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1.
Different fates of deposited and in a temperate forest in northeast China: a 15N tracer study
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Jun Liu Bo Peng Zongwei Xia Jianfei Sun Decai Gao Weiwei Dai Ping Jiang Edith Bai 《Global Change Biology》2017,23(6):2441-2449
Increasing atmospheric reactive nitrogen (N) deposition due to human activities could change N cycling in terrestrial ecosystems. However, the differences between the fates of deposited and are still not fully understood. Here, we investigated the fates of deposited and , respectively, via the application of 15NH4NO3 and NH415NO3 in a temperate forest ecosystem. Results showed that at 410 days after tracer application, most was immobilized in litter layer (50 ± 2%), while a considerable amount of penetrated into 0–5 cm mineral soil (42 ± 2%), indicating that litter layer and 0–5 cm mineral soil were the major N sinks of and , respectively. Broad‐leaved trees assimilated more 15N under NH415NO3 treatment compared to under 15NH4NO3 treatment, indicating their preference for –N. At 410 days after tracer application, 16 ± 4% added 15N was found in aboveground biomass under treatment, which was twice more than that under treatment (6 ± 1%). At the same time, approximately 80% added 15N was recovered in soil and plants under both treatments, which suggested that this forest had high potential for retention of deposited N. These results provided evidence that there were great differences between the fates of deposited and , which could help us better understand the mechanisms and capability of forest ecosystems as a sink of reactive nitrogen. 相似文献
2.
Ahmed S. Elrys QiLin Zhu Chunlan Jiang Juan Liu Hamida H. H. Sobhy Qunli Shen Yves Uwiragiye Yanzheng Wu Khaled A. El-Tarabily Lei Meng Christoph Müller Jinbo Zhang 《Global Change Biology》2023,29(7):1905-1921
Tropical and subtropical forest biomes are a main hotspot for the global nitrogen (N) cycle. Yet, our understanding of global soil N cycle patterns and drivers and their response to N deposition in these biomes remains elusive. By a meta-analysis of 2426-single and 161-paired observations from 89 published 15 N pool dilution and tracing studies, we found that gross N mineralization (GNM), immobilization of ammonium () and nitrate (), and dissimilatory nitrate reduction to ammonium (DNRA) were significantly higher in tropical forests than in subtropical forests. Soil N cycle was conservative in tropical forests with ratios of gross nitrification (GN) to (GN/) and of soil nitrate to ammonium (NO3−/NH4+) less than one, but was leaky in subtropical forests with GN/ and NO3−/NH4+ higher than one. Soil NH4+ dynamics were mainly controlled by soil substrate (e.g., total N), but climatic factors (e.g., precipitation and/or temperature) were more important in controlling soil NO3− dynamics. Soil texture played a role, as GNM and were positively correlated with silt and clay contents, while and DNRA were positively correlated with sand and clay contents, respectively. The soil N cycle was more sensitive to N deposition in tropical forests than in subtropical forests. Nitrogen deposition leads to a leaky N cycle in tropical forests, as evidenced by the increase in GN/, NO3−/NH4+, and nitrous oxide emissions and the decrease in and DNRA, mainly due to the decrease in soil microbial biomass and pH. Dominant tree species can also influence soil N cycle pattern, which has changed from conservative in deciduous forests to leaky in coniferous forests. We provide global evidence that tropical, but not subtropical, forests are characterized by soil N dynamics sustaining N availability and that N deposition inhibits soil N retention and stimulates N losses in these biomes. 相似文献
3.
