山地河流浅滩深潭生境大型底栖动物群落比较研究——以重庆开县东河为例

浅滩和深潭是山地河流中常见的河流生境结构。2011年7月,在重庆开县东河上游双河口-杉木桥河段,选择21个浅滩和深潭,调查大型底栖动物,研究影响不同生境中底栖动物组成、分布和多样性的生态机理。结果表明:调查河段浅滩和深潭中大型底栖动物分别为31种和24种,密度分别为450.62 个/m²和86.24 个/m²,生物量分别为2.88 g/m²和0.55 g/m²。浅滩有指示种11种,即纹石蛾(Hydropsyche sp.)、假蜉(Iron sp.)、假二翅蜉(Pseudocloeon sp.)、舌石蛾(Glossosoma sp.)、高翔蜉(Epeorus sp.1)、背刺蜉(Notacanthurus sp.)、Heterocloeon sp、锯形蜉(Serratella sp.)、朝大蚊(Antocha sp.)、等蜉(Isonychia sp.)、溪颏蜉(Rhithrogena sp.)。深潭指示种仅蜉蝣(Ephemera sp.)和黑大蚊(Hexatoma sp.)两种。刮食者为两类生境的优势功能摄食类群。浅滩中滤食者和刮食者比例显著高于深潭,而收集者和捕食者显著低于深潭。两类生境中大型底栖动物群落结构差异显著。浅滩中大型底栖动物的密度、生物量、丰富度指数、Shannon-Wiener 指数、改进的Shannon-Wiener指数均明显高于深潭。受地貌形态、水力特征和冲淤变化规律影响的生境稳定性和异质性差异是导致大型底栖动物群落差异的主要原因。     

蟛蜞菊属和孪花菊属(菊科-向日葵族)的细胞学研究

研究了菊科向日葵族鳢肠亚族蟛蜞菊属(Sphagneticola O. Hoffm.)和孪花菊属(Wollastonia DC. ex Decne.)各2种植物的染色体数目和染色体形态。蟛蜞菊[S. calendulacea (L.) Pruski]的染色体数目为2n=50, 核型公式为2n=18m+30sm+2st,南美蟛蜞菊[S. trilobata (L.) Pruski]的染色体数目为2n=56, 核型公式为2n=24m+28sm+4st, 孪花菊[W. biflora (L.) DC.]的染色体数目为2n=30,核型公式为2n=24m+4sm+2st,山孪花菊[W. montana (Blume) DC.]的染色体数目为2n=74, 核型公式为2n=37m+31sm+6st。根据上述结果并结合以前的有关资料,推测蟛蜞菊属的染色体基数可能为x=14和x=25,而不应是x=15。该属的3个新世界热带种[S. brachycarpa (Baker) Pruski、S. gracilis (Richard) Pruski和南美蟛蜞菊]可能都基于x=14, 其中S. gracilis为二倍体(2n=2x=28), S. brachycarpa和南美蟛蜞菊为四倍体(2n=4x=56); 唯一的亚洲种(蟛蜞菊)可能是基于x=25的二倍体(2n=2x=50)。染色体资料不支持将山孪花菊(x=37)这一植物置于孪花菊属(x=15)中。     

将安龙花转移至马蓝属(爵床科)的形态特征依据

比较了安龙花(Dyschoriste sinica H. S. Lo)的模式标本与距药花属(Dyschoriste Nees)和马蓝属(Strobilanthes Bl.)部分种类的花粉和花的特征后,支持将安龙花转移到马蓝属,组合为Strobilanthes sinica (H. S. Lo) Y. F. Deng。安龙花隶属于马蓝属黄猄草群,它与日本马蓝(Strobilanthes japonica (Thunb.) Miq.)近似,但区别在于它的匍匐习性,叶矩圆状椭圆形,近无柄,花单生叶腋。因此,距药花属(Dyschoriste Nees)在中国并没有分布。     

