Nutrient deficiencies under stress in legumes: An overview - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 54

3.2 environmental stresses
and crop growth

environment and unlike animals they cannot run away
from environmental and anthropogenic stressors.
Stress avoidance and stress tolerance are the two broad
categories of avoiding/mitigating mechanisms. Plants
lack very specialized responses to environmental
stressors but there are a few general responses, which
include a high or low rate of growth or adaptation. The
rapid responses of plants and the changes in their met-
abolic pathways should not be regarded as responses to
environmental stressors (Figure 3.2). Both biotic and
abiotic stresses do affect growth and development of
plants. Frequently occurring stresses in nature are
noted below.

As already pointed out, both natural and anthropogeni-
cally derived stress factors occur in nature. Plants have
to cope with a plethora of potentially unfavourable
conditions. Nevertheless there are various indigenous
mechanisms triggered in plants when exposed to envi-
ronmental extremes. Nutrient deficiency in legumes
under drought and saline conditions affects growth of
the plants, altering their physiology including nitrogen
fixation, and extreme deficiencies can cause the death
of plants. Generalized mechanism of stress is elaborated
in figure 3.1.
The concept of stress was developed by Hans Selye in
1936; it refers to the unfavourable environmental con-
straints experienced by plants. Plants are bound to their

3.2.1 Drought and salt stresses
Water scarcity is a severe environmental constraint to
crop production (Masoumi et al., 2010). Drought stress
induces several changes, such as reductions in leaf area,
stem extension, root proliferation, and water use
efficiency. Worldwide, 20% of irrigated land is salt
affected. High salinity has a negative impact on the
growth of the plant, and in sensitive crops generally can
lead to plant death. It disrupts the ionic and osmotic
balance of the cell.

Alarm

Resistance

3.2.2 heavy metal stress
Heavy metal toxicity is one of the major stresses experi-
enced by plants. The high reactivity of metals can
influence plant growth, senescence and energy produc-
tion. If large amounts of metals are accumulated in
plants, they adversely affect the absorption and

Exhaustion

Figure 3.1 Mechanism of stress.

Optimum Mild stress Severe stress

Threshold stress

Compensation
Normal metabolism Stress metabolism Irreversible stress

Figure 3.2 Stressor dose and stress effect relationship in plants.