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 31 毫秒
1.
Over four hundred vegetation samples were collected for total Hg determination as part of a biogeochemical survey in the Precambrian Shield region near Huntsville, Ontario. An objective of the survey was to obtain accurate data describing the spatial and temporal variation of Hg concentrations in vegetation. Five tree species, clubmosses, mosses, lichen and fungi were collected along three transects each 8 to 10 km long. The samples were digested using a hot H2SO4/HNO3 mixture followed by cold-vapor AAS detection. Very low detection limits (less than 1.0 ng g−1) were achieved by performing the analyses in a clean, Hg-free laboratory. The Hg concentration of coniferous needles did not vary significantly over eight weeks of the summer, but did vary significantly between first and second year growth. In all tree species examined, Hg concentrations in needles/leaves were two to three times as high (by dry weight) as that in twig tissue from the same branch. Differences in Hg content between tissues of different types and ages constituted a major source of within-site variation between plants of the same species.  相似文献   

2.
Abstract

The seasonal patterns of foliage nutrient concentrations and contents were monitored for two growing seasons in an 11‐year—old Pinus el1iottii stand. In the first growing season after needle initiation, N, P, K, Mg, and Zn concentrations decreased, but this was followed by an increase in the fall and winter months. Another drop in concentration of all elements, except P, occurred in the second growing season. Decreases in total contents indicated that this drop was a result of translocation to other tissues. In contrast to the mobile elements, the concentration and fascicle contents of Ca, Mn, and Al increased with aging of the needles.

Between‐tree variability was least for N, P, and Zn and the N, K, Mg, Mn, and Zn in the current foliage had consistently lower variation than that in the 1‐year‐old foliage. Between‐tree variation for K was lower in the winter than the spring.

For pine foliage, recommended sampling period for N, P, Mg, and Zn is mid to late summer and for the other elements it is late fall to late winter.

There are several sources of variation that influence the level of nutrients in tree foliage. The most important of these, apart from the tree nutrient status, are seasonal fluctuations, variation between trees, and age of needles . Smaller sources of variation are associated with position of the needles within the crown, diurnal changes, year to year variation, and analytical errors1,2. These variables must be studied in order to develop suitable sampling techniques and in Pinus this has been undertaken for P. banksiana 1, P. taeda 3, P. strobus 4, P. resinosa 4, P. sylvestris 5, and P. radiata 6,7. However, foliage sampling has not been studied in detail for slash pine (Pinus elliottii Englem var. elliottii) and earlier studies with other pines have been largely confined to temperate or cool climates.

This study reports the variation in elemental concentrations with season, age of foliage, and between slash pine trees growing in a subtropical climate in Florida.  相似文献   

3.
Mercury Uptake by Trees: An Observational Experiment   总被引：1，自引：0，他引：1  
We conducted a simple observational experiment to test whether differences in Hg in tissue of red pine (Pinus resinosa Ait.) were related to soil or to atmospheric sources of Hg. We sampled two plantations in each of three areas, and within each plantation sampled two sites with different levels of soil Hg. Woody tissue Hg concentration differed by area, and differences in foliar concentrations, though not statistically significant, were ranked in the same order. Total mass of Hg in forest floor and mineral soil also differed by area, but with ranking opposite that of tissue. On an individual-tree basis, concentrations of Hg in 1994 needles (2-year old) were about twice those in 1995 needles (1-year old) (r = 0.77). Neither woody tissue Hg nor any measure of Hg in soil or forest floor were closely related to foliar levels and some relationships were inverse. We interpret the data to indicate that Hg in plant tissue is derived directly from the atmosphere, not the soil. Tissue concentration by area was closely related to the respective growing season length (1994 needles, r = 0.88; 1995 needles, r = 0.97; wood, r = 0.97), as was total mass of Hg in forest floor and surface mineral soil (r = – 0.80). Other climatic measures, such as growing degree days and actual evapotranspiration, had similar relationships. These relationships imply that both foliar uptake of Hg0 from the atmosphere and efflux of Hg from the soil system depend on biological activity.  相似文献   

