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941.
942.
草莓叶面积简易测定方法 总被引:16,自引:1,他引:16
以透明方格法作对照,分别与叶面积的其他简易测定法(叶长度×叶宽度的系数法、叶长度与叶面积的回归法、叶宽度与叶面积的回归法)比较。结果表明吐德拉(Tudla)叶面积的每种测定方法,以叶宽度与叶面积回归法最精确,计算公式是=7.0918x-13.4784穴公式中的x是叶宽度,y是叶面积,以下相同雪;鬼怒甘(Kinuama)叶面积的测定法也是叶宽度与叶面积回归法最精确,公式是=7.3187x-14.3288。杜克拉(Dukela)叶面积的测定法,推荐用叶宽度与叶面积的回归法,公式是=6.6393x-10.6411。y=a+bx^y=a+bx^y=a+bx^ 相似文献
943.
944.
Johnson Chris J. Boyce Mark S. Mulders Robert Gunn Anne Gau Rob J. Cluff H. Dean Case Ray L. 《Landscape Ecology》2004,19(8):869-882
Multiscale analyses are widely employed for wildlife-habitat studies. In most cases, however, each scale is considered discrete and little emphasis is placed on incorporating or measuring the responses of wildlife to resources across multiple scales. We modeled the responses of three Arctic wildlife species to vegetative resources distributed at two spatial scales: patches and collections of patches aggregated across a regional area. We defined a patch as a single or homogeneous collection of pixels representing 1 of 10 unique vegetation types. We employed a spatial pattern technique, three-term local quadrat variance, to quantify the distribution of patches at a larger regional scale. We used the distance at which the variance for each of 10 vegetation types peaked to define a moving window for calculating the density of patches. When measures of vegetation patch and density were applied to resource selection functions, the most parsimonious models for wolves and grizzly bears included covariates recorded at both scales. Seasonal resource selection by caribou was best described using a model consisting of only regional scale covariates. Our results suggest that for some species and environments simple patch-scale models may not capture the full range of spatial variation in resources to which wildlife may respond. For mobile animals that range across heterogeneous areas we recommend selection models that integrate resources occurring at a number of spatial scales. Patch density is a simple technique for representing such higher-order spatial patterns. 相似文献
945.
Herbicide translocation was investigated in a Haplic Luvisol from loess (clayey silt; Klein-Altendorf near Bonn, Germany) and a Eutric Cambisol (sandy loam; fluvial sediments on the lower Rhine terrace north of Bonn) using the herbicide diuron as an example. diuron was applied once a year in May at the recommended dose of 2.4 kg/ha. It rapidly degraded in the topsoil: the “time for 50% disappearance” (DT50) was 14–30 days. A population of adapted soil micro-organisms, which is repeatedly exposed to applications of the same compound every year, is thought to be responsible for this fast degradation. Remaining Diuron residues were largely degraded in the loess soil during the subsequent summer and became less mobile due to increasing binding strength. As a result, residue levels and leaching in the loess soil during the winter were negligible, with diuron traces of less than 10 µg/kg below the topsoil 11 months after application. Comparison of the translocation in a sandy loam soil showed—as expected—that diuron was leached to the subsoil to a higher extent than in clayey silt (loess). However, in the loess soil, diuron leached to the subsoil via macropores after 20 mm of natural precipitation within 1 week after herbicide application due to macropore flow. Colour tracer and analysis of the linings of earthworm burrows identified these macropores as preferred pathways of herbicide leaching. Macropore flow occurred in wet soil and moist soil with a sealed surface or crust but not in dry soil. Superficial mechanical soil cultivation before the herbicide application is discussed as one possibility to interrupt macropore entries and reduce herbicide leaching after its application in the spring. 相似文献
946.
Prof. Dr. Peter Lüdders 《Erwerbs-Obstbau》2004,46(4-5):117-122
The carambola (Averrhoa carambola L., family Oxalidaceae) is believed to have originated in Sri Lanka and the Moluccas but it has been cultivated in southeast Asia and Malaysia for many centuries. The evergreen tree is slow-growing, has a rounded crown and reaches 6 to 9 m in height. The 5- to 6-angled fruits (6 to 15 cm long and up to 9 cm wide) have thin, waxy, orange-yellow skin and juicy, yellow flesh. The fruit has a more or less pronounced oxalic acid odor and the flavor ranges from very sour to middle sweetish. The carambola is a tropical and subtropical tree, it can tolerate freezing temperature (?2°C) for short periods and sustain little damage. Trees can be propagated by seed, grafting, budding, and air layering. Tissue culture propagation has met only limited success. Plant spacing varies with growing region and cultural practices. Tree training is practiced intensively in different countries. Harvest timing and postharvest handling are critical to successful marketing of fresh fruit. Carambola is a nonclimateric fruit. Growers carefully harvest fruit by hand at color break — light green fruit with yellow color. The storage conditions should be 5 to 10°C and 85 to 95% relative humidity. Most carambola fruit is eaten fresh, used in salads, desserts, and cooked as star-shaped slices; fruit can also be dried, canned and frozen. The leaves have been eaten as a substitute for sorrel. Commercial production occurs in Taiwan, Malaysia, southern China, the Philippines, Australia, USA (Florida, Hawaii), Brazil, Suriname and Guyana. Production and consumption appears on the rise throughout the world and will most likely increase as selection and breeding for superior tasting cultivars with improved handling characteristics and storage conditions are found. 相似文献
947.
