Botanical Studies (2008) 49: 127-137.
Corresponding author: E-mail: email@example.com; Tel:
Water relations, hydraulic conductance, and vessel
features of three Caragana species of the Inner Mongolia
Plateau of China
Jing LI, Yu-Bao GAO*, Zhi-Rong ZHENG, and Zeng-Lu GAO
College of Life Science, Nankai University, Tianjin 300071, P. R. China
(Received June 20, 2007; Accepted November 21, 2007)
From early May to late September 2005, diurnal and seasonal changes in water relations, hy-
draulic conductance, vessel features, photosynthesis (DCA), transpiration (DCE), and water use efficiency
(WUE) were studied in the field for three Caragana species¡XC. microphylla Lam, C. davazamcii Sancz and
C. korshinskii Kom¡Xgrowing in different habitats in the Inner Mongolia Plateau of China. The three species
were generally exposed to severe environmental drought during most of the growing period. Among them, C.
korshinskii had the largest vessels and specific hydraulic conductivity (K
) in one-year-old twigs while the low-
est were recorded in C. microphylla. All three species had the highest K
in the summer and the lowest in the
spring. For the three species, the best leaf water status occurred in the autumn indicated by the largest diurnal
mean leaf water potential (£Z
) and the lowest leaf relative water deficit (RWD) while the severest leaf water
stresses occurred in the spring. Caragana microphylla had larger £Z
than the other two species, and the lowest
as well as the largest RWD occurred in C. korshinskii. The lowest RWD were found in C. davazamcii. The
three species had the largest DCA and DCE in the autumn while the lowest values occurred in the spring for C.
microphylla and C. davazamcii. Caragana korshinskii had the lowest DCA and DCE in the summer, which re-
sulted in a decrease in soil water loss. Leaf stomatal conductance (g
) and transpiration rate (E) were found to
be correlated to hydraulic conductance in soil-leaf continuum (G
) more closely than K
in one-year-old twigs.
Generally, the seasonal changes in G
were in accordance with those of DCA and DCE, with the exception of
C. davazamcii, which had the largest G
in the spring. Among the three species, C. davazamcii had the high-
est values of seasonal mean DCE and G
, and the lowest drought resistance during the growing period, which
was in line the higher soil water content in its habitat. In the spring, despite the high soil water content, C.
microphylla had the greatest resistance to the leaf water deficit raised by the low G
. In the autumn, the great-
est drought resistance occurred in C. korshinskii, which was exposed to the severest water stress due to low
soil water content. By analyses of seasonal changes of K
as well as their relationships with leaf gas
was approved to be more important than specific subportions (one-year-old twigs in this study)
in terms of leaf water supply.
Keywords: Caragana davazamcii; Caragana korshinskii; Caragan microphylla; Diurnal and seasonal change;
Growth rhythm; Hydraulic conductance; Leaf gas exchange; Vessel size.
Numerous studies have been done on plant water
relations over a long time period (Kramer, 1983;
Zimmermann, 1983; Holbrook and Putz, 1996; Donovan
et al., 2001), and it is widely recognized that plants
can regulate their transpiration by decreasing stomata
conductance in response to water deficit (Sperry, 2000).
In addition to the traditional theory that the signals of
chemicals like abscissic acid (ABA) (Ackerson and Radin,
1983; Zhang and Davies, 1987, 1990; Tardieu and Davies,
1992) can drive stomatal regulation, hydraulic signals
are being recognized as another mechanism (Fuchs and
Livingston, 1996; Meinzer et al., 1995, 1997; Borghetti et
al., 1998; Tausend et al., 2000).
There is substantial evidence that stomatal behavior
is positively correlated with hydraulic conductance of
the soil-leaf continuum (G
) in diverse plant species
and growth forms (Meinzer et al., 1990; Sperry and
Pockman, 1993; Irvine et al., 1998; Bond and Kavanagh,
1999; Sohan et al., 1999; Comstock, 2000; Sperry, 2000;
Hubbard et al., 2001). Such a close relationship between
vapor and liquid phase conductance results from an active
response of stomata to G
. When G
increased by partial defoliation or shading, stomatal
) and transpiration of the untreated foliage