4.
  相似文献   

5.
Chamber measurements of total ecosystem respiration (TER) in a native Canadian grassland ecosystem were made during two study years with different precipitation. The growing season (April–September) precipitation during 2001 was less than one-half of the 30-year mean (1971–2000), while 2002 received almost double the normal growing season precipitation. As a consequence soil moisture remained higher in 2002 than 2001 during most of the growing season and peak aboveground biomass production (253.9 g m−2) in 2002 was 60% higher than in 2001. Maximum respiration rates were approximately 9 μmol m−2 s−1 in 2002 while only approximately 5 μmol m−2 s−1 in 2001. Large diurnal variation in TER, which occurred during times of peak biomass and adequate soil moisture, was primarily controlled by changes in temperature. The temperature sensitivity coefficient (Q10) for ecosystem respiration was on average 1.83 ± 0.08, and it declined in association with reductions in soil moisture. Approximately 94% of the seasonal and interannual variation in R10 (standardized rate of respiration at 10 °C) data was explained by the interaction of changes in soil moisture and aboveground biomass, which suggested that plant aboveground biomass was good proxy for accounting for variations in both autotrophic and heterotrophic capacity for respiration. Soil moisture was the dominant environmental factor that controlled seasonal and interannual variation in TER in this grassland, when variation in temperature was held constant. We compared respiration rates measured with chambers and that determined from nighttime eddy covariance (EC) measurements. Respiration rates measured by both techniques showed very similar seasonal patterns of variation in both years. When TER was integrated over the entire growing season period, the chamber method produced slightly higher values than the EC method by approximately 4.5% and 13.6% during 2001 and 2002, respectively, much less than the estimated uncertainty for both measurement techniques. The two methods for calculating respiration had only minor effects on the seasonal-integrated estimates of net ecosystem CO2 exchange and ecosystem gross photosynthesis.  相似文献   

6.
This study aimed to understand the seasonal and spatial variations of N2O emissions from newly created littoral marshes in the drawdown area of the Three Gorges Reservoir (TGR), China. We measured N2O emissions at 10-day intervals during the growing season (early July to late September) in 2008. N2O emissions were measured with static chambers in four typical vegetation stands. The results showed great spatial variations of N2O emissions among the four stands. The greatest N2O emissions (0.052?±?0.063 mg N2O m?2?h?1) were from Scirpus triqueter stand, while the lowest N2O emissions (0.020?±?0.020 mg N2O m?2?h?1) were from Typha angustifolia stand. To such spatial variations in N2O emissions, standing water depths and soil water content may be important explaining factors. Besides spatial variations, we also found significant temporal variations of N2O emissions in this area. The temporal variation of N2O emissions in the growing season was not found significantly related to any measured factor in the study. However, based on principal component analysis, we consider it partly caused by thermal conditions and the marked temporal variation of the standing water depth in the growing season, which to some degree influenced the process of denitrification and N2O emissions. These results about TGR enable us to make a more reasonable estimate of N2O emissions from large dam reservoirs, particularly those with a large drawdown area in the growing season in an agricultural landscape.  相似文献   

7.
The Si concentration in 1 year old needles from Norway spruce (P. abies) was determined at 39 sites within an area of 150 km2. The sites had uniform elevation, precipitation and immission characteristics. The mean value was 1423 μg Si g?1, and the coefficient of variation between sites was 29 %. There was no correlation of Si concentration in needles with soil pH in the range of pH 3.5 to 7.6, but significant negative correlations with soil organic matter concentration and with the effective cation exchange capacity were found. Silicon in needles correlated positively with Al, La, and Fe in needles, but showed no correlation with 20 other elements. The seasonal variation of Si concentration in needles showed a nonuniform increase with time. The seasonal changes of Si were similar to those of Ca. The investigation of 4 successive needle age classes, however, showed a strictly linear increase of the Si concentrations.  相似文献   

