A sequential extraction procedure reveals that water management affects soil nematode communities in paddy fields

The effects of management in maintaining high rice yield with less water have received increasing attention in sub-tropical regions where seasonal drought is very severe. To test whether water management affects soil ecological process we compared the soil nematode communities in paddy field soils following water management treatments imposed during late rice cropping. The treatments were continuously flooded rice cultivation (CF), non-continuously flooded rice cultivations without (ZM) and with (M) rice straw mulching. A sequential extraction procedure involving Baermann extraction (Baermann) followed by centrifugal sugar flotation (centrifugation) was used to extract the whole nematode community. Based on the analysis of nematode abundance, genera composition, trophic groups and other ecological indices (Margalef richness index, Shannon index, maturity index, enrichment index and structure index), water management significantly affected the nematode community, with the non-continuously flooded condition, in particular combination with rice straw mulching (M), stimulating nematode development. There was a high abundance, richness, and structure in the nematode community in mulched treatments, indicating improved biodiversity and biological interactions. We hypothesize that soil microclimate and available food resources are affected by water management and directly or indirectly influence the establishment of different nematode communities. We suggested that studies aiming to test natural or anthropogenic influences on nematodes might be distorted by sole use of the Baermann method. Although the Baermann step in a sequential extraction procedure gave valuable information on nematode responses to soil treatments, it was not sufficient to detect effects on the whole nematode community. Our results demonstrate that the sequential extraction procedure is an effective tool to obtain comprehensive information on the whole nematode community, with both steps providing complementary ecologically relevant information, on how the soil ecosystem is affected by human management.