James Johnson Elisabeth Graf Pannatier Stefano Carnicelli Guia Cecchini Nicholas Clarke Nathalie Cools Karin Hansen Henning Meesenburg Tiina M. Nieminen Gunilla Pihl‐Karlsson Hugues Titeux Elena Vanguelova Arne Verstraeten Lars Vesterdal Peter Waldner Mathieu Jonard 《Global Change Biology》2018,24(8):3603-3619
Acid deposition arising from sulphur (S) and nitrogen (N) emissions from fossil fuel combustion and agriculture has contributed to the acidification of terrestrial ecosystems in many regions globally. However, in Europe and North America, S deposition has greatly decreased in recent decades due to emissions controls. In this study, we assessed the response of soil solution chemistry in mineral horizons of European forests to these changes. Trends in pH, acid neutralizing capacity (ANC), major ions, total aluminium (Altot) and dissolved organic carbon were determined for the period 1995–2012. Plots with at least 10 years of observations from the ICP Forests monitoring network were used. Trends were assessed for the upper mineral soil (10–20 cm, 104 plots) and subsoil (40–80 cm, 162 plots). There was a large decrease in the concentration of sulphate () in soil solution; over a 10‐year period (2000–2010), decreased by 52% at 10–20 cm and 40% at 40–80 cm. Nitrate was unchanged at 10–20 cm but decreased at 40–80 cm. The decrease in acid anions was accompanied by a large and significant decrease in the concentration of the nutrient base cations: calcium, magnesium and potassium (Bc = Ca2+ + Mg2+ + K+) and Altot over the entire dataset. The response of soil solution acidity was nonuniform. At 10–20 cm, ANC increased in acid‐sensitive soils (base saturation ≤10%) indicating a recovery, but ANC decreased in soils with base saturation >10%. At 40–80 cm, ANC remained unchanged in acid‐sensitive soils (base saturation ≤20%, ≤ 4.5) and decreased in better‐buffered soils (base saturation >20%, > 4.5). In addition, the molar ratio of Bc to Altot either did not change or decreased. The results suggest a long‐time lag between emission abatement and changes in soil solution acidity and underline the importance of long‐term monitoring in evaluating ecosystem response to decreases in deposition. 相似文献
4.
Decomposition nitrogen is better retained than simulated deposition from mineral amendments in a temperate forest
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Nitrogen (N) deposition (NDEP) drives forest carbon (C) sequestration but the size of this effect is still uncertain. In the field, an estimate of these effects can be obtained by applying mineral N fertilizers over the soil or forest canopy. A 15N label in the fertilizer can be then used to trace the movement of the added N into ecosystem pools and deduce a C effect. However, N recycling via litter decomposition provides most of the nutrition for trees, even under heavy NDEP inputs. If this recycled litter nitrogen is retained in ecosystem pools differently to added mineral N, then estimates of the effects of NDEP on the relative change in C (?C/?N) based on short‐term isotope‐labelled mineral fertilizer additions should be questioned. We used 15N labelled litter to track decomposed N in the soil system (litter, soils, microbes, and roots) over 18 months in a Sitka spruce plantation and directly compared the fate of this 15N to an equivalent amount in simulated NDEP treatments. By the end of the experiment, three times as much 15N was retained in the O and A soil layers when N was derived from litter decomposition than from mineral N additions (60% and 20%, respectively), primarily because of increased recovery in the O layer. Roots expressed slightly more 15N tracer from litter decomposition than from simulated mineral NDEP (7.5% and 4.5%) and compared to soil recovery, expressed proportionally more 15N in the A layer than the O layer, potentially indicating uptake of organic N from decomposition. These results suggest effects of NDEP on forest ?C/?N may not be apparent from mineral 15N tracer experiments alone. Given the importance of N recycling, an important but underestimated effect of NDEP is its influence on the rate of N release from litter. 相似文献
5.
Nitrogen supply modulates the effect of changes in drying–rewetting frequency on soil C and N cycling and greenhouse gas exchange
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Lourdes Morillas Jorge Durán Alexandra Rodríguez Javier Roales Antonio Gallardo Gary M. Lovett Peter M. Groffman 《Global Change Biology》2015,21(10):3854-3863
Climate change and atmospheric nitrogen (N) deposition are two of the most important global change drivers. However, the interactions of these drivers have not been well studied. We aimed to assess how the combined effect of soil N additions and more frequent soil drying–rewetting events affects carbon (C) and N cycling, soil:atmosphere greenhouse gas (GHG) exchange, and functional microbial diversity. We manipulated the frequency of soil drying–rewetting events in soils from ambient and N‐treated plots in a temperate forest and calculated the Orwin & Wardle Resistance index to compare the response of the different treatments. Increases in drying–rewetting cycles led to reductions in soil levels, potential net nitrification rate, and soil : atmosphere GHG exchange, and increases in and total soil inorganic N levels. N‐treated soils were more resistant to changes in the frequency of drying–rewetting cycles, and this resistance was stronger for C‐ than for N‐related variables. Both the long‐term N addition and the drying–rewetting treatment altered the functionality of the soil microbial population and its functional diversity. Our results suggest that increasing the frequency of drying–rewetting cycles can affect the ability of soil to cycle C and N and soil : atmosphere GHG exchange and that the response to this increase is modulated by soil N enrichment. 相似文献
6.