8.
Most soil respiration measurements are conducted during the growing season. In tundra and boreal forest ecosystems, cumulative winter soil CO2 fluxes are reported to be a significant component of their annual carbon budgets. However, little information on winter soil CO2 efflux is known from mid-latitude ecosystems. Therefore, comparing measurements of soil respiration taken annually versus during the growing season will improve the accuracy of ecosystem carbon budgets and the response of soil CO2 efflux to climate changes. In this study we measured winter soil CO2 efflux and its contribution to annual soil respiration for seven ecosystems (three forests: Pinus sylvestris var. mongolica plantation, Larix principis-rupprechtii plantation and Betula platyphylla forest; two shrubs: Rosa bella and Malus baccata; and two meadow grasslands) in a forest-steppe ecotone, north China. Overall mean winter and growing season soil CO2 effluxes were 0.15-0.26 μmol m−2 s−1 and 2.65-4.61 μmol m−2 s−1, respectively, with significant differences in the growing season among the different ecosystems. Annual Q10 (increased soil respiration rate per 10 °C increase in temperature) was generally higher than the growing season Q10. Soil water content accounted for 84% of the variations in growing season Q10 and soil temperature range explained 88% of the variation in annual Q10. Soil organic carbon density to 30 cm depth was a good surrogate for SR10 (basal soil respiration at a reference temperature of 10 °C). Annual soil CO2 efflux ranged from 394.76 g C m−2 to 973.18 g C m−2 using observed ecosystem-specific response equations between soil respiration and soil temperature. Estimates ranged from 424.90 g C m−2 to 784.73 g C m−2 by interpolating measured soil respiration between sampling dates for every day of the year and then computing the sum to obtain the annual value. The contributions of winter soil CO2 efflux to annual soil respiration were 3.48-7.30% and 4.92-7.83% using interpolated and modeled methods, respectively. Our results indicate that in mid-latitude ecosystems, soil CO2 efflux continues throughout the winter and winter soil respiration is an important component of annual CO2 efflux.  相似文献   

9.
A field plot experiment on fertilization with N, Mg and P in Scots pine forest was established. The experiment had a factorial design with three levels of N (0, 30 and 90 kg ha?1), two levels of Mg (0 and 1.5 kg ha?1) and two levels of P (0 and 5.3 kg ha?1). The application was done annually. There was a significant growth increase for the two N treatments. During a period of 5-years the mean increase in volume increment was 2.3 and 4.5 m3 ha?1 for the 30 N and 90 N kg ha?1 yr?1 treatments, respectively. This represents a percentage increase in volume increment of 53 and 102% compared to the untreated control plots. No significant growth effect of P and Mg application was detected, either alone or in combination with N. The needle nutrient concentrations have been followed along with the annual measurements. An increase in N-concentration was detected after the first growing season in the N treated trees. After five years the Mg concentrations in the needles are lower in these treatments. The one year old needles have concentrations as low as 0.05% Mg. No visible deficiency symptoms have been observed. The field experiment effects demonstrates that N is still the most limiting nutrient under these conditions and that there is a relative large potential for N accumulation in these forest types without negative effects.  相似文献   

10.
《Pedobiologia》2014,57(4-6):263-269
Nitrogen (N) availability is an important factor that determines ecosystem productivity and respiration, especially in N-limited alpine ecosystems. However, the magnitude of this response depends on the timing and amounts of N input. Moreover, we have only a limited understanding of the potential effects of the timing of N fertilization on ecosystem carbon (C) and N processes, and activities of the soil microbes. A nitrogen fertilization experiment was conducted in an alpine meadow on the Tibetan Plateau to determine how plant productivity and ecosystem respiration (RE) respond to the timing and amount of N application. In this study, half of the N was added either in the early spring (ES), before the growing season, or in the late fall (LF), after the growing season. All treatments received the other half of the N in mid-July. Three N levels (10, 20, 40 kg N hm−2 yr−1) were used for each of two N treatments, with no N addition used as a control. Plant aboveground biomass, ecosystem respiration (RE) and soil respiration (RS) were measured for the 2011 and 2012 growing seasons. The LF treatment enhanced ecosystem CO2 efflux compared with the ES treatment at high N addition levels, resulting from an increase of soil dissolved organic C (DOC) and soil microbial activity. The ES treatment resulted in increased plant aboveground biomass when compared with LF during both growing seasons, although this increase accounted for little variation in ecosystem and soil respiration. Overall, the ES treatment is likely to increase the ecosystem C pool, while the LF treatment could accelerate ecosystem C cycling, especially for the high N treatment. Our results suggest that supplying N during the early stage of the growing season benefits both forage production and soil C sequestration in this alpine ecosystem.  相似文献   

