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1.
Abstract. A series of fertilization experiments was carried out over a 5-yr period in a chalk grassland in Limburg (The Netherlands) as part of a study of the maintenance of species richness in species-rich grasslands. Phosphorus and nitrogen were shown to be the most limiting nutrients. Addition of both elements doubled above-ground production, and species richness dropped ca. 50 % in 0.01-m2 subplots, relative to controls. However, neither the above-ground production nor plant growth-forms were sufficient to explain the observed changes in species richness. Small-scale structural heterogeneity of the vegetation is probably critical for maintaining high levels of richness. Historically, high nitrogen, low phosphorus conditions were rarely encountered in the Dutch landscape and few species appear adapted to these conditions. Among the chalk grassland species, Brachypodiumpinnatum seems well adapted to these conditions, where it dominates and excludes most other species. A detailed understanding of the small-scale processes responsible for maintenance of species richness is critically important in efforts to maintain the biodiversity of natural ecosystems. 相似文献
2.
短花针茅荒漠草原土壤微生物群落组成及结构 总被引:5,自引:0,他引:5
为详细了解内蒙古短花针茅荒漠草原生态系统中土壤微生物群落组成与结构。对其土壤中微生物的总DNA提取后,采用高通量测序技术对土壤中细菌的16Sr DNA和真菌的ITS基因进行了序列测定,分析了短花针茅荒漠草原土壤中微生物群落结构特征。结果表明,共获得细菌OTUs13711个,真菌OTUs 5929个。物种分类显示,细菌种类隶属于29门57纲111目191科485属,其中优势类群为Gammaproteobacteria和Thermoleophilia,它们的相对丰度分别为32.68%和26.83%。真菌隶属于4门16纲45目78科105属,优势类群为Ascomycota和Basidiomycota,它们的相对丰度分别为35.76%和25.90%。土壤中细菌群落的多样性和丰富度均高于真菌。 相似文献
3.
Huaan Yang Jianbo Jian Xuan Li Daniel Renshaw Jonathan Clements Mark W. Sweetingham Cong Tan Chengdao Li 《BMC genomics》2015,16(1)
Background
Molecular marker-assisted breeding provides an efficient tool to develop improved crop varieties. A major challenge for the broad application of markers in marker-assisted selection is that the marker phenotypes must match plant phenotypes in a wide range of breeding germplasm. In this study, we used the legume crop species Lupinus angustifolius (lupin) to demonstrate the utility of whole genome sequencing and re-sequencing on the development of diagnostic markers for molecular plant breeding.Results
Nine lupin cultivars released in Australia from 1973 to 2007 were subjected to whole genome re-sequencing. The re-sequencing data together with the reference genome sequence data were used in marker development, which revealed 180,596 to 795,735 SNP markers from pairwise comparisons among the cultivars. A total of 207,887 markers were anchored on the lupin genetic linkage map. Marker mining obtained an average of 387 SNP markers and 87 InDel markers for each of the 24 genome sequence assembly scaffolds bearing markers linked to 11 genes of agronomic interest. Using the R gene PhtjR conferring resistance to phomopsis stem blight disease as a test case, we discovered 17 candidate diagnostic markers by genotyping and selecting markers on a genetic linkage map. A further 243 candidate diagnostic markers were discovered by marker mining on a scaffold bearing non-diagnostic markers linked to the PhtjR gene. Nine out from the ten tested candidate diagnostic markers were confirmed as truly diagnostic on a broad range of commercial cultivars. Markers developed using these strategies meet the requirements for broad application in molecular plant breeding.Conclusions
We demonstrated that low-cost genome sequencing and re-sequencing data were sufficient and very effective in the development of diagnostic markers for marker-assisted selection. The strategies used in this study may be applied to any trait or plant species. Whole genome sequencing and re-sequencing provides a powerful tool to overcome current limitations in molecular plant breeding, which will enable plant breeders to precisely pyramid favourable genes to develop super crop varieties to meet future food demands.Electronic supplementary material
The online version of this article (doi:10.1186/s12864-015-1878-5) contains supplementary material, which is available to authorized users. 相似文献4.
