Tillage effects outweigh seasonal effects on soil nematode community structure

Our understanding of tillage effect on soil community structure during the growing season remains limited. This study aims to test the hypothesis that (1) soil community responds specifically to tillage practices and these responses vary with the growing season; (2) the contribution of tillage to soil community is greater than or equal to that of growing season when considering the impact of tillage on soil properties. Therefore, the nematode community usually used as an indicator of soil organisms was investigated under a long-term (initiated in 2001) tillage experiment (CT, conventional tillage; RT, ridge tillage; NT, no tillage) in a Black soil (Typic Hapludoll) of Northeast China. Soil samples were taken in April, June and August of 2015 at 0–5 and 5–15 cm depths during the growing season of soybean (Glycine max Merr.). The results showed that nematodes responded specifically to tillage practices at both soil depths, and there was a consistent succession of specifically enriched genera from Filenchus in CT to Rhabditis in RT and then to Prismatolaimus in NT in 0–5 cm over the growing season. The response of nematodes to tillage was consistent with crop phenology to a certain degree. For example, the highest value of Helicotylenchus relative abundance in RT at 0–5 cm was observed in June, which corresponded with the maximum root activity period for soybeans. Variation partitioning analysis revealed that tillage played a more important role than growing season in constructing nematode community. The contribution of tillage was greatly increased in the model with soil properties as associated variables, indicating that tillage may indirectly affect nematode community through alteration of soil properties, such as pH at 0–5 cm and bulk density (BD) at 5–15 cm. These results provide strong support for our hypothesis and suggest that the effects of long-term conservation tillage on soil nematode community may be maintained throughout the growing season, which might be a cornerstone of conservation tillage benefits in temperate areas of the world.