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. 2007 Jun;99(6):1101-9.
doi: 10.1093/aob/mcm061. Epub 2007 Apr 27.

Nitrogen fixation associated with Suillus tomentosus tuberculate ectomycorrhizae on Pinus contorta var. latifolia

L R Paul  1 , B K Chapman, C P Chanway
Affiliations

Nitrogen fixation associated with Suillus tomentosus tuberculate ectomycorrhizae on Pinus contorta var. latifolia

L R Paul et al. Ann Bot. 2007 Jun.

Abstract

Background and aims: Tuberculate ectomycorrhizae are a unique form of ectomycorrhiza where densely packed clusters of mycorrhizal root tips are enveloped by a thick hyphal sheath to form a tubercle. The functional significance of such a unique structure has not previously been established. The purpose of the present study was to investigate and measure the potential nitrogenase activity associated with Suillus tomentosus/Pinus contorta tuberculate ectomycorrhizae in two stand ages, young and old, and across a range of nitrogen-poor soil conditions.

Methods: Short roots were compared with other mycorrhizae and non-mycorrhizal secondary roots using tuberculate ectomycorrhizae. Assessment of nitrogenase activity was determined and quantitative measurements were taken on tuberculate ectomycorrhizae in situ in a variety of different circumstances, by using an adaptation of the acetylene reduction assay.

Key results: Significant nitrogenase activity was measured associated with S. tomentosus/P. contorta tuberculate ectomycorrhizae whereas no nitrogenase activity was measured with non-tuberculate mycorrhizae or secondary roots without mycorrhizae. Average nitrogenase activity ranged from undetectable to 5696.7 nmol C2H4 g(-1) tubercle 24 h(-1). Maximum nitrogenase activity was 25,098.8 nmol C2H4 g(-1) tubercle 24 h(-1). Nitrogenase activity was significantly higher in young stands than in old stands of P. contorta. Season or some covariate also seemed to affect nitrogenase activity and there was suggestion of a site effect.

Conclusions: Suillus tomentosus/P. contorta tuberculate ectomycorrhizae are sites of significant nitrogenase activity. The nitrogenase activity measured could be an important contribution to the nitrogen budget of P. contorta stands. Season and stand age affect levels of nitrogenase activity.

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Figures

F<sc>ig</sc>. 1.
Fig. 1.
(A) Pinus contorta root with Suillus tomentosus tuberculate ectomycorrhizae cleaned of woody material ready for insertion into incubation tube. (B) Acetylene reduction assay incubation tube showing plunger assembly (P) inserted, gas retention vial (RV) within incubation tube, and retention vial septum (IS) placed in the vial opening. (C) Acetylene reduction assay incubation tube being flushed with inert argon gas via the injection line (AI) and being vented by the evacuation needle (EV). (D) Acetylene reduction assay incubation system showing evacuation syringe (ES), argon injection syringe (AS) and incubation tube (IT).
F<sc>ig</sc>. 2.
Fig. 2.
Data showing average nmol C2H4 g−1 Suillus tomentosus/Pinus contorta tubercle 24 h−1 based on soil type and stand age classes: (A) soil types from spring 1997, (B) stand age classes from spring 1997, (C) soil types from summer 1997, (D) stand age class from summer 1997, (E) soil types from summer 1998 and (F) stand age class from summer 1998. Maximum values are represented by asterisks. Dry basaltic = Alex Graham, Wet basaltic = Puntzi Lake, Granitic = Nimpo Lake; Class 2 = young stands (<40 years), Class 8 = old stands (>140 years).
See this image and copyright information in PMC

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