The carbon use efficiency (CUE) of grassland, a ratio of net primary production (NPP) to gross primary productivity (GPP), is an important index representing the capacity of plants to transfer carbon from the atmosphere to terrestrial biomass. In this study, we used the Moderate Resolution Imaging Spectroradiometer (MODIS) data to calculate the global grassland CUE, and explore the spatiotemporal dynamic of global grassland CUE from 2000 to 2013 to discuss the response to climate variations. The results showed that the average annual CUE of different grassland types follows an order of: open shrublands > non-woody grasslands > closed shrublands > woody savannas > savannas. The higher grassland CUE mainly occurred in the regions with cold and dry climate. By contrast, the regions with the lower grassland CUE were mostly in warm and wet environments. Moreover, the CUE exhibited a globally positive correlation with precipitation and a negative correlation with temperature. Therefore, the grassland CUE has considerable spatial variation associated with grassland type, geographical location and climate change. 相似文献
5.
BRUCE A. ROBERTSON PATRICK J. DORAN LIZ R. LOOMIS J. ROY ROBERTSON DOUGLAS W. SCHEMSKE 《Global Change Biology Bioenergy》2011,3(3):235-246
Federal mandates to increase biofuel production in North America will require large new tracts of land with potential to negatively impact biodiversity, yet empirical information to guide implementation is limited. Because the temperate grassland biome will be a production hotspot for many candidate feedstocks, production is likely to impact grassland birds, a group of major conservation concern. We employed a multiscaled approach to investigate the relative importance of arthropod food availability, microhabitat structure, patch size and landscape‐scale habitat structure and composition as factors shaping avian richness and abundance in fields of one contemporary (corn) and two candidate cellulosic biomass feedstocks (switchgrass and mixed‐grass prairie) not currently managed as crops. Bird species richness and species density increased with patch size in prairie and switchgrass, but not in corn, and was lower in landscapes with higher forest cover. Perennial plantings supported greater diversity and biomass of arthropods, an important food for land birds, but neither metric was important in explaining variation in the avian community. Avian richness was higher in perennial plantings with greater forb content and a more diverse vegetation structure. Maximum bird species richness was commonly found in fields of intermediate vegetation density and grassland specialists were more likely to occur in prairies. Our results suggest that, in contrast to corn, perennial biomass feedstocks have potential to provide benefits to grassland bird populations if they are cultivated in large patches within relatively unforested landscapes. Ultimately, genetic improvement of feedstock genets and crop management techniques that attempt to maximize biomass production and simplify crop vegetation structure will be likely to reduce the value of perennial biomass plantings to grassland bird populations. 相似文献
6.
Drought is frequently recorded as a result of climate warming and elevated concentration of greenhouse gases, which affect the carbon and water cycles in terrestrial ecosystems, particularly in arid and semi-arid regions. To identify the drought in grassland ecosystems and to determine how such drought affects grassland ecosystems in terms of carbon and water cycles across the globe, this study evaluated the drought conditions of global grassland ecosystems from 2000 to 2011 on the basis of the remotely sensed Drought Severity Index (DSI) data. The temporal dynamics of grassland carbon use efficiency (CUE) and water use efficiency (WUE), as well as their correlations with DSI, were also investigated at the global scale. Results showed that 57.04% of grassland ecosystems experienced a dry trend over this period. In general, most grassland ecosystems in the northern hemisphere (N.H.) were in near normal condition, whereas those in the southern hemisphere (S.H.) experienced a clear drying and wetting trend, with the year 2005 regarded as the turning point. Grassland CUE increased continually despite the varied drought conditions over this period. By contrast, WUE increased in the closed shrublands and woody savannas but decreased in all the other grassland types. The drought conditions affected the carbon and water use mainly by influencing the primary production and evapotranspiration of grass through photosynthesis and transpiration process. The CUE and WUE of savannas was most sensitive to droughts among all the grassland types. The areas of grassland DSI that showed significant correlations with CUE and WUE were 52.92% and 22.11% of the total grassland areas, respectively. Overall, droughts sufficiently explained the dynamics of grassland CUE, especially in the S.H. In comparison with grassland CUE, the grassland WUE was less sensitive to drought conditions at the global scale. 相似文献
7.
