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1.
Dissolved organic nitrogen (DON) has recently been recognized as an important component of terrestrial N cycling, especially
under N-limited conditions; however, the effect of increased atmospheric N deposition on DON production and loss from forest
soils remains controversial. Here we report DON and dissolved organic carbon (DOC) losses from forest soils receiving very
high long-term ambient atmospheric N deposition with or without additional experimental N inputs, to investigate DON biogeochemistry
under N-saturated conditions. We studied an old-growth forest, a young pine forest, and a young mixed pine/broadleaf forest
in subtropical southern China. All three forests have previously been shown to have high nitrate (NO 3−) leaching losses, with the highest loss found in the old-growth forest. We hypothesized that DON leaching loss would be forest
specific and that the strongest response to experimental N input would be in the N-saturated old-growth forest. Our results
showed that under ambient deposition (35–50 kg N ha −1 y −1 as throughfall input), DON leaching below the major rooting zone in all three forests was high (6.5–16.9 kg N ha −1 y −1). DON leaching increased 35–162% following 2.5 years of experimental input of 50–150 kg N ha −1 y −1. The fertilizer-driven increase of DON leaching comprised 4–17% of the added N. A concurrent increase in DOC loss was observed
only in the pine forest, even though DOC:DON ratios declined in all three forests. Our data showed that DON accounted for
23–38% of total dissolved N in leaching, highlighting that DON could be a significant pathway of N loss from forests moving
toward N saturation. The most pronounced N treatment effect on DON fluxes was not found in the old-growth forest that had
the highest DON loss under ambient conditions. DON leaching was highly correlated with NO 3− leaching in all three forests. We hypothesize that abiotic incorporation of excess NO 3− (through chemically reactive NO 2−) into soil organic matter and the consequent production of N-enriched dissolved organic matter is a major mechanism for the
consistent and large DON loss in the N-saturated subtropical forests of southern China.
Dr. YT Fang performed research, analyzed data, and wrote the paper; Prof. WX Zhu participated in the initial experimental
design, analyzed data, and took part in writing the paper; Prof. P Gundersen conceived the study and took part in writing;
Prof. JM Mo and Prof. GY Zhou conceived study; Prof. M Yoh analyzed part of the data and contributed to the development of
DON model. 相似文献
2.
The modification of large areas of tropical forest to agricultural uses has consequences for the movement of inorganic nitrogen
(N) from land to water. Various biogeochemical pathways in soils and riparian zones can influence the movement and retention
of N within watersheds and affect the quantity exported in streams. We used the concentrations of NO 3
− and NH 4
+ in different hydrological flowpaths leading from upland soils to streams to investigate inorganic N transformations in adjacent
watersheds containing tropical forest and established cattle pasture in the southwestern Brazilian Amazon Basin. High NO 3
− concentrations in forest soil solution relative to groundwater indicated a large removal of N mostly as NO 3
− in flowpaths leading from soil to groundwater. Forest groundwater NO 3
− concentrations were lower than in other Amazon sites where riparian zones have been implicated as important N sinks. Based
on water budgets for these watersheds, we estimated that 7.3–10.3 kg N ha −1 y −1 was removed from flowpaths between 20 and 100 cm, and 7.1–10.2 kg N ha −1 y −1 was removed below 100 cm and the top of the groundwater. N removal from vertical flowpaths in forest exceeded previously
measured N 2O emissions of 3.0 kg N ha −1 y −1 and estimated emissions of NO of 1.4 kg N ha −1 y −1. Potential fates for this large amount of nitrate removal in forest soils include plant uptake, denitrification, and abiotic
N retention. Conversion to pasture shifted the system from dominance by processes producing and consuming NO 3
− to one dominated by NH 4
+, presumably the product of lower rates of net N mineralization and net nitrification in pasture compared with forest. In
pasture, no hydrological flowpaths contained substantial amounts of NO 3
− and estimated N removal from soil vertical flowpaths was 0.2 kg N ha −1 y −1 below the depth of 100 cm. This contrasts with the extent to which agricultural sources dominate N inputs to groundwater
and stream water in many temperate regions. This could change, however, if pasture agriculture in the tropics shifts toward
intensive crop cultivation. 相似文献
3.