948.
甘肃省生态环境综合评价指标体系研究 总被引:12,自引:6,他引:12
甘肃省生态系统分为社会经济系统和自然生态系统两大类 ,社会经济系统指标体系由社会经济条件和人为环境压力构成 ;自然生态系统由水环境、森林生态系统、草地生态系统和土壤生态系统四个次一级系统组成 ,每个次一级生态系统由各自所属指标体系来系统评定。利用因子分析法、Delphi法和头脑风暴法经过多次综合专家意见最终确定 2 6项指标作为甘肃省生态环境质量综合评价体系。利用层次分析法 (AHP)定量各指标的权重。通过综合评价表明 ,甘南州、陇南地区、张掖地区的生态环境质量较好 ,甘肃中部广大黄土高原地区次之 ,河西走廊的武威市、金昌市和嘉峪关市环境质量最差。评价结果真实地反映了甘肃省生态环境的基本状况 ,说明该指标体系具有科学性 ,能够用于不同地区之间或同一地区不同时间的环境质量对比与变化研究。 相似文献
949.
Characterizing historical and modern fire regimes in Michigan (USA): A landscape ecosystem approach 总被引:4,自引:0,他引:4
Cleland David T. Crow Thomas R. Saunders Sari C. Dickmann Donald I. Maclean Ann L. Jordan James K. Watson Richard L. Sloan Alyssa M. Brosofske Kimberley D. 《Landscape Ecology》2004,19(3):311-325
We studied the relationships of landscape ecosystems to historical and contemporary fire regimes across 4.3 million hectares in northern lower Michigan (USA). Changes in fire regimes were documented by comparing historical fire rotations in different landscape ecosystems to those occurring between 1985 and 2000. Previously published data and a synthesis of the literature were used to identify six forest-replacement fire regime categories with fire rotations ranging from very short (<100 years) to very long (>1,000 years). We derived spatially-explicit estimates of the susceptibility of landscape ecosystems to fire disturbance using Landtype Association maps as initial units of investigation. Each Landtype Association polygon was assigned to a fire regime category based on associations of ecological factors known to influence fire regimes. Spatial statistics were used to interpolate fire points recorded by the General Land Office. Historical fire rotations were determined by calculating the area burned for each category of fire regime and dividing this area by fifteen (years) to estimate area burned per annum. Modern fire rotations were estimated using data on fire location and size obtained from federal and state agencies. Landtype Associations networked into fire regime categories exhibited differences in both historical and modern fire rotations. Historical rotations varied by 23-fold across all fire rotation categories, and modern forest fire rotations by 13-fold. Modern fire rotations were an order of magnitude longer than historical rotations. The magnitude of these changes has important implications for forest health and understanding of ecological processes in most of the fire rotation categories that we identified.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
950.
Dr. Joachim Kakau Dorothee Abdel-Kader Petra Müller Karl-Heinz Pastrik Luitgardis Seigner 《Gesunde Pflanzen》2004,56(4-5):95-104
Zusammenfassung In den Jahren 1999 bis 2003 wurde in Freiland-, Klimakammer- und Lagerungsversuchen überprüft, ob ein Risiko für die Übertragung des Erregers der Bakteriellen Ringfäule der Kartoffel (Clavibacter michiganensis ssp. sepedonicus) besteht, wenn (a) gesunde Kartoffelknollen in Kontakt mit Maschinen und Geräten kommen, die mit dem Erreger kontaminiert sind (indirekter Kontakt) und (b) gesunde Kartoffelknollen direkt in Kontakt mit infizierten Knollen kommen (direkter Kontakt). Nach indirektem Kontakt konnte nur beim nachfolgenden Anbau der kontaminierten Knollen in der Klimakammer Befall in Kraut und Knollen festgestellt werden. Im Freiland konnte der Erreger, auch bei wiederholtem Nachbau der geernteten Knollen, nicht nachgewiesen werden. Nach direktem Kontakt und nachfolgendem Anbau der kontaminierten Knollen in der Klimakammer und im Freiland, wurde der Erreger in allen Fällen in den geerntete Knollen nachgewiesen. Befall im Kraut wurde nur in dem Klimakammerversuch und in einem Freilandversuch ermittelt. Wurden durch direkten Kontakt kontaminierte Knollen eingelagert, konnte der Erreger in allen untersuchten Knollen festgestellt werden. Insgesamt besteht ein hohes Risiko, dass gesunde Knollen infiziert werden, wenn oberflächliche Kontaminationen mit dem Erreger erfolgen. Die Wahrscheinlichkeit von Infektionen steigt mit zunehmender Kontaminationsstärke. 相似文献