人工榆树林对温带草原植物多样性的影响 总被引:1,自引:0,他引:1
在样线和样方调查的基础上,研究了内蒙古四子王旗人工榆树林对温带草原物种多样性的影响.结果表明:榆树林对草原的物种多样性有明显影响.随榆树林树木密度的提高,林下草本植物的丰富度、均匀度和多样性等指数均呈降低趋势.靠近榆树林的草原群落的物种丰富度、均匀度和多样性等指数高于远离榆树林的草原群落.喜生于树林内部的草本植物有旱麦瓶,喜生于榆树林周边草原的草本植物有阿尔泰狗娃花、扁蓄豆、二裂委陵菜、赖草和糙隐子草等.可见,盲目排斥草原地区造林并非科学之举,应选择土壤水分相对丰富的地段营造适当规模的人工林,以促进草原地区的植物多样性保护. 相似文献
8.
The biogenic volatile organic compounds (VOC) emitted by the vegetation of a terrestrial ecosystem play a key role in both regional air quality and tropospheric chemistry. To describe the general emission properties of VOC of different plant functional groups (PFG) in a typical temperate grassland in Inner Mongolia, China, we randomly selected 175 plant species and measured the quantities of isoprene and monoterpene in situ. Results showed that most plants had low VOC emission potential at the species level,especially for some dominant plants, such as Leymus chinensis Tzvel., Stipa grandis Smirn., and Agropyron cristatum Gaertn. At the PFG level, the lowest VOC emission potential was found for perennial rhizome grasses, a major PFG in a typical temperate grassland ecosystem. The effects of overgrazing and subsequent vegetation succession on the emission of VOC by different plant life form functional groups (PLFG)were also discussed. 相似文献
9.
草原畜牧业温室气体排放现状、问题及展望 总被引:2,自引:0,他引:2
草原畜牧业生产系统是一个涉及环境、经济、社会多层面、且系统内部气候-土壤-草地-家畜-管理之间相互作用的复杂的社会生态系统。草原不仅为人类提供所需要的肉奶,也提供了多种生态系统服务。然而,草原畜牧业也是主要的温室气体排放源之一。减缓畜牧业温室气体排放的研究已成为当前气候变化科学研究关注的焦点。综述了国内外草原畜牧业温室气体排放研究现状,指出现有研究的不足主要集中在以下3个方面:(1)虽然生命周期评价方法广泛应用于草原畜牧业温室气体排放研究,但是存在诸多问题,导致目前的研究框架体系尚不完善,特别体现在以下几方面:是否考虑外部输入、是否考虑土壤有机碳、畜牧业温室气体排放强度指标的选择等;(2)缺乏单一环节减缓措施对草原畜牧业整体温室气体减排效果的研究;(3)目前对影响草原畜牧业温室气体排放强度的因素主要集中在生态系统层面的分析,忽略了社会系统的作用,无法反映社会系统与生态系统的相互反馈机制,导致机制阐释不完善。综上所述,未来仍需从以下三方面开展研究:(1)完善草原畜牧业研究框架体系及提升研究方法;(2)加强对单一环节减缓措施对草原畜牧业温室气体整体减排效果的综合评价;(3)基于社会生态系统的角度深入研究影响草原畜牧业温室气体排放强度差异的机制。一方面,这有助于深入理解草原畜牧业温室气体排放强度情况,也为低碳型草原畜牧业发展政策的制定提供思路借鉴;另一方面对于科学合理的可持续利用草场和恢复草地生态环境均具有重要意义。 相似文献
10.
