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1.
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
2.
Management of indigenous plant-microbe symbioses aids restoration of desertified ecosystems 总被引:10,自引:0,他引:10
Requena N Perez-Solis E Azcón-Aguilar C Jeffries P Barea JM 《Applied and environmental microbiology》2001,67(2):495-498
Disturbance of natural plant communities is the first visible indication of a desertification process, but damage to physical, chemical, and biological soil properties is known to occur simultaneously. Such soil degradation limits reestablishment of the natural plant cover. In particular, desertification causes disturbance of plant-microbe symbioses which are a critical ecological factor in helping further plant growth in degraded ecosystems. Here we demonstrate, in two long-term experiments in a desertified Mediterranean ecosystem, that inoculation with indigenous arbuscular mycorrhizal fungi and with rhizobial nitrogen-fixing bacteria not only enhanced the establishment of key plant species but also increased soil fertility and quality. The dual symbiosis increased the soil nitrogen (N) content, organic matter, and hydrostable soil aggregates and enhanced N transfer from N-fixing to nonfixing species associated within the natural succession. We conclude that the introduction of target indigenous species of plants associated with a managed community of microbial symbionts is a successful biotechnological tool to aid the recovery of desertified ecosystems. 相似文献
3.
Management of Indigenous Plant-Microbe Symbioses Aids Restoration of Desertified Ecosystems 总被引:12,自引:2,他引:10
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Natalia Requena Estefania Perez-Solis Concepcin Azcn-Aguilar Peter Jeffries Jos-Miguel Barea 《Applied microbiology》2001,67(2):495-498
Disturbance of natural plant communities is the first visible indication of a desertification process, but damage to physical, chemical, and biological soil properties is known to occur simultaneously. Such soil degradation limits reestablishment of the natural plant cover. In particular, desertification causes disturbance of plant-microbe symbioses which are a critical ecological factor in helping further plant growth in degraded ecosystems. Here we demonstrate, in two long-term experiments in a desertified Mediterranean ecosystem, that inoculation with indigenous arbuscular mycorrhizal fungi and with rhizobial nitrogen-fixing bacteria not only enhanced the establishment of key plant species but also increased soil fertility and quality. The dual symbiosis increased the soil nitrogen (N) content, organic matter, and hydrostable soil aggregates and enhanced N transfer from N-fixing to nonfixing species associated within the natural succession. We conclude that the introduction of target indigenous species of plants associated with a managed community of microbial symbionts is a successful biotechnological tool to aid the recovery of desertified ecosystems. 相似文献
4.
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
5.
Nitrogen balance in forest soils: nutritional limitation of plants under climate change stresses 总被引:4,自引:0,他引:4
H. Rennenberg M. Dannenmann A. Gessler J. Kreuzwieser J. Simon & H. Papen 《Plant biology (Stuttgart, Germany)》2009,11(S1):4-23
Forest ecosystems with low soil nitrogen (N) availability are characterized by direct competition for this growth-limiting resource between several players, i.e. various components of vegetation, such as old-growth trees, natural regeneration and understorey species, mycorrhizal fungi, free-living fungi and bacteria. With the increase in frequency and intensity of extreme climate events predicted in current climate change scenarios, also competition for N between plants and/or soil microorganisms will be affected. In this review, we summarize the present understanding of ecosystem N cycling in N-limited forests and its interaction with extreme climate events, such as heat, drought and flooding. More specifically, the impacts of environmental stresses on microbial release and consumption of bioavailable N, N uptake and competition between plants, as well as plant and microbial uptake are presented. Furthermore, the consequences of drying–wetting cycles on N cycling are discussed. Additionally, we highlight the current methodological difficulties that limit present understanding of N cycling in forest ecosystems and the need for interdisciplinary studies. 相似文献
6.
