ_PSⅡ为0.57。在单位SPAD下,茎中ETR是每单位SPAD 4.24 μmol·m ^-2·s^-1,是叶的2.3倍,实际光化学量子产量是每单位SPAD 0.08,是叶的3倍。在比较茎和叶ETR中观察到茎比叶有更强的强光适应能力。激光共聚焦图像观察到薇甘菊茎的叶绿体主要分布在两个区域:皮层区和维管束周围。对照以往关于茎中叶绿体功能的研究表明,可能分布在两个区域中的叶绿体功能上存在差别。如上,薇甘菊茎中存在一定的光合作用能力,且在叶绿体的光能利用瞬时效率上茎明显强于叶,但在茎中这些光合作用的具体作用仍不清楚。

Background and Aims Mikania micranth is a well-known invasive species. Study of its characteristics will increase our knowledge of invasive mechanisms and management of invasive species. Photosynthesis of leaves is one of the invasive characteristics of M. micranth, but no studies have focused on assimilation characteristics of its stems.

Methods We compared young green stems and mature leaves using the LI-6400 gas exchange and fluorescence system, as well as laser scanning confocal microscopy to observe the distribution of chlorophyll.

Key Results Electron transport rate (ETR) and actual photochemical efficiency of system Ⅱ (Φ_PSⅡ) of stems and leaves were positively correlated (0.97), suggesting similar photosynthetic structure in stems and leaves. The gas exchange rate under constant conditions was stable for leaves but fluctuating for stems, possibly because of the pore factor of stems. Under the same area and saturated light (PPFD=2 000 μmol·m ^-2·s^-1), the ETR of leaves was 42.44 μmol·m ^-2·s^-1 and the ETR of stems was 30.32 μmol·m ^-2·s^-1. However, under the same area and low light (PPFD=10 μmol·m ^-2·s^-1), the Φ_PSⅡ of leaves was 0.69 and the Φ_PSⅡ of stems was 0.57. The electron transport rate in stems was 4.24 per unit SPAD, 2.3 times that of leaves. Actual photochemical efficiency of system Ⅱ was 0.08 per unit SPAD, 3 times that of leaves. Our research also indicated that light adaptive ability was better in stems than in leaves. Chlorophyll existed mainly in two tissues: cortex and around vascular bundles. It is possible that there are different chlorophyll functions in different tissues.

Conclusions This study indicates that photosynthesis occurred in young green stems of M. micrantha and the instantaneous efficiency of light utilization in stems was higher than in leaves. Results were unclear regarding the function of chlorophyll in different tissues.