Converting deciduous forests to coniferous plantations and vice versa causes environmental changes, but till now insight into
the overall effect is lacking. This review, based on 38 case studies, aims to find out how coniferous and deciduous forests
differ in terms of throughfall (+stemflow) deposition and seepage flux to groundwater. From the comparison of coniferous and
deciduous stands at comparable sites, it can be inferred that deciduous forests receive less N and S via throughfall (+stemflow)
deposition on the forest floor. In regions with relatively low open field deposition of atmospheric N (<10 kg N ha −1 year −1), lower NH 4+ mean throughfall (+stemflow) deposition was, however, reported under conifers compared to deciduous forest, while in regions
with high atmospheric N pollution (>10 kg N ha −1 year −1), the opposite could be concluded. The higher the open field deposition of NH 4+, the bigger the difference between the coniferous and deciduous throughfall (+stemflow) deposition. Furthermore, it can be
concluded that canopy exchange of K +, Ca 2+ and Mg 2+ is on average higher in deciduous stands. The significantly higher stand deposition flux of N and S in coniferous forests
is reflected in a higher soil seepage flux of NO 3−, SO 42−, K +, Ca 2+, Mg 2+ and Al(III). Considering a subset of papers for which all necessary data were available, a close relationship between throughfall
(+stemflow) deposition and seepage was found for N, irrespective of the forest type, while this was not the case for S. This
review shows that the higher input flux of N and S in coniferous forests clearly involves a higher seepage of NO 3− and SO 42− and accompanying cations K +, Ca 2+, Mg 2+ and Al(III) into the groundwater, making this forest type more vulnerable to acidification and eutrophication compared to
the deciduous forest type. 相似文献
4.
Few data sets have characterized carbon (C) and nitrogen (N) pools in woody debris at sites where other aspects of C and N
cycling are studied and histories of land use and disturbance are well documented. We quantified pools of mass, C, and N in
fine and coarse woody debris (CWD) in two contrasting stands: a 73-year-old red pine plantation on abandoned agricultural
land and a naturally regenerated deciduous forest that has experienced several disturbances in the past 150 years. Masses
of downed woody debris amounted to 40.0 Mg ha −1 in the coniferous stand and 26.9 Mg ha −1 in the deciduous forest (20.4 and 13.8 Mg C ha −1, respectively). Concentrations of N were higher and C:N ratios were lower in the deciduous forest compared to the coniferous.
Pools of N amounted to 146 kg N ha −1 in the coniferous stand and 155 kg N ha −1 in the deciduous forest; both are larger than previously published pools of N in woody debris of temperate forests. Woody
detritus buried in O horizons was minimal in these forests, contrary to previous findings in forests of New England. Differences
in the patterns of mass, C, and N in size and decay classes of woody debris were related to stand histories. In the naturally
regenerated deciduous forest, detritus was distributed across all size categories, and most CWD mass and N was present in
the most advanced decay stages. In the coniferous plantation, nearly all of the CWD mass was present in the smallest size
class (less than 25 cm diameter), and a recognizable cohort of decayed stems was evident from the stem-exclusion phase of
this even-aged stand. These results indicate that heterogeneities in site histories should be explicitly included when biogeochemical
process models are used to scale C and N stocks in woody debris to landscapes and regions.
Received 27 April 2001; accepted 4 January 2002. 相似文献
5.
