Chromosome studies: Mexican Compositae

Chromosome observations reported here from 70 collections representing 65 species from 40 genera of Compositae (mostly Heliantheae) provide taxonomically useful information. First counts for 28 species, including the first count for Psacaliopsis, may prove to be especially interesting in relation to phyletic and taxonomic alignments of the taxa. Of special interest among first reports is 2n = 5 II for Stevia lita; other stevias have x = 11, 12, or 17. Thirteen of our counts differ from prior reports and may also be of particular interest in phyletic and taxonomic contexts.     

七种药用植物的染色体研究

对山东７种药用植物的染色体进行了研究。结果表明：田旋花（ＣｏｎｖｏｌｖｕｌｕｓａｒｖｅｎｓｉｓＬ）的染色体数目为２ｎ＝７８;蜜柑草（ＰｈｙｌａｎｔｈｕｓｍａｔｓｕｍｕｒａｅＨａｖａｔａ）的染色体数目为ｎ＝８８;挂红灯（ＰｈｙｓａｌｉｓａｌｋｅｋｅｎｇｉＬｖａｒｆｒａｎｃｈｅｔｉ（Ｍａｓｔ）Ｍａｋｉｎｏ）的染色体数目为２ｎ＝２４,核型公式为Ｋ（２ｎ）＝２４＝２ｍ＋１８ｓｍ＋２ｓｔ＋２ｓｔ（ｓａｔ）,核型“２Ａ”型;无剌曼陀罗（ＤａｔｕｒａｓｔｒａｍｏｎｉｕｍＬｖａｒｉｎｅｒｍｉｓ（Ｊａｃｑ）ＳｃｈｉｎｚｅｔＴｈｅｌ）的染色体数目为２ｎ＝２４,核型公式为Ｋ（２ｎ）＝２４＝２０ｍ＋４ｓｍ,核型“１Ｂ”型;决明（ＣａｓｉａｔｏｒａＬ）的染色体数目为２ｎ＝２６,核型公式为Ｋ（２ｎ）＝２６＝２４ｍ＋２ｓｍ,核型“１Ａ”型;荔枝草（ＳａｌｖｉａｐｌｅｂｅｉａＲＢｒ）的染色体数目为２ｎ＝１６,核型公式为Ｋ（２ｎ）＝１６＝６ｍ＋１０ｓｍ,核型“２Ａ”型;车前（ＰｌａｎｔａｇｏａｓｉａｔｉｃａＬ）的染色体数目为２ｎ＝３６,核型公式为Ｋ（２ｎ）＝３６＝３２ｍ＋４ｓｍ,核型“１Ａ”型。     

高山植物繁殖策略的研究进展

高山地区通常被认为是陆地上最为极端的生境之一,但却拥有许多形态特化的植物和较高的物种多样性。高山植物如何在严酷的环境中实现成功繁殖,这一问题倍受研究者们的关注。本文综合了国内外高山植物在资源分配、花形态对非生物环境因子的响应、动物传粉及其适应机制、果实和种子及克隆繁殖等繁殖策略方面的文献。为应对低温多雨雪的恶劣环境,一些高山植物采取花向日性、花冠闭合及花序保温结构等繁殖策略。高山植物的传粉者类群也发生了改变,主要为蜂类和蝇类。熊蜂(Bombusspp.)传粉的高效性,减少了高山环境对植物传粉造成的不利影响。当传粉者不可得时,植物不仅通过延迟自交和自助自交等机制来提供繁殖保障,还借助克隆繁殖及其他传粉机制(风媒或风虫媒)来维持种群的繁衍。依赖动物传粉的高山植物,可以采取增加繁殖构件的资源分配、加大"广告"投入以及较大的花展示或较长的花寿命来提高传粉者的拜访几率,以及借助泛化的花结构和选择合适的开花时间等策略来提高繁殖成功率。此外,大部分高山植物产生干果且具有持久的种子库,有利于种子的传播以及种子寻找萌发及幼苗生长的最佳外界环境。在今后的研究中,可着重探讨以下几个问题:(1)非生物环境因子对花形态的选择;(2)季节变化与繁殖策略;(3)群落水平上植物与传粉者的关系;(4)高山生态系统对全球变暖的响应。     