森林生态系统在全球碳(C)储量中占据极为重要的地位。菌根真菌广泛存在于森林生态系统中,在森林生态系统C循环过程中发挥重要的作用。阐述了不同菌根类型真菌在森林生态系统C循环过程中的功能,对比了温带/北方森林与热带/亚热带森林中菌根真菌介导的C循环研究方面新近取得的研究结果。发现温带和北方森林的外生菌根(EcM)植物对地上生物量C的贡献相对较小,然而是地下C储量的主要贡献者;以丛枝菌根(AM)共生为主的热带/亚热带森林地表生物量占比较高,表明AM植被对热带/亚热带森林地上生物量C的贡献相对较大。我们还就全球变化背景下,菌根真菌及其介导的森林生态系统C汇功能,以及不同菌根类型树种影响C循环的机制等进行了总结。菌根真菌通过影响凋落物分解、土壤有机质形成及地下根系生物量,进而影响整个森林生态系统的C循环功能。菌根介导的森林C循环过程很大程度上取决于(优势)树木的菌根类型和森林土壤中菌根真菌的群落结构。最后指出了当前研究存在的主要问题以及未来研究展望。本文旨在明确菌根真菌在森林生态系统C循环转化过程中的重要生态功能,有助于准确地评估森林生态系统C汇现状,为应对全球变化等提供重要的依据。 相似文献
7.
Nitrogen cycling in forest soils has been intensively studied for many years because nitrogen is often the limiting nutrient
for forest growth. Complex interactions between soil, microbes, and plants and the consequent inability to correlate δ15N changes with biologic processes have limited the use of natural abundances of nitrogen isotopes to study nitrogen (N) dynamics.
During an investigation of N dynamics along the 250-year-old successional sequence in Glacier Bay, Alaska, United States,
we observed several puzzling isotopic patterns, including a consistent decline in δ15N of the late successional dominant Picea at older sites, a lack of agreement between mineral N δ15N and foliar δ15N, and high isotopic signatures for mycorrhizal fungi. In order to understand the mechanisms creating these patterns, we developed
a model of N dynamics and N isotopes (Nitrogen Isotope Fluxes in Terrestrial Ecosystems, NIFTE), which simulated the major
transformations of the N cycle and predicted isotopic signatures of different plant species and soil pools. Comparisons with
field data from five sites along the successional sequence indicated that NIFTE can duplicate observed patterns in δ15N of soil, foliage, and mineral N over time. Different scenarios that could account for the observed isotopic patterns were
tested in model simulations. Possible mechanisms included increased isotopic fractionation on mineralization, fractionation
during the transfer of nitrogen from mycorrhizal fungi to plants, variable fractionation on uptake by mycorrhizal fungi compared
to plants, no fractionation on mycorrhizal transfer, and elimination of mycorrhizal fungi as a pool in the model. The model
results suggest that fractionation during mineralization must be small (˜2‰), and that no fractionation occurs during plant
or mycorrhizal uptake. A net fractionation during mycorrhizal transfer of nitrogen to vegetation provided the best fit to
isotopic data on mineral N, plants, soils, and mycorrhizal fungi. The model and field results indicate that the importance
of mycorrhizal fungi to N uptake is probably less under conditions of high N availability. Use of this model should encourage
a more rigorous assessment of isotopic signatures in ecosystem studies and provide insights into the biologic transformations
which affect those signatures. This should lead to an enhanced understanding of some of the fundamental controls on nitrogen
dynamics.
Received: 1 July 1998 / Accepted: 23 December 1998 相似文献
8.
In this study we show that the natural abundance of the nitrogen isotope 15, δ15N, of plants in heath tundra and at the tundra-forest ecocline is closely correlated with the presence and type of mycorrhizal
association in the plant roots. A total of 56 vascular plant species, 7 moss species, 2 lichens and 6 species of fungi from
four heath and forest tundra sites in Greenland, Siberia and Sweden were analysed for δ15N and N concentration. Roots of vascular plants were examined for mycorrhizal colonization, and the soil organic matter was
analysed for δ15N, N concentration and soil inorganic, dissolved organic and microbial N. No arbuscular mycorrhizal (AM) colonizations were
found although potential host plants were present in all sites. The dominant species were either ectomycorrhizal (ECM) or
ericoid mycorrhizal (ERI). The δ15N of ECM or ERI plants was 3.5–7.7‰ lower than that of non-mycorrhizal (NON) species in three of the four sites. This corresponds
to the results in our earlier study of mycorrhiza and plant δ15N which was limited to one heath and one fellfield in N Sweden. Hence, our data suggest that the δ15N pattern: NON/AM plants > ECM plants ≥ ERI plants is a general phenomenon in ecosystems with nutrient-deficient organogenic
soils. In the fourth site, a␣birch forest with a lush herb/shrub understorey, the differences between functional groups were
considerably smaller, and only the ERI species differed (by 1.1‰) from the NON species. Plants of all functional groups from
this site had nearly twice the leaf N concentration as that found in the same species at the other three sites. It is likely
that low inorganic N availability is a prerequisite for strong δ15N separation among functional groups. Both ECM roots and fruitbodies were 15N enriched compared to leaves which suggests that the difference in δ15N between plants with different kinds of mycorrhiza could be due to isotopic fractionation at the␣fungal-plant interface.
