Bulb Development in Onion (Allium cepa L.) III. Effects of the Size of Adjacent Plants, Shading by Neutral and Leaf Filters, Irrigation and Nitrogen Regime and the Relationship between the Red: Far-red Spectral Ratio in the Canopy and Leaf Area Index

Field experiments were done to investigate why onion crops witha high leaf area index (LAI) initiate bulb scales and maturesooner than those with a low LAI. When small plants were growneither mixed with large plants or in pure stands, those in themixed stands initiated bulb scales earlier than those in purestands. The timing of bulb development therefore depended onthe size of neighbouring plants and the LAI of the stand andwas not simply determined by the size or age of individual plants.Shading plots with neutral filters which caused no spectralchanges slightly accelerated bulb development compared to unshadedplots but shading by a canopy of climbing pea and bean leaveshad a larger effect. Lack of irrigation advanced bulb maturitybut in the highly irrigated treatments plots of high plant densitystill initiated bulb scales and matured before those of lowdensity. Quantitative relationships between the change in R : FR andeither LAI or total radiation interception were determined foronion leaf canopies. It is suggested that the decrease in thered to far-red spectral ratio (R : FR) as LAI increases maybe the cause of the earlier bulb scale initiation and maturitythat occurs as LAI increases. Onion, Allium cepa (L.), spacing, competition, leaf area index, red: far red, irrigation, nitrogen, shading, bulbing     

Trehalase,invertase, and amylase activities in the black scale,Saissetia oleae,and their relation to host adaptability

In young females of the black scale, Saissetia oleae, the optimum conditions for invertase activity involve a reaction mixture of pH 5.5 and 2% sucrose at 37°C for 60 min; for amylase, pH 6.0 and 0.5% starch at 37°C for 45 min; and for trehalase, pH 5.5 and 1.5% trehalose at 37°C for 60 min. At optimal conditions and using standard enzyme activity units, both invertase and trehalase activities were much higher (about 8-fold) than that of amylase, indicating the importance of these enzymes in food digestion and energy supply.The enzyme activities were strongly affected by various host plants. Trehalase activity in scales reared on potato sprouts was about 3.5- and 4-fold that obtained in scales reared on oleander and citrus plants, respectively. An increase of about 40% for invertase and 60% amylase activity was obtained in scales reared on potato sprouts as compared with those reared on oleander or citrus plants.A good correlation was observed between enzyme activity-especially of trehalase-and scale development. The duration of one generation of the black scale reared on potato sprouts was 2.5 to 3 months, on oleander 4 to 5 months, and on citrus above 6 months. These results suggest that trehalase and to some extent invertase could be used as parameters to assess the adaptability of the black scale to its host plant.     

Distribution and dispersal of desert mistletoe is scale-dependent, hierarchically nested

Spatial patterns are important to many ecological processes, and scale is a critical component of both patterns and processes. I examined the pattern and scale of the spatial distribution of infection of host plants by the desert mistletoe, Phoradendron californicum, in a landscape that spans several square kilometers. I also studied the relationship between mistletoe infection and seed dispersal. I found elevated seed rain in areas with a high prevalence of mistletoes and I found that a greater proportion of trees receive seeds than are infected, suggesting that mistletoes will be aggregated in space. Using nested analysis of variance and variograms, I found that mistletoe infections were distributed in hierarchical patches. Mistletoes were aggregated within trees and mistletoe prevalence was correlated at scales of <1500 m, and at scales >4000 m. Patterns at the largest scales were correlated with elevation: sites at higher elevations showed reduced mistletoe infection compared to those at lower elevations. I propose that at small scales, mistletoe distributions are primarily the result of aggregation of seed-dispersing birds, and that the elevational effect could reflect the recent colonization of higher elevations by the mistletoes' mesquite hosts or the limits of the mistletoes' physiological tolerance to freezing-induced cavitation.     

