Effects of simulated storm sizes and nitrogen on three Chihuahuan Desert perennial herbs and a grass     

W.G. Whitford  Y. Steinberger 《Journal of Arid Environments》2011,75(9):861-864

Establishment and growth of three perennial herbs and a small tussock grass were studied in an experiment that provided simulated rainfall of 6 mm week⁻¹ or 25 mm once per month and nitrogen fertilization in combination with the different simulated rainfall regimes. Wild onion, Allium macropetalum, failed to establish in plots receiving 25 mm month⁻¹ simulated rainfall. The perennial composite, Bahia absinthifolia, occurred at higher densities in plots that were not irrigated but there were no differences in biomass in any of the irrigation or fertilization treatments. Desert holly, Perezia nana, failed to establish in nitrogen fertilized plots and developed higher abundance and biomass in plots receiving 25 mm month⁻¹. Nitrogen fertilization had either no effect or an adverse effect on the perennial herbs. The tussock grass, Dasychloa pulchella exhibited highest abundance and biomass with 6 mm week⁻¹ added water plus nitrogen. Since global climate change will affect both rain storm frequency and size and atmospheric nitrogen deposition, the results of this study are applicable to understanding vegetation responses climate change.  相似文献   

Community composition, distribution, and contribution of microbenthos in offshore sediments from the Yellow Sea   总被引：1，自引：0，他引：1  

Zhaocui Meng  Kuidong Xu  Yanli Lei 《Continental Shelf Research》2011,31(14):1437-1446

We investigated the spatial distribution and composition of microbenthos in the seafloor sediments from 48 stations in the Yellow Sea using epifluorescence microscopy and quantitative protargol staining techniques. The bacterial abundance ranged from 2.4×10⁸ to 1.9×10⁹ cells cm⁻³ in the wet sediment, about three orders of magnitude higher than that of phototrophic (PNFs, from 6.4×10⁵ to 8.8×10⁶ cells cm⁻³) and heterotrophic nanoflagellates (HNFs, from 5.8×10⁴ to 5.9×10⁶ cells cm⁻³) and four orders of magnitude higher than that of cyanobacteria (from 2.3×10⁴ to 2.3×10⁶ cells cm⁻³) in the upper 5 cm of sediments. The abundance of diatoms varied greatly, from 3-1.1×10⁵ cells cm⁻³ in the upper 8 cm of sediments, whereas those of heterotrophic microflagellates (HMFs, 1-182 cells cm⁻³) and ciliates (1-221 cells cm⁻³) were less varied and lower. The biomass partitioning indicates the primary importance of benthic bacteria (50.3 μg C cm⁻³ on average), followed by PNFs (40.7 μg C cm⁻³), HNFs (19.3 μg C cm⁻³), and finally by cyanobacteria (8.8 μg C cm⁻³). Benthic diatoms (0.8 μg C cm⁻³), ciliates (0.15 μg C cm⁻³), and HMFs (0.03 μg C cm⁻³) contribute relatively small fractions to the total biomass of the microbenthos. About 95% of diatoms, 77% of ciliates, and 56% of HMFs were distributed in the upper 2 cm of sediments, whereas no distinct vertical distributions were observed for bacteria, cyanobacteria, PNFs, and HNFs. The microbenthos are quantitatively important in the shallow seafloor, wherein their main components have an average abundance three orders of magnitude higher than the corresponding planktonic organisms in the same sea area. Our estimates indicate that pico-sized phytobenthos might contribute a large proportion to the primary production. Benthic ciliates and heterotrophic flagellates contribute about 90% to the estimated combined metabolic rate of micro- and meiobenthic consumers in the whole sea area, with nanoheterotrophs accounting for the majority. The data suggest the potential for the rapid primary and secondary production of microbenthos and detrital utilization in the shallow seafloor sediments of the Yellow Sea.  相似文献   

黄海冷水团及周边海域夏初小型底栖动物现存量及空间分布研究   总被引：3，自引：1，他引：2       下载免费PDF全文

王家栋  类彦立  徐奎栋  杜永芬 《海洋与湖沼》2011,42(3):359-366

2007年6月经由专项航次对黄海冷水团及邻近海域共48个站位（北黄海17个,南黄海31个1的小型底栖动物组成、丰度和生物量及沉积环境进行了研究。所调查站位的小型底栖动物平均丰度达（2195±1599）ind／10cm^2,平均生物量为（1843±1291）μg dwt／10cm^2,冷水团内的平均丰度较冷水团外站位低约...  相似文献   

