Centre for Ecology and Hydrology

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Centre for Ecology and Hydrology
Introduction

• The upland regions of Scotland are dominated by a
  contrasting mosaic of ericoid mycorrhizal (ErM)
  dominated heath and arbuscular mycorrhizal (AM)
  dominated grassland communities.
• Both mycorrhizal types improve host plant
  nutrition in pot studies and may therefore affect
  species interactions in the field.
• The ErM shrub Calluna vulgaris and invasive AM
  grass Nardus stricta were used as model species
  to investigate the potential role of mycorrhizas
  in the observed replacement of heathland by
  grassland ( ).

Invasion of Calluna heath (right) by Nardus
grassland (left) reduces grazing quality and
game-bird breeding habitats.
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1) ErM colonization inhibits Nardus root growth
in surface organic layers...

• Nardus was grown alone, or in competition with
  Calluna, in a layered organic/sand substrate (
  ), with and without inoculation with the ericoid
  mycorrhizal endophyte Hymenoscyphus ericae, and
  with and without the addition of nitrogen.

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The substrate consisted of a surface organic
layer. This approximated organic matter
distribution in a natural heathland soil.
Suppression of Nardus growth by Calluna
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• Calluna proliferated roots in, and excluded
  Nardus roots from, the organic surface substrate
  layer irrespective of mycorrhizal status or
  nitrogen fertilisation ( ). This resulted in
  Calluna being a superior competitor over Nardus
  for nutrients ( ).
• Irrespective of fertiliser treatment, ErM
  colonisation of Calluna caused a further
  reduction in Nardus root length in the organic
  layer ( )and reduced Nardus leaf blade
  production ( ) but did not reduce Nardus shoot
  nutrient content (as indicated by an increase in
  shoot phosphorus concentration ( )).
• This suggests that ErM suppression of Nardus
  growth was not due to enhanced nutrient
  competition, but to non-nutritional interference.

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Nardus plants did not produce as many leaf blades
when grown with ErM Calluna.
Nardus plants grown with ErM Calluna had greater
concentrations of phosphorus in their shoots.
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2) AM colonization of Nardus increases with host
density...
RLC of Nardus increases with Nardus cover at
Glen Clunie.
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RLC of Nardus is negatively correlated with
Nardus shoot phosphorus concentration at Glen Shee
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RLC increases with Nardus cover at Glen Shee,
but only after variation due to Nardus tissue
phosphorus concentration is removed.
RLC of Nardus bioassay transplants in Calluna
and Nardus swards.
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Conclusions

• Suppression of Nardus root growth in surface
  organic horizons by ErM colonised Calluna, and
  lack of AM inoculum availability in Calluna
  swards are suggested as potential below-ground
  constraints to the rate at which Nardus invades
  Calluna heath.