Nested spatial biodiversity patterns of nematode genera in a New Zealand forest and pasture soil     

Christien H EttemaGregor W Yeates 《Soil biology & biochemistry》2003,35(2):339-342

Biodiversity has a spatial dimension, which we estimated by examining generic turnover (beta diversity) of nematodes in adjacent forest and pasture sites. Dissimilarity was estimated in small and intermediate scale transects, the distribution of sampling points being determined by spatial simulated annealing. On an average, the forest yielded fewer nematodes per 24 mm dia 0-10 cm deep core than did pasture (435 vs 2818) but more genera (23.7 vs 19.1). Dissimilarity analysis suggests generic turnover is higher in forest than pasture, at both scales. At the small scale both communities have comparable dissimilarities up to 0.6 m, but only in forest does increasing distance increase dissimilarity. At the intermediate scale no spatial structure was apparent in the pasture nematode community, but in forest dissimilarity increased with distance, with no plateau. Quantifying the difference in spatial patterns between ecosystems illustrates the utility of geostatistical methods for addressing soil biodiversity.  相似文献   

制备竹LYOCELL纤维对原料竹浆的要求   总被引：1，自引：0，他引：1  

蒋应梯  许炯 《竹子研究汇刊》2005,24(2):41-43,52

简要介绍了竹Lyocell纤维的制备原理和工艺,阐述了原料竹纤维素的聚合度对其在氧化甲基吗啉溶剂中溶解性能的影响,介绍了制取竹Lyocell纤维的竹浆原料的精制纯化方法,并提出制备竹Lyocell纤维对竹浆原料--竹纤维素的要求.  相似文献   

福建柏人工林天然更新的幼株空间分布格局     

李大岔  盖新敏 《福建林业科技》2001,(Z1)

根据比较频次法、聚集度指标法对福建省宁德福口国有林场福建柏人工林天然更新的幼株空间分布格局进行研究。结果表明其分布呈聚集分布。这一结果有助于探讨建柏林的天然更新理论 ,而且对建柏林的经营管理也具有一定的意义。  相似文献   

Platelets in equine recurrent airway obstruction     

Hammond A  Bailey SR  Marr CM  Cunningham FM 《Research in veterinary science》2007,82(3):332-334

Platelets contribute to the pathogenesis of human allergic airway disease. The aim of this study was to compare platelet activating factor (PAF)-induced platelet aggregation and thromboxane (Tx) production, plasma Tx and 5-hydroxytryptamine (5-HT) in ponies with recurrent airway obstruction (RAO), an hypersensitivity to inhaled antigens, and normal ponies, before and after antigen exposure. Plasma 5-HT was significantly higher in ponies with RAO but was not further increased by antigen challenge. There was no difference between PAF-induced platelet aggregation or Tx production, or in plasma Tx before or after challenge. These data suggest there may be a difference between platelet 5-HT uptake in RAO and normal ponies but do not provide evidence of platelet activation following antigen exposure.  相似文献   

A quantification of short-term macroaggregate dynamics: influences of wheat residue input and texture     

Steven De Gryze  Johan Six  Roel Merckx 《Soil biology & biochemistry》2005,37(1):55-66

Soil structure and soil aggregation play an important role in an array of processes such as soil erodibility, organic matter protection and soil fertility. Modeling attempts of these processes would benefit substantially from including soil structural parameters such as soil aggregation. However, quantitative data on soil structural dynamics is lacking. Therefore, we conducted short-term (3 weeks) incubations to acquire necessary soil structural parameters for modeling purposes. Prior to incubation, all structures >53 μm were destroyed from three soils with varying texture but under similar management. Five different amounts of wheat residue, ranging from 0 to 3 wt%, were added to each of these soils. After 3 weeks, samples were analyzed for large water-stable macroaggregates (>2000 μm) using a wet sieving method and for fungal growth using epifluorescence microscopy. Aggregate formation increased linearly with increasing amounts of residue at a rate of 12.0±1.24 g aggregates g⁻¹ residue added. We found no differences in aggregate formation among the three soils, even though the equilibrium level of macroaggregates differed in the field. While amounts of water-stable macroaggregates in the sandy loam and the silt loam soil corresponded well with fungal lengths, this was not the case for the silty clay loam soil. This suggests that fungi are less important in aggregate formation in more clayey soils. Cumulative respiration correlated well (r=0.89-0.91) with water-stable macroaggregates for all three soils. A model assuming an aggregate formation rate proportional to the respiration rate was very successful in fitting the measured aggregate amounts. This model predicted about 65% of the changes in aggregation when different amounts were added, and about 85% of the changes in aggregation over time. This model yielded a macroaggregate turnover time of 40-60 days. The quantitative results presented here can directly be incorporated into models describing and predicting soil aggregate dynamics, as a determining factor for physical protection of organic matter within a soil.  相似文献   

Influence of FGD Gypsum on the Properties of a Highly Erodible Soil under Conservation Tillage     

