Roles of succession,light, nutrients and disturbance on population vigor and maintenance of the rare plant Solidago shortii (Asteraceae)

Results of field and glasshouse experiments on Solidago shortii, and our observations on this species over many years, were used to construct a conceptual model of the roles of succession, light, soil nutrients and disturbance on population vigor and maintenance of this federal-endangered species. As cover of woody vegetation increased at a population site between 1986 and 1992, number of flowering ramets of S. shortii significantly decreased but number of vegetative ramets remained nearly constant. Adult plants transplanted into a redcedar thicket and those shaded in a glasshouse produced many fewer flowering ramets and capitula per flowering ramet and less biomass and had higher mortality than those in the open. Seedlings/juveniles shaded in a glasshouse had significantly less dry biomass; lower RGR, NAR, leaf area and root/shoot ratio and higher LAR, SLA and LWR than nonshaded ones. In a field site and glasshouse, fertilized plants (NPK) consistently had more flowering ramets and capitula per flowering ramet than nonfertilized ones. Hierarchy of dry weight of plants grown in a glasshouse in soils derived from five types of bedrock was phosphatic limestone > calcareous shale > sandstone > black shale = dolomite. Flowering and biomass production in the field-fertilizer and soil-type experiments were associated closely with levels of P. Number of flowering ramets significantly increased in plants transferred from shaded to nonshaded glasshouse conditions, but no such increase occurred after opening the canopy above plants in a thicket. Both high light and high nutrient levels apparently are necessary to maintain high vigor of S. shortii. In areas subject to invasion by woody plants, periodic high intensity disturbance may be required to prevent population extirpation.     

Effects of pollen quality and quantity on pollen limitation in Crataegus monogyna (Rosaceae) in NW Spain

Pollen limitation occurs when plants produce less fruits and/or seeds than they would with adequate pollen receipt. If the addition of cross-pollen to stigmas increases fruit/seed production, it is interpreted as an evidence of pollen limitation. Much of the limitation may be associated with the quality rather than quantity of pollen; however, most studies do not discriminate between the two, which may lead to misinterpretation of the results. We studied the effects of quality and quantity of pollen on the reproduction of a northern Spanish population of Crataegus monogyna. The treatments included self- and cross-pollination, and supplementation to open and bagged flowers. The response variables considered were number of pollen grains per stigma, pollen tubes per style, and initial and final fruit set. In the Cantabrian range, C. monogyna requires insect pollinators to set fruit and is partially self-incompatible. We found that the number of pollen tubes did not differ between cross- and self-pollination treatments; however, self-pollinated flowers set less fruits than flowers that received pure cross-pollen or were supplemented with both cross- and self-pollen. The experimental design allowed us to infer qualitative rather than quantitative pollen limitation. Comparison of the number of pollen grains and tubes, and initial and final fruit set among pollination treatments suggested post-zygotic embryo selection against selfed progeny.     

Effects of inbreeding and pollen donor provenance and diversity on offspring performance under environmental stress in the rare plant Cochlearia bavarica

Habitat degradation and loss can reduce size and genetic variability of natural populations, increasing individual homozygosity and average relatedness between individuals. While the resulting inbreeding depression may be reduced by natural selection under prevailing environmental conditions, it may increase again under environmental stress. To investigate the effect of environmental stress on offspring performance and the expression of inbreeding depression, we hand-pollinated maternal plants in small (< 100, n=5) and large populations (> 400 flowering plants, n=5) of the rare plant Cochlearia bavarica (Brassicaceae) and raised the offspring under experimentally manipulated water and light regimes (normal or reduced supply). In addition to considering natural variation in inbreeding levels due to population size, we manipulated pollen donor provenance and diversity. Maternal plants were pollinated with nine donors from a different population or with one or nine donors from the same population. One further inflorescence of each maternal plant was exposed to free pollination. Offspring growth and survival were monitored over 300 days. Offspring performance varied significantly among populations and maternal plants. Environmental stress interacted significantly with these factors. However, there was no general indication that offspring from small populations were more negatively affected. In seven out of 10 populations, offspring derived from between-population pollination performed better than offspring derived from within-population pollination. Also, in five out of 10 populations, average offspring size was higher after within-population pollination with nine than after pollination with one pollen donor. These results suggest low genetic diversity within C. bavarica populations, both smaller and larger ones. Interactions between environmental stress and pollination treatment indicated that using pollen donors from outside a population or increasing the number of pollen donors can reduce inbreeding depression, but that this beneficial effect is impaired under stressful conditions.     

A new species of Scorzonera (Asteraceae) from Khorasan, Iran

Scorzonera joharchii sp. nov. is described from the Khorasan, east of Birjand, Iran. It is similar to S. tuberosa from which it mainly differs in its tomentose indumentum, longer pappus and villous and longer achenes.     

