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1.
Despite efforts to understand the factors that determine soil organic carbon (SOC) stocks in terrestrial ecosystems, there
remains little information on how SOC turnover time varies among ecosystems, and how SOC turnover time and C input, via plant
production, differentially contribute to regional patterns of SOC stocks. In this study, we determined SOC stocks (gC m−2) and used soil radiocarbon measurements to derive mean SOC turnover time (years) for 0–10 cm mineral soil at ten sites across
North America that included arctic tundra, northern boreal, northern and southern hardwood, subtropical, and tropical forests,
tallgrass and shortgrass prairie, mountain grassland, and desert. SOC turnover time ranged 36-fold among ecosystems, and was
much longer for cold tundra and northern boreal forest and dry desert (1277–2151 years) compared to other warmer and wetter
habitats (59–353 years). Two measures of C input, net aboveground production (NAP), determined from the literature, and a
radiocarbon-derived measure of C flowing to the 0–10 cm mineral pool, I, were positively and SOC turnover time was negatively associated with mean annual evapotranspiration (ET) among ecosystems.
The best fit model generated from the independent variables NAP, I, annual mean temperature and precipitation, ET, and clay content revealed that SOC stock was best explained by the single
variable I. Overall, these findings indicate the primary role that C input and the secondary role that C stabilization play in determining
SOC stocks at large regional spatial scales and highlight the large vulnerability of the global SOC pool to climate change. 相似文献
2.
Indicators for nitrogen status and leaching in subtropical forest ecosystems,South China 总被引:7,自引:1,他引:6
The deposition of nitrogen (N) is high in subtropical forest in South China and it is expected to increase further in the
coming decades. To assess effects of increasing deposition on N cycling, we investigated the current N status of two selected
40–45-year-old masson pine-dominated Chinese subtropical forest stands at Tieshanping (TSP, near Chongqing City) and Caijiatang
(CJT in Shaoshan, Hunan province), and explored the applicability of several indicators for N status and leaching, suggested
for temperate and boreal forest ecosystems. Current atmospheric N deposition to the systems is from 25 to 49 kg ha−1 year−1. The concentration of total N in the upper 15 cm of the soil is from as low as 0.05% in the B2 horizon to as high as 0.53% in the O/A horizon. The concentration of organic carbon (C) varies from 0.74 (B2) to 9.54% (O/A). Pools of N in the upper 15 cm of the soils range from 1460 to 2290 kg N ha−1, where 25–55% of the N pool is in the O/A horizon (upper 3 cm of the soil). Due to a lack of a well-developed continuous
O horizon (forest floor), the C/N ratio of this layer cannot be used as an indicator for the N status, as is commonly done
in temperate and boreal forests. The net N mineralization rate (mg N g−1 C year−1) in individual horizons correlates significantly with the C/N ratio, which is from as high as 18.2 in the O/A horizon to
as low as 11.2 in the B2 horizon. The N2O emission flux from soil is significantly correlated with the KCl extractable NH4+–N in the O/A horizon and with the net nitrification in the upper 15 cm of the soil. However, the spatial and temporal variation
of the N2O emission rate is high and rates are small and often difficult to detect in the field. The soil flux density of mineral N,
defined as the sum of the throughfall N input rate and the rate of in situ net N mineralization in the upper 15 cm of the
soil, i.e., the combination of deposition input and the N status of the system, explains the NO3− leaching potential at 30 cm soil depth best. The seasonality of stream water N concentration at TSP and CJT is climatic and
hydrologically controlled, with highest values commonly occurring in the wet growing season and lowest in the dry dormant
season. This is different from temperate forest ecosystems, where N saturation is indicated by elevated NO3− leaching in stream water during summer. 相似文献
3.
Biodegradation of glyphosate in sod-podzol soil by both the indigenous micro flora and the introduced strain Ochrobactrum anthropi GPK 3 was studied with respect to its sorption and mobility. The experiments were carried out in columns simulating the vertical
soil profile. Soil samples studied were taken from soil horizons 0–10, 10–20, and 20–30 cm deep. It was found out that the
most of the herbicide (up to 84%) was adsorbed by soil during the first 24 h; the rest (16%) remained in the soluble fraction.
