Affiliations: Dinghushan Forest Ecosystem Research Station, South
China Botanical Garden, Chinese Academy of Sciences, Zhaoqing 526070,
China | Biological Sciences, Binghamton University-SUNY,
Binghamton, NY 13902-6000, USA | Forest and Landscape Denmark, Hoersholm Kongevej 11,
2970, Denmark | The Graduate School of the Chinese Academy of
Sciences, Beijing 100039, 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 NH_4^+-N and NO_3^--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 NH_4^+-N in the
mature forest. In contrast, inorganic N (both NH_4^+-N and
NO_3^--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.
Keywords: N deposition, N saturation, extractable inorganic N, soil solution inorganic N, subtropical China
