15N2 measurement of nitrogen fixation by legumes and actinorhizals: theory and practice

Wood, M.; McNeill, Ann

doi:10.1007/bf00025049

Cited by 6 publications

(2 citation statements)

References 9 publications

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“…We determined d15N in shoots of legume and non-legume material collected in June 1995, October 1995, June 1996, and October 1996Finnigan MAT, Bremen, Germany). The fraction of legume N originating from symbiotic fixation was calculated as %N dfa ¼ ( 15 N nonl À 15 N leg )/( 15 N nonl À 15 N atm ), where 15 N leg , 15 N nonl , and 15 N atm are the 15 N mole fractions of N in legumes, all non-legume plants present in the plot, and atmospheric N 2 , respectively (Wood and McNeill 1993). Plant N and P pools were determined by dry combustion (CHN-900, LECO Instruments) and by a micro-Kjehldahl-type wet digestion and colorimetric determination of PO 4 3À (Niklaus et al 1998a).…”

Section: Nitrogen and Phosphorus Relationsmentioning

confidence: 99%

INTERACTIVE EFFECTS OF PLANT SPECIES DIVERSITY AND ELEVATED CO₂ON SOIL BIOTA AND NUTRIENT CYCLING

Niklaus

Alphei

Kampichler

et al. 2007

Ecology

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Terrestrial ecosystems consist of mutually dependent producer and decomposer subsystems, but not much is known on how their interactions are modified by plant diversity and elevated atmospheric CO2 concentrations. Factorially manipulating grassland plant species diversity and atmospheric CO2 concentrations for five years, we tested whether high diversity or elevated CO2 sustain larger or more active soil communities, affect soil aggregation, water dynamics, or nutrient cycling, and whether plant diversity and elevated CO2 interact. Nitrogen (N) and phosphorus (P) pools, symbiotic N2 fixation, plant litter quality, soil moisture, soil physical structure, soil nematode, collembola and acari communities, soil microbial biomass and microflora community structure (phospholipid fatty acid [PLFA] profiles), soil enzyme activities, and rates of C fluxes to soils were measured. No increases in soil C fluxes or the biomass, number, or activity of soil organisms were detected at high plant diversity; soil H2O and aggregation remained unaltered. Elevated CO2 affected the ecosystem primarily by improving plant and soil water status by reducing leaf conductance, whereas changes in C cycling appeared to be of subordinate importance. Slowed-down soil drying cycles resulted in lower soil aggregation under elevated CO2. Collembola benefited from extra soil moisture under elevated CO2, whereas other faunal groups did not respond. Diversity effects and interactions with elevated CO2 may have been absent because soil responses were mainly driven by community-level processes such as rates of organic C input and water use; these drivers were not changed by plant diversity manipulations, possibly because our species diversity gradient did not extend below five species and because functional type composition remained unaltered. Our findings demonstrate that global change can affect soil aggregation, and we advocate that soil aggregation should be considered as a dynamic property that may respond to environmental changes and feed back on other ecosystem functions.

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Section: Nitrogen and Phosphorus Relationsmentioning

confidence: 99%

INTERACTIVE EFFECTS OF PLANT SPECIES DIVERSITY AND ELEVATED CO₂ON SOIL BIOTA AND NUTRIENT CYCLING

Niklaus

Alphei

Kampichler

et al. 2007

Ecology

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“…where 15 N leg , 15 N nonleg , and 15 N atm are the 15 N-mole fractions of the total N in legumes, all nonlegume plants present in the plot, and atmospheric N 2 , respectively (Wood and McNeill 1993). Ecosystem-level nitrogen retention was estimated as the amount of the 15 N label applied in 1995 that was recovered either in the plant biomass harvested in subsequent years, or still remained in plants, microbes, litter, or soil at termination of the experiment five years later.…”