Yves Bawin Tom Ruttink Ariane Staelens Annelies Haegeman Piet Stoffelen Jean-Claude Ithe Mwanga Mwanga Isabel Roldán-Ruiz Olivier Honnay Steven B. Janssens 《植物分类学报:英文版》2021,59(5):953-963
Interspecific hybridization events have played a major role in plant speciation, yet the evolutionary origin of hybrid species often remains enigmatic. Here, we inferred the evolutionary origin of the allotetraploid species Coffea arabica, which is widely cultivated for Arabica coffee production. We estimated genetic distances between C. arabica and all species that are known to be closely related to C. arabica using genotyping-by-sequencing (GBS) data. In addition, we reconstructed a time-calibrated multilabeled phylogenetic tree of 24 species to estimate the age of the C. arabica hybridization event. Ancestral states of self-compatibility were also inferred to shed new light on the evolution of self-compatibility in Coffea. Coffea canephora and C. eugenioides were confirmed as the putative progenitor species of C. arabica. These species most likely hybridized between 1.08 million and 543 000 years ago, coinciding with periods of environmental upheaval, which may have induced range shifts of the progenitor species that facilitated the emergence of C. arabica. 相似文献
11.
Contrasting changes in the abundance and diversity of North American bird assemblages from 1971 to 2010
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Aafke M. Schipper Jonathan Belmaker Murilo Dantas de Miranda Laetitia M. Navarro Katrin Böhning‐Gaese Mark J. Costello Maria Dornelas Ruud Foppen Joaquín Hortal Mark A. J. Huijbregts Berta Martín‐López Nathalie Pettorelli Cibele Queiroz Axel G. Rossberg Luca Santini Katja Schiffers Zoran J. N. Steinmann Piero Visconti Carlo Rondinini Henrique M. Pereira 《Global Change Biology》2016,22(12):3948-3959
Although it is generally recognized that global biodiversity is declining, few studies have examined long‐term changes in multiple biodiversity dimensions simultaneously. In this study, we quantified and compared temporal changes in the abundance, taxonomic diversity, functional diversity, and phylogenetic diversity of bird assemblages, using roadside monitoring data of the North American Breeding Bird Survey from 1971 to 2010. We calculated 12 abundance and diversity metrics based on 5‐year average abundances of 519 species for each of 768 monitoring routes. We did this for all bird species together as well as for four subgroups based on breeding habitat affinity (grassland, woodland, wetland, and shrubland breeders). The majority of the biodiversity metrics increased or remained constant over the study period, whereas the overall abundance of birds showed a pronounced decrease, primarily driven by declines of the most abundant species. These results highlight how stable or even increasing metrics of taxonomic, functional, or phylogenetic diversity may occur in parallel with substantial losses of individuals. We further found that patterns of change differed among the species subgroups, with both abundance and diversity increasing for woodland birds and decreasing for grassland breeders. The contrasting changes between abundance and diversity and among the breeding habitat groups underscore the relevance of a multifaceted approach to measuring biodiversity change. Our findings further stress the importance of monitoring the overall abundance of individuals in addition to metrics of taxonomic, functional, or phylogenetic diversity, thus confirming the importance of population abundance as an essential biodiversity variable. 相似文献
12.
藏北地区生态与环境敏感性评价 总被引:5,自引:0,他引:5
藏北地区自然条件极为严酷,生态与环境非常脆弱和敏感。采用地理信息系统手段与综合评价方法,对藏北地区主要生态与环境敏感性问题进行评估,分析了土壤侵蚀、沙漠化和草地退化等方面的敏感性空间分异规律,指出了今后生态与环境建设的优先区域。结果表明:藏北地区土壤侵蚀敏感区占土地总面积的42.5%,主要分布于东中部区域;藏北地区沙漠化敏感区面积较大(占土地总面积的78.8%),主要分布在人类活动强度相对较低的西北部;藏北中东部和北部地区草地退化较为严重,尤其是藏北地区冰川与雪山及其周围等气候变化较为敏感区域和交通要道沿线等人类活动较为频繁区域的草地退化相对严重,对草地退化也比较敏感,是今后草地退化治理和恢复的优先区。 相似文献
13.
