Morphological Characters Useful for the Delimitation of Taxa Within Viola Subsect. Viola (Violaceae): A Morphometric Study from the West Carpathians

Forty-nine morphological characters were scored or measured on 44 populations (376 individuals) of Viola subsect. Viola from the West Carpathians and adjacent areas (Slovakia, Czech Republic, Austria and Hungary). The presence of six species, namely V. alba (represented by subsp. alba), V. ambigua, V. collina, V. hirta, V. odorata and V. suavis s.l. was revealed based on pollen fertility, cytological and morphometric analyses. The morphological characters traditionally used to delimit taxa within the subsection and those revealed by our study as most reliable are widely discussed. A key for identifying the taxa and most common hybrids of subsection Viola occurring in the West Carpathians is presented. Chromosome counting and flow cytometry were used to determine the ploidy levels of the populations studied. All individuals of V. alba subsp. alba, V. collina, V. hirta and V. odorata were tetraploid, while those of V. ambigua and V. suavis s.l. were octoploid.     

Anatomical studies on selected species of Viola (Violaceae)

Cross‐sections of roots, stems, petioles and peduncles were investigated in 12 species of Viola distributed mainly in northern Iran: V. kitaibeliana, V. arvensis, V. occulta, V. tricolor (sect. Melanium), V. somchetica (sect. Plagiostigma), V. spathulata (sect. Spathulidium ined.), V. alba, V. odorata, V. sintenisii (sect. Viola subsect. Viola), V. caspia, V. reichenbachiana and V. rupestris (sect. Viola subsect. Rostratae). General anatomical features of Viola species are discussed. The following characters were found to be taxonomically informative: cross‐section shapes of the aerial stem, petiole and peduncle as well as the number of vascular bundles in the aerial stem. In taxa of sect. Melanium, stem cross‐sections are elliptic with two wings, but they are semi‐circular with two wings in taxa of sect. Viola subsect. Rostratae. Within the latter subsection, the number of vascular bundles in the stem can be used to delimit the species V. caspia, V. reichenbachiana and V. rupestris. Calcium oxalate crystals were observed in all vegetative organs of taxa belonging to sect. Viola. All examined taxa had a secondary structure with the exception of V. somchetica. Our results show that anatomical characters are useful for delimiting species, subsections, and sections within Viola.     

Cleistogamy and phylogenetic position of Viola uliginosa (Violaceae) re‐examined

Viola uliginosa is an endangered species throughout its range in Central Europe. Based on an unusual combination of morphological characters, including a reported lack of cleistogamous (CL) flowers, it was previously placed in the monotypic subsection Repentes, section Viola. Available individual phylogenetic analyses identify V. uliginosa as a lineage deeply embedded in section Viola, but hitherto its exact position was unknown. Here we confirm the occurrence of cleistogamy in V. uliginosa. Unlike other species of section Viola, V. uliginosa produced both chasmogamous and CL flowers at the same time, not at different times of the year (seasonal cleistogamy). The two flower types differed conspicuously in morphology and microstructure, especially in size and shape of the pistil and stamens as confirmed by scanning electron microscopy. Secondly, we resolved the phylogenetic position of V. uliginosa as a lineage deeply embedded in subsection Rostratae by means of a multigene multispecies coalescent analysis using *BEAST. In this analysis, V. mirabilis and V. uliginosa were successive sisters to the rest of subsection Rostratae and, because allopolyploids exist between V. mirabilis and the last one, subsection Rostratae needs to comprise all these taxa to be monophyletic. The evolution of key morphological traits is briefly discussed.     