11.
 Nitrogen (N) fluxes through the major plant pools of an alder (Alnus sinuta)-sweet corn (Zea mays) alley cropping system were determined over the course of two cropping seasons. Alder trees were injected with 15NO3–N to directly follow the flow of N between alder and corn. The contribution of the above- and below-ground tree N to corn was determined by exchanging the labeled above-ground prunings (green manure) with those from unlabeled plots. During the first growing season after coppicing of the injected alders, 18% of the alder 15N was taken up by the corn with 12% coming from the above-ground prunings. Of the 15N remaining in the tree/stump following coppicing, the majority was recovered by corn plants within the rows next to the labeled trees during the first growing season. Earlier recovery of 15N by corn in the labeled root plots compared to the labeled pruning plots indicated the importance of root turnover in supplying N to corn, especially following coppicing. By the end of the first and second growing seasons, 34% and 38% of the 15N initially present in prunings was recovered in corn plants, respectively. Approximately 80% of the total injected 15N was found in the soil during the second growing season; however, the turnover of above- and below-ground alder components supplied only 3–4% of the N required by corn during the year of green manure application. Thus, most of the corn N demand was met by mineralization of residual soil N within the 2 years of coppicing and green manure additions. Continued internal cycling of tree N and movement of soil N into more labile pools would presumably allow more alder N to become available over time. The synchronization between N mineralization from the hedgerow green manure components and nutrient uptake of the alley crop remains a major challenge in alley cropping and other green manure systems. Received: 9 April 1999  相似文献   

12.
Loblolly pine seedlings of five half-sib families were grown under ambient, subambient (approximately 0.6 × ambient), and elevated [ambient + 60 ppb O3 (120 μg m?3)] O3 levels for one growing season in open-topped chambers. Diameter and height of the seedlings were measured periodically over the growing season, and above ground and below ground biomass were determined at harvest. Significant genetic differences were found in above ground volume (D 2H) 1 mo after 03 fumigation began and continued until harvest. Biomass of secondary needles and coarse and fine roots also differed significantly among families. Elevated O3 resulted in significantly decreased D 2H and secondary needle biomass relative to seedlings grown in ambient air. Seedlings receiving subambient O3 levels were intermediate in size, but were not significantly different from seedlings fumigated at ambient O3 levels. Root and stem biomass did not differ significantly among treatments. A significant interaction of O3 and genotype was detected, suggesting that the response of loblolly pine to O3 is influenced by genotype.  相似文献   

13.
The possible effects of excreta of the Great Cormorant Phalacrocorax carbo on decomposition processes and dynamics of nutrients (N, P, Ca, K, Mg) and organic chemical components (lignin, total carbohydrates) were investigated in a temperate evergreen coniferous forest near Lake Biwa in central Japan. Two-year decomposition processes of needles and twigs of Chamaecyparis obtusa were examined at two sites, control site never colonized by the cormorants (site C) and colonizing site (site 2). Mass loss was faster in needles than in twigs. Mass loss of these litter types was faster at site C than at site 2, which was ascribed to the decreased mass loss rate of acid-insoluble ‘lignin’ at site 2. Net immobilization of N, P, and Ca occurred in needles and twigs at site 2; whereas at site C, mass of these elements decreased without immobilization during decomposition. Duration of immobilization phase of these nutrients at site 2 was estimated to be 1.6 to 2.5 years in needles and 19.6 to 23.5 years in twigs. Immobilization potential (maximum amount of exogenous nutrient immobilized per gram initial material) was similar between needles and twigs for N and Ca but was about 10 times higher in twigs than in needles for P. δ13C in needles was relatively constant during the first year and then increased during the second year, whereas δ13C in twigs was variable during decomposition. Acid-insoluble fraction was depleted in 13C compared to whole needles (1.6-2.1‰) and twigs (2.0-2.5‰). δ15N of needles and twigs and their acid-insoluble fractions approached to δ15N of excreta during decomposition at site 2. This result demonstrated the immobilization of excreta-derived N into litter due to the formation of acid-insoluble lignin-like substances complexed with excreta-derived N. No immobilization occurred in K and Mg and their mass decreased during decomposition at both sites. Based on these results of nutrient immobilization during decomposition and on the data of litter fall and excreta amount at site 2, we tentatively calculated stand-level immobilization potential of litter fall and its contribution to total amount of N and P deposited as excreta. Thus, the potential maximum amount immobilized into litter fall (needles and twigs) was estimated to account for 5-7% of total excreta-derived N and P.  相似文献   

