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 15 毫秒
1.
High-elevation red spruce-Fraser fir forests in the Southern Appalachian mountains: 1) receive among the highest rates of atmospheric deposition measured in North America, 2) contain old-growth forests, 3) have shown declines in forest health, 4) have sustained high insect-caused fir mortality, and 5) contain poorly buffered soils and stream systems. High rates of nitrogen and sulphur deposition (1900 and 2200 Eq·ha–1·yr–1, respectively) are dominated by dry and cloud deposition processes. Large leaching fluxes of nitrate-nitrogen (100–1400 Eq·ha–1·yr–1) occur within the soil profile. We have expanded the study to the watershed scale with monitoring of: precipitation, throughfall, stream hydrology, and stream chemistry. Two streamlets drain the 17.4 ha Noland Divide Watershed (1676–1920m) located in the Great Smoky Mountains National Park. A network of 50 20x20 m plots is being used to assess stand structure, biomass, and soil nutrient pools. Nitrate is the predominant anion in the streamlets (weighted concentrations: 47 and 54 eq·L–1 NO3 –; 31 and 43 eq·L–1 SO4 2–). Watershed nitrate export is extremely high (1000 Eq·ha–1 yr–1), facilitating significant base cation exports. Stream acid neutralizing capacity values are extremely low (–10 to 20 eq·L–1) and episodic acidifications (pH declines of a full unit in days or weeks time) occur. Annual streamwater sulfate export is on the order of 770 Eq·ha–1yr–1 or about one-third of total annual inputs, indicating there is net watershed sulfate retention. The system is highly nitrogen saturated (Stage 2, Stoddard, 1994) and this condition promotes both chronic and episodic stream acidification.  相似文献   

2.
Atmospheric deposition of N and S on terrestrial and aquatic ecosystems causes effects induced by eutrophication and acidification. Effects of eutrophication include forest damage, NO3 pollution of groundwater and vegetation changes in forests, heathlands and surface waters due to an excess of N. Effects of acidification include forest damage, groundwater pollution, and loss of fish populations due to Al mobilization. Critical loads (deposition levels) for N and S on terrestrial and aquatic ecosystems in the Netherlands related to these effects have been derived by empirical data and steady-state acidification models. Critical loads of N generally vary between 500 and 1500 mol c ha?1 yr?1 for forests, heathlands and surface waters and between 1500 and 3600 for phreatic groundwaters. Critical loads of total acid (S and N) vary between 300 to 500 mol c ha?1 yr?1 for phreatic groundwaters and surface waters and between 1100 to 1700 mol ha?1 yr?1 for forests. On the basis of the various critical loads a deposition target for total acid of 1400 mol c ha?1 yr?1 has been set in the Netherlands from which the N input should be less than 1000 mol c ha?1 yr?1. This level, to be reached in the year 2010, implies an emission reduction of 80–90% in SO2, NO x and NH3 in the Netherlands and of about 30% in neighboring countries compared to 1980 emissions.  相似文献   

3.
Input-output fluxes of nitrogen (N) and other ecosystem data from 64 European forest ecosystem studies have been compiled in a database (ECOFEE). Sites with high N deposition (up to 64 kg N ha–1yr–1) were characterized by high input of ammonia/ammonium. The deposition of oxidized N was usually only 10 to 15 kg N ha–1yr–1 Of all the sites included, 60 % leached more than 5 kg N ha–1yr–1. Elevated nitrate leaching appeared at inputs above 10 kg N ha–1yr–1. At several sites with inputs of 15–25 kg N ha–1yr–1 nitrate leaching approached the N input, whereas ammonium dominated sites with high input still retained c. 50 % of the input.  相似文献   

4.
Computer assessments of the atmospheric chemistry and air quality of the past, present, and future rely in part on inventories of emissions constructed on appropriate spatial and temporal scales and with appropriate chemical species. Accurate inventories are also of substantial utility to field measurement scientists and the regulatory and policy communities. The production of global emissions inventories is the task of the Global Emissions Inventory Activity (GEIA) of the International Global Atmospheric Chemistry Project (IGAC). This paper presents a summary of recent emissions inventories from GEIA and other programs for reference year 1985, with special attention directed to emissions of the acid-related compounds CO2 (6.2 Pg C yr–1 anthropogenic), SOx (65 Tg S yr–1 anthropogenic and 15 Tg S yr–1 natural), NOx (21 Tg N yr–1 anthropogenic and 15–20 Tg N yr–1 natural), HCl (55 Tg Cl yr–1 total), and NH3 (45 Tg N yr–1 total). The global acid-equivalent flux of about 4.2 Teq H+yr–1 is about equally attributable to SOx and NOx emissions. For some of the acid-related species, historic inventories are available for a century or more; all show dramatic emissions increases over that period. IPCC scenario IS92a is used here as the basis for constructing global acid-related emissions estimates for selected years to 2100; among the results are that acid equivalent emissions are expected to more than double in the coming century.  相似文献   