三峡库区172m蓄水期间泥、沙沉降对低位狗牙根种群的影响

三峡库区消落带植物恢复不仅面临长期淹水逆境,还面临泥沙、干旱等环境因素的胁迫。2009年实验、调查研究了三峡库区长寿段低位消落带的狗牙根(Cynodon dactylon L.)种群,探讨了泥、沙沉降对狗牙根种群的影响。结果表明,泥沉降和沙沉降均显著促进了狗牙根芽的萌发,而抑制了狗牙根的芽形成和萌发苗的生长,且前者的抑制作用显著大于后者。泥沉降导致总芽数、萌发苗的茎长和茎宽分别比对照低65.4%(P<0.05)、97.0%(P <0.05)、31.2%(P <0.05),而沙沉降导致前述参数分别比对照低17.1%(P<0.05)、21.2%(P<0.05)、1.0%(P>0.05)。分别将被沉降泥掩埋的狗牙根移植、掩埋于12cm厚的泥和沙中,40d后对照和S'_d组(覆盖沙)狗牙根芽萌发后均能在地面上形成正常的分株,而S'_l组(覆盖泥)的萌发芽无法穿透覆盖层,形成分株。S'_l组狗牙根芽的萌发率显著高于对照和S'_d组,但其萌发苗的茎长和茎节数均显著低于对照,分别为对照的30.3%(P<0.05)、80.4%(P<0.05);而S'_d组分株的茎长、茎节数、叶片数、叶长和叶宽均显著高于对照组,分别比后者高87.9%(P<0.05)、53.0%(P<0.05)、24.2%(P<0.05)、23.4%(P<0.05)和24.1%(P<0.05)。S'_l组萌发苗的鲜质量、干质量和干鲜质量比分别比对照组低83.3%(P<0.05)、86.2%(P<0.05)、15.8%(P<0.05);而S'_d组萌发苗的鲜质量、干质量和干鲜质量比分别比对照组高76.8%(P<0.05)、110.1%(P<0.05)、20.0%(P<0.05)。表明,低位消落带的狗牙根对沙沉降具有较强的适应能力,而对泥沉降的适应能力较低,泥沉降是库区低位消落带狗牙根种群恢复的主要影响因素之一。     

耕作措施对冬小麦田杂草生物多样性及产量的影响

在连续5a秸秆全量还田的免耕、旋耕、耙耕、深松和常规耕作试验地中,设置了除草和不除草处理,研究了其对杂草总密度、优势杂草种类、生物多样性指数和冬小麦产量的影响,并分析了杂草与小麦间的竞争关系。结果表明,麦田杂草主要有7种,分别是麦蒿(Descuminia sophia (L.) Webb ex Prantl)、荠菜(Capsella bursa-pastoris (L.) Medik)、燕麦(Avena sativa L.)、田旋花(Convolvulus arvensis L.)、刺儿菜(Cirsium setosum (Willd.) Bieb.)、繁缕(Stellaria media (L.) Vill.)、麦家公(Lithospermum arvense L.)。在未除草条件下,免耕、深松的杂草总密度显著提高;而在除草条件下,杂草密度显著下降。免耕、深松、常规耕作在未除草条件下,优势杂草种类为麦蒿、荠菜,旋耕、耙耕条件下的优势杂草为麦蒿;而除草后各处理的优势杂草均只有麦蒿。耙耕、常规耕作措施在未除草条件下杂草群落具有较高的物种丰富度和均匀度。无论哪种耕作措施,除草能提高冬小麦产量,其中以深松耕作结合除草处理的小麦产量最高。在小麦抽穗期,未除草处理杂草株高接近或高于小麦株高,会造成杂草与小麦间的光竞争,对小麦的生长状况有显著影响,从而导致小麦产量降低。     

