Relationship of crop and rainfall to soil nematode community structure in perennial agroecosystems

Population densities in soil of nematodes belonging to different genera were monitored for 3 years in a citrus grove and an adjacent bahiagrass pasture in Florida, USA, to determine whether indices of community structure or densities of key genera were more useful in characterizing the soil nematode communities of these very different perennial agroecoystems. Population densities of Acrobeles, Aphelenchus, Cervidellus, Ironus, Paratrichodorus, and Zeldia were consistently greater (P less than or equal to 0.10) in the citrus site, where 64% to 83% of the nematodes found were bacterivores and only 1% to 16% herbivores. The pasture, containing 19% to 47% bacterivores and 25% to 67% herbivores, had greater numbers of Bunonema, Criconema, Criconemella, Eucephalobus, Hemicriconemoides, Miconchus, Tylenchorhynchus, and Wilsonema. Several indices of nematode community structure also showed consistent differences with site. The Shannon-Weaver diversity index, calculated across trophic groups, was greater in the pasture, but Simpson's index and the ratio of decomposers to herbivores were greater in citrus, reflecting the preponderance of bacterivores at that site. Within each site, population densities of nematodes in several key genera were correlated with rainfall over time, but correlations between rainfall and indices of community structure were infrequent. (C) 1997 Elsevier Science B.V.