Effects of simulated elevated carbon dioxide concentrations on soil meso- and micro-fauna diversity and trophic structure in the Sanjiang Plain

Understanding the response characteristics of wetland soil fauna under elevated CO₂ concentrations is fundamental to wetland biodiversity conservation. The aim of this study was to assess the effect of high CO₂ concentrations (370, 550, and 700 ppm) on the soil fauna of a Calamagrostis angustifolia wetland in the Sanjiang Plain. Experiments were conducted in an open top chamber using the Tullgren and Baermann funnels to extract soil animals. The results showed that: 1) a total of 4, 985 soil fauna belonging to 62 groups (statistics presented to the family level except for Acerentomata; statistics for larvae and adults presented separately) from 7 classes in 13 orders were obtained and they showed significant differences under different CO₂ concentrations (P < 0.05). 2) With the increase in CO₂ concentrations, the abundance of soil fauna increased and the Pielou index decreased significantly (P < 0.05), but no significant changes were observed in the Shannon-Wiener, Simpson, and Margalef indexes (P > 0.05). 3) With the increase in CO₂ concentrations, the abundance of omnivorous and saprophagous functional groups increased significantly (P < 0.05), but the abundance and group number of phytophagous and predatory functional groups exhibited no significant change (P > 0.05). 4) Redundancy analysis revealed the relationship between the total number of soil fauna and soil organic matter, soil total phosphorus, and Calamagrostis angustifolia biomass with significant correlation (P < 0.05) observed between them. However, the total number of soil fauna had an insignificant effect on other soil environmental factors (P > 0.05). It is obvious that Calamagrostis angustifolia biomass, soil organic matter, and soil total phosphorus affect the abundance distribution and the distribution characteristics of functional groups of soil meso- and micro-fauna in the Sanjiang Plain.