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1.
Our current ability to detect and predict changes in forest ecosystem productivity is constrained by several limitations.
These include a poor understanding of belowground productivity, the short duration of most analyses, and a need for greater
examination of species- or community-specific variability in productivity studies. We quantified aboveground net primary productivity
(ANPP) over 3 years (1999–2001), and both belowground NPP (BNPP) and total NPP over 2 years (2000–2001) in both mesic and
xeric site community types of the mixed mesophytic forest of southeastern Kentucky to examine landscape variability in productivity
and its relation with soil resource [water and nitrogen (N)] availability. Across sites, ANPP was significantly correlated
with N availability (R2 = 0.58, P = 0.028) while BNPP was best predicted by soil moisture content (R2 = 0.72, P = 0.008). Because of these offsetting patterns, total NPP was unrelated to either soil resource. Interannual variability
in growing season precipitation during the study resulted in a 50% decline in mesic site litter production, possibly due to
a lag effect following a moderate drought year in 1999. As a result, ANPP in mesic sites declined 27% in 2000 compared to
1999, while xeric sites had no aboveground production differences related to precipitation variability. If global climate
change produces more frequent occurrences of drought, then the response of mesic sites to prolonged moisture deficiency and
the consequences of shifting carbon (C) allocation on C storage will become important questions. 相似文献
2.
Steven S. Perakis Douglas A. Maguire Thomas D. Bullen Kermit Cromack Richard H. Waring James R. Boyle 《Ecosystems》2006,9(1):63-74
Nitrogen (N) is a critical limiting nutrient that regulates plant productivity and the cycling of other essential elements
in forests. We measured foliar and soil nutrients in 22 young Douglas-fir stands in the Oregon Coast Range to examine patterns
of nutrient availability across a gradient of N-poor to N-rich soils. N in surface mineral soil ranged from 0.15 to 1.05%
N, and was positively related to a doubling of foliar N across sites. Foliar N in half of the sites exceeded 1.4% N, which
is considered above the threshold of N-limitation in coastal Oregon Douglas-fir. Available nitrate increased five-fold across
this gradient, whereas exchangeable magnesium (Mg) and calcium (Ca) in soils declined, suggesting that nitrate leaching influences
base cation availability more than soil parent material across our sites. Natural abundance strontium isotopes (87Sr/86Sr) of a single site indicated that 97% of available base cations can originate from atmospheric inputs of marine aerosols,
with negligible contributions from weathering. Low annual inputs of Ca relative to Douglas-fir growth requirements may explain
why foliar Ca concentrations are highly sensitive to variations in soil Ca across our sites. Natural abundance calcium isotopes
(δ44Ca) in exchangeable and acid leachable pools of surface soil measured at a single site showed 1 per mil depletion relative
to deep soil, suggesting strong Ca recycling to meet tree demands. Overall, the biogeochemical response of these Douglas-fir
forests to gradients in soil N is similar to changes associated with chronic N deposition in more polluted temperate regions,
and raises the possibility that Ca may be deficient on excessively N-rich sites. We conclude that wide gradients in soil N
can drive non-linear changes in base-cation biogeochemistry, particularly as forests cross a threshold from N-limitation to
N-saturation. The most acute changes may occur in forests where base cations are derived principally from atmospheric inputs. 相似文献
3.
Sílvia Fernanda Mardegan Gabriela Bielefeld Nardoto Niro Higuchi Marcelo Zacharias Moreira Luiz Antonio Martinelli 《Trees - Structure and Function》2009,23(3):479-488
Addressing spatial variability in nitrogen (N) availability in the Central Brazilian Amazon, we hypothesized that N availability
varies among white-sand vegetation types (campina and campinarana) and lowland tropical forests (dense terra-firme forests) in the Central Brazilian Amazon, under the same climate conditions.
Accordingly, we measured soil and foliar N concentration and N isotope ratios (δ15N) throughout the campina-campinarana transect and compared to published dense terra-firme forest results. There were no differences between white-sand vegetation
types in regard to soil N concentration, C:N ratio and δ15N across the transect. Both white-sand vegetation types showed very low foliar N concentrations and elevated foliar C:N ratios,
and no significant difference between site types was observed. Foliar δ15N was depleted, varying from −9.6 to 1.6‰ in the white-sand vegetations. The legume Aldina heterophylla had the highest average δ15N values (−1.5‰) as well as the highest foliar N concentration (2.1%) while the non-legume species had more depleted δ15N values and the average foliar N concentrations varied from 0.9 to 1.5% among them. Despite the high variation in foliar
δ15N among plants, a significant and gradual 15N-enrichment in foliar isotopic signatures throughout the campina–campinarana transect was observed. Individual plants growing in the campinarana were significantly enriched in 15N compared to those in campina. In the white-sand N-limited ecosystems, the differentiation of N use seems to be a major cause of variations observed in
foliar δ15N values throughout the campina–campinarana transect. 相似文献
4.