内蒙古锡林郭勒盟草原产草量动态遥感估算 总被引:6,自引:0,他引:6
草原产草量的监测是草地资源空间动态研究的重要衡量指标,是草地资源合理利用和载畜平衡监测的重要依据.基于371个样地调查数据和2005~2009年的MODIS-NDVI遥感数据,建立地面样方的产草量与遥感数据的关系模型,模拟分析了内蒙古锡林郭勒盟草原产草量的时空分布.结果表明:(1)建立的各模型方程均有较好的相关关系,其中幂函数的相关关系最优,通过预留样方数据的验证,模型精度为78%,幂函数模型作为遥感估测应用可行;(2)锡林郭勒盟草原的产草量5年平均为3455万吨,折合干草总量为1112万吨,平均单产为567.23kg/hm2,草原产草量的空间分布呈东高西低的格局;(3)2005~2009年,锡林郭勒盟草原产草量有明显的波动,干草变化范围为800~1400万吨,变异系数为20.42%;(4)不同草地类型的产草量及其年际间变化存在较大的差异,荒漠类草原产草量低,年际间变化较大;草甸类草原产草量高,年际间变化相对较小.草原产草量的时空变化还与降水量、气温等主要气候因素关系密切,特别是受降水量的时空变化影响显著.研究结果可以为中国草地资源的保护及合理利用提供参考依据. 相似文献
14.
Pattern and process in above-ground and below-ground components of grassland ecosystems 总被引:1,自引:0,他引:1
Abstract. This paper describes patterns of below-ground components in grassland ecosystems. It provides estimates of the contribution of below-ground organs to the total phytomass of the community and of different species to the below-ground phytomass; it describes the distribution of above- and below- ground organs of different species and the spatial and temporal correlation between above-ground and below-ground phyto-mass – both total standing crop and net primary production. 10 Siberian grasslands (meadows and steppes) were investigated during 15 yr. Ca. 70 % of the living phytomass is located in the soil and no less than 70 % of the net primary production is allocated in below-ground organs. Phytomass distribution in the soil layer is more homogeneous than above-ground. For some species the spatial distribution within 1-m2 plots of the green and below-ground phytomass is similar, for others it is quantitatively or qualitatively different. According to the dominance-diversity curve, the above-ground size hierarchy is much stronger than the below-ground one. The active growth of above- and below-ground organs of a species may occur at different times of the season and it varies from year to year. Allocation of organic substances to rhizomes and roots occurs simultaneously and with proportional intensity. 相似文献
15.
EP-1 不育剂对长爪沙鼠野生种群增长的控制作用 总被引:2,自引:0,他引:2
长爪沙鼠在内蒙古地区的分布非常广泛,长期以来由其造成的“鼠害” 不仅给农牧业生产带来危害,而且还传播疾病。2009 年3 ~ 10 月,在内蒙古鄂尔多斯荒漠草原,利用复合不育剂左炔诺孕酮- 炔雌醚(EP-1)
对长爪沙鼠野生种群进行了不育控制试验研究。结果表明,复合不育剂EP-1 对长爪沙鼠种群结构和种群密度均有显著影响,在5 月和6 月两个繁殖高峰期,不育剂EP-1 显著降低了幼体出生的数量,实验区与对照区幼体组
成差异和成体组成差异均达到极显著(P < 0.01)。在8 ~ 10 月,实验区和对照区种群结构组成中,幼体之间、成体之间差异均达到显著和极显著(P < 0.05, P < 0.01)。在整个发育生长期,实验区长爪沙鼠幼体种群从6 月
份开始出现,9 月达到数量最高值,幼体种群全年呈现下降趋势。而对照区幼体种群从5 月份开始出现,且数量在5 月份达到全年的最高值,幼体种群与实验区相反呈增长趋势。实验区种群总体数量全年呈下降趋势,而对
照区相反,呈增长趋势。因此,复合不育剂EP-1 显著降低了长爪沙鼠种群的繁殖率、幼体出生比例和种群密度,可以对长爪沙鼠野生种群起到有效的繁殖控制作用,进而降低该鼠对农牧业生产的危害和对人类疾病传播
的风险。 相似文献
对长爪沙鼠野生种群进行了不育控制试验研究。结果表明,复合不育剂EP-1 对长爪沙鼠种群结构和种群密度均有显著影响,在5 月和6 月两个繁殖高峰期,不育剂EP-1 显著降低了幼体出生的数量,实验区与对照区幼体组
成差异和成体组成差异均达到极显著(P < 0.01)。在8 ~ 10 月,实验区和对照区种群结构组成中,幼体之间、成体之间差异均达到显著和极显著(P < 0.05, P < 0.01)。在整个发育生长期,实验区长爪沙鼠幼体种群从6 月
份开始出现,9 月达到数量最高值,幼体种群全年呈现下降趋势。而对照区幼体种群从5 月份开始出现,且数量在5 月份达到全年的最高值,幼体种群与实验区相反呈增长趋势。实验区种群总体数量全年呈下降趋势,而对
照区相反,呈增长趋势。因此,复合不育剂EP-1 显著降低了长爪沙鼠种群的繁殖率、幼体出生比例和种群密度,可以对长爪沙鼠野生种群起到有效的繁殖控制作用,进而降低该鼠对农牧业生产的危害和对人类疾病传播
的风险。 相似文献
16.
