首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 46 毫秒
1.
Instantaneous mortality rates of the common planktonic copepod Oithona similis were investigated for the first time in Kola Bay, a region of the Barents Sea that is influenced by freshwater discharge. The rates were estimated in different seasons (December, May, September 2005 and July 2006). A vertical life table approach (VLT) was used to assess mortality. The total abundance of O. similis (copepodites IV and V, and adults) was highest in autumn and lowest in winter. The maximum mortality of O. similis for the stage pair copepodite IV–copepodite V (0.005 ± 0.001 day?1) occurred in December 2005, while the highest mortality rates for the pairs copepodite VM–adult male (0.453 ± 0.026 day?1) and copepodite VF–adult female (0.228 ± 0.006 day?1) occurred in summer 2006. Simple regression analyses showed that the total abundance of each stage and the mortality rates were positively significantly correlated with water temperature. The mortality rates for the stage pairs copepodite VM–adult male and copepodite VF–adult female were positively significantly correlated with chlorophyll a concentration. The abundance and mortality rate of O. similis in each season was determined by life cycle factors, and possibly by the dynamics of its food resources and potential predators.  相似文献   

2.
《Polar Science》2014,8(2):166-182
The larch forests on the permafrost in northeastern Mongolia are located at the southern limit of the Siberian taiga forest, which is one of the key regions for evaluating climate change effects and responses of the forest to climate change. We conducted long-term monitoring of seasonal and interannual variations in hydrometeorological elements, energy, and carbon exchange in a larch forest (48°15′24′′N, 106°51′3′′E, altitude: 1338 m) in northeastern Mongolia from 2010 to 2012. The annual air temperature and precipitation ranged from −0.13 °C to −1.2 °C and from 230 mm to 317 mm. The permafrost was found at a depth of 3 m. The dominant component of the energy budget was the sensible heat flux (H) from October to May (H/available energy [Ra] = 0.46; latent heat flux [LE]/Ra = 0.15), while it was the LE from June to September (H/Ra = 0.28, LE/Ra = 0.52). The annual net ecosystem exchange (NEE), gross primary production (GPP), and ecosystem respiration (RE) were −131 to −257 gC m−2 y−1, 681–703 gC m−2 y−1, and 423–571 gC m−2 y−1, respectively. There was a remarkable response of LE and NEE to both vapor pressure deficit and surface soil water content.  相似文献   

3.
Six geothermal sources distributed in the north and south of Tunisia were examined monthly during the period from August 2009 to April 2010, in order to determine mats communities' abundance and biodiversity. Twenty-seven taxa, belonging to three taxonomic groups: Cyanobacteria, Bacillariophyta and Chlorophyta were identified. The Cyanobacteria group was more prominent with a particular dominance of two genera Phormidium and Spirulina. Their maximum abundance was respectively 919.2 ± 44.2 103 cells ml−1 and 652.8 ± 92.6 103 cells ml−1. The dominant mats morphologies in prospected sites were filaments. Results demonstrate that biodiversity values ranged between 0.16 and 1.15 bits. cell−1. The spatial variations showed that the regional specificity in mats species biodiversity and abundance between north and south were not signified, whereas, each site had specific species. Temporal variations showed an increase of microalgae and prokaryotes abundance in the dry season.  相似文献   

4.
《Polar Science》2014,8(3):283-297
Long-term changes in phytoplankton biomass and community composition are important in the ecosystem and biogeochemical cycle in the Southern Ocean. We aim to ultimately evaluate changes in phytoplankton assemblages in this region on a decadal scale. However, yearly continuous data are lacking, and long-term datasets often include seasonal variability. We evaluated the seasonal changes in phytoplankton abundance/composition across latitudes in the Indian Ocean sector of the Southern Ocean via multi-ship observations along the 110°E meridian from 2011 to 2013. The chlorophyll a concentration was 0.3–0.5 mg m−3 in the Subantarctic Zone (40–50°S) and 0.4–0.6 mg m−3 in the Polar Frontal Zone (50–60°S); pico-sized phytoplankton (<10 μm), mainly haptophytes, were dominant in both zones. In the Antarctic Divergence area (60–65°S), the chlorophyll a concentration was 0.6–0.8 mg m−3, and nano-sized phytoplankton (>10 μm), mainly diatoms, dominated. Chlorophyll a concentrations and phytoplankton community compositions were the same within a latitudinal zone at different times, except during a small but distinct spring bloom that occurred north of 45°S and south of 60°S. This small seasonal variation means that this part of the Southern Ocean is an ideal site to monitor the long-term effects of climate change.  相似文献   

