Chemistry Reference
In-Depth Information
sintetico, which grows well on fertile soils in South America, had a smaller,
less-branched root system. Such results demonstrate that substantial genetic
variability exists for root traits that determine the relative distribution of roots
in different soil layers and thereby influence the acquisition of resources. This
variation was exploited by crossing deep-rooted and shallow-rooted genotypes
of bean to obtain recombinant in-bred lines and it was found that lines with the
highest P-acquisition efficiency had shallower root systems.
124
At least two
factors are believed to contribute to this greater P efficiency of shallower root
systems compared with deeper root systems: first, spatial coincidence of root
and resource, and second, lower intra-plant inter-root competition. Such
genotypes have the added benefit that their increased growth often results in
greater ground cover and less P loss by erosion of topsoil.
125
In soyabean, too,
the most P-efficient genotypes had longer and larger root systems with a
greater proportion of the root system in the topsoil.
126
Significant correlations between root architectural features and P uptake
and P-use efficiency have also been found in a wide range (355) of Brassica
oleracea L. accessions. Many measures of P-use efficiency were correlated with
root development and architecture, especially with lateral root number, length
and growth rate.
127
Physiological P-use efficiency varied four- to five-fold in a
range of commercial genotypes, suggesting that there is potential to breed
more efficient cultivars. Similarly, a study of two soyabean genotypes, together
with their 88 recombinant in-bred lines, found that P-use efficiency was
significantly correlated with root length, surface area, root width and root
depth.
126
d
n
1
r
2
n
g
|
1
d
n
6
h
3
These correlations, together with the high broad-sense heritability
values
of
the
root
traits,
suggest
the
feasibility
of
screening
P-efficient
genotypes through selection of simple root traits in the field.
Root architectural traits are also important in water-limited environ-
ments,
128,129
with relations demonstrated between the angular orientation of
roots and the subsequent extraction of soil water.
128
There is some evidence
that root growth angles in cereals are related to the environment in which the
plants evolved. For example, wild and landrace barleys tend to have a
narrower angular spread than modern cultivars as a consequence of their
evolution in water-limited conditions.
129,130
Modern cultivars tend to have a
wider angular spread which allows them to exploit the concentrated topsoil
nutrients of fertilised agricultural soils.
Marrying the architectural requirements for soil resources that are mobile,
such as water and nitrate, with those that are relatively immobile, such as
phosphorus, poses a considerable challenge to plant breeders, but one that is
very important if sustainable intensification of crop production is to be achieved.
5 Concluding Remarks
Soils are important capital resources that underpin the functioning of many
ecosystem services and especially food production. In the recent past the
pressing
need
to
increase
production
has
resulted
in
many
detrimental
