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排序方式: 共有98条查询结果,搜索用时 156 毫秒
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Frauke Kleemann Maximilian von Fragstein Barbara Vornam Annika Müller Christoph Leuschner Andrea Holzschuh Teja Tscharntke Reiner Finkeldey Andrea Polle 《European Journal of Forest Research》2011,130(5):707-716
Knowledge on phenological, morphometric, and phytochemical variation of local progenies of European aspen (Populus tremula, L.) is limited. The goal of this study was to characterize variation in growth and ecologically important leaf properties
in aspen full-sib families in relation to interacting organisms (mycorrhiza, endophytes, and insects) and to determine whether
these interactions were affected by soil application of a systemic fungicide. In local progenies, within-family variation
of neutral molecular genetic markers (nuclear microsatellites) was higher than between families. Significant variation in
growth, production of phenolic defensive compounds and other phytochemical leaf traits was found between families. Phenolic
compounds showed clear negative correlation with generalist herbivores, but did not result in negative trade-off with biomass
production. Differences in mycorrhizal colonization were not found among full-sib families and application of a systemic fungicide
suppressed neither mycorrhizal colonization nor infestation with insects. However, a strong suppression of endophytes occurred,
whose long-term consequences may require attention when fungicides are used in agroforestry plantations. 相似文献
4.
The course of events from taking a food into the mouth to the perception of the food's flavor involves many steps, from dilution with saliva, mastication, and transportation of the compounds to the olfactory epithelium to transformation into signals that go to the brain. In addition, there are also the effects of the food's structure and properties. In this study, a proton-transfer-reaction mass spectrometer (PTR-MS) was used to investigate how four pectin-containing systems with different structures and strengths affected the release of aroma compounds in a model mouth and in the nose of an assessor. Both the model mouth and the in-nose measurements showed that the strength and structure of pectin-containing systems are important with regard to the quantity of aroma compounds that are released. Mastication and saliva were also shown to have a large influence on how much of the aroma compound is released from the mouth to the nose. 相似文献
5.
Density‐dependent processes have repeatedly been shown to have a central role in salmonid population dynamics, but are often assumed to be negligible for populations at low abundances relative to historical records. Density dependence has been observed in overall spring/summer Snake River Chinook salmon Oncorhynchus tshawytscha production, but it is not clear how patterns observed at the aggregate level relate to individual populations within the basin. We used a Bayesian hierarchical modelling approach to explore the degree of density dependence in juvenile production for nine Idaho populations. Our results indicate that density dependence is ubiquitous, although its strength varies between populations. We also investigated the processes driving the population‐level pattern and found density‐dependent growth and mortality present for both common life‐history strategies, but no evidence of density‐dependent movement. Overwinter mortality, spatial clustering of redds and limited resource availability were identified as potentially important limiting factors contributing to density dependence. The ubiquity of density dependence for these threatened populations is alarming as stability at present low abundance levels suggests recovery may be difficult without major changes. We conclude that density dependence at the population level is common and must be considered in demographic analysis and management. 相似文献
6.
Annika Kangas Rasmus Astrup Johannes Breidenbach Jonas Fridman Terje Gobakken Kari T. Korhonen 《Scandinavian Journal of Forest Research》2018,33(4):397-412
The Nordic countries have long traditions in forest inventory and remote sensing (RS). In sample-based national forest inventories (NFIs), utilization of aerial photographs started during the 1960s, satellite images during the 1980s, laser scanning during the 2000s, and photogrammetric point clouds during the 2010s. In forest management inventories (FMI), utilization of aerial photos started during the 1940s and laser scanning during the 2000s. However, so far, RS has mostly been used for map production and research rather than for estimation of regional parameters or inference on their accuracy. In recent years, the RS technology has been developing very fast. At the same time, the needs for information are constantly increasing. New technologies have created possibilities for cost-efficient production of accurate, large area forest data sets, which also will change the way forest inventories are done in the future. In this study, we analyse the state-of-the-art both in the NFIs and FMIs in the Nordic countries. We identify the benefits and drawbacks of different RS materials and data acquisition approaches with different user perspectives. Based on the analysis, we identify the needs for further development and emerging research questions. We also discuss alternatives for ownership of the data and cost-sharing between different actors in the field. 相似文献
7.
