『Abstract
Soil solutions at 15 cm and 60 cm depths under a Korean pine
and broadleaf mixed forest (＞200 years old) at Changbai mountain,
northeast China, were sampled using porous ceramic suction cups
from July 2006 to October 2007, to study the effect of nitrogen
(N) addition on the concentrations of dissolved nitrous oxide
(N2O) and carbon dioxide (CO2),
dissolved organic matter and inorganic N. The actual concentrations
of dissolved N2O and CO2
in soil solutions could be obtained using a combination of continual
three phase equilibrations and gas chromatography. The dissolved
CO2 concentrations in soil solutions at 15
cm and 60 cm depths varied from 4.3 to 15.5 and from 3.5 to 18.3
μg CO2-C ml-1, respectively, and
dissolved N2O concentrations at both depths
varied from 1.8 to 34.9 and from 2.5 to 99.3 ng N2O-N
ml-1, respectively. The addition of N sources such
as (NH4)2SO4,
NH4Cl and KNO3 at a
rate of 4.5 g N/m2 each year tended to decrease concentrations
of dissolved organic carbon (DOC) in soil solutions at 60 cm depth
in 2007, which was contrary to the increase in dissolved CO2 concentrations under N-fertilized forest plots.
However, the N addition did not give an obvious effect on the
concentrations of dissolved CO2 and DOC in
soil solutions at 15 cm depth. There was an increase in concentrations
of NH4+-N, NO3--N
and dissolved organic nitrogen (DON) of soil solutions under N-fertilized
forest plots. Rainfall after thawing in spring could promote the
accumulation of dissolved N2O in soil solutions
at 15 cm and 60 cm depths, particularly at 60 cm depth under the
(NH4)2SO4
added plots, due to mineralization of DON and nitrification. All
the tested properties of soil solutions at 15 cm and 60 cm depths
were well correlated. Among these properties, the dissolved N2O concentrations of soil solutions at both depths
were better correlated with the DON concentrations at 60 cm depth,
and the dissolved CO2 concentrations at 15
cm depth with the DOC concentrations at both depths. Hence, both
DOC and DON can contribute to the formation of dissolved CO2 and N2O in the soil solution
at varying depths under N-fertilized forest plots, respectively.
Our observations strongly indicate that N inputs to temperate
forest floors can affect the status of N and carbon processes
in underlying forest soils.
Keywords: Dissolved CO2 and N2O;
Dissolved organic carbon and organic nitrogen; Nitrogen addition;
Soil solution; Temperate old-growth forest; Volcanic soil』
1. Introduction
2. Materials and methods
2.1. Description of forest site and soil properties
2.2. Effects of N addition on soil solution chemistry under forest
stand
2.3. Measurement of dissolved N2O and CO2 concentrations in soil solution
2.4. Measurement of concentrations of dissolved organic C, total
N, NH4+-N and NO3--N
2.5. Calculation and statistical analysis
3. Results
3.1. Effect of phase equilibration times on the measurement
of dissolved gas concentrations in forest soil solution
3.2. Henry's constants for N2O and CO2 in forest soil solution
3.3. Effect of N addition on concentrations of DOC, DON and inorganic
N in forest soil solution
3.4. Effect of N addition on dissolved N2O
concentration in forest soil solution
3.5. Effect of N addition on dissolved CO2
concentration in forest soil solution
4. Discussion
4.1. Origin of dissolved N2O in soil
solution under N-fertilized forest stands
4.2. Effects of N inputs on carbon processes in underlying forest
soil
5. Concluding remark
Acknowledgements
References