Perspectives of reducing the deleterious effect of de-icing salt upon vegetation

Summary The protective effect of a nutrient solution upon young forest plants, seriously stressed by de-icing salt (NaCl) were investigated. The results show, that the adsorbed salt ions in the soil are already exchanged at low concentrations (2 bars), whilst plant survival and growth showed only at higher concentrations (10 bars) a significant optimum.     

Arginine and salinity stress affect morphology and metabolism of Indian borage (Plectranthus amboinicus lour.)

Essential oil of Indian borage has different activities such as anti-bacterial and anti-malarial. Salinity stress has harmful effects on the productivity of aromatic plants. This study aimed decrease the harmful effect of sodium chloride (NaCl) on Indian borage plants by adapting them to salinity stress through the use of arginine. Plants were exposed to NaCl (0, 2 and 4 g/L) and/or arginine (0, 150 and 300 mg/L). Morphological characters (leaf area, total fresh and dry herbs as well as total fresh and dry roots), essential oil composition, photosynthetic pigments, proline, soluble sugars, crude protein, nutrients (NPK), antioxidant enzymes activities and protein banding patterns of Indian borage plants were evaluated. Obtained results were statistically analyzed using 2-way analysis of variance. Salinity treatments decreased morphological characters, photosynthetic pigments, crude protein and nutrient contents. Salinity promoted the accumulation of essential oil and its major constituents (carvacrol, thymol, γ-terpinene and limonene), proline, soluble sugars and the activities of antioxidant enzymes. Plants treated with salinity x arginine resulted in higher values of all growth characters and chemical composition than those treated with salinity only. On the other hand, salinity x arginine produced various changes in the number of bands. It may be concluded that application of arginine resulted in positive increases in growth, yield and chemical constituents of Indian borage under NaCl stress. So this study indicated that arginine resulted in a reduction of the hazards effect of salt stress.     

Savannah woodland vegetation in the South‐East District of South Australia: the influence of evaporative aerodynamics on the foliage structure of the understorey invaded by introduced annuals

Abstract Evaporative aerodynamics determine the foliage projective cover of the understorey of perennial tussock grasses and associated perennial herbs in the savannah woodland dominated by Eucalyptus camalduknsis on gleyed podsolic soils in the Mediterranean climate of the South‐East District of South Australia. By the mid 1940s, winter‐spring evapotranspiration from the ‘thin’ leaves (with low leaf specific weight) of introduced annual plants was depleting surface soil water and thus reducing the annual growth of the summer‐growing savannah understorey; perennial herbs between the tussock grasses were the first to succumb to this competition. During spring, the percentage of the ground covered by the savannah understorey was increased by 10% in the subhumid zone to 30% in the humid zone as the pre‐European perennial herbs between the tussock grasses were replaced by introduced annuals. Application of phosphatic fertilizer to the understorey increased the growth of introduced annuals, which formed a dense stratum during their winter‐spring growing season, increasing evapotranspiration and leading eventually to the extinction of the native perennial grasses. When the savannah understorey, invaded by introduced annuals in the mid‐1940s, was converted to improved pasture, the percentage of ground covered by the seasonal foliage was increased by 20–30%; 100% coverage of overlapping foliage resulted in the humid zone.     

