Leaf nitrogen productivity as a mechanism driving the success of invasive annual grasses under low and high nitrogen supply     

J.J. James   《Journal of Arid Environments》2008,72(10):1775-1784

Invasion of the historically perennial-dominated landscapes in the Great Basin by exotic winter annual grasses is one of the most serious plant invasions in North America. Evidence suggests invasive annuals outperform native perennials under N-poor and N-rich conditions. The objective of this study was to identify key traits contributing to the success of invasive annual grasses in these environments. Three invasive annual grasses, two native perennial grasses and one introduced perennial grass were exposed to three levels of N supply. Root biomass, root length, root N uptake rate, root and leaf morphology, leaf nitrogen productivity (leaf NP) as well as biomass and N allocation were quantified over four harvests. Path analysis indicated that leaf NP was the key trait contributing to variation in N capture among the species. Species with a higher leaf NP produced more root length and consequently captured more N under a range of soil N availability. This suggests variation in leaf NP may be one critical trait determining the ability of the resident plant community to resist establishment of these invaders. Restoration programs may be able to increase weed resistance by specifically selecting for this trait in revegetation efforts.  相似文献   

Methane levels in shallow subtropical lake sediments: Dependence on the trophic status of the lake and allochthonous input     

Leonardo M. Furlanetto  Claudio C. MarinhoCleber Palma-Silva  Edélti F. AlbertoniMarcos Paulo Figueiredo-Barros  Francisco de Assis Esteves 《Limnologica》2012,42(2):151-155

The vertical sediment profiles (10 cm) of the margins of three shallow subtropical lakes (Rio Grande, Brazil) with different trophic states and surrounding areas were evaluated to identify the effects of the allochthonous input on the methane concentration in the sediment. Sediment cores were collected to quantify the organic matter content (OM) and total carbon (TC), total nitrogen (TN), total phosphorous (TP) and methane (CH₄) concentrations.The three lakes were distinguished according to the trophic status and classified as oligotrophic, dystrophic and eutrophic. The natural characteristics of the dystrophic and eutrophic lakes have been changed due to the allochthonous input of leaves and twigs (Eucalyptus sp.) and the excreta of birds, respectively. In the eutrophic lake, the allochthonous input contributed to high autochthonous production. The highest values of OM, TC, TN and TP were found in the superficial sediments of the dystrophic and eutrophic lakes. The accumulation of allochthonous organic matter in the littoral zone promoted changes in the vertical sediment profiles and contributed to increases in the CH₄ concentrations in the sediment.  相似文献   

Iron in the southeastern Bering Sea: Elevated leachable particulate Fe in shelf bottom waters as an important source for surface waters   总被引：1，自引：0，他引：1  

Matthew P. Hurst  Ana M. Aguilar-Islas  Kenneth W. Bruland 《Continental Shelf Research》2010

Surface transects and vertical profiles of total and leachable particulate Fe, Mn, Al and P, along with dissolved and soluble Fe were obtained during August 2003 in the southeastern Bering Sea. High concentrations of leachable particulate Fe were observed in the bottom waters over the Bering Sea shelf with an unusually high percentage of the suspended particulate Fe being leachable. Leachable particulate Fe averaged 81% of total particulate Fe, and existed at elevated concentrations that averaged 23 times greater than dissolved Fe in the isolated cool pool waters over the mid shelf where substantial influence of sedimentary denitrification was apparent. The elevated leachable particulate Fe is suggested to be a result of sedimentary Fe reduction in surficial sediments, diffusion of Fe(II) from the sediments to the bottom waters, and subsequent oxidation and precipitation of reduced Fe in the overlying bottom waters. Eddies and meanders of the Bering Slope Current can mix this Fe-rich water into the Green Belt at the outer shelf-break front. Elevated levels of leachable particulate Fe were observed in surface waters near the Pribilof Islands where enhanced vertical mixing exists. Storm events and/or cooling during fall/winter with the resultant destruction of the thermally stratified two-layer system can also mix the subsurface water into surface waters where the elevated leachable particulate Fe is a substantial source of biologically available Fe.  相似文献   

Biogeochemical Characterizations and Reclamation Strategies of Saline Sodic Soil in Northeastern China   总被引：3，自引：0，他引：3  

Junbao Yu  Franz X. Meixner  Fu Yang  Huifeng Wu  Xiaobing Chen 《洁净——土壤、空气、水》2010,38(11):1010-1016