5.
We used the needle trace method to investigate changes in the state of a Scots pine (Pinus sylvestris L.) stand in a bog (Voorepera) in the north-eastern part of Estonia, the most polluted area of the country. Additionally, we chose six sampling sites in other parts of Northeast Estonia (polluted area) and eight sites in southern Estonia (unpolluted area) to compare the state of pine stands in different bogs. During the period of 1964–1997, the radial growth had increased from 0.27 to 2.16 mm yr–1 and the annual shoot length from 0.10 to 0.28 m in Voorepera. Mean values of the period (1.13 mm yr–1 and 0.26 m, respectively) were two and four times higher in Voorepera than the average of the other bogs (0.5 mm yr–1 and 0.06 m, respectively). Maximum needle age fluctuated between three and five growing seasons in Voorepera, the mean (four growing seasons) was similar to that of other bogs (four growing seasons). Except radial growth, which was 0.6 mm yr–1 in the polluted area and 0.4 mm yr–1 in the unpolluted area, other indices of trees' health (shoot growth, needle age, nitrogen concentration in needles) and substrate conditions (water pH and N concentration) did not show clear differences between polluted and unpolluted areas. We conclude that air pollution from oil shale industry (thermal power plant and chemical factories) enhances the growth of pines in bogs, which can induce drastic changes in these ecosystems. However, the effect is currently obvious only in the vicinity of pollution sources.  相似文献   

6.
Critical acid loads for Dutch forests were derived using a multi-layer steady-state model that includes canopy interactions, nutrient cycling, mineral weathering and N transformations. Values were calculated for combinations of 12 tree species and 23 soil types for a 10×10 km grid. Critical acid loads thus derived increased with decreasing soil depth. Nearly 90% of the values varied approximately between 1500 and 4000 molc ha?1 yr?1 at 10 cm soil depth and between 750 and 2000 molc ha?1 yr?1 at the bottom of the rootzone. Separate critical loads calculated for N and S at the bottom of the rootzone varied between approximately 300 and 1000 molc ha?1 yr?1 for N and between 150 and 1250 molc ha?1 yr?1 for S. Using deposition data of 1990, a median reduction of the deposition by approximately 75% was calculated to achieve the critical loads at the bottom of the rootzone. The overall uncertainty in this value was estimated to be about 10%, although it can be much larger for specific soil types such as clay and peat soils. For N a larger reduction deposition percentage was calculated than for S, especially for coniferous forests with a high present N input.  相似文献   

7.
Summary Soil enzyme activities (acid and alkaline phosphatase, arylsulfatase, -glucosidase, urease and amidase) were determined (0- to 20-cm depth) after 55 years of crop-residue and N-fertilization treatment in a winter wheat (Triticum aestivum L.)-fallow system on semiarid soils of the Pacific Northwest. All residues were incorporated and the treatments were: straw (N0), straw with fall burn (N0FB), straw with spring burn (N0SB), straw plus 45 kg N ha–1 (N45), straw plus 90 kg N ha–1 (N90), straw burned in spring plus 45 kg N ha–1 (N45SB), straw burned in spring plus 90 kg N ha–1 (N90SB), straw plus 2.24 T ha–1 pea-vine residue and straw plus 22.4 T ha–1 of straw-manure. Enzyme activities were significantly (P<0.001) affected by residue management. The highest activities were observed in the manure treated soil, ranging from 36% (acid phosphatase) to 190% increase in activity over the control (N0). The lowest activities occurred in the N0FB (acid phosphatase, arylsulfatase and -glucosidase) and N90 treated soils (alkaline phosphatase, amidase and urease). Straw-burning had a significant effect only on acid phosphatase activity, which decreased in spring burn treated soil when inorganic N was applied. Urease and amidase activity decreased with long-term addition of inorganic N whereas the pea vine and the manure additions increased urease and amidase activity. There was a highly significant effect from the residue treatments on soil pH. Arylsulfatase, urease, amidase and alkaline phosphatase activities were positively correlated and acid phosphatase activity was negatively correlated with soil pH. Enzyme activities were strongly correlated with soil organic C and total N content. Except for acid phosphatase, there was no significant relationship between enzyme activity and grain yield.Journal Paper No. 8072 of the Agricultural Experimental Station, Oregon State University, Corvallis, OR 97331, USA  相似文献   

