Agriculture Reference
In-Depth Information
NUE
¼
NAcE
NUtE
While Chapin (
1980
) defined NUE simply as the inverse of the tissue nutrient
concentration, NUtE can be further sub-divided into nutrient productivity (NP) and
mean residence time, the period in which a certain nutrient can be used for
production (MRT; Berendse and Aerts
1987
). In the 1980s, Vitousek and
co-workers (Vitousek
1982
; Birk and Vitousek
1986
) defined the nitrogen use
efficiency (NitUE) of perennials as the amount of organic matter, which is lost
from a plant or permanently stored in wood, divided by the amount of N lost or
permanently stored. It was shown that NitUE of
Pinus taeda
L. stands decreased
with increasing N availability. A more general definition was suggested by
Berendse and Aerts (
1987
), who identified MRT and nitrogen productivity (NitP)
as the main components of NitUE:
NitUE
¼
NitP
MRT
According to Berendse and Aerts (
1987
), NitP describes the instantaneous rate
of carbon fixation or biomass production per unit N present in the plant while MRT
is a measure for the period in which N can be used for carbon fixation. This concept
of MRT can theoretically be extended to other nutrients and plant species. In
fertilisation models NP can be used to calculate the nutrient flux density that is
necessary to maintain an optimal nutrient concentration in the plant (Ingestad
1988
)
but this again refers to the field and not to NUE at the plant level.
It is well known that plant species and ecotypes, which naturally grow in
nutrient-poor soils possess mechanisms to increase the MRT of nutrients
e.g.
slow growth, high accumulation of nutrients and efficient remobilization of such
storage capacities or a reduction of nutrient loss (V
´
zquez de Aldana and Berendse
1997
). In soils where nutrients are available in excess or at least where nutrient
availability is not the limiting factor, there is less selective pressure on developing
such mechanisms. It is more important to have a high NP to grow fast and compete
with neighbouring individuals for space and light and one way to reach this might
be having a high nutrient throughput rather than a long MRT. Studies under
controlled conditions with plants from both soil types showed that in the short
term fast growing species were the better competitors in both optimal and limiting
N conditions while in the longer term, plants from nutrient-poor soils outcompeted
fast growing species under limiting conditions (Chapin
1980
; Wedin and Tilman
1990
; Berendse et al.
1992
). It is considered that these differences in NUE between
plants, which originated from soils with different nutrient concentrations, are due to
differences in the underlying physiology, morphology and development. Van der
Werf et al. (
1993
) showed how important morphological traits are for adapting
NUE to the respective nutrient concentration in the soil. For instance, a high
investment in root mass served for the high NP of fast growing species, though it
should be noted that the majority of these studies on NUE dealt with wild species
and N.
