Large‐scale patterns of fish diversity and assemblage structure in the longest tropical river in Asia          下载免费PDF全文

Ratha Chea  Sovan Lek  Pengbun Ngor  Gaël Grenouillet 《Ecology of Freshwater Fish》2017,26(4):575-585

Although the Mekong River is one of the world's 35 biodiversity hot spots, the large‐scale patterns of fish diversity and assemblage structure remain poorly addressed. This study aimed to investigate the fish distribution patterns in the Lower Mekong River (LMR) and to identify their environmental determinants. Daily fish catch data (i.e. from December 2000 to November 2001) at 38 sites distributed along the LMR were related to 15 physicochemical and 19 climatic variables. As a result, four different clusters were defined according to the similarity in assemblage composition and 80 indicator species were identified. While fish species richness was highest in the Mekong delta and lowest in the upper part of the LMR, the diversity index was highest in the middle part of the LMR and lowest in the delta. We found that fish assemblages changed along the environmental gradients and that the main drivers affecting the fish assemblage structure were the seasonal variation of temperature, precipitation, dissolved oxygen, pH and total phosphorus. Specifically, upstream assemblages were characterised by cyprinids and Pangasius catfish, well suited to low temperature, high dissolved oxygen and high pH. Fish assemblages in the delta were dominated by perch‐like fish and clupeids, more tolerant to high temperatures, and high levels of nutrients (nitrates and total phosphorus) and salinity. Overall, the patterns were consistent between seasons. Our study contributes to establishing the first holistic fish community study in the LMR.  相似文献   

王正非林火蔓延模型改进研究     

张晓婷  刘培顺  王学芳 《山东林业科技》2020,50(1):1-6,40

王正非林火蔓延模型是目前国内比较先进的森林火灾蔓延模型,但是由于林火行为的复杂性,此模型在准确率和普适性方面仍存在许多不足。本文结合已有的成果进一步改进王正非模型,增加了可燃物湿度对林火蔓延速度的影响,改进了林火初始速度的计算方式。针对各种坡度对林火蔓延行为的影响给出了一个计算公式。与改进前相比,改进后的模型使其对林火蔓延情况的预估更为精准。  相似文献   

河南省食用菌科技推广存在的问题及对策   总被引：1，自引：0，他引：1  

侯军  段春燕  杜爱玲  谢清华  吴祖峰 《河南科技大学学报(农学版)》2001,21(3):184-185

综合分析了河南省食有菌科技推广中存在的生产经营缺乏宏观引导，科技推广存在自发性和盲目性，体制不协调和食用菌生产本身的不可控因素较多等问题，提出了加强宏观引导，微观调控，建立健全食用菌行业管理，食用菌龙头企业建设，开发建设规模生产基地等具体措施，为食用菌的产业化大发展提供了参考依据。  相似文献   

暖卫工程施工质量通病的发生与防治     

段长毅  何军  冉宪文 《林业科技情报》2001,33(2):51-51

本文论述了暖卫工程跑、冒、滴、漏、堵等五大质量通病的发生原因及防治方法建议等。  相似文献   

A novel approach to studying the effects of temperature on soil biogeochemistry using a thermal gradient bar     

N. Fenner    D. J. Dowrick    M. A. Lock    C. R. Rafarel  & C. Freeman 《Soil Use and Management》2006,22(3):267-273

The temperature dependence of chemical reaction rates and microbial metabolism mean that temperature is a key factor regulating soil trace gas emissions and hydrochemistry. Here we evaluated a novel approach for studying the thermal response of soils, by examining the effects of temperature on gas emissions and hydrochemistry in (a) peat and (b) soil from a Sitka spruce plantation. A thermal gradient was applied along an aluminium bar, allowing soil to be incubated contemporaneously from 2 to 18 °C. The approach demonstrated clear differences in the biogeochemical responses of the two soil types to warming. The peat showed no significant emission of CH₄ at temperatures below 6 °C, while above 6 °C, a marked increase in the rate of release was apparent up to 15 °C (Q₁₀ = 2.5) with emissions being similar between 15 and 18 °C. Conversely, CH₄ emissions from the forest soil did not respond to warming. Nitrate availability in the peat decreased by 90% between 2 and 18 °C (P < 0.01), whereas concentrations in the forest soil did not respond. Sulphate availability in the peat decreased significantly with warming (60%, P < 0.01), while the forest soil showed the opposite response (a 30% increase, P < 0.01). Conventionally, thermal responses are studied by incubating individual soil samples at different temperatures, involving lengthy preparation and facilities to incubate samples at different temperatures simultaneously. Data collected on a given thermal response is usually limited and thus interpolated or extrapolated. The thermal gradient method overcomes these problems, is simple and flexible, and can be adapted for a wide range of sample types (not confined to soil). Such apparatus may prove useful in the optimization of management practices to mitigate the effects of climate change, as thermal responses will differ depending on land use and soil type.  相似文献   

Effect of sodium nitrite and sodium chloride on growth of lactic acid bacteria.     