The adsorbed glyphosate was completely extractable by alkali. No irreversible binding of glyphosate was observed. By the end
of the experiment (21st day), glyphosate was only found in extractable fractions. The comparison of the effect of the introduced
O. anthropi GPK 3 and indigenous microbial community on the total toxicant content (both soluble and absorbed) in the upper 10 cm soil
layer showed its reduction by 42% (21 mg/kg soil) and 10–12% (5 mg/kg soil), respectively. Simultaneously, 14–18% glyphosate
moved to a lower 10–20 cm layer. Watering (that simulated rainfall) resulted in a 20% increase of its content at this depth;
6–8% of herbicide was further washed down to the 20–30 cm layer. The glyphosate mobility down the soil profile reduced its
density in the upper layer, where it was available for biodegradation, and resulted in its concentration in lower horizons
characterized by the absence (or low level) of biodegradative processes. It was shown for the first time how the herbicide
biodegradation in soil can be increased manifold by introduction of the selected strain O. anthropi GPK 3. 相似文献
4.
Vázquez Núñez E García Gaytán A Luna-Guido M Marsch R Dendooven L 《Biodegradation》2009,20(2):191-198
In a previous study, remediation of anthracene from soil was faster in the top 0–2 cm layer than in the lower soil layers.
It was not clear whether this faster decrease was due to biotic or abiotic processes. Anthracene-contaminated soil columns
were covered with black or transparent perforated polyethylene so that aeration occurred but that fluctuations in water content
were minimal and light could reach (LIGHT treatment) or not reach the soil surface (DARK treatment), or left uncovered so
that soil water content fluctuate and light reached the soil surface (OPEN treatment). The amount of anthracene, microbial
biomass C, and microbial activity as reflected by the amount of CO2 produced within 3 days were determined in the 0–2 cm, 2–8 cm, and 8–15 cm layer after 0, 3, 7, 14, and 28 days. In the 0–2 cm
layer of the OPEN treatment, 17% anthracene remained, 48% in the LIGHT treatment and 61% in the DARK treatment after 28 days.
In the 2–8 cm and 8–15 cm layer, treatment had no significant effect on the dissipation of anthracene from soil after 14 and
28 days. It was found that light and fluctuations in water content stimulated the removal of anthracene from the top 0–2 cm
soil layer, but not from the lower soil layers. It can be speculated that covering contaminated soil or pilling it up will
inhibit the dissipation of the contaminant. 相似文献
5.
Concentration and Fluxes of Dissolved Organic Carbon (DOC) in Three Norway Spruce Stands along a Climatic Gradient in Sweden 总被引:6,自引:3,他引:3
Leaching of dissolved organic carbon (DOC) from the forest floor and transport in soil solution into the mineral soil are
important for carbon cycling in boreal forest ecosystems. We examined DOC concentrations in bulk deposition, throughfall and
in soil solutions collected under the O and B horizons in three Norway spruce stands along a climatic gradient in Sweden.
Mean annual temperature for the three sites was 5.5, 3.4 and 1.2 °C. At each site we also examined the effect of soil moisture
on DOC dynamics along a moisture gradient (dry, mesic and moist plots). To obtain information about the fate of DOC leached
from the O horizon into the mineral soil, 14C measurements were made on bulk organic matter and DOC. The concentration and fluxes of DOC in O horizon leachates were highest
at the southern site and lowest at the northern. Average DOC concentrations at the southern, central and northern sites were
49, 39 and 30 mg l−1, respectively. We suggest that DOC leaching rates from O horizons were related to the net primary production of the ecosystem.
Soil temperature probably governed the within-year variation in DOC concentration in O horizon leachates, but the peak in
DOC was delayed relative to that of temperature, probably due to sorption processes. Neither soil moisture regime (dry, mesic
or moist plots) nor seasonal variation in soil moisture seemed to be of any significance for the concentration of DOC leached
from the O horizon. The 14C measurements showed that DOC in soil solution collected below the B horizon was derived mainly from the B horizon itself,
rather than from the O horizon, indicating a substantial exchange (sorption–desorption reactions) between incoming DOC and
soil organic carbon in the mineral soil. 相似文献
6.