新疆巴音布鲁克草原白蘑蘑菇圈土壤真菌多样性分析 总被引:1,自引:0,他引:1
【背景】新疆巴音布鲁克草原为我国第二大高山草原,草原上生长的白蘑(Tricholoma mongolicum Imai)属于口蘑属(Tricholoma)的一种,可形成典型的蘑菇圈。【目的】了解巴音布鲁克草原白蘑蘑菇圈圈上及其两侧土壤真菌的物种组成和群落结构特点,为研究白蘑蘑菇圈的形成与生长及其子实体的发生提供一定的理论依据。【方法】采用Illumina HiSeq平台高通量测序技术研究白蘑蘑菇圈周围土壤真菌的物种组成丰富度和菌群结构多样性。【结果】测定有效序列经注释得到809个操作分类单元(Optical taxonomic unit,OTU),分为5个门、26个纲、79个目、166个科、232个属;蘑菇圈上土壤真菌的物种丰富度、群落结构多样性以及特异性物种均低于圈外及圈内,蘑菇圈上特有真菌物种为Xylodonnothofagi、Agaricales、Phaeococcomyces、Ochrocladosporium adansoniae、Coniochaeta ligniaria、未知子囊菌、 Tomentella amyloapiculata、 Dothideomycetes、Incertea_sedis_Helotiales。【结论】研究表明白蘑蘑菇圈的形成影响土壤真菌的分布,圈上优势真菌类群对其他真菌类群具有抑制作用,蘑菇圈向外生长可能与微生物群落结构失衡有关。 相似文献
17.
Jacqueline Loos Ine Dorresteijn Jan Hanspach Pascal Fust László Rakosy Joern Fischer 《PloS one》2014,9(7)
European farmland biodiversity is declining due to land use changes towards agricultural intensification or abandonment. Some Eastern European farming systems have sustained traditional forms of use, resulting in high levels of biodiversity. However, global markets and international policies now imply rapid and major changes to these systems. To effectively protect farmland biodiversity, understanding landscape features which underpin species diversity is crucial. Focusing on butterflies, we addressed this question for a cultural-historic landscape in Southern Transylvania, Romania. Following a natural experiment, we randomly selected 120 survey sites in farmland, 60 each in grassland and arable land. We surveyed butterfly species richness and abundance by walking transects with four repeats in summer 2012. We analysed species composition using Detrended Correspondence Analysis. We modelled species richness, richness of functional groups, and abundance of selected species in response to topography, woody vegetation cover and heterogeneity at three spatial scales, using generalised linear mixed effects models. Species composition widely overlapped in grassland and arable land. Composition changed along gradients of heterogeneity at local and context scales, and of woody vegetation cover at context and landscape scales. The effect of local heterogeneity on species richness was positive in arable land, but negative in grassland. Plant species richness, and structural and topographic conditions at multiple scales explained species richness, richness of functional groups and species abundances. Our study revealed high conservation value of both grassland and arable land in low-intensity Eastern European farmland. Besides grassland, also heterogeneous arable land provides important habitat for butterflies. While butterfly diversity in arable land benefits from heterogeneity by small-scale structures, grasslands should be protected from fragmentation to provide sufficiently large areas for butterflies. These findings have important implications for EU agricultural and conservation policy. Most importantly, conservation management needs to consider entire landscapes, and implement appropriate measures at multiple spatial scales. 相似文献
18.
