Objective Litter is the main source of carbon and nitrogen in forest soils. The effect of litter decomposition on soil carbon and nitrogen by leaching was studied through analyzing the changes of dissolved carbon and nitrogen in litter or soil leaching solution, for exploring the relationship between litter decomposition and soil carbon and nitrogen.

Method Soil and litter in broad-leaved and coniferous forests were collected from subtropical forests. Six treatments were set, including litter, soil, litter + soil, nitrogen + litter, nitrogen + soil, and litter + soil + nitrogen. Three replicates were set for each treatment. The nitrogen addition amount was 120mg NH₄ ⁺ -N·kg⁻¹ soil. The amount of litter added in coniferous and broad-leaved forests was 12.1 g·kg⁻¹ and 19.7 g·kg⁻¹, respectively. The litter was placed on the surface of soil or quartzite, and the soil moisture was controlled at 60% water-holding capacity. An incubation experiment was carried out with nitrogen addition by leaching to simulate nitrogen deposition in a dark incubator at 25 ℃ for 220 days. During the incubation period, the nitrogen solution leached in 5 times with different nitrogen amounts, each with 110 mL of solution (80, 10, 10, 10, 10 mg NH₄ ⁺ -N in sequence according to the number of leaching times), and the leaching solution was collected and measured.. In addition, the dissolved organic carbon (DOC) and nitrogen (DON), and NH₄ ⁺ -N and NO₃⁻-N in the leaching solution were also measured.

Result The results showed that the litter leaching solution had lower inorganic nitrogen and DON, and higher DOC. Litter addition significantly reduced the NO₃⁻-N by 22.6% and 29.9% in the coniferous forest and broad-leaved forest soil leaching solution, respectively and increased the DOC by 181.4% in the coniferous forest soil leaching solution. However, litter addition significantly decreased the DON by 39.2% in the broad-leaved forest soil leaching solution and MBN by 53.2% in the broad-leaved forest soil. Under nitrogen addition, the interception of added nitrogen by litter was less, and the interception of litter in broad-leaved forest litter was higher than that in coniferous forest. Litter input to soil by leaching decreased DOC, while DON increased. Nitrogen addition increased soil leaching inorganic nitrogen and coniferous forest soil leaching solution DON, but the effect of litter on reducing soil nitrogen leaching was not weakened by nitrogen addition.

Conclusion The litter slows down the negative impact of soil NO₃⁻-N output on water environment. Nitrogen addition can affect soil nitrogen changes by altering the output of DOC and DON in broad-leaved and coniferous forest litters.