Molecular markers in Viola L. subsect. Viola: Application and taxonomic implications for the identification of dubious herbarium specimens

Abstract

The authors report the use of nuclear [internal transcribed spacer (ITS) sequences 1 and 2] and chloroplast DNA (trnS-trnG intergenic spacer sequences) in Viola subsect. Viola for separate tracking of maternal lineages and detecting dubious herbarium specimens. A phylogenetic investigation carried out on ITS data after removal of all material with possible hybrid origin showed that V. hirta is a monophyletic unit, whereas V. odorata includes at least V. collina and V. jaubertiana, as well as three sequences of V. alba subsp. dehnhardtii from literature. In some, among the sampled individuals, the morphological attribution to one species is contradicted by nuclear DNA, which indicated a wide distance from other non-specific individuals from different locations and closer proximity to a different species. Chloroplast DNA data for the same individuals, on the contrary concurred with morphological evidence. These findings confirm document univocal correlation between our chosen chloroplast sequences and the studied taxa at species or subspecies level; these sequences have the appropriate variability range to be employed for detection of the maternal lineage of unknown Viola samples.     

Transfer of resistance to the beet cyst nematode (Heterodera Schachtii Schm.) from Sinapis alba L. (white mustard) to the Brassica napus L. gene pool by means of sexual and somatic hybridization

Summary Sexual and somatic hybrid plants have been produced between Sinapis alba L. (white mustard) and Brassica napus L. (oil-seed rape), with the aim to transfer resistance to the beet cyst nematode Heterodera schachtii Schm. (BCN) from white mustard into the oil-seed rape gene pool. Only crosses between diploid accessions of S. alba (2n = 24, S_a1S_a1) as the pistillate parent and several B. napus accessions (2n = 38, AACC) yielded hybrid plants with 31 chromosomes. Crosses between tetraploid accessions of S. alba (2n = 48, S_a1S_a1S_a1S_a1) and B. napus were unsuccessful. Somatic hybrid plants were also obtained between a diploid accession of S. alba and B. napus. These hybrids were mitotically unstable, the number of chromosomes ranging from 56 to more than 90. Analysis of total DNA using a pea rDNA probe confirmed the hybrid nature of the sexual hybrids, whereas for the somatic hybrids a pattern identical to that of B. napus was obtained. Using chloroplast (cp) and mitochondrial (mt) DNA sequences, we found that all of the sexual F₁ hybrids and somatic hybrids contained cpDNA and mtDNA of the S. alba parent. No recombinant mtDNA or cpDNA pattern was observed. Three BC₁ plants were obtained when sexual hybrids were back-crossed with B. napus. Backcrossing of somatic hybrids with B. napus was not successful. Three sexual hybrids and one BC₁ plant, the latter obtained from a cross between a sexual hybrid and B. napus, were found to show a high level of BCN resistance. The level of BCN resistance of the somatic hybrids was in general high, but varied between cuttings from the same plant. Results from cytological studies of chromosome association at meiotic metaphase I in the sexual hybrids suggest partial homology between chromosomes of the AC and S_a1 genomes and thus their potential for gene exchange.     

Genetic structure of a hybrid zone between two violets,Viola rossii Hemsl. and V. bissetii Maxim.: dominance of F1 individuals in a narrow contact range

The genetic composition of a hybrid zone can provide insight into the evolution of diversification in plants. We carried out morphological and amplified fragment length polymorphism analyses to investigate the genetic composition of a hybrid zone between two violets, Viola bissetii Hemsl. and Viola rossii Maxim. Our aim was to clarify the formation and maintenance of hybrids between these Viola species. We found that most hybrid individuals (V. bissetii × V. rossii) were of the F₁ generation, with a few of the F₂ generation. We found no backcrosses. The scarcity of post‐F₁ hybrids indicates that a species barrier is established between the parental species. The F₁‐dominated hybrid zone occupied only a narrow, intermediate ecotone between the parental habitats, suggesting that selection by environmental factors against hybrids may help to maintain the current conditions in this hybrid zone.     

Hybridization between Triticum aestivum L. and Agropyron michnoi Roshev.

