Agriculture Reference
In-Depth Information
Other Mineral Nutrients
Whilst effects of CO
2
enrichment on plant N are relatively consistent and well
documented, there is little consensus about most other mineral nutrients. It is
important to recognise that different mineral nutrients are not independent of
each other: they can share or co-regulate common uptake and metabolic pathways,
and are regulated in an interdependent manner by plant growth or assimilate
availability. We have more detailed knowledge on interactions between P and N
or S and N (Hawkesford and De Kok
2007
; White and Hammond
2008
), but
interactions apply to other mineral nutrients as well. Although not investigated in
great detail under high [CO
2
], it is safe to assume that such interactions play an
important role in modifying the CO
2
response of selected mineral elements and
their metabolism.
Recent reviews mostly suggest that elevated [CO
2
] also leads to decreased tissue
concentrations of mineral nutrients other than N, but results are inconsistent: For
example, one recent synthesis paper found significant decreases in 11 (if N is
excluded) elements in elevated [CO
2
] grown plant tissues, including Mg, K, P, S,
Fe, Ca, Mn, and Zn (McGrath and Lobell
2013
). In apparent contrast, Duval
et al. (
2012
) found only a few significant changes in leaf mineral concentrations
(excluding N) in crops (excluding legumes) and N-fixers: in that analysis, among all
investigated mineral nutrients, only leaf Mg concentrations were significantly
decreased under CO
2
enrichment in both functional groups. In legume leaves, B
and Fe decreased as well, whereas Mn even increased significantly. However,
results for grasses were different again, and perhaps most surprisingly, this study
found no significant effects of elevated [CO
2
] on grain nutrients (Duval et al.
2012
).
In several other studies, which focused on the effects on grains rather than vegeta-
tive plant parts, there seems to be overall agreement that the elements N, S, Mg, Ca,
Zn, and Na are significantly reduced under CO
2
enrichment while contrasting
results are reported for K, Mn, P and Fe (Fangmeier et al.
1999
; Fernando
et al.
2012
;H¨gy and Fangmeier
2008
;H¨gy et al.
2013
; Manderscheid et al.
1995
).
Some of these discrepancies may be due to different nutrient supply conditions,
which is important for some micronutrients. Apparently contradictory results may
also point out some in principle problems with many synthesis papers, where the
analysed data set may be biased by particular exposure or growing systems, or
factors analysed independently (such as, for example, crop type) may be strongly
confounded by other factors. For example, it is common that data from different
crop types or plant functional groups come from separate groups of experiments
(for example, different large scale FACE experiments), and are therefore poten-
tially confounded by factors such as climate or soil. Further, environmental grow-
ing conditions can mediate nutrient responses to elevated [CO
2
]: in one FACE
study, variations in rainfall and/or temperature had a significant effect on the
response on macro and micro mineral concentrations in wheat grains to CO
2
enrichment (Fernando et al.
2012
).