Plant community diversity and composition affect individual plant performance

Effects of plant community diversity on ecosystem processes have recently received major attention. In contrast, effects of species richness and functional richness on individual plant performance, and their magnitude relative to effects of community composition, have been largely neglected. Therefore, we examined height, aboveground biomass, and inflorescence production of individual plants of all species present in 82 large plots of the Jena Experiment, a large grassland biodiversity experiment in Germany. These plots differed in species richness (1–60), functional richness (1–4), and community composition. On average, in more species-rich communities, plant individuals grew taller, but weighed less, were less likely to flower, and had fewer inflorescences. In plots containing legumes, non-legumes were higher and weighed more than in plots without legumes. In plots containing grasses, non-grasses were less likely to flower than in plots without grasses. This indicates that legumes positively and grasses negatively affected the performance of other species. Species richness and functional richness effects differed systematically between functional groups. The magnitude of the increase in plant height with increasing species richness was greatest in grasses and was progressively smaller in legumes, small herbs, and tall herbs. Individual aboveground biomass responses to increasing species richness also differed among functional groups and were positive for legumes, less pronouncedly positive for grasses, negative for small herbs, and more pronouncedly negative for tall herbs. Moreover, these effects of species richness differed strongly between species within these functional groups. We conclude that individual plant performance largely depends on the diversity of the surrounding community, and that the direction and magnitude of the effects of species richness and functional richness differs largely between species. Our study suggests that diversity of the surrounding community needs to be taken into account when interpreting drivers of the performance of individual plants.     

Seed supply of native and cultivated grasses in pine forests of the southwestern United States and the potential for vegetation recovery following wildfire

In this study we examined seed supply (seed banks and seed rain) and vegetation of seeded cultivated grasses and naturally occurring native grasses following a wildfire in northern New Mexico, USA. We specifically examined density of native and cultivated grass seeds and plants in areas of high, moderate, and low fire severity. We also examined the similarity between density of native and cultivated grass seeds to density of above ground plants. Density of native grass seed per square meter was higher in areas that burned under low fire severity (85.18 ± 44.83) compared to areas of moderate (18.52 ± 11.26) and high (7.41 ± 4.90) fire severity; however, differences were not statistically significant due, in part, to the high error associated with estimates. Density of cultivated grass seed per square meter was higher than that of native grass seed in areas of high (439.60 ± 117.98) and moderate (437.02 ± 146.50) fire severity, areas that were seeded with cultivated grasses after the wildfire for erosion control. Density of seeded grass plants per square meter was also higher than that of native grass plants in areas of high (18.78 ± 4.59 versus 0.33 ± 0.24) and moderate (8.22 ± 1.76 versus 0.22 ± 0.15) fire severity. There was a higher correspondence between the density of cultivated grass seeds and plants (highest value 0.32 ± 0.11) compared to density of native grass seeds and plants (highest value 0.05 ± 0.04). The high density of seeds, plants, and correspondence indicated that seeds from cultivated grasses are more likely to establish as post-fire vegetation than seeds from native grasses. Seeding with cultivated grasses following a wildfire may slow or inhibit recovery of native grasses in the short term. Longer-term implications for site occupancy deserve further study.     

The distribution and ecology of coastal species on roadsides

The invasion of roadsides by coastal species is a response to the use of de-icing salt. The most widespread species on Britain's roadsides, Puccinellia distans, occurs in the north and east of England and Wales. This distribution is due to the varying use and effects of de-icing salt which are related in turn to regional differences in climate and traffic density. On roadsides, seed dispersal is greater in the direction of traffic flow and the smaller seeds of Puccinellia distans are carried further than the larger seeds of Plantago maritima. Species on roadsides occur in distinct zones with the coastal species confined to the saline road margin. The causes of this zonation were investigated by examining seedling establishment in experimental plots. Seedlings were only able to establish in grass plots when the salinity was sufficiently high to kill the competing glycophytic grasses. On bare soil, the halophytes established and grew satisfactorily when salt was added but grew very poorly in the absence of salt. After two years Plantago maritima overcame this apparent requirement for salt on bare soil but Puccinellia distans and Spergularia marina did not.Acknowledgements: N. E. Scott was in receipt of a N.E.R.C. Studentship. The authors wish to thank the members of the B.S.B.I. and the Biological Records Office for information on species distribution.     

The Placopsis trachyderma – Raoulia – community, a special type of biological soil crusts in the braided rivers of southern New Zealand

The braided rivers with their ever-changing water channels are recognized as one of New Zealand's most distinctive and important ecosystem. We made a survey of the vegetation on the shingle plains in the upper reaches of the braided rivers of South Island. A well-defined colonizing vegetation type was recognized. It consists of lichens, mosses, low herbs, low cushion plants and tufted grasses, and mat-forming plants. Because of the close mechanical connection between the thalli of the lichens of the genus Placopsis (Agyraceae: Ascomycota) with moss cushions and spreading mats of vascular plants, we see this Placopsis trachyderma – Raoulia – community as a special type of biological soil crusts.     

