1,721,017 research outputs found
Contrasting patterns of leaf solute accumulation and salt adaptation in four phreatophytic desert plants in a hyperarid desert with saline groundwater
No full textThe seasonal variation of leaf solutes was investigated in four perennial phreatophytes in the natural vegetation surrounding a river oasis in the Chinese Taklamakan desert in order to elucidate their adaptation to saline groundwater. Leaves of the herbaceous perennial legume Alhagi sparsifolia, the poplar tree Populus euphratica, the salt cedar Tamarix ramosissima, and the C(4) shrub Calligonum caput-medusae were collected at the end of each month during the growing season 1999 and analysed for cation, anion, organic acid, carbohydrate, glycinebetaine, and proline concentrations. The species revealed considerable differences in the foliar solute composition and their seasonal variation. Tamarix had high foliar mineral salt concentrations throughout the season but excreted the accumulated salts via salt glands. The three other species showed different degrees of ion regulation and ion selectivity. Calligonum had generally very low mineral ion concentrations, tolerated moderate Cl(-) concentrations and excluded Na(+). Populus effectively excluded Cl(-) from its leaves but Na(+) and total solute concentrations increased towards the end of the season which lead to K:Na ratio smaller than one in October. Alhagi showed the highest degree of ion selectivity by excluding Na(+) but accumulating Ca(2+) in its leaves. Mineral salt composition of xylemsap in Alhagi and Calligonian indicated that both species showed a similar degree of ion selectivity in the roots and that ion retransloction is probably another important mechanism to maintain low salt concentrations in the leaf. The cyclitols chiro-inositol and pinitol were the major compatible solutes in the plants and N-containing solutes like proline or glycinebetaine occurred only in minor concentrations or were absent, respectively. All plant species were well adapted to the moderate salinity of the NaCl dominated groundwater and no signs of salt related drought stress, ion toxicity or nutrient imbalance were observed. (C) 2003 Elsevier Ltd. All rights reserved
Regulation of the water status in three co-occurring phreatophytes at the southern fringe of the Taklamakan Desert
No full textAims We investigated the regulation of the water status in three predominant perennial C3 phreatophytes (Alhagi sparsifolia, Populus euphratica, Tamarix ramosissima) at typical sites of their occurrence at the Southern fringe of the hyperarid Taklamakan Desert (north-west China). Methods In the foreland of the river oasis of Qira (Cele), we determined meteorological variables, plant biomass production, plant water potentials (psi(l)) and the water flux through the plants. We calculated the hydraulic conductance on the flow path from the soil to the leaves (k(SL)) and tested the effects of k(SL) psi(L) and the leaf-to-air difference in the partial pressure of water vapour (Delta w) on stomatal regulation using regression analyses. Important Findings Despite high values of plant water potential at the point of turgor loss, all plants sustained psi(L) at levels that were high enough to Maintain transpiration throughout the growing season. In A. sparsitolia, stomatal resistance (r(s); related to leaf area or leaf mass) was most closely correlated with k(SL);. whereas in P. euphratica, similar to 70%, of the variation in r(s) was explained by Delta w. In T. ramosissima, leaf area-related r(s) was significantly correlated with psi(L) and k(SL). The regulation mechanisms are in accordance with the growth patterns and the Occurrence of the species in relation to their distance to the ground water
Water relation characteristics of Alhagi sparsifolia and consequences for a sustainable management
No full textWater relation characteristics of the desert legume Alhagi sparsifolia were investigated during the vegetation period from April to September 1999 in the foreland of Qira oasis at the southern fringe of the Taklamakan Desert, Xinjiang Uygur Autonomous Region of China. The seasonal variation of predawn water potentials and of diurnal water potential indicated that Alhagi plants were well water supplied over the entire vegetation period. Decreasing values in the summer months were probably attributed to increasing temperatures and irradiation and therefore a higher evapotranspirative demand. Data from pressure-volume analysis confirmed that Alhagi plants were not drought stressed and xylem sap flow measurements indicated that Alhagi plants used large amounts of water during the summer months. Flood irrigation had no influence on water relations in Alhagi probably because Alhagi plants produced only few fine roots in the upper soil layers. The data indicate that Alhagi sparsifolia is. a drought-avoiding species that utilizes ground water by a deep roots system, which is the key characteristic to adjust the hyper-arid environment. Because growth and survival of Alhagi depends on ground water supply, it is important that variations of ground water depth are kept to a minimum. The study will provide a theoretical basis for the restoration and management of natural vegetation around oasis in and regions