西藏岩浆岩放射性生热率的实验研究   总被引：3，自引：0，他引：3  

沈显杰  杨淑贞 《岩石学报》1989,5(4):83-92

测定了采自喜马拉雅和冈底斯地块露头和钻孔的97块岩石标本的放射性生热率(A),结果表明:藏南花岗岩(n=12)和藏北花岗岩(n=24)的平均生热率A值分别为3.2±1.5μW/m~3和2.6±1.6μW/m~3,与全球17个热流省的统计数据相比,两者均具有中等的放射性生热元素丰度;两者的平均钍铀比十分接近,分别为4.4±2.7和4.5±1.4,岩浆分异程度属中等。这些说明了:(1)本文作者在前期研究中选用的A值量级是适宜的;(2)花岗岩类作为壳内主要的放射性生热岩层,其生热率A值并未呈现异常量级。换言之,应着重从构造演化过程及其诱发的深部热作用机制,探讨藏南藏北高热流异常的成因。  相似文献   

Habitat use of inter‐tidal chitons – role of colour polymorphism          下载免费PDF全文

Vanessa Mendonça  Catarina Vinagre  Henrique Cabral  Ana C. F. Silva 《Marine Ecology》2015,36(4):1098-1106

This study presents a new approach to examining European chiton habitat use according to morphological characteristics. Time‐search transects were conducted on four Portuguese rocky shores at two shore levels. The chiton species, abundance and individual morphometric features were recorded and related to the substratum dominant epiphytes and surface roughness. The chiton Lepidochitona cinerea (Linnaeus 1767) was the dominant species (77%), followed by Leptochiton algesirensis (Capellini 1859) (15%) and Acanthochitona crinita (Pennant 1777) (8%). Species abundance did not vary significantly with shore level or amongst shores. Six colour morphs were considered for Lepidochitona cinerea, four for A. crinita and one for Lepidochiton algesirensis. Substratum characteristics significantly explained the variation in species and colour morph distribution. There was a high correlation between the presence/absence and type of epiphytic algae and the substratum surface roughness level. We hypothesize that three mechanisms operating either independently or in interaction may explain the non‐random distribution of colour polymorphisms according to their habitat characteristics: (i) presence of algae that are part of their diet; (ii) use of rock as shelter – for instance, crevices and cover resulting from algae fronds and; (iii) morph–rock colour matching as a camouflage mechanism to reduce predation pressure.  相似文献   

Annual and spatial variation in the abundance length and condition of juvenile turbot (Psetta maxima L.) on nursery grounds on the west coast of Ireland: 2000–2007     

Paula S. Haynes  Deirdre Brophy  David McGrath  Roisin O'Callaghan  Stephen Comerford  Paul Casburn 《Journal of Sea Research》2010,64(4):494-504

Turbot (Psetta maxima Linnaeus) is a high value commercially exploited marine flatfish which occurs in European waters, from the Northeast Atlantic to the Arctic Circle, the Baltic and Mediterranean Sea. In Ireland, turbot are the most valuable commercial non-quota species. Very little is known about their population dynamics in the wild, in particular during the sandy beach nursery phase of the life history. In 2000, a survey was established to assess flatfish species on nursery grounds on the west coast of Ireland. Eleven sandy beaches were assessed for 0+ turbot by beach seining, over an eight year period (2000–2007) during the months of August and September. The objective of the study was to estimate juvenile turbot abundance and size structure to determine if any spatial and annual trends existed. Large scale variability in the recruitment of fish to nursery grounds may be indicative of fluctuations in the adult stock. Turbot were found to recruit to five beaches consistently over the eight year period. Temporal and spatial variability in the relative abundance and length of turbot was discerned, with no apparent overall trend. However, certain nursery grounds were shown in most of the years examined to support higher abundances of turbot in comparison to other areas over the eight year period. Turbot abundances on nursery grounds were significantly correlated with mean spring sea temperatures during the pelagic stage. The condition of turbot did not significantly differ on an annual or spatial scale. Mean densities of 0+ turbot along the Irish coast were found to be similar and at times higher than other areas in Europe, ranging from 0.1 (± 0.3) individuals 1000 m^− 2 to 18.5 (± 6.9) individuals 1000 m^− 2. Mean turbot total length on beaches ranged from 3.8 cm (± 0.6) to 6.6 cm (± 4.3). The observed spatial and temporal variability in abundance and length highlights the need for long-term studies when assessing juvenile flatfish populations. Results from the present study have provided much needed baseline data on wild juvenile turbot populations which is severely lacking for this species both on an Irish and on a European scale.  相似文献   