Interspecific and seasonal dietary differences of Himalayan thar, chamois and brushtail possums in the central Southern Alps, New Zealand

Himalayan thar or tahr (Hemitragus jemlahicus), Alpine chamois (Rupicapra rupicapra) and brushtail possums (Trichosurus vulpecula) are native to the Himalaya, Europe and Australia, respectively, but are now sympatric in parts of the central Southern Alps, New Zealand. All three species are managed as pests by the Department of Conservation. We analysed the diets of 246 thar, 78 chamois and 113 possums collected in the central Southern Alps during 1988–1996. The diets of thar and chamois strongly overlapped, but thar ate more grasses and less herbs and woody plants than chamois. The diet of possums differed from the diets of thar and chamois, containing a different suite of herbs and almost no grasses. The diets of thar, chamois and possums varied seasonally. Contrary to expectation, the diets of adult male and female thar were similar during the period when they are spatially segregated (October–May). Chamois sampled outside the thar range ate more species than those sampled inside the thar range, suggesting that the presence of thar modifies the diet of chamois. If managers wish to protect the dominant Chionochloa snow tussocks then thar should be controlled; chamois should be controlled to protect herbs such as Ranunculus spp.; and possums should be controlled if Podocarpus nivalis or Muehlenbeckia axillaris need to be protected. However, managers need to be aware of the potential for chamois to increase in abundance, at least in some sites, if thar are controlled to low abundance, and that this could lead to different impacts on plant populations.     

Soluble inorganic tissue phosphorus and calcicole-calcifuge behaviour of plants

BACKGROUND AND AIMS: Natural and semi-natural, non-fertilized calcareous soils are consistently low in soluble and easily exchangeable phosphate. An over-utilization, or possibly an immobilization, of inorganic P in the tissues of calcifuge plants may take place, if such plants are forced to grow on a calcareous soil, though this has not been experimentally demonstrated. The objectives of this study are, therefore, to elucidate if calcifuge plants, when forced to develop on a calcareous soil, not only have lower total P (Ptot) concentrations in their leaves than calcicole plants grown on such soil, but also a lower proportion of Ptot as water-soluble, inorganic phosphate. Such differences may be of importance in understanding the calcicole-calcifuge behaviour of plants. MATERIALS AND METHODS: Plants of five calcicole and five calcifuge herbs and three calcicole and three calcifuge grasses were cultivated in a glasshouse on a moderately acid Cambisol and a calcareous Rendzic Leptosol using seeds of wild populations from southern Sweden. The calcifuges were: Corynephorus canescens, Deschampsia flexuosa, Holcus mollis, Digitalis purpurea, Lychnis viscaria, Rumex acetosella, Scleranthus annuus and Silene rupestris. The calcicoles were: Melica ciliata, Phleum phleoides, Sesleria caerulea, Arabis hirsuta, Sanguisorba minor, Scabiosa columbaria, Silene uniflora ssp. petraea and Veronica spicata. KEY RESULTS: At harvest, calcifuges had much lower leaf tissue concentrations of Ptot and Pi than calcicoles when grown on the calcareous soil, and biomass production of the calcifuges was poor on this soil. Moreover, the calcifuge herbs had, on average, a lower proportion of their Ptot as Pi than had the calcicole herbs. The calcifuge herbs were also unable to avoid excessive uptake of Ca from the calcareous soil. The calcifuge grasses maintained a similar proportion of Ptot as Pi as the calcicole grasses, but their growth was still poor on the calcareous soil. CONCLUSIONS: On calcareous soil, very little Pi in the tissues of calcifuge herbs is, at any time, available for use in various physiological functions. This is of importance to their photosynthesis, growth, competition and final survival on such soils.     

