Agriculture Reference
In-Depth Information
For the successful development of new improved plant varieties a number of
pre-requisites must be met: (i) there must be genetic variability available (ii) there
must be an ability to readily identify the genes associated with this phenotypic
variability and (iii) the trait must be readily inheritable (Foulkes et al.
2009
).
Although genetic variation for nutrient efficiency has been identified in many arable
crops (e.g. Sve
ˇ
njak and Rengel
2006
in canola), there are relatively few reports of
the development of new varieties with greater NutUE. There are also arguments
that rather than directly selecting for traits such as improved NutUE, breeding for
yield improvement alone (which many plant breeders indicate is their number one
priority) has also contributed to increased N harvest index and increased N uptake
(Sadras and Lawson
2013
). However, as highlighted in this chapter, there may be a
number of opportunities to identify specific target traits, for example employing the
developing knowledge on the mechanisms underlying the decline of plant nutrients
under elevated [CO
2
].
Because a key challenge in developing new varieties is managing the complexity
of interactions between traits and environmental conditions, elevated [CO
2
] must be
taken into consideration in realistic field settings. FACE experiments can play a key
role in assessing breeding traits, but also evaluating nutrient management under the
future climate conditions (including drought). Current FACE experiments mostly
target [CO
2
] expected for 2040-2050 (550
mol mol
1
air), which is timely for
selection efforts considering that the turnaround time from trait identification to a
new variety can be 10-20 years (Chapman et al.
2012
). Whilst changes in crop
management practices, such as new fertiliser products, application rates and timing
strategies, may require less lead time than the development of new crop varieties,
they will be most effectively applied and tested in the right combination with the
right crop varieties under the relevant environmental conditions. Dealing with
below ground processes, especially those associated with roots and soils, poses
particular difficulties, and adds complexity to the system. This complexity cannot
be avoided, as shown by the importance of roots and soil processes in the interac-
tion of high [CO
2
] with plant nutrition. The use of 3-D functional simulation
modelling (Dunbabin et al.
2013
) offers considerable promise, especially when
combined with new technology such as x-ray computer tomography that allows
better imaging of root growth within soils. More flexible exposure systems that
combine the advantages of a FACE system (free air without enclosure effects) with
the use of large soil cores (such as the “SoilFACE” system as part of the AGFACE
facilities; Butterly et al.
2012
) or lysimeters and rhizotron access also offer oppor-
tunities to investigate relevant plant nutrition processes in the field.
In summary, it will be important to consider increasing [CO
2
] in further
improvements of crop nutrition and NutUE, either by genetic or managements
adaptations. Facilities that enable crop growth under elevated [CO
2
] will therefore
play an increasing role in such efforts, alongside technologies that control other key
factors such as water supply or temperature regimes.
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