The growth of forest species in soil development chronosequences becomes increasingly phosphorus (P)-limited with time, as
P is weathered, eroded and leached from soil. Foliar nitrogen (N) concentrations also tend to decrease with soil age when
vegetation may be limited in both N and P. Here we report on soil development in temperate rain forests along three New Zealand
chronosequences that have minimal pollution and disturbance from human activities, at Franz Josef, Waitutu and Central Volcanic
Plateau, and on factors influencing soil net N mineralization (aerobic; 56 days) and foliar N and P concentrations. Except
in very young soils (<500 years), at least 85% of total-P in mineral soil (0–10 cm) was transformed to organic-P. In each
chronosequence, total-P declined with time, and foliar N:P ratios (mass) generally increased from 8 to 15–18, suggesting P
was more limiting than N in the oldest soils of the chronosequence. There was a negative relationship between net N mineralization
and C:N ratio for mineral soil. For the FH (organic) layer, net N mineralization had the strongest relationships with total-N
concentration (positively) and C:organic-P ratio (negatively); however, relationships varied with forest group, suggesting
that other factors were also important. Foliar P of kamahi (Weinmannia racemosa Linn. f.), a dominant canopy species, was related to soil organic-P, suggesting mineralization was an important process for
tree nutrition.Foliar N was positively related to N concentration in the FH layer, but was not significantly related to any
measured property in mineral soil, possibly because of the wide range of soils. The consistent declines in both soil and foliar
P across the contrasting chronosequences strongly suggest that vegetation becomes progressively P-limited during long-term
ecosystem development. 相似文献
5.
Correlations between foliar δ15N and nitrogen concentrations may indicate plant-mycorrhizal interactions 总被引:1,自引:0,他引:1
Nitrogen isotope measurements may provide insights into changing interactions among plants, mycorrhizal fungi, and soil processes
across environmental gradients. Here, we report changes in δ15N signatures due to shifts in species composition and nitrogen (N) dynamics. These changes were assessed by measuring fine
root biomass, net N mineralization, and N concentrations and δ15N of foliage, fine roots, soil, and mineral N across six sites representing different post-deglaciation ages at Glacier Bay,
Alaska. Foliar δ15N varied widely, between 0 and –2‰ for nitrogen-fixing species, between 0 and –7‰ for deciduous non-fixing species, and between
0 and –11‰ for coniferous species. Relatively constant δ15N values for ammonium and generally low levels of soil nitrate suggested that differences in ammonium or nitrate use were
not important influences on plant δ15N differences among species at individual sites. In fact, the largest variation among plant δ15N values were observed at the youngest and oldest sites, where soil nitrate concentrations were low. Low mineral N concentrations
and low N mineralization at these sites indicated low N availability. The most plausible mechanism to explain low δ15N values in plant foliage was a large isotopic fractionation during transfer of nitrogen from mycorrhizal fungi to plants.
Except for N-fixing plants, the foliar δ15N signatures of individual species were generally lower at sites of low N availability, suggesting either an increased fraction
of N obtained from mycorrhizal uptake (f), or a reduced proportion of mycorrhizal N transferred to vegetation (T
r). Foliar and fine root nitrogen concentrations were also lower at these sites. Foliar N concentrations were significantly
correlated with δ15N in foliage of Populus, Salix, Picea, and Tsuga heterophylla, and also in fine roots. The correlation between δ15N and N concentration may reflect strong underlying relationships among N availability, the relative allocation of carbon
to mycorrhizal fungi, and shifts in either f or T
r.
Received: 14 December 1998 / Accepted: 16 August 1999 相似文献
6.