海南岛的外来植物

通过对海南岛野生或半野生外来入侵植物的调查,报道了153种外来植物,并对近年来在海南岛大面积分布而未报道过的入侵种进行简要介绍。对海南外来植物种类组成、原产地、生活型与危害程度的分析发现:(1)外来植物中有66.67%来自美洲,美洲种的96%为热带美洲成分,几乎所有来自美洲的草本植物往往成为遍布海南各地农田、果园、胶林、草地的有害杂草;(2)外来草本与藤本植物具有较强的入侵能力和较大的危害;(3)绝大多数草本与藤本植物常形成单一优势群落,破坏平地、低丘陵原有的生态系统。     

城市化地区河岸带植被特征及其与河岸硬度的关系——以晋江市为例

确立了滨河河道硬度与滨河土地硬度两个指标,用以研究城市化地区河岸带的植物构成、多样性与均匀度、优势植物等特征与河岸硬度的关系。选定晋江市都市区12条主要河流作为研究对象,通过样地调查收集数据,并采用相应指数进行数据处理分析,结果表明:(1)调查河流的河岸带植被物种共计70科143属159种,其中乔木20科30属41种,灌木15科15属20种,草本35科98属98种,草本居主导地位,河流间种类分布不均衡;(2)河岸带植物乔灌草区系均以广义热带性成分居多,其次为世界性成分、温带性成分,无中国特有分布类型,乔木中广义热带成分占绝对主导,直观反映地带性特征,灌木与草本中的温带成分多于乔木中的温带成分,类型趋于多元,种类更丰富;(3)从河岸植被优势植物构成来看,主要优势乔木与灌木基本为本土植物,而主要草本中外来植物入侵严重,对地带性植物景观的指示显然不及乔木与灌木;(4)从河岸植被的人工美学属性来看,灌木优势植物中园林观赏植物的种类数显著多于乔木、草本优势植物,反映出晋江人工审美主导的滨河景观空间主要改变与塑造了灌木层植被景观;(5)从河岸植物的人居需求属性来看,龙眼、杨桃等多见于庭院林、水岸林的水果树种也在河岸植被中频繁出现,反映出人口密集区由于对植物生产用途的重视而对河岸植被产生的影响;(6)滨河土地硬度与河道硬度对河岸带灌木植物的影响最强烈,二者均对河岸带植物多样性造成威胁,且前者具有更大的影响力,而后者直接影响了河岸植物的分布形态,出于生产与审美目的的人为干扰对河岸带植物优势种的影响力随滨河硬度的增加而加强,低滨河硬度有助留存原生植被群落;(7)天然弯曲的河流形态对河流植被特征具有积极影响,有助于保留更多本土植被类型,并能在某种程度上丰富乔灌草的植物种类,但这种缓和作用无法根本扭转河岸硬化对植物多样性的胁迫影响。研究表明,城市化地区河流的岸带植被特征与沿线人为干扰类型和强度密切相关,恢复与塑造河岸生态景观要以乡土植被为主,通过乔木景观塑造地带性景观,并以灌木与草本丰富植被景观。     

Effects of salinity and benzyl adenine on development and function of microhairs of Zea mays L

Bicellular microhairs are present on the surfaces of leaves of grasses with the exception of the Pooideae. In some halophytic grasses, these glandular hairs secrete salt, suggesting the intriguing question ‘can the microhairs of grasses that do not normally encounter salinity also secrete salt?’ Microhairs were counted in replicas of the adaxial and abaxial surfaces of leaves of various ages of maize plants growing either in the absence of salt or in the presence of 40, 80 or 120 mM NaCl. The number of microhairs per unit area of adaxial leaf surface of the youngest leaf almost doubled as the salinity increased from zero to 120 mM NaCl; on the abaxial surface, the number of microhairs increased by 50%. Spraying this leaf with benzyl adenine (BA) caused, when averaged across salinities and surfaces, a 32% increase in the number of microhairs. Salinity reduced leaf area but in all the salinity treatments, spraying with BA increased the total number of microhairs per leaf. Washing leaves of plants provided estimates of the loss of salt from those leaves. There were large differences between the Na:K molar ratios in the washing solution and the leaf tissue, indicating a high selectivity for sodium over potassium for loss from the leaf. BA did not influence the efficiency of salt loss, expressed per microhair, at any salinity level, but did increase loss per leaf. Thus, BA increased salt loss from plants due to its influence on the number of microhairs and leaf area, but not due to its effect on the efficiency of the secretion process per se.     

