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1.
Fine root turnover in forest ecosystems in relation to quantity and form of nitrogen availability: a comparison of two methods 总被引:20,自引:0,他引:20
John D. Aber Jerry M. Melillo Knute J. Nadelhoffer Charles A. McClaugherty John Pastor 《Oecologia》1985,66(3):317-321
Summary Two methods of estimating fine root production and turnover are compared for 13 forest ecosystems exhibiting a wide range in form (NH4
+ vs. NO3
-) and quantity of available nitrogen. The two methods are by comparison of seasonal maxima and minima in biomess and by nitrogen budgeting. Both methods give similar results for stands with low rates of nitrification. The budgeting method predicts higher fine root turnover and productivity than the max-min method for systems with significant rates of nitrification. 相似文献
2.
Natural<Superscript>15</Superscript> N Abundance of Plants and Soil N in a Temperate Coniferous Forest 总被引:3,自引:0,他引:3
Keisuke?Kobakkoba@depe.titech.ac.jp" title="kkoba@i.kyoto-u.ac.jp kkoba@depe.titech.ac.jp" itemprop="email" data-track="click" data-track-action="Email author" data-track-label="">Email author Muneto?Hirobe Lina?Koyama Ayato?Kohzu Naoko?Tokuchi Knute John?Nadelhoffer Eitaro?Wada Hiroshi?Takeda 《Ecosystems》2003,6(5):457-469
Measurement of nitrogen isotopic composition (15N) of plants and soil nitrogen might allow the characteristics of N transformation in an ecosystem to be detected. We tested the measurement of 15N for its ability to provide a picture of N dynamics at the ecosystem level by doing a simple comparison of 15N between soil N pools and plants, and by using an existing model. 15N of plants and soil N was measured together with foliar nitrate reductase activity (NRA) and the foliar NO3– pool at two sites with different nitrification rates in a temperature forest in Japan. 15N of plants was similar to that of soil NO3– in the high-nitrification site. Because of high foliar NRA and the large foliar NO3– pool at this site, we concluded that plant 15N indicated a great reliance of plants on soil NO3– there. However, many 15N of soil N overlapped each other at the other site, and 15N could not provide definitive evidence of the N source. The existing model was verified by measured 15N of soil inorganic N and it explained the variations of plant 15N between the two sites in the context of relative importance of nitrification, but more information about isotopic fractionations during plant N uptake is required for quantitative discussions about the plant N source. The model applied here can provide a basis to compare 15N signatures from different ecosystems and to understand N dynamics. 相似文献
3.
Climate and species affect fine root production with long-term fertilization in acidic tussock tundra near Toolik Lake,Alaska 总被引:3,自引:0,他引:3
Long-term fertilization of acidic tussock tundra has led to changes in plant species composition, increases in aboveground
production and biomass and substantial losses of soil organic carbon (SOC). Root litter is an important input to SOC pools,
although little is known about fine root demography in tussock tundra. In this study, we examined the response of fine root
production and live standing fine root biomass to short- and long-term fertilization, as changes in fine root demography may
contribute to observed declines in SOC. Live standing fine root biomass increased with long-term fertilization, while fine
root production declined, reflecting replacement of the annual fine root system of Eriophorum vaginatum, with the long-lived fine roots of Betula nana. Fine root production increased in fertilized plots during an unusually warm growing season, but remained unchanged in control
plots, consistent with observations that B. nana shows a positive response to climate warming. Calculations based on a few simple assumptions suggest changes in fine root
demography with long-term fertilization and species replacement could account for between 20 and 39% of the observed declines
in SOC stocks. 相似文献
4.
Forest nitrogen sinks in large eastern U.S. watersheds: estimates from forest inventory and an ecosystem model 总被引:4,自引:2,他引:2
Goodale Christine L. Lajtha Kate Nadelhoffer Knute J. Boyer Elizabeth W. Jaworski Norbert A. 《Biogeochemistry》2002,(1):239-266
The eastern U.S. receives elevated rates of Ndeposition compared to preindustrial times, yetrelatively little of this N is exported indrainage waters. Net uptake of N into forestbiomass and soils could account for asubstantial portion of the difference between Ndeposition and solution exports. We quantifiedforest N sinks in biomass accumulation andharvest export for 16 large river basins in theeastern U.S. with two separate approaches: (1)using growth data from the USDA ForestService's Forest Inventory and Analysis (FIA)program, and (2) using a model of forestnitrogen cycling (PnET-CN) linked to FIAinformation on forest age-class structure. Themodel was also used to quantify N sinks in soiland dead wood, and nitrate losses below therooting zone. Both methods agreed that netgrowth rates were highest in the relativelyyoung forests on the Schuylkill watershed, andlowest in the cool forests of northern Maine. Across the 16 watersheds, wood export removedan average of 2.7 kg N ha–1 yr–1(range: 1–5 kg N ha–1 yr–1), andstanding stocks increased by 4.0 kg N ha–1yr–1 (–3 to 8 kg N ha–1 yr–1). Together, these sinks for N in woody biomassamounted to a mean of 6.7 kg N ha–1yr–1 (2–9 kg N ha–1 yr–1), or73% (15–115%) of atmospheric N deposition. Modeled rates of net N sinks in dead wood andsoil were small; soils were only a significantnet sink for N during simulations ofreforestation of degraded agricultural sites. Predicted losses of nitrate depended on thecombined effects of N deposition, and bothshort- and long-term effects of disturbance. Linking the model with forest inventoryinformation on age-class structure provided auseful step toward incorporating realisticpatterns of forest disturbance status acrossthe landscape. 相似文献
5.
