独叶草叶二叉分枝脉序中网结脉和盲脉的形态学研究

对独叶草营养叶二叉分枝脉序及其中的网结脉和盲脉的形态学研究表明：(1)网结脉中2条完全汇合的与靠近脉中完全分离的叶脉之间未发现任何形式的维管束汇合的中间类型及网结脉中具有不同程度的连接脉退化痕迹的事实表明,网结脉不可能由靠近脉产生,相反,由于网结脉中联结脉的退化而形成开放脉;(2)盲脉是通过伴随着齿退化的达齿脉的退化、网结脉中联结脉的间断、非网结脉由分枝处间断三种方式产生的;(3)越裂片脉的出现及其可以形成网结脉的现象表明独叶草营养叶可能曾具有较为复杂的脉序,这种叶脉也呈现出退化的趋势;(4)独叶草营养叶的二叉分枝脉序可能是一种退化性状,而网结脉的出现可能是这种退化过程中的残留痕迹。     

蕤核的花粉形态及叶片微观结构

运用光学显微镜和扫描电镜对蕤核的花粉形态及叶片微观结构进行了观察。结果表明:蕤核花粉体积小,近球形,辐射对称,具三沟,外壁具条纹状纹饰。上下表皮均有角质层,但形态不同。下表皮有气孔分布,气孔略下陷,气孔密度每平方毫米200～300个,气孔存在三种状态。叶片为异面叶,栅栏组织细胞由2～3层柱状细胞构成,排列紧密,海绵组织由管状细胞构成,细胞间隙大。蕤核虽属于中生植物,但叶片微观结构趋近于旱生植物的特征。     

Pollen discounting and the evolution of selfing in Arenaria uniflora (caryophyllaceae)

Although most models of mating system evolution assign a central role to the male transmission advantage of selfing genotypes, empirical data on the male fitness consequences of increased self-pollination are still uncommon. Here, I use measures of pollen import and export by focal plants in genotyped arrays to investigate the effects of floral morphology and pollination environment on self and outcross male function. Plants from an autogamous population of Arenaria uniflora (Caryophyllaceae) exhibit complete pollen discounting relative to closely related outcrossers, as do morphologically intermediate F1 hybrids between the two populations. However, the low cumulative male fitness of hybrids probably results from reduced pollen number or competitive ability, rather than a nonlinear relationship with floral morphology. When surrounded by selfers, plants from the outcrosser population self-fertilize at nearly the same rate as selfers (>80%), but have much lower self male fitness due to reduced fruit set. Because outcross siring success is also extremely low (<8%) in this treatment, these mate-limited outcrossers are at male fitness disadvantage to both pseudocleistogamous selfers and nonlimited outcrossers. The relative male fitness of plants with different mating systems appears dependent on the ecological context, as well as on morphological trade-offs.     

Do submerged aquatic plants influence periphyton community composition for the benefit of invertebrate mutualists?

• 1 It has been suggested that submerged aquatic plants can influence the periphyton which grows on their surfaces, making it nutritionally beneficial to snails. In return, preferential feeding by snails clears the plants from a potential competitor, with both plants and grazers gaining from this mutualistic relationship.
• 2 A highly replicated experiment was conducted, in which the nature of the plant (isoetid and elodeid types compared with similar shaped inert substrata), the nutrient availability (10–200 µg L^‐1 P, 0.2–4 mg L^‐1 N) and the influence of periphyton grazers, Physa fontinalis, were controlled. The plants were cleaned of periphyton before use and an algal inoculum added to all treatments. At the end of the growth period, quantitative measures of the periphyton community composition were made and related to the treatments using both ordination and analysis of variance.
• 3 Grazing had the largest influence on community composition and algal numbers. A community of unicellular and adpressed filamentous forms developed in the presence of snails, and of erect filamentous forms in their absence. Three algal species, Cocconeis placentula, Chamaesiphon incrustans and Aphanochaete repens, increased in real numbers in the presence of snails, probably as a result of reduced competition whilst being able to withstand grazing.
• 4 The second largest effect was the influence of host plant. However, differences between the two artificial plants were as great as between the real plants and their artificial counterparts, indicating that physical structure was as important as any active contribution by the plants. Nutrients had a small but significant effect on community composition, but not all species responded in the same way to nutrient enrichment.
• 5 Although submerged aquatic plants exert an influence over the community composition of the periphyton which develops on their surfaces, it is unlikely that they manipulate it to make it more attractive to grazers such as snails.

