Long-term nitrogen addition alters the community and energy channel but not diversity of soil nematodes in a subtropical forest

Summary

Research has indicated that increases in nitrogen (N) deposition can greatly affect ecosystem processes and functions. There is limited information about the effects of long-term N addition on soil nematodes and their functional composition, although nematodes are the most abundant multicellular animals on Earth.
We conducted a field experiment in 2004 with four levels of N addition (0, 60, 120, and 240 kg N ha-1 yr-1) in a subtropical Cunninghamia lanceolata forest. Soil samples with three depths (0–20, 20–40 and 40–60 cm) were collected and the community structure, diversity and trophic groups of soil nematodes were determined in 2014.
N addition significantly increased the abundance of bacterial- and fungal-feeding nematodes, but decreased the abundance of plant-feeding nematodes at the 0-20 cm soil layer. Accordingly, the plant parasite index and enrichment index decreased but the basal index and channel index increased, which weaken the importance of the plant-based energy..., Experimental design
In December 2003, 12 experimental plots were established in a 6-ha section of the Chinese fir plantation. Each plot was 20 m × 20 m and had similar site conditions. In each plot, a central area of 15 m × 15 m was designated for treatments, arranging one of four levels of N. The treatment codes N0, N1, N2, and N3 indicated the loading of 0, 60, 120, and 240 kg N ha-1 yr-1, respectively. Each treatment was represented by three randomly assigned replicate plots. Urea [CO(NH2)2] was used as the N source, and the required quantity was dissolved in 20 L of water per plot. From January 2004 to January 2014 (when plots were sampled), 20 L of N solution was sprayed onto the soil surface in the central area (15 m × 15 m) of each plot once per month. Control plots (N0) were sprayed with the same volume of water without CO(NH2)2.
Soil sampling and the extraction and identification of nematodes
In January 2014 (after 10 years of N application), soil cores were collected from each..., ,