Sources of nitrate in rivers draining sixteen watersheds in the northeastern U.S.: Isotopic constraints 总被引:3,自引:4,他引:3
Mayer Bernhard Boyer Elizabeth W. Goodale Christine Jaworski Norbert A. van Breemen Nico Howarth Robert W. Seitzinger Sybil Billen Gilles Lajtha Kate Nadelhoffer Knute Van Dam Douwe Hetling Leo J. Nosal Miloslav Paustian Keith 《Biogeochemistry》2002,(1):171-197
The feasibility of using nitrogen and oxygenisotope ratios of nitrate (NO3
–) forelucidating sources and transformations ofriverine nitrate was evaluated in a comparativestudy of 16 watersheds in the northeastern U.S.A. Stream water was sampled repeatedly at theoutlets of the watersheds between January andDecember 1999 for determining concentrations,15N values, and 18Ovalues of riverine nitrate.In conjunction with information about land useand nitrogen fluxes,15Nnitrate and18Onitrate values providedmainly information about sources of riverinenitrate. In predominantly forested watersheds,riverine nitrate had mean concentrations ofless than 0.4 mg NO3
–-N L–1,15Nnitrate values of lessthan +5, and 18Onitratevalues between +12 and +19. This indicatesthat riverine nitrate was almost exclusivelyderived from soil nitrification processes withpotentially minor nitrate contributions fromatmospheric deposition in some catchments. Inwatersheds with significant agricultural andurban land use, concentrations of riverinenitrate were as high as 2.6 mg NO3
–-NL–1 with 15Nnitratevalues between +5 and +8 and18Onitrate values generallybelow +15. Correlations between nitrateconcentrations, 15Nnitratevalues, and N fluxes suggest that nitrate inwaste water constituted a major, and nitrate inmanure a minor additional source of riverinenitrate. Atmospheric nitrate deposition ornitrate-containing fertilizers were not asignificant source of riverine nitrate inwatersheds with significant agricultural andurban land use. Although complementary studiesindicate that in-stream denitrification wassignificant in all rivers, the isotopiccomposition of riverine nitrate sampled at theoutlet of the 16 watersheds did not provideevidence for denitrification in the form ofelevated 15Nnitrate and18Onitrate values. Relativelylow isotopic enrichment factors for nitrogenand oxygen during in-stream denitrification andcontinuous admixture of nitrate from theabove-described sources are thought to beresponsible for this finding. 相似文献
6.
Lori vandenEnden Serita D. Frey Knute J. Nadelhoffer James M. LeMoine Kate Lajtha Myrna J. Simpson 《Biogeochemistry》2018,141(2):183-197
With climate change, forests are expected to receive increased inputs of carbon (C) and nitrogen (N) but it is unclear how this will modify forest C cycling and storage at the molecular-level. To investigate the response of forest soil organic matter (SOM) to changes in soil inputs, a study area was established in a Michigan hardwood forest as part of the Detrital Input and Removal Treatments (DIRT) network. Experimental treatments were comprised of both exclusions of detrital inputs (No Litter, No Roots, No Inputs) and additions of C and N (Double Litter, N-Addition, Double Litter?+?N, Wood). After 10 years of treatment, the soils were characterized using elemental analysis, molecular biomarker techniques, nuclear magnetic resonance spectroscopy, and microbial biomass C measurements. Although manipulation of detrital inputs did not significantly change the soil C and N content after 10 years, alterations in the cycling and distribution of SOM components were observed. Root exclusion enhanced SOM degradation, while doubling litter favoured the degradation of more labile forms of soil C such as unsaturated n-alkanoic acids and simple sugars. N-Addition and Double Litter?+?N increased the concentrations of extractable biomarkers, including aliphatic and cyclic lipids and compounds derived from cutin, suberin, and lignin. Microbial biomass C also varied with experimental litter input manipulations and N addition, and these data were consistent with the observed changes in SOM composition. Overall, the observed shifts in SOM chemistry after 10 years of manipulating ecosystem inputs highlight the sensitivity of natural systems to changes in amounts of C and N inputs from roots and litter, and N inputs from external sources. 相似文献
7.