8.
Critical loads maps for UK freshwaters have been produced on a 10×10 km grid square basis, and used to map critical load exceedances under various deposition scenarios. A single lake or stream site was selected to represent the most sensitive water body in each grid square using predefined criteria. In the UK a major programme of data screening and validation has been undertaken in order to address issues of accuracy and validity. A major part of this validation exercise, the within-square variability study, is designed to test the extent to which the site chosen for mapping represents the most sensitive water body within each grid square or mapping unit. Sampling of all lake sites in thirty-two randomly chosen 10 × 10 km grid squares has shown that in two thirds of cases, the selection exercise has identified a site in the lowest critical load class within a square. However, up to a third of all sites selected to represent grid squares could be replaced by more sensitive sites with a critical load smaller by at least one Skokloster class. The mean overestimate of diatom model critical loads for sulphur in the within-square variability study is 0.188 keq ha–1 yr–1. This means that current critical load maps show overestimates for some grid squares. In order to determine where the most sensitive site has not been identified, further work on catchment scale classification of freshwater sensitivity is being carried out.  相似文献   

9.
A spatial and temporal investigation of dissolved inorganic nitrogen (DIN; NO3, NO2 and NH4) was conducted under various water discharge conditions in Lanyang-Hsi, a subtropical mountainous stream, which drains through distinct degrees of agriculture-influenced sub-watersheds. In both the cultivated and non-cultivated sub-watersheds, NO3 was the most abundant species accounting for >80% of total DIN, while NH4 and NO2 accounted for <15% and=" 5%=" of=" din,=" respectively.=" agricultural=" activities=" along=" the=" riverbank=" led=" to=" significantly=" higher=">3 concentrations (13–246 M) and DIN yields (1300–3800 kg N km–2 yr–1) in main channel when compared to those of non-cultivated tributaries (9–38 M for NO3 and 550–740 kg N km–2 yr–1 for yield). The much lower and less variable DIN yields observed in tributary stations (mean = 660 ± 120 kg N km–2 yr–1) are considered as the present day background of DIN yield, which is significantly higher than those of most natural watersheds in other regions. Elevated atmospheric DIN deposition is likely the cause for the high background DIN yield. Human activity within the watershed results in additional DIN yield, which accounted for 49% of total N export. However, the reported atmospheric DIN input in northern Taiwan (1800 kg N km–2 yr–1) is much higher than the background DIN yield implying that a major fraction (70%) of atmospheric inputs are retained or processed within the watershed. A dilution pattern occurred in the main channel where high NO3 concentrations from the upstream sources decreased significantly in downstream direction due to inputs of NO3-diluted water from non-cultivated areas. We adopted a two-source mixing model to predict the NO3 dilution pattern. This model revealed a third yet not recognized N source in the lower part of watershed. Model results also indicated the importance of water discharge rate in regulating the relative contribution to total DIN export among these sources.  相似文献   

10.
Long-term changes in the chemistry of precipitation (1978–94) and 16 lakes (1982–94) were investigated in the Adirondack region of New York, USA. Time-series analysis showed that concentrations of SO4 2–, NO3 –, NH4 + and basic cations have decreased in precipitation, resulting in increases in pH. A relatively uniform rate of decline in SO4 2– concentrations in lakes across the region (1.81±0.35 eq L–1 yr–1) suggests that this change was due to decreases in atmospheric deposition. The decrease in lake SO4 2– was considerably less than the rate of decline anticipated from atmospheric deposition. This discrepancy may be due to release of previously deposited SO4 2– from soil, thereby delaying the recovery of lake water acidity. Despite the marked declines in concentrations of SO4 2– in Adirondack lakes, there has been no systematic increase in pH and ANC. The decline in SO4 2– has corresponded with a near stoichiometric decrease in concentrations of basic cations in low ANC lakes. A pattern of increasing NO3 – concentrations that was evident in lakes across the region during the 1980's has been followed by a period of lower concentrations. Currently there are no significant trends in NO3 – concentrations in Adirondack lakes.  相似文献   

