Agriculture Reference
In-Depth Information
On the level of nutrient uptake from the soil there are manifold co-influences
known, but their whole extent is still far from being understood. Many of these are
caused by the charged nature of ions when dissolved in water. If, for example, N is
taken up predominantly as positive charged ammonium, the uptake of other cations
such as magnesium and calcium is impaired, probably in order to maintain a
balance of charge (Haynes and Goh
1978
). On the other hand, plants that are
supplied with nitrate absorb less phosphate than plants supplied with ammonium
(Riley and Barber
1971
). Similarly, do sulfate or nitrate show a higher accumula-
tion in the plant if the other is missing in the root medium (Steingr¨ver et al.
1986
;
Koralewska et al.
2009
), either due to a replacement as an osmolyte in the vacuole
or to a balance of anion-cation uptake,
i.e.
a balance of charge. This is a hint that
increasing the storage capacity of the vacuole for one nutrient could decrease the
capacity for others of the same charge. Interactions of the uptake of nutrients with
different charge have been observed, for example for sulfate and iron (Paolacci
et al.
2013
). Here a direct interaction on the level of uptake does not seem likely. In
contrast a higher uptake of sulfate under iron deficiency is suggested to serve for the
production of S-containing defence compounds and a coupling of both nutrients
could be due to their combination in Fe-S clusters (Forieri et al.
2013
). Another
example of the interactive effects of the uptake of different nutrients has been
shown for sulfate, nitrate and ammonium (Clarkson et al.
1989
) and there are many
more reported. The direct linkage between the uptake of different nutrients, how-
ever, is under critical discussion. Studies in which plants were exposed to an
atmospheric S source while deprivation occurred in the rhizosphere show an
apparent uncoupling of sulfate and nitrate uptake (Westerman et al.
2000
,
2001
;
Stulen and De Kok
2012
).
Another potential conflict in the uptake of different nutrients arises if they use
the same uptake system. This may be true, for instance, for the transport of
phosphate and sulfate across the chloroplast membrane, which was reported to be
competitive (Gross et al.
1990
). As well as Liebig
s “law of the minimum” states
that identifying and increasing the amount of the most limiting factor can increase
plant production, there is the far less popular but equally important “law of the
optimum” formulated by Liebscher (see review Browne
1942
). It states that the
increase of such a limiting factor contributes more to the productivity of the system,
the closer all other factors are to their optimum. Liebscher studied N, P and K
nutrition of crops and was one of the first researchers to demonstrate the strong
interactive component of different nutrients and their contributions to yield. It does
not contradict Liebig
'
s “law of the minimum” but shows that reality is more
complex. Improvement of NUtE for any of the three nutrients N, P and K requires
a balanced supply with the other two (Janssen
1998
).
An important question for the future improvement of plant NUE is whether
interferences with other efficiencies exist, especially if those turn out to be real
physical trade-offs. Such trade-offs usually arise from the involvement of physio-
logical mechanisms in several efficiencies. Studies on different tree species showed
intraspecific inverse relationships between water use efficiency (WUE) and NitUE
(Field et al.
1983
; Reich et al.
1989
), which appear to explain the spatial distribution
'