5.
Mean tree biomass and soil carbon (C) densities for 39 map sheet grids (1° lat. × 1.5° long.) covering the Acacia woodland savannah region of Sudan (10–16° N; 21–36° E) are presented. Data from the National Forest Inventory of Sudan, Harmonized World Soil Database and FAO Local Climate Estimator were used to calculate C densities, mean annual precipitation (MAP) and mean annual temperature (MAT). Above-ground biomass C and soil organic carbon (SOC, 1 m) densities averaged 112 and 5453 g C m−2, respectively. Below-ground biomass C densities, estimated using root shoot ratios, averaged 33 g C m−2. Biomass C densities and MAP increased southwards across the region while SOC densities were lowest in the centre of the region and increased westwards and eastwards. Both above-ground biomass C and SOC densities were significantly (p < 0.05) correlated with MAP (rs = 0.84 and rs = 0.34, respectively) but showed non-significant correlations with MAT (rs = −0.22 and rs = 0.24, respectively). SOC densities were significantly correlated with biomass C densities (rs = 0.34). The results indicated substantial under stocking of trees and depletion of SOC, and potential for C sequestration. Up-to-date regional and integrated soil and forest inventories are required for planning improved land-use management and restoration.  相似文献   

6.
This study was designed to test hypotheses about the combined effects of short-term, seasonal grazing with seasonal drought, fire, and carbon enrichment on soil microarthropod communities in a Chihuahuan Desert grassland. The study was conducted in eighteen 0.5 ha plots following three consecutive years of treatment: six plots intensively grazed in summer, six in winter, and six not grazed. There was no difference in perennial grass cover on the summer-grazed and winter-grazed plots. Intensive seasonal grazing had no effect on the abundance and community composition of soil microarthropods. Within each plot there were six subplots: summer rain-out, winter rain-out, burned, glucose amendment, rain-out control and burn-glucose control. Fire and carbon enrichment had no significant effect on soil microarthropod abundance or community composition. The average number of microarthropods ranged from 8915 ± 1422 m−2 in the ungrazed, unburned plots to 7175 ± 1232 m−2 in the winter-grazed, unburned plots. Microarthropod densities in the glucose-amended plots were 8917 ± 4902 m−2 in the winter-grazed plots and 10,731 ± 863 m−2 in the glucose-amended, summer-grazed subplots.The prostigamatid mite, Tydeus sp., was the most abundant microarthropod taxon in all treatment plots.  相似文献   

7.
Following the southward shift of rainfall isolines in the Sahel at the end of the 1960s, Gerbillus nigeriae appeared in northern Senegal in the mid-1990s, and two resident Gerbillidae (Taterillus pygargus and Taterillus gracilis) subsequently declined. We investigated the causal role of the capacity to conserve water in such climate-related shifts in the distribution of these Gerbillidae by comparing the effects of a water-poor diet on the water-efflux rate (W−out) of freshly trapped adults pre-acclimatized to a water-rich diet. During the 12-day period of water restriction in all species, 30-50% of individuals became hyperactive and showed greater weight loss and higher W−out than the remaining inactive individuals. Such emergence of migratory strategists within populations could accelerate the expansion of G. nigeriae. On a water-poor diet, T. gracilis showed a lower capacity to conserve water (higher W−out) than T. pygargus and G. nigeriae, in both inactive (W−out = 44.5 ± 1.8 vs 29.6 ± 0.8 vs 27.4 ± 0.7 ml kg−0.82.day−1, respectively) and hyperactive individuals (W−out = 60.4 ± 1 vs 45.4 ± 0.7 vs 44 ± 0.8 ml kg−0.82.day−1, respectively). We propose that the capacity to conserve water accounted for both expansion of G. nigeriae and decline of T. gracilis, whereas competition between T. pygargus and G. nigeriae could account for the decline of T. pygargus.  相似文献   