11.
The applicability of critical load (CL) methodology for thedetermination of natural terrestrial ecosystem sensitivity to sulfur acidity loading in South Korea was investigated.The sulfur critical load values, CLmaxS, were calculated for the terrestrial ecosystems of South Korea using the steady-state mass balance approach. The corresponding mapping of CLmaxS was carried out on the scale of 11 × 14 km grid cells. The estimated CLmaxS values depend on the low rate of soil chemical base cation weathering (mainly, 200–400 eq ha-1 yr-1), relativelylow base cation depositions (mainly less than 450 eq ha-1 yr-1) and base cation uptake (predominantly 300–400 eq ha-1 yr-1), and in significant degree on high valuesof acid neutralizing capacity. The latter in turn is connectedwith relatively high values of surface runoff (maximum 9000 m3 ha-1 yr-1). It has been shown that about 75%of CLmaxS values are in the range of 1000–2000 eq ha-1 yr-1 and about 15% are relatively low values(<1000 eq ha-1 yr-1). About 10% of ecosystems haveCL values more than 2000 eq ha-1 yr-1. The sensitiveand very sensitive ecosystems occur in the southeastern part of the country whereas the sustainable ecosystems are wide spread in the northeastern part. In accordance with sulfur critical load and sulfur deposition patterns, in 1994–1997 the CLmaxS values were found to be exceeded in about 40% of total number of Korean ecosystems, mainly in the southeastern part of the country. The average yearly valuesof exceedances varied from 176 to 3100 eq ha-1 yr-1.  相似文献   

12.
Critical loads for N and S on Dutch forest ecosystems have been derived in relation to effects induced by eutrophication and acidification, such as changes in forest vegetation, nutrient imbalances, increased susceptibility to diseases, nitrate leaching, and Al toxicity. The criteria that have been used are N contents in needles, nitrate concentrations in groundwater (drinking water), and NH4/K ratios, Ca/Al ratios, and Al concentrations in the soil solution. Assuming an equal contribution of N and S, all effects seem to be prevented at a total deposition level below 600 molc ha?1 yr?1 due to N uptake by stemwood and acid neutralization by base cation weathering. The most serious effects will probably be prevented at total deposition levels between 1500 and 2000 molc ha?1 yr?1. The current average deposition in the Netherlands is 4900 molc ha?1 yr?1.  相似文献   

13.
Critical loads for N, S and total acidity, and amounts by which they are exceeded by present atmospheric loads, were derived for coniferous and deciduous forests in Europe using the one-layer steady-state model START. Results indicated that present acid loads exceed critical values in approximately 45% of the forested area i.e. 52% of all coniferous forests and 33% of all deciduous forests. The area exceeding critical loads was nearly equal for N (50%) and S (52%). However, the maximum exceedances were much higher for S (up to 12000 molc ha?1 yr?1 in Czechoslovakia, Poland and Germany) than for N (up to 3500 molc ha?1 yr?1 in the Netherlands, Belgium and Germany). Furthermore, the critical N loads derived refer to the risk of increased vegetation changes. Higher values, i.e. lower exceedances, were found for N when it was related to an increased risk in forest vitality decrease. The uncertainty in the area exceeding critical loads was estimated to be about ±50% of the given value. This is mainly due to uncertainties in the chemical criteria that have been used. However, despite the uncertainties involved it is clear that large exceedances in critical N and S loads occur in Western and Central Europe. This coincides with the area where a decrease in forest vitality has been reported.  相似文献   

14.
Many ecosystems in Switzerland suffer from eutrophication due to increased atmospheric nitrogen (N) input. In order to get an overview of the problem, critical loads for nutrient N were mapped with a resolution of 1×1 km applying two methods recommended by the UN/ECE: the steady state mass balance method for productive forests, and the empirical method for semi-natural vegetation, such as natural forests, (sub-)alpine or species-rich grassland and raised bogs. The national forest inventory and a detailed atlas of vegetation types were used to identify the areas sensitive to N input. The total N input was calculated as the sum of NO3 ?, NH4 +, NH3, NO2 and HNO3 wet and dry deposition. Wet deposition was determined on the basis of a precipitation map and concentration measurements. Dry deposition was calculated with inferential methods including land-use specific deposition velocities. The concentration fields for NH3 and NO2 were obtained from emission inventories combined with dispersion models. Reduced N compounds account for 63% of total deposition in Switzerland. As indicated by exceeded critical loads, the highest risk for harmful effects of N deposition (decrease of ecosystem stability, species shift and losses) is expected on forests and raised bogs in the lowlands, where local emissions are intense. At high altitudes and in dry inner-alpine valleys, deposition rates are significantly lower.  相似文献   

