233 research outputs found

    Short-Term Effects of Phosphorus Application on Phosphorus Content in Soil and Dominant Species under Ungrazed and Grazed Conditions in the Tibetan Plateau

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    Phosphorus (P) availability in soils is an important indicator for health and growth in plants. The available phosphorus (AP) content of alpine meadow soil in northern China is low. Previous studies of alpine meadow have reported that soil nutrient levels have been significantly improved after a 9-year enclosure (Wu et al. 2010b) whereas continuous grazing over 19 years reduced total P (TP) by 25% in a Leymus chinensis steppe (Li 2001). Many studies have shown that the application of P fertilizer can improve dry matter production and forage quality in cultivated grasslands (Shi et al. 2007). However, the benefits of applying P fertiliser to alpine meadow in terms of increases in soil AP content and P concentrations in plants in both grazed and ungrazed meadows are less well known. The objective of this study was to investigate the short-term effects of P application on the AP content in top soil and total P content in the foliage of dominant meadow plant species

    Does the Short-Term Grazing Affect Functional Group and Plant Species Diversity of Alpine Meadow in the Tibetan Plateau?

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    Grazing affects the physiological and ecological characteristics of the plant community, through livestock intake and trampling (Georgiadis et al. 1989). Previous studies in the Qinghai-Tibetan Plateau have shown that the composition and structure of alpine meadow plant communities respond to grazing (Niu et al. 2010). However, the changes to functional groups and species diversity caused by grazing are not well documented, especially with regards to short term effects (McLaren 2008). In this study, different grazing rates were used to determine the relationship between functional groups, community diversity and yak stocking rates. The objective of this study was to reveal plant functional group responses to grazing and to predict the evolutionary trend of alpine meadow plant functional groups and community diversity under different grazing conditions, thereby providing a theoretical basis for the management of degraded grassland and the conservation of grassland diversity

    Leaf Nitrogen and Phosphorus Stoichiometry of Natural Plant Community and Restorable Plant Community in the Northern Qinghai-Tibet Plateau, China

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    The human engineering activities (highway, railway, cable, gas line and high line construction) has a negative impact on the alpine grassland ecosystem in the Qinghai-Tibet Plateau (QTP), and the natural restoration of plant community in land used for engineering construction is an important part of the rehabilitation of the degraded alpine grassland ecosystem. Previous studies have shown that the plant species and community diversity relationship in natural plant community and restorable plant community vary with the elevation (Guo et al. 2007) and restoration duration of land for engineering construction is more than 20 years at present (Ma et al. 2004). Understanding the mechanisms of plant species replacement in the process of plant restoration is important to restore the land used for engineering construction. The ecological stoichiometry is considered as an effective tool to disclose the inter-specific competition process and determine the succession trend (GĂŒsewell 2004; GĂŒsewell 2005; Yin et al. 2010). However, the stoichiometry relationship between natural plant community and restorable plant community is not well known yet. The objective of this study is to investigate the nitrogen (N) and phosphorus (P) stoichiometry of natural plant community and restorable plant community and its changes with elevation

    Numerical investigation of flow unsteadiness and heat transfer on suction surface of rotating airfoils within a gas turbine cascade

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    The effects of the periodical turbulence and pressure fluctuation on suction surface heat transfer over airfoils of a row of rotor blades with a certain type have been investigated numerically in this paper. The calculation is performed using model with the numerical results of pressure fluctuation and heat transfer performance over 4 sample points being analyzed and compared with existing experimental data. It shows that the static pressure change has significant impact on heat transfer performance of the fore suction surface, especially in the active region of the shock waves formed from the trailing edge of upstream nuzzles. While, for the rear suction surface, the flow turbulence contributes more to the heat transfer change over the surface, due to the reduced pressure oscillation through this region. Phase shifted phenomenon across the surface can be observed for both pressure and heat transfer parameters, which should be a result of turbulence migration and wake passing across the airfoil

    Effect of Plateau Pika (\u3cem\u3eOchotonacurzionae\u3c/em\u3e) Disturbance on Soil Microelements Content in Alpine Meadow

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    The plateau pika (Ochotonacurzoniae) creates the extensive disturbance on alpine meadow ecosystem in the QinghaiTibetan Plateau (Smith and Foggin, 1999, Delibes-Mateos et al., 2011), especially on soil nutrient (Davidson et al., 2012). Previous studies show that intermediate active burrows of plateau pika improved soil macro-element (organic matter, total nitrogen and total phosphorus) in alpine meadow (Guo et al., 2012). However, there is little knowledge about the underlying contribution of plateau pika disturbance in determining soil microelement in alpine meadow. The density of active burrow entrances is used to divide the disturbances levels of plateau pika to determine the effect of various disturbance levels of plateau pika on soil microelement content of alpine meadow in the Qinghai-Tibetan Plateau in this study

