6 Combined Abiotic Stress in Legumes 137
Photosynthetic activity does not show a defined pattern, maybe due to lack
of information. Even with the limited data, it can be seen that in all the cases
examined, D1 was unchanged by the imposition of combined stresses. D2 protein
had a synergistic effect in combined stress. It is important to point out that in
drought and heat stress were considered in these studies, and some of these respons-
es were observed in T. pratense and in two related species such as L. japonicus
and L. corniculatus. Other species should be evaluated to see the conservation
in the response of D2, which is suggested to disassemble to induce inhibition of
photosystem activity, and protect cells from oxidative damage caused by its own
activity.
6.6 Forage Legumes Field Productivity and Combined
Environmental Stress
Legumes have a high level of productive diversification and flexible utilization. The
same species can be usefully exploited for different purposes such as soil protection
from erosion; green manure crop; mulching; cover crop in vineyards, orchards and
firebreak lines; high quality honey production; landscape enhancement and medici-
nal use. Consequently, forage legumes were adapted to a wide range of soil types,
climatic conditions and management systems (Sánchez-Díaz 2001 ).
Legumes, as many other crops, have been bred to maximize productivity (forage
or grain). But this productivity is always affected by adverse environmental factors.
Perennial forage legumes are a good model to analyse the responses of adaptability
of plants under field conditions. This is because during the whole plant growth and
development cycle, plants are subjected to various types of abiotic stresses, both
singly and in combinations.
Low temperatures and periods of water saturation in soils are common during
the winters in many regions and in the other side periods of low water regime
combined with high temperatures are common during summers. To these we must
add other combinations of stresses such as periods of high radiation or toxic ions
(Na+ or heavy metals) produced by changes in the physicochemical conditions of
the soils.
Further, abiotic stress can affect the legume plants at different developmental
stages. So legumes growing under field conditions must have adaptation process
triggered by stress in seedling, vegetative or reproductive stages. For example, for
seedling emergence, the optimal conditions in the field are established at the end of
winter (Fig. 6.3).
Legumes are adapted to different environmental conditions by setting the de-
velopmental stages, such as reseedling capacity that is an important characteristic
for the perpetuation of L. corniculatus. Yield of L. corniculatus during 3 years with
seed set and without seed set, reveal the importance in reseedling (Fig. 6.4, Ayala
and Carámbula 2009 ).