Agriculture Reference
In-Depth Information
increased stomatal and trichomatous densities, and larger xylem vessels
are common heat induced features in plant (Srivastava et al., 2011). Early
maturation has been often closely correlated with smaller yield losses un-
der high temperature, whichmay beat tributed to the engagement of an
escape mechanism (Adams et al., 2001; Rodríguez et al., 2005). Plants
growing in a hot climate avoid heat stress by reducing the absorption of
solar radiation. The presence of small hairs (tomentose) that form a thick
coat on the surface of the leaf as well as cuticles, protective waxy covering
facilitate this. Besides, orientation of the leaf blades may also change and
leaf blades often turn away from light and orient themselves parallel to
sun rays, the phenomenon being termed paraheliotropism. Rolling of leaf
blades is another physical mechanism of reduction of solar radiation. Leaf
size may be reduced in order to avoid heat stress. Smaller leaves evacuate
heat more quickly due to smaller resistance of the air boundary layer in
comparison with large leaves. Transpiration is another adaptive mecha-
nism to control heat stress. In well-hydrated plants, intensive transpiration
prevents leaves from heat stress, and leaf temperature may be 6 °C or even
10-15 °C lower than ambient temperature. Avoidance mechanisms such
as leaf abscission, leaving heat resistant buds have been found in plants.
Desert annuals complete their entire reproductive cycle during the cooler
months to avoid the heat stress (Fitter and Hay, 2002). Such morphologi-
cal and phenological adaptations are commonly associated with biochemi-
cal adaptations favoring net photosynthesis at high temperature conditions
(in particularC4 and CAM photosynthetic pathways), although C3 plants
are also common in desert floras (Fitter and Hay, 2002). The degree of
leaf rolling may be affected by high temperature. Leaf rolling has a physi-
ological role in adaptation potential by increasing the efficiency of water
metabolism under high temperature (Sarieva et al., 2010).
High temperature stress can also be avoided by crop management prac-
tices,
viz
., selection of proper sowing methods, choice of proper sowing
date, cultivars, irrigation methods,etc.For example, in sub tropical zones,
cool-season vegetables such as lettuce when sown in the late summer may
show incomplete germination and emergence due to high soil temperature
(Hall, 2011). This incomplete emergence problem can be overcome by
sowing the lettuce seed into dry beds during the day and then sprinkling
water to the beds during the late afternoon. Seed priming can be another
potential solution to this problem. It involves placing the seed in an os-
motic solution for several days at moderate temperatures and then drying
