1、方向对入侵克隆植物空心莲子草小片段生存和生长的影响方向对入侵克隆植物空心莲子草小片段生存和生长的影响摘要背景：在干扰过后小克隆片段建立和成长的能力是植物克隆生长重要的生态优势和一些引种克隆植物入侵力的主要因素。我们假定水平位置取向（典型的匐枝植物）能够增加散布的克隆片段的生存和生长，当片段更小的时候这种取向的影响能被加强因为这样只会有更少的储备供给最初的生长方法/主要发现：为了验证这些假说，我们把空心莲子草单节点匍匐茎片段在距离水品位置0,45,90度位置与片段的远端或近端把留下的1或3cm的匍匐茎的无性系分株作比较。像预计的一样，当片段被水平放置是片段的生存和生长状况最好。和预期相比，当固着
2、的匍匐茎更长的时候取向的这些影响就更强。取向相对匍匐茎的长度对片段表现有更小的影响，较短的匍匐茎的成活率在60%左右而较长的匍匐茎的存活率在90%左右。结论/意义：结果支持取向能够影响小克隆片段建立这一假设，同时表明比起小片段，大片段收到取向的影响更大。也表明取向对克隆断裂的影响低于储藏资源对其的影响。前言在干扰过后小克隆片段建立和成长的能力是植物克隆生长重要的生态优势和一些引种克隆植物入侵力的主要因素。自然干扰例如洪水、地震、践踏经常打断一个或者一些克隆植物的无性系分株并分散它们。这些片段的建造能力可能有助于植物种群的的恢复力和是水生的、引进的克隆植物大规模传播的原因。因此理解掌控小克隆片段
3、生存和生长的因素有重要的科学和现实意义。一个可能的因素是一个克隆片段里包含的储藏物质数量，匍匐枝是具匍匐茎的克隆植物重要的储藏器官。匍匐枝的节间能够储藏可溶性碳水化合物和蛋白质可在转移到相连的无性系分株中。Dong et al. (2010) 最近报道空心莲子草的生活力和生长随着相连匍匐枝的伸长而增加。在这一研究中我们在先前研究的基础上继续探讨分散的方向和单节点克隆片段是否也能影响它们的生存和生长和这是否依赖相邻匍匐茎的节间，通过类似储藏器官的功能。在干扰和分散之后，这些小的克隆片段位移到偏离典型的垂直生长方向。离开水平位置可以诱导内生性生长物质在片段新芽中的非对称分布，使得他们由于重力刺激定
4、位到垂直方向。这可能延缓发芽并增加对节间中存储物质的依赖。例如，当两种类型的片段都被水平放置时，芦竹的水平茎片段相较其垂直茎片段有更高的萌发力，这也许和片段中生长素的分布不同有关。来自克隆植物水平茎水平方向的片段可能增加了片段的建立，这种作用将会随着相连的匍匐茎节间长度的缩短得到加强并减少储藏物质。我们因此猜测：1）水平取向能够增加小克隆片段的生存和生长，2）取向效应将会随着片段中相连匍匐茎节间的长度增加而减弱。我们在温室试验中对具有匍匐茎的入侵植物空心莲子草 三个假设进行了检验结果片段的取向对它们的生存和最后大小有高度显著的作用（table 1）(MANOVA: Wilks = 0.36;
5、F = 3.24; P,0.001)。对没一个个体的尺寸进行测量后发现，水平0处理的片段表现最好(Figs. 1A and 2AE)。没有证据表明种植片段的表现在远端朝上时比近端朝上有更好的表现(Figs. 1 and 2)。在水平位置片段的生存力和最终尺寸达到最大这一结果很大程度上与预期相符。取向的互动效应和片段的匍匐茎长度的最终大小显著相关(MANOVA: Wilks = 0.42, F = 2.68, P,0.001)。在单因素方差分析中，取向的影响和匍匐茎长度对两种尺寸测量值、叶片的数目和新匍匐茎的长度匍匐茎长度相互作用。对2cm长的片段进行五个方向上的处理，叶片的数目，匍匐茎的长度以
6、及叶面积没什么不同，但是当片段设为6cm长时，在水平0处理条件下叶片数、匍匐茎长度和叶面积都达到最大(Fig. 2G, H, J)。当匍匐茎长度更长时取向的影响更大，这和第二个预期的结果相反。匍匐茎的长度影响空心莲子草的生存和最终的大小。By every measure,当片段和更长的匍匐茎相连时表现更好。长度对存活力有着极其强烈的影响，60%与2cm长匍匐茎相连的片段90%与6cm长的匍匐茎相连的片段。讨论当无性系分株在水平方向上时，空心莲子草单节点匍匐茎片段的存活率和最终尺寸都达到最高。这和假设一致即水平放置能够增加小克隆片段的建立正如可能因干扰而创造或者消除，可能提供了固定在水平位置的倾
7、向能够对具有匍匐茎的克隆植物有益这一首先公开的建议。当节点在种植时只有很短的匍匐茎茎节相连时，取向对establishment和空心莲子草单节点克隆片段最初的生长的影响并不大，当节点与较长的匍匐枝相连时影响大些。这些结果与 第二个假设不一致，一个可能的解释是片段在拥有更多的储藏物质的时候，事实上对诸如水平位置这一有利条件有更强的反应能力。这可以为以后进一步研究提供了改进建议。有更长匍匐茎相连的片段有更高的生存可能性，如果存活了将有更大的尺寸。这一结果和先前对空心莲子草的研究以及对其它克隆植物的研究结果一致，这表明小克隆片段匍匐茎节间的存活率的积极影响是至少部分是由于匍匐茎中的储藏物质。在本研究
8、中观察到的相对小的取向的影响，空心莲子草向下分布的取向在生态中是否扮演重要的角色还不确定，诸如在引入一个新区域后迅速传播到一个新的大区域的能力。然而，这一研究提供了一个初步迹象即克隆片段固定在水平位置的趋势能够增加establishment的成功率。因为匍匐茎的长度对小克隆片段的生长和存活率以及减小克隆片段的尺寸方面有重大影响因此它们的储藏物质可能是控制空心莲子草侵袭力的有效方法。材料和方法研究物种和传播空心莲子草是一种苋科多年生据匍匐茎的草本植物。原产于南美Parana河流域，其已经入侵到包括中国在内的很多国家。在中国的空心莲子草很少产生可育的种子，取而代之的是通过现有植物匍匐茎进行无性繁殖
9、或者通过和无性系分株一样小的分散的片段的establishment，即一个匍匐茎节点能够承载根和两片对生叶。克隆片段的分散导致了中国一些地方空心莲子草的分布范围迅速扩大，在中国，无论是水生还是陆生环境这些物种已经导致了严重的生态和农业问题。在水中，空心莲子草能形成致密的垫层并能排除本地物种。在陆地上，他们向本地植物群落一样入侵牧场和农田。植物材料在2009年4月中旬采集于江西省并在北京一个人工池塘里进行了七个月的无性繁殖。在2009年10月11号，980个克隆片段，每个片段都带有一个带根的匍匐茎节点、两片叶以及两端的匍匐茎节间，被从母株分离用于实验。每一个片段节间的两端都至少4cm长并且所有的
10、片段都来自空心莲子草的成熟的斜生茎。实验设计这一实验在五个方向处理上采用析因实验（-90，-45,0，45，90）和两个匍匐茎长度上的处理（2cm和6cm），结合偏离水平位置0，45，或90 向上（45和90）或前端部的匍匐茎向下（-45-90）方向取向处理。在匍匐茎长度处理方面，匍匐茎末端或前端都被留下1-3cm与之相连，每一个片段片段都有2-6cm匍匐茎与之连着。14个片段被随机分配到盛有按土壤和泥炭1:1混合70个塑料容器中（长37.7，宽627.5 深614.2），去模拟中国南部法相空心莲子草地区的土壤。每一个片段的节点和叶子被放置在土壤表面，然后覆盖1cm厚的蛭石用以维持土壤水分。为
11、了避免匍匐茎潜在的光合作用，避免通过贮藏茎的支持片段的establishment，我们用锡箔包裹部分暴露在光下的匍匐茎。每天都给容器供应足量的自来水以保持土壤潮湿。7个容器被随机分配给10个处理组合中的一个，容器被视作重复。实验从2009年10月11号开始到2009年12月11号持续九个星期。实验地点在北京大学林业科技有限公司进行。试验期间温室的平均温度为15.3，通过两台温度记录仪(iButton DS1923; Maxim Integrated Prod-ucts, USA)每小时测量。数据测量分析2009年12月11至14号，我们数每一片段节点和叶片的数目，计算叶面积以及新匍匐茎的长度，