Contribution to the taxonomy of Turkish Scorzonera (Asteraceae) taxa based on vegetative anatomy

In the present study, the general stem, root and leaf anatomical features of 59 Scorzonera L. s.l. (Asteraceae) taxa collected from Turkey are presented and evaluated by cluster and principal coordinate analysis. Numerical analyses based on 26 anatomical traits showed that arrangement of tracheal elements in the root, presence of cortical bundles, latex canals, secretory cells and aerenchyma in the stem and mesophyll are valuable for grouping Scorzonera taxa. Dendograms inferred from anatomical data were generally congruent with the traditional subgeneric classification of Scorzonera (Scorzonera L., Podospermum DC., Pseudopodospermum (Lipsch. et Krasch.) Lipsch.). However, the present study also show that the examined species may not be identified only based on the internal morphology of root, stem and leaf. In addition, the results support to treat Podospermum as a distinct genus.     

A new species of Scorzonera (Asteraceae) from Anatolia, Turkey

Scorzonera aytatchii sp. nov. is described from the Aydos Mountain (C4: Konya) in Turkey. It is related to S. rigida , from which it mainly differs in its hairy achene.     

Tyrolobibenzyls E and F from Scorzonera humilis and distribution of caffeic acid derivatives,lignans and tyrolobibenzyls in European taxa of the subtribe Scorzonerinae (Lactuceae,Asteraceae)

A chemosystematic study of the subtribe Scorzonerinae, a subtribe of the Lactuceae tribe of the Asteraceae family was performed, using the recently discovered tyrolobibenzyls as well as lignans and caffeic acid derivatives as diagnostic characters. In addition to the known compounds two new tyrolobibenzyls (E and F) were isolated and their structures were established by mass spectrometry and 1D and 2D NMR spectroscopy. Twenty four samples from rootstocks of seventeen different Scorzonerinae taxa, comprising members of three genera (Podospermum, Scorzonera, and Tragopogon), were analyzed. Tyrolobibenzyls A (1), B (2), C (5), D (3), E (6), and F (4) were identified in crude extracts by means of HPLC retention times, on-line UV spectra and on-line MS/MS spectra. Quantification of these compounds was performed by HPLC, using 2,2-bis-(4-hydroxyphenyl)-propane as an internal standard. Tyrolobibenzyls A-F were only detected in samples from Scorzonera humilis, while chlorogenic acid and 3,5-dicaffeoylquinic acid were detected in all samples investigated. In contrast, caffeoyl tartaric acid and cichoric acid were not detectable in any member of the subtribe Scorzonerinae.     

A rare continual flowering strategy and its influence on offspring quality in a gynodioecious plant

The majority of angiosperms have a single annual bout of reproduction; species that flower continually throughout the year are rare. Ochradenus baccatus is a gynodioecious, desert shrub whose principal flowering period is associated with the winter rains, although large individuals also remain in flower during the hot, dry summer. The goal of this study was to examine the reproductive consequences of continual flowering in a large population of O. baccatus in Israel. Over the two years of this study, 60% of individuals flowered continuously. The number of fruit and seeds per fruit were greater in winter. Winter seeds were ～12% heavier than summer seeds and had significantly higher germination rates (80 vs. 60%, respectively). Although summer seeds were smaller and less likely to germinate, we propose that the benefit derived from their production lies in their ability to capitalize on the first winter rains. These early rain events provide a head start on establishment and growth in the hostile desert environment. Plants that delay reproduction until the onset of rains risk having their offspring face the dry conditions of spring and summer.     

Genetic incompatibility and offspring quality in the tristylous plant Lythrum salicaria (Lythraceae)

The purpose of this study was to determine the incompatibility relationships among the three different morphs of the tristylous plant Lythrum salicaria, and to assess whether there are fitness consequences to breakdown in incompatibility. Twenty-four different types of pollinations were performed using all possible combinations of anthers and stigmas. These can be grouped as legitimate pollinations (pollinations from the appropriate anther level of a compatible morph), illegitimate intermorph pollinations (pollinations from the inappropriate anther level of a compatible morph), intramorph pollinations (pollinations between individuals of the same morph), and self pollinations. Legitimate pollinations produced significantly more seed than illegitimate intermorph pollinations, intramorph pollinations, and self pollinations. The difference between legitimate and illegitimate intermorph pollination success is particularly interesting because pollen for these crosses came from the same genetic individual. Pollination types also differed in offspring quality. In the rare examples where progeny were produced by illegitimate intermorph pollinations, the progeny did not have significantly lower values for seedling growth traits compared to legitimate progeny. Seedlings produced by self pollinations had significantly lower values for four out of six seedling growth traits measured. Comparisons of legitimate and self progeny traits indicate that inbreeding depression for most traits is close to or above 0.5. The finding that some seed were produced from illegitimate pollinations suggests that there is variation among individuals in incompatibility. There was a significant effect of parental morph type on the probability of breakdown in incompatibility with the midstyled maternal parents setting more seed from illegitimate pollinations.     