Nitrogen (N) inputs from atmospheric deposition can increase soil organic carbon (SOC) storage in temperate and boreal forests, thereby mitigating the adverse effects of anthropogenic CO2 emissions on global climate. However, direct evidence of N-induced SOC sequestration from low-dose, long-term N addition experiments (that is, addition of < 50 kg N ha−1 y−1 for > 10 years) is scarce worldwide and virtually absent for European temperate forests. Here, we examine how tree growth, fine roots, physicochemical soil properties as well as pools of SOC and soil total N responded to 20 years of regular, low-dose N addition in two European coniferous forests in Switzerland and Denmark. At the Swiss site, the addition of 22 kg N ha−1 y−1 (or 1.3 times throughfall deposition) stimulated tree growth, but decreased soil pH and exchangeable calcium. At the Danish site, the addition of 35 kg N ha−1 y−1 (1.5 times throughfall deposition) impaired tree growth, increased fine root biomass and led to an accumulation of N in several belowground pools. At both sites, elevated N inputs increased SOC pools in the moderately decomposed organic horizons, but decreased them in the mineral topsoil. Hence, long-term N addition led to a vertical redistribution of SOC pools, whereas overall SOC storage within 30 cm depth was unaffected. Our results imply that an N-induced shift of SOC from older, mineral-associated pools to younger, unprotected pools might foster the vulnerability of SOC in temperate coniferous forest soils. 相似文献
6.
Nitrous oxide (N 2O) emissions from grazed grasslands are estimated to be approximately 28% of global anthropogenic N 2O emissions. Estimating the N 2O flux from grassland soils is difficult because of its episodic nature. This study aimed to quantify the N 2O emissions, the annual N 2O flux and the emission factor (EF), and also to investigate the influence of environmental and soil variables controlling
N 2O emissions from grazed grassland. Nitrous oxide emissions were measured using static chambers at eight different grasslands
in the South of Ireland from September 2007 to August 2009. The instantaneous N 2O flux values ranged from -186 to 885.6 μg N 2O-N m −2 h −1 and the annual sum ranged from 2 ± 3.51 to 12.55 ± 2.83 kg N 2O-N ha −1 y −1 for managed sites. The emission factor ranged from 1.3 to 3.4%. The overall EF of 1.81% is about 69% higher than the Intergovernmental
Panel on Climate Change (IPCC) default EF value of 1.25% which is currently used by the Irish Environmental Protection Agency
(EPA) to estimate N 2O emission in Ireland. At an N applied of approximately 300 kg ha −1 y −1, the N 2O emissions are approximately 5.0 kg N 2O-N ha −1 y −1, whereas the N 2O emissions double to approximately 10 kg N ha −1 for an N applied of 400 kg N ha −1 y −1. The sites with higher fluxes were associated with intensive N-input and frequent cattle grazing. The N 2O flux at 17°C was five times greater than that at 5°C. Similarly, the N 2O emissions increased with increasing water filled pore space (WFPS) with maximum N 2O emissions occurring at 60–80% WFPS. We conclude that N application below 300 kg ha −1 y −1 and restricted grazing on seasonally wet soils will reduce N 2O emissions. 相似文献
7.
Biometric based carbon flux measurements were conducted over 5 years (1999–2003) in a temperate deciduous broad-leaved forest
of the AsiaFlux network to estimate net ecosystem production (NEP). Biometric based NEP, as measured by the balance between
net primary production (including NPP of canopy trees and of forest floor dwarf bamboo) and heterotrophic respiration (RH),
clarified the contribution of various biological processes to the ecosystem carbon budget, and also showed where and how the
forest is storing C. The mean NPP of the trees was 5.4 ± 1.07 t C ha −1 y −1, including biomass increment (0.3 ± 0.82 t C ha −1 y −1), tree mortality (1.0 ± 0.61 t C ha −1 y −1), aboveground detritus production (2.3 ± 0.39 t C ha −1 y −1) and belowground fine root production (1.8 ± 0.31 t C ha −1 y −1). Annual biomass increment was rather small because of high tree mortality during the 5 years. Total NPP at the site was
6.5 ± 1.07 t C ha −1 y −1, including the NPP of the forest floor community (1.1 ± 0.06 t C ha −1 y −1). The soil surface CO 2 efflux (RS) was averaged across the 5 years of record using open-flow chambers. The mean estimated annual RS amounted to
7.1 ± 0.44 t C ha −1, and the decomposition of soil organic matter (SOM) was estimated at 3.9 ± 0.24 t C ha −1. RH was estimated at 4.4 ± 0.32 t C ha −1 y −1, which included decomposition of coarse woody debris. Biometric NEP in the forest was estimated at 2.1 ± 1.15 t C ha −1 y −1, which agreed well with the eddy-covariance based net ecosystem exchange (NEE). The contribution of woody increment (Δbiomass + mortality)
of the canopy trees to NEP was rather small, and thus the SOM pool played an important role in carbon storage in the temperate
forest. These results suggested that the dense forest floor of dwarf bamboo might have a critical role in soil carbon sequestration
in temperate East Asian deciduous forests. 相似文献
8.
