Geoscience Reference
In-Depth Information
14.8
plant adaptation to environmental stress
Plants have various mechanisms that allow them to survive
and often prosper in the complex environments in which they
live. Adaptation to the environment is characterised by genetic
changes in the entire population that have been fixed by natural
selection over many generations. In contrast, individual plants
can also respond to changes in the environment, by directly
altering their physiology or morphology to allow them to bet-
ter survive the new environment. These responses require no
new genetic modifications, and if the response of an individual
improves with repeated exposure to the new environmental
condition, then the response is one of acclimation.
Adaptation to
heat stress
Living organisms can be classified into three groups, subject
to the preferred temperature of growth. These are (a)
psy-
chrophiles
, which grow optimally at low temperature ranges
between 0°C and 10°C; (b)
mesophiles
, which favour moder-
ate temperature and grow well between 10°C and 30°C; and
(c)
thermophiles
, which grow well between 30°C and 65°C or
even higher. There is a great variation among the plant species
in terms of their response and tolerance to high temperature.
Plant adaptation to heat stress includes avoidance and tolerance
mechanisms which employ a number of strategies (Figure 14.6).
Under high-temperature conditions, plants exhibit various
mechanisms for surviving which include long-term evolution-
ary phenological and morphological adaptations and short-term
avoidance or acclimation mechanisms such as changing leaf
orientation, transpirational cooling or alteration of membrane
lipid compositions. Closure of stomata and reduced water loss,
increased stomatal and trichomatous densities, and larger xylem
vessels are common heat-induced features in plant (Srivastava
et al. 2012). Plants growing in a hot climate avoid heat stress
by reducing the absorption of solar radiation. This ability is
supported by the presence of small hairs (tomentose) that form
a thick coat on the surface of the leaf as well as cuticles, protec-
tive waxy covering. In such plants, leaf blades often turn away
from light and orient themselves parallel to sun rays (parahe-
liotropism). Solar radiation may also be reduced by rolling leaf
blades. Plants with small leaves are also more likely to avoid
heat stress: they evacuate heat to ambient more quickly due to
smaller resistance of the air boundary layer in comparison with
large leaves. Plants rely on the same anatomical and physiologi-
cal adaptive mechanisms that are deployed in a water deficit to