The distribution of cell wall polymers during antheridium development and spermatogenesis in the Charophycean green alga, Chara corallina

Background and Aims

The production of multicellular gametangia in green plants represents an early evolutionary development that is found today in all land plants and advanced clades of the Charophycean green algae. The processing of cell walls is an integral part of this morphogenesis yet very little is known about cell wall dynamics in early-divergent green plants such as the Charophycean green algae. This study represents a comprehensive analysis of antheridium development and spermatogenesis in the green alga, Chara corallina.

Methods

Microarrays of cell wall components and immunocytochemical methods were employed in order to analyse cell wall macromolecules during antheridium development.

Key Results

Cellulose and pectic homogalacturonan epitopes were detected throughout all cell types of the developing antheridium including the unique cell wall protuberances of the shield cells and the cell walls of sperm cell initials. Arabinogalactan protein epitopes were distributed only in the epidermal shield cell layers and anti-xyloglucan antibody binding was only observed in the capitulum region that initially yields the sperm filaments. During the terminal stage of sperm development, no cell wall polymers recognized by the probes employed were found on the scale-covered sperm cells.

Conclusions

Antheridium development in C. corallina is a rapid event that includes the production of cell walls that contain polymers similar to those found in land plants. While pectic and cellulosic epitopes are ubiquitous in the antheridium, the distribution of arabinogalactan protein and xyloglucan epitopes is restricted to specific zones. Spermatogenesis also includes a major switch in the production of extracellular matrix macromolecules from cell walls to scales, the latter being a primitive extracellular matrix characteristic of green plants.     

Riparian vegetation: degradation, alien plant invasions, and restoration prospects

Rivers are conduits for materials and energy; this, the frequent and intense disturbances that these systems experience, and their narrow, linear nature, create problems for conservation of biodiversity and ecosystem functioning in the face of increasing human influence. In most parts of the world, riparian zones are highly modified. Changes caused by alien plants — or environmental changes that facilitate shifts in dominance creating novel ecosystems — are often important agents of perturbation in these systems. Many restoration projects are underway. Objective frameworks based on an understanding of biogeographical processes at different spatial scales (reach, segment, catchment), the specific relationships between invasive plants and resilience and ecosystem functioning, and realistic endpoints are needed to guide sustainable restoration initiatives. This paper examines the biogeography and the determinants of composition and structure of riparian vegetation in temperate and subtropical regions and conceptualizes the components of resilience in these systems. We consider changes to structure and functioning caused by, or associated with, alien plant invasions, in particular those that lead to breached abiotic‐ or biotic thresholds. These pose challenges when formulating restoration programmes. Pervasive and escalating human‐mediated changes to multiple factors and at a range of scales in riparian environments demand innovative and pragmatic approaches to restoration. The application of a new framework accommodating such complexity is demonstrated with reference to a hypothetical riparian ecosystem under three scenarios: (1) system unaffected by invasive plants; (2) system initially uninvaded, but with flood‐generated incursion of alien plants and escalating invasion‐driven alteration; and (3) system affected by both invasions and engineering interventions. The scheme has been used to derive a decision‐making framework for restoring riparian zones in South Africa and could guide similar initiatives in other parts of the world.     

毛乌素沙地油蒿种群点格局分析

油蒿(Artemisia ordosica)是我国北方农牧交错带的重要固沙植物,研究其种群格局对理解种群生态过程和改善流沙治理技术具有重要意义。点格局分析法是20世纪末发展起来的多尺度空间格局分析方法。通过研究油蒿种群的点格局,发现油蒿种群的空间分布格局和空间关联性同空间尺度、植株形体大小以及生境3种因素有密切联系。在较小的空间尺度上,油蒿种群倾向于非随机分布(集群分布比均匀分布常见),个体间有较强的空间关联(正关联比负关联常见);当空间尺度大于临界值后,油蒿种群倾向于服从随机分布,同时种群的空间关联性减弱。幼小油蒿植株具有明显的集群分布趋势,高大植株则表现出聚集强度的降低趋势;形体大小的差异越大,植株间的正关联关系越弱,或者负关联关系越强。与固定沙地相比,半固定沙地油蒿种群的集群分布现象更加明显,同时种群的空间正关联关系更强。研究结果表明,当通过移栽油蒿成体治理流动沙地时,应尽量将其栽种成集群分布而非均匀分布的形式,以提高植株成活率。     

