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1.
Hydrobiologia - In order to monitor recovery from acidification caused by acid atmospheric deposition, desmids and water chemistry were sampled in three Dutch moorland pools regularly from 1978 to... 相似文献
2.
Atmospheric Deposition to the Turkey Lakes Watershed: Temporal Variations and Characteristics 总被引:3,自引:0,他引:3
We investigated the atmospheric concentrations and deposition fluxes of major ions to the Turkey Lakes Watershed (TLW) between
1980 and 1996. During that time, daily SO4
2− concentrations in precipitation decreased markedly, while NO3
−, NH4
+, and H+ concentrations remained roughly constant. It appears that precipitation acidity did not decrease in spite of declining SO4
2− concentrations due to a concurrent and counterbalancing decrease in the concentrations of Ca2+, Mg2+, and K+ in precipitation. The reasons for the decline in base cations are unknown, but this decline is probably related to decreasing
emissions of soil-derived particles from agricultural, industrial, and road sources. A similar situation was seen during the
same period in other parts of Canada, the eastern United States, and Europe. Wet, dry, and total (wet + dry) deposition fluxes
of sulphur (S) and nitrogen (N) were estimated annually for the years 1980–96. The 17-year mean annual total (wet + dry) deposition
of S to the watershed was estimated at 38.5 mmol m−2 y−1 (range 24.3–50.3). Total S deposition decreased by 35% from the early 1980s (1982–84) to the mid-1990s (1994–96), a decline
consistent with the 23% decline in annual SO2 emissions in eastern North America during the same period. In contrast, the annual total (wet + dry) deposition of oxidized
N ranged from 39.8 to 60.4 mmol m−2 y−1, with a 15-year mean of 50.1 mmol m−2 y−1 and a net increase of 10% between the early 1980s (1983–85) and the mid-1990s (1994–96). This is in keeping with a 10% increase
in NOx emissions in eastern North America during the same period. For both S and N (oxidized), wet deposition dominated over dry
deposition as the major mechanism for atmospheric input to the watershed. Annually, wet deposition accounted for approximately
two-thirds of the total atmospheric deposition of both S and N. Dry S deposition was due more to gaseous SO2 deposition (two-thirds of dry S deposition) than to particulate SO4
2− deposition (one-third of dry S deposition). Dry deposition of oxidized N, however, was dominated (95%) by gaseous HNO3 deposition, with minimal input from particulate NO3
− deposition. Compared to several selected watershed/forest sites in Canada, the United States, and Europe, the estimated total
deposition of S and N at the TLW was relatively high during the measurement period.
Received 5 October 1999; accepted 1 March 2001. 相似文献
3.
Diatom-based paleolimnological techniques were used to study 14 lakes from two regions of Nova Scotia which represent regions
of high and low sulphate deposition. Using decadal scale intervals, changes in diatom assemblages and diatom-inferred pH were
tracked in relation to deposition of anthropogenic-sourced strong acids. Eight study lakes were located in Kejimkujik National
Park in the southwestern part of the province, which receives an annual sulphate deposition (2000–2002) of ~10.5 kg ha−1 yr−1. These lakes showed significant changes in diatom assemblages with overall diatom-inferred acidification of ~0.5 pH units
starting between 1925 and 1940, with the timing of acidification related to pre-industrial (or pre−1850) lakewater pH. Six
study lakes were located in Cape Breton Highlands National Park, in northern Nova Scotia, a region of lower sulphate deposition.
These lakes did not show any consistent trends in diatom assemblages or inferred pH values consistent with recent acidic deposition,
but rather variations that may be related to climatic influences. Nova Scotia lakes that have been most impacted by acidic
deposition had the lowest pre-industrial lakewater pH values and were in an area of relatively high sulphate deposition.
Handling editor: K. Martens 相似文献
4.