     

独叶草的光合生理生态特性

应用CI-301PS便携式光合测定仪对独叶草(Kingdonia uniflora)营养叶的光合生理生态特征进行了研究.结果表明:独叶草的净光合速率(Pn)日变化曲线呈双峰型,峰值出现在13:30和16:30左右,具有明显的光合"午休"现象;其叶片的蒸腾速率(Tr),水分利用率(WUE)的变化也呈双峰型.自然条件下,独叶草叶片净光合速率与光合有效辐射(PAR)、蒸腾速率、气孔导度(Gs)之间都具有多项式回归关系,R2分别为0.2082、0.2016和0.0582(n=129,P＜0.05),但独叶草叶片净光合速率与空气温度(Ta)相关性不显著(P＞0.05).独叶草叶片的光补偿点(LCP)、光饱和点(LSP)分别为14.93和215.76 μmol·m-2·s-1,只能适应较窄的光照环境.     

独叶草的不育雄蕊、花被片和可育雄蕊对传粉昆虫和传粉的影响

为确定独叶草（Kingdonia uniflora）不育雄蕊、花被片和可育雄蕊对传粉昆虫和传粉的影响,分别进行去除不育雄蕊（A组）,去除花被片（B组）,去除可育雄蕊（C组）和对照组（D组）处理。结果表明：昆虫访花频率分别为A组0．4次／h、B组0次／h、C组0．9次／h、D组2．2次／h;被授粉花朵百分比分别为A组29．09％、B组40．38％、C组70.91％、D组91．67％;被授粉心皮百分比分别为A组17．77％、B组20．94％、C组为40．58％、D组为75．27％。与对照组相比,处理后被授粉花朵百分比、被授粉心皮百分比下降幅度均为A组〉B组〉C组。结合昆虫访花频率与不育雄蕊蜜汁的分泌量呈正比,可确定不育雄蕊产生的蜜汁是吸引昆虫访花的最主要因素。花被片为昆虫取食提供停歇的平台,可育雄蕊与花被片产生的色差及可育雄蕊提供的花粉,是吸引昆虫的辅助因素。     

Rapid oxygen exchange across the leaves of Littorella uniflora provides tolerance to sediment anoxia

1. Littorella uniflora and Lobelia dortmanna are prominent small rosette species in nutrient‐poor, soft‐water lakes because of efficient root exchange of CO₂ and O₂. We hypothesise that higher gas exchange across the leaves of L. uniflora than of L. dortmanna ensures O₂ uptake from water and underlies its greater tolerance to sediment anoxia following organic enrichment. 2. We studied plant response to varying sediment O₂ demand and biogeochemistry by measuring photosynthesis, gas exchange across leaves and O₂ dynamics in plants during long‐term laboratory and field studies. Frequent non‐destructive sampling of sediment pore water was used to track changes in sediment biogeochemistry. 3. Addition of organic matter triggered O₂ depletion and accumulation of , Fe²⁺ and CO₂ in sediments. Gas exchange across leaf surfaces was 13–16 times higher for L. uniflora than for L. dortmanna. Oxygen in the leaf lacunae of L. uniflora remained above 10 kPa late at night on anoxic sediments despite organic enrichment. Leaf content of N and P of L. uniflora remained sufficient to keep up photosynthesis despite prolonged sediment anoxia, whereas nutrient content was too low for long‐term survival of L. dortmanna. 4. High gas exchange across L. uniflora leaves improves its performance and survival on anoxic sediments compared with L. dortmanna. Lobelia dortmanna uses the same gas‐tight leaves in air and water, which makes it highly susceptible to sediment anoxia but more cost‐effective in ultra‐oligotrophic environments because of slow leaf turnover.     