14.
小麦玉米轮作条件下不同生物质炭对土壤腐殖物质的影响   总被引：2，自引：0，他引：2  
生物质炭是有效的土壤固碳材料.通过1年的田间试验探究了小麦玉米轮作施用花生壳生物质炭和木材生物质炭后盐化潮土腐殖物质(HS)含量及化学结构的变化.试验设置不施肥(CK)、常规单施化肥(T1)、花生壳生物质炭(T2)、木材生物质炭(T3)4个处理.结果表明,与CK和T1处理相比,小麦季和玉米季生物质炭处理的土壤有机碳(s...  相似文献   

15.
The concentration of fluoride in needles, its effects on tree defoliation and on decomposition of needles (litter), and its subsequent accumulation in the upper soil horizons were observed in pine plantations near and far from a new aluminum smelter. Pinus taeda and Pinus palustris stands within 0.8 km of the smelter had significantly higher levels of foliar F than a P. taeda stand 1.8 km from the source. Neither temporal patterns nor amounts of needlefall were altered by airborne F from the smelter. In addition, elevated levels of foliar F did not affect the rate of decomposition of pine needles over a period of 6 mo. Soluble F in soil samples increased significantly in the upper 10 cm of the soils at the sites nearest the F source over a period of 7 yr since the start of F emissions.  相似文献   

16.
No-tillage (NT) is becoming increasingly attractive to farmers because it clearly reduces production costs relative to conventional tillage (CT). However, many producers in southern Italy are reluctant to adopt this practice because NT can have contrasting consequences on grain yield depending on weather conditions. The effect of NT and CT on continuous durum wheat (Triticum durum Desf.) under rainfed Mediterranean conditions was studied, over a 3-year period (2000–2002) at two locations (Foggia and Vasto) in southern Italy. Yield, grain quality [thousand kernel weight (TKW), test weight (TW) and protein content (PC)] and soil water content were assessed.Higher yield was obtained with NT than CT in the first 2 years at Foggia. In contrast, mean yield and quality parameters at Vasto were similar for the two treatments, except in the third year in which CT produced more than NT (4.6 Mg ha−1 versus 2.9 Mg ha−1). At Foggia, TW and TKW were higher in NT than CT in all years. Highest PC was obtained under CT (19.6% and 15.5% for CT versus 14.7% and 11.4% for NT, respectively, in the growing season 2000–2001 and 2001–2002) indicating that grain was shriveled with low starch accumulation.At Foggia, where this study was part of a long-term experiment started in 1995, a strong correlation was observed between yield and rainfall during the wheat growing season. The coefficient of determination (R2) values for CT and NT were 0.69* and 0.31 ns, respectively, and the regression straight line crossed around 300 mm of rainfall. These results indicate that NT was superior below this rainfall value, whereas more rainfall enhanced yield in CT. We conclude that NT performed better at Foggia with limited rainfall during the durum wheat growing season. The superior effect of NT in comparison to CT, was due to lower water evaporation from soil combined with enhanced soil water availability.  相似文献   