Stable isotope characteristics across narrow savanna/woodland ecotones in Wolfe Creek Meteorite Crater,Western Australia

The stable isotopic composition (δ¹³C) of sediments from lakes are frequently analyzed to reconstruct the proportion of the regional vegetation that used either the C₃ or C₄ photosynthetic pathways, often without conducting a detailed survey of the current local vegetation. We performed a study on the modern vegetation composition within the Wolfe Creek Meteorite Crater to complement our future paleoecological investigation of the crater. A bull’s-eye pattern exists where C₄ grasses dominate an outer ring and salt tolerant species, including shrubs, herbs, chenopods, and halophytic algae, dominate the inner pan of the crater. The ecotone between the inner and outer zones is narrow and occupied by tall (>7 m) Acacia ampliceps, with some C₄ grasses in the understory. Along with the highest water table and most saline soils the center of the crater has C₃ plants present with the highest δ¹³C and δ¹⁵N values. The range of δ¹³C and δ¹⁵N values from the analysis of surface soil organic matter (OM) was much smaller compared with the range of values from plant materials implying that either: (1) the current plant OM has not yet been integrated into the soils, or (2) processes within the soil have acted to homogenize isotopic variability within the crater. The application of a two end member mixing model to calculate %C₄ and %C₃ biomass from the δ¹³C of surface soil OM was complicated by: (1) the crater containing both a dry habitat with C₄ grasses and a central pan with C₄ halophytic plants and, (2) the large variation in the δ¹³C of the plants and soil OM.     

生态恢复和经济发展悖论中毒害草的地位及悖论解决途径

探讨了毒害草存在的生态价值、利用价值及毒害草防治的弊端。认为过度放牧是畜牧业陷入困境的主要原因,毒害草的繁衍只是草原退化的直接反映,防除缺乏依据。现有的防治措施存在各种弊端,对环境和生物多样性保护不利;并指出毒害草可以覆盖地面、减少水土流失,对草原生态系统的保护和恢复有利,故认为毒害草的大量繁衍是草原生态系统与放牧系统协同进化的结果,是草原生态系统发展的防御机制,具有极大生态价值。同时提出草原生态系统可持续发展要从人的生存和经济发展着眼,要改变现有生活模式,发展多种经营,实行跨区域经济补偿;要控制人口数量,对现有人口要实现城镇化。     

杭州西溪湿地植物组成及其与水位光照的关系

 杭州西溪湿地是在自然湿地基础上,并在一千多年农渔耕作用下形成的城市边缘次生湿地。随着工业化和城市化,它的面积急剧萎缩,植被受 干扰,生态脆弱,不久前成立的西溪国家湿地公园已经将保护提上日程。该文在报道这类特殊湿地植被结构和物种多样性的基础上试图回答下 列问题：何种小生境利于保护本地和湿地植物多样性？入侵种在各种小生境中的影响如何？怎样防控？根据调查,将西溪湿地草本层的小生境 分成5种类型：强光高基、弱光(有树遮光)高基、强光低基、强光高渚和强光低渚。采用分层和随机取样相结合的方法调查这5种小生境下的植 物群落组成,以重要值作为变量来计算物种多样性指数并排序。共26个地点,约234 m²的样方。结果显示在农渔耕的背景下,水位高低及光照 等自然因子对植物组成具有一定的选择作用。强光高基生境物种丰富度最高,其中本土、木本和豆科植物数量最多,而入侵种、湿生物种数量 最低;强光低渚生境的情况正好相反。强光高基生境有利于保持本土植物多样性,降低入侵种的竞争能力,但不利于湿地植物的存在;强光低 基有中度本土植物多样性及抵御入侵种的能力,有较大的草本比例和湿地植物比例,是一个保持良好的湿地环境。有利于湿地植物的低湿生境 目前在西溪比例较低,湿地植物偏少,这主要与西溪先前人类从事农业和渔业活动有关。在去除影响景观、影响本土物种多样性的入侵种的同 时,可考虑增加低湿的生境,并补种湿地物种。     

