Herbaceous layer development during spring does not deplete soil nitrogen in the Portuguese montado     

D.O. Otieno  H. MirzaeiM.Z. Hussain  Y.L. LiM.W.T. Schmidt  M. Wartinger  E. Jung  N. RibeiroJ.S. Pereira  J. Tenhunen 《Journal of Arid Environments》2011,75(3):231-238

Nitrogen (N) content in the soil and in the herbaceous biomass were monitored during spring of 2004-2006 to determine how the herbaceous layer development influences soil N availability in the montado ecosystem of southern Portugal. Highest (246.6 ± 52.7 g m⁻²) and lowest (123.2 ± 89.5 g m⁻²) peak biomass occurred in 2006 and 2005 respectively. Total soil N within the top 20 cm soil profile ranged between 0.2 ± 0.1% in February and 0.41 ± 0.2% in May, while available soil N was lowest (5 ± 2 μg g⁻¹soil) in February but increased three-to-five fold in March and was >17.5 μg g⁻¹soil at senescence in May. Significant (p < 0.001) increase in total N in the aboveground pool occurred between February and May. There was however, no decay in soil N content. Instead, the herbaceous vegetation enhanced soil N input and N retention in the ecosystem. Most of the herbaceous plants were annuals with large reserves of organic N at senescence, which returned to the soil as detritus. The herbaceous vegetation is a critical component of the montado that contributes to N recharge and cycling within the ecosystem.  相似文献   

Influence of livestock on the regeneration of fodder trees along ephemeral rivers of Namibia     

P.M. Moser-Nørgaard  M. Denich 《Journal of Arid Environments》2011,75(4):371-376

Faidherbia albida and Acacia erioloba (Mimosoideae) are important fodder trees for livestock and wildlife along the westward flowing ephemeral rivers of the Namib Desert. Together with other, mainly woody vegetation, F. albida and A. erioloba line these rivers and present a linear oasis in a resource poor environment. For centuries nomadic to semi-nomadic inhabitants seasonally utilised the resources of these ephemeral rivers to survive in the otherwise harsh desert environment. In the past decades, more permanent settlements were established along these rivers, with small stock subsistence farmers making a living from the available resources. Livestock (mainly goats) usually moves freely around, feeding on the available vegetation.This study investigated the influence of free moving animals on the regeneration and recruitment of F. albida and A. erioloba along the Kuiseb ephemeral river. It was found that a large numbers of recently emerged seedlings were removed soon after germination. In addition, tree densities of adult versus juvenile individuals differed in areas with large numbers of livestock. The overall height increase and health of juvenile plants were influenced negatively by browsing livestock. In general, browsing pressure differed spatially and was higher close to the main water channel.  相似文献   

Positive plant interactions in the Iberian Southeast: Mechanisms, environmental gradients, and ecosystem function     

F.I. Pugnaire  C. Armas  F.T. Maestre 《Journal of Arid Environments》2011,75(12):1310-1320

Semi-arid ecosystems are privileged sites to address the effects of plant interactions on community structure and dynamics because environmental conditions are demanding and may change quickly, altering in significant ways the balance between positive and negative effects among neighboring plants. Plant interaction processes have been well documented in the semi-arid region of Southeast Spain over the last 15 years. In this article we review the growing body of research on plant–plant interactions available from this area, highlighting its importance in increasing our knowledge on this field of study. This review has been organized in five sections, i) facilitation mechanisms; ii) the nurse effect; iii) the balance of interactions and environmental, ontogenic, temporal, and spatial gradients; iv) the effects of facilitation on biodiversity; and, v) facilitation and ecosystem functioning. Mechanisms of facilitation in these systems are relatively well known, but not completely explored. In these environments competition, mainly for water, is intense between neighbors and switches in intensity from belowground to aboveground as productivity increases. By contrast, facilitation may decrease quickly with increasing productivity, although the balance between facilitation and competition is not fully understood, and is further complicated because shifts can also be driven by factors such as life history or physiology of interacting species. Positive interactions are critical for maintaining biodiversity in some ecosystems in SE Spain, but their role as a driver of ecosystem functioning is less clear. Research on plant–plant interactions in this region has been highly influential and has contributed to our overall understanding of plant community dynamics. Despite the important progress achieved during the last 15 years, there is still substantial scope for exploring the effects of plant interactions at the ecosystem level, and their role as modulators of disturbances such as the current global environmental change.  相似文献   