The effects of plant population size on the interactions between the endangered plant Scorzonera humilis, a specialised herbivore, and a phytopathogenic fungus

We studied the effects of population size on the interactions between Scorzonera humilis (Asteraceae), its specialised seed-feeding fly Heterostylodes macrurus (Anthomyidae) and its specific systemic smut fungus Ustilago scorzonerae (Ustilaginales). The number of seeds developing per plant (potential seed production) strongly increased with population size in S. humilis. However, because seed predation by the seed feeding fly H. macrurus and the negative impact of the pathogen U. scorzonerae also increased, realised seed production was not related to population size. The probability of occurrence of H. macrurus increased with the population size of its host plant and its abundance increased more than proportionally. This suggests that Allee effects reduce insect abundance in small populations of S. humilis . The probability of occurrence of the fungus U. scorzonerae also increased with plant population size. Within populations, large genets were more likely to be infected than small ones. The systemic pathogen U. scorzonerae reduces the effective population size of its host because all flowers of an infected individual are sterilised. Nevertheless, in most populations the impact of the fly on reproduction was stronger than that of the pathogen, because most genets were not infected. Both parasites were rarer than the host plant itself, supporting the trophic-level hypothesis of island biogeography. Our results suggest that habitat fragmentation may release plants from parasites and pathogens. These positive effects of isolation and small population size may mask negative effects of fragmentation on, for instance, the quantity and quality of pollination.     

Effects of light quality and quantity on growth of the clonal plant Eichhornia crassipes

Summary Plant canopy shade reduces photosynthetic photon flux density (PPFD) and ratio of red to far-red light (z). Both effects can cause plants to increase potential for light acquisition through vertical growth and leaf area expansion. Clonal plants such as Eichhornia crassipes might alternatively increase light interception via horizontal growth of stolons or rhizomes and placement of new ramets in less shaded microsites. Effect of simulated canopy shade and component effects of PPFD and z were tested by filtering or adding light uniformly, to a whole group of connected ramets, or locally, to individual ramets within a group. In uniform treatments, low PPFD reduced total growth but low z did not. Low PPFD and low z independently reduced stolon and ramet production and caused etiolation of petioles; effect of low PPFD plus low z on ramet production was greater than that of either factor alone. Lateral clonal growth thus did not seem to be a response to uniform shading; instead, uniformly low PPFD or low z increased partitioning to established ramets. Low z changed partitioning without changing total growth. In local treatments, reduction of growth of individual ramets due to low PPFD and inhibition of new ramet production attributable to spectral composition of light were mitigated when connected ramets were unshaded; plants may respond differently to patchy than to uniform shade.     

A new species of Scorzonera L. (Asteraceae) from south Anatolia, Turkey

A new species Scorzonera gokcheoglui O. Ünal & R. S. Göktürk sp. nov. from south Anatolia is described and illustrated. Its relationships with S. argyria and S. pisidica are discussed. A map showing the distribution of the species and other related species is given.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 142 , 465–468.     

Genetic diversity and hierarchical population structure of a rare autotetraploid plant,Aster kantoensis (Asteraceae)

We sampled 17 populations of a rare autotetraploid Aster kantoensis (Asteraceae) from three river systems located in central Japan, and studied them for allelic variation at 22 enzyme loci. There was no significant correlation between the actual population size and three genetic diversity parameters, suggesting that the effective population size was very small even for the large populations, i.e., even large populations may still have a high probability of being of recent origin and remain influenced by the founder effect. Compared to other autotetraploid species, the total genetic variation of A. kantoensis is small. The number of alleles and gene diversity of a population were not significantly different among the river systems, although the percentage of polymorphic loci was different. Genetic differentiation among river systems was larger than between populations within the river systems, thereby indicating that gene flow between river systems is small, especially between the Kinu River system and Tama or Sagami River systems.     