We used sugar maple litter double-labeled with 13C and 15N to quantify fluxes of carbon (C) and nitrogen (N) between litter and soil in a northern hardwood forest and the retention
of litter C and N in soil. Two cohorts of litter were compared, one in which the label was preferentially incorporated into
non-structural tissue and the other structural tissue. Loss of 13C from this litter generally followed dry mass and total C loss whereas loss of 15N (20–30% in 1 year) was accompanied by large increases of total N content of this decaying litter (26–32%). Enrichment of
13C and 15N was detected in soil down to 10–15 cm depth. After 6 months of decay (November–May) 36–43% of the 13C released from the litter was recovered in the soil, with no differences between the structural and non-structural labeled
litter. By October the percentage recovery of litter 13C in soil was much lower (16%). The C released from litter and remaining in soil organic matter (SOM) after 1 year represented
over 30 g C m−2 y−1 of SOM accumulation. Recovery of litter 15N in soil was much higher than for C (over 90%) and in May 15N was mostly in organic horizons whereas by October it was mostly in 0–10 cm mineral soil. A small proportion of this N was
recovered as inorganic N (2–6%). Recovery of 15N in microbial biomass was higher in May (13–15%) than in October (about 5%). The C:N ratio of the SOM and microbial biomass
derived from the labeled litter was much higher for the structural than the non-structural litter and for the forest floor
than mineral SOM, illustrating the interactive role of substrates and microbial activity in regulating the C:N stoichiometry
of forest SOM formation. These results for a forest ecosystem long exposed to chronically high atmospheric N deposition (ca.
10 kg N ha−1 y−1) suggest possible mechanisms of N retention in soil: increased organic N leaching from fresh litter and reduced fungal transport
of N from soil to decaying litter may promote N stabilization in mineral SOM even at a relatively low C:N ratio. 相似文献
7.
Jared L. DeForest Jiquan Chen Steve G. McNulty 《International journal of biometeorology》2009,53(2):127-134
The contribution of the organic (O) horizon to total soil respiration is poorly understood even though it can represent a
large source of uncertainty due to seasonal changes in microclimate and O horizon properties due to plant phenology. Our objectives
were to partition the CO2 effluxes of litter layer and mineral soil from total soil respiration (SR) and determine the relative importance of changing
temperature and moisture mediating the fluxes. We measured respiration in an oak-dominated forest with or without the O horizon
for 1 year within the Oak Openings Region of northwest Ohio. Mineral soil and O horizon respiration were subtracted from mineral
soil respiration (MSR) to estimate litter respiration (LR). Measurements were grouped by oak phenology to correlate changes
in plant activity with respiration. The presence of the O horizon represented a large source of seasonal variation in SR.
The timing of oak phenology explained some of the large changes in both SR and LR, and their relationship with temperature
and moisture. The contribution to SR of respiration from the mineral soil was greatest during pre-growth and pre-dormancy,
as evident by the low LR:MSR ratios of 0.65 ± 0.10 (mean ± SE) and 0.69 ± 0.03, respectively, as compared to the other phenophases.
Including moisture increased our ability to predict MSR and SR during the growth phenophase and LR for every phenophase. Temperature
and moisture explained 85% of the variation in MSR, but only 60% of the variation in LR. The annual contribution of O horizon
to SR was 48% and the ratio of litter to soil respiration was tightly coupled over a wide range of environmental conditions.
Our results suggest the presence of the O horizon is a major mediator of SR. 相似文献
8.
