Agriculture Reference
In-Depth Information
of these constraints such as high salinity (Poorter and Perez-Soba
2001
), supported
by the finding that high [CO
2
] generally increases assimilate allocation to below
ground processes including root growth and exudation (Lynch and St. Clair
2004
).
However, Munns et al. (
1999
) found that whereas there was a positive interaction
between [CO
2
] and salinity at low CO
2
levels, there was no CO
2
fertilisation effect
at high [CO
2
].
Outlook: Traits and Practices to Improve Crop Nutrition
and Quality Under High [CO
2
]
Given the extent of nutrient deficiencies globally and the financial (e.g. steadily
increasing fertiliser prices) and environmental (e.g. eutrophication of water ways)
cost of managing nutrients in agricultural systems it is not surprising that consid-
erable research has been devoted to improving NutUE in crops especially that of N
and P in both low and high input systems (Wiesler et al.
2001
; Hawkesford
2011
).
This research has encompassed genetic solutions (Hirel et al.
2007
), improved
fertiliser forms (e.g. Chen et al.
2008
; McLaughlin et al.
2011
) as well as systems
approaches such as better predictions of crop nutrient requirements through
improved soil testing and predictions of crop nutrient demand often via the use of
computer simulation models (e.g. Carberry et al.
2002
; Moeller et al.
2009
). As
shown in this chapter, elevated [CO
2
] shifts the relative resource availability
towards photosynthetically fixed C and therefore affects the trade-offs that are
key to optimising plant traits and crop management in practice (Sadras and
Calderini
2009
). Recently, the argument that crop improvement should explicitly
take into account elevated [CO
2
] has gained some traction, particularly as it was
shown that traits selected by breeders over the past 100 years were not necessarily
beneficial under increased [CO
2
] (Ainsworth et al.
2008
; Tausz et al.
2013
; Ziska
et al.
2012
). Similarly, management practices should be evaluated under elevated
[CO
2
], as plant growth changes in amount and timing, and this will affect nutrient
demand, uptake and utilisation.
Most aspects of plant NutUE will improve as a consequence of the CO
2
fertilisation effect (Table
9.1
), but the overall increased nutrient demand of crops
accumulating more biomass ensures that the quest for optimum plant nutrition and
NutUE remains of paramount importance. Elevated [CO
2
] will only accentuate the
“yield quality conundrum”, e.g. the fact that mineral nutrients or protein concen-
trations decrease as crop yields increase (Hawkesford
2011
). The main challenge
will be how to supply sufficient N to maintain grain protein concentrations under
high [CO
2
], but the issues are similar for other nutrients, as their global supplies are
becoming limited (such as P), they play important role in grain quality (such as S),
or micronutrients such as Fe and Zn that are crucial to human health. Genetic
(breeding or biotechnological) and management improvements targeting the quality
yield conundrum particularly under elevated [CO
2
] are therefore a high priority in
agricultural research.