Birds as eutrophicating agents: a nutrient budget for a small lake in a protected area 总被引:1,自引:0,他引:1
Sources of nitrogen and phosphorus were measured for a small pool, Brown Moss, which is a Site of Special Scientific Interest
in the UK. The site is designated for its macrophyte and bird interest and comprises several pools flanked by heath and woodland.
Currently the largest pool has high mean concentrations of total N and P (4 ± 2.4 mg N l−1 and 389 ± 254 μg P l−1), and also suffers from water table fluctuation and recreational impact. There are no point sources of nutrients but potential
diffuse sources include direct rainfall, drainage from surrounding heathland and potentially from distal agricultural land,
some septic tank drainage and bird excreta. Nutrients are also released from the sediments. Amongst external sources of phosphorus,
birds contributed 234 mg m−2 yr−1 (73%), land drainage 63 mg m−2 yr−1 (20%), and rainfall 24 mg m−2 yr−1 (7%). Major bird species were dabbling ducks and geese. For external sources of nitrogen, the most important was land drainage
(2,860 mg m−2 yr−1 and 64%), followed by rainfall (870 mg m−2 yr−1 and 19%) and birds (741 mg m−2 yr−1 and 11%) There was substantial internal loading of phosphorus (1670 mg m−2 yr−1) so that internal loading dominated the overall phosphorus budget (84%). The nitrogen budget was dominated by land drainage,
though for short periods, geese made a major contribution. Restoration of the site to the status required by European legislation
will be very difficult, if not impossible in the medium-term. 相似文献
5.
The deposition and cycling of carbon and nitrogen in carbonate sediments located between coral reefs on the northern and central
sections of the Great Barrier Reef were examined. Rates of mass sediment accumulation ranged from 1.9 kg m−2 year−1 (inshore reefs) to 2.1–4.9 kg m−2 year−1 (between mid-shelf reefs); sedimentation was minimal off outer-shelf reefs. Rates of total organic carbon decomposition ranged
from 1.7 to 11.4 mol C m−2 year−1 and total nitrogen mineralization ranged from 77 to 438 mmol N m−2 year−1, declining significantly with distance from land. Sediment organic matter was highly reactive, with mineralization efficiencies
ranging from 81 to 99% for organic carbon and 64–100% for nitrogen, with little C and N burial. There was no evidence of carbonate
dissolution/precipitation in short-term incubation experiments. Rates of sulfate reduction (range 0–3.4 mmol S m−2 day−1) and methane release (range 0–12.8 μmol CH4 m−2 day−1) were minor or modest pathways of carbon decomposition. Aerobic respiration, estimated by difference between total O2 consumption and the sum of the other pathways, accounted for 55–98% of total carbon mineralization. Rates of ammonification
ranged from 150 to 1,725 μmol NH4 m−2 day−1, sufficient to support high rates of denitrification (range 30–2,235 μmol N2 m−2 day−1). N2O release was not detected and rates of NH4
+ and NO2
− + NO3
− efflux were low, indicating that most mineralized N was denitrified. The percentage of total N input removed via denitrification
averaged ≈75% (range 28–100%) with little regenerated N available for primary producers. Inter-reef environments are therefore
significant sites of energy and nutrient flow, especially in spatially complex reef matrices such as the Great Barrier Reef. 相似文献
6.