15.
The critical load concept is now accepted throughout Europe as a means of estimating the sensitivity of key components of aquatic and terrestrial ecosystems to atmospheric inputs of sulphur (S) and nitrogen (N). Current UK freshwater maps, based on steady-state water chemistry, are derived using a critical acid neutralising capacity (ANCLIM) value of zero eql–1, which is based on the probability of occurrence of salmonid fish in lakes. In practice most acidification damage to salmonid fish occurs in nursery streams at the emergence and first feeding stages. In general a clear relationship exists between salmon (Salmo salar L.) and trout (S. trutta L.) densities in Scottish streams and ANC values. However, differences between sites depend on which ANC value is used (eg maximum, minimum or mean). By contrast, when the exceedance of critical loads is compared with salmonid densities the relationship is less clear because many exceeded sites have good salmonid densities. Many of these latter sites are found in north-west Scotland where sea-salt inputs are high and ANC is usually greater than zero eql–1, although diatom-based studies indicated slight acidification of these waters, with a point of change in diatom flora close to ANC=20 eql–1. These false exceedances are probably due to preferential adsorption of acidic SO4 deposition which results in an overestimate of exceedance values. All sites with a mean ANC 0 are fishless but some sites with negative minimum ANC values had normal salmonid densities. Consequently a mean ANCLIM value of zero in the critical load equations for UK freshwaters appears to be too low to protect salmonid stocks. Values between 20–50 eql–1 represent a more realistic range if prevention of long term damage to salmonid stocks is to be achieved.  相似文献   

16.
Information on N cycling in dryland crops and soils as influenced by long-term tillage and cropping sequence is needed to quantify soil N sequestration, mineralization, and N balance to reduce N fertilization rate and N losses through soil processes. The 21-yr effects of the combinations of tillage and cropping sequences was evaluated on dryland crop grain and biomass (stems + leaves) N, soil surface residue N, soil N fractions, and N balance at the 0–20 cm depth in Dooley sandy loam (fine-loamy, mixed, frigid, Typic Argiboroll) in eastern Montana, USA. Treatments were no-tilled continuous spring wheat (Triticum aestivum L.) (NTCW), spring-tilled continuous spring wheat (STCW), fall- and spring-tilled continuous spring wheat (FSTCW), fall- and spring-tilled spring wheat–barley (Hordeum vulgare L.) (1984–1999) followed by spring wheat–pea (Pisum sativum L.) (2000–2004) (FSTW-B/P), and spring-tilled spring wheat–fallow (STW-F). Nitrogen fractions were soil total N (STN), particulate organic N (PON), microbial biomass N (MBN), potential N mineralization (PNM), NH4-N, and NO3-N. Annualized crop grain and biomass N varied with treatments and years and mean grain and biomass N from 1984 to 2004 were 14.3–21.2 kg N ha−1 greater in NTCW, STCW, FSTCW, and FSTW-B/P than in STW-F. Soil surface residue N was 9.1–15.2 kg N ha−1 greater in other treatments than in STW-F in 2004. The STN at 0–20 cm was 0.39–0.96 Mg N ha−1, PON 0.10–0.30 Mg N ha−1, and PNM 4.6–9.4 kg N ha−1 greater in other treatments than in STW-F. At 0–5 cm, STN, PON, and MBN were greater in STCW than in FSTW-B/P and STW-F. At 5–20 cm, STN and PON were greater in NTCW and STCW than in STW-F, PNM and MBN were greater in STCW than in NTCW and STW-F, and NO3-N was greater in FSTW-B/P than in NTCW and FSTCW. Estimated N loss through leaching, volatilization, or denitrification at 0–20 cm depth increased with increasing tillage frequency or greater with fallow than with continuous cropping and ranged from 9 kg N ha−1 yr−1 in NTCW to 46 kg N ha−1 yr−1 in STW-F. Long-term no-till or spring till with continuous cropping increased dryland crop grain and biomass N, soil surface residue N, N storage, and potential N mineralization, and reduced N loss compared with the conventional system, such as STW-F, at the surface 20 cm layer. Greater tillage frequency, followed by pea inclusion in the last 5 out of 21 yr in FSTW-B/P, however, increased N availability at the subsurface layer in 2004.  相似文献   

