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N2 fixation and cycling in Alnus glutinosa, Betula pendula and Fagus sylvatica woodland exposed to free air CO2 enrichment

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journal contribution
posted on 24.10.2013, 15:10 by Jonathan MillettJonathan Millett, Douglas Godbold, Andrew R. Smith, Helen Grant
We measured the effect of elevated atmospheric CO on atmospheric nitrogen (N ) fixation in the tree species Alnus glutinosa growing in monoculture or in mixture with the non-N -fixing tree species Betula pendula and Fagus sylvatica. We addressed the hypotheses that (1) N fixation in A. glutinosa will increase in response to increased atmospheric CO concentrations, when growing in monoculture, (2) the impact of elevated CO on N fixation in A. glutinosa is the same in mixture and in monoculture and (3) the impacts of elevated CO on N cycling will be evident by a decrease in leaf δ N and by the soil-leaf enrichment factor (EF), and that these impacts will not differ between mixed and single species stands. Trees were grown in a forest plantation on former agricultural fields for four growing seasons, after which the trees were on average 3.8 m tall and canopy closure had occurred. Atmospheric CO concentrations were maintained at either ambient or elevated (by 200 ppm) concentrations using a free-air CO enrichment (FACE) system. Leaf δ N was measured and used to estimate the amount (N ) and proportion (%N ) of N derived from atmospheric fixation. On average, 62% of the N in A. glutinosa leaves was from fixation. The %N and N for A. glutinosa trees in monoculture did not increase under elevated CO , despite higher growth rates. However, N fixation did increase for trees growing in mixture, despite the absence of significant growth stimulation. There was evidence that fixed N was transferred from A. glutinosa to F. sylvatica and B. pendula, but no evidence that this affected their CO response. The results of this study show that N fixation in A. glutinosa may be higher in a future elevated CO world, but that this effect will only occur where the trees are growing in mixed species stands.

History

School

  • Social Sciences and Humanities

Department

  • Geography and Environment

Published in

Oecologia

Volume

169

Issue

2

Pages

541 - 552

Citation

MILLETT, J. ... et al, 2012. N2 fixation and cycling in Alnus glutinosa, Betula pendula and Fagus sylvatica woodland exposed to free air CO2 enrichment. Oecologia, 169 (2), pp.541-552.

Publisher

© Springer-Verlag

Version

AM (Accepted Manuscript)

Acceptance date

31/10/2011

Publication date

2011-12-18

Notes

The final publication is available at link.springer.com.

ISSN

0029-8549

Language

en