Effect of Increased Carbon Dioxide and Temperature on Runoff Chemistry at a Forested Catchment in Southern Norway (CLIMEX Project) 总被引:3,自引:1,他引:2
Richard F. Wright 《Ecosystems》1998,1(2):216-225
CLIMEX (Climate Change Experiment) is an integrated, whole-ecosystem research project that focuses on the response of forest
ecosystems at the catchment scale to increased CO2 and temperature. KIM catchment (860 m2) is completely enclosed by a transparent greenhouse, receives deacidifed “clean” rain, and has elevated CO2 (560 ppmv) and elevated air temperature (3°–5°C above ambient). The uppermost 20% of the catchment is partitioned off, is
not subject to changed CO2 or temperature, and serves as an untreated control. Fluxes of nitrate and ammonium in runoff from KIM catchment increased
from 2 mmol m−
2 y−
1 each in the 3 years before treatment to 6 and 3 mmol m−
2 y−
1, respectively, in the 3 years after treatment (May 1994–April 1997), despite a 15 mmol m−
2 y−
1 decrease in N dry deposition due to the sealing of the walls to the enclosure. N flux in runoff from three reference catchments
and the control section did not change. The net loss of inorganic N was thus about 20 mmol m−
2 treated soil y−
1. There were no changes in organic N or total organic carbon in runoff. The ecosystem switched from a net sink to a net source
of inorganic nitrogen (N). The increased loss of N may be due to accelerated decomposition of soil organic matter induced
by higher temperature. Due to many decades of N deposition from long-range transported pollutants, the ecosystem prior to
treatment was N saturated. If global change induces persistent losses of inorganic N on a regional scale, the result may be
a significant increase in nitrate concentrations in fresh waters and N loading to coastal marine ecosystems. In regions with
acid sensitive waters, such as southern Norway, the increased nitrate release caused by global change may offset improvements
achieved by reduced sulfur and N deposition.
Received 15 October 1997; accepted 18 November 1997. 相似文献
7.
Jacot Katja A. Lüscher Andreas Nösberger Josef Hartwig Ueli A. 《Plant and Soil》2000,225(1-2):201-211
The significance of symbiotic N2 fixation in legumes (Trifolium alpinum L., T. nivale Sieber, T. pratense L., T. badium Schreber, T. thalii Vill., T. repens L., Lotus alpinus [DC.] Schleicher, L. corniculatus L., Vicia sativa L.) and other N sources for the N budget of grassland ecosystems was studied along an altitudinal gradient in the Swiss Alps.
The total annual symbiotic N2 fixation was compared with other sources of N for plant growth of the total plant community (mineralisation and wet deposition).
The contribution of symbiotically fixed N to total above-ground N yield of the swards decreased from at least 16% to 9% with
increasing altitude where legumes were present. This decrease was due to a decrease in the yield proportion of legumes from
15% at 900 and 1380 m a.s.l. to 5% at 2100 and 2300 m a.s.l. (no legumes were found above 2750 m a.s.l.) and not to a decline
in the activity of symbiotic N2 fixation. With increasing altitude legumes are more patchily distributed. The high symbiotic N2 fixation of individual plants up to their altitudinal limit is not primarily the result of low mineral N availability since
an addition of NH4
+ or NO3
− fertiliser at 2300 m a.s.l. led either to no decrease or only to a minor decrease in symbiotic N2 fixation. At 1380 m a.s.l., N mineralisation (13.45 g N m−2 yr−1) appeared to be the main source of N for growth of the sward; N from symbiosis (at least 1.0 g to 2.6 g N m−2 yr−1) and wet deposition (0.4 g to 0.6 g m−2 yr−1) was not a significant N source for plant growth at this altitude. At 2100 m a.s.l., the combined amounts of N from symbiotic
N2 fixation (at least 0.1 g N m−2 yr−1) and wet deposition (0.3 g N m−2 yr−1) appeared to be similarly important for plant growth as soil N mineralisation (0.47 g N m−2 yr−1). At high altitudes, wet N deposition and symbiotic N2 fixation together represent a significant source of N for the grassland ecosystem while at low altitudes these N inputs appear
to be much less important.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
8.
