Effects of elevated atmospheric CO2 on nematode trophic groups in a Chinese paddy-field ecosystem

Soil fauna plays significant roles in the detritus food webs of agroecosystems, they are the essential contributors to the decomposition of soil organic matter, mineralization of plant nutrients and nutrient cycling. Some evidences indicate that soil fauna of the detritus food webs appears to show positive, neutral or negative responses to global change, especially atmospheric CO2 enrichment across different studies. Soil nematodes are representative of a large portion of this fauna, since they are abundant and trophically diverse in most soils. The free-air CO2 enrichment (FACE) technology was used to expose three plots of rice (Oryza sativa) under elevated (ambient + 200 mumol.mol-1) atmospheric CO2, while three control plots were outfitted with FACE apparatus under ambient CO2. Nematode trophic groups were monitored in this study at depths of 0-5 cm and 5-10 cm during rice jointing and ripening stages in Wuxi site, China. Significant differences were found between depths and sampling dates in the total numbers of nematodes, bacterivores, plant parasites and omnivores-predators during the study period. The total numbers of nematodes and bacterivores at the 5-10 cm depth were higher in treatment plots than in control plots across all sampling dates. At 0-5 cm depth, the numbers of bacterivores were higher in treatment plots than in control plots, while those of omnivores-predators exhibited an inverse trend during the study period. Significant differences were also observed between treatment plots and control plots in the numbers of fungivores in our experiment.