12、把每一个片段的根、叶以及新匍匐茎分离并将它们防止的70条件下干燥48小时称量重量。我们并没有把种植时与片段相连的克隆节间包括在内，因为这些不同处理的匍匐茎的匍匐茎部分的长度和质量必然不同。为了分析，我们首先统计了每一个容器中存活片段的尺寸。为了检测处理对存活率的影响，我们对长度和初始匍匐茎长度as fixed effects进行了方差分析。我们进行了多元方差分析，把相同的效应以及全部物种生存对策作为因变量。与多因素方差分析一起报道记录的每种对策单独的方差分析，也被计算。Student-Newman-Keuls测试用来检测每十个取向组合之间以及五个取向处理和匍匐茎长度处理之间的差异。假设：1 2
13、Effects of Orientation on Survival and Growth of Small Fragments of the Invasive, Clonal Plant Alternanthera philoxeroidesBi-Cheng Dong , Ming-Xiang Zhang*, Peter Alpert, Guang-Chun Lei, Fei-Hai Yu*1College of Nature Conservation, Beijing Forestry University, Beijing, China, 2 Biology Department, Un
14、iversity of Massachusetts, Amherst, Massachusetts, United States of AmericaAbstractBackground: The ability of small clonal fragments to establish and grow after disturbance is an important ecological advantage of clonal growth in plants and a major factor in the invasiveness of some introduced, clon
15、al species. We hypothesized that orientation in the horizontal position (typical for stoloniferous plants) can increase the survival and growth of dispersed clonal fragments, and that this effect of orientation can be stronger when fragments are smaller and thus have fewer reserves to support initia
16、l growth. Methodology/Principal Findings: To test these hypotheses, we compared performance of single-node pieces of stolon fragments of Alternanthera philoxeroides planted at angles of 0, 45 or 90away from the horizontal position, with either the distal or the proximal end of the fragment up and wi
17、th either 1 or 3 cm of stolon left attached both distal and proximal to the ramet. As expected, survival and growth were greatest when fragments were positioned horizontally. Contrary to expectations, some of these effects of orientation were stronger when attached stolons were longer. Orientation h
18、ad smaller effects than stolon length on the performance of fragments; survival of fragments was about 60% with shorter stolons and 90% with longer stolons. Conclusions/Significance: Results supported the hypothesis that orientation can affect establishment of small clonal fragments, suggested that
19、effects of orientation can be stronger in larger rather than smaller fragments, and indicated that orientation may have less effect on establishment than amount of stored resources.IntroductionThe ability of small clonal fragments to establish and grow after disturbance is an important ecological ad
20、vantage of clonal growth in plants and a major factor in theinvasiveness of some introduced, clonal species 14. Natural disturbances such as floods, erosion and trampling often break off small units of one or a few ramets of clones and disperse them 2,5,6. Ability of these fragments to establish pro
21、bably contributes to the resilience of natural plant communities and may largely account for the large- scale spread of aquatic, introduced, clonal species. It is thus of scientific and practical interest to understand the factors that control the survival and growth of small clonal fragments. One l
22、ikely factor is the amount of stored resources contained in a fragment, and an important storage organ in some stoloniferous, clonal plants is the stolon 7,8. The internodes of stolons can store soluble carbohydrates and proteins 9,10 that can be retranslo-cated to attached ramets 7,11,12. Dong et a