Takehiro Sasaki Masatoshi Katabuchi Chiho Kamiyama Masaya Shimazaki Tohru Nakashizuka Kouki Hikosaka 《Biodiversity and Conservation》2012,21(6):1577-1588
Understanding of the scaling of diversity is critical to enhance conservation strategies for subalpine moorland ecosystems
vulnerable to future environmental changes. However, a paucity of quantitative data strongly limits such attempts. In this
study, we used an additive diversity partitioning framework and quantified diversity patterns of moorland plant communities
across hierarchical spatial scales, within- and between-sample transects, and between sites (corresponding to α and two levels
of β diversity). Moorland sites markedly differed in size (range 1,000–160,000 m2) and were isolated from each other to varying extents within an inhospitable matrix (i.e., forests). We found that β diversity
components were consistently higher, whereas the local α diversity component was consistently lower than expected by chance.
We observed substantial contribution at the between-site scale to total species richness. By focusing on diversity patterns
of moorland plant communities across multiple hierarchical spatial scales, we could thus identify the scale at which regional
diversity is maximized. Our results suggest that protection of as many moorland sites as possible, to ensure beta diversity
between sites, will effectively conserve total diversity. The use of additive diversity partitioning is a major step forward
in providing strategies for the biological conservation of subalpine moorland ecosystems vulnerable to future environmental
changes. 相似文献
9.
Temporal and spatial trends in nitrogen and phosphorus inputs to the watershed of the Altamaha River,Georgia, USA 总被引:4,自引:0,他引:4
The watershed of the Altamaha River, Georgia, is one of the largest in the southeastern U.S., draining 36,718 km2 (including parts of metro Atlanta). We calculated both nitrogen (fertilizer, net food and feed import, atmospheric deposition,
and biological N fixation in agricultural and forest lands) and phosphorus (fertilizer and net food and feed import) inputs
to the watershed for 6 time points between 1954 and 2002. Total nitrogen inputs rose from 1,952 kg N km−2 yr−1 in 1954 to a peak of 3,593 kg N km−2 yr−1 in 1982 and then declined to 2,582 kg N km−2 yr−1 by 2002. Phosphorus inputs rose from 409 kg P km−2 yr−1 in 1954 to 532 kg P km−2 yr−1 in 1974 before declining to 412 kg P km−2 yr−1 in 2002. Fertilizer tended to be the most important input of both N and P to the watershed, although net food and feed import
increased in importance over time and was the dominant source of N input by 2002. When considered on an individual basis,
fertilizer input tended to be highest in the middle portions of the watershed (Little and Lower Ocmulgee and Lower Oconee
sub-watersheds) whereas net food and feed imports were highest in the upper reaches (Upper Oconee and Upper Ocmulgee sub-watersheds).
Although the overall trend in recent years has been towards decreases in both N and P inputs, these trends may be offset due
to continuing increases in animal and human populations. 相似文献
10.
Acidification of Soil in a Dry Land Winter Wheat-sorghum/corn-fallow Rotation in the Semiarid U.S. Great Plains 总被引:4,自引:0,他引:4
David D. Tarkalson José O. Payero Gary W. Hergert Kenneth G. Cassman 《Plant and Soil》2006,283(1-2):367-379
Soil pH is decreasing in many soils in the semiarid Great Plains of the United States under dry land no-till (NT) cropping
systems. This study was conducted to determine the rate of acidification and the causes of the acidification of a soil cropped
to a winter wheat (Triticum aestivum L.)-grain sorghum [Sorghum bicolor (L.) Moench]/corn (Zea mays L.)-fallow rotation (W-S/C-F) under NT. The study was conducted from 1989 to 2003 on soil with a long-term history of either
continuous NT management [NT(LT)] (1962–2003) or conventional tillage (CT) (1962–1988) then converted to NT [NT(C)] (1989–2003).
