High selfing and high inbreeding depression in peripheral populations of Juncus atratus

The mating system of a plant is the prime determinant of its population genetic structure. However, mating system effects may be modified by postzygotic mechanisms like inbreeding depression. Furthermore, historical as well as contemporary ecological factors and population characteristics, like the location within the species range can contribute to genetic variability. Using microsatellite markers we assessed the population genetic structure of the wind-pollinated Juncus atratus in 16 populations from peripheral and nearly central areas of the distribution range and studied the mating system of the species. In three peripheral populations, outcrossing rates at seeds stage were low (mean t(m) = 5.6%), suggesting a highly autogamous mating system. Despite this fact, on adult stage both individual heterozygosity (mean H(O) = 0.48) and gene diversity (mean H(E) = 0.58) were high even in small populations. Inbreeding coefficients were consistently low among all populations (mean F(IS) = 0.15). Within the three peripheral populations indirect estimates of lifetime inbreeding depression were surprisingly high (delta(eq) = 0.96) and inbreeding depression could be shown to act mostly on early seedling establishment. Similar conditions of autogamy combined with high inbreeding depression are typical for plants with a large lifetime genomic mutation rate that cannot avoid selfing by geitonogamy. However, the results presented here are unexpected for small-statured, herbaceous plants. Substantial genetic differentiation among all populations was found (mean F(ST) = 0.24). An isolation-by-distance pattern was apparent on large scale but not on local scale suggesting that the overall pattern was largely influenced by historical factors, e.g. colonization, whereas locally genetic drift was of greater importance than gene flow. Peripheral populations exhibited lower genetic diversity and higher inbreeding coefficients when compared with subcentral populations.     

A Study on the Genus Juncus Linn. from China

Juncus Linn. is a cosmopolitan genus with about 240 species, widely distributed in both hemispheres, but most abundant in the frigid and temperate zones. In the present paper, a revision of this genus in China is made, and a key to the species is provided. This paper also presents a systematic arrangement of the genus Juncus Linn. from China, recognizing six subgenera, 14 sections (includ. ten new), four series (includ. two new), 77 species (includ. 14 new), one subspecies (new) and ten varieties (includ. four new). They are as follows: Subgen. 1. Genuini Buchen. Sect. 1. Inflexi K. F. Wu, sect. nov. Sect. 2. Effusi (V. Krecz. et Gontsch. )K. F. Wu, stat. nov. Subgen. 2. Pseudotenageia V. Krecz. et Gontsch. Sect. 1. Kangpuenses K. F. Wu, sect. nov. Sect. 2. Compressi (V. Krecz. et Gontsch. )K. F. Wu, stat. nov. Sect. 3. Tenues (V. Krecz. etGontsch.)K. F. Wu, stat. nov. Subgen. 3. Poiophylli Buchen. Sect. 1. Nigroviolacei K. F. Wu, sect. nov. Sect. 2. Bufonii (V. Krecz. et Gontsch. )K. F. Wu, stat. nov. Subgen. 4. Graminifolii Buchen. Subgen. 5. Septati Buchen. Sect. 1. Allioides K. F. Wu, sect. nov. Sect. 2. Articulati K. F. Wu, sect. nov. Ser. 1. Articulati V. Krecz. et Gontsch. Ser. 2. Dongchuanenses K. F. Wu, ser, nov. Subgen. 6. Alpini Buchen. Sect. 1. Triglumes K. F. Wu, sect. nov. Ser. 1. Triglumes K. F. Wu, ser. nov. Ser. 2. Benghalenses K. F. Wu, ser. nov. Sect. 2. Minimi K. F. Wu, sect. nov. Sect. 3. Sikkimenses K. F. Wu, sect. nov. Sect. 4. Concinni K. F. Wu, sect. nov. Sect. 5. Sphacelati K. F. Wu, sect. nov.     

江浙地区席草品种比较解剖与质量分析

江浙地区４个席草品种地上茎的表面都有纵行条纹,条纹的深浅、数量影响了茎表面的光洁度。基本组织厚度、纤维束、维管束的排列方式、大小、纤维细胞平均长度及它们单位体积内的数量在４个品种中的差异影响了席草４个品种茎秆的坚韧性。髓部细胞的特化、富含气体的海绵状组织的形成及基本组织内出现的腔隙道使席草茎秆具有较好的弹性和耐压力。     