Pollen quantity and quality as explanations for low seed set in small populations exemplified by Eupatorium (Asteraceae)

As plant populations decrease in size, reduced seed set may contribute to their ultimate extirpation. In this study, effects of pollen quantity and compatibility relationships (quality) on seed set were investigated in a rare species (Eupatorium resinosum) and a closely related common species (E. perfoliatum). The impact of pollen quantity was studied through pollen supplementation experiments in two populations of each species. Addition of pollen increased seed set only in the smaller population of E. resinosum. Compatibility relationships (pollen quality) were investigated in a diallel crossing experiment using ten genotypes from the same populations. Plants from the smaller population of E. resinosum were found to be 40% cross-incompatible, which was higher than the larger population of E. resinosum and the two populations of E. perfoliatum, the latter showing signs of self-compatibility in some individuals. In addition the variance in number of compatible matings per individual was higher in the smaller population of E. resinosum. These results are consistent with a computer simulation model that investigated the effect of small population size on S-allele diversity. Sufficient pollination accompanied by a partial breakdown of the incompatibility system may account, in part, for the relative success of E. perfoliatum.     

转基因插入对水稻花粉活力和杂交结实的影响

以花粉活力和杂交结实率评价转基因插入对水稻品种异交潜力的影响.选用含bar、crylAb、BADH和Xa21等4种基因的5份转基因水稻品系研究转基因插入对转基因受体品种花粉离体萌发率的影响.结果表明,不同受体品种花粉离体萌发率差异显著;转基因水稻花粉离体萌发率在0.416～0.584间,与受体品种(0.004～0.574)相近;转基因品种与相应受体品种间花粉离体萌发率差异不显著.对所选配的26个人工杂交组合杂种结实调查表明,bar、crylAb基因的插入对受体品种杂交结实率影响显著,而Xa21基因的插入对受体品种杂交结实率影响较小;转基因水稻品种(花粉供体)与非转基因水稻品种的杂交结实率变幅为0.056～0.13,在受体品种(花粉供体)与非转基因水稻品种的杂交结实率范围(0.052～0.417)之内.本研究花粉离体萌发和杂交结实结果表明转基因的插入对水稻品种异交潜力的影响甚微.     

Effect of enhanced UV-B radiation on pollen quantity,quality, and seed yield in Brassica rapa (Brassicaceae)

We conducted three experiments to examine the influence of ultraviolet-B radiation (UV-B; 280–320 nm) exposure on reproduction in Brassica rapa (Brassicaceae). Plants were grown in a greenhouse under three biologically effective UV-B levels that simulated either an ambient stratospheric ozone level (control), 16% (“low enhanced”), or 32% (“high enhanced”) ozone depletion levels at Morgantown, WV, USA in mid-March. In the first experiment, we examined whether UV-B level during plant growth influenced in vivo pollen production and viability, and flower production. Pollen production and viability per flower were reduced by ≈50% under both enhanced UV-B levels relative to ambient controls. While plants under high-enhanced UV-B produced over 40% more flowers than plants under the two lower UV-B treatments, whole-plant production of viable pollen was reduced under high-enhanced UV-B to 17% of that of ambient controls. Whole-plant production of viable pollen was reduced under low-enhanced UV-B to 34% of ambient controls. In the second experiment, we collected pollen from plants under the three UV-B levels and examined whether source-plant UV-B exposure influenced in vitro pollen germination and viability. Pollen from plants under both enhanced-UV-B treatments had initially lower germination and viability than pollen from the ambient level. After in vitro exposure to the high-enhanced UV-B levels for 6 h, viability of the pollen from plants grown under ambient UV-B was reduced from 65 to 18%. In contrast, viability of the pollen from plants grown under both enhanced UV-B treatments was reduced to a much lesser extent: only from ≈43 to 22%. Thus, ambient source-plant pollen was more sensitive to enhanced UV-B exposure. In the third experiment, we used pollen collected from source plants under the three UV-B levels to fertilize plants growing under ambient-UV-B levels, and assessed subsequent seed production and germination. Seed abortion rates were higher in plants pollinated with pollen from the enhanced UV-B treatments, than from ambient UV-B. Despite this, seed yield (number and mass) per plant was similar, regardless of the UV-B exposure of their pollen source. Our findings demonstrate that enhanced UV-B levels associated with springtime ozone depletion events have the capacity to substantially reduce viable pollen production, and could ultimately reduce reproductive success of B. rapa.     

Effects of competition on lifetime estimates of inbreeding depression in the outcrossing plant Crepis sancta (Asteraceae)

Inbreeding depression was studied in two populations of a Mediterranean allogamous colonizing species Crepis sancta. In order to test the hypothesis that the magnitude of inbreeding depression can be modified by successional processes, the growth and survival of individuals resulting from two generations of inbred crosses including selfing were analysed with interspecific competition (in natural vegetation) and without interspecific competition (by removing natural vegetation). Inbreeding depression was weak for seed production. Germination was little affected by inbreeding but mortality and the number of capitula showed inbreeding depression, especially in the presence of competition. This suggests that inbreeding depression is very sensitive to variations in environmental conditions such as interspecific competition. As a consequence, inbreeding depression cannot be considered as constant in natural conditions.