Effects of forest clearing and succession on the carbon and nitrogen content of soils in Puerto Rico and US Virgin Islands 总被引:8,自引:0,他引:8
Soil samples from mature and secondary forests and agricultural sites in three subtropical life zones of Puerto Rico and the
US Virgin Islands were collected to determine the effects of forest conversion to agriculture and succession on soil organic
carbon (C) and nitrogen (N) contents. Site characteristics that may affect soil C and N (slope, elevation, aspect, and texture)
were as uniform as possible. Carbon contents (to 50 cm depth or bedrock) of cultivated sites, as a percent of corresponding
mature forests, were lower in the wet (44%) and moist (31%) than in the dry (86%) life zones whereas N contents were relatively
high regardless of life zone (60–130% of the mature forests). Conversion of forests to pasture resulted in less soil C and
N loss than conversion to crops. The time for recovery of soil C and N during succession was approximately the same in all
three life zones, about 40–50 yr for C about 15–20 yr for N. However, the rate of recovery of soil C was faster in the wet
and moist life zone, whereas N appeared to recover faster in the dry life zone. Evidence for loss of soil C during cultivation
and gain during succession to soil depths of 50–100 cm is presented. 相似文献
9.
Land-use and land-cover strongly influence soil properties such as the amount of soil organic carbon (SOC), aggregate structure and SOC turnover processes. We studied the effects of a vegetation shift from forest to grassland 90 years ago in soils derived from andesite material on Barro Colorado Island (BCI), Panama. We quantified the amount of carbon (C) and nitrogen (N) and determined the turnover of C in bulk soil, water stable aggregates (WSA) of different size classes (<53 μm, 53–250 μm, 250–2000 μm and 2000–8000 μm) and density fractions (free light fraction, intra-aggregate particulate organic matter and mineral associated soil organic C). Total SOC stocks (0–50 cm) under forest (84 Mg C ha−1) and grassland (64 Mg C ha−1) did not differ significantly. Our results revealed that vegetation type did not have an effect on aggregate structure and stability. The investigated soils at BCI did not show higher C and N concentrations in larger aggregates, indicating that organic material is not the major binding agent in these soils to form aggregates. Based on δ13C values and treating bulk soil as a single, homogenous C pool we estimated a mean residence time (MRT) of 69 years for the surface layer (0–5 cm). The MRT varied among the different SOC fractions and among depth. In 0–5 cm, MRT of intra-aggregate particulate organic matter (iPOM) was 29 years; whereas mineral associated soil organic C (mSOC) had a MRT of 124 years. These soils have substantial resilience to C and N losses because the >90% of C and N is associated with mSOC, which has a comparatively long MRT. 相似文献
10.
Matteo Campioli Anders Michelsen Andreas Demey Annemie Vermeulen Roeland Samson Raoul Lemeur 《Ecosystems》2009,12(5):760-776
Mesic–dry tundras are widespread in the Arctic but detailed assessments of net primary production (NPP) and ecosystem carbon
(C) stocks are lacking. We addressed this lack of knowledge by determining the seasonal dynamics of aboveground vascular NPP,
annual NPP, and whole-ecosystem C stocks in five mesic–dry tundras in Northern Sweden with contrasting microtopography, altitude,
and dominant species. Those measurements were paralleled by the stock assessments of nitrogen (N), the limiting nutrient.
The vascular production was determined by harvest or in situ growing units, whereas the nonvascular production was obtained
from average species growth rates, previously assessed at the sites. Results showed that aboveground vascular NPP (15–270 g m−2), annual NPP (214–282 g m−2 or 102–137 g C m−2) and vegetation biomass (330–2450 g m−2) varied greatly among communities. Vegetation dominated by Empetrum hermaphroditum is more productive than Cassiope tetragona vegetation. Although the large majority of the apical NPP occurred in early-mid season (85%), production of stems and evergreen
leaves proceeded until about 2 weeks before senescence. Most of the vascular vegetation was belowground (80%), whereas most
of the vegetation production occurred aboveground (85%). Ecosystem C and N stocks were 2100–8200 g C m−2 and 80–330 g N m−2, respectively, stored mainly in the soil turf and in the fine organic soil. Such stocks are comparable to the C and N stocks
of moister tundra types, such as tussock tundra.
