Effects Of Land Use Change On Soil Nematode Communities In Huang-Huai-Hai Region

In agricultural ecosystems,changes in land use practices can lead to changes in soil habitats,which in turn can affect the composition,diversity and abundance of soil organisms that live in them,and the ecosystems that they dominate.As a major grain-producing region in China,understanding the effects of land use change on soil biological communities of the Huang-Huai-Hai region can help us better understand soil health and thus contribute to sustainable agriculture.Nematodes are widely distributed in the soil and are highly sensitive to environmental changes.Different ecological indicators of nematodes can be used to indicate changes in the soil environment,and these advantages can help us better study how changes in land use practices affect soil ecosystem processes.Previous studies have mostly selected different land use practices at one site,but few studies have selected multiple sampling sites and repeated sampling.In this study,five representative agricultural sampling stations in the Huang-Huai-Hai region,located in Hengshui,Laiyang,Yuanyang,Xuzhou,and Mengcheng,were selected.A completely unfertilized field treatment within the station was used as a control,and adjacent land use types were selected outside the station,including conventionally fertilized farmland,fallow land and planted forests converted from conventionally fertilized farmland.The effects of different land use practices on soil nematode community were evaluated based on soil nematode density,community composition and structure,diversity indices,and ecological function indices in combination with soil physical and chemical properties.The main conclusions of this study are as follows.(1)The different land use practices,such as conventionally fertilized farmlands,fallow lands and planted forests converted from conventionally fertilized farmlands,had no significant effect on the total density of soil nematodes compared to completely unfertilized farmlands.However,the densities of bacterial nematodes were significantly higher in conventionally fertilized farmlands and fallow lands than in completely unfertilized farmlands;the colonizer-persister(c-p)group of nematodes,the densities of c-p1 nematodes were also significantly higher in other soils under land use practices than in completely unfertilized farmlands,and the densities of c-p2 nematodes were significantly higher in conventionally fertilized farmlands and fallow lands than in completely unfertilized farmlands.(2)Compared to completely unfertilized farmlands,different land use practices such as conventionally fertilized farmlands,fallow lands and planted forests converted from conventional fertilized farmlands resulted in some shifts in the community composition of soil nematodes,tending to occur at some lower trophic levels of bacterial-feeding and fungal-feeding nematodes,with few shifts in omnivorouspredatory nematodes.In terms of the ratios of different trophic groups,compared to completely unfertilized farmlands,conventional fertilized farmlands and fallow lands significantly increased the ratio of microbivorous to plant-parasitic nematodes,significantly decreased the ratio of omnivorous-predatory nematodes to microbivorous nematodes,and fallow lands significantly decreased the ratio of fungal-feeding to bacterial-feeding nematodes and significantly promoting the ratio of bacterial-feeding to microbivorous nematodes,while planted forests had no significant effect on the ratios of the trophic groups.(3)Compared to completely unfertilized farmlands,conventional fertilization,and conversion of conventional fertilized farmlands to fallow lands and planted forests did not significantly affect the diversity of soil nematodes at the genus level,except that conventional fertilized farmlands significantly reduced the nematode Shannon-Wiener diversity index.(4)Compared to completely unfertilized farmland,conventionally fertilized farmland can result in the suppression of high trophic level K-strategists and the dominance of low trophic level r-strategists.(5)Compared to completely unfertilized farmlands,changes in organic carbon are more likely to affect nematode communities relative to soil nitrogen-related properties.In summary,different land use practices did not significantly affect the total density of soil nematodes compared to completely unfertilized farmlands,and the taxonomic diversity of soil nematodes at the family/genus level was not sensitive to the change in land use practices,but there was a shift in the community composition of soil nematodes,mainly in the lower trophic levels of bacterial and fungal feeding nematodes.Additionally,the structural index was significantly lower and the basal index was significantly higher in conventionally fertilized farmlands than in completely unfertilized farmlands,suggesting that disturbances from human agricultural practices such as fertilization may cause r-strategists at lower trophic level to become dominant taxa and K-strategists at higher trophic level,to become more suppressed.Compared to completely unfertilized farmlands,different land use practices,such as conventionally fertilized farmlands,fallow lands and planted forests converted from conventionally fertilized farmlands,significantly reduced the maturity index of free-living nematodes and significantly increased the ratio of plant-parasitic nematode maturity index to free-living nematode maturity index,suggesting that the status of soil health and the ability to resist external disturbances may be reduced under these land use practices.In addition,structural equation modelling analysis showed that conventional fertilization,and conversion of conventional fertilized farmlands to fallow lands and planted forests had a negative impact on nematode communities,reflecting a decline in soil health and reduced ability to resist external interference.In conclusion,the above results on nematode communities reflect to some extent the health of soil food webs under different land use practices,providing information on soil biology for the development of local land use policies and data to better serve sustainable agriculture.