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Different Climatic Zones (different + climatic_zone)
Selected AbstractsLate Quaternary vadose carbonate diagenesis in coastal and desert dune and beach sands: is there a palaeoclimatic signal?EARTH SURFACE PROCESSES AND LANDFORMS, Issue 12 2004Sue McLaren Abstract A study of the variation in cement amounts in aeolianite and sandy beach calcarenites that range in age from Holocene to Last Interglacial is used to assess whether a palaeoclimatic control on vadose diagenesis can be identi,ed. Examples are taken from modern-day arid to subhumid settings and represent a geographical distribution ranging from Libya and Oman, to the Mediterranean, the Caribbean and Mexico. The results indicate that a palaeoclimatic signal can be identi,ed in some deposits. However, in other sediments there is substantial variability in mean cement abundance within deposits as well as between these sand bodies. Moreover, many of the better cemented sediments are located in areas where there is accelerated diagenesis, such as in the sea spray zone, close to the groundwater table or near to a palaeosurface, rather than in climatically wet regions. The inference is that palaeoclimatic interpretations are substantially complicated by other factors that affect diagenetic processes and change. Therefore caution is needed when studying the role of climate in vadose diagenesis in the light of the effects of other intrinsic and extrinsic controls. This paper does not aim to provide a de,nitive comparison of sites from different climatic zones. The approach taken here is: (a) to see if there is an overall palaeoclimatic signal in the samples studied; (b) to use examples to illustrate how explanations/controls other than those relating to climate can account for the variabilities observed; and (c) if there is a climatic effect, to see if it is the main over-riding control on vadose diagenesis. The conclusions drawn from this research highlight that it is possible to misinterpret evidence if the study is approached with preconceived notions of simplistic relationships between diagenesis and climate. Copyright © 2004 John Wiley & Sons, Ltd. [source] Nitrogen fixation in seagrass meadows: Regulation, plant,bacteria interactions and significance to primary productivityECOLOGY LETTERS, Issue 1 2000D.T. Welsh The rhizosphere sediments of seagrasses are generally a site of intense nitrogen fixation activity and this can provide a significant source of "new" nitrogen for the growth of the plants. In this paper, I review the data concerning nitrogen fixation in seagrass ecosystems, the transfer of the fixed nitrogen from the bacteria to the plants and its contribution to the overall productivity of seagrasses in different climatic zones. The relationship between the plants and diazotrophic heterotrophic bacteria in the rhizosphere is discussed, particularly focusing on the potentially important role of nitrogen-fixing, sulphate-reducing bacteria. The regulation of nitrogen fixation rates in the rhizosphere by photosynthetically driven oxygen and fixed carbon release by the plant roots and rhizomes, and the availability of ammonium in the porewater, is assessed. Finally, the hypothesis that a mutualistic or symbiotic association exists between the seagrasses and heterotrophic nitrogen fixers in the rhizosphere, based on the mutual exchange of fixed carbon and nitrogen, is discussed. [source] Modeled interactive effects of precipitation, temperature, and [CO2] on ecosystem carbon and water dynamics in different climatic zonesGLOBAL CHANGE BIOLOGY, Issue 9 2008YIQI LUO Abstract Interactive effects of multiple global change factors on ecosystem processes are complex. It is relatively expensive to explore those interactions in manipulative experiments. We conducted a modeling analysis to identify potentially important interactions and to stimulate hypothesis formulation for experimental research. Four models were used to quantify interactive effects of climate warming (T), altered precipitation amounts [doubled (DP) and halved (HP)] and seasonality (SP, moving precipitation in July and August to January and February to create summer drought), and elevated [CO2] (C) on net primary production (NPP), heterotrophic respiration (Rh), net ecosystem production (NEP), transpiration, and runoff. We examined those responses in seven ecosystems, including forests, grasslands, and heathlands in different climate zones. The modeling analysis showed that none of the three-way interactions among T, C, and altered precipitation was substantial for either carbon or water processes, nor consistent among the seven ecosystems. However, two-way interactive effects on NPP, Rh, and NEP were generally positive (i.e. amplification of one factor's effect by the other factor) between T and C or between T and DP. A negative interaction (i.e. depression of one factor's effect by the other factor) occurred for simulated NPP between T and HP. The interactive effects on runoff were positive between T and HP. Four pairs of two-way interactive effects on plant transpiration were positive and two pairs negative. In addition, wet sites generally had smaller relative changes in NPP, Rh, runoff, and transpiration but larger absolute changes in NEP than dry sites in