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1.
Impact of long-term nitrogen addition on carbon stocks in trees and soils in northern Europe 总被引:4,自引:2,他引:2
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
2.
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
3.
A field experiment was conducted at the Bangladesh Rice Research Institute, Joydebpur, Dhaka during the late wet season. Basal
application of P at both 5 and 10 kg ha−1 significantly increased total biomass production and nitrogen fixation byAzolla pinnata R. Brown (local strain). Addition of both 5 and 10 kg P ha−1 in equal splits at inoculation and at six day intervals thereafter during growth periods of 12, 24 and 36 days increased
biomass production and nitrogen fixation by Azolla over that attained with the basal application. Biomass and nitrogen fixation
using a split application of 5 kg P ha−1 exceeded that attained with basal application of 10 kg P ha−1 and split application of 10 kg P ha−1 resulted in 0.58, 11.2, and 18.3 t ha−1 more biomass, and 0.47, 18.9, and 18.3 more kg fixed N ha−1 at 12, 24 and 36 days, respectively, than the same amount applied as a basal application. Analyses indicated that the critical
level of dry weight P in Azolla for sustained growth was in the range of 0.15–0.17%. Compared with the control, where no P
was added, and additional 30 and 36 kg N ha−1 were fixed after 24 and 36 days, respectively, when P was provided at 10 kg ha−1 using a split application. A separate field study showed that flooded rice plants received P from incorporated Azolla with
about 28% of the P present in the supplied Azolla being incorporated into the rice plants. 相似文献
4.
N and P budgets quantify inputs and outputs of nutrients at the catchment scale to allow evaluation of inputs and outputs
as well as inferences about transport and processing based on unaccounted-for nutrients. N and P budgets were constructed
for two catchments in southeastern Michigan with markedly different numbers of impoundments, over two years, to evaluate the
influence of impoundments on nutrient fluxes from each catchment. The Huron, with 88 impoundments >10 ha, stored 156 kg P km−2 y−1, while the Raisin (with 14 impoundments) had a net export of 102 kg P km−2 y−1. The Huron catchment also stored and denitrified more N than the Raisin catchment – 2,418 kg N km−2 y−1 compared to 1,538 kg N km−2 y−1. Riverine export of N and P also varied markedly between the catchments, with the Huron River exporting 288 kg N and 7 kg P km−2 y−1 and the Raisin River exporting 1,268 kg N and 34 kg P km−2 y−1. We then re-calculated budget results from previous studies using the approach of the present study, altering input and outputs
fluxes as well as system boundaries to obtain comparable budgets. For these comparable budgets, annual P outputs on average
accounted for 77% of inputs whereas N outputs accounted for only 39% of N inputs. Across catchments, the percent of inputs
exported by the river averaged 16% for N and 5% for P, indicating more effective retention of P than N. 相似文献
5.
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
6.
Changes in the Above- and Below-ground Biomass and Nutrient Pools of Ground Vegetation After Clear-cutting of a Mixed Boreal Forest 总被引:3,自引:0,他引:3
Marjo Palviainen Leena Finér Hannu Mannerkoski Sirpa Piirainen Michael Starr 《Plant and Soil》2005,275(1-2):157-167
Ground vegetation may act as a sink for nutrients after clear-cutting and thus decrease leaching losses. Biomass and nutrient
(N, P, K, Ca) pools of ground vegetation (mosses, roots and above-ground parts of field layer) were determined one year before
and five years after clear-cutting of a Norway spruce (Picea abies (L.) H. Karst.) dominated boreal mixed forest stand in
eastern Finland (63°51′ N, 28°58′ E). Before clear-cutting the average biomass of ground vegetation was 5307 kg ha−1, with nutrient contents of 46.9 kg N ha−11, 4.1 kg P ha−11, 16.2 kg K ha−11 and 13.9 kg Ca ha−11. The biomass and nutrient pools decreased after clear-cutting being lowest in the second year, the biomass decreasing by
46–65% in the cut plots. The nutrient pools decreased as follows: N 54–72%, P 36–68%, K 51–71% and Ca 57–74%. The decrease
in ground vegetation nutrient uptake, and the observed reduced depth of rooting may decrease nutrient retention after clear-cutting
and decomposing dead ground vegetation is a potential source of leached nutrients. These negative effects of clear-cutting
on the nutrient binding capacity of ground vegetation was short-lived since the total biomass and nutrient pools returned
to pre-cutting levels or were even greater by the end of the 5-year study period. 相似文献
7.