However, differences in δ15N between soil N forms absorbed by the plants could also contribute to the wide differences in plant δ15N found in most heath and forest tundra ecosystems. We hypothesize that during microbial immobilization of soil ammonium the
microbial N pool could become 15N-depleted and the remaining, plant-available soil ammonium 15N-enriched. The latter could be a main source of N for NON/AM plants which usually have high δ15N. In contrast, amino acids and other soil organic N compounds presumably are 15N-depleted, similar to plant litter, and ECM and ERI plants with high uptake of these N forms hence have low leaf δ15N. Further indications come from the δ15N of mosses and lichens which was similar to that of ECM plants. Tundra cryptogams (and ECM and ERI plants) have previously
been shown to have higher uptake of amino acid than ammonium N; their low δ15N might therefore reflect the δ15N of free amino acids in the soil. The concentration of dissolved organic N was 3–16 times higher than that of inorganic N
in the sites. Organic nitrogen could be an important N source for ECM and, in particular, ERI plants in heath and forest tundra
ecosystems with low release rate of inorganic N from the soil organic matter.
Received: 8 June 1997 / Accepted: 28 February 1998 相似文献
9.
Petroleum hydrocarbon contamination in boreal forest soils: a mycorrhizal ecosystems perspective 总被引:2,自引:0,他引:2
Robertson SJ McGill WB Massicotte HB Rutherford PM 《Biological reviews of the Cambridge Philosophical Society》2007,82(2):213-240
The importance of developing multi-disciplinary approaches to solving problems relating to anthropogenic pollution is now clearly appreciated by the scientific community, and this is especially evident in boreal ecosystems exposed to escalating threats of petroleum hydrocarbon (PHC) contamination through expanded natural resource extraction activities. This review aims to synthesize information regarding the fate and behaviour of PHCs in boreal forest soils in both ecological and sustainable management contexts. From this, we hope to evaluate potential management strategies, identify gaps in knowledge and guide future research. Our central premise is that mycorrhizal systems, the ubiquitous root symbiotic fungi and associated food-web communities, occupy the structural and functional interface between decomposition and primary production in northern forest ecosystems (i.e. underpin survival and productivity of the ecosystem as a whole), and, as such, are an appropriate focal point for such a synthesis. We provide pertinent basic information about mycorrhizas, followed by insights into the ecology of ecto- and ericoid mycorrhizal systems. Next, we review the fate and behaviour of PHCs in forest soils, with an emphasis on interactions with mycorrhizal fungi and associated bacteria. Finally, we summarize implications for ecosystem management. Although we have gained tremendous insights into understanding linkages between ecosystem functions and the various aspects of mycorrhizal diversity, very little is known regarding rhizosphere communities in PHC-contaminated soils. This makes it difficult to translate ecological knowledge into environmental management strategies. Further research is required to determine which fungal symbionts are likely to survive and compete in various ecosystems, whether certain fungal - plant associations gain in ecological importance following contamination events, and how PHC contamination may interfere with processes of nutrient acquisition and exchange and metabolic processes. Research is also needed to assess whether the metabolic capacity for intrinsic decomposition exists in these ecosystems, taking into account ecological variables such as presence of other organisms (and their involvement in syntrophic biodegradation), bioavailability and toxicity of mixtures of PHCs, and physical changes to the soil environment. 相似文献
10.