海南尖峰岭热带山地雨林不同空间尺度和径级水平的物种丰富度与个体密度关联

以海南尖峰岭热带山地雨林为研究对象, 基于尖峰岭原始林60 hm²大样地, 分析了7个不同空间尺度(5 m × 5 m、10 m × 10 m、20 m × 20 m、40 m × 40 m、60 m × 60 m、80 m × 80 m、100 m × 100 m)、3个不同径级(胸径(DBH) ≥ 1.0 cm、DBH ≥ 2.5 cm、DBH ≥ 7.5 cm)物种丰富度与个体密度之间的关联性, 以期为负密度制约效应等研究的尺度选择提供参考依据。研究结果表明, 物种丰富度和个体密度之间的关联性是基于空间尺度存在的, 并受分析植株径级大小的影响。DBH ≥ 1.0 cm时, 在4个空间尺度下(5 m × 5 m、10 m × 10 m、20 m × 20 m、40 m × 40 m), 物种丰富度随个体密度增加而增加, 但物种丰富度和个体密度两者间的相关性随取样空间尺度的增大而逐渐下降; 在其他3个空间尺度下(60 m × 60 m、80 m × 80 m、100 m × 100 m), 两者间没有显著相关性。当DBH ≥ 2.5 cm和DBH ≥ 7.5 cm时, 物种丰富度和个体密度间的相关性随空间尺度变化的趋势也与上述结果基本一致; 在60 m × 60 m的空间尺度上, DBH ≥ 1.0 cm时物种丰富度和个体密度相关性不显著, DBH ≥ 2.5 cm和DBH ≥ 7.5 cm两个径级的物种丰富度和个体密度表现出弱相关性。DBH ≥ 2.5 cm和DBH ≥ 7.5 cm时, 各空间尺度下物种丰富度和个体密度之间的决定系数几乎一致, 但高于DBH ≥ 1.0 cm时两者之间的决定系数, 说明大径级植株的个体密度和物种丰富度之间有更强的关联性, 负密度制约效应和自疏效应可能是产生这种现象的主要原因。     

Ultrastructure of the scale-covered zoospores of the green alga Chaetosphaeridium, a possible ancestor of the higher plants and bryophytes

The zoospores of the green alga Chaetosphaeridium globosum are covered on all surfaces with tiny diamond-shaped scales similar to those of the prasinophycean flagellates and the Charales. The flagella also bear striated hairs (hair scales) so far considered to be a characteristic of the Prasinophyceae. The flagellar apparatus differs from that observed in the Prasinophyceae, shows many similarities to that of the Charales, and is identical with the "Vierergruppe" of the pteridophytes, cycads and bryophytes.
The zoospores are opisthokont, with two flagella inserted subapically. There is a lateral chloroplast containing typical grana and intergranal lamellae, but no eyespot. The very complicated Golgi body/contractile vacuole system comprises 10–20 contractile vacuoles. A microbody occupies a characteristic position in the cell, and in a young germling contains a crystalline inclusion.
The ultrastructure of the zoospore supports the old theory that the ancestors of the higher plants may well be found among Coleochaete and its relatives, past and present.     

Bennettitales from the Grisethorpe Bed (Middle Jurassic) at Cayton Bay, Yorkshire, UK

Middle Jurassic fossil plants from the Grisethorpe Bed at Cayton Bay and Grisethorpe Bay, Yorkshire, UK, are preserved in a soft claystone, and plant mesofossils recovered by sieving reveal excellent details of external structure. Studies of these mesofossils complement previous work on macrofossils from the Grisethorpe Bed and allow the plant fossils in this classic flora to be studied in a similar way to those preserved in Cretaceous mesofloras. Bennettitales, a key group in discussions of how angiosperms may be related to other seed plants, are especially well represented among mesofossils from the Grisethorpe Bed. Abundant bennettitalean leaves, scale leaves, and fragments of pollen and ovulate organs provide new information on these extinct plants. In particular, a specimen of Williamsoniella coronata (presumed aborted) shows only weak differentiation between interseminal scales and ovules and provides further evidence of homology between these structures.     