During the last 15–20 years, re-establishment of freshwater riparian wetlands and remeandering of streams and rivers have
been used as a tool to mitigate nutrient load in downstream recipients in Denmark. The results obtained on monitoring four
different streams and wetland restoration projects are compared with respect to hydrology, i.e. flow pattern and discharge
of ground or surface water, retention of phosphorus (P), and removal of nitrogen (N). Furthermore, the monitoring strategies
applied for quantifying the post-restoration nutrient retention are evaluated. The four wetland restoration projects are the
Brede River restoration (including river valley groundwater flow, remeandering and inundation), Lyngbygaards River restoration
(groundwater flow, irrigation with drainage water, inundation with river water and remeandering), Egeskov fen (fen re-establishment
and stream remeandering) and Egebjerg Meadows (fen restoration and hydrological reconnection to Store Hansted River). Retention
of phosphorus varied between 0.13 and 10 kg P ha−1 year−1, while the removal of nitrogen varied between 52 and 337 kg N ha−1 year−1. The monitoring strategy chosen was not optimal at all sites and would have benefitted from a knowledge on local hydrology
and water balances in the area to be restored before planning for the final monitoring design. Furthermore, the outcome concerning
P retention would have benefitted from a more frequent sampling strategy. 相似文献
8.
Denitrification Potential in Lake Sediment Increases Across a Gradient of Catchment Agriculture 总被引:1,自引:0,他引:1
Intensification of catchment agriculture has increased nutrient loads and accelerated eutrophication in some lakes, often
resulting in episodic harmful algal blooms or prolonged periods of anoxia. The influence of catchment agriculture on lake
sediment denitrification capacity as a nitrogen (N) removal mechanism in lakes is largely unknown, particularly in contrast
to research on denitrification in agricultural streams and rivers. We measured denitrification enzyme activity (DEA) to assess
sediment denitrification potential in seven monomictic and three polymictic lakes that range in the proportion of agriculture
in the catchment from 3 to 96% to determine if there is a link between agricultural land use in the lake catchment and sediment
denitrification potential. We collected sediment cores for DEA measurements over 3 weeks in austral spring 2008 (October–November).
Lake Okaro, with 96% catchment agriculture, had approximately 15 times higher DEA than Lake Tikitapu, with 3% catchment agriculture
(232.2 ± 55.9 vs. 15.9 ± 4.5 μg N gAFDM−1 h−1, respectively). Additionally, sediment denitrification potential increased with the proportion of catchment in agriculture
(R
2 = 0.85, P < 0.001). Our data suggest that lakes retain a high capacity to remove excess N via denitrification under increasing N loads
from higher proportions of catchment agriculture. However, evidence from the literature suggests that despite a high capacity
for denitrification and longer water residence times, lakes with high N loads will still remove a smaller proportion of their
N load. Lakes have a denitrification potential that reflects the condition of the lake catchment, but more measurements of
in situ denitrification rates across lake catchments is necessary to determine if this capacity translates to high N removal
rates. 相似文献
9.