There is growing evidence from different sources that prolonged high N deposition causes a shift from nitrogen (N) limitation
to nitrogen and phosphorus (P) co-limitation or even P limitation in many terrestrial ecosystems. However, the number of ecosystems
where the type of limitation has been directly tested by longer-term full-factorial field experiments is very limited. We
conducted a 5-year fertilization experiment with N and P in the Lüneburger Heide (NW Germany) to test the hypothesis that,
following decades of elevated atmospheric N inputs, plant growth in dry lowland heaths may have shifted from N to N–P co-limitation
or P limitation. We also tested whether the plant tissue N:P ratio reflects the type of nutrient limitation in a continental
lowland heathland. Experimental plots dominated by Calluna vulgaris received regular additions of N (50 kg N ha −1 y −1), P (20 kg P ha −1 y −1), a combination of both, or water only (control) from 2004 to 2008. Over the whole study period, a highly significant positive
N effect on shoot length was found, thus indicating N limitation. We conclude that a clear shift from N limitation to N–P
co-limitation or P limitation has not yet occurred. Tissue N:P ratios showed a high temporal variability and no relationship
between tissue N:P ratio and the shoot length response of Calluna to nutrient addition was found. The N:P tool is thus of limited use at the local scale and within the range of N:P ratio
observed in this study, and should only be used as a rough indicator for the prediction of the type of nutrient limitation
in lowland heathland on a larger geographical scale with a broader interval of N:P ratio. 相似文献
9.
Soil mineral weathering may serve as a sink for atmospheric carbon dioxide (CO 2). Increased weathering of soil minerals induced by elevated CO 2 concentration has been reported previously in temperate areas. However, this has not been well documented for the tropics
and subtropics. We used model forest ecosystems in open-top chambers to study the effects of CO 2 enrichment alone and together with nitrogen (N) addition on inorganic carbon (C) losses in the leachates. Three years of
exposure to an atmospheric CO 2 concentration of 700 ppm resulted in increased annual inorganic C export through leaching below the 70 cm soil profile. Compared
to the control without any CO 2 and N treatments, net biocarbonate C (HCO 3
−-C) loss increased by 42%, 74%, and 81% in the high CO 2 concentration treatment in 2006, 2007, and 2008, respectively. Increased inorganic C export following the exposure to the
elevated CO 2 was related to both increased inorganic C concentrations in the leaching water and the greater amount of leaching water.
Net annual inorganic C (HCO 3
−-C and carbonate C: CO 3
2−-C) loss via the leaching water in the high CO 2 concentration chambers reached 48.0, 49.5, and 114.0 kg ha −1 y −1 in 2006, 2007, and 2008, respectively, compared with 33.8, 28.4, and 62.8 kg ha −1 y −1 in the control chambers in the corresponding years. The N addition showed a negative effect on the mineral weathering. The
decreased inorganic C concentration in the leaching water and the decreased leaching water amount induced by the high N treatment
were the results of the adverse effect. Our results suggest that tropical forest soil systems may be able to compensate for
a small part of the atmospheric CO 2 increase through the accelerated processing of CO 2 into HCO 3
−-C during soil mineral weathering, which might be transported in part into ground water or oceans on geological timescales. 相似文献
10.