Holly Croft Jing M. Chen Xiangzhong Luo Paul Bartlett Bin Chen Ralf M. Staebler 《Global Change Biology》2017,23(9):3513-3524
Improving the accuracy of estimates of forest carbon exchange is a central priority for understanding ecosystem response to increased atmospheric CO2 levels and improving carbon cycle modelling. However, the spatially continuous parameterization of photosynthetic capacity (Vcmax) at global scales and appropriate temporal intervals within terrestrial biosphere models (TBMs) remains unresolved. This research investigates the use of biochemical parameters for modelling leaf photosynthetic capacity within a deciduous forest. Particular attention is given to the impacts of seasonality on both leaf biophysical variables and physiological processes, and their interdependent relationships. Four deciduous tree species were sampled across three growing seasons (2013–2015), approximately every 10 days for leaf chlorophyll content (ChlLeaf) and canopy structure. Leaf nitrogen (NArea) was also measured during 2014. Leaf photosynthesis was measured during 2014–2015 using a Li‐6400 gas‐exchange system, with A‐Ci curves to model Vcmax. Results showed that seasonality and variations between species resulted in weak relationships between Vcmax normalized to 25°C () and NArea (R2 = 0.62, P < 0.001), whereas ChlLeaf demonstrated a much stronger correlation with (R2 = 0.78, P < 0.001). The relationship between ChlLeaf and NArea was also weak (R2 = 0.47, P < 0.001), possibly due to the dynamic partitioning of nitrogen, between and within photosynthetic and nonphotosynthetic fractions. The spatial and temporal variability of was mapped using Landsat TM/ETM satellite data across the forest site, using physical models to derive ChlLeaf. TBMs largely treat photosynthetic parameters as either fixed constants or varying according to leaf nitrogen content. This research challenges assumptions that simple NArea– relationships can reliably be used to constrain photosynthetic capacity in TBMs, even within the same plant functional type. It is suggested that ChlLeaf provides a more accurate, direct proxy for and is also more easily retrievable from satellite data. These results have important implications for carbon modelling within deciduous ecosystems. 相似文献
7.
Explaining the doubling of N2O emissions under elevated CO2 in the Giessen FACE via in‐field 15N tracing
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Gerald Moser André Gorenflo Kristof Brenzinger Lisa Keidel Gesche Braker Sven Marhan Tim J. Clough Christoph Müller 《Global Change Biology》2018,24(9):3897-3910
Rising atmospheric CO2 concentrations are expected to increase nitrous oxide (N2O) emissions from soils via changes in microbial nitrogen (N) transformations. Several studies have shown that N2O emission increases under elevated atmospheric CO2 (eCO2), but the underlying processes are not yet fully understood. Here, we present results showing changes in soil N transformation dynamics from the Giessen Free Air CO2 Enrichment (GiFACE): a permanent grassland that has been exposed to eCO2, +20% relative to ambient concentrations (aCO2), for 15 years. We applied in the field an ammonium‐nitrate fertilizer solution, in which either ammonium () or nitrate () was labelled with 15N. The simultaneous gross N transformation rates were analysed with a 15N tracing model and a solver method. The results confirmed that after 15 years of eCO2 the N2O emissions under eCO2 were still more than twofold higher than under aCO2. The tracing model results indicated that plant uptake of did not differ between treatments, but uptake of was significantly reduced under eCO2. However, the and availability increased slightly under eCO2. The N2O isotopic signature indicated that under eCO2 the sources of the additional emissions, 8,407 μg N2O–N/m2 during the first 58 days after labelling, were associated with reduction (+2.0%), oxidation (+11.1%) and organic N oxidation (+86.9%). We presume that increased plant growth and root exudation under eCO2 provided an additional source of bioavailable supply of energy that triggered as a priming effect the stimulation of microbial soil organic matter (SOM) mineralization and fostered the activity of the bacterial nitrite reductase. The resulting increase in incomplete denitrification and therefore an increased N2O:N2 emission ratio, explains the doubling of N2O emissions. If this occurs over a wide area of grasslands in the future, this positive feedback reaction may significantly accelerate climate change. 相似文献
8.