Summary Intergeneric hybrids between Triticum aestivum cv Chinese Spring (2n=6x=42, AABBDD) and Agropyron michnoi Roshev. (2n=4x=28, PPPP) were obtained by embryo culture. Their spike characteristics were similar to those of common wheat but, unlike their parents, they were long-awned. The average meiotic chromosome pairing at MI of F₁ hybrids was: 6.39 I +3.75 rodII+8.64 ringII+0.81 III+0.30 IV+0.04 V, the bivalent and multivalent formation of which was much higher than expected from the genomic formulae. It is especially worthwhile to note that the F₁ hybrids were self-fertile, self set being 0.15%, and seeds were easily obtained from the backcross of f₁ plants with hexaploid and tetraploid wheats; here the seed set was more than 20.0%. The polyploid taxa and the position of A. Michnoi in Agropyron are discussed.     

Host adaptation in the anther smut fungus Ustilago violacea (Microbotryum violaceum): infection success,spore production and alteration of floral traits on two host species and their F1-hybrid

It is often assumed that host specialization is promoted by trade-offs in the performance of parasites on different host species, but experimental evidence for such trade-offs is scant. We studied differences in performance among strains of the anther smut fungus Ustilago violacea from two closely related host plant species, Silene alba and S. dioica, on progeny of (1) the host species from which they originated, (2) the alternative host species, and (3) inter-specific hybrids. Significant intra-specific variation in the pathogen was found for both infection success on a range of host genotypes (virulence) and components of spore production per infected host (aggressiveness) (sensu Burdon 1987). Strains did not have overall higher virulence on conspecifics of their host of origin than on strains from the heterospecific host, but they did have a significantly (c. 3 times) higher spore production per infected male host. This finding suggests that host adaptation may have evolved with respect to aggressiveness rather than virulence. The higher aggressiveness of strains on conspecifics of their host of origin resulted both from higher spore production per infected flower (spores are produced in the anthers), and greater ability to stimulate flower production on infected hosts. The latter indicates the presence of adaptive intraspecific variation in the ability of host manipulation. As transmission of the fungus is mediated by insects that are both pollinators of the host and vectors of the disease, we also assessed the effect of strains on host floral traits. Infection resulted in a reduction of inflorescence height, flower size, and nectar production per flower. Strains did not differ in their effect on nectar production, but infection with strains from S. alba resulted in a stronger reduction of inflorescence height and petal size on both host species. Vectors may therefore in principle discriminate among hosts infected by different strains and affect their efficiency of transmission. Contrary to assumptions of recent hypotheses about the role of host hybrids in the evolution of parasites, hybrids were not generally more susceptible than parental hosts. It is therefore unlikely that the rate of evolution of the pathogen on the parental species is slowed down by selection for specialization on the hybrids.     

A reappraisal of intrageneric classification ofTalaromyces based on the ubiquinone systems

Ubiquinone profiles of 25 strains ofTalaromyces were determined using reversed-phase high performance liquid chromatography. Together with data of earlier authors, examination of the most recently described species allowed us to solve some taxonomic problems in the intrageneric classification. Ubiquinone Q-10(H₂) was found in the majority ofTalaromyces species with aPenicillium anamorph, which are mostly placed in seriesFlavi andLutei of sectionTalaromyces. Flavi andLutei are closely related and homogeneous taxa based on their morphological characters used in the section. However, exceptionol prfiles were consistently shown byT. trachyspermus and the allied taxa of seriesTrachyspermi of the sectionTalaromyces, in which a mixture of ubiquinone Q-10(H₂) and ubiquinone Q-10(H₄) was found. Thus the accommodation ofT. trachyspermus and the allied taxa in the sectionTalaromyces was not supported by their ubiquinone systems.Trachyspermi is distinguished from other taxa ofTalaromyces by its production of white ascomata and rapid growth at 37°C. A new section,Trachyspermus, is proposed herein. SectionEmersonii showed heterogeneity; the ubiquinone profiles (Q-10(H₂) or Q-10 and Q-10(H₂)) inTalaromyces with aGeosmithia anamorph were relatively homogeneous, whereas those of another group with aPaecilomyces anamorph were considerably variable. OnlyTalaromyces with aGeosmithia anamorph can be placed in the sectionEmersonii.     