8.
Asian-dust (yellow-sand) phenomena observed in Japan have been increasing in recent years, especially from 2000 to 2002. The main cause is severe dust events in arid and semi-arid regions of northeast Asia. The dust source area in northeast Asia (target area: 35°–45°N and 100°–115°E) was identified with reference to past results, and the relationship between the yellow-sand phenomena observed in Japan and dust outbreaks in the target area was examined during the springtime (March to May) from 1993 to 2002. The annual change in the number of dust phenomena observed in Japan agreed well with the Dust Storm Frequency (DSF) in the target area (R2 = 0.8796). Even though strong wind (≧7.0 m s−1) has a profound effect on dust storms (R2 = 0.515), coverage of the Normalized Differential Vegetation Index (NDVI), ranging from 0 to 0.1 (bare land with snow cover) and 0.1 to 0.2 (bare land) in April, also affected dust storms in the target area (R2 = 0.486 and 0.418).  相似文献   

9.
In this article we evaluate the potential use of Cladonia foliacea tissue N content, C:N ratio, and phosphomonoesterase (PME) activity as biomarkers of N deposition by means of a field experiment. In order to do this, we continuously added NH4NO3 to a semi-arid shrubland at four rates: 0, 10, 20 and 50 kg N ha−1 yr−1 starting in October 2007. Tissue N content and C:N ratios, considered as N stress indicators, significantly increased and decreased, respectively, after 1.5 years. The response found suggests N saturation above 20 kg N ha−1 yr−1. After 2.5 years, extracellular PME activity increased with 20 kg N ha−1 yr−1 and this was attributed to an induced nutritional (N to P) imbalance. Above this threshold, PME significantly decreased as a consequence of the physiological stress caused by extra N. Effects on PME were dependent on the soil properties (pH and Ca and Mg availability) experienced by C. foliacea. PME response suggests a critical load of ∼26.4 kg N ha−1 yr−1 (20 kg N ha−1 yr−1 + background) for this lichen. Further tissue chemistry and PME evaluations in C. foliacea and soil surveys conducted along wide N deposition gradients will confirm the potential use of this species as a biomonitor of N pollution and the importance of soil properties on its ability to respond to atmospheric reactive N.  相似文献   

10.
Shrubs play an important role in water-limited agro-silvo-pastoral systems by providing shelter and forage for livestock, for erosion control, to maintain biodiversity, diversifying the landscape, and above all, facilitating the regeneration of trees. Furthermore, the carbon sink capacity of shrubs could also help to mitigate the effects of climate change since they constitute a high proportion of total plant biomass. The contribution of two common extensive native shrub species (Cistus ladanifer L. and Retama sphaerocarpa (L.) Boiss.) to the carbon pool of Iberian dehesas (Mediterranean agro-silvo-pastoral systems) is analyzed through biomass models developed at both individual (biovolume depending) and community level (height and cover depending).The total amount of carbon stored in these shrubs, including above- and belowground biomass, ranges from 1.8 to 11.2 Mg C ha−1 (mean 6.8 Mg C ha−1) for communities of C. ladanifer and from 2.6 to 8.6 Mg C ha−1 (mean 4.5 Mg C ha−1) for R. sphaerocarpa. These quantities account for over 20–30% of the total plant biomass in the system. The potential for carbon sequestration of these shrubs in the studied system ranges 0.10–1.32 Mg C ha−1 year−1 and 0.25–1.25 Mg C ha−1 year−1 for the C. ladanifer and R. sphaerocarpa communities' respectively.  相似文献   