Sean T. Berthrong Chris M. Yeager Laverne Gallegos-Graves Blaire Steven Stephanie A. Eichorst Robert B. Jackson Cheryl R. Kuske 《Applied and environmental microbiology》2014,80(10):3103-3112
Biological nitrogen fixation is the primary supply of N to most ecosystems, yet there is considerable uncertainty about how N-fixing bacteria will respond to global change factors such as increasing atmospheric CO2 and N deposition. Using the nifH gene as a molecular marker, we studied how the community structure of N-fixing soil bacteria from temperate pine, aspen, and sweet gum stands and a brackish tidal marsh responded to multiyear elevated CO2 conditions. We also examined how N availability, specifically, N fertilization, interacted with elevated CO2 to affect these communities in the temperate pine forest. Based on data from Sanger sequencing and quantitative PCR, the soil nifH composition in the three forest systems was dominated by species in the Geobacteraceae and, to a lesser extent, Alphaproteobacteria. The N-fixing-bacterial-community structure was subtly altered after 10 or more years of elevated atmospheric CO2, and the observed shifts differed in each biome. In the pine forest, N fertilization had a stronger effect on nifH community structure than elevated CO2 and suppressed the diversity and abundance of N-fixing bacteria under elevated atmospheric CO2 conditions. These results indicate that N-fixing bacteria have complex, interacting responses that will be important for understanding ecosystem productivity in a changing climate. 相似文献
11.
ERIK A. HOBBIE PAUL T. RYGIEWICZ† MARK G. JOHNSON† ANDREW R. MOLDENKE‡ 《Global Change Biology》2007,13(7):1386-1397
Understanding ecosystem carbon (C) and nitrogen (N) cycling under global change requires experiments maintaining natural interactions among soil structure, soil communities, nutrient availability, and plant growth. In model Douglas-fir ecosystems maintained for five growing seasons, elevated temperature and carbon dioxide (CO2) increased photosynthesis and increased C storage belowground but not aboveground. We hypothesized that interactions between N cycling and C fluxes through two main groups of microbes, mycorrhizal fungi (symbiotic with plants) and saprotrophic fungi (free-living), mediated ecosystem C storage. To quantify proportions of mycorrhizal and saprotrophic fungi, we measured stable isotopes in fungivorous microarthropods that efficiently censused the fungal community. Fungivorous microarthropods consumed on average 35% mycorrhizal fungi and 65% saprotrophic fungi. Elevated temperature decreased C flux through mycorrhizal fungi by 7%, whereas elevated CO2 increased it by 4%. The dietary proportion of mycorrhizal fungi correlated across treatments with total plant biomass (n= 4, r2= 0.96, P= 0.021), but not with root biomass. This suggests that belowground allocation increased with increasing plant biomass, but that mycorrhizal fungi were stronger sinks for recent photosynthate than roots. Low N content of needles (0.8–1.1%) and A horizon soil (0.11%) coupled with high C : N ratios of A horizon soil (25–26) and litter (36–48) indicated severe N limitation. Elevated temperature treatments increased the saprotrophic decomposition of litter and lowered litter C : N ratios. Because of low N availability of this litter, its decomposition presumably increased N immobilization belowground, thereby restricting soil N availability for both mycorrhizal fungi and plant growth. Although increased photosynthesis with elevated CO2 increased allocation of C to ectomycorrhizal fungi, it did not benefit plant N status. Most N for plants and soil storage was derived from litter decomposition. N sequestration by mycorrhizal fungi and limited N release during litter decomposition by saprotrophic fungi restricted N supply to plants, thereby constraining plant growth response to the different treatments. 相似文献
12.
New perspectives on forest soil carbon and nitrogen cycling processes: Roles of arbuscular mycorrhizal versus ectomycorrhizal tree species
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《植物生态学报》2017,41(10):1113
Nearly all tree species develop symbiotic relationships with either arbuscular mycorrhizal (AM) or ectomycorrhizal (EM) fungi to acquire nutrients from soils, and hence influence soil carbon (C) and nitrogen (N) cycles in terrestrial ecosystems. It is crucial to understand the differences in soil C and N cycles between AM and EM forests and the underlying mechanisms. In this review, we first compared the differences in the soil C and N cycles between AM and EM forests, and synthesized the underlying mechanisms from perspectives of the inputs, stabilization, and outputs of soil C and N in forest ecosystems. We also compared the responses of soil C and N cycles between AM and EM forests to global changes. In this field, one major research priority is comparing the structure and function (including the soil C and N cycles) between AM and EM forest ecosystems to provide theoretical basis and solid data for improving forest productivity and ecosystem services. The second research focus is deepening the understanding of the effects of interactions between aboveground litter and belowground mycorrhiza and free-living microbes on soil C and N cycles to reveal the potential underlying mechanisms in forests with different mycorrhizal symbioses. Third, the research methodology and new techniques need refining and applying to explicitly focus on scaling up the fine-scale measurements to better expound and predict the C and N cycles in forest ecosystems. Finally, more studies on the stability of soil organic matter among different mycorrhizal forests are needed to precisely assess responses of the structure and function of forest ecosystems to global changes. 相似文献
13.