The input of phosphorus (P) through mineral aerosol dust deposition may be an important component of nutrient dynamics in
tropical forest ecosystems. A new dust deposition calculation is used to construct a broad analysis of the importance of dust-derived
P to the P budget of a montane wet tropical forest in the Luquillo Mountains of Puerto Rico. The dust deposition calculation
used here takes advantage of an internal geochemical signal (Sr isotope mass balance) to provide a spatially integrated longer-term
average dust deposition flux. Dust inputs of P (0.23 ± 0.08 kg ha −1 year −1) are compared with watershed-average inputs of P to the soil through the conversion of underlying saprolite into soil (between
0.07 and 0.19 kg ha −1 year −1), and with watershed-average losses of soil P through leaching (between 0.02 and 0.14 kg ha −1 year −1) and erosion (between 0.04 and 1.38 kg ha −1 year −1). The similar magnitude of dust-derived P inputs to that of other fluxes indicates that dust is an important component of
the soil and biomass P budget in this ecosystem. Dust-derived inputs of P alone are capable of completely replacing the total
soil and biomass P pool on a timescale of between 2.8 ka and 7.0 ka, less than both the average soil residence time (~15 ka)
and the average landslide recurrence interval (~10 ka). 相似文献
11.
Late-successional forests in the upper Great Lakes region are susceptible to nitrogen (N) saturation and subsequent nitrate
(NO 3−) leaching loss. Endemic wind disturbances (i.e., treefall gaps) alter tree uptake and soil N dynamics; and, gaps are particular
susceptible to NO 3− leaching loss. Inorganic N was measured throughout two snow-free periods in throughfall, forest floor leachates, and mineral
soil leachates in gaps (300–2,000 m 2, 6–9 years old), gap-edges, and closed forest plots in late-successional northern hardwood, hemlock, and northern hardwood–hemlock
stands. Differences in forest water inorganic N among gaps, edges, and closed forest plots were consistent across these cover
types: NO 3− inputs in throughfall were significantly greater in undisturbed forest plots compared with gaps and edges; forest floor leachate
NO 3− was significantly greater in gaps compared to edges and closed forest plots; and soil leachate NO 3− was significantly greater in gaps compared to the closed forest. Significant differences in forest water ammonium and pH
were not detected. Compared to suspected N-saturated forests with high soil NO 3− leaching, undisturbed forest plots in these late-successional forests are not losing NO 3− (net annual gain of 2.8 kg ha −1) and are likely not N-saturated. Net annual NO 3− losses were observed in gaps (1.3 kg ha −1) and gap-edges (0.2 kg ha −1), but we suspect these N leaching losses are a result of decreased plant uptake and increased soil N mineralization associated
with disturbance, and not N-saturation. 相似文献
12.
Old growth forest soils are large C reservoirs, but the impacts of tree-fall gaps on soil C in these forests are not well
understood. The effects of forest gaps on soil C dynamics in old growth northern hardwood–hemlock forests in the upper Great
Lakes region, USA, were assessed from measurements of litter and soil C stocks, surface C efflux, and soil microbial indices
over two consecutive growing seasons. Forest floor C was significantly less in gaps (19.0 Mg C ha −1) compared to gap-edges (39.5 Mg C ha −1) and the closed forest (38.0 Mg C ha −1). Labile soil C (coarse particulate organic matter, cPOM) was significantly less in gaps and edges (11.1 and 11.2 Mg C ha −1) compared to forest plots (15.3 Mg C ha −1). In situ surface C efflux was significantly greater in gaps (12.0 Mg C ha −1 y −1) compared to edges and the closed forest (9.2 and 8.9 Mg C ha −1 y −1). Microbial biomass N (MBN) was significantly greater in edges (0.14 Mg N ha −1) than in the contiguous forest (0.09 Mg N ha −1). The metabolic quotient (qCO 2) was significantly greater in the forest (0.0031 mg CO 2 h −1 g −1/mg MBC g −1) relative to gaps or edges (0.0014 mg CO 2 h −1 g −1/mg MBC g −1). A case is made for gaps as alleviators of old growth forest soil C saturation. Relative to the undisturbed closed forest,
gaps have significantly less labile C, significantly greater in situ surface C efflux, and significantly lower decreased qCO 2 values. 相似文献
13.