秦岭天然次生油松林冠层降雨再分配特征及延滞效应

为了研究秦岭典型地带性植物油松林冠层降雨再分配特征及延滞效应,选择陕西宁陕县秦岭森林生态系统国家野外科学观测研究站55龄天然次生油松林,从2006-2008年(5-10月份)对林外降水、穿透降雨和树干茎流进行定位观测。利用其中100次实测数据进行分析研究,结果表明:总降雨量为1576.4 mm,穿透降雨量为982.9 mm,树干茎流量为69.5 mm,冠层截留量为524. 0mm,分别占总降雨量的62.4%、4.4%和33.2%。降雨分配与降雨量级密切相关,降雨量级增大,穿透降雨率和茎流率呈增大趋势,截留率呈降低趋势,变化幅度分别为46.6%-68.9%、0.8%-9.2%、53.4%-22.0%。穿透降雨量、树干茎流量和林冠截留量与林外降雨量之间的关系分别为:TF=0.6548P-0.4937,R²＝0.9596;SF=-0.2796+0.0452P+0.0005P²,R²＝0.8179;I=0.5958P^0.8175,R²＝0.8064。降雨事件发生后,穿透降雨和树干茎流出现的时间与降雨发生的时间并不同步,均表现出一定的延滞性,随着降雨量级增大,滞后时间表现出逐渐缩短的趋势((78.5±8.8)-(16.0±0.0) min,(111.0±33.0)-(41.2±0.0) min)。降雨终止时,特别是当降雨量>10.0 mm,穿透降雨终止时间也存在一定的延滞性((3.2±2.6)-(12.0±0.0) min)。但树干茎流终止时间先于降雨终止时间,降雨量级越小,树干茎流终止时间愈早((-58.3±21.5)-(-9.8±0.0) min)。     

越南植物Michelia tonkinensis(木兰科)的模式考订

Michelia tonkinensis A. Chev.这个名称在发表时未指定模式,曾被处理为M. balansae (Aug. DC.) Dandy的异名。在查阅了其原白和原始材料后,确认采自越南北部Tuyen Quang省的标本——Fleury 37.667 (P)是该种唯一的原始材料,应该作为模式看待,同时确认Michelia tonkinensis是一独立的种,不应该处理为M. balansae的异名。此外,还提供了M. tonkinensis的异名、俗名、描述、分布及查阅的标本等综合信息。     

江西虾脊兰属一新变型——异钩距虾脊兰

描述了产自江西的兰科(Orchidaceae)虾脊兰属(Calanthe R. Br.)植物一新变型——异钩距虾脊兰 (Calanthe graciliflora f. jiangxiensis B. Li, L. J. Kong et B. Y. Yang),并绘制了线条图。该新变型与原变型钩距虾脊兰(C. graciliflora Hayata)的主要区别为距末端分裂为2个不等的短尖。     

假臭草等12种植物对白花鬼针草幼苗的化感作用

用具有化感作用或潜在抑草活性的12种植物的叶片水浸液对白花鬼针草(Bidens alba)幼苗进行处理,对其幼苗的生长 进行研究,以期筛选出对白花鬼针草生长有较强抑制作用的植物种类。结果表明,12种供体植物叶片水浸液(0.05 g DW mL^-1) 均能显著抑制白花鬼针草幼苗的生长(P<0.05),综合化感效应(SE)均为负值(≤-0.2),抑制强度依次为假臭草(Eupatorium catarium)>胜红蓟(Ageratum conyzoides)>海芋(Alocasia macrorrhiza)>水茄(Solanum torvum)>马缨丹(Lantana camara)>薇甘菊(Mikania micrantha)>构树(Broussonetia papyrifera)>南美蟛蜞菊(Wedelia trilobata)>三裂叶薯(Ipomoea triloba)>葛藤(Pueraria lobata)>鸡矢藤(Paederia scandens)>五爪金龙(Ipomoea cairica),其中假臭草叶水浸液浓度仅为0.04 g DW mL^-1时就可以使白花鬼针草死亡。假臭草和胜红蓟的茎水浸液也可以显著抑制白花鬼针草的生长(P<0.05),抑制效果略低于叶水浸液。回归分析表明,假臭草叶水浸液浓度与白花鬼针草的生物量等指标之间有线性回归关系(R²>0.85, P<0.001),随着水浸液浓度的增加,白花鬼针草的生物量等指标下降。防除白花鬼针草时使用假臭草和胜红蓟的茎、叶水浸液, 其有效浓度低且资源丰富,可作为白花鬼针草天然除草剂的主要资源植物。     