Growth,phenology and N-utilization by invasive populations of Gunnera tinctoria

智利大叶草(Gunnera tinctoria)是一种不同寻常的固氮植物，已入侵到了世界各地，通常入侵到低蒸发需求和/或高降雨的环境。 在许多可以解释其作为一个成功的引入物种的机制中，差异性的物候特征可能起重要作用，但这可能取决于在次优化条件下生长和利用 营养物质的能力。我们研究了智利大叶草在物候和固氮能力方面是否具有优势，并将其与受智利大叶草入侵影响最大的本地物种灯芯草 (Juncus effusus)进行了比较。2016–2017年，我们每周或每两周对爱尔兰阿奇尔岛的长期种群进行物候学评估。在测量土壤温度，湿度和氧化还原电位的同时，收集了叶和花序数，叶总面积，光截获和地上生物量的数据。利用δ ¹⁵N 同位素并结合原位乙炔还原测量的方法评估了用于支持季节生长的固氮能力的重要性。研究结果表明，2016–2017年，智利大叶草和灯芯草开始生长的时间不同，智利大叶草叶片出现和展叶的时间较早，水分利用率较高时地上生物量最大。智利大叶草的早期生长依赖于预先形成的结构，5月下旬冠层发育达到最大，并且早于灯芯草。虽然在3月份观察到固氮作用，但这对冠层发育后期的生长有更显著的贡献。基于δ ¹⁵N 同位素分析结果表明，早期生长主要与根状茎的氮转移有关，而幼苗主要依赖于固氮作用。这一发现强调了养分调动对早期生长的重要性，并表明固氮能力的重要性可能在不同的发育过程中有所不同，并且其在入侵过程的不同阶段也是如此。     

Nutrient requirements of ephemeral plant species from wet,mesotrophic soils

Abstract. Nanocyperion plant communities occur on wet, more or less nutrient‐poor and sparsely vegetated soils in temperate climates and are characterized by tiny, very shortlived plant species. Most of these have become locally extinct. It is generally assumed that drainage and eutrophication were the most important reasons for this decrease. However, chemical analysis of soil pore water from plots on growth sites of these ephemerals showed that phosphorus availability was relatively high. In a greenhouse experiment, the growth of ephemeral species was strongly limited by the amount of available phosphorus, whereas there was little or no limitation to the growth of other plant species from this habitat. At low phosphorus concentrations, the ephemeral species reached their reproductive phase within the same period, but showed a strong reduction in the amount of flowers that were produced. We concluded that ephemeral species in particular require a minimum amount of phosphorus for reproduction. Other species on nutrient‐poor, wet soils have a longer life span and can postpone flowering in nutrient‐poor soils. In contrast to other short‐lived plant species from the same habitat, the growth of ephemeral species was barely stimulated by enhanced nitrogen availability. Apparently, the ephemerals are adapted to low nitrogen concentrations. The occurrence on nitrogen‐poor and relatively phosphorus‐rich soils suggests that this community may be very sensitive to nitrogen deposition. Reduced phosphorus availability below the minimum requirements of ephemerals, for example after acidification or the exclusion of human activities, has possibly contributed to the decrease of ephemeral plant species.     

Ecological restoration on former agricultural soils: Feasibility of in situ phosphate fixation as an alternative to top soil removal

In Europe, high phosphorus (P) concentrations form the most important constraint on the ecological restoration of biodiverse vegetation on former agricultural soils, because they lead to dominance of highly competitive species like Juncus effusus or to algal blooms in flooded situations. Top soil removal is often not sufficient or not possible, so alternative methods have to be found. We therefore investigated whether modified bentonite clay to which 5% lanthanum had been added (LMC) and lime could effectively decrease bioavailable P and phosphate mobilization to the water layer in different soil types.A container experiment was performed using peaty and sandy soils with different Olsen-P concentrations, mixed with different doses of LMC and lime. The soils were exposed to two different common water regimes (moist and flooded). J. effusus seedlings were used as phytometers.Addition of LMC and lime lowered extractable P concentrations in some of the P-rich sandy soils. Only the highest LMC dose was able to decrease phosphate mobilization to the water layer in the sandy soils. However, neither LMC nor lime was sufficiently effective in reducing Olsen-P concentrations and J. effusus growth. Lime addition eventually even led to additional nutrient mobilization by alkalinization and increased mineralization of the soil.Our experiments therefore show that LMC and lime are not feasible alternatives to top soil removal, because they are inefficient in preventing dominance of highly competitive species under moist or shallowly flooded conditions. LMC may only be used to prevent phosphate mobilization to the water layer in deeply flooded situations, which may allow for a more biodiverse vegetation development.     

