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1.
Summary   The purpose of this comment paper is to highlight the need for more research that aims to develop strategies and methods for establishing and maintaining native grasses in degraded pastures. Clues to finding the best strategies are linked to the vigorous debate concerning the relationship between biodiversity and ecosystem function, which has resonated in ecological research for more than 20 years. Studies aimed at investigating the operational validity of the 'sampling effect' hypothesis vs. the 'niche complementarity' hypothesis could provide valuable direction on how to successfully re-establish healthy and stable native pasture communities, including the number of species and functional groups needed. Once strategies have been developed, then practical methods on grazing management and sowing are also needed. In the long run, research initiatives in this direction could act to benefit the conservation of native grass diversity, while at the same time, sustain important ecological (and economic) functions such as production, nutrient cycling and resistance to invasion.  相似文献   

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Thirty-five subjects participated in (1) a pretreatment session during which arousal was measured while subjects anticipated and then viewed a stressful film; (2) four 20-min treatment sessions during which subjects received either contingent EMG biofeedback (biofeedback treatment), instructions to attend to a variable pitch tone (attention-placebo control), instructions to relax as much as possible (instructions-only control), or instructions to sit quietly (no-treatment control); and (3) a posttreatment session that was identical to the pretreatment session. Results indicate that when compared to the subjects in the control conditions, subjects who received EMG biofeedback were not effective in reducing frontalis EMG levels during treatment or while viewing the stressful film, but they were effective in reducing frontalis EMG levels while anticipating the stressful film. There was no evidence that EMG biofeedback influenced either skin conductance or self-reports of arousal.This research was supported in part by Bio-Medical and General Research Fund grants from the University of Kansas to David S. Holmes. Appreciation is due to B. Kent Houston, Edward F. Morrow, and Charles A. Hallenbeck for their contributions to the project.  相似文献   

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R L Naumov 《Parazitologiia》1990,24(2):97-101
Evaluation of all known ticks attractants was made to ascertain their suitability to be combined with pesticide in order to control populations of pasture ticks of the genera Ixodes and Dermacentor. Search for attractants among the pheromones of aggregation (for the genus Ixodes) and among substances determining the host's odour (for both genera) was concluded to be most promising.  相似文献   

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Aims

Biochars, being good sorbents of organic compounds, can reduce the mobility of pesticides in soil and subsequent pollution to groundwater, but may also impact on the efficacy of soil-applied herbicides. The aim of this study is to seek a potential solution to this problem.

Methods

We prepared a wood biochar at a relatively low heat treatment temperature (350 °C), and used it as an adsorptive carrier for incorporating the herbicides 2,4-D and acetochlor, and also as a soil amendment. Release experiment through a thin soil layer and leaching experiment through a soil column were used to evaluate the effectiveness of the biochar for controlling the release and leaching of herbicides in soil.

Results

The release experiments demonstrated that the low-temperature biochar could control the release of herbicides in soil, and the leaching experiments showed that this biochar significantly reduced the leached amount of herbicides by 1/2?~?3/4, depending on the depth (5?~?15 cm) of biochar-amended topsoil. High retention of herbicides in the biochar-amended topsoil was observed.

Conclusions

The results suggest that the low temperature biochar, if applied properly in soil, may be useful for extending the efficacy of herbicides while controlling their potential pollution.  相似文献   

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Strategies for improving efficient phosphorus utilization in crops and pastures: 1. Conventional and marker assisted selection breeding; 2. Transgenic modification; 3. Optimization of P fertilization and cultivation management.
Highlights? Phosphorus efficiency is improved via conventional and marker assisted selection breeding. ? The vital genes are applied to improve P efficiency through biotech. ? Optimization of P fertilization and cultivation management improves P efficiency. ? It is vital to integrate bioengineering, P fertilization and cultivation management.  相似文献   

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The aims of this study were to investigate how antennal olfactory cells of tsetse (Diptera: Glossinidae) code odour quality and how they are able to discriminate between attractive and repellent odours. For Glossina pallidipes Austen, a survey is presented of the cells' responses to attractive (1-octen-3-ol, acetone, 3-methylphenol, carbon dioxide) and repellent stimuli (2-methoxyphenol, acetophenone, lactic acid, naphthalene). In addition, the responses of these cells to binary mixtures and the dose-response curves of 1-octen-3-ol, 3-methylphenol, 2-methoxyphenol and acetophenone are presented. A minority of the cells responded to one attractant or repellent only, whereas the vast majority were excited by more than one of the attractive and/or repellent stimuli. It is proposed that the peripheral olfactory cells of tsetse discriminate between different compounds via an across-fibre pattern coding, in which the cells that specifically code for attractants or repellents may play a substantial role in composing a unique excitation pattern that informs the central nervous system about the specificity of odours.  相似文献   

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Blood-feeding success of female horseflies, Hybomitra expollicata Pandellé and Tabanus bromius L. (Diptera: Tabanidae), was studied. Bloodmeal weights of flies permitted different periods of residence on a horse's belly were estimated, and related to subsequent ovarian development and the number of mature eggs produced. Fitness gain per visit to a host (as estimated by the number of mature eggs produced) increased more rapidly with residence time on the host for H.expollicata than for T.bromius. H.expollicata inhibed blood more rapidly and, above a threshold bloodmeal size, produced a consistently higher number of eggs per unit weight of blood ingested. The feeding strategies of the two species are compared.  相似文献   

