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1.
Snow regimes affect biogeochemistry of boreal ecosystems and are altered by climate change. The effects on plant communities,
however, are largely unexplored despite their influence on relevant processes. Here, the impact of snow cover on understory
community composition and below-ground production in a boreal Picea abies forest was investigated using a long-term (8-year) snow cover manipulation experiment consisting of the treatments: snow
removal, increased insulation (styrofoam pellets), and control. The snow removal treatment caused longer (118 vs. 57 days)
and deeper soil frost (mean minimum temperature −5.5 vs. −2.2°C) at 10 cm soil depth in comparison to control. Understory
species composition was strongly altered by the snow cover manipulations; vegetation cover declined by more than 50% in the
snow removal treatment. In particular, the dominant dwarf shrub Vaccinium myrtillus (−82%) and the most abundant mosses Pleurozium schreberi (−74%) and Dicranum scoparium (−60%) declined strongly. The C:N ratio in V. myrtillus leaves and plant available N in the soil indicated no altered nitrogen nutrition. Fine-root biomass in summer, however, was
negatively affected by the reduced snow cover (−50%). Observed effects are attributed to direct frost damage of roots and/
or shoots. Besides the obvious relevance of winter processes on plant ecology and distribution, we propose that shifts in
the vegetation caused by frost damage may be an important driver of the reported alterations in biogeochemistry in response
to altered snow cover. Understory plant performance clearly needs to be considered in the biogeochemistry of boreal systems
in the face of climate change. 相似文献
2.
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
3.
模拟大气氮沉降对中国森林生态系统影响的研究进展 总被引:3,自引:0,他引:3
人类活动加剧了活性氮的生产和排放,并导致氮沉降日益增加并全球化。目前,人类活动对全球氮循环的干扰已经超出了地球系统安全运行的界限。中国已成为全球氮沉降的高发区域,高氮沉降已经威胁到生态系统的健康和安全,并成为生态文明建设过程中亟待理清和解决的热点问题。对国际上和中国森林生态系统模拟氮沉降研究的概况进行了综述,并从生物学和非生物学两大过程重点阐述模拟氮沉降增加对中国主要森林生态系统影响的研究进展。中国自2000年以后才开始重视大气氮沉降产生的生态环境问题,中国科学院华南植物园在国内森林生态系统模拟氮沉降试验研究上做出了开创性的贡献。模拟氮沉降研究表明,持续高氮输入将会显著改变森林生态系统的结构和功能,并威胁生态系统的健康发展,特别是处于氮沉降热点区域的中国中南部。森林生态系统的氮沉降效应依赖于系统的氮状态、土地利用历史、气候特征、林型和林龄等。最后,对未来的研究提出了一些建议,包括加强长期跟踪研究和不同气候带站点之间的联网研究,特别是在森林生态系统对长期氮沉降响应与适应的过程机制、地下碳氮吸存潜力研究、以及与其他全球变化因子的耦合研究等方面,以期为森林生态系统的可持续发展提供理论基础和管理依据。 相似文献
4.
Experimentally increased soil temperature causes release of nitrogen at a boreal forest catchment in southern Norway 总被引:5,自引:0,他引:5
Boreal forest ecosystems are sensitive to global warming, caused by increasing emissions of CO2 and other greenhouse gases. Assessment of the biological response to future climate change is based mainly on large-scale models. Whole-ecosystem experiments provide one of the few available tools by which ecosystem response can be measured and with which global models can be evaluated. Boreal ecosystem response to global change may be manifest by alterations in nitrogen (N) dynamics, as N is often the growth limiting nutrient. The CLIMEX (Climate Change Experiment) project entails catchment-scale manipulations of CO2 (to 560 ppmv) and temperature (by + 3 to + 5 °C) to whole forest ecosystems in southern Norway. Soil temperature is increased at 400-m2 EGIL catchment by means of electric cables placed on the soil surface. Soil warming at EGIL catchment caused an increase in nitrate and ammonium concentrations in runoff in the first year of treatment. We hypothesize that higher temperature increased N release by mineralization. Whether these responses are only transient will be shown by additional years' treatment. 相似文献
5.
