蕨类植物配子体发育及化感作用的研究

我国的蕨类植物资源十分丰富，约有2600多种，占全世界12000种的1/5强，其中许多种具有很高的观赏价值。在欧美的一些国家，蕨类植物已经成为花卉行业的一个重要组成部分，早已进入家庭居室、宾馆、商场、办公楼和其它公共场所，绿化和美化人们的生活环境。到目前为止，全世界共已栽培成功观赏蕨类植物700多种（品种），而我国仅有十多种投入花卉市场作为盆景和切花配叶，尚未形成一定的规模。繁殖技术不过关是造成蕨类植物在我国花卉市场难以迅速发展的障碍之一。目前国内对蕨类植物的需求主要靠野外采挖得以满足，对野生蕨类植物资源造成严重的破坏，再加上自然生态环境的恶化，致使许多物种濒临灭绝。因此，加强相关的基础研究、繁殖技术和外界环境对蕨类植物影响的研究，对蕨类植物资源的利用和保护具有重要的研究价值和现实意义。 作者在近五年的研究过程中，建立了蕨类植物孢子无菌培养技术，观察记录了蕨类植物配子体的形态发育，为建立蕨类植物快速有效的繁殖技术体系打下了良好的基础。在此研究基础上，探讨了对蕨类植物生长发育构成威胁的外界环境之一—外来入侵植物紫茎泽兰对蕨类植物的生长发育的化感作用。紫茎泽兰为目前国际上研究的热点入侵植物之一，对我国农业、林业等已造成很大破坏，并对蕨类植物资源构成一定威胁。蕨类植物配子体发育过程是蕨类植物生活史中相对脆弱的环节，最容易受化感作用的影响。但迄今为止，国际上尚未开展任何紫茎泽兰对蕨类植物（包括孢子体阶段和配子体阶段）的化感作用的研究。为保护蕨类植物自然资源，填补这一研究领域的空白，开展了紫茎泽兰对蕨类植物配子体发育过程的化感作用的研究。实验结果如下： （1）建立了金毛狗（已被列入《濒危野生动植物种国际贸易公约》（CITES）附录II 名单）、凤尾蕨属植物如傅氏凤尾蕨、剑叶凤尾蕨、蜈蚣草、银脉凤尾蕨、溪边凤尾蕨、疏裂凤尾蕨、西南凤尾蕨等多种蕨类植物的孢子无菌培养技术体系。 （2）采用无机培养基培养、土壤培养和滤纸培养三种培养方法，显微镜下观察傅氏凤尾蕨、剑叶凤尾蕨、蜈蚣草、银脉凤尾蕨、溪边凤尾蕨、疏裂凤尾蕨、西南凤尾蕨、三角鳞毛蕨、乌毛蕨、普通针毛蕨、金毛狗的孢子萌发及配子体形态发育的整个过程，研究了上述蕨类植物孢子萌发的类型、配子体各发育阶段的形态特征以及到达每个发育阶段所需的时间，为蕨类植物的繁殖技术提供了科学的依据，同时为蕨类植物系统进化和形态分类学研究提供了重要的基础资料。 （3）以金毛狗、普通针毛蕨、疏裂凤尾蕨为受体植物，研究了紫茎泽兰对这三种蕨类植物的配子体发育的化感作用。选择蕨类植物孢子萌发、假根生长、配子体形态、配子体发育各阶段及所占比例为测定指标，结果表明：紫茎泽兰根、茎、叶提取液可以对这三种蕨类植物的配子体发育产生不同程度的化感作用。表现为：延迟这三种蕨类植物的孢子萌发，降低其孢子萌发率，抑制假根的伸长，并且上述抑制作用随紫茎泽兰提取液浓度的升高而增强。随着紫茎泽兰叶水提液浓度的升高，金毛狗配子体发育阶段会滞后。在紫茎泽兰根提取液处理下，普通针毛蕨配子体上的假根发生畸变。随着时间的推移，这种现象削弱或基本消失。随着根和叶提取液的浓度升高，普通针毛蕨配子体发育阶段将会滞后。高浓度的紫茎泽兰根提取液能改变疏裂凤尾蕨的配子体的形态，并使疏裂凤尾蕨的配子体发育阶段滞后，浓度越高效果越显著。这三种蕨类植物在受到紫茎泽兰化感作用的影响后表现不同，推测与它们对紫茎泽兰所含有的化感物质的不同敏感度有关。