Nitrogen was applied as ammonium nitrate (AN) at a rate of 23 kg N ha−1 in 1989 and as urea ammonium nitrate (UAN) at an average annual rate of 50 kg N ha−1 from 1990 to 2003 for both NT treatments. Soil samples were collected at depth increments of 0–5, 5–10, 10–15, and 15–30 cm
in the spring of 1989 and 2003. Acidification rates for the NT(LT) and NT(C) treatments were 1.13 and 1.48 kmol H+ ha−1 yr−1 in the 0–30 cm depth, respectively. The amount of CaCO3 needed to neutralize the acidification is 57 and 74 kg ha−1 yr−1 for the NT(LT) and NT(C) treatments, respectively. A proton budget estimated by the Helyar and Porter [1989, Soil Acidity
and Plant Growth, Academic Press] method indicated that NO3− leaching from the 30 cm depth was a primary cause of long-term acidification in this soil. Nitrate leaching accounted for
59 and 66% of the H+ from the acid causing factors for NT(LT) and NT(C) treatments, respectively. The addition of crop residues to the soil neutralized
62 and 47% of the acidity produced from the leaching of NO3−, and 37 and 31% of the acid resulting from NO3− leaching and the other acid-causing constituents for the NT(LT) and NT(C) treatments, respectively. These results document
that surface soils in dry land W-S/C-F rotations under NT are acidifying under current management practices. Improved management
to increase nitrogen uptake efficiency from applied fertilizer would help reduce the rate of acidification. The addition of
lime materials to prevent negative impacts on grain yields may be necessary in the future under current management practices.
A contribution of the university of Nebraska Agricultural Research Division, Lincoln, NE 68583. Journal series No. 15120 相似文献
11.
Quantification of methane emissions from Chinese rice fields (Zhejiang Province) as influenced by fertilizer treatment 总被引:7,自引:0,他引:7
Reiner Wassmann Helmut Schütz Hans Papen Heinz Rennenberg Wolfgang Seiler Dai Aiguo Shen Renxing Shangguan Xingjian Wang Mingxing 《Biogeochemistry》1993,20(2):83-101
Methane emissions from rice paddies were quantified by using an automatic field system stationed in Zhejiang Province, one
of the centres for rice cultivation in China. The data set showed pronouned interannual variations over 5 consecutive vegetation
periods; by computing average values of all experimental plots the annual emissions were 177 g CH4 m−2 yr−1 in 1987, 50 g CH4 m−2 yr−1 in 1988, and 187 g CH4 m−2 yr−1 in 1989.
The field preparations encompassed 4 different treatments: (1) no fertilizers, (2) mineral fertilizer (KCl, K2SO4), (3) organic manure (rape seeed cake, animal manure), (4) mineral fertilizer plus organic manure. The methane emission rates
of the different fertilizer treatments did not show significant differences. The mean emission rates, calculated over the
entire observation period of 5 seasons, were 30.4 mg CH4 m−2 h−1 (non-fertilized plot) and 28.3 mg CH4 m−2 h−1 (mineral fertilizers). These values indicate a high level of methane production even without additional input of organic
material into the rice-soils. In the other plots, the organic fertilizers were added once per vegetation period at app. 1
t fresh weight per ha, a relatively low application rate by agronomical standards. The mean emission rates were 35.1 mg CH4 m−2 h−1 when manure was applied as sole fertilizer and 27.5 mg CH4 m−2 h−1 when applied jointly with potassium fertilizers.
Based on the results of this study we estimate a range of 18–28 Tg CH4 yr−1 as the total methane emission from Chinese rice fields. However, more field data from representative sites in China are needed
to reduce the uncertainties in this estimate. 相似文献
12.
D. G. Zamolodchikov V. I. Grabovskii G. N. Kraev 《Contemporary Problems of Ecology》2011,4(7):706-715
A regional forest carbon budget accounting technique based on carbon pools balance with incomes from growing woodstocks and
losses from harvesting, fires and other disturbances have been developed. Forest carbon budgets of the Russian administrative
units during 1988–2009 have been accounted. The carbon sink to Russian forests have increased from 80 Mt C × yr−1 in 1988 to 230–240 Mt C × yr−1 in late 2000s. This tendency is explained with the decline in harvesting, which have started in 1990s. European part of Russia
was found to have higher areally averaged carbon sink compared with the Asian part. It have been associated with peculiar
ways of wildfires governance in these two parts. 相似文献
13.