During 1999–2001 the chemical composition and fluxes were measured in rainfall, throughfall, soil solution and stream water
in a remote forested site in the Italian Alps. The analysis of temporal patterns revealed the differential behaviour of nitrogen
and sulphur and suggested that different mechanisms controlled their flux. No important changes in sulphate concentration
and fluxes emerged as the solution passed through the various components of the forest ecosystem, and temporal variations
of SO4 in the soil solution and stream were likely driven by the physical process of dilution. The availability of nitrate and ammonia,
by contrast, was drastically reduced as throughfall water entered the soil and passed through the mineral layers, irrespective
of season. The calculated hydrochemical budget based on throughfall and soil solution N fluxes revealed that ~80% N retention
in the forest soil, corresponding to 12 kg ha−1 yr−1, despite a relatively high N deposition loading (15 kg ha−1 yr−1). Most of the leached nitrogen (90%) was in the organic form. Indicators of the N status of this ecosystem, such as C/N ratio
in solid and solution phase of the soil and N foliage content as well as land use history were examined. Despite the strong
N retention in the forested part of the catchment, the stream water N–NO3 levels were consistently above 10 μg l−1 suggesting that the Val Masino catchment as a whole was less efficient in processing atmospheric N inputs. This contrasting
N behaviour illustrates the role of landscape features, such as the soil cover and vegetation type, that is characteristic
of an alpine catchment. 相似文献
10.
Development of ground vegetation biomass and nutrient pools in a clear-cut disc-plowed boreal forest
Marjo Palviainen Leena Finér Ari Laurén Hannu Mannerkoski Sirpa Piirainen Michael Starr 《Plant and Soil》2007,297(1-2):43-52
Nutrient leaching from forest substrate after clear-cutting and subsequent soil preparation is strongly influenced by the
capacity of ground vegetation to sequester the released nutrients. We studied the rates and patterns of biomass and nutrient
accumulation in ground vegetation growing on ridges, in furrows and on undisturbed surfaces for 2–5 years after disc-plowing
in eastern Finland. The biomass of mosses on ridges remained significantly lower than that in furrows and on undisturbed surfaces.
Field layer biomass on ridges and in furrows was significantly lower than on undisturbed surfaces throughout the study period.
Field layer biomass increased more on ridges than in furrows. Root biomass on ridges and undisturbed surfaces was considerably
higher than in furrows. Five years after disc-plowing, total biomass and nutrient pools for ridges (biomass 4,975 kg ha−1, N 40 kg ha−1, P 5 kg ha−1, K 20 kg ha−1 and Ca 18 kg ha−1) and undisturbed surfaces (biomass 5,613 kg ha−1, N 43 kg ha−1, P 5 kg ha−1, K 22 kg ha−1 and Ca 18 kg ha−1) were similar, but considerably lower for furrows (biomass 1,807 kg ha−1, N 16 kg ha−1, P 2 kg ha−1, K 10 kg ha−1 and Ca 6 kg ha−1). Ridges covered 25% of the area, furrows 30 and 45% was undisturbed surfaces. Taking into account the proportion of each
type of surface, values for the whole prepared clear-cut area were 4,312, 34, 4, 18 and 14 kg ha−1 for biomass, N, P, K and Ca, respectively. Biomass and nutrient pools had not returned to uncut forest levels at the end
of the 5-year study period. The results indicate that mosses and field layer vegetation respond differently to soil preparation,
that the development of biomass on ridges, in furrows and on undisturbed surfaces proceeds at different rates, and that the
biomass and nutrient uptake of ground vegetation remains below pre-site preparation levels for several years. However, ridges,
which are known to be the most susceptible to leaching, revegetate rapidly.
Responsible Editor: Tibor Kalapos. 相似文献
11.
12.