Mycorrhizal fungi enhance plant nutrient acquisition and modulate nitrogen loss with variable water regimes 总被引:1,自引:0,他引:1
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Timothy M. Bowles Louise E. Jackson Timothy R. Cavagnaro 《Global Change Biology》2018,24(1):e171-e182
Climate change will alter both the amount and pattern of precipitation and soil water availability, which will directly affect plant growth and nutrient acquisition, and potentially, ecosystem functions like nutrient cycling and losses as well. Given their role in facilitating plant nutrient acquisition and water stress resistance, arbuscular mycorrhizal (AM) fungi may modulate the effects of changing water availability on plants and ecosystem functions. The well‐characterized mycorrhizal tomato (Solanum lycopersicum L.) genotype 76R (referred to as MYC+) and the mutant mycorrhiza‐defective tomato genotype rmc were grown in microcosms in a glasshouse experiment manipulating both the pattern and amount of water supply in unsterilized field soil. Following 4 weeks of differing water regimes, we tested how AM fungi affected plant productivity and nutrient acquisition, short‐term interception of a pulse, and inorganic nitrogen (N) leaching from microcosms. AM fungi enhanced plant nutrient acquisition with both lower and more variable water availability, for instance increasing plant P uptake more with a pulsed water supply compared to a regular supply and increasing shoot N concentration more when lower water amounts were applied. Although uptake of the short‐term pulse was higher in rmc plants, possibly due to higher N demand, AM fungi subtly modulated leaching, decreasing losses by 54% at low and high water levels in the regular water regime, with small absolute amounts of leached (<1 kg N/ha). Since this study shows that AM fungi will likely be an important moderator of plant and ecosystem responses to adverse effects of more variable precipitation, management strategies that bolster AM fungal communities may in turn create systems that are more resilient to these changes. 相似文献
9.
G. Stoelken K. Pritsch J. Simon C. W. Mueller T. E. E. Grams J. Esperschuetz 《Plant biosystems》2013,147(3):537-546
Abstract In a lysimeter study with young beech trees, the effects of elevated ozone concentration on the decomposition and fate of nitrogen in 15N‐labeled leaf litter were analyzed after one growing season. Nitrogen in the litter was dominated by a relatively inert, residual fraction, but easily decomposable nitrogen was present in substantial amounts. Nitrogen loss was significantly higher at twice‐ambient ozone which was largely attributed to an enhanced mobilization of residual nitrogen. Enhanced mobilization of nitrogen from litter at twice‐ambient ozone exposure resulted in additional 15N incorporation into the soil down to 30 cm depth. Only 0.41–0.62% of the nitrogen in the litter was incorporated into plant material at both ozone concentrations. Twice‐ambient ozone exposure changed the distribution of the nitrogen taken up from litter inside the beech trees in favor of the shoot, where it may have been used in biosynthetic processes required for defense reactions. 相似文献
10.
Agnieszka Wujeska‐Klause Kristine Y. Crous Oula Ghannoum David S. Ellsworth 《Global Change Biology》2019,25(4):1282-1295
Rising atmospheric CO2 concentrations is expected to stimulate photosynthesis and carbohydrate production, while inhibiting photorespiration. By contrast, nitrogen (N) concentrations in leaves generally tend to decline under elevated CO2 (eCO2), which may reduce the magnitude of photosynthetic enhancement. We tested two hypotheses as to why leaf N is reduced under eCO2: (a) A “dilution effect” caused by increased concentration of leaf carbohydrates; and (b) inhibited nitrate assimilation caused by reduced supply of reductant from photorespiration under eCO2. This second hypothesis is fully tested in the field for the first time here, using tall trees of a mature Eucalyptus forest exposed to Free‐Air CO2 Enrichment (EucFACE) for five years. Fully expanded young and mature leaves were both measured for net photosynthesis, photorespiration, total leaf N, nitrate () concentrations, carbohydrates and reductase activity to test these hypotheses. Foliar N concentrations declined by 8% under eCO2 in new leaves, while the fraction and total carbohydrate concentrations remained unchanged by CO2 treatment for either new or mature leaves. Photorespiration decreased 31% under eCO2 supplying less reductant, and in situ reductase activity was concurrently reduced (?34%) in eCO2, especially in new leaves during summer periods. Hence, assimilation was inhibited in leaves of E. tereticornis and the evidence did not support a significant dilution effect as a contributor to the observed reductions in leaf N concentration. This finding suggests that the reduction of reductase activity due to lower photorespiration in eCO2 can contribute to understanding how eCO2‐induced photosynthetic enhancement may be lower than previously expected. We suggest that large‐scale vegetation models simulating effects of eCO2 on N biogeochemistry include both mechanisms, especially where is major N source to the dominant vegetation and where leaf flushing and emergence occur in temperatures that promote high photorespiration rates. 相似文献
11.