Michelle C. Mack 《Biotropica》2011,43(4):433-441
We explored patterns of soil and foliar nutrients across nine mature forest sites in Costa Rica, where mean annual precipitation (MAP) ranged between 3500 and 5500 mm, altitude ranged between 200 and 1200 m, and species composition varied among sites. Our objective was to investigate the relationship between rainfall and plant or soil nutrient characteristics to better understand the potential long‐term effects that alterations in MAP could have on the nutrient dynamics of wet forest plant communities. Indicators of soil N availability (net mineralization and nitrification) decreased with MAP but were not related to foliar N. Soil and foliar P, by contrast, were not correlated with MAP but were positively correlated with each other. Thus, across our gradient foliar P was a better predictor of soil nutrient availability than foliar N. There were wide differences in foliar nutrient concentrations and N:P ratios among species within sites. At each site, legumes had higher mean percent N than nonlegumes, resulting in higher N:P ratios for legumes. Taken together, these data suggest that, at least in these forests, a climate‐driven decrease in MAP could cause an increase in net N mineralization and nitrification for the wetter sites. However, this may not affect productivity at the community level because of low P availability, complex feedbacks between soil and foliar nutrients, and interactions with other biological and environmental factors such as elevation. 相似文献
7.
Relationships among net primary productivity, nutrients and climate in tropical rain forest: a pan-tropical analysis 总被引:2,自引:0,他引:2
Cleveland CC Townsend AR Taylor P Alvarez-Clare S Bustamante MM Chuyong G Dobrowski SZ Grierson P Harms KE Houlton BZ Marklein A Parton W Porder S Reed SC Sierra CA Silver WL Tanner EV Wieder WR 《Ecology letters》2011,14(9):939-947
Tropical rain forests play a dominant role in global biosphere-atmosphere CO(2) exchange. Although climate and nutrient availability regulate net primary production (NPP) and decomposition in all terrestrial ecosystems, the nature and extent of such controls in tropical forests remain poorly resolved. We conducted a meta-analysis of carbon-nutrient-climate relationships in 113 sites across the tropical forest biome. Our analyses showed that mean annual temperature was the strongest predictor of aboveground NPP (ANPP) across all tropical forests, but this relationship was driven by distinct temperature differences between upland and lowland forests. Within lowland forests (1000?m), a regression tree analysis revealed that foliar and soil-based measurements of phosphorus (P) were the only variables that explained a significant proportion of the variation in ANPP, although the relationships were weak. However, foliar P, foliar nitrogen (N), litter decomposition rate (k), soil N and soil respiration were all directly related with total surface (0-10?cm) soil P concentrations. Our analysis provides some evidence that P availability regulates NPP and other ecosystem processes in lowland tropical forests, but more importantly, underscores the need for a series of large-scale nutrient manipulations - especially in lowland forests - to elucidate the most important nutrient interactions and controls. 相似文献
8.
Productivity of semiarid grasslands is affected by soil water and nutrient availability, with water controlling net primary
production under dry conditions and soil nutrients constraining biomass production under wet conditions. In order to investigate
limitations on plants by the response of root–shoot biomass allocation to water and nitrogen (N) availability, a field experiment,
on restoration plots with rainfed, unfertilized control plots, fertilized plots receiving N (25 kg urea-N ha−1) and water (irrigation simulating a wet season), was conducted at two sites with different grazing histories: moderate (MG)
and heavy (HG) grazing. Irrigation and N addition had no effect on belowground biomass. Irrigation increased aboveground (ANPP)
and belowground net primary production (BNPP) and rain-use efficiency based on ANPP (RUEANPP), whereas N addition on rainfed plots had no effect on any of the measured parameters. N fertilizer application on irrigated
plots increased ANPP and RUEANPP and reduced the root fraction (RF: root dry matter/total dry matter), resulting in smaller N effects on total net primary
production (NPP) and rain-use efficiency based on NPP. This suggests that BNPP should be included in evaluating ecosystem
responses to resource availability from the whole-plant perspective. N effects on all measured parameters were similar on
both sites. However, site HG responded to irrigation with higher ANPP and a lower RF when compared to site MG, indicating
that species composition had a pronounced effect on carbon allocation pattern due to below- and aboveground niche complementarity. 相似文献
9.
The cold deserts of the Colorado Plateau contain numerous geologically and geochemically distinct sedimentary bedrock types.