Primary production of phytoplankton and secondary production of a daphnid and a chaoborid were studied in a small eutrophic
pond. The gross primary production of phytoplankton was 290 gC m−2 per 9 months during April–December. Regression analysis showed that the gross primary production was related to the incident
solar radiation and the chlorophylla concentration and not to either total phosphorus or total inorganic nitrogen concentration. The mean chlorophylla concentration (14.2 mg m−3), however, was about half the expected value upon phosphorus loading of this pond. The mean zooplankton biomass was 1.60
g dry weight m−2, of whichDaphnia rosea and cyclopoid copepods amounted to 0.69 g dry weight m−2 and 0.61 g dry weight m−2, respectively. The production ofD. rosea was high during May–July and October and the level for the whole 9 months was 22.6 g dry weight m−2.Chaoborus flavicans produced 10 complete and one incomplete cohorts per year. Two consecutive cohorts overlapped during the growing season. The
maximum density, the mean biomass, and the production were 19,100 m−2, 0.81 g dry weight m−2, and 11.7 g dry weight m−2yr−1, respectively. As no fish was present in this pond, the emerging biomass amounted to 69% of larval production. The production
ofC. flavicans larvae was high in comparison with zooplankton production during August–September, when the larvae possibly fed not only
on zooplankton but also algae. 相似文献
14.
Stream export of nitrogen (N) as nitrate (NO3−; the most mobile form of N) from forest ecosystems is thought to be controlled largely by plant uptake of inorganic N, such
that reduced demand for plant N during the non-growing season and following disturbances results in increased stream NO3− export. The roles of microbes and soils in ecosystem N retention are less clear, but are the dominant controls on N export
when plant uptake is low. We used a mass balance approach to investigate soil N retention during winter (December through
March) at the Hubbard Brook Experimental Forest by comparing NO3− inputs (atmospheric deposition), internal production (soil microbial nitrification), and stream output. We focused on months
when plant N uptake is nearly zero and the potential for N export is high. Although winter months accounted for only 10–15%
of annual net nitrification, soil NO3− production (0.8–1.0 g N m−2 winter−1) was much greater than stream export (0.03–0.19 N m−2 winter−1). Soil NO3− retention in two consecutive winters was high (96% of combined NO3− deposition and soil production; year 1) even following severe plant disturbance caused by an ice-storm (84%; year 2) We show
that soil NO3− retention is surprisingly high even when N demand by plants is low. Our study highlights the need to better understand mechanisms
of N retention during the non-growing season to predict how ecosystems will respond to high inputs of atmospheric N, disturbance,
and climate change. 相似文献
15.
The bioerosive potential of the intertidal chiton Acanthopleura gemmata on One Tree Reef was determined by quantification of CaCO3 in daily faecal pellet production of individuals transplanted into mesocosms after nocturnal-feeding forays. Mean bioerosive
potential was estimated at 0.16 kg CaCO3 chiton−1 yr−1. Bioerosion rates were estimated for populations on two distinct chiton habitats, reef margin (0.013 kg CaCO3 m−2 yr−1) and beachrock platform (0.25 kg CaCO3 m−2 yr−1). Chiton density on the platform was orders of magnitude greater than on the reef margin. The surface-lowering rate (0.16
mm m−2 yr) due to bioerosion by the beachrock population is a substantial contribution to the total surface-lowering rate of 2 mm
m−2 yr−1 previously reported for One Tree Reef across all erosive agents. At high densities, the contribution of A. gemmata to coral reef bioerosion budgets may be comparable to other important bioeroders such as echinoids and fish. 相似文献
16.