Fumikazu Akamatsu Koichi Ide Koji Shimano Hideshige Toda 《Landscape and Ecological Engineering》2011,7(1):109-115
Fixation of river flow passages and riverbed degradation may facilitate the development of higher floodplains with the establishment
of exotic species such as black locust (Robinia pseudoacacia L.). We quantitatively evaluated the relationship between nitrogen (N) levels in black locust trees and in sediments under
different flood disturbance regimes in a riparian area of the Chikuma River. In this study, allometric equations were developed
for relating leaf N content to diameter at breast height of black locust. The amount of leaf N in black locust increased with
distance from the river, reaching 159 kg N ha−1 at 180 m from the river. There was a small difference in N content between green and fallen leaves (0.2%), and so the leaf
N was almost equivalent to N input to riparian sediments. Fine sediments accumulated on the riparian area, where the amount
of sediments N increased with distance from the river, ranging from 1091 ± 767 to 4953 ± 2953 kg N ha−1. The N accumulation rates also increased with distance from the river, corresponding with the amount of leaf N in black locust
per unit area, but the former exceeded the latter. The sediment N accumulation might be accelerated by sediment trapping effect
due to riparian vegetation itself. A large input of N provided by invaded black locust might alter nutrient dynamics and native
plant community structure in the riparian area. 相似文献
13.
Ana Isabel Lillebø J. P. Coelho M. R. Flindt H. S. Jensen J. C. Marques C. B. Pedersen M. A. Pardal 《Hydrobiologia》2007,583(1):195-204
During the last decades the Mondego estuary has been under severe ecological stress mainly caused by eutrophication. In this
salt march system, Spartina maritima covers about 10.5 ha of the intertidal areas. The objective of the present study was to evaluate the effect of Spartina maritima marshes on the dynamics of phosphorus (P) binding in the surface sediment. We compare phosphate and oxygen fluxes, P-adsorption
capacity, phosphate concentrations and total amount, and the extractable P forms in the upper 20 cm of sediment in vegetated
sediment with adjacent mudflats without vegetation. Sediment pore-water profiles followed a clear trend, with lower P concentrations
in more superficial layers, and increasing with depth. The vegetated mudflats presented lower concentrations of dissolved
inorganic phosphorus than adjacent bare bottom mudflats, lower phosphate total amount, as well as higher P-adsorption capacity.
Results from the extraction procedure show that the superficial layers are the most important for estuarine phosphorus dynamics,
since maximum concentrations of labile P pools are present here. In contrast, higher proportions of refractory P pool are
found in deeper layers. Spartina marsh sediments had less total P, less iron bound P, and less exchangeable P than adjacent bare bottom mudflats. Also the
pool of loosely sorbed P is lower in the Spartina marsh. Phosphate regeneration from the sediment to the overlying water was only 11.8 kg ha−1 year−1 in vegetated sediment while 25.8 kg ha−1 year−1 in the bare mud flat. Plant uptake for growth combined with an enhanced P-adsorption capacity of the sediment, may explain
these differences. Therefore, Spartina marshes are very important agents in the sedimentary P cycle worldwide, and can be considered a useful management tool in
estuarine ecosystem recovery efforts. 相似文献
14.
Mark S. Castro Keith N. Eshleman Louis F. Pitelka Geoff Frech Molly Ramsey William S. Currie Karen Kuers Jeffrey A. Simmons Bob R. Pohlad Carolyn L. Thomas David M. Johnson 《Biogeochemistry》2007,84(3):333-348
The objective of this study was to evaluate the nitrogen (N) biogeochemistry of an 18–22 year old forested watershed in western
Maryland. We hypothesized that this watershed should not exhibit symptoms of N saturation. This watershed was a strong source
of nitrate (NO3
−) to the stream in all years, with a mean annual export of 9.5 kg N ha−1 year−1 and a range of 4.4–18.4 kg N ha−1 year−1. During the 2001 and 2002 water years, wet deposition of inorganic N was 9.0 kg N ha−1 year−1 and 6.3 kg N ha−1 year−1, respectively. Watershed N export rates in 2001 and 2002 water years were 4.2 kg N ha−1 year−1 and 5.3 kg N ha−1 year−1, respectively. During the wetter water years of 2003 and 2004, the watershed exported 15.0 kg N ha−1 year−1 and 18.4 kg N ha−1 year−1, rates that exceeded annual wet deposition of N by a factor of two (7.5 kg N ha−1 year−1 in 2003) and three (5.5 kg N ha−1 year−1 in 2004). Consistent with the high rates of N export, were high concentrations (2.1–3.3%) of N in foliage, wood (0.3%) and
fine roots, low C:N ratios in the forest floor (17–24) and mineral soil (14), high percentages (83–96%) of the amount of mineralized
N that was nitrified and elevated N concentrations (up to 3 mg N l−1) in soil solution. Although this watershed contained a young aggrading forest, it exhibited several symptoms of N saturation
commonly observed in more mature forests. 相似文献
15.
