Abstract: The construction of soil biodiversity gradient is a key step to examine the relationship between biodiversity and ecological function in the underground ecosystem. Previous methods used to construct soil biodiversity gradient are lack of wholeness. In this study, we proposed a new method that mixed the un-sterilized and sterilized soil with gamma radiation. Soil nematode community was used as model community because it covers several trophic levels. We determined whether soil nematode community in different crossmixing soils could maintain significant biodiversity differences, and whether soil properties could be consistent in different soils. Soils were collected from a natural woodland and an adjacent vegetable field. A greenhouse pot experiment was conducted with three treatments: (1) original vegetable field soil mixed with original woodland soil (FW); (2) sterilized vegetable field soil mixed with original woodland soil (SFW); (3) sterilized woodland soil mixed with original vegetable field soil (SWF). The results showed that there were no significant differences in soil pH, available potassium, organic matter, electrical conductivity, available phosphorus, total nitrogen and ammonium nitrogen between SFW and SWF, but soil nitrate nitrogen content in SWF was significantly higher than that of the other treatments (P<0.05). Bacterivores were predominant in SWF, accounting for more than 90% of the total population, while in SFW, bacterivores, and herbivores were dominant. The number of nematode taxa, Shannon index and trophic group diversity in SFW were significantly higher than those in SWF (P<0.05), whereas the dominance index showed an opposite trend. Nematode function index such as Wasilewska index, nematode channel ratio, maturity index, sigma maturity index, channel index and structure index showed significant differences between SFW and SWF. Results of principal component analysis showed that soil nematode communities were clearly different among the three treatments. In conclusion, this new method could effectively construct a nematode diversity gradient, while keeping similar physicochemical properties of the new mixed soils.

Key words: soil food web, biodiversity, regulation, soil sterilization, gamma irradiation.