Warming and drying suppress microbial activity and carbon cycling in boreal forest soils 总被引:4,自引:0,他引:4
Climate warming is expected to have particularly strong effects on tundra and boreal ecosystems, yet relatively few studies have examined soil responses to temperature change in these systems. We used closed‐top greenhouses to examine the response of soil respiration, nutrient availability, microbial abundance, and active fungal communities to soil warming in an Alaskan boreal forest dominated by mature black spruce. This treatment raised soil temperature by 0.5 °C and also resulted in a 22% decline in soil water content. We hypothesized that microbial abundance and activity would increase with the greenhouse treatment. Instead, we found that bacterial and fungal abundance declined by over 50%, and there was a trend toward lower activity of the chitin‐degrading enzyme N‐acetyl‐glucosaminidase. Soil respiration also declined by up to 50%, but only late in the growing season. These changes were accompanied by significant shifts in the community structure of active fungi, with decreased relative abundance of a dominant Thelephoroid fungus and increased relative abundance of Ascomycetes and Zygomycetes in response to warming. In line with our hypothesis, we found that warming marginally increased soil ammonium and nitrate availability as well as the overall diversity of active fungi. Our results indicate that rising temperatures in northern‐latitude ecosystems may not always cause a positive feedback to the soil carbon cycle, particularly in boreal forests with drier soils. Models of carbon cycle‐climate feedbacks could increase their predictive power by incorporating heterogeneity in soil properties and microbial communities across the boreal zone. 相似文献
6.
Edith Huber Wolfgang Wanek Michael Gottfried Harald Pauli Peter Schweiger Stefan K. Arndt Karl Reiter Andreas Richter 《Plant and Soil》2007,301(1-2):65-76
We investigated the nitrogen (N) dynamics of an alpine–nival ecotone on Mt. Schrankogel, Tyrol, Austria, in relation to temperature.
Natural abundance of 15N was used as a tool to elucidate differences in N cycling along an altitudinal transect ranging from 2,906 to 3,079 m, corresponding
to a gradient in mean annual temperature of 2.4 °C. The amount of total soil N, of plant available N and soil C/N ratio decreased
significantly with increasing altitude, whereas soil pH increased. Soil δ
15N decreased with increasing altitude from +2.2 to −2.1‰ and δ
15N of plant tissues (roots and leaves) decreased from −3.7 to −5.5‰. The large shift in soil δ
15N of 4.3‰ from the lowest to the highest site suggested substantial differences in N cycling in alpine and nival ecosystems
in the alpine nival ecotone investigated. We concluded that N cycling at the alpine–nival ecotone is likely to be controlled
by various factors: temperature, soil age and development, atmospheric N deposition and plant competition. Our results furthermore
demonstrate that the alpine–nival ecotone may serve as a sensitive indicator of global change. 相似文献
7.
Extracellular Enzyme Activities and Soil Organic Matter Dynamics for Northern Hardwood Forests receiving Simulated Nitrogen Deposition 总被引:5,自引:0,他引:5
Anthropogenic nitrogen enrichment alters decomposition processes that control the flux of carbon (C) and nitrogen (N) from
soil organic matter (SOM) pools. To link N-driven changes in SOM to microbial responses, we measured the potential activity
of several extracellular enzymes involved in SOM degradation at nine experimental sites located in northern Michigan. Each
site has three treatment plots (ambient, +30 and +80 kg N ha−1 y−1). Litter and soil samples were collected on five dates over the third growing season of N treatment. Phenol oxidase, peroxidase
and cellobiohydrolase activities showed significant responses to N additions. In the Acer saccharum–Tilia americana ecosystem, oxidative activity was 38% higher in the litter horizon of high N treatment plots, relative to ambient plots,
while oxidative activity in mineral soil showed little change. In the A. saccharum–Quercus rubra and Q. velutina–Q. alba ecosystems, oxidative activities declined in both litter (15 and 23%, respectively) and soil (29 and 38%, respectively) in
response to high N treatment while cellobiohydrolase activity increased (6 and 39% for litter, 29 and 18% for soil, respectively).
Over 3 years, SOM content in the high N plots has decreased in the Acer–Tilia ecosystem and increased in the two Quercus ecosystems, relative to ambient plots. For all three ecosystems, differences in SOM content in relation to N treatment were
directly related (r2 = 0.92) to an enzyme activity factor that included both oxidative and hydrolytic enzyme responses. 相似文献
8.