17.
《Applied soil ecology》2005,28(2):175-189
Small-scale spatial variation in N availability, substrate induced respiration (SIR) and population dynamics of nematodes in mineral soil and beech (Fagus sylvatica L.) litter were studied along two transects through a newly formed gap and surrounding forest in a semi-natural mixed deciduous forest in Denmark for three years after gap formation. In the litter, C/N ratio dropped, while decomposition rates and numbers of nematodes were stimulated in the gap as compared to under closed canopy. In contrast, the number of nematodes in soil were inhibited in the gap for two years after gap formation, but gradually recovered in the third year. Recovery was most marked in the northern part of the gap centre where dense regeneration of ash (Fraxinus excelsior L.) occurred. Omnivorous and predatory nematodes became more prevalent one year after gap formation. Effects on trophic groups of nematodes had disappeared by the end of the study period. The maturity index for nematodes was low one year after gap formation and was still lower in the gap than in the surrounding forest at the end of the study period. SIR in soil was lowest in the gap. Results thus indicate a stimulation of decomposers in the litter layer due to formation of the gap and a contrasting inhibition followed by recovery of decomposers in the soil, possibly governed by changes in C input from living roots. Soil C/N ratio, content of soil organic matter (SOM) and monthly nitrification and net N mineralization rates were not affected by a change in forest development phases caused by gap formation. However, seasonal trends and large spatial variation in net N mineralization and nitrification rates were apparent. Soil NH4–N concentrations dropped markedly at the onset of the growing season in the second year and remained lower in the gap than in the closed forest throughout the growing season, possibly reflecting an increased N demand of the ash regeneration.  相似文献   

18.
Eddy-covariance measurements of net ecosystem exchange of CO2 (NEE) and estimates of gross ecosystem productivity (GEP) and ecosystem respiration (RE) were obtained in a 2-4 year old Eucalyptus plantation during two years with very different winter rainfall. In the first (drier) year the annual NEE, GEP and RE were lower than the sums in the second (normal) year, and conversely the total respiratory costs of assimilated carbon were higher in the dry year than in the normal year.Although the net primary production (NPP) in the first year was 23% lower than that of the second year, the decrease in the carbon use efficiency (CUE = NPP/GEP) was 11% and autotrophic respiration utilized more resources in the first, dry year than in the second, normal year. The time variations in NEE were followed by NPP, because in these young Eucalyptus plantations NEE is very largely dominated by NPP, and heterotrophic respiration plays only a relatively minor role.During the dry season a pronounced hysteresis was observed in the relationship between NEE and photosynthetically active radiation, and NEE fluxes were inversely proportional to humidity saturation deficit values greater than 0.8 kPa. Nighttime fluxes of CO2 during calm conditions when the friction velocity (u*) was below the threshold (0.25 m s−1) were estimated based on a Q10 temperature-dependence relationship adjusted separately for different classes of soil moisture content, which regulated the temperature sensitivity of ecosystem respiration.  相似文献   

19.
Lentils contain a range of prebiotic carbohydrates; however, genotypic and environmental implications of these components have not been well understood. The objective of this study was to determine the genetic and environmental variation of carbohydrate concentrations in three commonly grown lentil cultivars in South Dakota, USA at two locations over two growing seasons. Significant genetic and environmental variation was found for most of the constituents evaluated. Raffinose-family oligosaccharides (RFO) ranged from 3161 mg 100g?1 at Bison and 3670 mg 100g?1 at Wall and from 3217 mg 100g?1 to 3650 mg 100g?1 between cultivars. Moreover, RFO content was strongly correlated to a simple plant stress index (SI) in which higher estimated plant stress (e.g., low precipitation) produced higher levels of RFO. These results demonstrate important differences in prebiotic concentrations, which can be used for future lentil breeding efforts when matching cultivars to diverse growing climates with highly variable growing season precipitation.  相似文献   

20.
In present study, pollutant effects on needle surface characteristics of Pinus sylvestris in the area affected by a nitrogen fertilizer plant have been investigated over 1994–1997 year period. Near the factory, sites with 15–25-year-old trees on a 0.5–22 km interval were chosen. Mean monthly concentrations of NO2 and NH3 varied across the transect in the range of 1.8–8.8 µg m?3 and 1.8 – 69.3 µg m?3, respectively. NH3 concentrations exceeded the critical level (>23 µg m?3) only in the 0.5 km vicinity. Assessment of needle surface wettability by measuring contact angles (CA) of water droplets and surface quality by measuring stomatal area covered by structural wax (SW) revealed significant (p<0.05) needle age, site, and year of sampling related differences. Comparison of SW between sites showed reliably (p<0.05) higher surface wax erosion on one-year-old needles sampled in the area, where ammonia concentration exceeds critical level. Significant correlations between site SW on one-year-old needles and distance from the pollution source, NO2 and NH3 concentrations were detected (r = 0.539; r = ? 0.495; r = ? 0.426; p<0.001, respectively). Correlations between CA and factors mentioned were lower.  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