Effect of light conditions of wheat growing on sensitivity of photosynthetic machinery to salt stress

Sensitivity of wheat (Triticum aestivum L.) seedlings to salt stress was investigated as dependent on light conditions of plant growing. In two-week-old seedlings grown on salt-free medium, aboveground organs were detached from the roots and subjected to a brief stress at different concentrations of NaCl. The extent of salt stress effect expressed as a decrease in the rate of the photosynthetic release of oxygen and the relative content of water and chlorophyll in the leaves greatly depended on light conditions of growing. The plants grown at low light intensity were notable for a greater sensitivity to NaCl in the medium. Plant responses to salt stress were different at low and high salt concentrations. At low NaCl concentrations (0.05–0.10 M) in the solution, in plants grown at low light intensity, the rate of photosynthesis calculated per unit of chlorophyll increased. This effect was not observed in plants grown at the higher light intensity. At high NaCl concentrations (0.2–0.4 M) in the medium, the rate of photosynthesis rapidly decreased in all the types of treatment, with the effect being most pronounced in plants grown at low light intensity. The obtained results suggest a narrow range of NaCl concentrations with an optimum at 0.1 M positively affecting the wheat seedlings physiological state upon salt stress development depending on light conditions of plant growing.     

Invertebrate herbivory increases along an experimental gradient of grassland plant diversity

Plant diversity is a key driver of ecosystem functioning best documented for its influence on plant productivity. The strength and direction of plant diversity effects on species interactions across trophic levels are less clear. For example, with respect to the interactions between herbivorous invertebrates and plants, a number of competing hypotheses have been proposed that predict either increasing or decreasing community herbivory with increasing plant species richness. We investigated foliar herbivory rates and consumed leaf biomass along an experimental grassland plant diversity gradient in year eight after establishment. The gradient ranged from one to 60 plant species and manipulated also functional group richness (from one to four functional groups—legumes, grasses, small herbs, and tall herbs) and plant community composition. Measurements in monocultures of each plant species showed that functional groups differed in the quantity and quality of herbivory damage they experienced, with legumes being more damaged than grasses or non-legume herbs. In mixed plant communities, herbivory increased with plant diversity and the presence of two key plant functional groups in mixtures had a positive (legumes) and a negative (grasses) effect on levels of herbivory. Further, plant community biomass had a strong positive impact on consumed leaf biomass, but little effect on herbivory rates. Our results contribute detailed data from a well-established biodiversity experiment to a growing body of evidence suggesting that an increase of herbivory with increasing plant diversity is the rule rather than an exception. Considering documented effects of herbivory on other ecosystem functions and the increase of herbivory with plant diversity, levels of herbivory damage might not only be a result, but also a trigger within the diversity–productivity relationship.     