低质量AGB星重元素的核合成   总被引：1，自引：0，他引：1  

王新舸  彭秋和 《天文学报》1996,37(3):243-253

本文以（１３）Ｃ（α，ｎ）（１６）Ｏ作为中子源，考虑到恒星核心质量随热脉冲数的变化及星风、超星风质量损失的影响，采用从（５６）Ｆｅ到（２１０）Ｂｉ的无分支ｓ过程反应通道，拟合了ＭＳ、Ｓ的重元素超丰．本文特别将恒星质量与ＡＧＢ内Ｓ过程核合成模型结合起来讨论．结果表明质量较大的恒星因对流较强而稀释因子较大，ＭＳ、Ｓ星在轻、重Ｓ元素丰度关系图中分别落入四个不同区域，由此可以粗略估计这些恒星的质量．２．５Ｍ　的ＡＧＢ星形成具有环状空腔的星体，最后演化成Ｔｃ—ｎｏ单星，可以解释双星系统伴星为主序星的ＡＧＢ星无Ｔｃ现象．  相似文献   

地球化学若干领域的回顾与展望   总被引：6，自引：2，他引：6  

欧阳自远  邹永廖  刘建忠  王世杰  李春来  徐琳 《地球科学进展》2001,16(5):617-623

对地球化学的某些领域，如元素的丰度和起源；地球与太阳系的化学演化；资源的勘察、利用与成因研究；元素的循环与示踪；环境地球化学；天体化学；分析与实验地球化学等在20世纪所取得的进展作了简短回顾。并对地球化学的某些领域，如全球变化研究与生态环境保护、新的洁净能源与矿产资源、防灾减灾和保障人群健康、征服太阳系并使之为人类社会的可持续发展服务等方面的发展前景作了简要论述。  相似文献   

Seasonal and Between-Substrate Variation in Mobile Epifaunal Community in a Multispecific Seagrass Bed of Otsuchi Bay, Japan   总被引：2，自引：0，他引：2  

Masahiro Nakaoka  Tetsuhiko Toyohara  & Masatoshi Matsumasa 《Marine Ecology》2001,22(4):379-395

Abstract. A seagrass bed in Otsuchi Bay, northeastern Japan, consists of three seagrass species ( Zostera marina, Z. caulescens and Z. caespitosa ) that differ in morphology and phenology. We studied the mobile epifaunal community in the seagrass bed to examine (1) whether seasonal and between-substrate variation in the epifaunal community agrees with variation in seagrass abundance and morphological complexity, and (2) whether patterns of seasonal and between-substrate variation vary among epifaunal species. We collected mobile epifauna from each of Z. marina and Z. caulescens on 11 occasions between October 1995 and November 1996 (at 1 – 1.5 month intervals) using a hand-closing net. A total of 9 842 individuals of mobile epiphytic animals were collected and they were classified into 80 taxa. Abundance and species richness of the epifaunal community were high in summer to autumn and low in winter to spring, and diversity index and evenness were higher in Z. marina than Z. caulescens . However, patterns of seasonal and between-substrate variation in these parameters did not parallel those in seagrass abundance and complexity. Most of the dominant epifaunal species showed significant seasonal and between-substrate variation in abundance, although their patterns varied greatly among individual species. A cluster analysis recognized several distinct groups of animals showing similar seasonal and between-substrate variation. Our findings suggest that the observed variation in the epifaunal community is not determined by a single or some strong external factors but by complex interactions of multiple factors operating differently for each component species.  相似文献   

胶州湾小型底栖生物的丰度和生物量   总被引：33，自引：5，他引：33  

张志南  周红  于子山  韩洁 《海洋与湖沼》2001,32(2):139-147

1995年 5月— 1 996年 1月 ,在胶州湾北部软底水域进行每 2月一次的调查。结果表明 ,小型底栖生物的年平均丰度为 1 .51× 1 0 6ind/m2 ,最高值出现在 95B1和 95B2站 ,分别为 2 .73× 1 0 6 和 2 .75× 1 0 6ind/m2 ,最低值出现在 95B3站 ,数量为 0 .46× 1 0 6ind/m2 。小型底栖生物的年平均生物量为 1 .32 g/m2 (干重 )。皮尔逊相关分析表明 ,小型生物的数量与以碳和氮表示的浮游植物的生物量呈负相关 ,相关系数分别为 - 0 .969和 - 0 .947(P <0 .0 5)。共鉴定出 1 4个小型生物类群。自由生活的海洋线虫占总数量的 86.6% ,底栖桡足类居第 2位 ,占总数量的 5.7%。按生物量 ,海洋线虫 (35.9% )、介形类 (32 .6% )、多毛类 (1 3.7% )和桡足类 (8.3% )共同构成小型动物的优势类群 ,80 %以上的小型生物分布在 0— 2cm以浅表层内。与国内外同类研究结果进行了比较 ,并对小型生物在胶州湾生态系中的作用进行了探讨  相似文献