Effects Of Long-Term Agricultural Practices On Soil Nematode Communities In The Huang-Huai-Hai Plain

Agricultural ecosystems provide the basis for human survival and development,and are of great significance to sustainable human development and human health.The Huang-Huai-Hai Plain is one of the most important grain production bases in China,mainly through the application of fertilization and straw return to the field and other agricultural practices to achieve grain production.Soil organisms are important components of belowrground ecosystems,and almost all soil processes are related to soil organisms,which have a great diversity and also perform important ecological functions.However,we lack an in-depth understanding of the effects of these common agricultural practices,particularly long-term agricultural practices,on soil biodiversity.Nematodes are the most abundant multicellular animals on Earth,they are also cosmopolite highly abundant in species and are often the dominant biological components in soil.In addition,nematodes occupy a key position in the soil food webs,therefore,understanding the effects of different agricultural practices on the composition and diversity of soil nematode communities and clarifying the changes in the ecological functions of soil microfood webs reflected by soil nematodes under different agricultural practices are important for establishing an evaluation system for the health level of agricultural ecosystems and providing a scientific basis for the healthy development of agricultural ecosystems,food security production and sustainable agricultural development.To investigate the effects of different agricultural practices(inorganic fertilizer application,organic fertilizer application,straw return,combined inorganic and organic fertilizer,and combined inorganic fertilizer application and straw return)on soil nematode communities.This study was conducted at five long-term research stations of agriculture ecosystems(Hengshui,Laiyang,Yuanyang,Xuzhou and Mengcheng),which are located in the Huang-HuaiHai Plain.The main results are as follows:(1)The composition of nematode community did not change under long-term agricultural practice,and only a few genera of bacterial-feeding and plant-parasitic nematodes changed,such as Cephalobus(bacterial-feeding nematodes)and Pratylenchus(plant-parasitic nematodes),(2)In present study,long-term agricultural practices did not affect on the diversity of nematodes,but had a positive effect on the bacterial-feeding nematodes at low trophic level(P<0.05),and tended to have a negative effect on the omnivorous-predatory nematodes at high trophic level(0.05<P<0.1).In addition,application of organic fertilizer decreased the density of fungal-feeding nematodes,while combination of inorganic fertilizers and straw returning increased the density of bacterial-feeding nematodes.(3)All long-term agricultural practices had positive effects on the basal index of nematodes,and the organic fertilizer application and the combination of inorganic fertilizer and straw return treatment reached a statistically significant level,while the organic fertilizer application and the combination of inorganic and organic fertilizer had significant negative effects on the structure index of nematodes.inorganic fertilizer application,organic fertilizer application,combined organic and inorganic fertilizer application treatment and the combination of inorganic fertilizer and straw return treatment had significant negative effects on maturity index.All the experimental treatments had little effect on the enrichment index and the maturity index of plant parasite nematodes.(4)The agricultural practices that had a greater effect on soil nematode energy fluxes were organic fertilizer application or combined organic and inorganic fertilizer application,the importance is above70%.Inorganic fertilizer application,combined organic and inorganic fertilizer application treatment and the combination of inorganic fertilizer and straw return treatment significantly increased the enriched metabolic footprint of soil nematodes,and tended to increase the metabolic footprint of bacterial-feeding nematodes.(5)All of the agricultural practices did not alter the ratio of microbivorous nematodes to plantparasitic nematodes on a long-term temporal scale.Taken together,long-term fertilization and straw return-related agricultural practices did not alter the community composition of nematodes in soil ecosystems,and only a few genera of bacterial-feeding and plant-parasitic nematodes changed,tending to negatively affect the density of omnivorous-predatory nematodes at higher trophic levels and positively affect the density of bacterial-feeding nematodes.However,long-term agricultural practices related to fertilizer application and straw return did not alter nematode diversity.All of the long-term agricultural practices positively affected nematode basal index and negatively affected nematode structural index,suggesting that these agricultural practices related to fertilization and straw return tended to alter nematode community structure by increasing the weight of r-strategists(low trophic level,small body size,sensitive to nutrient)and decreasing the weight of K-strategists(high trophic level,large body size,sensitive to disturbance).In addition,considering that the practices that had a greater effect on nematode energy fluxes were related to the organic fertilizer application(organic fertilizer application treatments and combined inorganic and organic fertilizer application treatments),it is possible that the application of organic fertilizers may be more likely to affect nematode activity.Inorganic fertilizer application,combined inorganic and organic fertilizer application treatment,combined inorganic fertilizer and straw return treatment significantly increased the enrichment metabolic footprint of nematodes,and tended to increase the bacterial footprint.In contrast,the experimental treatments related to fertilizer application and straw return did not affect the ratio of microbivorous nematodes to plant-parasitic nematodes,so these treatments may not have changed the effect of nematodes on crop growth.In conclusion,long-term fertilization and straw-return-related agricultural practices altered weights of different trophic groups of nematodes,and although the feedback on crop growth was not altered,the changes exhibited by the whole nematode community(e.g.,suppression of higher trophic level nematodes)reflect a possible reduction in the health of the soil food web,which in turn may inhibit the ecological function of the nematode community.