Bioremediation is an integrated management of a polluted ecosystem where different organisms are employed to catalyze the natural processes that decontaminate the environment. The potential role of bioremediation, particularly higher terrestrial plants (phytoremediation) research in the remediation of metal-polluted sites, has been the focus of much research in recent years. Arbuscular mycorrhizal fungi are soil microorganisms that establish mutual symbiosis with the majority of higher plants, providing direct links between fungi and roots. This paper reviews the incidence of arbuscular mycorrhizal fungi in metal polluted sites, their role in imparting metal tolerance to plants, the factors affecting arbuscular mycorrhizal fungi in metal polluted sites, and their mechanism of heavy metal tolerance. Particular attention is given to the current methodologies and challenges in this field. 相似文献
14.
Robert K. Antibus Chris Lauber Robert L. Sinsabaugh Donald R. Zak 《Plant and Soil》2006,288(1-2):173-187
Increased use of anthropogenically fixed N and the release of N in combustion products have led to concerns about possible long-term impacts on terrestrial ecosystems. Previous studies demonstrating the potential of atmospheric N deposition to influence forest soil carbon have focused on decomposition processes with much less known about potential impacts on mycorrhiza-derived carbon. Glomalin is a unique glycoprotein produced by arbuscular mycorrhizal (AM) fungi that has been implicated in the formation of soil aggregates and potentially a significant store of soil carbon. To determine the possible impact of experimental N deposition of such stores we examined the operationally defined glomalin-related soil protein (GRSP) levels over two growing seasons in three forest types receiving background N deposition (control) or treated with 80 kg N ha−1 year−1 as NaNO3. Three sites of each of three forest types, sugar maple-basswood (SMBW), sugar maple-red oak (SMRO), and black oak-white oak (BOWO), in northern Lower Michigan were studied during the 2001 and 2002 growing seasons. GRSP were extracted from air-dried soils with citric acid and measured by the Bradford method. Analysis of variance revealed significant differences related to forest type and sample date in easily extractable Bradford reactive (EE-BRSP) and Bradford-reactive soil protein (BRSP), but failed to detect significant effects of experimental N amendment. EE-BRSP and BRSP varied in a pattern that was consistent with an AM fungal origin; a pattern that reflected the mycorrhizal types of the dominant over and understory plants of each forest ecosystem. SMBW forests dominated by AM plants had the highest levels of protein. BOWO forests with low AM plant cover had the lowest protein levels and SMRO forests were intermediate. Both Bradford-reactive fractions and their ratio varied seasonally, generally being highest in fall samples. Significant correlations observed between BRSP fractions, phosphorous, and soil organic matter were likely related to covariation of soil properties across forest types. While not statistically significant, response patterns of BRSP to N deposition were ecosystem-specific and reflected mycorrhizal types of dominant species. Abundance of these proteins reflected previously observed changes in SOC in the two forest types examined with abundant AM hosts. Specifically, nitrate addition led to BRSP decreases in SMBW and increases in SMRO forests. Changes in BRSP accounted for a small fraction of the changes in SOC; appearing to increase as a fraction of residual SOC consistent with the idea that GRSP are recalcitrant. BRSP remained unchanged at BOWO sites despite a significant increase in SOC at these sites. Our results point to the potential of proteins as contributors to differential, mycorrhizal type-specific responses to changes in soil carbon following N amendment. 相似文献
15.
Insights into nitrogen and carbon dynamics of ectomycorrhizal and saprotrophic fungi from isotopic evidence 总被引:10,自引:0,他引:10
The successful use of natural abundances of carbon (C) and nitrogen (N) isotopes in the study of ecosystem dynamics suggests
that isotopic measurements could yield new insights into the role of fungi in nitrogen and carbon cycling. Sporocarps of mycorrhizal
and saprotrophic fungi, vegetation, and soils were collected in young, deciduous-dominated sites and older, coniferous-dominated
sites along a successional sequence at Glacier Bay National Park, Alaska. Mycorrhizal fungi had consistently higher δ15N and lower δ13C values than saprotrophic fungi. Foliar δ13C values were always isotopically depleted relative to both fungal types. Foliar δ15N values were usually, but not always, more depleted than those in saprotrophic fungi, and were consistently more depleted
than in mycorrhizal fungi. We hypothesize that an apparent isotopic fractionation by mycorrhizal fungi during the transfer
of nitrogen to plants may be attributed to enzymatic reactions within the fungi producing isotopically depleted amino acids,
which are subsequently passed on to plant symbionts. An increasing difference between soil mineral nitrogen δ15N and foliar δ15N in later succession might therefore be a consequence of greater reliance on mycorrhizal symbionts for nitrogen supply under
nitrogen-limited conditions. Carbon signatures of mycorrhizal fungi may be more enriched than those of foliage because the
fungi use isotopically enriched photosynthate such as simple sugars, in contrast to the mixture of compounds present in leaves.
