Abstract: Nitrogen (N) deposition and precipitation reduction can indirectly affect the degradation of plant residues in soil by modifying substrate quality of litters and fine roots. In this study, organic carbon (OC) content, C/N ratio, and lignin phenols in litters, fine roots and soil were measured under three treatments of N addition (NA), reducing precipitation (RP), RP + NA (RP-NA), and ambient condition (CK) in a broad-leaved Korean pine forest in Changbai Mountains. Biomass of fine roots under three treatments was significantly lower than that in the CK. There was no significant change in OC content and C/N in fine roots, litters and soil under NA and RP treatments. Lignin in litters, fine roots and soil mainly composed of V-type monomers. Compared to fine roots and soil, litters obviously had a higher proportion of S-type monomers and a lower proportion of C-type lignin. NA and RP significantly affected lignin content in fine roots, litters and soil. RP significantly increased the total amount of lignin in litter, whereas NA significantly reduced the total amount of soil lignin. The values of (Ad/Al)V and (Ad/Al)S of lignin in litters, fine roots and soil significantly changed under the three treatments compared to the CK. The ratio of ferulic acid to p-coumaric acid (F/C_i) in fine roots was approximate to that in soil. NA promoted the lignin oxidation of fine roots and RP inhibited its degradation. RP and RP-NA inhibited litter degradation, while the lignin was stable in soil under RP-NA. Our results suggest that nitrogen deposition and precipitation reduction would affect the chemical composition of fine roots, which indirectly change the chemical composition of organic matter into soil, and further influence the stability of soil organic matter.

Key words: fish,   , mesh size, species composition, total length distribution, Coilia nasus.