Soil salinity and sodicity is considered one of the most import impediments to agricultural development in Northeast China. The contents of TP and TK decrease with soil depth and high coefficients of variation were found in TOC, AN, and AP. Mean EC in the 0–50 cm soil layers ranged from 0.61 to 0.89 dS m^?1 and the average soluble ion concentrations in the topsoil (0–10 cm) were approximately 11.38 mmol L^?1 for Na⁺, 1.21 mmol L^?1 for Ca²⁺, and 0.40 mmol L^?1 for Mg²⁺. High SAR existed in the layers 10–50 cm, indicating the studied soil was bearing low salinity in the top layer and high sodic layer in the subsurface. The soil presented strong alkali reactions all through the profile with pH over 9.5. To improve and utilize saline sodic soil rationally, several strategies were put forward based on long‐term field studies and demonstration works. The results implied that ameliorating with sand, applying farm yard manure, regenerating salt tolerant grasses and leaching with groundwater, and growing rice were effective measures for improving physical and chemical qualities of saline sodic soil.  相似文献   

厦门湾上屿附近海域初级生产力及相关要素的时间系列   总被引：3，自引：3，他引：0  

陈飞舟  沈国英  黄奕普  李文权  陈敏 《台湾海峡》1999,18(1):33-41

1996年9－10月在厦门湾上屿附近近海域定点站连续6个航次测定了初级生产力和其它水文、化学和生物学要素,在较短的时间尺度内研究了初级生产力及相关要素的时间变异特征,初级生产力,叶绿素a,颗粒有机碳（POC）,总悬浮颗粒物（TSM）和营养盐等要素随时间的变化表明了沿岩水域海洋过程发生的短暂性和沿岸水体中颗粒物质来源的复杂性。  相似文献   

Oceanographic and meteorological forcing of the pelagic ecosystem on the Gulf of Cadiz shelf (SW Iberian Peninsula)     

L. Prieto  G. Navarro  S. Rodríguez-Gálvez  I.E. Huertas  J.M. Naranjo  J. Ruiz 《Continental Shelf Research》2009

The spatial and temporal distribution of physical, chemical and biological variables of the NE continental shelf of the Gulf of Cadiz were analyzed monthly during almost three annual cycles. This analysis was performed with the aim of deriving the main forcing factors controlling variability at inter-annual, seasonal and short-time scales. Meteorological forcing related to heavy episodes of rainfall that affected river discharges and the wind regime, controlled both the currents along the shelf together and the nutrient concentrations of the surface waters. Meteorological forcing in turn determined the subsequent development and maintenance of phytoplankton blooms. Superimposed on the seasonal cycle typical of temperate latitudes, the inputs of continental nutrients mainly from the Guadalquivir River, along with episodes of upwelling favored by the predominance of westerly winds triggered phytoplankton growth on the shelf, highlighting the markedly relevant role of this large estuary in the control of the biological activity on the shelf.  相似文献   

A retrospective analysis of nutrients and phytoplankton productivity in the Mississippi River plume     

Steven E. Lohrenz  Donald G. Redalje  Wei-Jun Cai  James Acker  Michael Dagg 《Continental Shelf Research》2008

Long-term patterns in riverine nutrient flux in the lower Mississippi River were examined in relationship to spatial and temporal patterns in surface nutrient concentrations, chlorophyll, and primary productivity in the outflow region in the northern Gulf of Mexico. A retrospective analysis of dissolved inorganic nutrient fluxes based on USGS water quality data and US Army Corps of Engineers discharge data from the 1950s to mid-2004 showed an increase in river-borne dissolved inorganic nitrogen (DIN) flux after 1967. Flux of DIN peaked in the early 1980s and has since fluctuated and shown a general decreasing trend since the early 1990s. Records for total phosphorus (total P) fluxes beginning in mid-1974 exhibited a variable but slight increasing trend up to 2004. The increase in fluxes during the 1970s and into the 1980s can be attributed to increases in both nutrient concentrations and river discharge. DIN concentrations since the 1980s have shown a decreasing trend. Total P concentrations exhibited large fluctuations, with no consistent long-term trend. Dissolved organic nitrogen (DON) concentrations and orthophosphate (Ortho P) peaked in the 1980s, declined relative to DIN and remained relatively low. DIN:Ortho P ratios were consistently well above the Redfield N:P ratio of 16:1. DIN:Total P ratios were variable and lower, fluctuating around the Redfield 16:1 value. Both DIN:Ortho P and DIN:Total P ratios were weakly, but significantly, correlated with river discharge and fluctuations were largely a reflection of higher DIN concentrations during high-discharge events. DIN:Ortho P ratios in surface waters of the outflow region adjacent to the birdfoot delta were higher in spring, consistent with seasonal variation in riverine DIN:Ortho P ratios. The seasonal signal diminished with increasing distance to the west of the delta, indicating a selective removal of DIN or source of Ortho P along the shelf. DIN fluxes and SeaWiFS satellite-derived chlorophyll showed seasonally elevated values during the first half of the year followed by generally lower values in late summer and fall. This seasonal signal diminished from east to west. The observed relationship between DIN flux and chlorophyll was consistent with ship-based observations of a linkage between riverine nutrient inputs and productivity. Long-term trends in river discharge were correlated with the Multivariate ENSO (El Niño Southern Oscillation) Index (MEI) (r=−0.281, p<0.0001), evidence that river discharge was influenced by global climatic trends.  相似文献   

