Biodiversity of indigenous tussock grassland sites in Otago, Canterbury and the central North Island of New Zealand II. Nematodes

Soil samples were taken from around the base of tussock plants and paired areas of inter-tussock vegetation at four native tussock grassland sites across New Zealand, in three consecutive summers. Seventy nematode taxa were identified with the plant associated nematode trophic group being the most abundant at three of the four sites. Of the plant parasitic nematodes, Criconema, Pratylenchus, and Helicotylenchus spp. were found at all sites, with Hemicycliophora, Longidorus, a putative Punctodera, and Rotylenchus found at only one site each. The observation of mermithid nematodes at three of the four sites, coupled with absence of insect parasitic Steinernema or Heterorhabditis sp. from microscopic observations and soil baiting suggests that the insect parasitism niche is occupied largely by mermithids in the tussock grassland habitats studied. A range of community indices were calculated, with Shannon-Weiner (2.10-2.39), Simpson dominance (0.129-0.205), Maturity Index (2.67-2.92), and Structure Index (67.7-87.5) being significantly different among sites. Total nematode abundance was significantly greater beneath tussock than inter-tussock vegetation, but the number of nematode taxa and species richness were significantly greater from inter-tussock samples. This suggests that tussocks may provide a more productive habitat but that the increased diversity of the vegetation in inter-tussock areas is reflected in some measures of nematode diversity. Comparisons are made and discussed with other studies of native grassland nematodes in New Zealand and worldwide.