不同光环境对桤木幼苗生长和光合特性的影响

通过设置3个光照强度(100%、56.2% 和12.5%)，模拟森林幼苗生长的旷地(采伐迹地)、林窗和林下光环境，研究不同光照强度对外来种台湾桤木和乡土种四川桤木幼苗的生长、光合特性以及生物量积累与分配的影响.结果表明： 低光环境限制了两种桤木幼苗形态指标的增长，适当遮荫的林窗环境比旷地更有利于幼苗的生长.台湾桤木幼苗具有较高的比叶面积和相对生长速率，较大的单叶面积、叶长、叶宽、株高和基径，较少的叶片数和较低的叶面积比、叶柄长.低光环境下,台湾桤木幼苗的最大净光合速率、光饱和点和表观光量子效率较高，光补偿点和暗呼吸速率较低.随着光照强度的降低，台湾桤木幼苗具有更高的根生物量比和更低的叶生物量比；四川桤木幼苗则相反，加剧了动物取食和机械损伤的风险.

Allelopathic effects of aqueous extracts from native Vitex negundo on the growth and photosynthesis traits of Eupatorium odoratum

Three light intensities (100%, 56.2%, and 12.5%) were installed to simulate the light regimes of opening field (cutting blank), forest gap, and understory, respectively, aimed to understand the effects of different light regimes on the seedling growth, photosynthetic characteristics, and biomass accumulation and allocation of alien species Alnus formosana and native species A. cremastogyne. Low light regime limited the seedling growth of the two alder species, while the light regime of forest gap was more favorable for the growth, in comparison with that of the opening field. Regardless of the light regimes, A. formosana seedlings had higher specific leaf area (SLA), relative growth rate (RGR), leaf area, leaf length, leaf width, plant height, and basal diameter, but smaller leaf number, leaf area ratio (LAR), and petiole length. Under low light regime, A. formosana seedlings had higher maximum net photosynthetic rate (P_{n max}), light saturation point (LSP), and apparent quantum yield (AQY), but smaller light compensation point (LCP) and dark respiration rate (R_day). With the decrease of light intensity, A. formosana seedlings had much higher root mass ratio (RMR) and much lower leaf mass ratio (LMR), implying that more carbon was allocated and stored to the roots rather than new leaves, whereas the A. cremastogyne seedlings were in adverse, i.e., more carbon was allocated to the above-ground parts, which might increase the risk of animal feeding and mechanical damage.