| Abstrakt: |
ABSTRACTThe ability of some ectomycorrhizal fungi to access organic sources of nitrogen is known to influence decomposition, nitrogen mineralisation and soil carbon storage. The consequences for aboveground ecosystem structure and processes are less well-documented. We used the LAI-2200C Plant Canopy Analyzer to compare leaf area index and understorey light availability of ectomycorrhizal Nothofagusstands and arbuscular mycorrhizal podocarp-broadleaf stands growing on similar soils at a dry forest site in the Wairarapa district of New Zealand’s North Island. N. solandriwas the sole overstorey tree in the three Nothofagusstands, and the ericaceous shrub Leucopogon fasciculatuswas prominent in the understorey. The three podocarp-broadleaf stands were more diverse and more varied, the major contributors to basal area being Elaeocarpus dentatus, Hedycarya arborea, Cyathea dealbata, Carpodetus serratusand Dacrydium cupressinum. Leaf area index of Nothofagusstands averaged one unit lower (4.04) than that of neighbouring podocarp-broadleaf stands (5.11). Average light availability under Nothofagusstands (3.6–4.9%) was twice that beneath podocarp-broadleaf stands (1.6–2.1%). The lower leaf area index, greater light transmittance, and monodominance of Nothofagusstands probably reflects suppression of arbuscular mycorrhizal species by ectomycorrhizal short-circuiting of the nitrogen cycle. This study expands the evidence of positive feedback mechanisms stabilising ectomycorrhizal dominance in some forests. |