外来入侵种紫茎泽兰竞争策略与扩散动态

紫茎泽兰（Eupatorium adenophorum Spreng.）作为重要的外来入侵种之一，已严重破坏了入侵地生态系统的结构与功能，同时使当地农林业生产蒙受巨大的损失。因此，明确紫茎泽兰的竞争策略与扩散潜力，对制定合理的控制措施具有重要意义。 土壤氮素增加常常有助于外来种的入侵，那么降氮能否抵制入侵呢？向土壤中添加碳素，增强微生物对氮素的吸收，从而降低土壤中可被植物吸收的氮素是目前常用的降氮方法。为检验这一假说对入侵种紫茎泽兰的适用性，选取入侵种紫茎泽兰和本地种禾本科雀麦（Bromus japonicus）、菊科鱼眼草（Dichrocephala integrifolia），分别单栽或与紫茎泽兰混栽，向各植物组合中添加碳素（按1650克有机质/平方米计）或氮素（按30克氮素/平方米计），并设立对照进行盆栽实验。在碳素添加条件下，紫茎泽兰地上与地下生物量分别比对照降低了71.9% 和 74.9%，而本地种的生物量却没有受到显著影响。同时，碳素添加导致紫茎泽兰对本地种的竞争强度（RII）明显下降。氮素添加则减弱或逆转了上述碳素的作用。因此，向土壤中添加碳素有助于抵抗氮沉降对外来种入侵的促进作用，特别对抵御那些与氮素有亲和力的入侵种更为有效。在不同氮素条件下，紫茎泽兰对本地种竞争中，资源竞争强度均明显大于化感作用。尽管在紫茎泽兰发育早期化感作用较小，但是，碳素添加使紫茎泽兰可利用氮素减少，激发了化感作用在竞争中占有更大的比例，说明资源竞争与化感是相互结合、共同发挥作用的。 去叶作为模拟采食方法之一，至少可以通过两种方式影响植物竞争。一是去叶对目标种生长产生负面影响，二是邻种去叶有利于目标种生长，进而改变种间竞争关系。基于以上假定，对紫茎泽兰与相邻本地种分别单栽、同种合栽和异种混栽，进行去叶处理。结果恰与假定相悖：在整个生长季内，去叶增加目标株生物量的1.0 – 198.9%。对于入侵种而言，当邻居本地种去叶时，紫茎泽兰能完全弥补竞争产生的负面效应，即它与未去叶的单栽紫茎泽兰生长无显著差异;而紫茎泽兰去叶降低了相邻本地种的生长，加剧了原本由于竞争给对本地种带来的负面影响。因此，去叶效应与邻种的存在与否及邻种的类型均有关。在应用生物控制对目标株采食时，特别是在没有造成严重伤害或致死情况下，可以使本来具有竞争优势的入侵种变得更具强势。竞争与去叶之间存在复杂的相互作用，采食带来的间接效应可能比预想的更为复杂。因此，在生物控制措施实施之前，充分地估计生物控制的间接作用至关重要。 为检验反应—扩散模型（reaction–diffusion model）能否正确模拟紫茎泽兰小尺度扩散速率，本研究调查了四川攀枝花山区5个不同的生境的紫茎泽兰群落。对各样地内紫茎泽兰定位和年龄确定，基于克里金插值法做出其入侵格局的等年线图，通过等年线之间的垂直距离即可得到紫茎泽兰扩散速率的经验值。同时，计算内禀增长率和扩散系数，根据模型计算得到扩散速率的预测值。结果表明：紫茎泽兰扩散速率经验值明显小于模型预测值。因此，尽管反应—扩散模型已在大尺度扩散预测方面得到广泛的应用和验证，但在小尺度上，由于没有借助于复杂的生活史模型和分层模型，单凭反应—扩散模型不足以得到准确的预测。另外，在没有遭受干扰的生境中，可以发现紫茎泽兰扩散早期存在明显的时滞期。倘若这种时滞效应在入侵扩散中是频繁发生的，那么在判定物种是否具有入侵性时，很可能由于物种处于时滞期而被误认为非入侵种。 基于紫茎泽兰入侵至中国60年来所收集到的441已知分布记录和23个环境变量，采用GARP模型对其潜在分布范围做出了预测，并通过Kappa和ROC（receiver–operator characteristic）对预测结果进行检验。结果表明紫茎泽兰目前分布以云贵高原为主体，逐渐向四川盆地东部、山东半岛、东南沿海、台湾沿海以及海南岛等地扩散。冷季降水量、年极端低温和年均最高温对分布影响较大。RDA（Redundancy Analysis）分析结果显示温度和降水是限制紫茎泽兰扩散的重要因素。在过去的20年里，紫茎泽兰已经从温度较高、天气波动较小的亚热带气候逐渐向气候温凉、降水减少的高海拔地区扩散。紫茎泽兰可以适应相对较宽的温度和降水梯度，年均温度在10—22 ˚C，年降水量在800—2000 mm区间均有分布。本研究结果为发展早期预警工作、防止紫茎泽兰在中国进一步入侵提供了科学依据。