Field studies of nitrogen fixation of Australian alpine plants and soils

Alpine grassland areas in Victoria and New South Wales have been subjected to summer grazing by cattle and sheep for well over a hundred years. Legumes other than a few species of shrubs, which provide a very small percentage of the vegetation cover in the grasslands, are absent. Other alpine communities include Sphagnum ‘mossbeds’ in the valleys and areas of snowgum woodland and shrubland. Virtually nothing is known of the mineral status of these communities and nothing of their nitrogen economy. On the Bogong High Plains, enclosure of grassland and of Sphagnum mossbeds from grazing and trampling has resulted, in the last few decades, in considerable changes in both cover and composition of the vegetation. A portable gas chromatogram was used to carry out determinations of the capacity of samples of the grassland and Sphagnum to support acetylene reduction to ethylene, by convention equated to a capacity to fix nitrogen. There appears to be a substantial capacity for acetylene reduction associated with the rhizosphere of the grasses (Poa australis agg.). The capacity of the Sphagnum for acetylene reduction is even greater and appears to be due to facultative anaerobes, abundant only in the upper, living part of the Sphagnum. These organisms may depend in part on leakage of photosynthate from the living Sphagnum. Associations of Sphagnum with blue-green algae appear to be unusual in contrast with work on Swedish subarctic mosses, which is discussed. The only non-leguminous Australian alpine plant so far examined for nitrogen fixation is Podocarpus lawrencei. A capacity for acetylene reduction was found for neither the nodules of the roots of this plant nor the associated soils.     

Chromosome counts for Mexican ferns

Chromosome numbers for 106 species in 36 genera of Mexican ferns are reported. Of these, 47 are first reports for the species. Ten additional counts differ from previous reports. These counts suggest taxa where additional sampling might aid in making taxonomic decisions.     

Mexican alpine plants in the face of global warming: potential extinction within a specialized assemblage of narrow endemics

Alpine ecosystems occur under extreme climatic conditions and, as a result, house a unique and vulnerable biota. They are very scarce at tropical latitudes; in Mexico occur mainly along the Trans-Mexican Volcanic Belt, where species richness is not high but narrow endemics stand out. We investigate the effects of climate change under hypothesized contrasting climate warming scenarios using ecological niche modeling of five microendemic alpine species. Occurrence data was obtained mainly from field trips, but herbaria were also examined. A total of 21 climatic and topographic variables, as well as individual selections of 12–16 variables were employed to construct models with Maxent and GARP. Depending on the number of occurrences, current models were validated with Partial-ROC or Jackknife procedures; and projections to 2050 and 2070 were made using two Representative Concentration Pathways and two Global Circulation Models. All species’ models showed a clear pattern of contraction under the explored scenarios; over 58 % of contemporary climatic distribution disappeared, suggesting that analyzed species face imminent extinction due to climatic habitat loss. The models are useful in representing the endemic component of Mexican alpine grassland by reciprocal correspondence in geographic distribution, and we consider it as a highly endangered ecosystem due to climate change, which is probably applicable to other tropical alpine ecosystems. The Pico de Orizaba volcano seems the best option to preserve due to its extension and elevation. However, further studies at finer scales are needed to improve in situ preservation and conservation strategies that include translocation, assisted migration and seed banking.     