Melissa A. Dawes Patrick Schleppi Stephan Hättenschwiler Christian Rixen Frank Hagedorn 《Global Change Biology》2017,23(1):421-434
Climate warming may alter ecosystem nitrogen (N) cycling by accelerating N transformations in the soil, and changes may be especially pronounced in cold regions characterized by N‐poor ecosystems. We investigated N dynamics across the plant–soil continuum during 6 years of experimental soil warming (2007–2012; +4 °C) at a Swiss high‐elevation treeline site (Stillberg, Davos; 2180 m a.s.l.) featuring Larix decidua and Pinus uncinata. In the soil, we observed considerable increases in the pool size in the first years of warming (by >50%), but this effect declined over time. In contrast, dissolved organic nitrogen (DON) concentrations in soil solutions from the organic layer increased under warming, especially in later years (maximum of +45% in 2012), suggesting enhanced DON leaching from the main rooting zone. Throughout the experimental period, foliar N concentrations showed species‐specific but small warming effects, whereas δ15N values showed a sustained increase in warmed plots that was consistent for all species analysed. The estimated total plant N pool size at the end of the study was greater (+17%) in warmed plots with Pinus but not in those containing Larix, with responses driven by trees. Irrespective of plot tree species identity, warming led to an enhanced N pool size of Vaccinium dwarf shrubs, no change in that of Empetrum hermaphroditum (dwarf shrub) and forbs, and a reduction in that of grasses, nonvascular plants, and fine roots. In combination, higher foliar δ15N values and the transient response in soil inorganic N indicate a persistent increase in plant‐available N and greater cumulative plant N uptake in warmer soils. Overall, greater N availability and increased DON concentrations suggest an opening of the N cycle with global warming, which might contribute to growth stimulation of some plant species while simultaneously leading to greater N losses from treeline ecosystems and possibly other cold biomes. 相似文献
12.
The hyphae of ectomycorrhizal and ericoid mycorrhizal fungi proliferate in nitrogen (N)-limited forests and tundra where the
availability of inorganic N is low; under these conditions the most common fungal species are those capable of protein degradation
that can supply their host plants with organic N. Although it is widely understood that these symbiotic fungi supply N to
their host plants, the transfer is difficult to quantify in the field. A novel approach uses the natural 15N:14N ratios (expressed as δ15N values) in plants, soils, and mycorrhizal fungi to estimate the fraction of N in symbiotic trees and shrubs that enters
through mycorrhizal fungi. This calculation is possible because mycorrhizal fungi discriminate against 15N when they create compounds for transfer to plants; host plants are depleted in 15N, whereas mycorrhizal fungi are enriched in 15N. The amount of carbon (C) supplied to these fungi can be stoichiometrically calculated from the fraction of plant N derived
from the symbiosis, the N demand of the plants, the fungal C:N ratio, and the fraction of N retained in the fungi. Up to a
third of C allocated belowground, or 20% of net primary production, is used to support ectomycorrhizal fungi. As anthropogenic
N inputs increase, the C allocation to fungi decreases and plant δ15N increases. Careful analyses of δ15N patterns in systems dominated by ectomycorrhizal and ericoid mycorrhizal symbioses may reveal the ecosystem-scale effects
of alterations in the plant–mycorrhizal symbioses caused by shifts in climate and N deposition.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
13.