In the area near Canyonlands National Park in Southeastern Utah, geochemical variation in geologic substrates is related to
the depositional environment with higher concentrations of Fe, Al, P, K, and Mg in sediments deposited in alluvial or marine
environments and lower concentrations in bedrock derived from eolian sand dunes. Availability of soil nutrients to vegetation
is also controlled by the formation of secondary minerals, particularly for P and Ca availability, which, in some geologic
settings, appears closely related to variation of CaCO3 and Ca-phosphates in soils. However, the results of this study also indicate that P content is related to bedrock and soil
Fe and Al content suggesting that the deposition history of the bedrock and the presence of P-bearing Fe and Al minerals,
is important to contemporary P cycling in this region. The relation between bedrock type and exchangeable Mg and K is less
clear-cut, despite large variation in bedrock concentrations of these elements. We examined soil nutrient concentrations and
foliar nutrient concentration of grasses, shrubs, conifers, and forbs in four geochemically distinct field sites. All four
of the functional plant groups had similar proportional responses to variation in soil nutrient availability despite large
absolute differences in foliar nutrient concentrations and stoichiometry across species. Foliar P concentration (normalized
to N) in particular showed relatively small variation across different geochemical settings despite large variation in soil
P availability in these study sites. The limited foliar variation in bedrock-derived nutrients suggests that the dominant
plant species in this dryland setting have a remarkably strong capacity to maintain foliar chemistry ratios despite large
underlying differences in soil nutrient availability. 相似文献
10.
Sapling growth as a function of light and landscape-level variation in soil water and foliar nitrogen in northern Michigan 总被引:3,自引:0,他引:3
Kobe RK 《Oecologia》2006,147(1):119-133
Interspecific differences in sapling growth responses to soil resources could influence species distributions across soil
resource gradients. I calibrated models of radial growth as a function of light intensity and landscape-level variation in
soil water and foliar N for saplings of four canopy tree species, which differ in adult distributions across soil resource
gradients. Model formulations, characterizing different resource effects and modes of influencing growth, were compared based
on relative empirical support using Akaike’s Information Criterion. Contrary to expectation, the radial growth of species
associated with lower fertility (Acer rubrum and Quercus rubra) was more sensitive to variation in soil resources than the high fertility species Acer saccharum. Moreover, there was no species tradeoff between growth under high foliar N versus growth under low foliar N, which would
be expected if growth responses to foliar N mediated distributions. In general, there was functional consistency among species
in growth responses to light, foliar N, and soil water availability, respectively. Foliar N influenced primarily high-light
growth in F. grandifolia, A. rubrum, and Q. rubra (but was not significant for A. saccharum). In A. saccharum and A. rubrum, for which soil water availability was a significant predictor, soil water and light availability simultaneously limited
growth (i.e., either higher light or water increased growth). Simple resource-based models explained 0.74–0.90 of growth variance,
indicating a high degree of determinism. Results suggest that nitrogen effects on forest dynamics would be strongest in high-light
early successional communities but that water availability influences growth in both early successional and understory environments. 相似文献
11.
Foliage litter quality and annual net N mineralization: comparison across North American forest sites 总被引:24,自引:0,他引:24
The feedback between plant litterfall and nutrient cycling processes plays a major role in the regulation of nutrient availability
and net primary production in terrestrial ecosystems. While several studies have examined site-specific feedbacks between
litter chemistry and nitrogen (N) availability, little is known about the interaction between climate, litter chemistry, and
N availability across different ecosystems. We assembled data from several studies spanning a wide range of vegetation, soils,
and climatic regimes to examine the relationship between aboveground litter chemistry and annual net N mineralization. Net
N mineralization declined strongly and non-linearly as the litter lignin:N ratio increased in forest ecosystems (r
2 = 0.74, P < 0.01). Net N mineralization decreased linearly as litter lignin concentration increased, but the relationship was significant
(r
2 = 0.63, P < 0.01) only for tree species. Litterfall quantity, N concentration, and N content correlated poorly with net N mineralization
across this range of sites (r
2 < 0.03, P = 0.17–0.26). The relationship between the litter lignin:N ratio and net N mineralization from forest floor and mineral soil
was similar. The litter lignin:N ratio explained more of the variation in net N mineralization than climatic factors over
a wide range of forest age classes, suggesting that litter quality (lignin:N ratio) may exert more than a proximal control
over net N mineralization by influencing soil organic matter quality throughout the soil profile independent of climate.
Received: 16 December 1996 / Accepted: 8 February 1997 相似文献
12.
Forest Productivity and Efficiency of Resource Use Across a Chronosequence of Tropical Montane Soils 总被引:7,自引:3,他引:4
13.
