In farmland shelterbelt systems, the decomposition and/or apoptosis of forest fine root litter could affect farmland soil properties at the tree-crop interface, particularly the soil nitrogen (N) cycling. However, how fine root litter affect the ammonia (NH3) and nitrous oxide (N2O) losses from farmland soil and the crop production is little known. A soil column experiment covering a whole rice season was conducted to evaluate the dynamics aforesaid in response to fine root litter of Populus (RP) and Metasequoia glyptostroboides (RM) with 0 and 240kgha-1 N fertilizer input. Both RP and RM had minimal impact on NH3 and N2O emissions from soils without N input. At 240kgN ha-1 input, RP significantly (p<0.05) increased total NH3 volatilization (including yield-scaled NH3 volatilization and emission factor) by 37.1%, while RM significantly (p<0.05) decreased it by 18.1%. Both fine root litter significantly (p<0.05) reduced the N2O emissions from paddy soil receiving 240kgN ha-1 by 22.7-27.1%. The reduction of N2O emission in N240+RM was primarily attributed to higher topsoil ammonium-N but lower nitrate-N contents that indicating a reduced nitrification rate during the mid-season drainage stage. In addition, the decreases in soil AOA amoA (-39.4%) and nirS (-23.7%) gene copies explained the mitigating effect of RP on N2O emission. Regardless of N fertilizer application or not, there was no statistically significant difference in rice grain yield between treatments with and without fine root litter, although RM reduced grain yield by 11.2-14.9% compared to treatments without fine root litter. In conclusion, the impact of fine root litter on N emissions via NH3 and N2O depends on both N input rates and fine root types. RM simultaneously reduce reactive farmland soil N losses via NH3 and N2O in the tree-crop interface soils with N input.
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