This paper explores the biological consequences of climate change by integrating the results of a tripartite investigation involving fumarole, field manipulation and laboratory incubation experiments. The geographical region for this research is the maritime Antarctic. Under contemporary climate conditions, the lithosols in this region support only a sparse cryptogamic flora of limited taxonomic diversity and low structural complexity. However, the existence in geothermal areas of temperate species (e.g. Campylopus introflexus, Marchantia polymorpha, Philonotis acicularis) growing outside their normal biogeographical range suggests that elevated temperature and humidity may alter the trajectory of community development towards Magellanic or Patagonian composition. Productivity is also likely to increase, as indicated by significantly greater vegetative biomass recorded beneath climate-ameliorating soil covers than in controls. Barren fellfield soil samples transplanted to the laboratory and incubated at temperatures of 2–25°C show rapid development of moss, algae and lichen propagules in the range 15–25°C. A variety of species develop that have not been recorded in the field. The presence of exotic taxa indicates the existence of a dormant propagule bank in maritime Antarctic soils and suggests that no significant delay is likely to occur between the onset of climate warming and community development: instead, rapid establishment of those species favoured by the new climate conditions will yield a distinct founder effect, with increasing above- and below-ground biomass stimulating biogeochemical cycling. It is argued that the combined results of this synthesis identify generic responses to climate change arising from the importance at high latitudes of low temperature and water availability as limiting factors: subject to other growth resources being non-limiting, a more consistent stimulatory response to climate change may be expected than in temperate or tropical regions. The tripartite approach, encompassing field, microcosm and laboratory methodologies, renders the conclusions more robust than any single study considered in isolation. 相似文献
8.
The fate of 15N-labelled nitrate additions to a northern hardwood forest in eastern Maine,USA 总被引:5,自引:0,他引:5
Knute J. Nadelhoffer Martha R. Downs Brian Fry John D. Aber Alison H. Magill Jerry M. Melillo 《Oecologia》1995,103(3):292-301
We followed the movements of 15N-labelled nitrate additions into biomass and soil pools of experimental plots (15×15 m each) in a mid-successional beech-maple-birch-spruce forest in order to identify sinks for nitrate inputs to a forest ecosystem. Replicate plots (n=3) were spray-irrigated with either 28 or 56 kg N ha–1 year–1 using 15N-labelled nitric acid solutions (15N = 344 ) during four successive growing seasons (April–October). The 15N contents of foliage, bolewood, forests floor and mineral soil (0–5 cm) increased during the course of treatments. Mass balance calculations showed that one-fourth to one-third of the nitrate applied to forest plots was assimilated into and retained by above ground plant tissues and surface soil horizons at both rates of nitrate application. Plant and microbial assimilation were of approximately equal importance in retaining nitrate additions to this forest. Nitrate use among tree species varied, however, with red spruce showing lower rates of nitrate assimilation into foliage and bolewood than American beech and other deciduous species. 相似文献
9.
Seasonal patterns of ammonium and nitrate uptake in nine temperate forest ecosystems 总被引:11,自引:2,他引:9
Summary Seasonal patterns of net N mineralization and nitrification in the 0–10 cm mineral soil of 9 temperate forest sites were analyzed using approximately monthlyin situ soil incubations. Measured nitrification rates in incubated soils were found to be good estimates of nitrification in surrounding forest soils. Monthly net N mineralization rates and pools of ammonium-N in soil fluctuated during the growing season at all sites. Nitrate-N pools in soil were generally smaller than ammonium-N pools and monthly nitrification rates were less variable than net N mineralization rates. Nitrate supplied most of the N taken up annually by vegetation at 8 of the 9 sites. Furthermore, despite the large fluctuations in ammonium-N pools and monthly net N mineralization, nitrate was taken up at relatively uniform rates during the growing season at most sites. 相似文献
10.
Martha R. Downs Knute J. Nadelhoffer Jerry M. Melillo John D. Aber 《Trees - Structure and Function》1993,7(4):233-236
Summary Seedlings of red maple, white pine, pitch pine and red pine were fertilized with nutrient solutions containing 4 levels of nitrate or ammonium additions. These levels corresponded to approximately 0.5, 1, 2 and 4 times normal availability of nitrogen in northeastern forests. Nitrate reductase (NR) activity was assayed in roots and leaves. Red maples treated with nitrate showed much higher leaf activities and higher ratios of leaf NR activity to root NR activity than any other species. Ammonium additions to red maple and white pine appeared to inhibit NR activity in leaves. With high nitrate additions, NR activity was induced in roots and leaves of pine species, but activity in roots remained much higher than in leaves. 相似文献