Water quality, nutrients and the water framework directive in an agricultural region: The lower Humber Rivers, northern England     

Colin Neal  Helen Davies  Margaret Neal 《Journal of Hydrology》2008,350(3-4):232-245

The water quality of rivers in the eastern part of the Humber Basin, north-eastern England is described from a baseflow survey (11–13 August 2006) of a wide range of water quality determinants, and long-term nutrient records of the Environment Agency of England and Wales (EA). The baseflow survey shows that the rivers are oversaturated with respect to dissolved CO₂ and calcite. They are sodium, potassium, lithium, boron, chloride, sulphate and fluoride bearing from a combination of atmospheric, within-catchment, agricultural and sewage effluent sources. Nitrate concentrations are uniform for rivers draining permeable bedrock but decrease for clay drainage areas. Soluble reactive phosphorus (SRP) concentrations are variable across the catchments reflecting the importance and variability of point sources and within-river processing. The EA data show annual oscillations for both NO₃ and SRP concentrations. Average NO₃ concentrations vary between 3.3 and 18.8 mgN/l and concentrations are low during the summer months. Average SRP concentrations vary between 23 and 1959 μg/l. Highest SRP concentrations generally occur when there is effluent input from sewage treatment works and agricultural point sources (e.g. overflow from slurry tanks, farmyard washings). Despite many of the rivers being nutrient rich, they are generally of good biological quality when point source inputs are not important.  相似文献   

Biogeochemical and ecological functioning of the low-salinity water lenses in the region of the Rhone River freshwater influence,NW Mediterranean Sea     

Frédéric Diaz  Jean-Jacques Naudin  Claude Courties  Peggy Rimmelin  Louise Oriol 《Continental Shelf Research》2008

A quasi-synoptic survey of a eulerian small grid was carried out twice during mid-spring 2002 in the Gulf of Lions, NW Mediterranean Sea. Analysis of hydrological core parameters reveal for the first time, in the region of freshwater influence (ROFI) of the Rhone River, the presence of low-salinity water (LSW) lenses. The present work details the biogeochemical and ecological functioning of the two LSW lenses from a combined analysis of nutrients and organic matter content, taxonomic assemblages of phytoplankton, primary productivity measurements and nitrogen regeneration fluxes. During the first survey, the lens observed is only detached in part from the Rhone River plume and is considered as a juvenile lens. In contrast, the second lens is totally detached from the plume forming a confined 3D structure with a large vertical development and is considered as having a more advanced maturity. A second survey, 4 days later, provided the opportunity to propose a complete sequence of ecological functioning of the LSW lenses, from their formation to a late stage of maturity just before dispersion. Nitrate contents and dissolved organic matter remain in high concentrations during the juvenile stages while the little available phosphate is rapidly exhausted. In such, an unbalanced-nutrient environment picoplankton appear to out-compete bacterioplankton for phosphate and other resources such as ammonium. In turn, the dominance of such prokaryotic assemblages could have involved the rapid development of microzooplankton. The sudden increase in phosphate observed in a more advanced stage of lens maturity is attributed to intense P-regeneration driven by the large abundance of microzooplankton. This top-down control does not seem to enable the prokaryotic assemblages to bloom again but the high concentrations of phosphate and nitrate favour the development of larger phytoplankton. These autotrophic communities rapidly exhaust nutrients and then decline in the confined ecosystem of the LSW lens that subsequently evolves towards oligotrophic conditions. In the observed last stage, small-sized phytoplankton again dominates the microbial assemblages and the trophic regime is mainly based on regenerated production. The long lifetime of the LSW lens compared to that of the Rhone River plume enables a deep transformation of the initial characteristics of the Rhone River freshwaters both in terms of nutrients balance and microbial food webs, especially through trophic cascading effects. Hence, we show that the LSW lenses have the potential to transfer nutrients and organic matter offshore but the nature (inorganic vs. organic) of the dominant compound exported will depend on the maturity of the lens at the time of its dispersion.  相似文献   

Regulation of eutrophication susceptibility in oligohaline regions of a northern Gulf of Mexico estuary, Mobile Bay, Alabama   总被引：2，自引：0，他引：2  

Lehrter JC 《Marine pollution bulletin》2008,56(8):1446-1460

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