In addition, some 13C fractionation may occur during transport processes from leaves to roots, and during fungal chitin biosynthesis. Stable isotopes
have the potential to help clarify the role of fungi in ecosystem processes.
Received: 7 January 1998 / Accepted: 9 November 1998 相似文献
16.
Spatial separation of litter decomposition and mycorrhizal nitrogen uptake in a boreal forest 总被引:4,自引:0,他引:4
Lindahl BD Ihrmark K Boberg J Trumbore SE Högberg P Stenlid J Finlay RD 《The New phytologist》2007,173(3):611-620
Our understanding of how saprotrophic and mycorrhizal fungi interact to re-circulate carbon and nutrients from plant litter and soil organic matter is limited by poor understanding of their spatiotemporal dynamics. In order to investigate how different functional groups of fungi contribute to carbon and nitrogen cycling at different stages of decomposition, we studied changes in fungal community composition along vertical profiles through a Pinus sylvestris forest soil. We combined molecular identification methods with 14C dating of the organic matter, analyses of carbon:nitrogen (C:N) ratios and 15N natural abundance measurements. Saprotrophic fungi were primarily confined to relatively recently (< 4 yr) shed litter components on the surface of the forest floor, where organic carbon was mineralized while nitrogen was retained. Mycorrhizal fungi dominated in the underlying, more decomposed litter and humus, where they apparently mobilized N and made it available to their host plants. Our observations show that the degrading and nutrient-mobilizing components of the fungal community are spatially separated. This has important implications for biogeochemical studies of boreal forest ecosystems. 相似文献
17.
Mycorrhizal responses to nitrogen fertilization in boreal ecosystems: potential consequences for soil carbon storage 总被引:1,自引:0,他引:1
Mycorrhizal fungi can contribute to soil carbon sequestration by immobilizing carbon in living fungal tissues and by producing recalcitrant compounds that remain in the soil following fungal senescence. We hypothesized that nitrogen (N) fertilization would decrease these carbon stocks, because plants should reduce investment of carbon in mycorrhizal fungi when N availability is high. We measured the abundance of two major groups of mycorrhizal fungi, arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) fungi, in the top 10 cm of soil in control and N-fertilized plots within three Alaskan boreal ecosystems that represented different recovery stages following severe fire. Pools of mycorrhizal carbon included root-associated AM and ECM structures; soil-associated AM hyphae; and glomalin, a glycoprotein produced by AM fungi. Total mycorrhizal carbon pools decreased by approximately 50 g C m−2 in the youngest site under N fertilization, and this reduction was driven mostly by glomalin. Total mycorrhizal carbon did not change significantly in the other sites. Root-associated AM structures were more abundant under N fertilization across all sites, and root-associated ECM structures increased marginally significantly. We found no significant N effects on AM hyphae. Carbon sequestered within living mycorrhizal structures (0.051–0.21 g m−2 ) was modest compared with that of glomalin (33–203 g m−2 ). We conclude that our hypothesis was only supported in relation to glomalin stocks within one of the three study sites. As N effects on glomalin were inconsistent among sites, an understanding of the mechanisms underlying this variation would improve our ability to predict ecosystem feedbacks to global change. 相似文献
18.