M. Williams Y. E. Shimabukuro D. A. Herbert S. Pardi Lacruz C. Renno E. B. Rastetter 《Ecosystems》2002,5(7):0692-0704
Transferring fine-scale ecological knowledge into an understanding of earth system processes presents a considerable challenge
to ecologists. Our objective here was to identify and quantify heterogeneity of, and relationships among, vegetation and soil
properties in terra firme rain forest ecosystems in eastern Amazonia and assess implications for generating regional predictions
of carbon (C) exchange. Some of these properties showed considerable variation among sites; soil textures varied from 11%
to 92% clay. But we did not find any significant correlations between soil characteristics (percentage clay, nitrogen [N],
C, organic matter) and vegetation characteristics (leaf area index [LAI], foliar N concentration, basal area, biomass, stem
density). We found some evidence for increased drought stress on the sandier sites: There was a significant correlation between
soil texture and wood δ13C (but not with foliar δ13C); volumetric soil moisture was lower at sandier sites; and some canopy foliage had large, negative dawn water potentials
(ψld), indicating limited water availability in the rooting zone. However, at every site at least one foliage sample indicated
full or nearly full rehydration, suggesting significant interspecific variability in drought vulnerability. There were significant
differences in foliar δ15N among sites, but not in foliar % N, suggesting differences in N cycling but not in plant access to N. We used an ecophysiological
model to examine the sensitivity of gross primary production (GPP) to observed inter- and intrasite variation in key driving
variables—LAI, foliar N, and ψld. The greatest sensitivity was to foliar N; standard errors on foliar N data translated into uncertainty in GPP predictions
up to ±10% on sunny days and ±5% on cloudy days. Local variability in LAI had a minor influence on uncertainty, especially
on sunny days. The largest observed reductions in ψld reduced GPP by 4%–6%. If uncertainty in foliar N estimates is propagated into the model, then GPP estimates are not significantly
different among sites. Our results suggest that water restrictions in the sandier sites are not enough to reduce production
significantly and that texture is not the key control on plant access to N.
Received 28 June 2001; accepted 13 March 2002. 相似文献
14.
Soil Phosphorus Fractionation and Phosphorus-Use Efficiency of a Bornean Tropical Montane Rain Forest During Soil Aging With Podozolization 总被引:2,自引:0,他引:2
We compared phosphorus (P) dynamics and plant productivity in two montane tropical rain forests (Mount Kinabalu, Borneo) that derived from similar parent materials (largely sedimentary rocks) and had similar climates but differed in terms of soil age. The younger site originated from Quaternary colluvial deposits, whereas the older site had Tertiary-age material. The older site had a distinctive spodic horizon, reduced levels of labile inorganic soil P, higher concentrations of recalcitrant organic soil P, and lower rates of net soil N mineralization. P fertilization led to soil nitrogen (N) immobilization in the P-deficient soil, indicating that soil N mineralization was limited by P at the P-deficient older site. Mean foliar nutrient concentration (on both a weight and an area basis) was similar at the two sites for all elements except P, which was lower at the older site. Aboveground net primary production (ANPP) was lower at the older site than at the younger one; this difference could be explained by the reduced availability of P and N (as down-regulated by P) at the older site. The relatively ample allocation of P and N to leaves, despite the reduced availability at the P-deficient old site, was attributable to its high resorption efficiency. High resorption resulted in lower concentrations of elements in leaf litter—that is, less decomposable low-quality litter. On the other hand, the concentration of leaf litter lignin was considerably lower at the older site; this appeared to be a de facto adaptive mechanism to avoid retarding litter decomposition. 相似文献
15.
Primary production and nitrogen allocation of field grown sugar maples in relation to nitrogen availability 总被引:2,自引:1,他引:1
Above ground net primary production (NPP), nitrogen (N) allocation, and retranslocation from senescing leaves were measured in 7 sugar-maple dominated sites having annual net N mineralization rates ranging from 26 to 94 kg · ha–1 · yr–1. The following responses were observed: (1) Green sun leaves on richer sites had higher N mass per unit leaf area than sun leaves on poorer sites; (2) Total canopy N varied much less than annual net mineralization, ranging from 81 to 111 kg · ha–1; (3) This was due to the existence of a large and relatively constant pool of N which was retranslocated from senescing leaves for use the following year (54 to 80 kg · ha–1); (4) The percentage of canopy N retranslocated by sugar maple was also relatively constant, but was slightly higher on the richer sites. Percent N in leaf litter did not change across the gradient; (5) Above ground NPP increased linearly in relation to N allocated above ground. Therefore, N use efficiency, expressed as above ground NPP divided by N allocated above ground was constant; (6) N use efficiency expressed as (NPP above ground/total N availability) was a curvilinear function of N availability; and (7) This pattern reflected a decreasing apparent allocation of N below ground with decreasing N availability. 相似文献
16.