醉马草免培养内生细菌的多样性

为了解醉马草内生细菌的组成和多样性,采用液氮研磨法提取醉马草总DNA,利用内生细菌16S rRNA基因特异性引物对醉马草总DNA 进行16S rRNA 基因扩增,构建醉马草内生细菌16S rRNA基因文库。对筛选到249个克隆进行Hae Ш酶切分析,得到57个操作分类单元(OTUs)。系统发育分析将其归为4个门:变形杆菌门(Proteobacteria)、厚壁菌门(Firmicutes)、放线菌门(Actinobacteria)、拟杆菌门(Bacteroidetes)以及1个未知类群。其中74%的克隆与可培养细菌中的37个属具有高的16S rRNA基因序列相似性 (97％-100％),其中芽孢杆菌属(Bacillus spp.)、红球菌属(Rhodococcus spp.)、黄杆菌属(Flavobacterium spp.)、黄单胞杆菌属(Xanthomonas spp.)最为丰富。另外26%的克隆序列与GenBank中已存细菌16S rRNA基因序列相似性小于96%。研究结果表明,醉马草中可培养内生细菌丰富,多样并且可能存在一些潜在新物种或新类群。     

Seed banks on Attalea phalerata (Arecaceae) stems in the Pantanal wetland, Brazil

Background and Aims

Seeds can accumulate in the soil or elsewhere, such as on the stems of palms when these are covered by persistent sheaths. These sheaths could act as a safe site for some species. Here, we studied whether persistent sheaths of the palm Attalea phalerata (Arecaceae) are available sites for seed accumulation in the Pantanal wetland of Brazil. We also investigated whether the composition, richness and diversity of species of seeds in the persistent sheaths are determined by habitat (riparian forest and forest patches) and/or season (wet and dry).

Methods

All accumulated material was collected from ten persistent sheaths along the stems of 64 A. phalerata individuals (16 per habitat and 16 per season). The material was then individually inspected under a stereomicroscope to record seed species and number.

Key Results

Of the 640 sheaths sampled, 65 % contained seeds (n = 3468). This seed bank included 75 species belonging to 12 families, and was primarily composed of small, endozoochoric seeds, with a few abundant species (Cecropia pachystachya and Ficus pertusa). Moraceae was the richest family (four species) and Urticaceae the most abundant (1594 seeds). Stems of A. phalerata in the riparian forest had 1·8 times more seeds and 1·3 times more species than those in forest patches. In the wet season we sampled 4·1 times more seeds and 2·2 more species on palm stems than in the dry season. Richness did not differ between habitats, but was higher in the wet season. Abundance was higher in forest patches and in the wet season.

Conclusions

Attalea phalerata stems contain a rich seed bank, comparable to soil seed banks of tropical forests. As most of these seeds are not adapted to grow in flooding conditions, palm stems might be regarded as safe sites for seeds (and seedlings) to escape from the seasonal flooding of the Pantanal.     

Comparative molecular cytogenetics of major repetitive sequence families of three Dendrobium species (Orchidaceae) from Bangladesh

Background and Aims

Dendrobium species show tremendous morphological diversity and have broad geographical distribution. As repetitive sequence analysis is a useful tool to investigate the evolution of chromosomes and genomes, the aim of the present study was the characterization of repetitive sequences from Dendrobium moschatum for comparative molecular and cytogenetic studies in the related species Dendrobium aphyllum, Dendrobium aggregatum and representatives from other orchid genera.

Methods

In order to isolate highly repetitive sequences, a c₀t-1 DNA plasmid library was established. Repeats were sequenced and used as probes for Southern hybridization. Sequence divergence was analysed using bioinformatic tools. Repetitive sequences were localized along orchid chromosomes by fluorescence in situ hybridization (FISH).

