Understanding the spatial distribution of plant-parasitic nematodes in a cultivated horizon is important to the management of plant-parasitic nematodes in agricultural soils. Nematode distribution in the field has been described as aggregated, which implies underlying spatial dependence in nematode data. Conventional statistics are generally inadequate to describe data that are spatially correlated. However, geostatistics has become a powerful tool for analyzing the spatial distribution of nematodes. Recent studies on the spatial variability of soils have focused on soil nutrients, heavy metals, and nematode trophic groups in Northeast China, however, there is no information on the spatial distribution of plant-parasitic nematodes in Chinese agroecosystems. The objectives of this study were to describe the field-scale spatial distribution of total plant-parasitic nematodes and their dominant genera in a Chinese Ecosystem Research Network (CERN) site in Northeast China, and develop maps illustrating their horizontal and vertical distribution patterns.
The spatial distribution characteristics of plant-parasitic nematodes in a cultivated horizon of a site-specific experimental field at the Shenyang Experimental Station of Ecology, Chinese Academy of Sciences, was investigated using traditional statistics combined with geostatistics. A 42m×30 m plot was divided into grids with 7m×5 m spacing including 49 sampling points. Soil samples were collected from depths of 0～10 cm and 10～20 cm. The results showed that genera of Helicotylenchus and Tylenchus were the most dominant plant-parasitic nematodes at both depths and Tylenchorchychus was the dominant genus at the 10～20 cm depth, with the three genera together representing 92% of total plant-parasitic nematodes on average. Geostatistical analysis indicated that a major part of this variability was spatially-dependent; variograms suggest that 48％～100% of sample population variance was related to spatial autocorrelation over ranges of 35～91 m at both depths except Tylenchorchychus at a depth of 10～20 cm. The mean numbers of total plant-parasitic nematodes, Helicotylenchus, Tylenchus, and Tylenchorchychus, were higher at the 0～10 cm depth than at the 10～20 cm depth. Similar distributions of total plant-parasitic nematodes and Helicotylenchus at each depth were observed, while Tylenchus and Tylenchorchychus nematodes exhibited a similar spatial trend for both depths. Our results reflect possible stronger dispersion of Tylenchus and Tylenchorchychus nematodes in vertical distribution. The maps obtained with kriging illustrate horizontal and vertical distribution patterns of plant-parasitic nematodes at the field scale.