Spatial and temporal patterns of Lolium rigidum–Avena sterilis mixed populations in a cereal field

Through a detailed case study of a two‐species (Lolium rigidum and Avena sterilis) weed community at contrasting scales, this paper examined factors that affect weed distribution across space and time in a commercial wheat field in north‐east Spain. A. sterilis showed relatively stable spatial distribution and spatial structure of its population over time at large scale, with well‐defined patches, although weed density rose quickly. L. rigidum showed poorly defined patches that were not stable across time. Interaction between species could explain to some degree the spatial distribution at large scale: a negative relationship was detected between the spatial structures of both weed populations. At fine scale, both species showed a clear interaction effect from primary dispersal (more important in A. sterilis) and secondary dispersal from combine harvesting (more important in L. rigidum).     

宁夏野生甘草分布空间异质性及分布格局研究

运用统计学中的半方差分析、分维分析和克里格插值方法对宁夏野生甘草Glycyrrhiza uralensis的分布格局及其过程进行了研究.结果表明,宁夏野生甘草不同尺度空间分布的异质性不十分强烈,在整个所有尺度上受简单过程控制.分布格局在较小尺度上受随机过程控制,而在较大尺度上受自相关关系影响较大.当甘草种群间的距离在0～58 m内,样点内甘草株数与距离有自相关关系,而当甘草种群间的距离大于58 m时,样点间甘草分布的变化失去了自相关关系.甘草的克隆繁殖方式和土壤质地的空间异质性及鼠兔危害是导致甘草分布空间异质性的重要原因.     

甘肃省产业空间结构及其生态效应分析

区域产业空间结构与生态环境之间存在着强烈的交互胁迫关系。本文分析了甘肃省产业空间结构特征、不同产业发展对生态环境的影响及产业空间结构的生态环境效应。得出以下结论:(1)甘肃省第一产业分布分散且与农业资源的空间分布态势基本一致,第二产业发展空间高度集中且与矿产资源分布一致,第三产业集中在大中城市和旅游资源丰富的地区;(2)甘肃省产业空间结构的生态环境效应具有明显的空间差异;(3)甘肃省生态环境地域分异与产业空间结构分异交互胁迫,强化了生态环境的地域分异,加剧了生态环境的脆弱性。     

兰州旅游圈旅游空间结构构建研究

区域旅游空间结构对于区域旅游业的发展具有重要的意义。文章在简要地梳理近些年来区域旅游空间结构研究成果的基础上,对于区域旅游空间结构的构建方法提出了自己的观点:根据游客的到访情况划分其内部结构,根据资源集聚态势和共同表现的主题进行功能分区,按照远近结合的原则确定优先发展区,根据服务功能确定旅游中心地。通过对兰州旅游圈深入的调查和研究,提出兰州旅游圈的空间结构构建模式:三个旅游圈层、七个旅游瓣区和十一个旅游功能区;在综合评价的基础上确定了圈内的七个优先发展区和若干个旅游中心地。最后,对于兰州旅游圈的旅游线路提出了设计方案。     

Testing the spatial significance of weed patterns in arable land using Mead's test

There is a need in weed science for statistical tests for patchiness and spatial pattern. The objective of this study was to investigate the performance of Mead’s test for detecting patterns in synthetic data and in real weed counts made in maize, and making a first assessment of its applicability in ecological studies on weeds. In an extension to Mead’s test, made here for the first time, we merge original quadrat count data into rectangular cells of m by n quadrats. Care was taken to rule out the effect of starting point on the test result. Using the synthetic data, we demonstrate the ability of the test to detect both patchiness and homogeneity as deviations from randomness. The first deviation results in right‐sided significance, and the second in left‐sided significance of the test. Analysis of the real weed patterns demonstrated patchiness at many scales for five of the six investigated species and lack of any deviation from randomness in the sixth: Taraxacum officinale. The latter was the only wind dispersing species in the dataset. No deviation towards homogeneity was found in any of the real weed species at any scale. All patchy patterns showed anisotropy, being elongated in the direction of field traffic. As it turns out, Mead’s test is well suited to detect departures from randomness in observed weed patterns and enhances the suite of diagnostic tools that can be employed by weed ecologists.     

Heterogeneity of the aerial concentration and deposition of ascospores of <Emphasis Type="Italic">Venturia inaequalis</Emphasis> within a tree canopy during the rain

Scab is an important disease of apple and its control depends almost exclusively on frequent use of fungicides. Primary scab infection in the spring assumes several steps: ascospore maturation, liberation of ascospores that become airborne, deposition on susceptible tissues, and infection. However, the spatial heterogeneity of ascospores within the tree canopy is unknown. Aerial concentration of ascospore (ACA), ascospore concentration in rain water (ACR) and ascospore deposition (AD) were therefore measured at six heights (20–257 cm from the ground) with rotating-arm air samplers, funnels, and greased glass slides, respectively, during five rain events in 2001 and in 2002. In addition, ACR and AD were measured at eight locations within tree canopy at 196 cm height. Apple scab was assessed at the end of the primary infection period in each sampling location within the apple tree. A similar experimental design was used in 2003 to study the spatial heterogeneity of both AD and primary scab lesions. ACA and AD decreased with increasing height, while ACR increased with increasing height. Based on both variance to mean ratio and the power law relationship in both years, the ACR was heterogeneous, while AD was heterogeneous only during the peaks of ascospore release. The ACR was significantly higher at the centre of the trees and the AD was significantly higher at the centre and at the western edge of the trees. Only the cumulative AD was significantly correlated with apple scab lesions at the same location (r = 0.83). In 2003, a similar pattern of spatial heterogeneity within the tree canopy was observed for AD and primary scab lesion counts and there was a linear relationship (R ² = 0.84) between these two variables. It was concluded that ACR and AD within the tree canopy are not randomly distributed at least during peaks of ascospore release and that AD is a good estimate of primary scab lesion development. This spatial heterogeneity should be considered when estimating ascospore deposition using mathematical models or when quantifying ascosporic inoculum using spore samplers.     