Ordination as a tool to characterize soil particle size distribution, applied to an elevation gradient at the north slope of the Middle Kunlun Mountains
No full textSoil particle-size distribution (PSD) is one of the most fundamental physical attributes of soil due to its strong influence on other soil properties related to water movement, productivity, and soil erosion. Characterizing variation of PSD in soils is an important issue in environmental research. Using ordination methods to characterize particle size distributions (PSDs) on a small-scale is very limited. In this paper, we selected the Cele River Basin on the north slope of the Middle Kunlun Mountains as a study area and investigated vegetation and soil conditions from 1960 to 4070 m a.s.l. Soil particle-size distributions obtained by laser diffractometry were used as a source data matrix. The Canonical Correspondence Analysis (CCA) ordination was applied to analyse the variation characteristics of PSDs and the relationships between PSDs and environmental factors. Moreover, single fractal dimensions were calculated to support the interpretation of the ordination results. Our results indicate that a differentiation of 16 particle fractions can sufficiently characterize the PSDs in CCA biplots. Elevation has the greatest effect on PSDs: the soil fine fractions increase gradually with increasing elevation. In addition, soil pH, water and total salt content are significantly correlated with PSDs. CCA ordination biplots show that soil and vegetation patterns correspond with one another, indicating a tight link between soil PSDs and plant communities on a small scale in arid regions. The results of fractal dimensions analysis were rather similar to CCA ordination results, but they yielded less detailed information about PSDs. Our study shows that ordination methods can be beneficially used in research into PSDs and, combined with fractal measures, can provide comprehensive information about PSDs. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved
Water use by perennial plants in the transition zone between river oasis and desert in NW China
No full textThe study aimed at establishing the role of two possible water sources (inundation, ground water) for the water supply to the perennial plant species Alhagi sparsifolia, Calligonum caput-medusae, Populus euphratica and Tamarix ramosissima growing in the transition zone between a river oasis and the open desert at the southern fringe of the Taklamakan desert (Xinjiang province, NW China). The basic hypothesis was that inundations, which normally occur in summer when rivers from a nearby mountain range carry high water, contribute significantly to the plants' water supply. When, in the first summer, inundations did not occur, four sites, each of which covered by a relatively dense stand of one species, were artificially flooded. Soil and plant water relations as well as meteorological variables were measured during two growing seasons. Water use efficiency of production (WUEp) was calculated by relating biomass production, which was determined using allometric regressions, to water use. The effects of artificial flooding on the plant water relations were negligible. Water use was relatively high, especially in the A. sparsifolia and the P euphratica stands and in a dense stand of T ramosissima (up to approx. 500 kgH(2)O m(-2) year(-1)). Using the total above-ground biomass in the calculation, WUEp was highest in C. caput-medusae and P euphratica, and lowest, in A. sparsifolia. From soil and plant water relations, and against the background of the climate and the productivity of the vegetation, it is concluded that all perennial plants in the transition zone between oases and desert in that region must have sufficient access to ground water to ensure long-term survival. Management of ground water such that it remains continuously accessible to the perennial plants is a prerequisite for the conservation and sustainable use of the vegetation in the transition zone. (c) 2005 Gesellschaft fur Okologie. Published by Elsevier GmbH. All rights reserved
Nitrogen application mitigates drought-induced metabolic changes in Alhagi sparsifolia seedlings by regulating nutrient and biomass allocation patterns
