Agriculture Reference
In-Depth Information
relevance of the underlying physiological processes (Fig.
1.2
) has to be analysed in
relation to the variables that modify it (Fig.
1.3
). Once the limiting processes are
identified, breeding or transgenic methods might lead to further improvement of
NUE. For success, the physical and physiological trade-offs that limit an improve-
ment in NUE have to be identified. This will be the topic of the last part of this
chapter.
NUE - Challenges from a Whole Plant Perspective
As stated previously, NP and MRT can be seen as sub-components of NUtE.
Consequently both could be targeted to improve NUE in cropping systems.
Berendse and Aerts (
1987
) have pointed out the apparent ecological trade-off of
NitP and MRT. While in nutrient-poor soils a long MRT is favourable, a high NitP
gives advantages in nutrient-rich soils. Plant species in nutrient-rich soils generally
possess a larger photosynthetic apparatus and can thereby rapidly make use of
higher N availability, while species in nutrient-poor soils are able to use spare
nutrients more economically. Theoretically, generalist species should combine both
traits, but evidence suggests that they are competitive (Berendse et al.
1987
). A later
study on species with different life forms in a sub-arctic environment confirmed this
negative relationship of NitP and MRT (Eckstein and Karlsson
1997
), and others
followed (Yasumura et al.
2002
; Silla and Escudero
2004
). Within the same
species, this trade-off also appears to be consistent, with higher N supply leading
to higher NitP but lower MRT (Yuan et al.
2005
) or the other way around (Yuan
et al.
2008
). High nutrient supply, however, may even lead to a decline of both
components in certain circumstances. A decline in NP can be caused by cross- and
self-shading and an accompanied decrease in photosynthetic activity and a lower
MRT can be the result of enhanced litter production or leaching (Meuleman
et al.
2002
).
As studies have almost exclusively focused on natural systems, perennials
and N, it is difficult to assess if a strict trade-off between NP and MRT exists in
agricultural crops and for all nutrients. As litter decomposability is not an issue in
annual crop production, a high NP and long MRT at the same time are desired to
maximize yield output and minimize nutrient input. The fact that traits, which lead
to either a high NP or a long MRT, are not co-occurring in nature does not
necessarily mean that breeding could not combine them. More integrated research
on the described underlying physiological processes and their possible trade-offs
are needed, including research with nutrients other than N.
In general, NUE is only studied for one single nutrient. There are few studies,
which address the question whether improving the NUE for one nutrient will affect
the NUE of others. Given the interactive and competitive nature of nutrients in
many physiological processes, it seems likely that increasing NUE for one nutrient
will also alter the NUE of others in a positive or negative manner.