《Communications in Soil Science and Plant Analysis》2012,43(16):2012-2023

Surface application of agricultural lime and fertilizers in no-till (NT) systems can be inadequate because of the excess time required for slowly soluble lime to improve soil aggregation such that water and nutrients move more rapidly into and down the soil profile. This study used fluidized gas desulfurization (FGD) gypsum as an alternative to lime because of its greater solubility and calcium (Ca) and sulfur (S) contents. Gypsum was applied to NT cotton (Gossypium hirsutum L.) plots at rates of 0, 2.24, 4.48, and 6.72 Mg ha^?1 for 3 years. After 1 year, Ca, S, and soil aggregation increased significantly (P ≤ 0.05) while exchangeable aluminum (Al) activities were reduced. These results indicate that FGD gypsum can increase NT cotton yields by increasing infiltration and soil water contents, reducing runoff, ameliorating exchangeable Al problems, and by providing a readily available source of S, a limiting nutrient in many cotton soils.  相似文献   

Monitoring the variation of soil quality with sewage sludge application rates in absence of rhizosphere effect     

《国际水土保持研究(英文)》2020,8(3):245-252

Agricultural soils in semi-arid regions have frequently been degraded due to adverse climatic conditions, organic matter depletion, and poor farming practices. To enhance soil quality, this study examines the reuse of sewage sludge (SS) as an available source of organic matter in a typical Mediterranean sandy-loam soil. Accordingly, we studied the cumulative effect of two annual applications of 40, 80 and 120 tons of sludge per ha on soil quality in absence of vegetation. The dose-dependent improvement of organic matter content was the most significant event that reflected sludge application rates, and consequently influenced other soil properties. Accordingly, soil structural stability increased by 13.3%, 28.8% and 59.4% for treatments SS-40, SS-80 and SS-120 respectively as compared to unamended control. Structural stability improvement was also confirmed by the dose-dependent variation of other edaphic factors including calcium content, the microbial quotient as well as Welt and C:N ratios. These parameters are involved in cementing soil aggregates by cation bridging, the formation of microbial mucilage, and clay-humic complexes. Soil magnetic susceptibility (SMS) was measured in situ as a possible rapid tool to evaluate soil condition. SMS showed significant correlation with sludge dose and stability amelioration testifying to the aggregation role that can play Al₂O₃ and particularly Fe₂O₃ minerals added by the hematite-rich sludge. Besides, analytical results and field observations revealed no trends of soil salinization or acidification by excessive sludge amounts. By avoiding the rhizosphere effect, outcomes could reflect the resilience and intrinsic capacity of the soil to cope with excessive sludge loads.  相似文献   

Spatial distribution of Collembola in presence and absence of a predator     

Ilaria Negri 《Pedobiologia》2004,48(5-6):585-588

Many Collembola species are characterised by an aggregative behaviour, which is closely related to communication and co-ordination between individuals. In spite of a general heavy predation pressure, a large number of Collembola is found in soil suggesting that they have developed defence strategies against predators.

This study investigates changes in spatial structure of gregarious Collembola species in presence of a predator. It is analysed if the gregarious lifestyle of Collembola populations functions as a defence strategy against predation. In presence of a predator distances between individuals in the Collembola species Folsomia candida and Heteromurus tetrophthalmus became closer, reducing the risk of individuals to be captured by predators. On the contrary, Onychiurus sinensis specimens, which were never caught probably because of the extrusion of repelling fluids by means of their pseudocelli, moved away from each another. Besides being a successful chemical defence against predation, repelling fluid secretion may effectively repel conspecifics, thereby keeping individuals at greater distance.  相似文献   

稻瘿蚊对水稻为害空间格局和抽样技术初步研究   总被引：1，自引：0，他引：1  

黄凤宽  罗善昱 《华南农业大学学报》1993,14(3):48-54

本文应用10个聚集度指标分析了不同时期稻瘿蚊为害株的空间格局,用Fuzzy聚类分析法测定空间格局的时序状态,并对田间抽样技术进行了探讨.结果表明:田间受害株密度不超过3株/丛时,受害株的空间格局是聚集型的;超过3株/丛时,则为均匀型的;受害株分布的基本成分是个体群,基本成分的分布是聚集型的;不同时期的为害株的空间格局可归纳为低密度前期和高密度后期两大类;田间的最适抽样部位是水稻的分蘖株;为害株的Iwao和改进的Iwao序贯抽样模型分别是: T′_0(n)=0.15n+t·(0.18n)~(1/2);T″_0(n)=0.15n-t·(0.18n)~(1/2) 和T′_0(n)=0.15n+t·(0.1342n)~(1/2);T″_0(n)=0.15n-t·(0.1342n)~(1/2)式中,T′_0(n),T″_0(n)分别为序贯抽样过程中累计标葱数的上限和下限;n为序贯抽样数;t为在给定的显著性水平下的t分布值.  相似文献   

桉蝙蛾幼虫空间分布型的研究、   总被引：1，自引：0，他引：1  

曹书阁  庞正轰  杨秀好  于永辉  丘润清 《安徽农业科学》2011,(19):11492-11495

[目的]研究桉蝙蛾幼虫的空间分布型。[方法]通过对广西北流市和陆川县等地的桉树人工林进行幼虫分布调查,共设10块标准地,采用6种不同的聚集度指标和回归模型分析法判断桉蝙蛾幼虫的空间分布格局。[结果]桉蝙蛾幼虫主要分布在1m以下树干基部;按蝙蛾幼虫的空间分布型主体为聚集分布,是环境因素的作用结果。桉蝙蛾幼虫在不同虫口密度下最适抽样数公式n=t2（1.1/m＋0.6744）/D2和序贯抽样决策限模式：T’0（n）,T″0（n）=n±1.332槡n（取m0=1）。[结论]研究结果为桉蝙蛾的调查取样和预测预报工作提供了科学依据。  相似文献