Nuclear cyp73 intron fragment length polymorphism supports morphological analysis of Salix species and hybrids

Abstract

The polyploid Salix alba L.–Salix fragilis L. hybrid complex still presents major difficulties in morphological identification. Most of the measured characters show a low diagnostic value for unambiguously identifying the parental species and their hybrid Salix × rubens Schrank due to continuous variation creating a large overlap in leaf and catkin morphology. Fragment length polymorphism of nuclear cyp73 intron markers was used to identify species and hybrids. This multilocus genotyping could be applied in a morphological analysis of trees from hybrid zones and allowed to demonstrate that morphological features of leaves and catkins clearly separated S. alba from S. fragilis. The hybrid individuals largely overlapped with both parental species but appeared to be morphologically more similar to S. fragilis than to S. alba. Cyp73 analysis of 11 Salix taxa revealed intermediate positions of two hybrid taxa with S. alba, namely S. × rubens and S. × sepulcralis Simonkai with their respective parental species S. fragilis and S. babylonica L. Additionally, the cyp73 intron multilocus genotypes clustered tetraploid taxa separately from diploid willows. Cyp73 introns are valuable markers for fast, reliable and straightforward genotyping in willow species and hybrids.     

Relative importance of ballistic and ant dispersal in two diplochorous Viola species (Violaceae)

Viola is one of the diplochorous plant genera that disperse their seeds in two ways, ballistic and ant dispersal. We compared the seed dispersal of two major Viola species of northern Japan, V. selkirkii and V. verecunda. The mean weight of seed was less in V. verecunda (0.42 ± SD 0.03 mg) than in V. selkirkii (0.61 ± 0.12 mg). The elaiosome of V. selkirkii (0.02 ± 0.004 mg) was larger than in of V. verecunda (0.006 ± 0.0004 mg), whereas the lipid component of elaiosome was not remarkably different between the two species. In ballistic dispersal, the mean dispersal distance was 56.0 ± 17.5 cm in V. verecunda but only 38.3 ± 5.1 cm in V. selkirkii. In ant dispersal, the mean dispersal distance was 28.1 ± 24.9 cm in V. selkirkii and 36.1 ± 33.7 cm in V. verecunda; however, the seed removal frequency of V. selkirkii (15.5%) was much higher than that of V. verecunda (3.0%). These results suggest that V. selkirkii is more dependent on ant dispersal while V. verecunda is more dependent on ballistic dispersal. The effect of seed predation was very serious in both species. In the quadrat census, 99.0% of V. selkirkii seeds and 99.1% of V. verecunda seeds were damaged by ground beetles, spiders, ticks, and others which frequently devoured diaspores. An experiment with V. verecunda seeds demonstrated that the overdispersion of seeds on the forest floor enhanced the frequency of removal by ants and reduced seed damage by predators.     

CHROMOSOME DIFFERENTIATION IN SEVERAL SPECIES OF MELILOTUS

Shastry , Sishta V. S., William K. Smith , and Delmer C. Cooper . (U. Wisconsin, Madison.) Chromosome differentiation in several species of Melilotus. Amer. Jour. Bot. 47(8) : 613–621. Illus. 1960.—Two species of the section Eumelilotus (M. alba and M. officinalis), 2 of Micromelilotus (M. messanensis and M. segetalis), 2 F₁ hybrids (M. officinalis × M. alba and M. messanensis × M. segetalis), 2 autotetraploids (M. alba and M. officinalis), and 1 allotetraploid (M. officinalis × M. alba), were utilized during the course of this investigation. The 4 species and F₁ hybrids have 16 somatic chromosomes and the tetraploids have twice that number (32). The 2 Eumelilotus species are completely isolated because of seed failure after cross pollination. The F₁ hybrid (M. officinalis × M. alba), obtained elsewhere by the use of embryo-culture techniques, was intermediate between the parents in certain morphological characters and was ca. 75% pollenfertile whereas the parents approached complete fertility. No structural differences between the chromosomes were evident at pachytene. Disturbances which led to the reduced fertility occurred at later stages of meiosis. The Micromelilotus species are cross compatible, but the F₁ hybrid (M. messanensis × M. segetalis) is highly sterile. Despite chromosome structural differences of various types evident at pachytene, bivalents regularly occur at metaphase I. Irregular distribution of the chromosomes at later stages of meiosis leads to high sterility. Species which readily cross but produce a hybrid of very low fertility are likely to compound chromosomal structural differences, because of abnormalities in meiosis, in contrast with species that are completely incompatible.     