17.
Sulphate deposition is the primary cause of acidification in northeastern North America, and new SO2 emission control is being implemented. However, continuation of existing levels of N deposition may undermine the environmental benefits derived from SO2 control. This likelihood has been assessed for Canadian lakes. Maximum N deposition (～13 kg N ha?1 yr?1) occurs in south-central Ontario and southwestern Quebec. Regional median NO 3 ? levels are generally low (<5 μeq L?1) suggesting that on average, N-based acidification is minor compared to the S-based component. However, examination of the seasonal NO 3 ? pattern at 5 intensively monitored basins reveals that 2 of them (in Ontario and Quebec) have incipient N saturation. A regional status for nitrogen-based acidification was qualitatively assessed by classifying survey data to identify cases of NO 3 ? leaching. Many lakes throughout southeastern Canada exhibit some leaching, particularly those in south-central Ontario and southwestern Quebec. While the evidence for a deposition-acidification link appears strong, sources of N other than the atmosphere should be considered for certain anomalous cases.  相似文献   

18.
This paper focuses on N balance in a paddy field planted with whole crop rice (Oryza sativa cv. Kusahonami). The experiment was conducted with two treatments during two rice-growing seasons: one was fertilized with N (160 kg N ha–1; 16N plot) and the other unfertilized (0N plot); both plots were fertilized with P and K. The N input from precipitation was 15 and 12 kg N ha–1 in 2002 and 2003, respectively. The N input from irrigation water reached as much as 123 and 69 kg N ha–1 in 2002 and 2003, respectively. This was because irrigation water contained higher NO3– concentrations ranging from 4 to 8 mg N l–1. The N uptake by rice plants was the major output: 118 and 240 kg N ha–1 in the 0N and 16N plots in 2002 and 103 and 238 kg N ha–1 in 2003, respectively. N losses by leaching were 4.8–5.3 and 6.5–7.3 kg N ha–1 in 2002 and in 2003, respectively. Laboratory experiments were carried out to estimate the amounts of N2 fixation and denitrification. Amount of N2 fixation was 43 and 0 kg N ha–1 in the 0N and 16N plots, respectively. Denitrification potential was quite high in both the plots, and 90% of the N input through irrigation water was lost through denitrification. Collectively, the total N inputs were relatively large due to irrigation water contaminated with NO3–, but N outflow loading, expressed as leaching–(irrigation water + precipitation + fertilizer), showed large negative values, suggesting that the whole crop rice field might serve as a constructed wetland for decreasing N.  相似文献   

19.
A simple dose-effect model expressing the relationships between lake acidity, weighted mean annual sulfate concentration in wet deposition, Ca, Mg and true color (as an index of organic anion concentration) is presented. The agreement between observed and estimated pH for more than a 1000 lakes is high according to the Pearson coefficients of correlation (0.81 to 0.90) and the standard error of estimation (0.22 to 0.27 pH unit). Results obtained with this model show that an airborne sulfate target loading of 20 kg ha?1 yr?1 would be too high to adequately protect sensitive lake ecosystems. A target loading of 15 kg ha?1 yr?1 in wet deposition would be best suited for the protection of the greater portion of sensitive lakes. However, a target loading of 10 kg ha?1 yr?1 would be required to protect the most sensitive lake ecosystems.  相似文献   

20.
Twenty fertilization experiments were set up in 1985 and 1986 in the Vosges mountains, using mostly calcareous or Mg fertilizers, in order to verify whether fertilization can attenuate defoliation and yellowing recently recorded in Silver fir and Norway spruce. In the Ardennes, a fertilization experiment set up in Norway spruce stands prior to the appearance of yellowing was assessed. In these areas, the total acid deposition is about 2 kg eq H+ ha–1 yr–1. Nitrogen deposition is much more important in the Ardennes (52 kg N ha–1 yr–1 in form of wet and dry deposition) than in the Vosges (16 kg N ha–1 yr–1). The results in the eight adult stands showed no uniform reaction to the treatments. Spontaneous improvement, further deterioration independently of the treatment, as well as a positive reaction to fertilization were observed. Additional N or P fertilization sometimes had a beneficial effect on Ca or Mg treatments. The selection of the stands with the best response turns out to be difficult, as the nutrient contents of needles alone seem not to be a satisfactory criterion for selection. Young plantations reacted positivley to the treatments. Soluble Mg fertilizer leads to an immediate response. Low solubility Ca-Mg fertilizers (Ca-Mg lime) did not produce reactions until three years after the application. In the Ardennes, in a 40 yr old spruce stand suffering from severe Mg deficiency, a Ca and Ca-phosphate fertilization applied 5 yr before yellowing appeared had positive effects on crown density, discoloration and wood production. Conversely, a single N fertilization in this experiment, as well as in a young plantation in the Vosges, had a marked negative effect on Mg nutrition, even at low levels.  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