Chao Mao Dan Kou Leiyi Chen Shuqi Qin Dianye Zhang Yunfeng Peng Yuanhe Yang 《Global Change Biology》2020,26(9):5290-5302
It had been suggested that permafrost thaw could promote frozen nitrogen (N) release and modify microbial N transformation rates, which might alter soil N availability and then regulate ecosystem functions. However, the current understanding of this issue is confined to limited observations in the Arctic permafrost region, without any systematic measurements in other permafrost regions. Based on a large‐scale field investigation along a 1,000 km transect and a laboratory incubation experiment with a 15N pool dilution approach, this study provides the comprehensive evaluation of the permafrost N status, including the available N content and related N transformation rates, across the Tibetan alpine permafrost region. In contrast to the prevailing view, our results showed that the Tibetan alpine permafrost had lower available N content and net N mineralization rate than the active layer. Moreover, the permafrost had lower gross rates of N mineralization, microbial immobilization and nitrification than the active layer. Our results also revealed that the dominant drivers of the gross N mineralization and microbial immobilization rates differed between the permafrost and the active layer, with these rates being determined by microbial properties in the permafrost while regulated by soil moisture in the active layer. In contrast, soil gross nitrification rate was consistently modulated by the soil content in both the permafrost and the active layer. Overall, patterns and drivers of permafrost N pools and transformation rates observed in this study offer new insights into the potential N release upon permafrost thaw and provide important clues for Earth system models to better predict permafrost biogeochemical cycles under a warming climate. 相似文献
14.
杉木人工林凋落物生态化学计量与土壤有效养分对长期模拟氮沉降的响应 总被引:2,自引:0,他引:2
凋落物分解的快慢和养分释放的速度决定了生态系统中土壤有效养分的供应。探讨全球变化条件下森林生态系统凋落物与土壤养分的变化规律,有利于深入认识凋落物-土壤相互作用的养分调控因素,从而揭示生态系统C、N、P循环。通过模拟氮沉降增加试验,分4个水平处理,分别为0、60、120、240 kg N hm~(-2)a~(-1)。模拟氮沉降13年后,分析了杉木人工林凋落物中不同组分(落叶、落枝、落果)生态化学计量与土壤有效养分(有效氮、碱解氮、速效磷、速效钾)的关系。结果表明:氮沉降(N1、N2和N3)显著提高了落叶和落枝的N含量,平均增幅分别为35.27%和32.21%;高水平氮沉降(N3)处理显著降低了落叶和落枝的C/N,平均降幅分别为25.95%和22.32%,但N3增加了落枝和落果N/P,平均增幅分别为38.4%和31.7%;氮沉降对凋落物各组分的C、P和C/P均影响不显著。氮沉降处理显著增加了土壤NO_3~--N和NH_4~+-N含量,均表现为N3N2N1N0,其中NO_3~--N含量更容易受氮沉降处理的影响,表现为更大的增幅。N2显著增加0—20 cm土层的碱解氮含量,N1显著降低0—20 cm土层的速效钾,但氮沉降对速效磷含量没有影响。凋落物生态化学计量与土壤有效养分之间的Pearson相关和冗余分析(RDA)表明,凋落物生态化学计量与土壤有效养分之间关系紧密,凋落物P含量(蒙特卡罗检验,P=0.018)和C/P比值(P=0.037)对土壤有效养分影响显著。凋落物中C/N比值、C/P比值与土壤有效养分呈显著负相关,其比值越高越不利于土壤有效养分的累积。 相似文献
15.
Forests in the American Pacific Northwest receive very little nitrogen (N) through atmospheric deposition; therefore, they can provide insights into how the N cycle functioned in other regions before heavy atmospheric deposition of inorganic N began. Our objectives were to determine (a) if the fate of organic N differed from the fate of inorganic N, (b) the effect that polyphenols have on the fate of organic N, and (c) the effect of season of addition on the fate of N inputs. We traced N added to in situ soil cores as ammonium, organic N, tannin-complexed organic N, and the N2-fixing lichen Lobaria oregana. Total 15N recovery was between 74% and 109% for all N additions. Total 15N recovery did not vary significantly from the first sampling date to the last date. The litter/organic horizon, as a bulk pool, was the largest N retention pool for all forms of N addition. Within the litter/organic horizon, the chloroform-extractable microbial biomass initially accounted for nearly all of the added N from the ammonium additions. On a different time scale, microbial biomass also played a noteworthy role in the retention of N from organic N, tannin-complexed organic N, and Lobaria. Complexing organic matter with tannin appeared to slow N cycling, but it did not significantly change the ultimate distribution of added organic N. Season of N addition had little effect on the retention of added N; however, where differences did occur, spring additions had lower recoveries than autumn additions. 相似文献
16.