Author Contributions Matteo Campioli, Anders Michelsen, Roeland Samson, Raoul Lemeur—conceived and designed study, Matteo Campioli, Anders Michelsen,
Andreas Demey, Annemie Vermeulen—performed research, Matteo Campioli—analyzed data, and Matteo Campioli—wrote the paper. 相似文献
11.
We present results on changes in soil properties following land use change over an approximately 55‐year period at Fort Benning, Georgia, U.S.A. Soil cores were taken at 129 locations that were categorized as reforested (field/bare ground in 1944 and forest in 1999), disturbed (field/bare ground in 1944 and 1999), or reference forests (forest in 1944 and 1999). Soil disturbance included historic agriculture (pre‐1944) and military training (post‐1944). Density in mineral soils exhibited a historic land use legacy effect (reference < reforested < disturbed). Rates of change in bulk density decreased with depth and estimated total times to reach reference forest levels ranged from 83 (0–10 cm) to 165 (30–40 cm) years. A land use legacy effect on C stock was apparent in the O‐horizon and in 30‐ to 40‐cm soil increment (reference > reforested > disturbed). Soil C stock in all other increments and in particulate organic matter was affected by disturbance; however, no legacy was apparent (reference = reforested > disturbed). For the entire soil profile (O‐horizon to 40 cm), rate of C accrual was 28 g m−2 yr−1 (1.5%/yr). Nitrogen stocks were affected by disturbance in the O‐horizon and 0‐ to 10‐cm increment; however, no legacy effect was detected (reference = reforested > disturbed). Nitrogen accumulated at 0.56 g m−2 yr−1 (0.6%/yr) for the entire soil profile. At Fort Benning, soil C and N stocks of reforested stands were similar to those of reference forested stands after approximately 55 years. However, soil bulk density was greater on reforested stands than reference forest stands at 55 years and may require an additional century to reach reference levels. 相似文献
12.
Dynamics of dissolved organic <Superscript>14</Superscript>C in throughfall and soil solution of a Norway spruce forest 总被引:1,自引:0,他引:1
Dissolved organic carbon (DOC) is an important component of the C cycle in forest ecosystems, but dynamics and origin of DOC
in throughfall and soil solution are yet poorly understood. In a 2-year study, we analyzed the radiocarbon signature of DOC
in throughfall and soil solution beneath the Oa horizon and at 90 cm depth in a Norway spruce forest on a Podzol soil. A two-pool
mixing model revealed that throughfall DOC comprised mainly biogenic C, i.e. recently fixed C, from canopy leaching and possibly
other sources. The contribution of fossil DOC from atmospheric deposition to throughfall DOC was on average 6% with maxima
of 8–11% during the dormant season. In soil solution from the Oa horizon, DO14C signature was highly dynamic (range from −8‰ to +103‰), but not correlated with DOC concentration. Radiocarbon signatures
suggest that DOC beneath the Oa horizon originated mainly from occluded and mineral associated organic matter fractions of
the Oa horizon rather than from the Oi or Oe horizon. Relatively old C was released in the rewetting phase following a drought
period in the late summer of 2006. In contrast, the DO14C signature indicated the release of younger C throughout the humid year 2007. In soil solutions from 90 cm depth, DO14C signatures were also highly dynamic (−127‰ to +3‰) despite constantly low DOC concentrations. Similar to the Oa horizon,
the lowest DO14C signature at 90 cm depth was found after the rewetting phase in the late summer of 2006. Because of the variation in the
DO14C signatures at this depth, we conclude that DOC was not equilibrated with the surrounding soil, but also originated from
overlaying soil horizons. The dynamics of DO14C in throughfall and soil solution suggest that the sources of DOC are highly variable in time. Extended drought periods likely
have a strong influence on release and translocation of DOC from relatively old and possibly stabilized soil organic matter
fractions. Temporal variations as well as the input of fossil DOC needs to be considered when calibrating DOC models based
on DO14C signatures. 相似文献
13.