Section: Symbiotic Dinitrogen Fixation and Nitrogen Retentionmentioning

confidence: 99%

SYNTHESIS OF A SIX‐YEAR STUDY OF CALCAREOUS GRASSLAND RESPONSES TO IN SITU CO₂ ENRICHMENT

Niklaus¹,

Körner²

2004

Ecological Monographs

113

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We exposed species-rich temperate calcareous grassland to elevated CO 2 (600 L/L) for six growing seasons and studied carbon (C) and nutrient (nitrogen [N] and phosphorus [P]) cycling, water relations, and plant community structure and diversity. CO 2 enrichment stimulated leaf-and ecosystem-level daytime CO 2 uptake and increased plant community productivity; relative CO 2 effects on aboveground biomass were predicted with r ϽϪ0.98 (r 2 Ͼ 0.95) by precipitation prior to biomass harvests. The underlying mechanisms were water savings due to reduced leaf conductance under elevated CO 2 , allowing for more growth in this temporarily water-limited ecosystem; this effect was more important in dry years. At the plant-species level, no effects of [CO 2 ] were found except for the subdominant sedges Carex flacca and C. caryophyllea, which responded positively to elevated CO 2 , mainly due to increased soil moisture. Bryophytes also responded to CO 2 enrichment for the same reason. At a more aggregate level, elevated CO 2 increased species evenness (but not richness). Community productivity was N-limited; legumes derived Ͼ90% of their N from atmospheric N 2 , but did not respond to elevated CO 2 because they were limited by low P availability. This ultimately also prevented larger community-level responses to elevated CO 2 because eventually extra legume N would have been transferred to nonlegumes, resulting in extra biomass. Higher biomass in elevated CO 2 was attained by increasing C:N and C:P ratios; total N and P in plant biomass remained unaffected by [CO 2 ]. N retention, legume dinitrogen fixation (both assessed with 15 N), and microbial net N immobilization did not change. Based on our findings, our main conclusions are: (1) The effect of elevated CO 2 is mainly indirect via effects on the hydrological cycle in this waterlimited ecosystem; (2) the C cycle responds more than mineral nutrient cycles; (3) low available P ultimately limited community productivity and responses to CO 2 , and this limitation may not be atypical for many natural ecosystems in which N inventories often are controlled by biologically available P; and (4) that interactions with variable environmental conditions critically co-determine CO 2 responses, which contrasts with greenhouse studies and emphasizes the importance of field studies in predicting long-term effects of increasing [CO 2 ] on natural ecosystems.

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Biological processes in soil

Wood

1995

Environmental Soil Biology

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15N2 measurement of nitrogen fixation by legumes and actinorhizals: theory and practice

Abstract: A gas-tight chamber has been constructed to calibrate the tSN isotope dilution method against direct L5N 2 measurements. The theoretical basis for such estimates is given, and the practical problems associated with the experiments are discussed.

Cited by 6 publications

References 9 publications

INTERACTIVE EFFECTS OF PLANT SPECIES DIVERSITY AND ELEVATED CO₂ON SOIL BIOTA AND NUTRIENT CYCLING

INTERACTIVE EFFECTS OF PLANT SPECIES DIVERSITY AND ELEVATED CO₂ON SOIL BIOTA AND NUTRIENT CYCLING

SYNTHESIS OF A SIX‐YEAR STUDY OF CALCAREOUS GRASSLAND RESPONSES TO IN SITU CO₂ ENRICHMENT

Biological processes in soil

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15N2 measurement of nitrogen fixation by legumes and actinorhizals: theory and practice

Abstract: A gas-tight chamber has been constructed to calibrate the tSN isotope dilution method against direct L5N 2 measurements. The theoretical basis for such estimates is given, and the practical problems associated with the experiments are discussed.

Cited by 6 publications

References 9 publications

INTERACTIVE EFFECTS OF PLANT SPECIES DIVERSITY AND ELEVATED CO2ON SOIL BIOTA AND NUTRIENT CYCLING

INTERACTIVE EFFECTS OF PLANT SPECIES DIVERSITY AND ELEVATED CO2ON SOIL BIOTA AND NUTRIENT CYCLING

SYNTHESIS OF A SIX‐YEAR STUDY OF CALCAREOUS GRASSLAND RESPONSES TO IN SITU CO2 ENRICHMENT

Biological processes in soil

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Product

Resources

About

INTERACTIVE EFFECTS OF PLANT SPECIES DIVERSITY AND ELEVATED CO₂ON SOIL BIOTA AND NUTRIENT CYCLING

INTERACTIVE EFFECTS OF PLANT SPECIES DIVERSITY AND ELEVATED CO₂ON SOIL BIOTA AND NUTRIENT CYCLING

SYNTHESIS OF A SIX‐YEAR STUDY OF CALCAREOUS GRASSLAND RESPONSES TO IN SITU CO₂ ENRICHMENT