Agriculture Reference
In-Depth Information
seeds and grains tend to decrease under elevated [CO
2
]. In many crops, particularly
cereals such as wheat or rice, concentrations of protein and minerals in grains are
important determinants of the nutritional value and functional properties (Erbs
et al.
2010
;H
ยจ
gy et al.
2009
).
The lower tissue N concentrations in conjunction with proportionally increased
carbon assimilation and its subsequent incorporation into storage and structural
material of the plant results in increased carbon to nitrogen ratio (C/N). This leads
to increased nitrogen use efficiency of plants under CO
2
enrichment (Fig.
9.1
;
Drake et al.
1997
). The same principle can be applied for other macro and
micronutrients, although less documented than for N. Although overall nutrient
concentrations in plant biomass are decreased under CO
2
enrichment, total nutrient
removal via grains or plant biomass, for example such as N, can increase under CO
2
enrichment (Conroy and Hocking
1993
; Lam et al.
2012b
). Such effects will have
significant consequences for food quality and the management of our agricultural
systems in a future high [CO
2
] world.
Nitrogen
N is the ecologically and economically most important mineral nutrient in cropping
systems globally, and has thus received intense attention so that knowledge of plant
N metabolism is comparably advanced relative to most other nutrients. It is there-
fore not surprising that the majority of research on interactions of nutrients with
high [CO
2
] in plants has focused on N. We will therefore discuss major principles of
plant nutrition changes under CO
2
enrichment using N as the main example.
Nitrogen Concentrations in Plant Tissues Under CO
2
Enrichment
Dry mass based tissue concentrations of nitrogen (N
m
) are generally lower in high
[CO
2
] grown plants, as confirmed by a number of recent synthesis papers (Ains-
worth and Long
2005
; Leakey et al.
2009
; Stitt and Krapp
1999
; Taub and Wang
2008
; Wang et al.
2013
). For example, leaf N
m
decreased by about 13 % across a
number of FACE experiments (Ainsworth and Long
2005
), or by an average of 9 %
for wheat across experiments with different CO
2
exposure systems and CO
2
concentrations (Wang et al.
2013
). This decrease is somewhat smaller on a leaf
area basis, only about 4 % across a number of FACE experiments (Leakey
et al.
2009
). The decrease in leaf N is consistently related to a decrease in total
leaf protein, specifically, and perhaps exclusively, to a decrease in the amount of
Rubisco protein (Leakey et al.
2009
). Decreased Rubisco content in leaves is linked
to photosynthetic downward acclimation under prolonged exposure to increased
[CO
2
] and may thus reflect changes in N allocation patterns.