This study was conducted to examine the influences of soil-moisture conditions on soil nitrogen (N) dynamics, including in
situ soil N mineralization, N availability, and denitrification in a pure Alnus japonica forest located in Seoul, central Korea. The soil N mineralization, N availability, and denitrification were determined using
the buried bag incubation method, ion exchange resin bag method, and acetylene block method, respectively. The annual net
N mineralization rate (kg N ha −1 year −1) and annual N availability (mg N bag −1) were 40.26 and 80.65 in the relatively dry site, −5.43 and 45.39 in the moist site, and 7.09 and 39.17 in the wet site,
respectively. The annual net N mineralization rate and annual N availability in the dry site were significantly higher than
those in the moist and wet sites, whereas there was no significant difference between the moist and wet sites. The annual
mean denitrification rate (kg N ha −1 year −1) in the dry, moist, and wet sites was 2.37, 2.76, and 1.59, respectively. However, there was no significant difference among
sites due to the high spatial and temporal variations. Our results indicate that soil-moisture condition influenced the in
situ N mineralization and resin bag N availability in an A. japonica forest, and treatments of proper drainage for poorly drained sites would increase soil N mineralization and N availability
and consequently be useful to conserve and manage the A. japonica forest. 相似文献
15.
The present study was undertaken to assess the benefit and compare the functioning of AM fungi on wheat grown conventionally
and on beds. Ten treatment combinations were used, treatments 1 and 2: no fertilizers with and without arbuscular mycorrhizal
(AM) fungi (In vitro produced Glomus intraradices); 3:100% of recommended NPK: (120 kg ha −1 N; 60 kg ha −1 P; 50 kg ha −1 K), and 4 and 5: 75% of recommended NPK dose with and without AM inoculation in a 5 × 2 split-plot design on wheat using
conventional/flat system and elevated/raised bed system. The maximum grain yield (3.84 t ha −1) was obtained in AM fungi inoculated plots of raised bed system applied with 75% NPK and was found higher (although non-
significant) than the conventional (3.73 t ha −1) system. The AM inoculation at 75% fertilizer application can save 8.47, 5.38 kg P and 16.95, 10.75 kg N ha −1, respectively, in bed and conventional system. While comparing the yield response with 100% fertilizer application alone,
AM inoculation was found to save 20.30, 15.79 kg P and 40.60, 31.59 kg N ha −1, respectively, in beds and conventional system. Mycorrhizal inoculation at 75% NPK application particularly in raised bed
system seems to be more efficient in saving fertilizer inputs and utilizing P for producing higher yield and growth unlike
non-mycorrhizal plants of 100% P. Besides the yield, mycorrhizal plants grown on beds had higher AM root colonization, soil
dehydrogenases activity, and P-uptake. The present study indicates that the inoculation of AM fungi to wheat under raised
beds is better response (although non-significantly higher) to conventional system and could be adopted for achieving higher
yield of wheat at reduced fertilizer inputs after field validation. 相似文献
16.
