Environmental and Experimental Botany 43 2000 131 – 139
Interaction of CO
2
enrichment and drought on growth, water use, and yield of broad bean Vicia faba
Dong-Xiu Wu
1
, Gen-Xuan Wang
State Key Laboratory of Arid Agroecology, Lanzhou Uni6ersity, Lanzhou
730000
, People
’
s Republic of China Received 10 April 1999; received in revised form 28 September 1999; accepted 9 October 1999
Abstract
Broad bean Vicia faba cv. Lincan II were grown in pots at two CO
2
concentrations 350 and 700 parts per million by volume ppmv and three soil water levels 80, 60 and 40 field water capacity in field open-top chambers
OTC
f
. Water deficit reduced plant shoot dry weight, bean yield, and water use efficiency WUE by over 40, 30, and 15, respectively, with higher relative reduction under elevated CO
2
. High CO
2
significantly increased leaf photosyn- thesis, plant growth, bean yield and WUE. The increase is significant only at sufficient water supply. Both CO
2
enrichment and water deficit influenced bean yield mainly through bean number. Harvest index was increased by both high CO
2
and drought. There were significant interactions between CO
2
enrichment and soil water deficit on plant growth and yield. On the basis of above results, it is concluded that the effects of CO
2
enrichment on plants depend on soil water status, and the negative effects induced by drought will be relatively more serious in the future at
increased CO
2
concentrations. © 2000 Elsevier Science B.V. All rights reserved.
Keywords
:
Broad bean; Carbon dioxide; Drought; Growth; Harvest index; Vicia faba; Water use; Yield www.elsevier.comlocateenvexpbot
1. Introduction
Atmospheric CO
2
concentration [CO
2
] is cur- rently increasing at a rate of 1.8 parts per million
by volume ppmv per year Houghton et al., 1990. It has been estimated that within the next
century the [CO
2
] will be double the pre-industrial level of 280 ppmv. That increase along with pro-
jected rises in other ‘greenhouse’ trace gases is likely to cause a change in climate IPCC, 1996.
Global circulation models predict a rise in global surface temperature by 1.5 – 5.9°C, changes in pre-
cipitation patterns and cloud cover in the next 50 – 70 years Washington and Meehl, 1984;
Wilson and Mitchell, 1987. Further, the fre- quency of extreme climatic events such as heat
and drought stresses are predicted to increase Mearns et al., 1984. CO
2
enrichment and the climate change could affect agricultural produc-
tivity. Precipitation is limited in large parts of the Loess Plateau in China and water is and will be a
limiting factor for agricultural productivity in this area and many other regions. Thus, it is impor-
Corresponding author. E-mail address
:
lilij7public.kfptt.ha.cn D.-X. Wu
1
Current address: Biology Department, Henan University, Kaifeng 475001, People’s Republic of China.
S0098-847200 - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 9 8 - 8 4 7 2 9 9 0 0 0 5 3 - 2
tant to consider both elevated CO
2
concentrations and differences in soil water in order to assess the
possible effects of climate change on crops. Numerous experiments have demonstrated that
in many C
3
species high atmospheric [CO
2
] leads to increases in the photosynthetic rate, whole
plant growth and water use efficiency WUE and decreases in stomatal conductance and transpira-
tion and photosynthesis is the most sensitive pro- cess to CO
2
enrichment Kimball, 1983; Drake and Leadley, 1991; Bowes, 1993; Poorter, 1993;
Idso and Idso, 1994; Jiang, 1995; Wang et al., 1998. While results of studies on the plant
canopy water use requirements are conflicting Al- len, 1990 water deficit, on the other hand, is well
established to constrain leaf photosynthesis, plant growth and water use requirements with the most
sensitive process being cell growth Hsiao, 1973; Turner, 1987. However, on the interactive effects
of CO
2
and other environmental factors on plants, publications are relatively fewer, and
among these there are two contradictory views. Some authors proposed that high [CO
2
] effects on plants were not affected by environmental stress
factors Idso and Idso, 1994 whereas other au- thors have reported or theoretically concluded
that high [CO
2
] effects vary among plant species under different environmental conditions Kim-
ball, 1983; Poorter, 1993, 1998; Thompson and Woodward, 1994; Hunt et al., 1995; Ziska et al.,
1996; Bunce, 1998. Some authors have even sug- gested that the positive effects of CO
2
can not be maintained when other environmental factors are
limiting Kramer, 1981; Poorter, 1998. So plant growth and yield response to CO
2
can depend on the availability of soil water Stronach et al.,
1994. However, judging by the available data on the interactions between CO
2
and other environ- mental factors, water stress, which is probably the
most important of the environmental interactions with elevated CO
2
, is one of the least well studied Bowes, 1993; Picon et al., 1997.
In this study, broad beans were grown under different combinations of CO
2
concentration and soil water levels and focused on the effect of
long-term exposure of plants to elevated CO
2
and drought on photosynthesis, growth and water use.
It was hypothesized that: 1 there would be inter- action between CO
2
and drought on growth and yield, and the effects of CO
2
enrichment on plants depend on soil water status; 2 CO
2
enrichment would promote plant canopy water use require-
ments due to the decrease in transpiration being over-offset by an increase in leaf area; 3 WUE
i
and WUE would be increased by CO
2
enrichment.
2. Materials and methods