Alejandro Loydi Kerstin Lohse Annette Otte Tobias W. Donath R. Lutz Eckstein 《Journal of Plant Ecology》2014,7(3):264
Aims After abandonment of grasslands, secondary succession leads to the invasion by woody species. This process begins with the accumulation of tree litter in the forest–grassland ecotone. Our objectives were to determine the relationships between litter amounts and vegetation composition and cover along natural forest–grassland ecotones and to experimentally study the initial effects of tree litter accumulation on grassland vegetation and on microsite conditions.Methods We established 11 transects varying from 12 to 15 m in length in different forest–grassland ecotones in the Lahn-Dill highlands, Germany, and measured the mass and cover of tree litter and the cover and composition of vegetation at five sequential positions along each transect by using 1 m 2 plots with five replications. In a field experiment, we established plots subjected to different litter amounts (0, 200 and 600g m ?2) and evaluated changes in grassland vegetation, soil temperature and soil nutrient availability below the litter layer.Important findings Tree litter amounts decrease from 650 to 65g m ?2 across the forest–grassland ecotone. Vegetation changed from shrubs and annual species (adapted to more stressful conditions) in the forests edge to grasses, rosettes and hemirosette species (with higher competitive abilities) in the grassland. These anthropogenic forest–grassland ecotones showed abrupt edges, and the two adjacent ecosystems were characterized by different species pools and functional groups. In the field experiment, the presence of a litter layer reduced vegetation biomass and cover; the species richness was only reduced in the treatment with high litter (600g m ?2). Additionally, adding litter on top of vegetation also reduced thermal amplitude and the number of frost days, while increasing the availability of some nutrients, such as nitrogen and aluminium, the latter being an indicator of soil acidification. Adding a tree litter layer of 600g m ?2 in grassland areas had strong effects on the composition and diversity of grassland vegetation by reducing the cover of several key grassland species. In, or near, forest edges, litter accumulation rapidly changes established vegetation, microsite conditions and soil nutrients. 相似文献
19.
如何满足草原野生有蹄类调查方法的假设前提条件 总被引:5,自引:2,他引:5
虽然调查草原有蹄类有许多方法,但考察中必须对有关方法进行修正。本文描述了笔者在青海省野牛沟调查3种草原有蹄类动物时,为满足样线法的假设前提而采取的具体措施。笔者建议,无论采用何种统计方法,都应当认真研究该方法的假设前提,并在研究报告中说明为满足假设而作出的细节安排。 相似文献
20.
Phytolith‐occluded carbon (PhytOC) is an important long‐term stable carbon fraction in grassland ecosystems and plays a promising role in global carbon sequestration. Determination of the PhytOC traits of different plants in major grassland types is crucial for precisely assessing their phytolith carbon sequestration potential. Precipitation is the predominant factor in controlling net primary productivity (NPP) and species composition of the semiarid steppe grasslands. We selected three representative steppe communities of the desert steppe, the dry typical steppe, and the wet typical steppe in Northern Grasslands of China along a precipitation gradient, to investigate their species composition, biomass production, and PhytOC content for quantifying its long‐term carbon sequestration potential. Our results showed that (a) the phytolith and PhytOC contents in plants differed significantly among species, with dominant grass and sedge species having relatively high contents, and the contents are significantly higher in the below‐ than the aboveground parts. (b) The phytolith contents of plant communities were 16.68, 17.94, and 15.85 g/kg in the above‐ and 86.44, 58.73, and 76.94 g/kg in the belowground biomass of the desert steppe, the dry typical steppe, and the wet typical steppe, respectively; and the PhytOC contents were 0.68, 0.48, and 0.59 g/kg in the above‐ and 1.11, 0.72, and 1.02 g/kg in the belowground biomass of the three steppe types. (c) Climatic factors affected phytolith and PhytOC production fluxes of steppe communities mainly through altering plant production, whereas their effects on phytolith and PhytOC contents were relatively small. Our study provides more evidence on the importance of incorporating belowground PhytOC production for estimating phytolith carbon sequestration potential and suggests it crucial to quantify belowground PhytOC production taking into account of plant perenniality and PhytOC deposition over multiple years. 相似文献