Ecosystem restoration by rewetting of degraded fens led to the new formation of large-scale shallow lakes in the catchment
of the River Peene in NE Germany. We analyzed the biomass and the nutrient stock of the submersed ( Ceratophyllum demersum) and the floating macrophytes ( Lemna minor and Spirodela polyrhiza) in order to assess their influence on temporal nutrient storage in water bodies compared to other freshwater systems. Ceratophyllum demersum displayed a significantly higher biomass production (0.86–1.19 t DM = dry matter ha −1) than the Lemnaceae (0.64–0.71 t DM ha −1). The nutrient stock of submersed macrophytes ranged between 28–44 kg N ha −1 and 8–12 kg P ha −1 and that of floating macrophytes between 14–19 kg N ha −1 and 4–5 kg P ha −1 which is in the range of waste water treatment plants. We found the N and P stock in the biomass of aquatic macrophytes being
20–900 times and up to eight times higher compared to the nutrient amount of the open water body in the shallow lakes of rewetted
fens (average depth: 0.5 m). Thereafter, submersed and floating macrophytes accumulate substantial amounts of dissolved nutrients
released from highly decomposed surface peat layers, moderating the nutrient load of the shallow lakes during the growing
season from April to October. In addition, the risk of nutrient loss to adjacent surface waters becomes reduced during this
period. The removal of submersed macrophytes in rewetted fens to accelerate the restoration of the low nutrient status is
discussed. 相似文献
17.
The aim of this study was to quantify the effects of fertiliser N on C stocks in trees (stems, stumps, branches, needles,
and coarse roots) and soils (organic layer +0–10 cm mineral soil) by analysing data from 15 long-term (14–30 years) experiments
in Picea abies and Pinus sylvestris stands in Sweden and Finland. Low application rates (30–50 kg N ha −1 year −1) were always more efficient per unit of N than high application rates (50–200 kg N ha −1 year −1). Addition of a cumulative amount of N of 600–1800 kg N ha −1 resulted in a mean increase in tree and soil C stock of 25 and 11 kg (C sequestered) kg −1 (N added) (“N-use efficiency”), respectively. The corresponding estimates for NPK addition were 38 and 11 kg (C) kg −1 (N). N-use efficiency for C sequestration in trees strongly depended on soil N status and increased from close to zero at
C/N 25 in the humus layer up to 40 kg (C) kg −1 (N) at C/N 35 and decreased again to about 20 kg (C) kg −1 (N) at C/N 50 when N only was added. In contrast, addition of NPK resulted in high (40–50 kg (C) kg −1 (N)) N-use efficiency also at N-rich (C/N 25) sites. The great difference in N-use efficiency between addition of NPK and
N at N-rich sites reflects a limitation of P and K for tree growth at these sites. N-use efficiency for soil organic carbon
(SOC) sequestration was, on average, 3–4 times lower than for tree C sequestration. However, SOC sequestration was about twice
as high at P. abies as at P. sylvestris sites and averaged 13 and 7 kg (C) kg −1 (N), respectively. The strong relation between N-use efficiency and humus C/N ratio was used to evaluate the impact of N
deposition on C sequestration. The data imply that the 10 kg N ha −1 year −1 higher deposition in southern Sweden than in northern Sweden for a whole century should have resulted in 2.0 ± 1.0 (95% confidence
interval) kg m −2 more tree C and 1.3 ± 0.5 kg m −2 more SOC at P. abies sites in the south than in the north for a 100-year period. These estimates are consistent with differences between south
and north in tree C and SOC found by other studies, and 70–80% of the difference in SOC can be explained by different N deposition. 相似文献
18.
Wetland buffers may play an important role in the retention of nitrogen (N) and phosphorus (P) that can be released in large quantities from forestry operations. In this study, we investigated the retention capacity of N and P of wetland vegetation comparing the control area with two experimental areas within one site before and after N and P pulse (45 kg N and 15 kg P) lasting one growing season (ca. 150 d). N and P pulse caused a significant increase in the plant biomass and N and P content in the upper experimental area, which received most of the added nutrients. Added N and P was mainly retained in the above and below ground parts of E. vaginatum, especially in storage organs and roots which form a long-term sink for nutrients. Total N retention in the plant biomass during the first year after N and P treatment ranged from 25.3 kg (equals to 126.7 kg N ha –1) in the upper experimental area to 6.1 kg (20.4 kg N ha –1) in the lower experimental area and 4.7 kg (15.7 kg N ha –1) in the control area. P retention ranged from 2.6 kg (13.1 kg P ha –1) in the upper experimental area to 1.0 kg (3.4 kg P ha –1) in the lower experimental area and 0.5 kg (1.8 kg P ha –1) in the control area. The retained proportions of N and P in the plant biomass in the two experimental areas were approximately 70% of the added N (45 kg N y –1) and approximately 25% of the added P (15 kg P y –1) during the first year after N and P addition in 1999. Our study shows that vigorously colonising and growing vegetation is the main factor in the retention of N, a significant factor in the retention of P in a constructed wetland buffer, and thus an important contributor to the prevention of detrimental effects of N and P leaching on watercourses. 相似文献
19.