Daniel D. Warnock Johannes Lehmann Thomas W. Kuyper Matthias C. Rillig 《Plant and Soil》2007,300(1-2):9-20
Experiments suggest that biomass-derived black carbon (biochar) affects microbial populations and soil biogeochemistry. Both
biochar and mycorrhizal associations, ubiquitous symbioses in terrestrial ecosystems, are potentially important in various
ecosystem services provided by soils, contributing to sustainable plant production, ecosystem restoration, and soil carbon
sequestration and hence mitigation of global climate change. As both biochar and mycorrhizal associations are subject to management,
understanding and exploiting interactions between them could be advantageous. Here we focus on biochar effects on mycorrhizal
associations. After reviewing the experimental evidence for such effects, we critically examine hypotheses pertaining to four
mechanisms by which biochar could influence mycorrhizal abundance and/or functioning. These mechanisms are (in decreasing
order of currently available evidence supporting them): (a) alteration of soil physico-chemical properties; (b) indirect effects
on mycorrhizae through effects on other soil microbes; (c) plant–fungus signaling interference and detoxification of allelochemicals
on biochar; and (d) provision of refugia from fungal grazers. We provide a roadmap for research aimed at testing these mechanistic
hypotheses. 相似文献
19.
Jack W. McFarland Roger W. Ruess Knut Kielland Kurt Pregitzer Ronald Hendrick Michael Allen 《Ecosystems》2010,13(2):177-193
Plant and microbial use of nitrogen (N) can be simultaneously mutualistic and competitive, particularly in ecosystems dominated
by mycorrhizal fungi. Our goal was to quantify plant uptake of organic and inorganic N across a broad latitudinal gradient
of forest ecosystems that varied with respect to overstory taxon, edaphic characteristics, and dominant mycorrhizal association.
Using 13C and 15N, we observed in situ the cycling dynamics of NH4
+ and glycine through various soil pools and fine roots over 14 days. Recovery of 15N as soil N varied with respect to N form, forest type, and sampling period; however, there were similarities in the cycling
dynamics of glycine and NH4
+ among all forest types. Microbial immobilization of 15N was immediately apparent for both treatments and represented the largest sink (~25%) for 15N among extractable soil N pools during the first 24 h. In contrast, fine roots were a relatively small sink (<10%) for both
N forms, but fine root 13C enrichment indicated that plants in all forest types absorbed glycine intact, suggesting that plants and microbes effectively
target the same labile soil N pools. Relative uptake of amino acid-N versus NH4
+ varied significantly among sites and approximately half of this variation was explained by mycorrhizal association. Estimates
of plant uptake of amino acid-N relative to NH4
+ were 3× higher in ectomycorrhizal-dominated stands (1.6 ± 0.2) than arbuscular mycorrhizae-dominated stands (0.5 ± 0.1).
We conclude that free amino acids are an important component of the N economy in all stands studied; however, in these natural
environments plant uptake of organic N relative to inorganic N is explained as much by mycorrhizal association as by the availability
of N forms per se. 相似文献
20.
Is microbial community composition in boreal forest soils determined by pH,C-to-N ratio,the trees,or all three? 总被引:11,自引:0,他引:11
In Fennoscandian boreal forests, soil pH and N supply generally increase downhill as a result of water transport of base cations
and N, respectively. Simultaneously, forest productivity increases, the understory changes from ericaceous dwarf shrubs to
tall herbs; in the soil, fungi decrease whereas bacteria increase. The composition of the soil microbial community is mainly
thought to be controlled by the pH and C-to-N ratio of the substrate. However, the latter also determines the N supply to
plants, the plant community composition, and should also affect plant allocation of C below ground to roots and a major functional
group of microbes, mycorrhizal fungi. We used phospholipid fatty acids (PLFAs) to analyze the potential importance of mycorrhizal
fungi by comparing the microbial community composition in a tree-girdling experiment, where tree belowground C allocation
was terminated, and in a long-term (34 years) N loading experiment, with the shifts across a natural pH and N supply gradient.
Both tree girdling and N loading caused a decline of ca. 45% of the fungal biomarker PLFA 18:2ω6,9, suggesting a common mechanism,
i.e., that N loading caused a decrease in the C supply to ectomycorrhizal fungi just as tree girdling did. The total abundance
of bacterial PLFAs did not respond to tree girdling or to N loading, in which cases the pH (of the mor layer) did not change
appreciably, but bacterial PLFAs increased considerably when pH increased across the natural gradient. Fungal biomass was
high only in acid soil (pH < 4.1) with a high C-to-N ratio (>38). According to a principal component analysis, the soil C-to-N
ratio was as good as predictor of microbial community structure as pH. Our study thus indicated the soil C-to-N ratio, and
the response of trees to this ratio, as important factors that together with soil pH influence soil microbial community composition. 相似文献