title: Dynamics of soil inorganic nitrogen and their responses to nitrogen additions in three subtropical forests, south China.
abstract: Three forests with different historical land-use, forest age, and species assemblages in subtropical China were selected to evaluate current soil N status and investigate the responses of soil inorganic N dynamics to monthly ammonium nitrate additions. Results showed that the mature monsoon evergreen broadleaved forest that has been protected for more than 400 years exhibited an advanced soil N status than the pine (Pinus massoniana) and pine-broadleaf mixed forests, both originated from the 1930's clear-cut and pine plantation. Mature forests had greater extractable inorganic N pool, lower N retention capacity, higher inorganic N leaching, and higher soil C/N ratios. Mineral soil extractable NH4(+)-N and NO3(-)-N concentrations were significantly increased by experimental N additions on several sampling dates, but repeated ANOVA showed that the effect was not significant over the whole year except NH4(+)-N in the mature forest. In contrast, inorganic N (both NH4(+)-N and NO3(-)-N) in soil 20-cm below the surface was significantly elevated by the N additions. From 42% to 74% of N added was retained by the upper 20 cm soils in the pine and mixed forests, while 0%-70% was retained in the mature forest. Our results suggest that land-use history, forest age and species composition were likely to be some of the important factors that determine differing forest N retention responses to elevated N deposition in the study region.
authors.affiliation: Dinghushan Forest Ecosystem Research Station, South China Botanical Garden, Chinese Academy of Sciences, Zhaoqing.
authors.forename: Yun-ting
authors.initials: YT
authors.lastname: Fang
authors.forename: Wei-xing
authors.initials: WX
authors.lastname: Zhu
authors.forename: Jiang-ming
authors.initials: JM
authors.lastname: Mo
authors.forename: Guo-yi
authors.initials: GY
authors.lastname: Zhou
authors.forename: Per
authors.initials: P
authors.lastname: Gundersen
mesh_terms: D000704:Analysis of Variance; D002244:Carbon / Q000032:analysis; D004784:Environmental Monitoring / Q000379:methods*; D006863:Hydrogen-Ion Concentration; D009566:Nitrates / Q000494:pharmacology*; D009584:Nitrogen / Q000032:analysis* / Q000737:chemistry; D010758:Phosphorus / Q000032:analysis; D012987:Soil / Q000032:analysis*; D013997:Time Factors; D014197:Trees / Q000378:metabolism; D014329:Tropical Climate
chemical_list: D009566:Nitrates; D012987:Soil; D010758:Phosphorus; D002244:Carbon; D009584:Nitrogen; C006568:ammonium nitrate