response to the treatments. The modeling results suggest new hypotheses to be tested in multifactor global change experiments. Likewise, more experimental evidence is needed for the further improvement of ecosystem models in order to adequately simulate complex interactive processes. [source] Environmental and Varietal Influences on the Fatty Acid Composition of Rapeseed, Soybeans and SunflowersJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 1 2010M. Werteker Abstract The fatty acid (FA) composition of oil crops is of some importance under technological as well as under nutritional aspects. The influence of temperature on this parameter in rapeseed, soybeans and sunflowers was investigated under practical agricultural conditions, whereby varietal variations were taken into account. The analysed plant material originated from variety testing trials located in different climatic zones of Austria. As a measure of the climatic conditions of a location, the mean temperature of the last 30 days before harvest was calculated. Despite the low temperature differences between the various locations, moderate but significant negative correlations between temperature and the share of linolenic (18 : 3), respectively, linoleic (18 : 2) acid on the whole quantity of FAs in rapeseed (R² = 0.18,0.42), soybeans (R² = 0.11,0.13) and sunflowers (R² = 0.15) were found. Furthermore, there was a good negative correlation in the case of sunflower seeds between temperature and oil level (R² = 0.45). The environmental influence on the share of polyunsaturated FAs differed between the different species. The results show that quality of vegetable oils is as well a question of environment as of variety. [source] Earlywood vessel size of oak as a potential proxy for spring precipitation in mesic sitesJOURNAL OF BIOGEOGRAPHY, Issue 12 2008Patrick Fonti Abstract Aim, In this study, we evaluate the importance of the mean earlywood vessel size of oaks as a potential proxy for climate in mesic areas. Location, The study was conducted in Switzerland at three forest sites dominated by oak (Quercus petraea and Q. pubescens). The three sites were in different climatic zones, varying mainly in terms of precipitation regime. Methods, Three 50-year-long site chronologies of mean earlywood vessel size and tree-ring widths were obtained at each site and related to monthly meteorological records in order to identify the main variables controlling growth. The responses of mean vessel size to climate were compared with those of the width variables to evaluate the potential climatic information recorded by the earlywood vessels. Results, The results show that the mean vessel size has a different and stronger response to climate than ring-width variables, although its common signal and year-to-year variability are lower. This response is better in particular at mesic sites, where it is linked to precipitation during spring, i.e. at the time of vessel formation, and is probably related to the occurrence of only a few processes controlling vessel growth, whereas radial increment is controlled by multiple and varying factors. Main conclusions, The mean earlywood vessel size of oak appears to be a promising proxy for future climate reconstructions of mesic sites, where radial growth is not controlled by a single limiting factor. [source] A world-wide study of high altitude treeline temperaturesJOURNAL OF BIOGEOGRAPHY, Issue 5 2004Christian Körner Abstract Aim, At a coarse scale, the treelines of the world's mountains seem to follow a common isotherm, but the evidence for this has been indirect so far. Here we aim at underpinning this with facts. Location, We present the results of a data-logging campaign at 46 treeline sites between 68° N and 42° S. Methods, We measured root-zone temperatures with an hourly resolution over 1,3 years per site between 1996 and 2003. Results, Disregarding taxon-, landuse- or fire-driven tree limits, high altitude climatic treelines are associated with a seasonal mean ground temperature of 6.7 °C (±0.8 SD; 2.2 K amplitude of means for different climatic zones), a surprisingly narrow range. Temperatures are higher (7,8 °C) in the temperate and Mediterranean zone treelines, and are lower in equatorial treelines (5,6 °C) and in the subarctic and boreal zone (6,7 °C). While air temperatures are higher than soil temperatures in warm periods, and are lower than soil temperatures in cold periods, daily means of air and soil temperature are almost the same at 6,7 °C, a physics driven coincidence with the global mean temperature at treeline. The length of the growing season, thermal extremes or thermal sums have no predictive value for treeline altitude on a global scale. Some Mediterranean (Fagus spp.) and temperate South Hemisphere treelines (Nothofagus spp.) and the native treeline in Hawaii (Metrosideros) are located at substantially higher isotherms and represent genus-specific boundaries rather than boundaries of the life-form tree. In seasonal climates, ground temperatures in winter (absolute minima) reflect local snow pack and seem uncritical. Main conclusions, The data support the hypothesis of a common thermal threshold for forest growth at high elevation, but also reflect a moderate region and substantial taxonomic influence. [source] | |||||||||||||