Unexpected reduction of soil mesofauna under canopy N deposition in a subtropical forest

Abstract Nitrogen (N) deposition is a worldwide environmental problem. Although the effects of N deposition on ecosystems have been widely studied, most of these studies failed to consider how the effects of N deposition were altered by plant canopy interception. Here, we compared the effects of canopy addition of N (CAN) vs. understory addition of N (UAN) on soil mesofauna in a monsoon evergreen broadleaf forest in Guangdong Province, South China; the CAN and UAN treatments (plus a control without N addition) were applied monthly (April to October) at two rates (25 and 50 kg N ha−1yr−1) started in April 2013. Soil mesofauna were extracted from the soil and quantified at 19th month (November 2014) and 31st month (November 2015) after the experiment began. We found significant effects of the addition approaches (CAN vs. UAN) on soil mesofauna. However, contrary to our expectations, the results showed a negative reaction of soil mesofauna to CAN approach compared with UAN approach. In 2015, the individuals, group richness and diversity of the mesofauna community, and the individuals of Oribatida and Collembola in CAN plots were significantly less than in UAN plots. This study discovered the different effects of CAN vs. UAN approaches on soil mesofauna. The negative effects of CAN on soil mesofauna would not be explained by the variation of reactive nitrogen but by some other non-N washed ions from the canopy into the soil. More attentions should be paid to the study on canopy process of N deposition in the future.