Response of black rot in cabbage to spatial distribution of inoculum

Disease progress of black rot in cabbage crop was studied over three years in field plots to compare the effects of uni-focal and multi-focal inoculum applied in equal amounts per plot. Disease progress (plant incidence and leaf incidence) was plotted over time, three dimensional maps were made, and disease aggregation was studied by means of geostatistics, black-black counts and Moran's I statistic. Black rot progress was primarily due to focus expansion. Secondary foci may appear at short distances from the initial focus but they usually merge with the expanding initial focus. Anisotropy occurred occasionally but was of minor importance. Disease proceeds faster in plots with multi-focal inoculation than in those with uni-focal inoculation. Probably, serious epidemics in Dutch cabbage fields originate from large numbers of foci.     

黄河流域旱涝灾害的时空分布特征

本文以月降水距平为指标,根据黄河流域典型台站４０年的降水资料,对黄河流域旱涝灾害的时空分布特征进行了分析,并进行了区域划分。     

An analysis of structure of tree seedling populations on a Lahar

The structure of a tree seedling population is dependent on the interaction of several processes including seed dispersal, germination, survival, and competition on a physical landscape. Structural components (composition, size distributions, spatial distributions, age distributions, density, and history) of a tree seedling population on the Muddy River Lahar on the east side of Mount St. Helens were examined over a range of extents (1/10 m to 1000 m). Many of these component have rarely been examined at the larger extents listed here. Composition reflected distances to seed source and seed morphology. Seedling sizes are inversely proportional to depth to a buried soil if one existed. Spatial patterns indicated that seedling are clustered for tree seedlings less than 200 m apart, random for tree seedling from 200 m to 400 m and uniform for seedling greater than 400 m apart. This was confirmed by two measures of multidimensional spatial point pattern. Age distributions did not reflect the size distributions; old seedlings could be almost any size, young seedlings were constrained to be small in size. Densities appear to be typical for forests in the area. History of disturbance events (the lahar establishment, and successive ash, pumice, and erosion) has strongly influenced this tree seedling community.     

Assessment of diffusive phosphate supply in soils by microdialysis

Standard procedures to assess P availability in soils are based on batch experiments with various extractants. However, in most soils P nutrition is less limited by bulk stocks but by strong adsorption and transport limitation. The basic principle of root‐phosphate uptake is to strip phosphate locally from the solid phase by forming a radial depletion zone in the soil solution, optionally enhanced by release of mobilizing substances. Microdialysis (MD), a well‐established method in pharmacokinetics, is capable to mimic important characteristics of P root uptake. The sampling is by diffusional exchange through a semipermeable membrane covering the probes with their sub‐mm tubular structure. Additionally, the direct environment of the probe can be chemically modified by adding, e.g ., carboxylates to the perfusate. This study is the first approach to test the applicability of MD in assessing plant available phosphate in soils and to develop a framework for its appropriate use.We used MD in stirred solutions to quantify the effect of pumping rate, concomitant ions, and pH value on phosphate recovery. Furthermore, we measured phosphate yield of top‐soil material from a beech forest, a non‐fertilized grassland, and from a fertilized corn field. Three perfusates have been used based on a 1 mM KNO₃ solution: pure (1), with 0.1 mM citric acid (2), and with 1 mM citric acid (3). Additionally, a radial diffusion model has been parametrized for the stirred solutions and the beech forest soil.Results from the tests in stirred solutions were in good agreement with reported observations obtained for other ionic species. This shows the principal suitability of the experimental setup for phosphate tests. We observed a significant dependency of phosphate uptake into the MD probes on dialysate pumping rate and on ionic strength of the outside solution. In the soils, we observed uptake rates of the probes between 1.5 × 10⁻¹⁵ and 6.7 × 10⁻¹⁴ mol s⁻¹ cm⁻¹ in case of no citrate addition. Surprisingly, median uptake rates were mostly independent of the bulk soil stocks, but the P‐fertilized soil revealed a strong tailing towards higher values. This indicates the occurrence of hot P spots in soils. Citrate addition increased P yields only in the higher concentration but not in the forest soil. The order of magnitude of MD uptake rates from the soil samples matched root‐length related uptake rates from other studies. The micro‐radial citrate release in MD reflects the processes controlling phosphate mobilization in the rhizosphere better than measurements based on “flooding” of soil samples with citric acid in batch experiments. Important challenges in MD with phosphate are small volumes of dialysate with extremely low concentrations and a high variability of results due to soil heterogeneity and between‐probe variability. We conclude that MD is a promising tool to complement existing P‐analytical procedures, especially when spatial aspects or the release of mobilizing substances are in focus.