In Finland, over 220,000 ha of arable land has been afforested in recent decades. To meet the goals of forest management on
afforested fields, information on the effects of former agricultural land use on soil fertility is needed. In this study,
we examine the soil fertility of 12 former arable fields afforested either 10 or 60–70 years ago with Norway spruce (Picea abies (L.) Karst.) and adjacent sites that have been forested continuously. Volumetric soil samples were collected from the organic
soil layer and from mineral soil to a depth of 40 cm. Soil samples were analyzed for pH, bulk density, organic matter content
and amounts of nutrients (Kjeldahl N, extractable P, K, Ca, Mg, Zn and B). On afforested fields, amounts of nutrients in the
mineral soil, especially in 10-year-old afforestations, were higher than on continuously forested sites. In the organic layer
plus the 0–40 cm soil layer, the 10-year-old afforestations had 68% more N, 41% more P, 83% more K, 252% more Ca, 6% more
Mg, 61% more Zn and 33% more B than the continuously forested sites at a comparable soil depth. In the 60–70-year-old afforestations,
the differences were significant only for N, Ca and Zn (20% more N, 121% more Ca and 115% more Zn than on the continuously
forested sites). The effects of agriculture on amounts of nutrients were most clearly detected in the former plough layer
(0–20 cm) of the 10-year-old afforestations and in the top layer (0–10 cm) of the older afforestations. Amounts of nutrients
in the organic layer of the afforested sites were lower, but their concentrations were higher than in the continuously forested
sites. On the 10-year-old afforestations, the bulk density of the mineral soil tended to be lower and the organic matter content
higher than on the continuously forested sites. On both young and old afforestations, soil pH was higher than on the continuously
forest sites. According to these results, changes in soil properties caused by agriculture have increased the soil fertility
and therefore probably also the site index. The results also suggest that changes in soil properties due to agricultural land
use are quite long lasting. 相似文献
14.
Plant and Soil N Response of Southern Californian Semi-arid Shrublands After 1 Year of Experimental N Deposition 总被引:1,自引:0,他引:1
Large inputs of atmospheric N from dry deposition accumulate on vegetation and soil surfaces of southern Californian chaparral
and coastal sage scrub (CSS) ecosystems during the late-summer and early-fall and become available as a pulse following winter
rainfall; however, the fate of this dry season atmospheric N addition is unknown. To assess the potential for dry season atmospheric
N inputs to be incorporated into soil and/or vegetation N pools, an in situ N addition experiment was initiated in a post-fire
chaparral and a mature CSS stand where 10 × 10 m plots were exposed to either ambient N deposition (control) or ambient +50 kg
N ha−1 (added N) added as NH4NO3 during a single application in October 2003. After 1 year of N addition, plots exposed to added N had significantly higher
accumulation of extractable inorganic N (NH4−N + NO3−N) on ion exchange resins deployed in the 0–10 cm mineral soil layer and higher soil extractable N in the subsurface (30–40 cm)
mineral soil than plots exposed to ambient N. Chaparral and CSS shrubs exposed to added N also exhibited a significant increase
in tissue N concentration and a decline in the tissue C:N ratio, and added N significantly altered the shrub tissue δ
15N natural abundance. Leaching of inorganic N to 1 m below the soil surface was on average 2–3 times higher in the added N
plots, but large within treatment variability cause these differences to be statistically insignificant. Although a large
fraction of the added N could not be accounted for in the shrub and soil N pools investigated, these observations suggest
that dry season N inputs can significantly and rapidly alter N availability and shrub tissue chemistry in Mediterranean-type
chaparral and CSS shrublands of southern California. 相似文献
15.
