Agriculture Reference
In-Depth Information
of species on either N-poor or water-deficient soils (Patterson et al.
1997
) but also
have implications for the improvement of NUE in agriculture. This trade-off has
stomatal as well as non-stomatal components (Reich et al.
1989
) depending on the
water and N status of the soil. How relevant it is for agricultural practice and crop
breeding towards an increased NUE has still to be clarified. It might help the case to
distinguish between the levels of NAcE and NUtE. If water is a limiting factor
during crop growth, NAcE usually increases in its relevance, as nutrient uptake is
physically coupled to water uptake. Climate change may mean seasonal droughts
appear more frequently in many regions of the world which further increases the
need for crops with a high WUE (Reynolds et al.
2011
). For wheat, for example, it
has been shown that under water limiting conditions genotypes with a greater root
biomass produce more grains, probably due to both a high WUE and NAcE during
early growth due to enhanced ability to capture water and reduce nitrate leaching
(Ehdaie et al.
2010
). Root traits are considered as a selection criterion especially
under drought conditions (Ren et al.
2012
) but there are strong interactions with
NAcE that have to be considered. For example, the responses of root architecture to
P and N deficiency are very different. While P deficiency leads to a shallow root
system, foraging for the immobile phosphate, N deficiency causes a deep, scarcely
branched root system. The latter is also associated with an efficient capture of water
during periodical drought (White et al.
2013
) implying that the NAcE for N and an
efficient water uptake are not in competition but share a similar morphological trait.
How the shallow root system that leads to a higher NAcE of P displays a constraint
to WUE needs to be further evaluated. However, there are also reports that show an
apparent negative interaction of N supply with WUE. High N supply leads to an
inhibition of the typical growth characteristics that lead to a higher WUE in
Sophora davidii
while appropriate or
low supply alleviated drought stress
(Wu et al.
2008
).
NUtE, NitUE and WUE show strong interactions due to their correlative effects
on stomatal conductance, gas exchange and photosynthesis. In wheat, a higher N
supply is reported to lead to an increase in WUE but at the same time to a decreased
NitUE (Shangguan et al.
2000
; Cabrera-Bosquet et al.
2007
). This trade-off
between NUtE and WUE is particularly noticeable if the N-to-grain price ratio in
an agricultural system is high (Sadras and Rodriguez
2010
). How the NUE of
nutrients other than N interferes with WUE is still an open question.
Other studies have revealed a trade-off between N and light use efficiency (LUE)
in canopies (Niinemets and Tenhunen
1997
; Hirose and Bazzaz
1998
). This can be
explained by the fact that a high concentration of N in leaves leads to a high LUE
but low NitUE. The impact of this trade-off again depends on the factors described
above. It becomes more relevant under shading conditions and for trees because the
build-up of the desired timber strongly depends on exploiting light efficiently
during the growing season.
Again, it should be noted that inverse relationships between certain plant traits
observed in nature do not necessarily display real physical trade-offs that cannot be
overcome in plant breeding. They might just reflect genetic adaptations to different
habitats or an ecological disadvantage of the combination of both traits (Veneklaas