Key Results

Characterization of the c₀t-1 library resulted in the detection of repetitive sequences including the (GA)_n dinucleotide DmoO11, numerous Arabidopsis-like telomeric repeats and the highly amplified dispersed repeat DmoF14. The DmoF14 repeat is conserved in six Dendrobium species but diversified in representative species of three other orchid genera. FISH analyses showed the genome-wide distribution of DmoF14 in D. moschatum, D. aphyllum and D. aggregatum. Hybridization with the telomeric repeats demonstrated Arabidopsis-like telomeres at the chromosome ends of Dendrobium species. However, FISH using the telomeric probe revealed two pairs of chromosomes with strong intercalary signals in D. aphyllum. FISH showed the terminal position of 5S and 18S–5·8S–25S rRNA genes and a characteristic number of rDNA sites in the three Dendrobium species.

Conclusions

The repeated sequences isolated from D. moschatum c₀t-1 DNA constitute major DNA families of the D. moschatum, D. aphyllum and D. aggregatum genomes with DmoF14 representing an ancient component of orchid genomes. Large intercalary telomere-like arrays suggest chromosomal rearrangements in D. aphyllum while the number and localization of rRNA genes as well as the species-specific distribution pattern of an abundant microsatellite reflect the genomic diversity of the three Dendrobium species.     

A comparative study of latex-producing tissues in genera of Liabeae (Asteraceae)

Laticifers are highly specialized living plant cells which produce and contain latex. Occurrence of latex was used to establish morphological affinities (i) between Liabeae and other Asteracean tribes, (ii) among the Liabean genera, and (iii) in order to obtain phylogenies within Liabeae. However, structures and types of latex-producing tissues in this tribe have not yet been studied anatomically. In the present paper latex-producing structures of aerial parts in species of Microliabum, Munnozia, and Paranephelius (Liabeae), from open areas in mid-elevation Andean forests and in Andean high-elevation habitats, were studied. In all the analyzed species, latex secretion was easily observed in stem and leaf blade hand sections. Laticifers accompanied vascular tissues in all the cases, throughout stems and leaves, and they were of the articulated anastomosed type, at least in fully developed stages. Laticifers were found facing both, the xylem and the phloem, except for Paranephelius stems, in which they occur merely next to the phloem. Leaf laticifers form a reticulum accompanying the vein system. The type of latex-producing tissue shared by Microliabum and Munnozia could be a character shared by common ancestry whereas the laticifer system of Paranephelius stems could represent an evolutionary novelty for this genus. The laticifer type described in this study in aerial parts of Liabeae may allow establishing morphological affinities with tribes Cichorieae and Arctoteae.     

Does land use change affect the interactions between two dry grassland species?

Over the last 20 years, a change in traditional land use practices has taken place in central Germany. Formerly species-rich dry grassland communities have been converted into communities with greatly reduced diversity in many places. Whereas grass species have expanded, several forbs have declined in abundance. For the present study, plant-plant interactions were assessed between the expanding grass Festuca rupicola and the forb Dianthus carthusianorum - two typical, companion grassland species - to ascertain any associated effects of land use change. A competition experiment was set up with replacement design, in which pots were placed in the open field and monitored over two consecutive years. In order to assess the performance of both species in monoculture (D9, F9) and mixture (D3F6, D6F3) the parameters biomass, length of flowering stems, number of flowering stems and number of flowers per individual, or length of panicles, were analyzed. Positive and negative interactions were evaluated using the “Relative Neighbour Effect” index (RNE). To simulate land use by grazing or mowing, individuals in half of the pots were clipped in the first year after sowing. At this time, performance of D. carthusianorum - in terms of length of flowering stems, number of flowering stems and number of flowers - was significantly affected: whereas the first parameter increased, both of the other parameters decreased with increasing presence of the grass species. However, RNE indicated facilitation with a low number of F. rupicola individuals, and competition with a high number of F. rupicola individuals. In contrast, F. rupicola did not show any significant differences in performance with increasing presence of D. carthusianorum, and the RNE switched from neutral interaction to facilitation. In the second year after sowing, the performance of D. carthusianorum in the various treatments did not differ, except for the length of the flowering stems. The simulation of land use practices did not affect the performance of D. carthusianorum, but F. rupicola showed significant differences in biomass and in length of the panicles, as was the case also between monocultures and mixtures. The performance of the grass species was clearly improved in the unclipped treatments. The RNE reflected competition against D. carthusianorum which became reduced in unclipped treatments, while F. rupicola became facilitated. There were no interactions between the different treatments (monocultures and mixtures) and the simulated land use change (clipped and unclipped). Our data suggest that although traditional land use practices, i.e. grazing and mowing, do not affect the development of D. carthusianorum, the abandonment of these practices has improved F. rupicola performance, which has led to the increasingly invasive character of this grass species over the last 20 years.     

