Environmental and Experimental Botany 44 2000 141 – 149
Nitrogen nutrition and water stress effects on leaf photosynthetic gas exchange and water use efficiency in
winter wheat
Z.P. Shangguan
a,
, M.A. Shao
a
, J. Dyckmans
b
a
State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conser6ation, Chinese Academy of Sciences, Northwest Sci-Tech Uni6ersity of Agriculture and Forestry, Yangling, Shannxi
712100
, P.R. China
b
Institute of Soil Science and Forest Nutrition, Uni6ersity of Go¨ttingen, Bu¨sgenweg
2
,
37077
Go¨ttingen, Germany Received 14 December 1999; received in revised form 21 June 2000; accepted 21 June 2000
Abstract
The responses of gas exchange and water use efficiency to nitrogen nutrition for winter wheat were investigated under well-watered and drought conditions. The photosynthetic gas exchange parameters of winter wheat are
remarkably improved by water and nitrogen nutrition and the regulative capability of nitrogen nutrition is influenced by water status. The effects of nitrogen nutrition on photosynthetic characteristics and on the limited factors to
photosynthesis are not identical under different water status. Intrinsic water use efficiency WUE
i
of the plants at the high-N nutrition was decreased by a larger value than that of the plants in the low-N treatment due to a larger
decrease in photosynthetic rate than in transpiration rate. Carbon isotope composition of plant material d
p
is increased by the increase of drought intensity. The d
p
at a given level of C
i
C
a
is reduced by nitrogen deficiency. Leaf carbon isotope discrimination D is increased by the increase of nitrogen nutrition and decreased by the increase of
drought intensity. Transpirational water use efficiency WUE
t
is negatively correlated with D in both nitrogen supply treatments and increased with the nitrogen supply. © 2000 Elsevier Science B.V. All rights reserved.
Keywords
:
Carbon isotope discrimination; Drought; Nitrogen supply; Photosynthesis; Triticum aesti6um; Wheat www.elsevier.comlocateenvexpbot
1. Introduction
Drought stress and nitrogen deficiency are ma- jor constraints to winter wheat production and
yield stability in most rainfed regions in China. Similar problems are encountered worldwide
Fischer and Turner, 1978; Lawlor, 1995. An efficient use of limited water resources and better
growth under both limited water and nitrogen supply are desirable traits for crops in drought
environments.
Physiological responses of plants to either drought or nitrogen deficiency have been well
documented. However the interactions between these two factors on plant morphological and
Corresponding author. Tel.: + 86-29-7019107; fax: + 86- 29-7012210.
E-mail addresses
:
zhoupingpublic.xa.sn.cn Z.P.
Shangguan, jdyckmagwdg.de J. Dyckmans. S0098-847200 - see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 0 9 8 - 8 4 7 2 0 0 0 0 0 6 4 - 2
physiological responses have received relatively little attention Mcdonald and Davies, 1996. In
beans Shimshi, 1970, coffee Tesha and Kumar, 1978, and winter wheat Shangguan, 1997, the
stomatal conductance g
s
increased with nitrogen nutrition under well-watered conditions and be-
came more sensitive to leaf water potential. It decreased as soil water became less available.
Other works on tea Nagarajah, 1981 and cotton Radin and Ackerson, 1989 have indicated an
opposite response, i.e. the stomatal sensitivity to leaf water potential was decreased by high nitro-
gen nutrition. A strong correlation was found between leaf conductance and leaf nitrogen con-
tent; however, this relationship was weaker than that between stomatal conductance and water po-
tential Radin and Parker, 1979; Bolton and Brown, 1980; Morgan, 1986; Shangguan and
Chen, 1990; Ciompi et al., 1996. Sugiharto et al. 1990 found a significiant positive correlation
between the photosynthetic capacity of leaves and their leaf nitrogen concentration suggesting that
most of the nitrogen used for synthesis of compo- nents of the photosynthetic apparatus. In particu-
lar, Rubisco, the leaf protein playing the major role in carbon assimilation, was strongly affected
by nitrogen deficiency Seemann et al., 1987. Although CO
2
and NO
3 −
assimilation are linked, it is not completely clear to what extent they are
coupled Lawlor, 1995. Therefore, further eluci- dation of the relation of leaf nitrogen content to
the gas exchange and water use is needed.
Water use efficiency indicates the performance of a crop growing under any environmental con-
straint. At the leaf level, intrinsic water use effi- ciency
WUE
i
is defined
as the
ratio of
photosynthetic rate P
n
to transpiration rate. To achieve the same P
n
at a lower g
s
, a higher Rubisco activity and capacity for electron trans-
port is required and thus a higher concentration of nitrogen in the leaf does not necessarily mean a
proportional increase in the rate of photosynthesis Shangguan et al., 1999. In crop plants with C
3
photosynthetic pathway, carbon isotope discrimi- nation D has been used to provide time-inte-
grated estimates of plant intrinsic water use efficiency Farquhar and Richards, 1984; Far-
quhar et al., 1989. Foliar D values of C
3
plants have also been used as an integrated measure of
the response of photosynthetic gas exchange to environmental variables such as humidity Winter
et al., 1982, salinity Guy et al., 1986, light intensity Zimmerman and Ehleringer, 1990, soil
water availability Meinzer et al., 1992, and ele- vated CO
2
Picon et al., 1996. A high but nega- tive correlation was found between carbon isotope
discrimination D and WUE
t
Ehdaie and Hall, 1991; Ismail and Hall, 1992 and D with WUE
i
Wright et al., 1988, 1994. Meinzer et al. 1990 reported simultaneous reductions in stomatal con-
ductance and D with increased WUE for water stressed cowpea. Rao and Wright 1994 showed
significant effects of location and water regime on D
for cowpea. Ehleringer et al. 1991 reported a high correlation between D and C
i
C
a
. To our knowledge, there is little information on the ef-
fects of the two major environmental constraints on photosynthetic gas exchange and D in winter
wheat.
Since different stress histories could signifi- cantly have effects on a number of physiological
mechanisms in wheat Morgan, 1984, the present study was designed to eliminate the uncertain
effect of nitrogen nutrition stress with growing plants in solution culture and imposing water
stress with polyethylene glycol PEG 6000. In this study, it was hypothesized that: 1 there would be
interaction between drought and nitrogen nutri- tion on photosynthetic gas exchange and water
use efficiency, and the effects of nitrogen nutrition on plants depend on solution water status; 2
WUE
t
and WUE
i
would be increased by the nitrogen nutrition supply. For verifying the hy-
potheses winter wheat was grown under different combinations of nitrogen nutrition and water sup-
ply levels and the study was focused on the effects of nitrogen deficiency and water stress on leaf
water status, photosynthesis, nitrogen content, and water use.
2. Materials and methods