Restoring soil C pools by reducing land use intensity is a potentially high impact, rapidly deployable strategy for partially
offsetting atmospheric CO2 increases. However, rates of C accumulation and underlying mechanisms have rarely been determined for a range of managed
and successional ecosystems on the same soil type. We determined soil organic matter (SOM) fractions with the highest potential
for sequestering C in ten ecosystems on the same soil series using both density- and incubation-based fractionation methods.
Ecosystems included four annual row-crop systems (conventional, low input, organic and no-till), two perennial cropping systems
(alfalfa and poplar), and four native ecosystems (early successional, midsuccessional historically tilled, midsuccessional
never-tilled, and late successional forest). Enhanced C storage to 5 cm relative to conventional agriculture ranged from 8.9 g C m−2 y−1 in low input row crops to 31.6 g C m−2 y−1 in the early successional ecosystem. Carbon sequestration across all ecosystems occurred in aggregate-associated pools larger
than 53 μm. The density-based fractionation scheme identified heavy-fraction C pools (SOM > 1.6 g cm−3 plus SOM < 53 μm), particularly those in macroaggregates (>250 μm), as having the highest potential C accumulation rates,
ranging from 8.79 g C m−2 y−1 in low input row crops to 29.22 g C m−2 y−1 in the alfalfa ecosystem. Intra-aggregate light fraction pools accumulated C at slower rates, but generally faster than in
inter-aggregate LF pools. Incubation-based methods that fractionated soil into active, slow and passive pools showed that
C accumulated primarily in slow and resistant pools. However, crushing aggregates in a manner that simulates tillage resulted
in a substantial transfer of C from slow pools with field mean residence times of decades to active pools with mean residence
times of only weeks. Our results demonstrate that soil C accumulates almost entirely in soil aggregates, mostly in macroaggregates,
following reductions in land use intensity. The potentially rapid destruction of macroaggregates following tillage, however,
raises concerns about the long-term persistence of these C pools. 相似文献
17.
N. Visalakshi 《Journal of biosciences》1994,19(1):103-116
Seasonality in fine root standing crop and production was studied in two tropical dry evergreen forests viz., Marakkanam reserve
forest (MRF) and Puthupet sacred grove (PSG) in the Coromandel coast of India. The study extended from December 89 to December
91 in MRF and from August 90 to December 91 in PSG with sampling at every 2 months. Total fine interval. Mean fine root standing
crop was 134 g m−2 in MRF and 234 g m−2 in PSG. root production was 104 g m−2 yr−1 in MRF and 117 g m−2 yr−1 in PSG. These estimates lie within the range for fine roots reported for various tropical forests. Rootmass showed a pronounced
seasonal pattern with unimodal peaks obtained during December in the first year and from October–December in the second year
in MRF. In PSG greater rootmass was noticed from June–October than other times of sampling. The total root mass in MRF ranged
from 114 to 145 g m−2 at the 13 sampling dates in the three sites.
The live biomass fraction of fine roots in MRF ranged from 46 to 203 g m−2 and in PSG it ranged from 141 to 359 g mm−2 during the study periods. The dead necromass fraction of fine roots ranged from 6 to 37 g m−2 in MRF and from 12 to 66 g m−2 in PSG. Fine root production peaked during December in both the forest sites. The necromass fraction of newly produced roots
was negligible.
Total N was slightly greater in PSG than in MRF. Whereas total P level was almost similar in both the sites. The study revealed
that season and site characteristics influenced fine root system. 相似文献
18.