Microgeographic countergradient variation in the wood frog, Rana sylvatica

Prior studies have shown that macrogeographic gradients in temperature associated with latitude and altitude can lead to countergradient patterns of variation in a number of taxa: individuals from colder environments are known to grow or develop faster than their conspecifics from warmer environments when placed in a common setting. In this study, I hypothesized that countergradient variation also is important at microgeographic scales. The wood frog, Rana sylvatica, breeds in open-canopied, temporary wetlands as well as those heavily shaded by vegetation. Shading leads to cooler thermal environments that are associated with embryonic development rates as much as 50% slower than those in unshaded wetlands. Wetlands with contrasting canopy environments are often found within tens or hundreds of meters of each other. In a common garden experiment, embryos from nearby natural wetlands displayed countergradient variation: individuals collected from shaded wetlands developed up to 12% faster than those collected from relatively unshaded wetlands. The results of this study suggest that the concept of countergradient variation may be extended to small scales of space. In addition, the rate and scale of vegetation dynamics (the agent of wetland shading) imply that divergence in development among residents of nearby wetlands may be relatively rapid, on the order of decades.     

Epigenetic variability in plants: Heritability,adaptability, evolutionary significance

DNA methylation is the most stable epigenetic modification with a well studied maintenance mechanism in the mitotically dividing cell generations. The plant DNA is methylated at sites of three types, CG, CHG and CHH. The methylation mechanisms of these sites are different and involve functional activity of various DNA methyltransferases and their accessory factors, that largely define the genome locus specificity of methylation. The genome methylation pattern, DNA methylome, in plants is inheritable not only in the dividing cell generations but also to a considerable extent in generations of the whole plants. A great number of spontaneous epimutations, both natural and experimental ones, are known, that have discernible phenotypic manifestations and are stably inheritable in the plant generations as Mendelian traits. A fundamental distinction of such epimutations from classical mutations is their reversibility. The higher plants epigenome is much more flexible compared with their genome. The single-nucleotide epimutation frequency is hundredfolds higher than the mutation frequency. This variability is probably a main source of the plant phenotypic plasticity, that enables them to adapt to changing environment on the time scales too short for adaptive mutations to occur. A dramatic increase in the plant population epigenetic variability on a practically unchanged genetic context is observed when the essential environmental factors are rapidly changing. Being flexible enough for such adaptive changes, on the other hand, epigenome is stable enough for these adaptive variations to be inheritable between the plant generations. Obviously, the epigenetic variations, that enable plants to adapt to the fast changing environmental factors, serve as material for natural selection and other evolutionary processes on the respective time scales. A still another aspect of evolutionary significance is a capability of epigenetic mechanisms to induce transient bursts of genetic variability by transposon mobilization.     

Host-plant leaps versus host-plant shuffle: a global survey reveals contrasting patterns in an oligophagous insect group (Hemiptera,Psylloidea)

Global analyses of interspecific interactions are rapidly increasing our understanding of patterns and processes at large scales. Understanding how biodiversity assembles and functions on a global scale will increasingly require analyses of complex interactions at different ecological and phylogenetic levels. We present an analysis of host-plant associations in the sap-sucking Psylloidea (～3,800 species) using the most comprehensive assemblage of host data for this group compiled from 66?% of published records. Psyllids are known for high levels of host specificity and host switching between related plants at local scales, but a global survey implicates historical processes that are not entirely consistent with those at local scales. In particular, saltationary host switching events appear to have been a key factor explaining the wide but patchy distribution of psyllid host-plants throughout the angiosperm phylogeny. Alternative explanations involving co-diversification with subsequent extinction seem implausible. At the seed plant family level, we compare associations for psyllids with those of their relatives the aphids, but, despite notable differences in biogeographic distributions, find few plant families (2%) that host only psyllids but not aphids, while a much larger percentage (31%) host aphids but not psyllids, and 43% of plant families distributed throughout the plant phylogeny host neither group.     