No full textGroundwater and its associated nutrients sustain the establishment and persistence of phreatophytes. Rapid root elongation immediately after germination is vital for desert species to access deep water sources to avoid water-deficit stress. However, the growth strategy and responses to nutrients and water of young phreatophyte seedlings before their roots reach the water table are poorly understood, especially in the scenarios of nitrogen (N) deposition and drought. We investigated how simulated N deposition and drought affect the plasticity of Alhagi sparsifolia seedlings by multiple eco-physiological mechanisms. Seedlings were planted under drought-stressed or well-watered conditions and subjected to various levels of N addition (0, 3.0, 6.0, or 9.0 gN⋅m). The amounts of N and water independently or interactively affected the photosynthetic traits, drought tolerance characteristics, morphological traits, biomass allocation strategy, and nutrient distribution patterns among the plant organs. Moreover, changes mediated by N addition at the leaf level reflected the drought acclimation of the seedlings, which may be related to biomass and nutrient partitioning between organs. The roots were found to be more sensitive to variation of the N:phosphorus (P) ratio, and greater proportions of biomass, N, and P were allocated to resource-acquiring organs (i.e., leaves and fine roots) than to other tissues. A. sparsifolia adopts numerous strategies to tolerate drought, and additional N input was crucial to enhance the growth of drought- stressed A. sparsifolia, which was mainly attributable to its positive impact on the N and P uptake capacity mediated by increased biomass allocation to the roots.Fil: Zhang, Zhihao. Chinese Academy of Sciences; República de China. Cele National Station of Observation and Research for Desert-Grassland Ecosystems; China. University of Chinese Academy of Sciences; ChinaFil: Tariq, Akash. Chinese Academy of Sciences; República de China. Cele National Station of Observation and Research for Desert-Grassland Ecosystems; ChinaFil: Zeng, Fanjiang. Chinese Academy of Sciences; República de China. Cele National Station of Observation and Research for Desert-Grassland Ecosystems; ChinaFil: Graciano, Corina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; ArgentinaFil: Zhang, Bo. Chinese Academy of Sciences; República de China. Cele National Station of Observation and Research for Desert-Grassland Ecosystems; Chin
Nitrogen and water addition regulate fungal community and microbial co-occurrence network complexity in the rhizosphere of Alhagi sparsifolia seedlings
No full textRhizosphere microbes are key regulators of phreatophyte establishment in extremely arid environments. Although it is known that increased nitrogen (N) deposition alters microbial communities in arid lands, the effect of N enrichment in soil on phreatophyte rhizospheric microbes remain poorly understood. In a mesocosms experiment, we characterized the diversity, composition of rhizospheric bacterial and fungal communities of Alhagi sparsifolia seedlings by high-throughput sequencing in four-level N additions under drought and well-watered regimes. The relationships between microbial communities and soil properties and plant traits were also quantified. N interacted with water explained the 42.1% variation on fungal community composition, and significantly altered their alpha-diversity which positively correlated with proline accumulation in leaves, while the rhizobacterial community exhibited stability to N and water inputs. The Mantel test showed that microbial community composition at the OTU level was interrelated to soil properties and plant traits. Co-occurrence network analyses suggested that low N input (0–3 g m−2 year−1) and drought stress caused more complex associations along with vulnerability to environmental interference. Our results proposed that rhizosphere bacterial and fungal communities of phreatophyte respond differently to N enrichment under divergent water regimes. Climate change could potentially affect desert plant-microbe interactions. These findings can contribute to predicting and managing ecological and evolutionary responses of the desert ecosystem under global changing scenarios.Fil: Zhang, Zhihao. Chinese Academy of Sciences; República de ChinaFil: Tariq, Akash. Chinese Academy of Sciences; República de ChinaFil: Zeng, Fanjiang. Chinese Academy of Sciences; República de ChinaFil: Graciano, Corina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Fisiología Vegetal. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Instituto de Fisiología Vegetal; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Agrarias y Forestales; ArgentinaFil: Sun, Feng. Southwest China Normal University; ChinaFil: Chai, Xutian. Chinese Academy of Sciences; República de ChinaFil: Ahmed, Zeeshan. Chinese Academy of Sciences; República de Chin
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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