11.
《Polar Science》2014,8(2):146-155
The Boreal black spruce forest is highly susceptible to wildfire, and postfire changes in soil temperature and substrates have the potential to shift large areas of such an ecosystem from a net sink to a net source of carbon. In this paper, we examine CO2 exchange rates (e.g., NPP and Re) in juniper haircap moss (Polytrichum juniperinum) and microbial respiration in no-vegetation conditions using an automated chamber system in a five-year burned black spruce forest in interior Alaska during the fall season of 2009. Mean ± standard deviation microbial respiration and NEP (net ecosystem productivity) of juniper haircap moss were 0.27 ± 0.13 and 0.28 ± 0.38 gCO2/m2/hr, respectively. CO2 exchange rates and microbial respiration showed temporal variations following fluctuation in air temperature during the fall season, suggesting the temperature sensitivity of juniper haircap moss and soil microbes after fire. During the 45-day fall period, mean NEP of P. juniperinum moss was 0.49 ± 0.28 MgC/ha following the five-year-old forest fire. On the other hand, simulated microbial respiration normalized to a 10 °C temperature might be stimulated by as much as 0.40 ± 0.23 MgC/ha. These findings demonstrate that the fire-pioneer species juniper haircap moss is a net C sink in the burned black spruce forest of interior Alaska.  相似文献   

12.
In hot, arid environments, non-burrowing mammals are at risk of overheating and dehydration, so human-induced reduction in thermal cover may constitute a threat for their survival. We studied the daytime activity rhythm, habitat use, and space use of the beira (Dorcatragus megalotis), a threatened antelope living in arid hills of the Horn of Africa, where tree cover is shrinking because of logging, and overgrazing by livestock. During the cool season (Nov.–Mar.; mean midday temperature: 28.5 °C), beira did not particularly seek shade, and alternated in the course of the day between short phases of activity and rest (median duration in Dec.–Feb.: 57.5 and 42.5 min, respectively). In contrast, during the hot season (May–Sep.; mean midday temperature: 39.1 °C), beira often foraged in a hill's shade, and midday resting phases were especially long (median duration in May–Jul.: 280 min) and spent in the shade of trees, or of rock shelters when available in the home range. Because of reduced diurnal movements when temperature was high, beira home ranges were smaller during the hot than during the cool season (mean ± SE: 0.25 ± 0.05 km2 in May–Jul. vs 0.42 ± 0.10 km2 in Dec.–Feb.). Whatever the season, beira mainly used areas supporting trees. The obtained results suggest that the decrease of tree cover in the areas inhabited by the beira constitutes a threat for the species survival.  相似文献   

13.
Two experiments were conducted in southern Kordofan State to determine the influence of Acacia senegal L., Balanites aegyptiaca L. and Azadirachta indica L. on millet (Pennisetum typhoides) yield, soil quality and to monitor decomposition and nutrients release from tree litters. Yield under A. indica (174.83 kg ha−1) and B. aegyptiaca (173.09 kg ha−1) were significantly higher than the control (121.43 kg ha−1). The lowest yield (111.04 kg ha−1) was recorded under A. senegal. Straw dry matter under B. aegyptiaca (1161.5 kg ha−1) and A. indica (857.8 kg ha−1) was significantly higher than both under A. senegal (321.8 kg ha−1) and the control (454.8 kg ha−1). Trees varied in their capacity to induce changes in soil properties whereas effects on soil N were not substantial. A. indica had a decomposition rate (0.6283 week−1) 2.0 times higher than that of B. aegyptiaca (0.2057 week−1) and A. senegal (0.267 week−1). The highest rate of P and K release from A. indica and B. aegyptiaca litters has resulted in significant accumulation in the soil indicating these tree litters are potential sources for these elements. The capacity of trees to improve soil fertility could offer an alternative management system for improved cultivation of field crops.  相似文献   