    Effects of Alternate Furrow Irrigation on the Forage Quality of Alfalfa (\u3cem\u3eMedicago sativa\u3c/em\u3e)

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    Alfalfa (Medicago sativa) is widely used to establish pasture to sustain animal production because of its high nutritional quality for livestock (Bouton, 2012). Therefore improving quality of alfalfa pasture is the main goal for establishing pasture throughout the world. Irrigation is an important approach for achieving high qualities of alfalfa pasture, however, the scarcity of water threatens the sustainability of world alfalfa production, requiring us to force on using water more efficiently (Liu and Guo, 2013). Alternate furrow irrigation has been proved as a water-saving technique to promote fruit quality of tomatoes and grapevines and the seed quality of cotton (Kirda et al., 2004, Dos Santos et al., 2003, Tang et al., 2005). But these studies only focus on harvesting the seed, fruits and tubers, while neglecting the vegetative mass. In this study, we investigated the effects of alternate furrow irrigation with different irrigation volumes on the quality of alfalfa

    Effect of Grazing on Soil Carbon and Nitrogen in Alpine Madow, Eastern of Tibetan Plateau

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    As the grassland ecosystem in the Tibetan Plateau is very fragile, overgrazing likely leads to more serious damages to it than other ecosystems. In the past 30 years, 37% of the alpine meadows have been heavily damaged by grazing causing degradation of native vegetation, a decline in species richness and feed value, and more seriously soil erosion (Six et al. 2004). The impact of grazing on alpine grasslands appears to be hysteresis, as the soil needs more time to recover than the vegetation. So analysing the effect of grazing intensity on soil characteristics is an important way to reveal how grazing influenced grassland ecosystem. Although much research about grazing effects on nutrients, immobilization of carbon (C) and nitrogen (N) in soils and soil microbes have been done in different terrestrial environments, similar effort has rarely focused on the Tibetan Plateau. In this study, soil organic carbon (SOC) and total nitrogen (STN) in 0-30 cm soil depth were measured in the alpine meadow at the northeastern margin of the Tibetan Plateau, to determine suitable grazing intensity from the viewpoints of soil health and fertility, and providing a scientific basis for guiding the reasonable use of the alpine meadow

    Gene by Social Context Interactions for Number of Sexual Partners among White Male Youths: Genetics‐Informed Sociology

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    In this study, we set out to investigate whether introducing molecular genetic measures into an analysis of sexual partner variety will yield novel sociological insights. The data source is the white male DNA sample in the National Longitudinal Study of Adolescent Health. Our empirical analysis has produced a robust protective effect of the 9R/9R genotype relative to the Any10R genotype in the dopamine transporter gene (DAT1). The gene-environment interaction analysis demonstrates that the protective effect of 9R/9R tends to be lost in schools in which higher proportions of students start having sex early or among those with relatively low levels of cognitive ability. Our genetics-informed sociological analysis suggests that the “one size” of a single social theory may not fit all. Explaining a human trait or behavior may require a theory that accommodates the complex interplay between social contextual and individual influences and genetic predispositions

    Frequency Offset Correction for OFDM Systems

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    In this paper, we propose a robust method to estimate carrier frequency offset (CFO) for orthogonal frequency division multiplexing (OFDM) systems. A training symbol with two identical halves is employed to measure the fractional part of the CFO. While the integral part is estimated by using a novel noise subspace based metric. Simulation results demonstrate that the proposed method can achieve an estimation range equal to the whole bandwidth of the OFDM signal

    Bioassessment of a Drinking Water Reservoir Using Plankton: High Throughput Sequencing vs. Traditional Morphological Method

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    Drinking water safety is increasingly perceived as one of the top global environmental issues. Plankton has been commonly used as a bioindicator for water quality in lakes and reservoirs. Recently, DNA sequencing technology has been applied to bioassessment. In this study, we compared the effectiveness of the 16S and 18S rRNA high throughput sequencing method (HTS) and the traditional optical microscopy method (TOM) in the bioassessment of drinking water quality. Five stations reflecting different habitats and hydrological conditions in Danjiangkou Reservoir, one of the largest drinking water reservoirs in Asia, were sampled May 2016. Non-metric multi-dimensional scaling (NMDS) analysis showed that plankton assemblages varied among the stations and the spatial patterns revealed by the two methods were consistent. The correlation between TOM and HTS in a symmetric Procrustes analysis was 0.61, revealing overall good concordance between the two methods. Procrustes analysis also showed that site-specific differences between the two methods varied among the stations. Station Heijizui (H), a site heavily influenced by two tributaries, had the largest difference while station Qushou (Q), a confluence site close to the outlet dam, had the smallest difference between the two methods. Our results show that DNA sequencing has the potential to provide consistent identification of taxa, and reliable bioassessment in a long-term biomonitoring and assessment program for drinking water reservoirs
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