4 Combination of Elevated CO 2 Levels and Soil Contaminants’ Stress ... 73
4.2.2 FACE System
The FACE system has been described in detail by Liu et al. ( 2002 ) and Okada et al.
( 2001 ). In brief, the FACE system consists of octagonal plots located in different
paddies having similar soils and agronomic histories. The plots have either elevat-
ed CO 2 levels (hereafter called FACE plots) or ambient CO 2 conditions (hereafter
called ambient plots). Each plot is ca. 80 m^2. In the FACE plots, plants were exposed
to elevated CO 2 levels within rings 12.5 m in diameter that emitted pure CO 2 from
the periphery toward the center through emission tubes located about 50–60 cm
above the canopy. In the ambient plots, plants were grown under ambient CO 2 con-
ditions. To minimize the CO 2 contamination, ambient plots were at least 90 m away
from the nearest FACE ring. The season-long average CO 2 concentration of the
ambient plots was about 370 μmol mol−1. The CO 2 concentration in the FACE plots
was constantly controlled at about 200 μmol mol−1 higher than in the ambient plots.
4.2.3 Crop Cultivation and Sample Preparation
Rice ( Oryza sativa L. cv. Wu Xiang jing 14) and wheat ( Triticum aestivum L. cv.
Yangmai 14) plants were grown in plastic pots in soils collected from a local farm.
The properties of the soils are shown in Table 4.1. Fresh soil was sieved through
a 3-mm sieve and kept in the dark until used. Soils were spiked with either Cu
or Cd; control soil was not spiked. Specified amounts of Cd in the form of a dis-
solved solution of CdCl 2 ·2H 2 O were added and thoroughly mixed into the soil as
0, 0.5, and 2.0 mg kg−1. Specified amounts of Cu in the form of a dissolved solu-
tion of CuSO 4 ·5H 2 O were added and thoroughly mixed into the soil as 0, 50, and
400 mg kg−1. The spiked and unspiked soils were then watered to field water capac-
ity and kept in the dark for 6 months. Prepared soil was placed in plastic pots (5 kg
soil per pot; 20 cm in diameter, 35 cm in height). Two FACE plots and two ambient
plots were used in this experiment; plants treated with Cu were grown on one FACE
plot and one ambient plot, and plants treated with Cd were grown on another FACE
plot and another ambient plot. Each treatment consisted of three replicate pots.
The experiments were conducted from June 2006 to October 2008. Rice–wheat
rotation was used. The first rice seeds were planted in June 2006, and the plants
were harvested in October 2006. The first wheat sowing was in November 2006,
with harvest in May 2007. The second rice sowing was in June 2007, with harvest
in October 2007. The second wheat sowing was in November 2007, with harvest in
May 2008. The third rice sowing was in June 2008.
Table 4.1 Physical and chemical characteristics of soils used in this study
Soil
spiked
with
Organic
matter
(g kg−1)Sand (%) Silt (%) Clay (%) pH Total Cu
(mg kg−1)Total Cd
(mg kg−1)Cu 17.3 57.8 28.5 13.7 6.92 21.7 0.15
Cd 18.4 56.1 29.6 14.3 7.21 18.9 0.11