Calcium isotope fractionation in alpine plants

In order to develop Ca isotopes as a tracer for biogeochemical Ca cycling in terrestrial environments and for Ca utilisation in plants, stable calcium isotope ratios were measured in various species of alpine plants, including woody species, grasses and herbs. Analysis of plant parts (root, stem, leaf and flower samples) provided information on Ca isotope fractionation within plants and seasonal sampling of leaves revealed temporal variation in leaf Ca isotopic composition. There was significant Ca isotope fractionation between soil and root tissue $\Updelta^{44/42}\hbox{Ca}_{\rm root-soil} \approx -0.40\,\permille$ in all investigated species, whereas Ca isotope fractionation between roots and leaves was species dependent. Samples of leaf tissue collected throughout the growing season also highlighted species differences: Ca isotope ratios increased with leaf age in woody species but remained constant in herbs and grasses. The Ca isotope fractionation between roots and soils can be explained by a preferential binding of light Ca isotopes to root adsorption sites. The observed differences in whole plant Ca isotopic compositions both within and between species may be attributed to several potential factors including root cation exchange capacity, the presence of a woody stem, the presence of Ca oxalate, and the levels of mycorrhizal infection. Thus, the impact of plants on the Ca biogeochemical cycle in soils, and ultimately the Ca isotope signature of the weathering flux from terrestrial environments, will depend on the species present and the stage of vegetation succession.     

Chromosome counts of some Mongolian plants

The paper gives the chromosome numbers of 45 species from 72 Mongolian localities, belonging to the genera:Amygdalus, Asparagus, Astragalus, Cancrinia, Caragana, Chamaerhodos, Chelidonium, Chesneya, Dianthus, Hypecoum, Lathyrus, Lilium, Oxytropis, Papaver, Potentilla, Schizonepeta, Sibbaldia, Thermopsis, Trifolium, Trigonella, Vicia. Chromosome morphology of three species ofChamaerhodos and taxonomical remarks on some other species are added. A new combinationSibbaldia sericea (Grubov) Soják is proposed.     

Nitrogen and carbon storage in alpine plants

Alpine plants offer unique opportunities to study the processesand economics of nutrient storage. The short alpine growingseason forces rapid completion of plant growth cycles, whichin turn causes competition between vegetative and reproductivegrowth sinks during the early part of the growing season. Mobilizationof stored nitrogen and carbon reserves facilitates competingsinks and permits successful completion of reproduction beforethe onset of winter stress. We discuss the theoretical frameworkfor assessing the costs and benefits of nutrient storage inalpine plants in order to lay the foundation for interpretationof observations. A principal point that has emerged from pasttheoretical treatments is the distinction between reserve storage,defined as storage that occurs with a cost to growth, and resourceaccumulation, defined as storage that occurs when resource supplyexceeds demand, and thus when there is no cost to growth. Wethen discuss two case studies, one already published and onenot yet published, pertaining to the storage and utilizationof nitrogen and carbon compounds in alpine plants from NiwotRidge, Colorado. In the first case, we tested the hypothesisthat the seasonal accumulation of amino acids in the rhizomeof N-fertilized plants of Bistorta bistortoides provides anadvantage to the plant by not imposing a cost to growth at thetime of accumulation, but providing a benefit to growth whenthe accumulated N is remobilized. We show that, as predicted,there is no cost during N accumulation but, not as predicted,there is no benefit to future growth. In the presence of N accumulation,reliance on stored N for growth increases, but reliance on current-season,soil-derived N decreases; thus the utilization of availableN in this species is a ‘zero sum’ process. Inherentmeristematic constraints to growth cause negative feedback thatlimits the utilization of accumulated N and precludes long-termadvantages to this form of storage. In the second case study,we discuss new results showing high concentrations of cyclicpolyol (cyclitol) compounds in the leaves of many alpine speciesdominant in the dry fellfield habitat. In Artemisia scopulorum,cyclitols were induced as the growing season progressed, andreached highest concentrations during the dry, late-summer months.Leaf cyclitol concentrations were high in all four species ofthe Caryophyllaceae that we examined and appeared to be constitutivecomponents of the leaf carbohydrate pool as concentrations werehigh through the entire growing season. We observed correlationsamong seedling abundance, seeding survivorship and the presenceof high leaf cyclitol concentrations. We propose that the primaryfunction of cyclitols in the leaves of alpine, fellfield herbsis to promote drought tolerance through osmotic protection,and enhance fitness by improving seedling survival. We consideredthe possibility that cyclitols also function as carbon storagecompounds that are remobilized at the end of the growing seasonand used to support growth the following year. Our observationsdo not support this hypothesis in the Caryophyllaceae becausethe requirement for high constitutive concentrations year-after-yearprevents long-term advantages of storage and remobilization.However, in A. scopulorum, remobilization of cyclitols followingthe end of the growing season may provide storage substratesthat can be used for growth the following season. From our analysiswe conclude that it is difficult to use current theory thatis embedded in the economic concept of costs and benefits tointerpret observed dynamics in nitrogen and carbon allocation.Future theoretical developments that move away from an abstractfoundation embedded in cost-benefit tradeoffs and toward phenotypicintegration of source-sink relationships will improve our abilityto merge observations and theory.     