Nutrient dynamics on a precipitation gradient in Hawai'i 总被引:10,自引:0,他引:10
We evaluated soil and foliar nutrients in five native forests in Hawai'i with annual rainfall ranging from 500 mm to 5500 mm.
All of the sites were at the same elevation and of the same substrate age; all were native-dominated forests containing Metrosiderospolymorpha Gaud. Soil concentrations of extractable NO3-N and PO4-P, as well as major cations (Ca, Mg, and K), decreased with increasing annual precipitation, and δ15N values became more depleted in both soils and vegetation. For M.polymorpha leaves, leaf mass per area (LMA) and lignin concentrations increased significantly, while δ13C values became more depleted with increasing precipitation. Foliar phosphorus, and major cation (Ca, Mg, and K) concentrations
for M.polymorpha all decreased significantly with increasing precipitation. For other native forest species, patterns of LMA, δ13C, and δ15N generally mirrored the pattern observed for M.
polymorpha. Decreasing concentrations of available rock-derived nutrients in soil suggest that the effect of increased rainfall on leaching
outweighs the effect of increasing precipitation on weathering. The pattern of decreased foliar nutrient concentrations per
unit leaf area and of increased lignin indicates a shift from relatively high nutrient availability to relatively high carbon
gain by producers as annual precipitation increases. For nitrogen cycling, the pattern of higher inorganic soil nitrogen concentrations
in the drier sites, together with the progressively depleted δ15N signature in both soils and vegetation, suggests that nitrogen cycling is more open at the drier sites, with smaller losses
relative to turnover as annual precipitation increases.
Received: 24 March 1997 / Accepted: 19 September 1997 相似文献
17.
Joseph J. Hendricks John D. Aber Knute J. Nadelhoffer Richard D. Hallett 《Ecosystems》2000,3(1):57-69
Nitrogen controls on fine root substrate quality (that is, nitrogen and carbon-fraction concentrations) were assessed using
nitrogen availability gradients in the Harvard Forest chronic nitrogen addition plots, University of Wisconsin Arboretum,
Blackhawk Island, Wisconsin, and New England spruce-fir transect. The 27 study sites encompassed within these four areas collectively
represented a wide range of nitrogen availability (both quantity and form), soil types, species composition, aboveground net
primary production, and climatic regimes. Changes in fine root substrate quality among sites were most frequently and strongly
correlated with nitrate availability. For the combined data set, fine root nitrogen concentration increased (adjusted R
2 = 0.46, P < 0.0001) with increasing site nitrate availability. Fine root “extractive” carbon-fraction concentrations decreased (adjusted
R
2 = 0.32, P < 0.0002), “acid-soluble” compounds increased (adjusted R
2 = 0.35, P < 0.0001), and the “acid-insoluble” carbon fraction remained relatively high and stable (combined mean of 48.7 ± 3.1% for
all sites) with increasing nitrate availability. Consequently, the ratio of acid-insoluble C–total N decreased (adjusted R
2 = 0.40, P < 0.0001) along gradients of increasing nitrate availability. The coefficients of determination for significant linear regressions
between site nitrate availability and fine root nitrogen and carbon-fraction concentrations were generally higher for sites
within each of the four study areas. Within individual study sites, tissue substrate quality varied between roots in different
soil horizons and between roots of different size classes. However, the temporal variation of fine root substrate quality
indices within specific horizons was relatively low. The results of this study indicate that fine root substrate quality increases
with increasing nitrogen availability and thus supports the substrate quality component of a hypothesized conceptual model
of nitrogen controls on fine root dynamics that maintains that fine root production, mortality, substrate quality, and decomposition
increase with nitrogen availability in forest ecosystems in a manner that is analogous to foliage. 相似文献
18.
Accurately predicting the effects of global change on net carbon (C) exchange between terrestrial ecosystems and the atmosphere
requires a more complete understanding of how nutrient availability regulates both plant growth and heterotrophic soil respiration.
