1021-4437/04/5104- © 2004
Russian Journal of Plant Physiology, Vol. 51, No. 4, 2004, pp. 469–475. Translated from Fiziologiya Rastenii, Vol. 51, No. 4, 2004, pp. 521–528.
Original Russian Text Copyright © 2004 by Ivanov, Ivanova, Ronzhina, Chechulin, Tserenkhand, Gunin, P’yankov.
The current trend in environmental changes can be
deﬁned as climate aridization and an expansion of the
area of arid regions. Changing temperature and water
regime can lead to the changes in botanical and geo-
graphical zones, the displacement of species area, and
the changes in the competition relationships between
plants in the ecosystems .
Recent studies by the Joint Russian–Mongolian
Multidisciplinary Biological Expedition revealed an
expansion of Chinese ephedra (
) in sev-
eral regions of the Gobi Tien Shan . Ephedra actively
tussocks, which are the main cenosis-form-
ing species of steppe communities in mountain ecosys-
becomes not only the dominant and sub-
dominant, but also an ediﬁcator species. In the late
1960s–early 1970s, Chinese ephedra was mentioned as
a plant species that is rare in these communities .
However, according to the data by Gurvantes weather
station (Mongolia), the annual precipitation steadily
decreased from 180 mm in 1975 to 80 mm in 1990 .
Expansion of ephedra, in parallel with the increase
in climate aridity, is due to several morphological, ana-
tomical, and physiological adaptations. To date, mor-
phological characteristics of Chinese ephedra are well
studied. This plant is a perennial evergreen xeromor-
phic rhizome-type small shrub of 10–20 cm in height.
Various authors studied seasonal and daily changes in
photosynthesis [4, 5] and transpiration [6, 7] rates in
some representatives of the
genus. Studies of
physiological processes provide valuable information
about ecological characteristics of plant species. How-
ever, these data reﬂect adaptation of an individual plant
function to current growth season or day conditions.
Owing to a high lability of physiological characteris-
Structural and Functional Grounds for
Expansion in Mongolian Steppe Ecosystems
L. A. Ivanov*, L. A. Ivanova**, D. A. Ronzhina**, M. L. Chechulin**, G. Tserenkhand***,
P. D. Gunin****, and V. I. P’yankov
*Botanical Garden, Ural Division, Russian Academy of Sciences, ul. 8 Marta 202, Yekaterinburg, 620144 Russia;
fax: 7(3432) 10-3859, e-mail: Leonid.Ivanov@usu.ru
**Department of Plant Physiology, Ural State University, Yekaterinburg
***Institute of Botany, Mongol Academy of Sciences, Ulan-Bator
****Severtsov Institute of Evolution and Ecology, Russian Academy of Sciences, Moscow
Received August 4, 2003
—Morphological and structural characteristics of photosynthetic organs, diurnal changes in photosyn-
thetic and transpiration rates, and the efﬁciency of water use were studied in three plant species from mountain-
steppe ecosystems in Mongolia,
P. Smirn., and
ex Regel. The species studied differed in the structural and functional mechanisms for the adaptation of photo-
synthetic apparatus to arid conditions.
has thick, vertical assimilating shoots, which are characterized
by a high density (620 mg/cm
) and a small proportion of photosynthetic tissues (13%). The proportion of meso-
phyll in the leaves of
was two and three times higher, respectively. The low con-
tent of phototrophic tissues in
shoot was compensated for by a high photosynthetic activity of single
chloroplasts (25 mg CO
chloroplast h)), which was six times higher, than in two other species. Daily
course of photosynthesis and transpiration in
differed from those of
the absence of the midday depression.
had the highest efﬁciency of water use (45 mg CO
to a low transpiration rate (0.25 g/g fr wt h). It is concluded that, in
, the main strategy for adaptation
to arid stress is to develop in the shoot a few photosynthesizing cells of high assimilation activity. Such struc-
tural organization of photosynthetic organs in ephedra contributes to its higher efﬁciency of water use and sta-
bility of physiological characteristics under changing environmental conditions. These speciﬁc features of the
structure of assimilating organs and their functional features contribute to a greater expansion of
increasing climate aridization in Mongolia.
Key words: Allium polyrhizum - Ephedra sinica - Stipa glareosa - photosynthesis - transpiration - leaf anatomic
characteristics - mesophyll - aridization - adaptation - Mongolia
: chlp—chloroplast; CMI/V—cell membrane
index, or the total area of the cell surface in photosynthetic tissues
per unit leaf volume.