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Potassium sorbate, sodium benzoate, sulfur dioxide, and diethylpyrocarbonate (DEPC) were tested for their effectiveness in preventing the outgrowth ofByssochlamys nivea Westling ascospores. Sulfur dioxide was the most inhibitory of the test antimycotics, complete inhibition of colony formation occurring in acidified (pH 3.5) potato dextrose agar containing 50 ppm of the preservative. Complete inhibition ofB. nivea ascospore outgrowth in grape juice stored for 60 days was noted in the presence of 300 ppm sulfur dioxide, 400 ppm potassium sorbate, and 600 ppm DEPC. Growth was observed in grape juice containing 1000 ppm sodium benzoate. The presence of up to 100 ppm potassium sorbate in grape juice during heat activation appears to have a stimulatory effect on breaking dormancy, while the other test preservatives at this concentration decrease the heat resistance ofB. nivea ascospores. The time elapsed between heat shock and exposure to DEPC or sodium benzoate is critical with respect to the sensitivity of ascospores to these preservatives.  相似文献   

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新烟碱类杀虫剂拌种对麦蚜田间防效及药剂残留动态分析   总被引:1,自引:0,他引:1  
为了分析两代新烟碱类杀虫剂吡虫啉和噻虫嗪拌种对麦蚜的防治效果的差异以及2种药剂在小麦叶片内的残留动态,采用吡虫啉和噻虫嗪有效剂量0.5、1.0、2.0和4.0g/kg小麦种子在播种前进行1次性拌种处理,随后调查了不同处理下田间麦蚜的种群密度,并对不同时期小麦叶片内的药剂残留进行了监测。结果表明:吡虫啉有效剂量2.0和4.0g/kg,噻虫嗪有效剂量1.0、2.0和4.0g/kg小麦种子播前拌种能有效的降低田间麦蚜的种群数量。在4月10日前,吡虫啉在小麦叶片内的含量明显高于噻虫嗪,4月28日后两者差异不明显。与吡虫啉相比,噻虫嗪对麦蚜具有更高的生物活性和控制效果。  相似文献   

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Poly-beta-hydroxybutyrate (PHB) and other polyesters can be produced by various species of bacteria. Of the possible carbon sources, methane could prove to be one of the most suitable substrates for the manufacture of PHB. The methanotrophic strain Methylocystis sp. GB 25 DSM 7674 was applied in order to accumulate PHB in a rapid, non-sterile process. Cultivation was performed in two stages: a continuous growth phase (dilution rate 0.17 h(-1)) and a PHB accumulation phase under deficiency conditions of an essential nutrient (e.g. phosphorus) in batch culture. The PHB content of the biomass was as high as 51%; efficiency was the highest during the first 5 h of the product formation process. The PHB produced is of very high quality, having a high molecular mass of up to 2.5 x 10(6) Da. In order to monitor and control the process, a rapid analysis method based upon turbidimetry in the visible range (438 nm) was applied. Moreover, the PHB content of the biomass was determined using an FT-IR-spectroscopic method with ATR sampling and multivariate calibration. We achieved a value of 1.4% as the best standard error of cross validation. The nitrogen content of the PHB final product (a product quality parameter) was estimated by spectroscopic method in the visible range.  相似文献   

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The identification of sex attractants was undertaken for potential use in the study of two biological control agents against Rubus spp. in Hawaii. Attractants for Croesia zimmermani (Lepidoptera: Tortricidae) and Schreckensteinia festaliella (Lepidoptera: Heliodinidae) were developed by field screening a variety of putative lures in sticky traps, based on attractants for congeneric species. Croesia zimmermani was most attracted to E11-tetradecen-1-ol and E11-tetradecenal, while S. festaliella was attracted to (10,12)-(E,E)-hexadecadienal alone. Development of monitoring systems based on sex attractants can enable better evaluation of biocontrol programmes, and provide cost-effective information on presence/absence, density, phenology, synchrony with the host, dispersal rate and other useful parameters.  相似文献   

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On rangelands, uneven or unmanaged livestock distribution can adversely affect plant community composition, riparian function, or displace wildlife. These issues have historic precedents and are still a challenge for those managing rangelands. A thorough understanding of the mechanisms governing livestock distribution can help land and livestock managers avoid or ameliorate many deleterious effects. To that end, this research tested hypotheses that grazing cattle seek nutritionally superior portions of rangeland pastures. Global positioning system (GPS) collars were used to track cattle movement and activity in three, 800+ ha pastures where the spatial distribution of standing crop, crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), and forage digestibility (in situ dry matter disappearance (ISDMD)) were mapped in late spring. Four of five analyses implied grazing cattle spatially responded to forage quantity/quality attributes. Analyses indicated cattle favored higher than average CP (P = 0.006) and ISDMD (P = 0.078), and lower than average NDF (P = 0.003) and standing crop (P = 0.069) locales. No significant effect (P = 0.954) occurred with ADF analyses. Correlations among those variables imply cattle may simultaneously respond to more than one nutritional attribute as they select foraging locales. Stepwise regression, however, relating grazing distribution to geophysical and forage quantity/quality characteristics were extremely poor predictors of where cattle grazed. Listed in order of entry, the model implied elevation above or below stock water, horizontal distance to stock water, forage CP content, and degree of slope were the site specific attributes most associated with cattle distribution. We speculate that cattle interactions with landscape level nutritional dynamics may at least partially explain seasonal changes in distribution and forage use by cattle across the landscape. These findings should help land and livestock managers understand, explain, and manipulate livestock distribution on their holdings.  相似文献   

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