Jorge Durán Alexandra Rodríguez Jennifer L. Morse Peter M. Groffman 《Global Change Biology》2013,19(9):2826-2837
Despite growing recognition of the role that cities have in global biogeochemical cycles, urban systems are among the least understood of all ecosystems. Urban grasslands are expanding rapidly along with urbanization, which is expected to increase at unprecedented rates in upcoming decades. The large and increasing area of urban grasslands and their impact on water and air quality justify the need for a better understanding of their biogeochemical cycles. There is also great uncertainty about the effect that climate change, especially changes in winter snow cover, will have on nutrient cycles in urban grasslands. We aimed to evaluate how reduced snow accumulation directly affects winter soil frost dynamics, and indirectly greenhouse gas fluxes and the processing of carbon (C) and nitrogen (N) during the subsequent growing season in northern urban grasslands. Both artificial and natural snow reduction increased winter soil frost, affecting winter microbial C and N processing, accelerating C and N cycles and increasing soil : atmosphere greenhouse gas exchange during the subsequent growing season. With lower snow accumulations that are predicted with climate change, we found decreases in N retention in these ecosystems, and increases in N2O and CO2 flux to the atmosphere, significantly increasing the global warming potential of urban grasslands. Our results suggest that the environmental impacts of these rapidly expanding ecosystems are likely to increase as climate change brings milder winters and more extensive soil frost. 相似文献
9.
Landscape Controls on Organic and Inorganic Nitrogen Leaching across an Alpine/Subalpine Ecotone,Green Lakes Valley,Colorado Front Range 总被引:5,自引:0,他引:5
Here we report measurements of organic and inorganic nitrogen (N) fluxes from the high-elevation Green Lakes Valley catchment
in the Colorado Front Range for two snowmelt seasons (1998 and 1999). Surface water and soil samples were collected along
an elevational gradient extending from the lightly vegetated alpine to the forested subalpine to assess how changes in land
cover and basin area affect yields and concentrations of ammonium-N (NH4-N), nitrate-N (NO3-N), dissolved organic N (DON), and particulate organic N (PON). Streamwater yields of NO3-N decreased downstream from 4.3 kg ha−1 in the alpine to 0.75 kg ha−1 at treeline, while yields of DON were much less variable (0.40–0.34 kg ha−1). Yields of NH4-N and PON were low and showed little variation with basin area. NO3-N accounted for 40%–90% of total N along the sample transect and was the dominant form of N at all but the lowest elevation
site. Concentrations of DON ranged from approximately 10% of total N in the alpine to 45% in the subalpine. For all sites,
volume-weighted mean concentrations of total dissolved nitrogen (TDN) were significantly related to the DIN:DON ratio (R
2 = 0.81, P < 0.001) Concentrations of NO3-N were significantly higher at forested sites that received streamflow from the lightly vegetated alpine reaches of the catchment
than in a control catchment that was entirely subalpine forest, suggesting that the alpine may subsidize downstream forested
systems with inorganic N. KCl-extractable inorganic N and microbial biomass N showed no relationship to changes in soil properties
and vegetative cover moving downstream in catchment. In contrast, soil carbon–nitrogen (C:N) ratios increased with increasing
vegetative cover in catchment and were significantly higher in the subalpine compared to the alpine (P < 0.0001) Soil C:N ratios along the sample transect explained 78% of the variation in dissolved organic carbon (DOC) concentrations
and 70% of the variation in DON concentrations. These findings suggest that DON is an important vector for N loss in high-elevation
ecosystems and that streamwater losses of DON are at least partially dependent on catchment soil organic matter stoichiometry.
Received 26 July 2001; accepted 6 May 2002. 相似文献
10.
Boreal Shield rocky ridges at the Experimental Lakes Area, northwestern Ontario, contain two plant/soil communities with
contrasting N cycles. Picea mariana–Pinus banksiana”forest islands” are N limited whereas the lichen, moss, and grass community (or “lichen patches”) on the surrounding bedrock
outcrops appear intrinsically N saturated. The potential for this landscape to retain a N input of eightfold ambient levels
was tested with a 2-y addition of 40 kg N ha-1 y-1 as NaNO3 to one small catchment (0.40 ha). The elevated N input was poorly retained by the whole catchment during snowmelt. However,
during the growing season, N retention in the treated catchment remained as efficient as in references. Forest islands and
bedrock surfaces responded in opposite fashions to the elevated N input. By the second year of N addition, bedrock surfaces
no longer retained additional N inputs. In contrast, N-amended and reference forest islands retained a similar proportion
of N inputs, indicating that forest islands did not become N saturated. The response of the whole catchment to N addition
was more similar to forest islands than bedrock surfaces. Even if forest islands only cover a small proportion of catchment
area, they can have a strong impact on whole catchment element export because most of the water must move through at least
one island before leaving the system. Because the different components of the boreal shield landscape are hydrologically connected,
N saturation may occur as a cascading effect in this ecosystem. Monitoring boreal shield landscapes by using outlets at the
lower end of the hydrological cascade can fail to detect the impacts of perturbations such as increased N deposition on upper
components.