薇甘菊对其入侵地植物种子萌发和幼苗生长的化感影响

薇甘菊主要入侵我国华南的广东、海南和云南三省，给当地造成了严重的危害，其强烈的化感作用被认为是其成功入侵的原因之一。而目前对薇甘菊化感作用的研究还较少，因而对薇甘菊化感作用的认识还有待深入的研究。另外，在对入侵植物入侵群落进行恢复时，由于入侵植物的凋落物以及生长过的土壤都还含有化感物质，常常导致恢复难以继续。因而选择抗化感能力强的物种来恢复薇甘菊的入侵地也成为该研究的一个主题。本文以薇甘菊为实验材料来研究薇甘菊化感作用对植物种子活力、种子萌发和幼苗生长的影响，同时筛选化感抗性强的物种以进行薇甘菊入侵地的恢复工作。其主要结论如下： 1、薇甘菊根和叶的提取液对植物种子活力、种子萌发和幼苗生长都有很大的抑制作用，并且这种抑制作用随着提取液浓度的升高以及处理时间的延长而加强，这证明了薇甘菊具有很强的化感作用。 2、一些植物种子萌发和幼苗生长在低、中浓度提取液以及高浓度提取液的短时间的处理下能被促进，不过在高浓度的提取液以及长时间的处理下都被抑制，这说明化感作用是抑制还是促进作用在很大程度上受到提取液浓度和处理时间的影响。 3、薇甘菊提取液（50 g L-1）对紫薇(Lagerstroemia indica)、刺槐(Robinia pseudoacacia)、黑麦草(Lolium perenne)和西葫芦（Cucurbita pepo）种子处理50-100 h就能极大的影响到其后的种子萌发和幼苗生长，这说明薇甘菊在短时间（50-100 h）就能给植物产生极强的化感作用，也进一步证实薇甘菊很强的化感作用。 4、由于各物种进化历史的不同，而且各物种在对薇甘菊的化感抗性上也存在着差异，所以各物种对薇甘菊提取液的化感反应也各不相同。 5、薇甘菊根提取液对刺槐和紫薇幼苗根的生长的影响要大于叶提取液对刺槐和紫薇幼苗根的生长的影响，而对刺槐和紫薇种子萌发率、初始萌发时间、萌发速率以及幼苗株高的影响却是叶提取液的化感作用强。这支持了一个新的假设：由于物种间代谢的多样性，至少在根和叶对受试植物根的化感影响方面，对于一些物种来说根的化感作用可能强于叶的化感作用，对于另一些物种来说叶的化感作用可能强于根的化感作用。 6、薇甘菊叶提取液对西葫芦种子活力、种子萌发和幼苗生长的化感影响大，而对其后开花时间以及开花的数目没有明显的影响，这说明薇甘菊对西葫芦生活史前期的化感影响要大于对西葫芦生活史后期的化感影响。 7、薇甘菊叶的水提取液对种子萌发的抑制作用要大于对幼苗生长的抑制作用;对非豆科植物种子萌发的影响要大于对豆科植物种子萌发的影响，而对非豆科植物幼苗生长的影响要小于对豆科植物幼苗生长的影响;对本地种的抑制作用要大于对外来归化种的抑制作用。 本研究证实了薇甘菊强烈的化感作用，根提取液对受体植物幼根生长的影响大于叶提取液对受体植物幼根生长的影响，这种化感作用可能极大的促进了薇甘菊的入侵。另外，在恢复薇甘菊入侵群落时，考虑到薇甘菊的化感作用，理应选择外来的已经归化了的非豆科植物的幼苗。

