Influence of soil faunal properties and understory fine root on soil organic carbon in a “mesh bag” approach

• A special type of fine mesh bags was applied to exclude fine root out of soil.
• Understory fine root influences more variations of SOC than each faunal properties.
• Faunal diversity seems more important than individual taxa abundances to SOC.
• Evenness of abundances between taxa seems more important than taxa richness to SOC.

The obstruction of fine mesh bag has been widely applied to study the functions of plant fine roots and soil fauna in ecosystems. However, plant fine roots and soil fauna can both be either excluded from the soil within fine mesh bags or admitted into the soil without mesh bags or within coarse mesh bags, because of their similar ranges of body width. As a result, both their effects could be influenced by fine mesh bags. In this study, we investigated the effects of soil fauna and understory fine roots on soil organic carbon, with a special type of fine mesh bags designed for obstructing the growth of understory fine roots into soil with free access of soil fauna. Results showed that both the biomass of understory fine roots and soil faunal diversity along with soil total carbon and microbial biomass carbon were significantly reduced by the fine mesh bags (P < 0.01). Boosting regression tree models showed that the understory fine roots contributed more in the variations of soil organic carbon than soil faunal properties. Faunal biodiversity represented by Pielou’s evenness index was more important than taxa richness and individual abundances of taxa. Results suggest that understory fine roots may be more influential in soil organic carbon than faunal factors, and both their functions could be influenced by fine mesh bags in a mesh bag study. Evenness of individual abundances between taxa could be more important than taxa richness for the influence of soil fauna community on soil organic carbon.