H Korkeala  T Alanko  T Tiusanen 《Acta veterinaria Scandinavica》1992,33(1):27-32

The effect of NaNO2 and NaCl on the growth of 24 lactic acid bacteria strains isolated from vacuum-packed cooked ring sausages were examined by analyzing different growth parameters with Bioscreen. NaNO2 had a very limited effect on the growth of lactic acid bacteria at 50 and 100 mg/l but at 400 mg/l a more pronounced inhibitory effect was found. Bacterial growth was enhanced by 1-2% (w/v) of added NaCl, while NaCl concentrations above 3% (w/v) had a clear inhibitory effect. Leuconostoc isolates seemed to be more sensitive to sodium nitrite and sodium chloride than homofermentative lactobacilli strains. Among homofermentative lactobacilli, the strains resembling Lactobacillus curvatus were more sensitive to NaCl than those resembling Lactobacillus sake.  相似文献   

Effect of planting density of maize on the progress and spread of northern leaf blight fromExserohilum turcicum infested residue source     

E. Adipala  J. P. Takan  M. W. Ogenga-Latigo 《European journal of plant pathology / European Foundation for Plant Pathology》1995,101(1):25-33

Effect of plant density (37,037, 44,444 and 55,555 plants/ha) on the increase of northern leaf blight in time and space on two maize cultivars planted at spacings of 90, 75 and 60 between rows and 30 cm within rows was investigated.Exserohilum turcicum infested maize residue was used as an inoculum source. Maize density did not significantly affect the disease indices, but significantly influenced the grain yield of the two cultivars. In contrast, the two cultivars differed significantly (P0.01) in disease severity, but not grain yield. Higher disease severities and grain yields were associated with higher plant densities, whereas the apparent infection rate was lower in higher plant density. Distance from the maize residue (inoculum source) significantly influenced disease severity. The percentage leaf area blighted, area under disease progress curve and disease progress curve intercept decreased with distance from the maize residue area, but the apparent infection rate on EV8429-SR appeared to increase with distance. Disease gradients (b) were higher in closely planted maize and flattened with time in one location only.  相似文献   

Spread of potato virus Y in potato cultivars (Solanum tuberosum L.) with different levels of sensitivity     

Nata&#x;a Mehle  Maja Kova   Nata&#x;a Petrovi   Maru&#x;a Pompe Novak  &#x;pela Baebler  Hana Kre i Stres  Kristina Gruden  Maja Ravnikar 《Physiological and Molecular Plant Pathology》2004,64(6):19

The aim of this work was to correlate the appearance of the symptoms, multiplication and spread of virus after mechanical inoculation of potato (Solanum tuberosum L.) cultivars showing different levels of susceptibility and sensitivity to Potato virus Y^NTN (PVY^NTN). The potato cultivars used were the resistant cultivar Sante and susceptible cultivars Igor, Pentland squire and Désirée. The spread of the virus PVY^NTN in infected plants was monitored using different methods: DAS-ELISA, tissue printing, immuno-serological electron microscopy and real-time PCR. In all three susceptible cultivars, the virus was detected in the inoculated leaves 4–5 days after inoculation. From there virus spread rapidly, first into the stem, then more or less simultaneously to the upper leaves and roots. Real-time PCR was shown to be very sensitive and enabled viral RNA to be detected in non-inoculated leaves of susceptible cultivar Igor earlier than other methods. Therefore, for exact studies of plant–virus interaction, a combination of methods which detect viruses on the basis of their different properties (coat protein, morphology or RNA) should be used to monitor the spread of viruses.  相似文献   

Wind-mediated spread of Rice yellow mottle virus (RYMV) in irrigated rice crops     

S. Sarra  P. Oevering  S. Guindo  D. Peters † 《Plant pathology》2004,53(2):148-153

A study was carried out to demonstrate that Rice yellow mottle virus (RYMV), a virus known to be transmitted by beetles, can spread between rice plants by direct leaf contact caused by wind. Almost all healthy plants surrounding an infected plant became infected when exposed to a fan blowing for 15 min at a distance of 50 cm. Spread of RYMV by plant contact, mediated by wind, was also demonstrated in field experiments, the extent of spread depending on plant density. Infection was almost 10 times higher in plots with a density of 33 plants m⁻² than in plots with 16 plants m⁻². Less spread was observed in plots protected by 1·5 m high windscreens. It is suggested that wind-mediated spread of RYMV may result from abrasive contact between leaves of plants.  相似文献   

基于氮梯度加载下的温室核桃砧木苗生长生理特性变化     

王健健  宋岩  图荪江.阿卜力米提  刘春花  张锐 《现代农业科技》2019,(24)

【目的】探究新疆核桃砧木苗生长特征及生理特性对氮梯度的响应,为核桃砧木苗施氮标准化的探究奠定基础。【方法】以阿克苏厚皮农家种质核桃砧木苗为研究对象,进行不同梯度的氮素诱导,测定核桃砧木苗生长及生理指标。【结果】基于氮梯度加载下的核桃砧木苗株高、地径、叶片数、叶长、光合色素含量、可溶性蛋白质含量、可溶性糖含量、硝酸还原酶活性、谷氨酰胺合成酶活性均呈上升趋势,并在15 g.a^-1.m^-2处理下达到最高值。【结论】适量地增施氮肥有利于核桃砧木苗的生长、提高砧木苗体内营养物质含量以及促进氮代谢能力。  相似文献