Physiological Basis of Plant Nutrient Use Efficiency – Concepts, Opportunities and Challenges for Its Improvement - Nutrient Use Efficiency in Plants - page 8

Fig. 1.2 Plant NUE has a
complex physiological basis
with interacting cellular and
whole plant processes. After
the acquisition of a nutrient
it contributes directly or
indirectly to the production
of biomass and the final
yield. Storage and
remobilization are
important processes that
buffer asynchronies in
nutrient demand and
availability and the efficient
reallocation of nutrients
between different plant
organs is a crucial process
during plant development.
Especially in cereals the
translocation of nutrients to
the finally harvested sink
organ, the grains, is of
particular importance.
Nutrient loss can happen in
several ways and displays a
general constraint for NUE
Nutrient storage is another process of importance and can be functionally
sub-divided into accumulation, reserve formation and recycling (Chapin
et al. 1990 ). Accumulation summarizes the increase of compounds that are not
directly related to growth. They accumulate simply because the availability exceeds
the demand of the plant metabolism for these compounds. Reserve formation in
contrast describes metabolically controlled storage in designated storage com-
pounds. In this way compounds that otherwise would promote growth are stored
in a form that does not. The formation of these storage compounds directly
competes with growth and other processes that would use the compound in its
original form as a substrate. In the process of recycling, compounds that originally
contributed to growth promotion or other physiological functions but which would
be lost are actively broken down to be used for future growth (Chapin et al. 1990 ).
The significance of nutrient storage and remobilization for NUE depends on
nutrient availability. A study with a number of hybrids of corn ( Zea mays L .)
revealed that under low N supply differences in NitUE between hybrids are related
to variation in the utilization of stored N. However if N supply was high, acquisition
efficiency became more important (Moll et al. 1982 ). A low ability to remobilize N
leads to a lowered N harvest index in Brassica napus (Rossato et al. 2001 ). Sim-
ilarly for S the limits of storage capacity and remobilization efficiency of sulfate are