Jessica Schenck Annika Djurle Dan Funck Jensen Cecilia Müller Martin O'Brien Rolf Sprndly 《Grass and Forage Science》2019,74(1):29-41
The use of wrapped forage bales with high dry‐matter (DM) content implies risk of fungal growth inside the wrapping, and impaired feed quality. Since fungi may be unevenly distributed in bales, the method of sampling can influence the outcome of the analysis. Three common sampling methods for detection of fungi in wrapped forage were compared: direct plating of visible mouldy patches on bale surfaces (Method I), direct plating of pieces of foliage from drilled core samples (Method II) and quantitative analysis dilution series of drilled core samples (Method III). All samples were cultured on two media at two temperatures. Samples were collected from 124 farms in Sweden and Norway. Using Methods I, II and III, fungi were detected on 52%, 77% and 56% of the farms respectively. Fifty‐two fungal species were identified using a combination of culturing and molecular methods. The most predominant species were Arthrinium spp., found on 55% of the farms, followed by Penicillium roqueforti at 48% of the farms. Incubation at 25°C resulted in higher numbers of all genera, except Aspergillus, compared to incubation at 37°C. The different methods of sampling and culturing did not identify the same fungal species within the same bale. Analysing one bale per farm resulted in detection of less than half the number of species compared to analysing three bales. Of the sampling and culturing methods compared, direct plating of drilled core samples cultivated at malt extract agar at 25°C performed best in terms of qualitative analysis of fungi species. 相似文献
8.
侧流道泵或侧通道泵(side channel pump)是一种介于容积式泵和离心泵之间的径向式叶片泵,由叶轮一侧有一个横截面为半圆形的侧流道而得名,通常具有超低比转数特性和自吸能力,其体积小,流量低,但是扬程却很高.与普通离心泵相比,侧流道泵作为一种新型泵,更适用于极端条件下气液两相流体和接近临界状态流体的输送.首先介绍了侧流道泵的组成和工作原理,简要阐述了流体在侧流道泵内的运动轨迹.同时,按照时间顺序分析了侧流道泵的研究情况,重点分析了近年来国内外关于侧流道泵的研究现状.最后根据前面所述的研究成果,展望了侧流道泵研究的发展趋势.认为优化设计可提高侧流道泵的性能,完善侧流道泵理论模型,利用先进的内部流动测试手段,例如PIV,LDA等,分析测量侧流道泵内部流动规律和旋涡演变机理,设计开发多功能侧流道泵是今后侧流道泵的研究重点. 相似文献
9.
Markus Holopainen Antti Mäkinen Jussi Rasinmäki Juha Hyyppä Hannu Hyyppä Harri Kaartinen Risto Viitala Mikko Vastaranta Annika Kangas 《European Journal of Forest Research》2010,129(5):899-907
The objective was to compare tree-level airborne laser-scanning (ALS) data accuracy with standwise estimation data accuracy
as input data for forest planning, using tree- and stand-level simulators. The influence of the input data accuracy was studied
with respect to (1) timing of the next thinning or clear-cutting and (2) the relative variation in the predicted income of
the next logging expressed as the net present value (NPV). The timing and predicted NPV of thinning and clear-cutting operations
were considered separately. The research was based on Monte Carlo simulations carried out with the tree- and stand-level simulators
using a simulation and optimisation (SIMO) framework. The simulations used treewise measurements taken on 270 circular plots
measured at the Evo Field Station, Finland, as input data. Deviations in the tree data measured were generated according to
the mean standard errors found in standwise field estimation and tree-level ALS. The accuracy factors of ALS individual tree
detection were based on the EUROSDR/ISPRS Tree Extraction Project. The results show that input data accuracy significantly
affects both the timing and relative NPV of loggings. Tree-level ALS produces more accurate simulation results than standwise
estimation with the error levels assumed. Diameter-based characteristics are the most important input data in all simulations.
Accurate tree height estimates cannot be fully utilised in current simulators. 相似文献
10.
Antti Mäkinen Markus Holopainen Annika Kangas Jussi Rasinmäki 《European Journal of Forest Research》2010,129(5):887-897
Developments in the field of remote sensing have led to various cost-efficient forest inventory methods at different levels
of detail. Remote-sensing techniques such as airborne laser scanning (ALS) and digital photogrammetry are becoming feasible
alternatives for providing data for forest planning. Forest-planning systems are used to determine the future harvests and
silvicultural operations. Input data errors affect the forest growth projections and these effects are dependent on the magnitude
of the error. Our objective in this study was to determine how the errors typical to different inventory methods affect forest
growth projections at individual stand level during a planning period of 30 years. Another objective was to examine how the
errors in input data behave when different types of growth simulators are used. The inventory methods we compared in this
study were stand-wise field inventory and single-tree ALS. To study the differences between growth models, we compared two
forest simulators consisting of either distance-independent tree-level models or stand-level models. The data in this study
covered a 2,000-ha forest area in southern Finland, including 240 sample plots with individually measured trees. The analysis
was conducted with Monte Carlo simulations. The results show that the tree-level simulator is less sensitive to errors in
the input data and that by using single-tree ALS data, more precise growth projections can be obtained than using stand-wise
field inventory data. 相似文献