14.
《Polar Science》2014,8(4):370-384
An anomalous phytoplankton bloom was recorded in the Indian Ocean sector of the Antarctic Zone (AZ) of the Southern Ocean (SO) during the austral summer, 2011. Possible mechanisms for the triggering of such a large bloom were analyzed with the help of in situ and satellite data. The bloom, which formed in January 2011, intensified during February and weakened by March. High surface chlorophyll (Chl) concentrations (0.76 mg m−3) were observed in the area of the bloom (60°S, 47°E) with a Deep Chlorophyll Maximum (DCM) of 1.15 mg m−3 at a depth of 40–60 m. During 2011, both the concentration and spatial extent of sea ice were high on the western side of the bloom, between 0°E and 40°E, and enhanced freshwater influx was observed in the study area as a result of melting ice. A positive Southern Annular Mode (SAM) (with a resultant northward horizontal advection) and an intense La Niña during 2010–2011 are possible reasons for the high sea-ice concentrations. The enhanced Chl a observed in the study region, which can be attributed to the phytoplankton bloom, likely resulted from the influx of nutrient-laden freshwater derived from melting sea ice.  相似文献   

15.
Quantifying the variability and allocation patterns of aboveground carbon stocks across plantation forests is central in deriving accurate and reliable knowledge and understanding of the extent to which these species contribute to the global carbon cycle and towards minimizing climate change effects. The principal objective of this study was to quantify the variability and allocation patterns of aboveground carbon stocks across Pinus and Eucalyptus plantation forests, tree-structural attributes (i.e. stems, barks, branches and leaves) and age groups, using models developed based on remotely sensed data. The results of this study demonstrate that aboveground carbon stocks significantly (α = 0.05) vary across different plantation forest species types, structural attributes and age. Pinus taeda and Eucalyptus grandis species contained aboveground carbon stocks above 110 t C ha−1, and Eucalyptus dunii had 20 t C ha−1. Across plantation forest tree structural attributes, stems contained the highest aboveground carbon stocks, when compared to barks, branches and leaves. Aboveground carbon stock estimates also varied significantly (α = 0.05) with stand age. Mature plantation forest species (i.e. between 7 and 20 years) contained the highest aboveground carbon stock estimates of approximately 120 t C ha−1, when compared to younger species (i.e. between 3 and 6 years), which had approximately 20 t C ha−1. The map of aboveground carbon stocks showed distinct spatial patterns across the entire study area. The findings of this study are important for understanding the contribution of different plantation forest species, structural attributes and age in the global carbon cycle and possible climate change moderation measures. Also, this study demonstrates that data on vital tree structural attributes, previously difficult to obtain, can now be easily derived from cheap and readily-available satellite data for inventorying carbon stocks variability.  相似文献   

16.
We used biodegradable dissolved organic carbon (BDOC) incubations, specific ultraviolet absorbance (SUVA254, indicator of aromatic carbon content) and laboratory experiments to determine the bioavailability and chemical composition of dissolved organic matter (DOM) leached from fresh leaves and litter aged on a seasonally dry floodplain for 2, 4, and 6 months. Our objective was to elucidate how litter age and solar radiation affect the bacterial utilization of DOM released from floodplain leaf litter when inundated. Leachate percent BDOC ranged from 22 to 47% for three different leaf species and significantly decreased (p < 0.05) with increasing litter age. However, total BDOC (mg C L−1) was unrelated to litter age. Bacterial utilization of DOM leachate collected from litter aged on the floodplain for four and six months significantly increased following 48 h of irradiation for all species but there was no difference for leachate from fresh and two month old litter. The photo-mediated increase in percent BDOC was concomitant with a decrease in aromatic carbon content, as SUVA254 values decreased on average 9 ± 6% for light exposure experiments. Our findings demonstrate that sunlight moderates the degradation of plant litter in the terrestrial environment through the photo-mediated shift in DOM composition and its bioavailability in streams.  相似文献   