Despite the extensive literature on the effect on soil properties of afforestation of former arable land, we still lack full
understanding of whether the changes proceed in the same direction and at the same rate, and of how long is required to achieve
a state of soil equilibrium typical of a natural forest ecosystem. Therefore, as part of a study comparing post-arable sandy
soils (Dystric Arenosols) afforested with Scots pine (Pinus silvestris L.) with arable soils and soils of continuous coniferous forests, the range and direction of changes in pH, organic carbon
(Corg), total nitrogen (Ntot), ammonium (N-NH4) and nitrates (N-NO3) in soil solution, total (Ptot) and available (Pav) phosphorus were determined. The studies were carried out in south-east Poland (51°30′-51°37′N, 22°20′-22°35′E). Ten paired
sites of afforested soils (five with 14- to 17-year-old stands and five with 32- to 36-year-old stands) with adjacent cultivated
fields, and five sites of continuous forest with present stands of ca. 130–150 years old were selected. Soil samples were
taken from the whole thickness of master horizons and, in the case of the A horizon of the afforested soils, from three layers:
0–5 (A0–5), 5–10 (A5–10) and 10–20 cm (A10–20). The cultivated soils in the Ap horizon showed higher pH (by ca. 1.0 unit), lower Corg and C:N, similar Ntot, lower N-NH4, higher N-NO3, higher Ptot and Pav contents compared with the Ah horizon of continuous forest soils. The results indicated decreased soil pH in the former plough
layer of the afforested soils, with the greatest decrease observed in the 0–5 cm layer. In these soils, the Corg content was considerably higher in the A0–5 layer, but lower in the two deeper layers and in the whole A horizon (0–20 cm) compared with the Ap horizon of the arable
soils. The results indicate that the Corg content, after an initial phase of decline, again achieved a level characteristic of arable soils. The Ntot content in all layers of the A horizon of the afforested soils was lower than in the Ap horizon of the arable soils, and
showed a reduction with stand age, especially in deeper layers. The C:N ratios in the mineral topsoil increased with stand
age. N-NH4 content increased and N-NO3 decreased after afforestation. The Ptot and Pav contents in all layers and in the whole A horizon of the afforested soils, on stands of both ages, was lower than in the
Ap of the cultivated soils. From the results, it could be concluded that, after more than 30 years of tree growth, the soils
of the A horizon were still more similar to arable than to continuous forest soils with respect to Corg, Ptot and Pav. With respect to pH, N-NH4 and N-NO3, especially in the 0–5 cm layer, they were more similar to continuous forest soils than to cultivated soils, but with respect
to Ntot and C:N ratio they were somewhere in between. 相似文献
16.
The role of roots penetrating various undisturbed soil horizons beneath loose layer in water use and shoot growth of maize
was evaluated in greenhouse experiment. 18 undisturbed soil columns 20 cm in diameter and 20 cm in height were taken from
the depths 30–50 cm and 50–70 cm from a Brown Lowland soil, a Pseudogley and a Brown Andosol (3 columns from each depth and
soil). Initial resistance to penetration in undisturbed soil horizons varied from 2.5 to 8.9 MPa while that in the loose layer
was 0.01 MPa. The undisturbed horizons had a major effect on vertical arrangement of roots. Root length density in loose layer
varied from 96 to 126 km m-3 while in adjacent stronger top layers of undisturbed horizons from 1.6 to 20.0 km m-3 with higher values in upper horizons of each soil. For specific root length, the corresponding ranges were 79.4–107.7 m g-1 (on dry basis) and 38.2–63.7 m g-1, respectively. Ratios of root dry weight per unit volume of soil between loose and adjacent undisturbed layers were much
lower than those of root length density indicating that roots in undisturbed horizons were produced with considerably higher
partition of assimilates. Root size in undisturbed horizons relative to total roots was from 1.1 to 38.1% while water use
from the horizons was from 54.1 to 74.0%. Total water use and shoot growth were positively correlated with root length in
undisturbed soil horizons. There was no correlation between shoot growth and water use from the loose layers. 相似文献
17.