Die Fagus-Sippen Europas und ihre geographisch-soziologische Korrelation zur Verbreitung der Assoziationen des Fagion s.l.

Studies of the beeches and beech woods of eastern central Europe revealed, that in the postglacial period not only Fagus sylvatica (L.) emend. reimmigrated from the refugial territories in the SE-as has generally been accepted, but also the transitional taxa, which originated from hybrids with F. orientalis Lipsky. The NW area limit of these intermediate taxa must be revised. The presence in central Europe of these taxa-which form own Fagion alliances and associations in the SE (Fagus intermedia ssp. moesiaca and ssp. taurica) as well as the presence of other southeastern species in central European beach woods shows, that their postglacial development is parallel to, but different from other areas. The taxon Fagus intermedia (ssp. neglecta and ssp. transitus) became differential taxa of a central European region of the Fagion medioeuropaeum. Plant sociologists are therefore requested to make new and critical analyses of the beech woods in Europe, with special attention to the Fagus taxa, in order to establish in detail the geographical distribution and phytosociological significance of Fagus intermedia.The author offers to determine or revise Fagus material (herbarium collections).

Danksagung. Ich möchte meinen tiefsten und allzeitigen Dank besonders den Herren Prof. Dr. A. O. Horvat (Pécs), Prof. Dr. Ch. Moulopoulos, Prof. Dr. B. Jovanovié, Prof. Dr. I. Dumitriu-Tataranu, Prof. Dr. R. Bornkamm, Prof. Dr. M. A. Kotschkin, Prof. Dr. P. Fukarek, Prof. Dr. K. Browicz für gewährte Unterstützung aussprechen und ganz besonders unserem unvergeßlichen verstorbenen Prof. Dr. Drs. h.c. R. Tüxen, der mir zur Fortführung dieser Studien Mut machte.     

Ribosomal RNA genes structure in somePopulus spp. (Salicaceae) and their hybrids

The tandemly repeated multigene families encoding 18S and 25S rRNAs were studied at the restriction enzyme level inPopulus alba L.,Populus deltoides Bartr. exMarsh.,Populus trichocarpa Torr. & Gray and in the hybrids between the last two mentioned species. The analysis of single and double digestion with EcoRI, BamHI, XbaI, and SstI endonucleases showed the presence of single repetitive unit types of 12.25 and 11.75kb inP. alba andP. trichocarpa, respectively.P. deltoides showed two rDNA gene types having the same length (12.25Kb) but different nucleotide sequence in the IGS. The rDNAs genes ofP. deltoides andP. triochocarpa are inherited codominantly in their hybrids.     

Genetic variation and natural hybridization betweenOrchis laxiflora andOrchis palustris (Orchidaceae)

