Effects of simulated nitrogen deposition on decomposition of single and mixed leaf litters in the plantation and natural forests of Pinus tabulaeformis.

Through a long-term in situ simulated nitrogen (N) deposition experiment, we explored the response and mechanism of single and mixed leaf litters decomposition to exogenous nitrogen addition in warm-temperate Chinese pine (Pinus tabulaeformis) forests. The levels of simulated N deposition were set as control (0 kg/(hm2a), N0), low N (50 kg/(hm2a), N1), medium N (100 kg/(hm2a), N2), and high N (150 kg/(hm2a), N3). Litterbag method was used for decomposition of single P. tabulaeformis litter, single Quercus liaotungensis litter, mixed P. tabulaeformis-Q. liaotungensis litter in the natural forest and single P. tabulaeformis litter in the plantation. The results showed that the time of 95% mass loss was 7.58 years for single P. tabulaeformis litter, 4.89 years for single Q. liaotungensis litter and 6.92 years for mixed P. tabulaeformis-Q. liaotungensis litter in the natural forest. And the time of 95% mass loss was 8.03 years for single P. tabulaeformis litter in the plantation. N deposition significantly accelerated the decomposition of single P. tabulaeformis litter in the plantation while inhibited that of single Q. liaotungensis litter in the natural forest. At the start, N deposition increased the rates of mass loss of single P. tabulaeformis litter and mixed P. tabulaeformis-Q.liaotungensis litter in the natural forest; however, it inhibited the decomposition of single P. tabulaeformis litter and had no significant effect on the decomposition of mixed P. tabulaeformis-Q. liaotungensis litter at the later stage of decomposition. Our results provide basic data for material cycling and energy flow of Chinese pine forest ecosystems under the context of increased N deposition.