Impacts of urbanisation on biodiversity: the role of species mobility,degree of specialisation and spatial scale

Urbanisation has an important impact on biodiversity, mostly driving changes in species assemblages, through the replacement of specialist with generalist species, thus leading to biotic homogenisation. Mobility is also assumed to greatly affect species’ ability to cope in urban environments. Moreover, specialisation, mobility and their interaction are expected to greatly influence ecological processes such as metacommunity dynamics and assembly processes, and consequently the way and the spatial scale at which organisms respond to urbanisation. Here we investigate urbanisation impacts on distinct characteristics of species assemblages – namely specialisation degree in resource use, mobility and number of species, classified according to both characteristics and their combination – for vascular plants, butterflies and birds, across a range of spatial scales (from 1 × 1 km plots to 5 km‐radius buffers around them). We found that the degree of specialisation, mobility and their interaction, greatly influenced species’ responses to urbanisation, with highly mobile specialist species of all taxonomic groups being affected most. Two different patterns were found: for plants, urbanisation induced trait divergence by favouring highly mobile species with narrow habitat ranges. For birds and butterflies, however, it reduced the number of highly mobile specialist species, thus driving trait convergence. Mobile organisms, across and within taxonomic groups, tended to respond at larger spatial scales than those that are poorly mobile. These findings emphasize the need to take into consideration species’ ecological aspects, as well as a wide range of spatial scales when evaluating the impact of urbanisation on biodiversity. Our results also highlight the harmful impact of widespread urban expansion on organisms such as butterflies, especially highly mobile specialists, which were negatively affected by urban areas even at great distances.     

SPATIAL HETEROGENEITY AND SIMILARITY OF ADULT PLANTS AND SEEDLINGS IN 'BLACK SOIL LAND' SECONDARY WEED COMMUNITY, QINGHAI-TIBETAN PLATEAU

 在样线调查基础上, 用半方差函数、分形维数、空间自相关等方法对青藏高原“黑土滩”次生毒杂草群落地上成体植株、幼苗空间的异质性, 二者物种构成的相似性及其尺度特征进行分析。结果表明, “黑土滩”次生毒杂草群落在较大尺度上地上成体植株物种数的空间依赖性强, 异质性高, 而个体密度则较均匀; 幼苗物种数在小尺度上空间异质性高, 幼苗密度在大尺度上空间异质性较高, 幼苗密度独立于其物种分布, 高密度的幼苗分布在微地形下和群落间隙中, “黑土滩”毒杂草植物幼苗充分利用空余生态位进行群落补充; “黑土滩”群落在不同尺度上地上成体植株与幼苗物种构成相似性变化的规律性不大; “黑土滩”群落幼苗靠其高密度特征完成群落更新, 植物群落幼苗更新力强, 导致“黑土滩”毒杂草群落趋于稳定。因此, 建议加强干扰以减弱“黑土滩”次生毒杂草群落稳定趋势, 这对恢复“黑土滩”具有重要指导意义。     

Origins, distribution, and local co-occurrence of polyploid cytotypes in Solidago altissima (Asteraceae)

There is growing realization that intraspecific polyploidy in plants has important implications for the evolution of plant diversity and for plant and plant-herbivore community dynamics. Nonetheless, the rate at which polyploid cytotypes arise and their fate in local mixed-cytotype populations are not well understood. Although within- and especially among-population cytotype variation has been documented in many plants, particularly at the largest (continental) spatial scales, local and regional distributions of cytotypes have been well characterized only for a handful of species. Furthermore, few if any studies have addressed both local and regional patterns in the same plant species with sufficient power to detect cytotype variation on both scales. We assessed the co-occurrence and frequency distributions of diploid, tetraploid, and hexaploid cytotypes of Solidago altissima (Asteraceae) at local and regional spatial scales, sampling across a zone of presumed ploidy-form overlap in the midwestern United States. Determining ploidy by flow cytometry, we found many local populations containing two or three cytotypes, with the relative frequencies of cytotypes varying dramatically even among neighboring populations. AFLP marker data suggest that polyploid cytotypes of S. altissima likely have multiple origins from different diploid lineages. Our results are consistent with recent perspectives on polyploidization as an evolutionarily dynamic phenomenon with frequent multiple origins of higher-ploidy cytotypes.     

