Assessing nitrogen fixation in mixed- and single-species plantations of 'Eucalyptus globulus' and 'Acacia mearnsii'

Forrester, David I; Schortemeyer, Marcus; Stock, William D; Bauhus, Jurgen; Khanna, Partap K; Cowie, Annette

doi:10.1093/treephys/27.9.1319

Author(s)

Forrester, David I

Schortemeyer, Marcus

Stock, William D

Bauhus, Jurgen

Khanna, Partap K

Cowie, Annette

Publication Date

2007

Abstract

Mixtures of 'Eucalyptus globulus' Labill. and 'Acacia mearnsii' de Wildeman are twice as productive as 'E. globulus' monocultures growing on the same site in East Gippsland, Victoria, Australia, possibly because of increased nitrogen (N) availability owing to N₂ fixation by 'A. mearnsii'. To investigate whether N2 fixation by 'A. mearnsii' could account for the mixed-species growth responses, we assessed N₂ fixation by the accretion method and the 15N natural abundance method. Nitrogen gained by 'E. globulus' and 'A. mearnsii' mixtures and monocultures was calculated by the accretion method with plant and soil samples collected 10 years after plantation establishment. Nitrogen in biomass and soil confirmed that 'A. mearnsii' influenced N dynamics. Assuming that the differences in soil, forest floor litter and biomass N of plots containing 'A. mearnsii' compared with 'E. globulus' monocultures were due to N₂ fixation, the 10-year annual mean rates of N₂ fixation were 38 and 86 kg ha⁻¹ year⁻¹ in 1:1 mixtures and 'A. mearnsii' monocultures, respectively. Nitrogen fixation by 'A. mearnsii' could not be quantified on the basis of the natural abundance of 15N because such factors as mycorrhization type and fractionation of N isotopes during N cycling within the plant confounded the effect of the N source on the N isotopic signature of plants. This study shows that 'A. mearnsii' fixed significant quantities of N₂ when mixed with 'E. globulus'. A decline in δ15N values of 'E. globulus' and 'A. mearnsii' with time, from 2 to 10 years, is further evidence that N2 was fixed and cycled through the stands. The increased aboveground biomass production of 'E. globulus' trees in mixtures when compared with monocultures can be attributed to increases in N availability.

Citation

Tree Physiology, 27(9), p. 1319-1328

ISSN

1758-4469

0829-318X

Link

https://hdl.handle.net/1959.11/9008

Language

en

Publisher

Oxford University Press

Title

Assessing nitrogen fixation in mixed- and single-species plantations of 'Eucalyptus globulus' and 'Acacia mearnsii'

Type of document

Journal Article

Entity Type

Publication

Author(s)	Forrester, David I Schortemeyer, Marcus Stock, William D Bauhus, Jurgen Khanna, Partap K Cowie, Annette
Publication Date	2007
Abstract	Mixtures of 'Eucalyptus globulus' Labill. and 'Acacia mearnsii' de Wildeman are twice as productive as 'E. globulus' monocultures growing on the same site in East Gippsland, Victoria, Australia, possibly because of increased nitrogen (N) availability owing to N₂ fixation by 'A. mearnsii'. To investigate whether N2 fixation by 'A. mearnsii' could account for the mixed-species growth responses, we assessed N₂ fixation by the accretion method and the 15N natural abundance method. Nitrogen gained by 'E. globulus' and 'A. mearnsii' mixtures and monocultures was calculated by the accretion method with plant and soil samples collected 10 years after plantation establishment. Nitrogen in biomass and soil confirmed that 'A. mearnsii' influenced N dynamics. Assuming that the differences in soil, forest floor litter and biomass N of plots containing 'A. mearnsii' compared with 'E. globulus' monocultures were due to N₂ fixation, the 10-year annual mean rates of N₂ fixation were 38 and 86 kg ha⁻¹ year⁻¹ in 1:1 mixtures and 'A. mearnsii' monocultures, respectively. Nitrogen fixation by 'A. mearnsii' could not be quantified on the basis of the natural abundance of 15N because such factors as mycorrhization type and fractionation of N isotopes during N cycling within the plant confounded the effect of the N source on the N isotopic signature of plants. This study shows that 'A. mearnsii' fixed significant quantities of N₂ when mixed with 'E. globulus'. A decline in δ15N values of 'E. globulus' and 'A. mearnsii' with time, from 2 to 10 years, is further evidence that N2 was fixed and cycled through the stands. The increased aboveground biomass production of 'E. globulus' trees in mixtures when compared with monocultures can be attributed to increases in N availability.
Citation	Tree Physiology, 27(9), p. 1319-1328
ISSN	1758-4469 0829-318X
Link	https://hdl.handle.net/1959.11/9008
Language	en
Publisher	Oxford University Press
Title	Assessing nitrogen fixation in mixed- and single-species plantations of 'Eucalyptus globulus' and 'Acacia mearnsii'
Type of document	Journal Article
Entity Type	Publication

Assessing nitrogen fixation in mixed- and single-species plantations of 'Eucalyptus globulus' and 'Acacia mearnsii'

Files: