2.3. Soil sampling and soil property measurement
Soil sampling followed immediately after gas sampling was completed.
Two soil cores (0–10 cm) under each chamber were collected
by hand-operated soil samplers (5 cm in diameter), one for the measurement
of root biomass while the other for soil properties. Live
roots of plants were carefully washed, separated from dead ones and
dried at 60 °C until reaching constantweight. Analyses of soil properties
all followed the standard methods described by Page et al. (1982). One
third of fresh soil samples were used for measurements of water content,
NO3
−-N and NH4
+-N contents while the remaining was air dried
and sieved through a 2 mm sieve. Soil pH was determined by the soil
pHmeter (Hanna HI 9025) and total organic carbon (TOC)was calculated
according to the loss on ignition at 550 °C. Contents of NO3
−-N, NH4
+-
N, total Kjeldahl nitrogen (TKN) and total phosphorus (TP) were analyzed
by a flow injection analyzer (Futura II, Alliance Instruments).