To determine the sources and sinks of atmospherically deposited Pb at a forested watershed (Plastic Lake) in central Ontario,
Canada, Pb pools and fluxes through upland, wetland and lake compartments were measured during 2002/2003 and compared with
previous measurements taken between 1989 and 1991. In 2002/2003, annual bulk deposition of Pb was 0.49 mg m−2 compared with 1.90–1.30 mg m−2 in 1989–1991. Annual Pb concentrations in stream water draining the upland part of the catchment were very low (0.04 μg l−1) and were approximately half those measured in 1989–1991 (0.11–0.08 μg l−1). Leaching losses in stream water were small and mass balance estimates indicate almost complete retention (>95%) of atmospherically
deposited Pb in upland soils. In contrast, annual Pb concentrations in stream water draining a wetland were between 0.38 and
0.77 μg l−1, with the highest concentration occurring in 2002/2003 and mass balance calculations indicate that the wetland is a net source
of Pb in all measured years. Lead concentrations in the lake outflow were low and the average Pb concentration measured in
2002/2003 (0.09 μg l−1) was approximately half the value recorded in 1989–1991 (0.19 μg l−1 both years). Annual mass balance estimates indicate that the lake retained between 2.47 mg m−2 (1989/1990) and 1.42 mg m−2 (2002/2003) and that in 2002/2003 68% of the Pb input to the lake is derived from the terrestrial catchment. These estimates
are higher than sediment core records, which indicate around 18 mg m−2 Pb was retained in sediment during the 1990s. Nevertheless, Pb concentrations decrease with sediment depth and 206Pb/207Pb concentrations increase with depth, a pattern also observed in mineral soils that reflects the substantial contribution
of anthropogenic Pb to the watershed. Lead isotope data from soil and sediment indicate a recent anthropogenic Pb signal (206Pb/207Pb ∼ 1.185) in upper soils and sediments and an older anthropogenic signal (206Pb/207Pb ∼ 1.20) in deeper soil and sediment. Lead isotope data in sediment and vegetation indicate that practically all the Pb
cycled in the forest at Plastic Lake is anthropogenic in origin. 相似文献
16.
Takuya Kajimoto 《Ecological Research》1989,4(1):55-69
Aboveground biomass and litterfall ofPinus pumila scrubs, growing on the Kiso mountain range in central Japan, were investigated from 1984 to 1985. The biomass of two research
plots (P1 and P2) with different scrub heights was estimated by two methods, the stratified clip technique and the allometric
method. Aboveground total biomass estimated by the latter method reached 181 ton d.w. ha−1 in P1 and 132 ton d.w. ha−1 in P2. Creeping stems contributed to about half of the total biomass. Although estimates of woody organs differed between
the two plots, leaf biomass estimates were almost the same at 15.5 ton d.w. ha−1. The canopies of the twoP. pumila scrubs were characterized by a large mean leaf area density of 5.0 m2 m−3. Despite this large area density, relatively moderate attenuation of light intensity was observed. Specific leaf area generally
increased with reduced leaf height. Annual total litterfall was estimated to be 3.60 ton d.w. ha−1 yr−1 in P1 and 2.39 ton d.w. ha−1 yr−1 in P2. Annual leaf fall in both plots was approximately 2.0 ton d.w. ha−1 yr−1. Leaves fell mainly in early autumn. Annual loss rates of branches, estimated as the sum of annual branch litterfall and
the amount of newly formed attached dead branches, were 0.29 ton d.w. ha−1 yr−1 in P1 and 0.37 ton d.w. ha−1 yr−1 in P2. 相似文献
17.