ULTRASTRUCTURAL COMPARISION OF POLLEN GRAINS FROM 2n, 3n,AND 4n PLANTS OF EUPHORBIA DULCIS

Pollen development in plants with different ploidy levels of Euphorbia dulcis is similar but some ultrastructural differences do occur. In pollen of diploid plants large aggregations of rough endoplasmic reticulum [RER] are attached to the pollen wall near the young generative cell but such aggregations are not present in other karyotypes. Plastids are detected only in young generative cells of triploid plants. In diploid plants the generative cell becomes spindle-shaped, in triploid and tetraploid plants it remains round during the movement from the pollen wall to the center of the vegetative cell. The intine surrounding the generative cell in 3n plants is thinner than that found in 2n and 4n plants. Pollen grains in tetraploid plants are twice as large as those in diploid plants. Pollen viability is 90% in 2n plants, but only 10% in 4n plants.     

Functional–structural plant models: a growing paradigm for plant studies

A number of research groups in various areas of plant biology as well as computer science and applied mathematics have addressed modelling the spatiotemporal dynamics of growth and development of plants. This has resulted in development of functional–structural plant models (FSPMs). In FSPMs, the plant structure is always explicitly represented in terms of a network of elementary units. In this respect, FSPMs are different from more abstract models in which a simplified representation of the plant structure is frequently used (e.g. spatial density of leaves, total biomass, etc.). This key feature makes it possible to build modular models and creates avenues for efficient exchange of model components and experimental data. They are being used to deal with the complex 3-D structure of plants and to simulate growth and development occurring at spatial scales from cells to forest areas, and temporal scales from seconds to decades and many plant generations. The plant types studied also cover a broad spectrum, from algae to trees. This special issue of Annals of Botany features selected papers on FSPM topics such as models of morphological development, models of physical and biological processes, integrated models predicting dynamics of plants and plant communities, modelling platforms, methods for acquiring the 3-D structures of plants using automated measurements, and practical applications for agronomic purposes.     

Kaolin-based particle film technology affects tomato physiology,yield and quality

Environmental stress can affect development and yield of tomato plants. This study was undertaken to investigate the underlying mechanism asserted by kaolin on tomato physiology by evaluating its effect on leaf, canopy and inner fruit temperatures, gas exchange at the leaf and canopy scales, above ground biomass, yield and fruit quality.The study was carried out under field conditions in Southern Italy. Treatments were plants treated with kaolin-based particle film (Surround^® WP) suspension and untreated plants (control).Kaolin application slightly increased leaf and canopy scale temperatures by 1.0 and 0.4 °C, respectively, transpiration rate decreased at both scales. On calm days (wind speed <0.5 m s^?1) with a prevalently clear sky at midday, inner fruit temperature (t_f) of kaolin-treated plants was 4.4 °C lower than the t_f of control plants, while in days with clear sky-windy, and cloudy-calm, the t_f did not differ.At leaf scale, net assimilation was reduced by 26% in kaolin-coated treatments. Stomatal conductance decreased by 53%, resulting in reductions of 34 and 15% in transpiration and internal CO₂ concentration, respectively. Gas exchange parameters measured at canopy scale were similarly affected. In kaolin-treated plants, assimilation and evapotranspiration rates were reduced by 17 and 20%, respectively, while dark respiration was not affected. Above ground dry biomass decreased by 6.4%.Marketable yield in kaolin-treated plants was 21% higher than those measured in control plants; this is possibly related to the 96 and 79% reduction in sunburned fruit and those damaged by insects, respectively, and to the 9% increase in mean fruit weight. Kaolin treatment increased lycopene fruit content by 16%, but did not affect total soluble solids content, fruit dry matter, juice pH, titratable acidity or tomato fruit firmness. The use of kaolin-based particle film technology would be an effective tool to alleviate heat stress and to reduce water stress in tomato production under arid and semi-arid conditions.