Received 1 December 1998; accepted 8 April 1999. 相似文献
11.
全球气候变化对陆地植物碳氮磷生态化学计量学特征的影响 总被引:4,自引:3,他引:1
全球气候变化背景下生物地球化学循环的响应规律和陆地植物适应对策已受到广泛关注.本文在分析气候变暖和降水变化对不同生态系统植物C∶N∶P的影响、CO2浓度升高对不同光合途径物种元素的影响,以及氮沉降对土壤 植物元素影响的短期和长期效应等基础上,从植物生理特性和土壤有效营养元素变化等方面揭示了其可能存在的内在机理,以期为研究C、N、P化学元素在土壤 植物之间传递与调节机制、陆地生态系统结构和功能,以及生物地球化学元素循环对气候变化的响应提供理论依据.最后提出了该领域研究中存在的问题及对今后研究的展望. 相似文献
12.
Dissolved organic matter (DOM) is an important fraction in carbon (C) and nutrient budgets for aquatic ecosystems and can
have broad effects on food webs and nutrient cycling. To look at the role land use cover and climate might play in DOM transport
from the boreal region, the export of total organic carbon (TOC), total organic nitrogen (TON) and dissolved organic phosphorus
(DOP) was estimated for Finnish main rivers and their sub-catchments, altogether 86 catchments, situated between latitudes
60° N and 69° N and covering 297,322 km2, 88% of the total area of Finland. On an average, 94% of the TOC, 90% of the total nitrogen (TN) and 40% of the total phosphorus
(TP) in Finnish rivers was in a dissolved form. The majority of the DOM export from Finnish catchments consists of organic
C. The TOC export increased with increasing peatland proportion (r = 0.39, p = 0.003), while TON export increased with the increasing percentage of agricultural land (r = 0.60, p <0.001). Although upstream lakes covered only on average 9% of the catchment area, they were the most important predictor
for TOC, TON and DOP export (r = −0.83, r = −0.82 and r = −0.61, respectively). The higher the upstream lake percentage, the lower the export indicating organic matter retention
in lakes. 相似文献
13.
Kobayashi Makoto Takuya Kajimoto Lina Koyama Gaku Kudo Hideaki Shibata Yosuke Yanai J. H. C. Cornelissen 《Ecological Research》2014,29(4):593-606
The winter climate is changing in many parts of the world, and it is predicted that winter climate change will modify the structure and function of plant–soil systems. An understanding of these changes and their consequences in terrestrial ecosystems requires knowledge of the linkage between above- and below-ground components as well as the species interactions found in plant–soil systems, which have important implications for biogeochemical cycles. However, winter climate-change studies have focused on only a part of the ecosystem or ecological process. We summarize here recent findings related to the effects of winter climate and its changes on soil nitrogen (N) dynamics, greenhouse gas (N2O) emissions from the soil, N use by individual plants, vegetation development, and interactions between vegetation and pollinators to generate an integrative understanding of the response of the plant–soil system to winter climate change. This review indicates that the net effects on plants, soil microbes, pollinators, and the associated biogeochemical cycles are balanced among several processes and are highly variable depending on the context, such as the target species/functional group, original winter condition of the habitat, and type of climate change. The consequences of winter climate change for species interactions among plants, associated animals, and biogeochemical cycles are largely unknown. For further research, a large-scale comparative study to measure ecosystem-level functions is important, especially in less-cold ecosystems. 相似文献
14.