Christine L. Goodale Steven A. Thomas Guinevere Fredriksen Emily M. Elliott Kathryn M. Flinn Thomas J. Butler M. Todd Walter 《Biogeochemistry》2009,93(3):197-218
Atmospheric deposition contributes a large fraction of the annual nitrogen (N) input to the basin of the Susquehanna River,
a river that provides two-thirds of the annual N load to the Chesapeake Bay. Yet, there are few measurements of the retention
of atmospheric N in the Upper Susquehanna’s forested headwaters. We characterized the amount, form (nitrate, ammonium, and
dissolved organic nitrogen), isotopic composition (δ15N- and δ18O-nitrate), and seasonality of stream N over 2 years for 7–13 catchments. We expected high rates of N retention and seasonal
nitrate patterns typical of other seasonally snow-covered catchments: dormant season maxima and growing season minima. Coarse
estimates of N export indicated high rates of inorganic N retention (>95%), yet streams had unexpected seasonal nitrate patterns,
with summer peaks (14–96 μmol L−1), October crashes (<1 μmol L−1), and modest rebounds during the dormant season (<1–20 μmol L−1). Stream δ18O-nitrate values indicated microbial nitrification as the primary source of stream nitrate, although snowmelt or other atmospheric
source contributed up to 47% of stream nitrate in some March samples. The autumn nitrate crash coincided with leaffall, likely
due to in-stream heterotrophic uptake of N. Hypothesized sources of the summer nitrate peaks include: delayed release of nitrate
previously flushed to groundwater, weathering of geologic N, and summer increases in net nitrate production. Measurements
of shale δ15N and soil-, well-, and streamwater nitrate within one catchment point toward a summer increase in soil net nitrification
as the driver of this pattern. Rather than seasonal plant demand, processes governing the seasonal production, retention,
and transport of nitrate in soils may drive nitrate seasonality in this and many other systems. 相似文献
18.
Increasing phosphorus supply in subsurface soil in northern Australia: Rationale for deep placement and the effects with various crops 总被引:6,自引:0,他引:6
Three field experiments involving wheat, lucerne or cotton were established at different sites in the semiarid cropping regions
of northern Australia, to test whether the deep placement of P fertiliser improved P availability, compared to the conventional
practice of placing the fertiliser beside or adjacent to the seed. At Mulga View, near St George in southern Queensland on
a red Kandosol soil with a Colwell soil test value of 19 mg P kg soil−1 in the top 10 cm, there was no response to 10 kg P ha−1 applied in the 5–7 cm layer. However, increasing the depth of placement of 10 kg P ha−1 from 5–7 to 10–15 cm resulted in increased shoot growth and grain yield of spring wheat (Triticum aestivum) by 43 and 30%, respectively. A further grain yield increase of 43% to 3.2 t ha−1 resulted when the deep P rate was increased from 10 to 40 kg P ha−1. At Roma, in southern Queensland, on a grey/brown Vertosol with a Colwell soil test value of 15 mg P kg soil−1, there was no difference in the winter growth of lucerne (Medicago sativa) when P fertiliser had been applied at 5–7 cm depth at rates of 10 and 40 kg P ha−1. Shoot dry matter yields were around 2 t ha−1. However dry matter yields increased significantly to 2.6 and 3.7 t ha−1 when 10 and 40 kg P ha−1, respectively were applied at the 10–15 cm depth. The third experiment was carried out on a grey Vertosol at Kununurra in
Western Australia. Significant increases in the yield of seed cotton (Gossypium hirsutum) occurred when 50 kg P ha−1 was applied at depth (10–15 and 25–30 cm), compared with the conventional placement at 7–10 cm, with maximum yield response
to deep placement occurring with DAP, and the minimal response with MAP. The cotton was grown on raised beds and the crop
was irrigated according to district practice. The response to deep P at all sites was attributed to the rapid drying of the
soil surface layers, reducing the availability of soil or fertiliser P in these layers. The deep fertiliser P remained available
during the growing season and alleviated the P deficiency that appears to be a feature of these soils when the surface layers
become dry. 相似文献
19.