Identification and characterization of microsatellite loci in the rush Juncus effusus (Juncaceae)1

? Premise of the study: Microsatellite markers were developed for the common wetland plant Juncus effusus to assess levels of within- and among-population genetic diversity. ? Methods and Results: Using a next-generation sequencing approach we identified new microsatellite loci, from which 23 were further characterized in a large population of J. effusus. Expected heterozygosity ranged from 0 to 0.64 with a mean of 0.407. Inbreeding coefficients (mean = 0.984) were very high, confirming earlier suggestions of an inbred mating system. Cross-amplification was tested in J. conglomeratus, J. inflexus, J. drummondii, and J. filiformis, with best results in the former. ? Conclusions: The described microsatellite markers will be helpful in assisting studies on, e.g., reproduction, taxonomy, and phylogeography in J. effusus and related species.     

Nitrogen addition does not reduce belowground competition in a salt marsh clonal plant community in Mississippi (USA)

Previous studies have suggested that belowground competition for nutrients influences plant zonation in salt marshes. In this study, I tested the hypothesis that competition for nitrogen structured a clonal plant community in a nitrogen-limited salt marsh in coastal Mississippi, USA. In contrast to most previous field studies that have investigated mechanisms of competition, I examined clonal growth responses of established genets of a nitrogen-demanding low-intertidal species (Spartina alterniflora) to nitrogen addition and the removal of a nitrogen-conserving high-intertidal species (Juncus roemerianus). Nitrogen addition stimulated clonal invasion of the Juncus zone by Spartina but did not reduce the significant competitive effects of Juncus on Spartina. Simulated Juncus shade did not reduce invasion of the Juncus zone by Spartina, indicating that belowground competition reduced clonal invasion. In the last year of the study, the border shifted unexpectedly towards the Spartina zone, resulting in competitive displacement of Spartina by Juncus. Nitrogen addition did not prevent or slow this displacement, further contradicting the nitrogen competition hypothesis. Although growth rates were much more strongly limited by nitrogen in Spartina than in Juncus, nitrogen addition did not cause the displacement of Juncus by Spartina after three growing seasons. I conclude that zonation of Spartina and Juncus is maintained by preemption of space and greater tolerance of low nitrogen supplies by Juncus in the high marsh. These results contrast sharply with findings of reduced belowground competition with nutrient addition in previous studies and highlight the important role of nutrient-mediated competition for space between clonal plants.     

Leaf growth,senescence and decomposition of Juncus maritimus Lam. in a coastal Mediterranean marsh

In this study, the growth, senescence, leaf loss and nutrient dynamics of Juncus maritimus were followed to examine litter decay in a Mediterranean coastal marsh. Decomposition was studied in dead leaves still attached to the plant and in leaves placed in litterbags (detached leaves/litter) on the sediment surface. The dynamics of fungi, meiofauna and epiphytes associated with detached litter were also followed. No significant differences were observed between decay rates in dead leaves attached to plants (0.0017 day⁻¹) and detached leaves (0.0015 day⁻¹) in litter bags. The percentage of ash-free dry weight lost was inversely proportional to the C:N and C:P ratios in plant detritus during decay, indicating N and P limitation for the decomposer community inhabiting decaying J. maritimus litter and uptake of these nutrients from the environment. Water availability and high temperatures on the sediment surface increased the density of meiofauna and epiphyton and decreased fungal biomass during the first 20 days of the experiment. The density of ciliates and nematodes in decomposing litter was inversely related to the C:N ratio and directly related to the percentage of AFDW lost. On the basis of these observations, it was concluded that meiofauna are primary colonizers of J. maritimus leaf litter.     

Allelochemical autotoxicity in the emergent wetland macrophyte Juncus effusus (Juncaceae)

Bioassays for allelochemical toxicity of aboveground Juncus effusus tissues were conducted with seeds and seedlings of Eleocharis obtusa and Scirpus cyperinus, two emergent sedge species (Cyperaceae) found sympatric with J. effusus, and with seeds and seedlings of J. effusus itself to evaluate potential autotoxicity. Bioassays were performed under controlled, axenic conditions with aqueous shoot extract treatments simulating in situ dissolved organic carbon concentrations. With respect to the two sedge species, neither shoot development nor seedling biomass accrual was significantly suppressed by lyophilized whole extracts from J. effusus. Although the extracts induced no significant reduction in growth of E. obtusa or S. cyperinus, biomass-specific chlorophyll a concentration was significantly reduced in E. obtusa seedlings. In contrast, seedlings of J. effusus exhibited significant reductions of biomass and chlorophyll a concentrations, and seedling shoot development was retarded in response to leachate exposure. Results of the present study suggest that J. effusus seedlings possess autotoxic sensitivity to extracts of dead, aboveground tissues of adult plants.