23、l. (2010) recently showed that the survival and growth of ramets of Alternanthera philoxeroides increased with increasing length of attached stolons. In this study, we build upon that previous finding to ask whether the orientation of dispersed, single-node clonal fragments can also affect their sur
24、vival and growth, and whether this depends upon the length of attached stolon internodes, through their function asstorage organs. After disturbance and dispersal, such small clonal fragments might become positioned in orientations away from the horizontal, which is the typical orientation for growt
25、h. Departure from the horizontal position may induce asymmetric distribution of endogenous growth substances (e.g. auxins) in the new buds offragments, and make them reorient toward the vertical due to gravity stimulation 13,14. This could slow sprouting and increase reliance on stored resources in
26、internodes. For instance, fragments of horizontal stems of giant reed (Arundo donax) had a higher sprouting ability than fragments of vertical stems when both types of fragments were positioned horizontally 15,16, and this was related to differences in the distributions of auxins in the fragments. H
27、orizontal orientation of fragments from the horizontal stems of clonal plants might thus increase establishment of the fragments and this effect might be stronger in fragments with shorter lengths of attached stolon internodes and thus less stored resources.We therefore hypothesized 1) that horizont
28、al orientation can increase the survival and growth of small clonal fragments, and 2) that this effect of orientation will be less in fragments with greater length of attached stolons. We tested these hypotheses in a greenhouse experiment with the invasive, stoloniferous plant Alternanthera philoxer
29、oides.ResultsThe orientation of fragments had highly significant effects on their survival (Table 1) and final size (MANOVA: Wilks = 0.36; F = 3.24; P,0.001). For each individual measure of size (Table 1), fragments performed the best in the 0 (horizontal) treatment (Figs. 1A and 2AE). There was no
30、evidence that performance of fragments planted at a given angle was better when their distal than when their proximal ends were oriented upwards (Figs. 1 and 2). Results thus largely met the prediction that survival and final size would be greatest when fragments were horizontal. The interactive eff
31、ect of orientation and stolon length on final size of fragments was significant (MANOVA: Wilks = 0.42, F = 2.68, P,0.001). In separate ANOVAs, effect of orientation interacted with effect of stolon length on two measures of size, number of leaves and length of new stolons (Table 1). Number of leaves
32、, stolon length and leaf area did not differ among the five orientation treatments when the fragments were 2 cm long, but were the largest in the 0 (horizontal) treatment when the fragments were 6 cm long (Fig. 2G, H, J). Effects of orientation were thus greater when stolon length was longer, the opposite of the second predicted result. Stolon length affected survival (Table 1) and final size of A. philoxeroides (MANOVA: Wilks l = 0.27, F = 28.30, P,0.001). By every measure, fragments performed better when attached to longer stolons (Table 1, Figs. 1 and 2). Length ha