Allelopathic mechanism of pyrogallol to Microcystis aeruginosa PCC7806 (Cyanobacteria): From views of gene expression and antioxidant system

Pyrogallol is a potent allelochemical on Microcystis aeruginosa, but its allelopathic mechanism is not fully known. In order to explore this mechanism, gene expressions for prx, mcyB, psbA, recA, grpE, fabZ under pyrogallol stress were studied, and activities of the main antioxidant enzymes were also measured. The results showed that expression of grpE and recA showed no significant change under pyrogallol stress, while psbA and mcyB were up-regulated at 4 mg L-1. Both prx and fabZ were up-regulated even under exposure to 1 mg L-1 pyrogallol concentration. The activities of superoxide dismutase (SOD) and catalase (CAT) were enhanced under pyrogallol stress. Levels of malodialdehyde (MDA) at 2 and 4 mg L-1 pyrogallol were significantly higher than those of the controls. It was concluded that oxidant damage is an important mechanism for the allelopathic effect of pyrogallol on M. aeruginosa. (c) 2009 Elsevier Ltd. All rights reserved.

Allelopathic interactions between the Potamogeton spp and toxic cyanobacteria (Microcystis aeruginosa)

This study aimed to investigate the allelopathic activities between 3 Potamogeton spp. (Potamogeton maackianus, Potamogeton malaianus and Potamogeton pectinatus) and the toxic cyanobacteria (Microcystis aeruginosa). All Potamogeton spp inhibited the growth of M. aeruginosa in both coexistence and exudates experiments. Inhibition of M. aeruginosa growth by plant exudates depended strongly on the biomass of P malaianus. Initial pH (6.5-9.8) did not influence the inhibitory effects of P. malaianus exudates. However, the M. aeruginosa inhibited the net photosynthesis and respiration of all three pondweed test spp.. The decreases in photosynthesis and respiration were probably caused by the toxic compounds released by M. aeruginosa, rather than its shading effects. The M. aeruginosa also decreased the nutrients (phosphorus and nitrogen) uptake rates of macrophytes. The absorption rates of phosphorus and nitrogen and net photosynthesis were decreased sharply. These results will help to restore submerged plants in eutrophic waters.

Allelopathic effects of phenolic compounds present in submerged macrophytes on Microcystis aeruginosa

In laboratory studies, the allelopathic effects of 3 (Hydrocharitaceae family) submerged macrophytes (Elodea nuttallii (Planch) St. John, Hydrilla verticillata (L.f.) Royle and Vallisneria spiralis L.) were investigated on two strains of Microcystis aeruginosa. Both aqueous methanol extracts and exudates of three macrophytes inhibited the growth of both strains of Microcystis aeruginosa, After 3-days culture, E nuttallii, H. verticillata and V. spiralis excreted 0.8, 0.3 and 1.0% of total phenolic compounds (TPC), respectively, into the surrounding water. After removing phenolic compounds by polyvinylpolypyrrolidone (PVPP)), the plant exudates showed very weak activity. The inhibitory rates of exudates of E. nuttallii, H. verticillata and V. spiralis, against non-toxic M. aeruginosa were decreased by 35.7, 43.4 and 59.1% respectively. Thus 3 submerged macrophytes released the phenolic compounds into the surrounding water, to inhibit the growth of M. aeruginosa. This information may help us in understanding the mechanism of allelopathy in aquatic ecosystems and to control the algal bloom in eutrophic water bodies.