Biological soil crusts composed of cyanobacteria, green algae, bryophytes, and lichens colonize soils in arid and semiarid
ecosystems worldwide and are responsible for significant N input to the soils of these ecosystems. Soil crusts also colonize
active sand dunes in more humid regions, but studies of structure and function of such sand dune crusts are lacking. We identified
the cyanobacterial, algal, and bryophytic constituents and N production and leachates of biological soil crusts that colonize
beach dunes at the Indiana Dunes National Lakeshore along southern Lake Michigan in Indiana, USA. To determine the role of
these crusts in this system, we conducted a greenhouse experiment in which intact soil cores with biological crusts were subjected
to artificial rainfall over a full growing season. The volume and N content of leachate from the cores were quantified in
relation to degree of crust development, taxonomic composition, rainfall volume and intensity, light intensity, and the presence
of plant litter. Net N throughput significantly exceeded N inputs to cores in rainwater. Net N outputs from crusts to subsurface
soil ranged from 0. 01 to 0.19 g NH
4
+
-N m−2 yr−1 and 0.01 to 0.61 g NO
3
–
N m−2 yr−1. Thus, total inorganic N inputs associated with biological soil crusts ranged from 0.02 g N m−2 yr−1 to 0.8 g N m−2 yr−1. High volume (≥2 cm) rainfall resulted in more N leaching than low volume events, and plant litter added over the surface
of crusted soil cores significantly increased the amount of N in leachate. Exploratory path analysis revealed direct and indirect
linkages among environmental factors, crust development, and crust composition in regulating the throughput of H2O and N from these intact soil cores. Biological soil crusts at this site, combined with other properties of the soil surface,
substantially increase N inputs to this water- and nutrient-limited sand dune ecosystem. 相似文献
19.
Iron Additions Reduce Sulfate Reduction Rates and Improve Seagrass Growth on Organic-Enriched Carbonate Sediments 总被引:4,自引:0,他引:4
Here we demonstrate, through experimental iron additions to a Mediterranean seagrass meadow, that iron plays a pivotal role
in seagrass systems on carbonate sediments, directly through its role as a limiting nutrient, and indirectly by stimulating
phosphorus recycling through the activity of the enzyme alkaline phosphatase and by buffering the development of reduced conditions
in sediments. Iron additions were performed throughout the active root zone (30 cm depth) to two Posidonia oceanica meadows, one on organic-enriched sediments and one on organic poor sediments (Reference). Seagrass growth, nutrient incorporation
and sediment biogeochemical conditions were followed for four months. Iron additions had positive effects on seagrass growth
(leaf production increased with 55%) and nutrient incorporation (increased 46–91%) in the organic-enriched site, increasing
to levels found at the Reference site. There was no effect of iron additions in the Reference seagrass meadow suggesting that
iron was not the most important controlling factor at this site. The iron pools were about two times higher compared to the
organic-enriched site. The main effect on the sediment biogeochemical conditions at the organic-enriched site was a suppression
of sulfate reduction activity to the levels encountered at the Reference site (6.7 mmol m−2d−1 vs. 4.7–5.9 mmol m−2d−1). This suggests that the sulfide stress on the seagrasses was removed and that the iron availability increased due to reduced
precipitation of iron-sulfides and thus improving seagrass growth conditions in these organic-enriched sediments. 相似文献
20.
Forests soils should be neither sinks nor sources of carbon in a long-term perspective. From a Swedish perspective the time
since the last glaciation has probably not been long enough to reach a steady state, although changes are currently very slow.
In a shorter perspective, climatic and management changes over the past 100 years have probably created imbalances between
litter input to soils and organic carbon mineralisation. Using extant data on forest inventories, we applied models to analyse
possible changes in the carbon stocks of Swedish forest soils. The models use tree stocks to provide estimates of tree litter
production, which are fed to models of litter decomposition and from which carbon stocks are calculated. National soil carbon
stocks were estimated to have increased by 3 Tg yr−1 or 12–13 g m−2 yr−1 in the period 1926–2000 and this increase will continue because soil stocks are far from equilibrium with current litter
inputs. The figure obtained is likely to be an underestimation because wet sites store more carbon than predicted here and
the inhibitory effect of nitrogen deposition on soil carbon mineralisation was neglected. Knowledge about site history prior
to the calculation period determines the accuracy of current soil carbon stocks estimates, although changes can be more accurately
estimated. 相似文献