Vegetation changes following sheep grazing in abandoned mountain meadows

Abstract. Sheep grazing was investigated as an alternative to traditional management of meadows in the Krkono?e Mts. Until the second World War these meadows were mown in mid‐summer and grazed by cattle for the rest of the season. Subsequent abandonment of the meadows has resulted in decreasing species richness. Degradation phases of the former communities have been replacing the original species‐rich vegetation. Significant changes were apparent six years after the introduction of sheep grazing. In grazed plots the proportion of dominant herbs (Polygonum bistorta and Hypericum maculatum) decreased and grasses (Deschampsia cespitosa, Festuca rubra, Agrostis capillaris, Anthoxanthum alpinum) increased. The increase in grasses was positively correlated with an increase in several herbs. The proportion of some herbs increased despite being selectively grazed (Adenostyles alliariae, Melandrium rubrum, Veratrum lobelianum). Any losses caused by grazing of mature plants were probably compensated by successful seedling establishment. Cessation of grazing resulted in significant changes in vegetation within three years. The cover of nitrophilous tall herbs and grasses (e.g. Rumex alpestris, Holcus mollis, Deschampsia cespitosa, Geranium sylvaticum) increased in the abandoned plots. In the plots grazed for nine years cover of species‐rich mountain meadow species increased (e.g. fine‐leaved grasses, Campanula bohemica, Potentilla aurea, Viola lutea, Silene vulgaris). The main conservation risk is the expansion of a competitive species with low palatability, Deschampsia cespitosa. This species can be suppressed by a combination of grazing and mowing. In order for grazing to be effective, the number of sheep should be proportional to meadow production. This may be difficult to maintain as production is variable and is impossible to predict at the beginning of a growing season. A large part of the biomass may thus remain intact in some years. Negative effects of grazing may be, at least partly, eliminated by a combination of cutting and grazing.     

Using plant functional types to compare vegetation structure of alien-invaded and uninvaded Acacia nilotica savannas

Four plant functional types (PFTs) were used to compare the vegetation structure of an alien-invaded Acacia nilotica savanna with one of negligible invasions. Heights, canopy covers and species richness of three native PFTs (woody plants, grasses and herbs) and one alien PFT (woody plants) were measured in 14, 1-m² quadrats sampled in a stratified-random pattern in a 400-m² plot demarcated in each savanna. In the uninvaded plot, mean heights of native PFTs were stratified. In the invaded plot, the mean height of aliens extended into the native woody stratum with the lower range of native woody PFT heights reduced to the grass stratum. Discriminant analysis of canopy covers and species richness of the four PFTs revealed significant differences in composition between plots with the alien PFT being the most important variable correlated with these differences. Univariate analysis confirmed the dominance of alien woody plants in the invaded plot but also showed significant reductions in the canopy covers and species richness of native herbs and grasses compared to those in the uninvaded plot. These results suggest that PFTs can rapidly measure small-scale, spatial differences in the physiognomy, composition and species richness of A. nilotica savannas when invaded by alien woody plants.     

Effect of paclobutrazol on wheat salt tolerance at pollination stage

The effects of paclobutrazol (PBZ) (0, 30, 60, and 90 ppm) and NaCl (0, 75, 150, and 225 mM) treatments on a salt-tolerant (Karchia-65) cultivar of wheat (Triticum aestivum L.) at the pollination stage were studied. Salt stress decreased plant height, the length and area of the flag leaf, fresh and dry weights of the shoot, roots, and flag leaf, and water content. On the background of salinity, PBZ treatment further suppressed plant height. Although plants growth was suppressed in PBZ-treated plants, PBZ treatment moderated the negative effect of salinity on some growth parameters. Under PBZ treatments, plants tissues accumulated more watersoluble carbohydrates and reducing sugars than control plants, with the exception of water-soluble carbohydrates in the roots. The Na⁺ content in roots significantly (p ≤ 0.05) increased at 150 and 225 mM NaCl, but PBZ treatment moderated the harmful effect of the highest levels of salinity. Salinity with or without PBZ treatment improved the K⁺, P, and N contents in plants. It is reasonably to suggest that the protection and increasing salt tolerance caused by PBZ was due to the mechanism nearly similar to the salt-tolerant cultivar physiological systems. These observations suggest that PBZ treatment has the potential to increase salt tolerance with a limiting damage caused by salt stress even in salt-tolerant plants. This text was submitted by the authors in English. Published in Russian in Fiziologiya Rastenii, 2009, Vol. 56, No. 2, pp. 278–284.