Deciduous forests may respond differently from coniferous forests to the anthropogenic deposition of nitrogen (N). Since fungi,
especially ectomycorrhizal (EM) fungi, are known to be negatively affected by N deposition, the effects of N deposition on
the soil microbial community, total fungal biomass and mycelial growth of EM fungi were studied in oak-dominated deciduous
forests along a nitrogen deposition gradient in southern Sweden. In-growth mesh bags were used to estimate the production
of mycelia by EM fungi in 19 oak stands in the N deposition gradient, and the results were compared with nitrate leaching
data obtained previously. Soil samples from 154 oak forest sites were analysed regarding the content of phospholipid fatty
acids (PLFAs). Thirty PLFAs associated with microbes were analysed and the PLFA 18:2ω6,9 was used as an indicator to estimate
the total fungal biomass. Higher N deposition (20 kg N ha −1 y −1 compared with 10 kg N ha −1 y −1) tended to reduce EM mycelial growth. The total soil fungal biomass was not affected by N deposition or soil pH, while the
PLFA 16:1ω5, a biomarker for arbuscular mycorrhizal (AM) fungi, was negatively affected by N deposition, but also positively
correlated to soil pH. Other PLFAs positively affected by soil pH were, e.g., i14:0, a15:0, 16:1ω9, a17:0 and 18:1ω7, while
some were negatively affected by pH, such as i15:0, 16:1ω7t, 10Me17:0 and cy19:0. In addition, N deposition had an effect
on the PLFAs 16:1ω7c and 16:1ω9 (negatively) and cy19:0 (positively). The production of EM mycelia is probably more sensitive
to N deposition than total fungal biomass according to the fungal biomarker PLFA 18:2ω6,9. Low amounts of EM mycelia covaried
with increased nitrate leaching, suggesting that EM mycelia possibly play an important role in forest soil N retention at
increased N input. 相似文献
20.
Anthropogenic N deposition may change soil conditions in forest ecosystems as demonstrated in many studies of coniferous forests,
whereas results from deciduous forests are relatively scarce. Therefore the influence of N deposition on several variables
was studied in situ in 45 oak-dominated deciduous forests along a N deposition gradient in southern Sweden, where the deposition ranged from
10 to 20 kg N ha −1 year −1. Locally estimated NO
−
3
deposition, as measured with ion-exchange resins (IER) on the soil surface, and grass N concentration (%) were positively
correlated with earlier modelled regional N deposition. Furthermore, the δ 15N values of grass and uppermost soil layers were negatively correlated with earlier modelled N deposition. The data on soil
NO
−
3
, measured with IER in the soil, and grass N concentration suggest increased soil N availability as a result of N deposition.
The δ 15N values of grass and uppermost soil layers indicate increased nitrification rates in high N deposition sites, but no large
downward movements of NO
−
3
in these soils. Only a few sites had NO
−
3
concentrations exceeding 1 mg N l −1 in soil solution at 50 cm depth, which showed that N deposition to these acid oak-dominated forests has not yet resulted
in extensive leaching of N. The δ 15N enrichment factor was the variable best correlated with NO
−
3
concentrations at 50 cm and is thus a variable that potentially may be used to predict leaching of NO
−
3
from forest soils. 相似文献
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