An acetylated galactomannoglucan from the stems of Dendrobium nobile Lindl

A water-soluble polysaccharide DNP-W2 composed of glucose, mannose, and galactose in the molar ratio of 6.1:2.9:2.0 had been isolated from the stems of Dendrobium nobile. Its molecular weight was 1.8 × 10⁴ Da determined by HPGPC. Structural features of DNP-W2 were investigated by a combination of chemical and instrumental analysis, including FTIR, GC, GC-MS, periodate oxidation-Smith degradation, methylation analysis, partial acid hydrolysis, and NMR spectroscopy. The results showed that DNP-W2 is a 2-O-acetylgalactomannoglucan and has a backbone consisting of (1→4)-linked β-d-Glcp, (1→6)-linked β-d-Glcp, and (1→4)-linked β-d-Manp, with branches at O-6 of (1→4)-linked β-d-Glcp and β-d-Manp. The branches are composed of α-d-Galp. The acetyl groups are substituted at O-2 of (1→4)-linked Manp. Preliminary tests in vitro reveals that DNP-W2 can stimulate ConA- and LPS-induced T and B lymphocyte proliferation.     

Contrasting submergence tolerance in two species of stem-succulent halophytes is not determined by differences in stem internal oxygen dynamics

Background and Aims Many stem-succulent halophytes experience regular or episodic flooding events, which may compromise gas exchange and reduce survival rates. This study assesses submergence tolerance, gas exchange and tissue oxygen (O₂) status of two stem-succulent halophytes with different stem diameters and from different elevations of an inland marsh.Methods Responses to complete submergence in terms of stem internal O₂ dynamics, photosynthesis and respiration were studied for the two halophytic stem-succulents Tecticornia auriculata and T. medusa. Plants were submerged in a glasshouse experiment for 3, 6 and 12 d and O₂ levels within stems were measured with microelectrodes. Photosynthesis by stems in air after de-submergence was also measured.Key Results Tecticornia medusa showed 100 % survival in all submergence durations whereas T. auriculata did not survive longer than 6 d of submergence. O₂ profiles and time traces showed that when submerged in water at air-equilibrium, the thicker stems of T. medusa were severely hypoxic (close to anoxic) when in darkness, whereas the smaller diameter stems of T. auriculata were moderately hypoxic. During light periods, underwater photosynthesis increased the internal O₂ concentrations in the succulent stems of both species. Stems of T. auriculata temporally retained a gas film when first submerged, whereas T. medusa did not. The lower O₂ in T. medusa than in T. auriculata when submerged in darkness was largely attributed to a less permeable epidermis. The submergence sensitivity of T. auriculata was associated with swelling and rupturing of the succulent stem tissues, which did not occur in T. medusa.Conclusions The higher submergence tolerance of T. medusa was not associated with better internal aeration of stems. Rather, this species has poor internal aeration of the succulent stems due to its less permeable epidermis; the low epidermal permeability might be related to resistance to swelling of succulent stem tissues when submerged.     