Andrew J. Burton Julie C. Jarvey Mickey P. Jarvi Donald R. Zak Kurt S. Pregitzer 《Global Change Biology》2012,18(1):258-266
Specific root respiration rates typically increase with increasing tissue N concentration. As a result, it is often assumed that external factors inducing greater root N concentration, such as chronic N deposition, will lead to increased respiration rates. However, enhanced N availability also alters root biomass, making the ecosystem‐level consequences on whole‐root‐system respiration uncertain. The objective of this study was to determine the effects of chronic experimental N deposition on root N concentrations, specific respiration rates, and biomass for four northern hardwood forests in Michigan. Three of the six measurement plots at each location have received experimental N deposition (3 g ‐N m?2 yr?1) since 1994. We measured specific root respiration rates and N concentrations of roots from four size classes (<0.5, 0.5–1, 1–2, and 2–10 mm) at three soil depths (0–10, 10–30, and 30–50 cm). Root biomass data for the same size classes and soil depths was used in combination with specific respiration rates to assess the response of whole‐root‐system respiration. Root N and respiration rate were greater for smaller diameter roots and roots at shallow depths. In addition, root N concentrations were significantly greater under chronic N deposition, particularly for larger diameter roots. Specific respiration rates and root biomass were unchanged for all depths and size classes, thus whole‐root‐system respiration was not altered by chronic N deposition. Higher root N concentrations in combination with equivalent specific respiration rates under experimental N deposition resulted in a lower ratio of respiration to tissue N. These results indicate that relationships between root respiration rate and N concentration do not hold if N availability is altered significantly. For these forests, use of the ambient respiration to N relationship would over‐predict actual root system respiration for the chronic N deposition treatment by 50%. 相似文献
17.
Nitrogen Addition Shapes Soil Phosphorus Availability in Two Reforested Tropical Forests in Southern China 总被引:3,自引:0,他引:3
Xiankai Lu Jiangming Mo Frank S. Gilliam Hua Fang Feifei Zhu Yunting Fang Wei Zhang Juan Huang 《Biotropica》2012,44(3):302-311
Scant information is available on how soil phosphorus (P) availability responds to atmospheric nitrogen (N) deposition, especially in the tropical zones. This study examined the effect of N addition on soil P availability, and compared this effect between forest sites of contrasting land‐use history. Effects of N addition on soil properties, litterfall production, P release from decomposing litter, and soil P availability were studied in a disturbed (reforested pine forest with previous understory vegetation and litter harvesting) and a rehabilitated (reforested mixed pine/broadleaf forest with no understory vegetation and litter harvesting) tropical forest in southern China. Experimental N‐treatments (above ambient) were the following: Control (no N addition), N50 (50 kg N ha?1 yr?1), and N100 (100 kg N ha?1 yr?1). Results indicated that N addition significantly decreased soil P availability in the disturbed forest. In the rehabilitated forest, however, soil P availability was significantly increased by N addition. Decreases in soil P availability may be correlated with decreases in rates of P release from decomposing litter in the N‐treated plots, whereas the increase in soil P availability was correlated with an increase in litterfall production. Our results suggest that response of soil P availability to N deposition in the reforested tropical forests in southern China may vary greatly with temporal changes in tree species composition and soil nutrient status, caused by different land‐use practices. 相似文献
18.
