Geoscience Reference
In-Depth Information
Similarly, Simon et al. (1992) reported that moderate water
stress imposed on sweet basil resulted in higher oil content and
greater total oil yield. Furthermore, the authors indicated that
water stress changed essential oil composition: water stress
increased linalool and methyl chavicol and reduced sesqui-
terpenes. Contrary to the previously mentioned report, short-
term stress (withholding irrigation for 8 days) did not change
essential oil yield and oil composition of
Melaleuca alternifo-
lia
(List et al., 1999). In
Isatis indigotica
, extreme water stress
has been found to reduce the production of indirubin. However,
superior yield and quality could both be obtained at 45-70%
of field capacity (Tan et al., 2008). A lot of investigations have
showed that water stress increased secondary metabolite accu-
mulation in medical plants, such as
Salvia miltiorrhiza
(Liu
et al., 2011),
Bupleuri radix
(Zhu et al., 2009),
Catharanthus
roseus
(Abdul et al., 2007), and
Rehmannia glutinosa
(Gaer t n.)
(Chung et al., 2006). The content of total flavonoids in
Tribulus
terrestris
under high levels of water treatment is higher than
that occurring in low-water treatments (Yang et al., 2010). In
Ginkgo biloba
, drought stress has been found to promote the
growth of quercetin content and to inhibit the increase of rutin
in the leaves (He and Zhong, 2003). In
S. baicalensis
Georgi,
baicalin increased steadily in the stems and leaves under lower
water stress, and it decreased sharply under heavy water stress
(Liu et al., 2010).
Water stress reduced fresh and dry weights of
Satureja
hortensis
L. (savoury) plants. Severe water stress increased
essential oil content more than moderate water stress. The
main constituents, such as carvacrol, increased under moderate
water stress, while α-terpinene content decreased under mod-
erate and severe water stress of
Satureja hortensis
L. (Baher
et al., 2002). Essential oil, total carbohydrate and proline con-
tents were pronouncedly increased with increasing stress lev-
els of
Salvia officinalis
L. (Sage) plants (Hendawy and Khalid,
2005). Sahu (1972) reported that overall growth of
Rauvolfia
serpentina
plantation diminished with increasing water stress,
but root growth was less influenced than shoot growth. Root
yield of the crop grown without irrigation was less than the
irrigated ones.
Soil
The edaphic factor pertains to the substratum upon which
the plant grows and from which it derives its mineral nutri-
ents and much of its water supply. It involves physical, chemi-
cal and biological properties of soils (Mason, 1946a,b). These
properties of soil, namely physical, chemical and biological,