Genetic divergence between population samples ofOrchis laxiflora and ofO. palustris from various European locations was studied by electrophoretic analysis of 25 enzyme loci. An average genetic distance of D_Nei = 1.24 was found between the two taxa, with 12 out of 25 loci showing alternative alleles (diagnostic loci). Genetic heterogeneity was observed within bothO. laxiflora andO. palustris, when northern and southeastern populations were compared, being lower in the former taxon (D = 0.06), than in the latter (D = 0.16). Karyologically, 2n = 36 was found for bothO. laxiflora andO. palustris. O. laxiflora andO. palustris produce hybrids, described asO. ×intermedia. Genotype analysis of several sympatric samples showed the presence of hybrid zones, including F₁ hybrids and, in low proportions, recombinant classes, putatively assigned to F_n and backcrosses, as well as a few introgressed individuals of both taxa. These data indicate that hybrids are only partially fertile, with a very limited mixing up of the two parental gene pools; this is also shown by the lack of significant lowering of genetic distances when sympatric and allopatric heterospecific samples are compared. Accordingly,O. laxiflora andO. palustris form a syngameon; nevertheless they can be considered as good taxonomic species, with virtually distinct gene pools, which evolve independently. The genetic variability inO. laxiflora andO. palustris is remarkably low ( _e = 0.05 and _e = 0.02, respectively). In particular, nearly complete absence of polymorphic loci was found inO. palustris from northcentral Europe. Two hypotheses are considered to explain the low genetic variability of this endangered species.     

Experimental documentation of natural hybridization inCactaceae: Origin of Lloyd's Hedgehog Cactus,Echinocereus ×lloydii

The origin ofEchinocereus ×lloydii Britt. & Rose, pro sp. (Lloyd's Hedgehog Cactus) was investigated using comparative morphology, cytology, biochemistry, and particularly, artificial hybridization. Numerous artificial crosses between the putative parentsE. coccineus Engelm. (a species of claret-up cactus) andE. dasyacanthus Engelm. (Texas Rainbow Cactus) were successful, resulting in the production of hundreds of seeds with hybrid embryos. The F₁ hybrid progeny (i.e., syntheticE. ×lloydii) grew to sexual maturity in about four and one-half years, whereupon successful backcrosses and F₂ generation hybrids were also obtained. The known F₁ hybrids closely approximated naturalE. ×lloydii. The fertility of these syntheticE. ×lloydii was high, like their natural counterparts. The populations ofE. ×lloydii in Pecos County, Texas are inferred to have originated as the result of natural interspecific hybridization. It is assumed thatE. ×lloydii or similar plants may arise wherever the parental taxa grow sympatrically.     

Species-specific acclimation to strong shade modifies susceptibility of conifers to photoinhibition

Photoinhibitory processes in the photosynthetic apparatus of the seedlings of Abies alba (Mill.), Picea abies (Karst.), and Pinus mugo (Turra) growing under strong shade (5 % of full solar irradiance) or full irradiance conditions were investigated in winter and spring using chlorophyll a fluorescence techniques. The extent of photoinhibition in needles as indicated by a decrease in maximum quantum yield of PS II photochemistry (F_v/F_m) depended on species, air temperature and acclimation to the light environment. Unexpectedly, shade-tolerant Abies alba was less affected by low-temperature photoinhibition compared to the other species. F_v/F_m recovered with increasing air temperature. During winter, the seedlings of Picea abies growing in shade showed higher F_v/F_m than those from full light. Non-photochemical quenching of fluorescence (NPQ) measured at the same levels of actinic light was higher in needles acclimated to full light except for Abies alba in February. Photosynthetic performance in term of ETR (apparent electron transfer rate) was also higher in full light-acclimated needles. In April, at ambient temperature, recovery of PS II efficiency from the stress induced by illumination with saturating light was faster in the needles of Picea abies than in those of Abies alba. The shade-acclimated needles of Abies alba and Picea abies showed greater down-regulation of PS II induced by high light stress.     