模拟氮沉降对两种竹林不同凋落物组分分解过程养分释放的影响 总被引:4,自引:0,他引:4
利用原位分解袋法研究了华西雨屏区苦竹(Pleioblastus amarus)和撑绿杂交竹(Bambusa pervariabilis × Dendrocala mopsi)人工林几种凋落物组分在模拟氮沉降下分解过程中养分释放状态,试验周期为2 a。氮沉降水平分别为对照(CK, 0 g · m-2 · a-1)、低氮(5 g · m-2 · a-1)、中氮(15 g · m-2 · a-1)和高氮(30 g · m-2 · a-1),每月下旬定量地对各处理施氮(NH4NO3)。结果表明,苦竹林和杂交竹林凋落物主要由凋落叶、凋落箨和凋落枝组成,其中凋落叶约占80%;两个竹种凋落物在分解过程中养分元素释放的种间差异主要与初始养分元素含量有关;凋落物养分元素初始含量对元素释放模式和最终净释放率的大小具有重要的决定作用;目前,这两种竹林生态系统土壤氮输入主要以大气氮沉降(8.24 g · m-2 · a-1)为主,同时凋落物氮输入(苦竹和杂交竹林分别为1.93,5.07 g · m-2 · a-1)也是一个重要途径;模拟氮沉降对苦竹凋落物碳、磷、钾、钙元素和杂交竹凋落物碳、氮、磷、钾、钙、镁元素释放的抑制作用较弱,处理与对照之间元素总释放率差异一般小于10%;氮沉降显著抑制了苦竹林凋落物氮元素释放,减小幅度为19.0%-27.2%,但由于氮沉降增加对土壤肥力的直接改良作用,氮沉降的增加并不会因为凋落物分解速率的降低造成植物生长所需养分供应的减少;从短期来看,在氮沉降继续增加的情况下,该地区这类竹林生态系统的碳吸存能力仍可能会因为N沉降对植物生长的促进作用而增加。 相似文献
19.
Insect outbreaks alter nutrient dynamics in a southern African savanna: patchy defoliation of Colophospermum mopane savanna by Imbrasia belina larvae
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Invertebrate herbivore outbreaks have important impacts on system biogeochemical cycling, but these effects have been poorly documented in African savanna ecosystems. In semi‐arid African savannas, outbreaks of the lepidopteran Imbrasia belina (mopane worm) affect discrete patches of the dominant Colophospermum mopane trees; larvae may completely defoliate trees for up to six weeks during each of the early and late growing seasons. We studied the impact of mopane worm outbreaks on the availability of nitrogen (N), phosphorus (P), and potassium (K) within mopane savanna by quantifying major nutrient pools in defoliated and non‐defoliated savanna patches, including leaves, leaf litter, worm frass, and the soil beneath trees. Within an outbreak area, approximately 44 percent of trees were infested, supporting ~29,000 worms/ha, leading to ~640 kg/ha dry weight frass deposition at 1.4 g of frass/day‐individual (fourth or fifth instar), compared with an average 1645 kg/ha dry weight of leaf on trees most of which should be deposited by litterfall at the end of the growing season. Frass had twofold higher P, 10 percent higher K, but equivalent N content than litter. Taking frass and litter deposition together, the N, P, and K contents added due to the outbreak event at our study site were 0.88, 5.8, and 2.8 times those measured in non‐outbreak patches, a pattern which was reflected in the nutrient contents of soil surfaces beneath defoliated trees. Invertebrate herbivory appears to be an important driver for mopane savanna but has been largely neglected. 相似文献
20.
Lucas E. Nave Knute J. Nadelhoffer James M. Le Moine Linda T. A. van Diepen Jules K. Cooch Nicholas J. Van Dyke 《Ecosystems》2013,16(4):590-603
Forest succession may cause changes in nitrogen (N) availability, vegetation and fungal community composition that affect N uptake by trees and their mycorrhizal symbionts. Understanding how these changes affect the functioning of the mycorrhizal symbiosis is of interest to ecosystem ecology because of the fundamental roles mycorrhizae play in providing nutrition to trees and structuring forest ecosystems. We investigated changes in tree and mycorrhizal fungal community composition, the availability and uptake of N by trees and mycorrhizal fungi in a forest undergoing a successional transition (age-related loss of early successional tree taxa). In this system, 82–96% of mycorrhizal hyphae were ectomycorrhizal (EM). As biomass production of arbuscular mycorrhizal (AM) trees increased, AM hyphae comprised a significantly greater proportion of total fungal hyphae, and the EM contribution to the N requirement of EM-associated tree taxa declined from greater than 75% to less than 60%. Increasing N availability was associated with lower EM hyphal foraging and 15N tracer uptake, yet the EM-associated later-successional species Quercus rubra was nonetheless a stronger competitor for 15N than AM-associated Acer rubrum, likely due to the more extensive nature of the persistent EM hyphal network. These results indicate that successional increases in N availability and co-dominance by AM-associated trees have increased the importance of AM fungi in the mycorrhizal community, while down-regulating EM N acquisition and transfer processes. This work advances understanding of linkages between tree and fungal community composition, and indicates that successional changes in N availability may affect competition between tree taxa with divergent resource acquisition strategies. 相似文献