Models of soil development suggest that the nature of nutrient limitation changes over the course of ecosystem development,
transitioning from nitrogen (N) limitation in ‘young’ sites to phosphorus (P) limitation in ‘old’ sites. However, previous
research has focused primarily on plant responses to added nutrients, and the applicability of nutrient limitation-soil development
models to belowground processes has not been thoroughly investigated. Here, we assessed the effects of nutrients on soil C
cycling in three different forests that occupy a 4 million year substrate age chronosequence where tree growth is N limited
at the youngest site, co-limited by N and P at the intermediate-aged site, and P limited at the oldest site. Our goal was
to use short-term laboratory soil C manipulations (using 14C-labeled substrates) and longer-term intact soil core incubations to compare belowground responses to fertilization with
aboveground patterns. When nutrients were applied with labile C (sucrose), patterns of microbial nutrient limitation were
similar to plant patterns: microbial activity was limited more by N than by P in the young site, and P was more limiting than
N in the old site. However, in the absence of C additions, increased respiration of native soil organic matter only occurred
with simultaneous additions of N and P. Taken together, these data suggest that altered nutrient inputs into ecosystems could
have dissimilar effects on C cycling above- and belowground, that nutrients may differentially affect of the fate of different
soil C pools, and that future changes to the net C balance of terrestrial ecosystems will be partially regulated by soil nutrient
status. 相似文献
19.
Kyung Won Seo Su Jin Heo Yowhan Son Nam Jin Noh Sue Kyoung Lee Chun Gyeong Yoon 《Landscape and Ecological Engineering》2011,7(1):93-99
This study was conducted to examine the influences of soil-moisture conditions on soil nitrogen (N) dynamics, including in
situ soil N mineralization, N availability, and denitrification in a pure Alnus japonica forest located in Seoul, central Korea. The soil N mineralization, N availability, and denitrification were determined using
the buried bag incubation method, ion exchange resin bag method, and acetylene block method, respectively. The annual net
N mineralization rate (kg N ha−1 year−1) and annual N availability (mg N bag−1) were 40.26 and 80.65 in the relatively dry site, −5.43 and 45.39 in the moist site, and 7.09 and 39.17 in the wet site,
respectively. The annual net N mineralization rate and annual N availability in the dry site were significantly higher than
those in the moist and wet sites, whereas there was no significant difference between the moist and wet sites. The annual
mean denitrification rate (kg N ha−1 year−1) in the dry, moist, and wet sites was 2.37, 2.76, and 1.59, respectively. However, there was no significant difference among
sites due to the high spatial and temporal variations. Our results indicate that soil-moisture condition influenced the in
situ N mineralization and resin bag N availability in an A. japonica forest, and treatments of proper drainage for poorly drained sites would increase soil N mineralization and N availability
and consequently be useful to conserve and manage the A. japonica forest. 相似文献
20.
Response of Douglas-fir and amabilis fir to split-root nutrition with inorganic and organic nitrogen 总被引:1,自引:0,他引:1
There is limited understanding of the spatial plasticity of conifer root growth in response to inorganic and organic nitrogen
(N). In this study, slow-growing amabilis fir and fast-growing Douglas-fir, and slow- and fast-growing seedlots of the latter
species were examined for their ability to proliferate roots preferentially in compartments of sand/peat medium enriched in
organic and inorganic forms of N. In one experiment, N was supplied as 7.1 or 0.71 mM ammonium, nitrate and ammonium nitrate,
and in a second experiment, N was supplied as ammonium or glycine. The seedlings’ ability to compensate for the starvation
of a portion of the root system was assessed by measuring biomass of leaves, stems and roots, and foliar N concentration.
Both fast- and slow-growing seedlots of Douglas-fir and slow-growing amabilis fir were able to proliferate roots in compartments
of soil enriched with inorganic and organic N. In the first experiment, whole plant and root biomass was greatest when N was
provided as ammonium followed by nitrate, and in the second experiment, seedling whole and root biomasses did not differ between
ammonium and glycine treatments. All seedlings were able to compensate for the starvation of a portion of the root system,
thus total plant biomass did not differ between split-root treatments; however, foliar N contents were lower in the 7.1/0.71 mM
inorganic N split-root treatments. Foliar N concentrations were also lower in seedlings supplied with glycine. 相似文献