蕤核叶片解剖结构和组织化学定位研究

采用解剖学和组织化学方法,研究了蕤核(Prinsepia uniflora Batal.)叶片的解剖结构,并对叶片中的黄酮类、生物碱类及多糖的组织化学定位进行了研究。结果表明:蕤核叶片上表皮有角质层,下表皮有气孔分布,气孔密度为278个·mm-2,近轴面栅栏组织细胞2～3层,排列紧密而整齐,含有许多晶体;叶片主脉木质部发达,由多列导管组成。上述特征说明蕤核叶片的解剖结构与环境之间的适应性。组织化学定位显示黄酮多分布于栅栏组织和厚角组织,生物碱含量少,多糖均匀分布于叶肉中。     

Effect of leaf age on CAM activity in Littorella uniflora

In this study the effect of ontogenetic drift on crassulacean acid metabolism (CAM) was investigated in the aquatic CAM-isoetid Littorella uniflora. The results of this study strengthen the general hypothesis of CAM being a carbon-conserving mechanism in aquatic plants, because high-CAM capacity (45–183 μequiv. g⁻¹ FW) was present in all leaves of L. uniflora irrespective of age. Since possession of CAM in aquatic plants allows CO₂ uptake throughout the light/dark cycle, presence of CAM in all leaves influences the carbon balance of L. uniflora positively. On average for all lakes, different leaf classes accounted for 11–36% of the total dark CO₂ uptake by the individual plant.

The capacity for both CAM and photosynthesis declined with increasing leaf age, and was in the oldest leaves only 25–53% of the capacity in the youngest. The photosynthetic capacity was estimated to be sufficiently high to ensure refixation of the CO₂ released from malate during decarboxylation in the daytime. In line with this, a linear coupling between CAM capacity and photosynthetic capacity was found. Parallel to the change in photosynthetic capacity, an age-related change in total ribulose-bisphosphate carboxylase/oxygenase (rubisco) activity from 732 μmol C g⁻¹ DW h⁻¹ in the youngest leaves to 346 μmol C g⁻¹ DW h⁻¹ in the oldest was observed. In contrast, no significant change in phosphoenolpyruvate carboxylase (PEPcase) activity with leaf age was observed (means ranged between 46 and 156 μmol C g⁻¹ DW h⁻¹).     

稀有濒危植物独叶草种群分布格局的研究

独叶草 ( Kingdonia uniflora)是我国特有的稀有濒危植物 ,本研究应用方差 /均值比的 t检验、负二项参数、扩散型系数、丛生指标、Cassie指标、聚块性指标、Poisson分布和负二项分布的 χ2 拟合检验 ,对其种群的空间分布格局进行了研究。结果表明 :1独叶草种群总体呈聚集分布 ,t检验差异显著 ;k=1 .372 ;集群强度较高 ;Iδ=1 .730 >1 ;I=8.2 37,明显大于 0 ;CA=0 .72 9;m* /m=1 .72 9>1 ;离散分布拟合结果符合负二项分布模型。 2不同群落独叶草种群的聚集强度不同 ,牛皮桦 ( Betula utilis)群落的独叶草种群聚集强度最大 ,依次为箭竹( Sinarundinaria nitida)林、金背杜鹃 ( Rhododendron clementinae subsp.aureodorsale)灌丛、太白红杉 ( L arix chinensis)林、巴山冷杉 ( Abies fargesii)林。在此基础上 ,分析了格局形成的原因 ,提出了保护建议