衡水市滏阳河景观带植被配置分析     

刘红霞  李惠欣 《湿地科学与管理》2015,11(2):12-14

调查了衡水滏阳河岸景观带植被配置现状,在剖析景观带植被配置优势和问题的基础上,从适地适树,丰富季相景观,注重种植密度及乔灌藤花草合理搭配等方面提出了改进措施,以促进本区植被配置优化,充分发挥河岸植被的生态效益和社会效益。  相似文献   

Simulation and Validation of the Aerosol Optical Thicknessover China in 2006     

ZHANG Hu  ZHANG Min  CUI Zhenlei  WANG Yuesi  XIN Jinyuan 《Acta Meteorologica Sinica》2012,26(3):330-344

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Seasonal Dynamics of Rhizosphere Soil Microbial Abundances and Enzyme Activities under Different Vegetation Types in the Coastal Zone,Shandong, China          下载免费PDF全文

Gang Xu  Peng Chen  Jun‐Na Sun  Hong‐Bo Shao 《洁净——土壤、空气、水》2014,42(8):1115-1120

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Adsorption Kinetics of Acid Dye Acid Red 88 onto Magnetic Multi‐Walled Carbon Nanotubes‐Fe3C Nanocomposite          下载免费PDF全文

Wojciech Konicki  Iwona Pełech  Ewa Mijowska  Izabella Jasińska 《洁净——土壤、空气、水》2014,42(3):284-294

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Impact of a Phosphate Solubilizing Bacterium and an Arbuscular Mycorrhizal Fungus (Glomus etunicatum) on Growth,Yield and P Concentration in Wheat Plants          下载免费PDF全文

Jyoti Saxena  Minaxi  Anamika Jha 《洁净——土壤、空气、水》2014,42(9):1248-1252

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湖泊沉积物中元素相态的连续提取分析--以岱海为例   总被引：7，自引：1，他引：6  

金章东  邹成娟  李福春  王苏民  沈吉  梁文波 《湖泊科学》2005,17(1):47-53

如何利用湖泊/海洋沉积物地球化学代用指标有效地指示环境很大程度取决于元素的来源及其在沉积物中赋存形态的确定.对位于半干旱区的内蒙古岱海14个沉积物样品的连续提取实验及18个元素在水可溶态、可交换态、碳酸盐结合态、铁锰氧化物结合态、有机物结合态及残留态等六种赋存相态中含量变化进行了测试和研究,结合沉积物的矿物组成,结果表明在岱海流域内只经历了较弱的化学风化过程,除了Ca和Sr外,其他元素主要赋存于残留态中,只发生了很小程度的活化溶解.受元素亲合性和湖水物理化学状态的制约,出溶的Sr与Ca的赋存相态基本一致,而出溶的Pb、Be、Co、Cu、K、Mn、Fe等元素则与自生碳酸盐、有机质表现出一定的亲合性.元素在不同赋存相态中分布为地球化学环境代用指标的提取和解释提供了机理性的实验依据.  相似文献   

辽宁农村代表区域降水离子组成及与气态污染物相关性          下载免费PDF全文

刘厚凤  汪凯庆 《气象与环境学报》2011,27(2):62-68

对辽宁农村代表区域站点辽中县马龙村观测站2007年2月至2008年1月酸雨、气态污染物浓度观测资料进行了分析。结果表明：辽中观测站降水的化学组成阴离子主要为SO₄^2-和NO₃^-,阳离子主要是NH^₄+和Ca₂⁺, SO^₄2-/ NO₃^-比值为2.9, Na⁺/Cl^-比值较大,大于1。各种离子浓度冬春季高,夏秋季较低,表明研究区域降水酸化与污染关系不显著。实测的9种主要阴离子、阳离子总浓度比（∑阴离子/∑阳离子）与降水pH值相关性不高,表明目前酸雨研究观测的主要9种阴阳离子不能完全包括降水中的离子组成。降水酸性与近地面污染气体浓度相关各异,pH与NO_x、CO、NO₂和O₃浓度有比较明显的负相关,与SO₂浓度负相关不明显;降水pH值与颗粒物等碱性污染物浓度正相关明显。降水中主要致酸离子SO₄^2-和NO₃^-的浓度与相应酸性气体污染物SO2和NOx近地面浓度的相关不明显。  相似文献