Boreal ecosystems store 10–20 % of global soil carbon and may warm by 4–7 °C over the next century. Higher temperatures could increase the activity of boreal decomposers and indirectly affect decomposition through other ecosystem feedbacks. For example, permafrost melting will likely alleviate constraints on microbial decomposition and lead to greater soil CO2 emissions. However, wet boreal ecosystems underlain by permafrost are often CH4 sources, and permafrost thaw could ultimately result in drier soils that consume CH4, thereby offsetting some of the greenhouse warming potential of soil CO2 emissions. Climate change is also likely to increase winter precipitation and snow depth in boreal regions, which may stimulate decomposition by moderating soil temperatures under the snowpack. As temperatures and evapotranspiration increase in the boreal zone, fires may become more frequent, leading to additional permafrost loss from burned ecosystems. Although post-fire decomposition could also increase due to higher soil temperatures, reductions in microbial biomass and activity may attenuate this response. Other feedbacks such as soil drying, increased nutrient mineralization, and plant species shifts are either weak or uncertain. We conclude that strong positive feedbacks to decomposition will likely depend on permafrost thaw, and that climate feedbacks will probably be weak or negative in boreal ecosystems without permafrost. However, warming manipulations should be conducted in a broader range of boreal systems to validate these predictions. 相似文献
15.
Simulated climate change impacts on fluxes of carbon in Norway spruce ecosystems along a climatic transect in Sweden 总被引:2,自引:0,他引:2
Per-Erik Jansson Magnus Svensson Dan Berggren Kleja David Gustafsson 《Biogeochemistry》2008,89(1):81-94
A simulation study based on recent regional climate scenarios for Sweden investigated possible changes in carbon (C) dynamics
and net ecosystem exchange (NEE) of Swedish Norway spruce forest ecosystems. Four sites, representative of well-drained soils
in four regions, were included. Stand development was simulated for a 100-year rotation period using a coupled model describing
abiotic and biotic processes in the soil-plant-atmosphere system. Two IPCC climate change scenarios, corresponding to a mean
annual temperature increase of about 2°C (A2) or 3°C (B2) from the reference period 1961–1990 to a new period 2061–2090, were
considered. Annual maximum snow depth decreased with the increase in air temperature, whereas maximum soil frost depth and
mean annual soil temperature showed only small changes, especially for the sites in northern Sweden. Simulations suggested
that in the warmer climate, gross primary production (GPP) increased by 24–32% in northern Sweden and by 32–43% in the south.
In the north, the increase was related to the combined effect of air and soil temperature extending the growing season, whereas
in the south it was mainly governed by increased N availability due to increased soil temperature. NEE increased by about
20% (A2) or 25% (B2) at all sites, more or less solely due to increased accumulation of C in the tree biomass (including harvest
residues), since changes in soil C were small compared with the current climate. Both light use efficiency and water use efficiency
were improved in the future climate scenarios, despite increases in atmospheric CO2 not being considered. 相似文献
16.
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
17.
Determination of the direct causal factors controlling wildfires is key to understanding wildfire–vegetation–climate dynamics
in a changing climate and for developing sustainable management strategies for biodiversity conservation and maintenance of
long-term forest productivity. In this study, we sought to understand how the fire frequency of a large mixedwood forest in
the central boreal shield varies as a result of temporal and spatial factors. We reconstructed the fire history of an 11,600-km2 area located in the northwestern boreal forest of Ontario, using archival data of large fires occurring since 1921 and dendrochronological
dating for fires prior to 1921. The fire cycle decreased from 295 years for the period of 1820–1920 to approximately 100 years
for the period of 1921–2008. Spatially, fire frequency increased with latitude, attributable to higher human activities that
have increased fragmentation and fire suppression in the southern portion of the study area. Fire frequency also increased
with distance to waterbodies, and was higher on Podzols that were strongly correlated with moderate drainage and coniferous
vegetation. The temporal increase of fire frequency in the central region, unlike western and eastern boreal forests where
fire frequency has decreased, may be a result of increased warm and dry conditions associated with climate change in central
North America, suggesting that the response of wildfire to global climate change may be regionally individualistic. The significant
spatial factors we found in this study are in agreement with other wildfire studies, indicating the commonality of the influences
by physiographic features and human activities on regional fire regimes across the boreal forest. Overall, wildfire in the
central boreal shield is more frequent than that in the wetter eastern boreal region and less frequent than that in the drier
western boreal region, confirming a climatic top-down control on the fire activities of the entire North American boreal forest. 相似文献
18.