Relationship between the allelopathic activity and molecular structure of hydroxyl derivatives of benzoic acid and their effects on cyanobacterium Microcystis aeruginosa

The antialgal activities of benzoic acid, 2-hydroxybenzoic acid (salicylic acid), 3-hydroxybenzoic acid, 4-hydroxybenzoic acid, 3,5-dihydroxybenzoic acid and 3,4,5-trihydroxybenzoic acid (gallic acid) were studied on the growth of two strains of Microcystis aeruginosa (toxic FACHB 942 and non-toxic 469). The results showed that the sequence of 50% growth inhibition concentration (ErC50) of 6- compounds for both strains of M. aeruginosa followed the same order: gallic acid > 3,5-dihydroxybenzoic acid > 4-hydroxybenzoic acid > salicylic acid > 3-hydroxybenzoic acid > benzoic acid. The position and the numbers of hydroxy groups between the hydroxy group and carboxyl influenced the antialgal effects of phenolic acids. We also investigated the joint effects of benzoic acid, 4-hydroxybenzoic acid and 3,4,5-trihydroxybenzoic acid on the growth of M. aeruginosa ( toxic FACHB 942). The mixture of phenolic allelochemicals showed the synergistic effects.

Allelopathic effects on Scenedesmus obliquus by two submerged macrophytes Najas minor and Potamogeton malaianus

The allelopathic effects of two submerged macrophytes, Najas minor and Potamogeton malaianus, on growth, photosynthesis and antioxidant systems of Scenedesmus obliquus were assessed in coexistence experiments. The growth of S. obliquus was significantly suppressed by the two macrophytes. Moreover, P. malaianus showed the stronger growth inhibition effect on S. obliquus than N. minor. P. malaianus obviously inhibited the photosynthetic rate of S. obliquus, while N. minor had no inhibitory effect. Lipid peroxidation and three antioxidant enzymes activities (superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD)) of S. obliquus were investigated at the end of the co-cultures. The two macrophytes significantly enhanced the malondialdehyde (MDA) content, a product of lipid peroxidation, in S. obliquus. Activities of the three antioxidant enzymes of S. obliquus were simultaneously stimulated in P. malaianus treatment, while no significant variation of POD activity was observed in N. minor treatment. The results indicated that the two macrophytes N. minor and P. malaianus had significant allelopathic effects on S. obliquus. However, the two macrophytes influenced S. obliquus in different ways.

Allelopathic interactions between Potamogelon maackianus and Microcystis aeruginosa

The allelopathic interactions between Potamogeton maackianus and toxic cyanobacteria (Microcystis aeruginosa) were studied. P maackianus inhibited the growth of M. aeruginosa, both in a coexistence culture system and in exudates experimental culture system. M. aeruginosa also showed effects on the secondary metabolic biosynthesis and secreting behavior of P maackianus. The main lipophilic components of the hexane extracts and the exudates from the macrophyte were analyzed through GC-MS determination. The lipophilic components of the hexane extracts and the exudates from P. maackianus were influenced by M. aeruginosa or their released chemicals. Comparing the lipophilic constituents of the hexane extracts with those in the exudates, the results showed that weak polar compounds contained in the macrophytes can be secreted into the surrounding water. Many compounds, such as N-phenyl-2-naphthalenamine and isopropyl myristate, were detected both in the hexane extracts and the exudates. The changes of lipophilic components in the hexane extracts would be a response to the stress of toxic cyanobacteria or their released toxins. Those changes of exudates, especially the increased content of N-phenyl-2-naphthalenamine, might also be an induced defensive behavior mediated by the released toxins from M aeruginosa. The study results about reciprocal allelopathic responses between macrophytes and cyanobacteria can help in the management of eutrophic waters, and is also important information concerning strategies for recovering eutrophic waters.