The subalpine primary forests had been largely logged in the Eastern Qinghai-Tibetan Plateau during the second half of the 20th century. The harvesting sites were subsequently restored by natural regeneration, planting or their combined re-establishment methods leading to distinct forest types. Effects of such changes on the patterns of soil N mineralization are still poorly understood. We investigated soil net N mineralization and microbial community compositions in four forest types, i.e. Abies faxoniana primary forest (AF), Picea asperata broadleaved mixed forest (natural regeneration after artificial planting, MF), natural secondary forest (natural without assisted regeneration, NF) and Picea asperata plantation (artificial planting, PF) from June to November.
Results/Conclusions
Forest type had a significant effect on net ammonification rate, but not net nitrification rate. The cumulative ammonified N value was significantly higher in NF (11.40 g kg-1) and lower in PF (4.79 g kg-1), and the cumulative nitrified N value ranged from 17.75 to 27.98 g kg-1 without significant difference among forest types. However, the average net ammonification and net nitrification rates were statistically similar among forest types with generally negative values of the average net ammonification rate for MF and NF. Net ammonification and nitrification rates exhibited different monthly patterns. Net ammonification rate had the higher values at the end of the period, whereas net nitrification rate had the higher values at the middle of the period. The dynamic of net ammonification rate was greatly affected by soil NH4+ and SOM, temperature and microbial PLFAs, whereas that of net nitrification rate was primarily regulated by temperature and microbial community structure. Overall, our results suggested a larger supply and retention of ammonium N in the soil of NF, implying that NF might have a faster soil N turnover in this region.