III. Vertical distribution at eleven sites

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Abstract
Soil samples from 0–2.5, 2.5–5, 5–7.5, 7.5–10, 10–20, and 20–30 cm in Patumahoe, Oturoa, Rotoiti, Stratford, Egmont, Tokomaru, Kokotau, Kaitoke, Otiake, Edendale, and Waikiwi soils were collected in spring and total nematode populations found to be 1 097 000–9 595 000/m2. Over the 11 sites vertical distribution at the 6 depths (46, 24, 11, 7, 9, 3% in successive strata) was most significantly correlated with soil carbon and readily available soil phosphorus. It is considered the causal correlation of nematodes is with root growth. Correlations with soil physical factors are given. A total of 37 genera were identified, 14–20 being found at each site. Mean number of genera in the strata sampled was 14,13,12,9,10,6. The greatest diversity of genera occurred in Oturoa sand, a soil derived from a 90-year-old volcanic ash shower. Populations for each genus, depth, and site are given. Complementary distributions found include Aphelenchoides/Aphelenchus, Heterocephalobus/Cephalobus, Anaplectus/Plectus, Monhystera + Chromadoridae/ Rhabditidae + Plectidae. Tylenchida and Dorylaimida also appear to be complementary; the large biomass of the Dorylaimida populations suggests many of them may be directly dependent on plants for food, as are Tylenchida.