17.
Leaf chlorophyll meters can be used to support easy and efficient crop nitrogen (N) management. They can be used on tree species native to Central Asia that have been suggested for afforesting salt-affected croplands, but its use demands a priori calibration as the relationship between chlorophyll meter measurements and leaf N contents is crop/species specific. Data collected with a SPAD-502 leaf chlorophyll meter during 2006–2008 was used to generate a calibration dataset for the leaf N status of three tree species. The second-degree polynomial relationships between the SPAD-502 readings and total leaf chlorophyll and N content had higher predictive power than linear relationships for all species, although with differences among them. The validation was completed with the same species grown at a different location (difference in space) and with older trees (difference in age). The comparison between predicted and spectrophotometrically determined leaf N content showed a root mean square error (RMSE) of 25 mg g−1 DM, which corresponds to a relative RMSE of 10% for Elaeagnus angustifolia. For Gleditsia triacanthos and Robinia pseudoacacia they were 11 mg g−1 DM and 16%, 14 mg g−1 DM and 10%, respectively. The findings demonstrate that the SPAD-502 can with confidence be used for non-destructive assessment of tree foliar N status of these three species, although only within the range of the SPAD-502 values used for the calibration. Options for the use of the SPAD-502 for forest management in agroforestry-based land use systems in Central Asia are addressed.  相似文献   

18.
Laboratory experiments were conduced to assess the synergic effect of chilling and light on photosystem II photochemistry of the halophyte, Sarcocornia fruticosa, grown at different salinity concentrations (0, 170, 340, 510 and 1030 mM). Chlorophyll fluorescence was measured after chilling (at 5 °C in darkness) and light-chilling (at 5 °C and 700 μmol m?2 s?1) treatments, and after 24 h of recovery (at 20 °C and 75 μmol m?2 s?1). At 5 °C and 700 μmol m?2 s?1, plants grown with 0 and 170 mM NaCl showed the lowest Fv/Fm values, whereas quantum efficiency of PSII (ΦPSII) was higher for plants grown at 170 and 340 mM NaCl, these results being consistent after two exposures to chilling treatments. Susceptibility to photoinhibition decreases when low temperature and high light are combined with high salinity. Therefore, populations of S. fruticosa that occur in arid environments with salinities c. 340 mM could show a higher tolerance to light-chilling.  相似文献   

19.
Over the past century, the invasive halophytic shrub Tamarix ramosissima Ledeb. has increased in abundance and distribution in riparian ecosystems of western North America. These increases coincide with anthropogenic modification of river systems, which decrease the rate of periodic overbank flooding, leading to an increase in soil salinity. Increased soil salinity negatively impacts the physiology of native riparian tree species, but the impact of increased soil salinity on T. ramosissima physiology is incompletely known. To measure the impacts of soil salinity on T. ramosissima, we measured leaf-level responses across a broad range of surface-soil salinity concentrations at two sites in western Kansas. Photosynthesis at 2000 μmol m−2 s−1 (A2000), stomatal conductance to water (gs), intercellular CO2 concentration (Ci), and leaf δ13C showed little change over surface-soil salinities from 0.5 to 17.65 mmhos/cm. The small variation in leaf-level physiological responses suggests robust functioning of T. ramosissima across a broad range of surface-soil salinities. Leaf-level physiology and δ13C responses were assessed by canopy position, but responses were not significantly different. These results are among the first to show broad acclimation and robust physiological functioning for many leaf-level processes measured on mature trees grown across a wide surface-soil salinity gradient in the field.  相似文献   

20.
Fine root dynamics and longevity may reflect the results of plant adaptation. The minirhizotron technique was applied to investigate the fine root dynamics and longevity of Artemisia halodendron Turcz. ex Bess. in the mobile and fixed sand dunes in Inner Mongolia, Northern China. For over two years of study, the cumulative fine root length production and turnover were all significantly higher in the mobile than the fixed sand dunes at soil depths of 0–20, 20–40, and 40–60 cm. The annual fine root production (8.46 mm cm−2 y−1) and annual fine root turnover (7.38 mm cm−2 y−1) of shrubs in the mobile sand dunes are about 38 and 70 percent higher than those in the fixed sand dunes. The fine root lifespan is higher for those in the fixed (47 days) than in the mobile (33 days) sand dunes, consistent with the higher ratio of first- (distal) to second-order roots of the former. The root production and lifespan are consistent with the adaptive responses of A. halodendron in the two habitats. The differences in root dynamics and lifespan between the mobile and fixed sand dunes may significantly explain the changes in the C fixation rate with the restoration of desert soils.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号