Chromosome organization and dynamics in plants

The past few years have brought renewed interest in understanding the dynamics of chromosomes in interphase cells as well as during cell division, particularly meiosis. This research has been fueled by new imaging methods, particularly three-dimensional, high-resolution, and live microscopy. Major contributors are also new genetic tools that allow elucidation of mechanisms controlling chromosome behavior. Recent studies in plants have explored chromatin arrangement in interphase nuclei, chromosome interactions and movement during meiotic prophase I, and mechanisms that ensure correct segregation of chromosomes during anaphase. These studies shed light on chromosome dynamics in a small-genome plant Arabidopsis thaliana, as well as in plants with large and complex genomes of polyploid origin, such as wheat and maize.     

Chromosome variation in protoplast-derived potato plants

Summary Chromosomes have been studied in protoplast-derived potato plants of the tetraploid cultivars Maris Bard and Fortyfold. A high degree of aneuploidy was found amongst the regenerants of both cultivars but the nature of the chromosome variation differed. The Maris Bard regenerants were characterised by high chromosome numbers, a wide range of aneuploidy (46–92) and a low percentage of plants with the normal chromosome number (2n = 48), whereas a much higher proportion of the Fortyfold regenerants had 48 chromosomes and the variants were within a more limited aneuploid range. In both cultivars chromosome variation was found between calluses, within calluses and even within shoot cultures. The origin of the chromosome variation and the differences found between the two cultivars are discussed.We regret to report the death of Emrys Thomas since the initiation of this work     

Functional traits and root morphology of alpine plants

Background and Aims

Vegetation has long been recognized to protect the soil from erosion. Understanding species differences in root morphology and functional traits is an important step to assess which species and species mixtures may provide erosion control. Furthermore, extending classification of plant functional types towards root traits may be a useful procedure in understanding important root functions.

Methods

In this study, pioneer data on traits of alpine plant species, i.e. plant height and shoot biomass, root depth, horizontal root spreading, root length, diameter, tensile strength, plant age and root biomass, from a disturbed site in the Swiss Alps are presented. The applicability of three classifications of plant functional types (PFTs), i.e. life form, growth form and root type, was examined for above- and below-ground plant traits.

Key Results

Plant traits differed considerably among species even of the same life form, e.g. in the case of total root length by more than two orders of magnitude. Within the same root diameter, species differed significantly in tensile strength: some species (Geum reptans and Luzula spicata) had roots more than twice as strong as those of other species. Species of different life forms provided different root functions (e.g. root depth and horizontal root spreading) that may be important for soil physical processes. All classifications of PFTs were helpful to categorize plant traits; however, the PFTs according to root type explained total root length far better than the other PFTs.

Conclusions

The results of the study illustrate the remarkable differences between root traits of alpine plants, some of which cannot be assessed from simple morphological inspection, e.g. tensile strength. PFT classification based on root traits seems useful to categorize plant traits, even though some patterns are better explained at the individual species level.