The low plant productivity of boreal forests in general has been attributed to low soil N supply and low temperatures. Exceptionally
high productivity occurs in toe-slope positions, and has been ascribed to influx of N from surrounding areas and higher rates
of soil N turnover in situ. Despite large apparent natural variations in forest productivity, rates of gross soil N mineralization
and gross nitrification have never been compared in Fennoscandian boreal forests of contrasting productivity. We report contrasting
patterns of soil N turnover in three model ecosystems, representing the range in soil C-to-N ratios (19–41) in Fennoscandian
boreal forests and differences in forest productivity by a factor close to 3. Gross N mineralization was seven times higher
when soil, microbial, and plant C-to-N ratios were the lowest compared to the highest. This process, nitrification and potential
denitrification correlated with inorganic, total and microbial biomass N, but not microbial C. There was a constant ratio
between soil and microbial C-to-N ratio of 3.7±0.2, across wide ratios of soil C-to-N and fungi-to-bacteria. Soil N-cycling
should be controlled by the supplies of C and N to the microbes. In accordance with plant allocation theory, we discuss the
possibility that the high fungal biomass at high soil C-to-N ratio reflects a particularly high supply of plant photosynthates,
substrates of high-quality C, to mycorrhizal fungi. Methods to study soil N turnover and N retention should be developed to
take into account the impact of mycorrhizal fungi on soil N-cycling. 相似文献
19.
Evidence that Soil Carbon Pool Determines Susceptibility of Semi-Natural Ecosystems to Elevated Nitrogen Leaching 总被引:1,自引:0,他引:1
Christopher D. Evans Brian Reynolds Alan Jenkins Rachel C. Helliwell Christopher J. Curtis Christine L. Goodale Robert C. Ferrier Bridget A. Emmett Michael G. Pilkington Simon J. M. Caporn Jacky A. Carroll David Norris Jennifer Davies Malcolm C. Coull 《Ecosystems》2006,9(3):453-462
Deposition of reactive nitrogen (N) compounds has the potential to cause severe damage to sensitive soils and waters, but
the process of ‘nitrogen saturation’ is difficult to demonstrate or predict. This study compares outputs from a simple carbon–nitrogen
model with observations of (1) regional- and catchment-scale relationships between surface water nitrate and dissolved organic
carbon (DOC), as an indicator of catchment carbon (C) pool; (2) inter-regional variations in soil C/N ratios; and (3) plot
scale soil and leachate response to long-term N additions, for a range of UK moorlands. Results suggest that the simple model
applied can effectively reproduce observed patterns, and that organic soil C stores provide a critical control on catchment
susceptibility to enhanced N leaching, leading to high spatial variability in the extent and severity of current damage within
regions of relatively uniform deposition. Results also support the hypothesis that the N richness of organic soils, expressed
as C/N ratio, provides an effective indicator of soil susceptibility to enhanced N leaching. The extent to which current C/N
is influenced by N deposition, as opposed to factors such as climate and vegetation type, cannot be unequivocally determined
on the basis of spatial data. However, N addition experiments at moorland sites have shown a reduction in organic soil C/N.
A full understanding of the mechanisms of N-enrichment of soils and waters is essential to the assessment of current sensitivity
to, and prediction of future damage from, globally increasing reactive nitrogen deposition. 相似文献
20.
Clémentine Ols Martin P. Girardin Annika Hofgaard Yves Bergeron Igor Drobyshev 《Ecosystems》2018,21(5):1042-1057
The growth of high-latitude temperature-limited boreal forest ecosystems is projected to become more constrained by soil water availability with continued warming. The purpose of this study was to document ongoing shifts in tree growth sensitivity to the evolving local climate in unmanaged black spruce (Picea mariana (Miller) B.S.P.) forests of eastern boreal North America (49°N–52°N, 58°W–82°W) using a comparative study of field and modeled data. We investigated growth relationships to climate (gridded monthly data) from observed (50 site tree-ring width chronologies) and simulated growth data (stand-level forest growth model) over 1908–2013. No clear strengthening of moisture control over tree growth in recent decades was detected. Despite climate warming, photosynthesis (main driver of the forest growth model) and xylem production (main driver of radial growth) have remained temperature-limited. Analyses revealed, however, a weakening of the influence of growing season temperature on growth during the mid- to late twentieth century in the observed data, particularly in high-latitude (> 51.5°N) mountainous sites. This shift was absent from simulated data, which resulted in clear model-data desynchronization. Thorough investigations revealed that desynchronization was mostly linked to the quality of climate data, with precipitation data being of particular concern. The scarce network of weather stations over eastern boreal North America (> 51.5°N) affects the accuracy of estimated local climate variability and critically limits our ability to detect climate change effects on high-latitude ecosystems, especially at high altitudinal sites. Climate estimates from remote sensing could help address some of these issues in the future. 相似文献