Natural hybridization in JapaneseCalamagrostis

Morphological and pollen studies were made for the collections belonging toCalamagrostis langsdorffii, C. Sachalinensis, C. longiseta, C. nana and various intermediates between these species from central Honshu, the chromosome numbers of which were reported in a previous paper (Tateoka, 1976). Additional collections made from the Akaishi Range in 1976 were also subjected to the present work. The intermediates showed 0%, or nearly 0%, pollen stainability and a mosaic of morphological features of putative parental taxa which can be estimated to occur for F₁ hybrids. This estimation was sustained by a comparison with the pattern of character expressions for the artificially raised F₁ hybrids of various European species ofCalamagrostis as reported by Nygren (1962). These results as well as field observations strongly suggested that the intermediates may be wholly or almost wholly F₁ hybrids. The hybrids were sometimes found in abundance within a limited area, but seemed to have little capacity to migrate from the places where they originated. The following combinations, which were not previously recorded, were disclosed:C. longiseta×C. sachalinensis, C. langsdorffii×C. nana, C. langsdorffii×C. longiseta, C. longiseta×C. nana. Possibilities of introgression in these hybridizing species were discussed. The hybrids were tetraploids except one hexaploid which was discovered in a mixed population ofC. nana, C. longiseta and their putative F₁ hybrids at the tetraploid level. The hexaploid in question, which seemed to have resulted from the participation of an unreduced gamete, was very similar morphologically toC. nana subsp.hayachinensis distributed in the mountain far distant from central Honshu. Geographical distributions of the hybrid plants were surveyed through examination of the herbarium specimens.     

涝渍胁迫对入侵植物白花鬼针草及其本地近缘种金盏银盘生长和生理特性的影响

[目的]揭示涝渍胁迫下白花鬼针草与其本地近缘种金盏银盘的生长和生理特性差异。[方法]研究对照和涝渍胁迫下白花鬼针草和金盏银盘株高、新生不定根数目、净光合速率（P_n）、总生物量、相对生长速率、叶面积等生长和生理指标的变化。[结果]涝渍胁迫后入侵植物白花鬼针草比本地种金盏银盘保持了更高的株高、新生不定根数目和P_n（P<0.01）,更高的总生物量、相对生长速率、根生物量、茎生物量、叶生物量、叶面积（P<0.05）。涝渍胁迫10 d内,白花鬼针草根系活力和光系统II最大光量子产量显著高于金盏银盘（P<0.05）,涝渍胁迫20 d后2物种的2个参数趋于一致,这些结果表明涝渍对白花鬼针草生长的负面影响较小。涝渍胁迫前期更快的不定根生长速度和更高的根系脱氢酶活力可缓解涝渍对白花鬼针草的胁迫,减少了涝渍对光合系统的破坏,使其保持更高的P_n,从而有助于白花鬼针草保持更高的生长速率,是白花鬼针草耐受涝渍的生理机制。[结论]与本地近缘种金盏银盘相比,短期涝渍可使入侵植物白花鬼针草形成生长优势,华南地区雨季短期集中降水所形成的土壤涝渍有利于白花鬼针草的入侵。全球气候变化造成的降水不平衡性可能会加剧白花鬼针草在华南地区的入侵。     

碳酸氢盐处理下桑树和构树的生长、光合和抗逆性差异

为探究喀斯特生境中,在碳酸氢盐的胁迫下HCO^-₃对植株生长及生理特性的影响,该文以构树和桑树幼苗为研究对象,对不同浓度NaHCO₃溶液(0、15、30 mmol·L^-1)处理下植株的生长情况、光合能力、抗氧化酶活性、渗透调节物质含量和细胞膜系统损伤情况进行研究。结果表明:(1)在HCO^-₃处理下,构树和桑树的生长和光合能力均受到抑制,叶片细胞内均发生显著的抗氧化和抗渗透胁迫生理响应。(2)HCO^-₃对构树和桑树生长的抑制作用与其浓度有关,并有显著差异性(P<0.05)。(3)30 mmol·L^-1 HCO^-₃处理对植株生长、光合、抗氧化酶系统和渗透调节系统的抑制作用以及植物细胞的损伤情况要显著强于15 mmol·L^-1 HCO^-₃处理的效果。(4)同等浓度的HCO^-₃处理下,构树的生长、光合能力、抗氧化酶活性、渗透调节物质含量显著高于桑树,其叶片细胞损伤情况显著低于桑树。综上结果均表明,构树对碳酸氢盐胁迫的耐受能力要优于桑树。该研究为阐明桑科植物对喀斯特环境适应机制提供科学支撑。