Abstract: To reveal the effects of long-term nitrogen (N) addition on litter production of Pinus tabuliformis forest, a 7-year N addition experiment was carried out in natural and planted forests in Taiyue Mountain, Shanxi Province, which included four levels of N addition (CK, 0; LN, 50; MN, 100; HN, 150 kg N·hm^-2·a^-1). Litter components were divided into leaves, branches, fruits, flowers, barks, and miscellaneous (animal debris, bud scales, and other debris). Litter biomass was monitored monthly from 2015 to 2016. The results showed that N addition significantly increased mean annual litterfall biomass in the natural forest, with the order: HN (3.69 t·hm^-2·a^-1) > MN (3.12 t·hm^-2·a^-1) > LN (3.02 t·hm^-2·a^-1) > CK (2.68 t·hm^-2·a^-1). In the plantation, the mean annual litter production increased but then decreased with the increasing N gradient, with the order: LN (3.11 t·hm^-2·a^-1) > CK (3.08 t·hm^-2·a^-1) > MN (2.92 t·hm^-2·a^-1) > HN (2.60 t·hm^-2·a^-1), indicating that excess N application can reduce the litter biomass in the plantation. The proportion of mean annual leaf biomass was among 68.3%-75.4%, and fruit biomass ranged from 6.7% to 17.8%. Nitrogen addition significantlyaffected litter biomass of leaf, fruit and bark. The temporal variation of total litter biomass was a doublepeak pattern with peaks in June and October. In conclusion, litter production was significantly increased with increasing N level in the natural forest (P<0.001), but no significant effect was found in the plantation (P>0.05).

Key words: increased precipitation, biomass allocation, ephemeral plant, Gurbantunggut Desert