Botryosphaeriaceae from tuart (Eucalyptus gomphocephala) woodland, including descriptions of four new species

Eucalyptus gomphocephala (tuart) is a tree native to the southwest coast of Western Australia, where, in some areas, there is a significant decline in the health of tuart. Botryosphaeriaceous taxa have been isolated as endophytes and canker pathogens from numerous hosts in many parts of the world and have been implicated in the decline of E. gomphocephala. In the present study, endophytic fungi were isolated from a wide variety of native woody plant species (Acacia cochlearis, A. rostellifera, Allocasuarina fraseriana, Agonis flexuosa, Banksia grandis, E. gomphocephala, E. marginata and Santalum acuminatum), at two locations in native E. gomphocephala woodland; a site in decline at Yalgorup National Park and a healthy site at Woodman Point Regional Park. Of the 226 isolates obtained, 154 were botryosphaeriaceous taxa, 80 % of which were found to be Neofusicoccum australe, isolated from all hosts at both collection sites. Four new species are described, Dothiorella moneti, Dothiorella santali, Neofusicoccum pennatisporum, and a species belonging to a genus only recently included in the Botryosphaeriaceae, Aplosporella yalgorensis. The other species isolated were Botryosphaeria dothidea on the new hosts A. rostellifera, A. cochlearis and E. marginata and Dichomera eucalypti, on the new host E. marginata. None of the new species formed lesions on excised stems of their host species, E. gomphocephala, or a common plantation species, E. globulus. However, Neofusicoccum australe formed lesions on excised stems of E. globulus and E. gomphocephala.     

Huernia humpatana (Apocynaceae), a new species from southern Angola

A new species, Huernia humpatana Bruyns (Apocynaceae–Ceropegieae), closely related to H. similis N.E.Br., is described from the Chela Mountains of Huila Province in southern Angola. The two species are distinguished by the 5-angled and erect stems with more prominent tubercles up to 6 mm long joined into clear angles and separated by V-shaped grooves in H. humpatana as opposed to very obtusely 4-angled stems with tubercles only 2 mm long and only indistinct grooves between the angles in H. similis. Furthermore, in H. similis the nodding corolla is ± 9 mm in diameter with sepals ± 2 mm long, while in H. humpatana the horizontally facing corolla is 18–20 mm in diameter with sepals 4–6 mm long.     

空心莲子草响应南方菟丝子寄生的生长-防御权衡

为探讨全寄生植物南方菟丝子(Cuscuta australis)防治入侵植物空心莲子草(Alternanthera philoxeroides)的可行性,以二者野外天然生长的种群为研究对象,分析南方菟丝子寄生对空心莲子草生长及防御的影响,阐明空心莲子草在受到寄生胁迫时如何权衡自身生长与防御的关系,进而发展出一套应对南方菟丝子寄生的生长-防御策略。结果显示:(1)南方菟丝子寄生显著改变空心莲子草茎的形态,茎直径和平均节间长均增加,茎直径变化极显著(P0.01);(2)南方菟丝子寄生显著减少空心莲子草叶片数,但同时显著增加后者茎的分枝数,而茎上的节是潜在的无性繁殖体,故有利于空心莲子草的克隆繁殖;此外,南方菟丝子寄生显著降低了空心莲子草的根、茎、叶生物量和总生物量,抑制空心莲子草的生长;(3)南方菟丝子寄生显著增加空心莲子草茎的单宁、总酚、三萜皂苷含量,增强其防御能力;(4)南方菟丝子寄生的空心莲子草的生物量与茎部木质素、三萜皂苷、单宁和总酚含量均呈现显著负相关性(P0.01),对照组则不存在相关性;且寄生组较对照组相比,生物量的相对百分比显著低于对照组(P0.01),而用于防御的次生代谢产物总含量的相对百分比显著高于对照组(P0.01)。以上结果表明,受到南方菟丝子寄生胁迫后,空心莲子草改变自身的生长-防御策略,减少营养生长投入而将更多的资源投向克隆繁殖,同时增强对"防御"物质的投入,增强其防御能力,以利于后代生存和繁衍。