Bomb <Superscript>14</Superscript>C enrichment indicates decadal C pool in deep soil? 总被引:1,自引:0,他引:1
Studies of changes in soil organic carbon (SOC) stocks normally limit their focus to the upper 20–30 cm of soil, yet 0–20 cm
SOC stocks are only ∼40% of 0–1 m SOC. Accounting for only the upper 20–30 cm of SOC has been justifiable assuming that deeper
SOC is unreactive since it displays 14C-derived mean residence times of hundreds or thousands of years. The dramatic increase in the 14C content of the atmosphere resulting from thermonuclear testing circa 1963 allows the unreactivity of deep SOC to be tested
by examining whether deep soils show evidence of ‘bomb-14C’ incorporation. At depths of 40–100 cm, a well-studied New Zealand soil under stable pastoral management displays progressive
enrichment of over 200‰ across samplings in 1959, 1974 and 2002, indicating substantial incorporation of bomb 14C. This pattern of deep 14C enrichment—previously observed in 2 well-drained California grassland soils—leads to the hypothesis that roots and/or dissolved
organic C transport contribute to a decadally-reactive SOC pool comprising ∼10–40% of SOC below 50 cm. Deep reactive SOC may
be important in the global C cycle because it can react to land-use or vegetation change and may respond to different processes
than the reactive SOC in the upper 20–30 cm of soil. 相似文献
18.
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
19.
Charles T. Garten 《Acta Oecologica》2009,35(2):218-226
Changing inputs of carbon to soil is one means of potentially increasing carbon sequestration in soils for the purpose of mitigating projected increases in atmospheric CO2 concentrations. The effect of manipulations of aboveground carbon input on soil carbon storage was tested in a temperate, deciduous forest in east Tennessee, USA. A 4.5-year experiment included exclusion of aboveground litterfall and supplemental litter additions (three times ambient) in an upland and a valley that differed in soil nitrogen availability. The estimated decomposition rate of the carbon stock in the O horizon was greater in the valley than in the upland due to higher litter quality (i.e., lower C/N ratios). Short-term litter exclusion or addition had no effect on carbon stock in the mineral soil, measured to a depth of 30 cm, or the partitioning of carbon in the mineral soil between particulate- and mineral-associated organic matter. A two-compartment model was used to interpret results from the field experiments. Field data and a sensitivity analysis of the model were consistent with little carbon transfer between the O horizon and the mineral soil. Increasing aboveground carbon input does not appear to be an effective means of promoting carbon sequestration in forest soil at the location of the present study because a disconnect exists in carbon dynamics between O horizon and mineral soil. Factors that directly increase inputs to belowground soil carbon, via roots, or reduce decomposition rates of organic matter are more likely to benefit efforts to increase carbon sequestration in forests where carbon dynamics in the O horizon are uncoupled from the mineral soil. 相似文献
20.
Shifting sources of soil labile organic carbon after termination of plant carbon inputs in a subtropical moist forest of southwest China 总被引:1,自引:0,他引:1
Labile organic carbon (LOC) is a critical component of soil organic carbon (C) because of its intimate association with soil
heterotrophic respiration and role in the decomposition of resistant soil organic matter. In a subtropical moist evergreen
broad-leaved forest of southwest China, we examined changes of LOC and its potential turnover time, microbial biomass C (MBC),
and soil microbial activity of the organic and the 0–10 cm mineral soil layers with aboveground plant litter and belowground
root treatments. In February of 2004, removal of organic layer, root-trenching, and tree-girdling treatments were applied
alone and in combination to manipulate plant-C inputs. In 2006, root-trenching and tree-girdling treatments did not significantly
change LOC in the organic layer. In the 0–10 cm mineral soil layer, LOC increased substantially due to tree-girdling treatment,
especially in the plots of tree-girdling and the combinations of three treatments, but this increase was absent in 2007. Soil
MBC in these two layers generally did not change markedly after plant-C inputs manipulations except significant increase under
tree-girdling treatment in 2006. The potential turnover times of LOC increased in all plots with the plant-C inputs manipulations.
The lack of influence of plant-C inputs manipulations on LOC pools is likely due to high total soil organic C here, while
insignificant changes of MBC suggest the soil microbes are not C limited in this forest. The changes of the potential turnover
time of LOC imply that the sources of LOC have been shifted from fresh plant litter or root exudates to old soil organic C.
Our results suggest that LOC recently derived from plants is preferred by microbes when available, but microbes can also use
LOC from soil organic matter when fresh plant C is not available. 相似文献