Inhibition effects of N deposition on soil organic carbon decomposition was mediated by N types and soil nematode in a temperate forest

- Suppression effect of N deposition on SOC loss depend on N type and soil nematode.
- N deposition effect on SOC decomposition based on an alone N source is underestimated.
- N types alter response of N deposition effect on SOC decomposition to soil nematode.
- N types should be considered when assessing N deposition effect on soil C cycling.

Increasing nitrogen (N) deposition may alter soil organic carbon (SOC) decomposition, thereby strongly affecting SOC storage in terrestrial ecosystems. Its specific influence may depend on the different types of N deposition and soil nematodes. However, little is known about how N deposition and soil nematodes affect the SOC cycle process. To address this issue, we evaluated the effects of different types of N deposition on SOC decomposition under the conditions of applying nematocide or not in a temperate forest. Soils collected from the simulated N deposition forest for 5 years were incubated in the presence and absence of soil nematocide at 15 °C for 150 days. N deposition suppressed soil C cycle processes, such as SOC decomposition and soil enzyme activities, and caused the accumulation of labile SOC, which depended on N types. A mixture of inorganic and organic N (MN) deposition had the highest suppression of SOC decomposition at 31.5%, followed by organic N (ON) deposition (24.4%) and inorganic N (IN) deposition (19.8%), thereby suggesting that inhibition effects of N deposition on SOC decomposition based on a single IN or ON source are underestimated. Nematocide application stimulated SOC decomposition, with the highest in MN (19.5%), followed by IN (13.5%), ON (11.2%), and control treatment (4.6%). The stimulation effect of SOC decomposition by soil nematode exclusion also depended on N types. N deposition and soil nematode exclusion had no interactive effect on SOC decomposition. These results imply that atmospheric N deposition favors the increase of C stocks in soil by reducing the SOC loss, and that N types should be considered during assessment of N deposition effects on soil C cycle processes.