Soil carbon storage, litterfall and CO2 efflux in fertilized and unfertilized larch (Larix leptolepis) plantations 总被引:1,自引:0,他引:1
Choonsig Kim 《Ecological Research》2008,23(4):757-763
This study evaluated the effects of forest fertilization on the forest carbon (C) dynamics in a 36-year-old larch (Larix leptolepis) plantation in Korea. Above- and below-ground C storage, litterfall, root decomposition and soil CO2 efflux rates after fertilization were measured for 2 years. Fertilizers were applied to the forest floor at rates of 112 kg
N ha−1 year−1, 75 kg P ha−1 year−1 and 37 kg K ha−1 year−1 for 2 years (May 2002, 2003). There was no significant difference in the above-ground C storage between fertilized (41.20 Mg C
ha−1) and unfertilized (42.25 Mg C ha−1) plots, and the C increment was similar between the fertilized (1.65 Mg C ha−1 year−1) and unfertilized (1.52 Mg C ha−1 year−1) plots. There was no significant difference in the soil C storage between the fertilized and unfertilized plots at each soil
depth (0–15, 15–30 and 30–50 cm). The organic C inputs due to litterfall ranged from 1.57 Mg C ha−1 year−1 for fertilized to 1.68 Mg C ha−1 year−1 for unfertilized plots. There was no significant difference in the needle litter decomposition rates between the fertilized
and unfertilized plots, while the decomposition of roots with 1–2 mm diameters increased significantly with the fertilization
relative to the unfertilized plots. The mean annual soil CO2 efflux rates for the 2 years were similar between the fertilized (0.38 g CO2 m−2 h−1) and unfertilized (0.40 g CO2 m−2 h−1) plots, which corresponded with the similar fluctuation in the organic carbon (litterfall, needle and root decomposition)
and soil environmental parameters (soil temperature and soil water content). These results indicate that little effect on
the C dynamics of the larch plantation could be attributed to the 2-year short-term fertilization trials and/or the soil fertility
in the mature coniferous plantation used in this study. 相似文献
20.
Phosphorus (P) dynamics in the agriculturally-dominated Minnesota River (USA) were examined in the lower 40 mile reach in
relation to hydrology, loading sources, suspended sediment, and chlorophyll to identify potential biotic and abiotic controls
over concentrations of soluble P and the recycling potential of particulate P during transport to the Upper Mississippi River.
Within this reach, wastewater treatment plant (WWTP) contributions as soluble reactive P (SRP) were greatest during very low
discharge and declined with increasing discharge and nonpoint source P loading. Concentrations of SRP declined during low
discharge in conjunction with increases in chlorophyll, suggesting biotic transformation to particulate P via phytoplankton
uptake. During higher discharge periods, SRP was constant at ~0.115 mg l−1 and coincided with an independently measured equilibrium P concentration (EPC) for suspended sediment in the river, suggesting
abiotic control over SRP via phosphate buffering. Particulate P (PP) accounted for 66% of the annual total P load. Redox-sensitive
PP, estimated using extraction procedures, represented 43% of the PP. Recycling potential of this load via diffusive sediment
P flux under anoxic conditions was conservatively estimated as ~17 mg m−2 d−1 using published regression equations. The reactive nature and high P recycling potential of suspended sediment loads in the
Minnesota River has important consequences for eutrophication of the Upper Mississippi River. 相似文献