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RESORPTION PROFICIENCY
BASED ON NUTRIENT CONCENTRATION IN
SENESCED LEAVES
COMPLETE
RESORPTION
INCOMPLETE
RESORPTION
I
T
E
M
E
I
E
< 0.7% N
> 1.0% N
< 0.05% P
> 0.08% P
DECIDUOUS SPP.
DECIDUOUS SPP.
< 0.04% P
> 0.05% P
EVERGREEN SPP.
EVERGREEN SPP.
Fig. 10.2 Resorption proficiency of nitrogen ( N ) and phosphorus ( P ). Proficiency is the ratio of
mass of each nutrient to the leaf mass at leaffall. If the ratio is less than the values in the figure,
resorption is complete; it is considered incomplete if the ratio is greater. SPP. , species. (From
Killingbeck 1996)
potential resorption. Killingbeck (1996) also distinguished resorption proficiency
from efficiency (Fig. 10.2 ). Efficiency is the percentage difference between nutrient
concentration per unit area of a green leaf immediately before shedding to the ini-
tial concentration of the green leaf. Proficiency, simply the nutrient concentration
of fallen leaves, is directly relevant to biogeochemical cycling (Parton et al. 2007),
whereas efficiency is more directly relevant to foliar function and leaf longevity.
The value of efficiency varies greatly among species, but the value of proficiency
does not vary so much (Killingbeck 1996, 2004).
On average, a little less than half the nitrogen and a little more than half the
phosphorus in a leaf is resorbed (Eckstein et al. 1999; Kobe et al. 2005; Yuan and
Chen 2009), but in light of the huge range of interspecific variation in resorption
efficiency and the lack of any correlation between nitrogen resorption efficiency
(NRE) and phosphorus resorption efficiency (PRE) (Fig. 10.3 ), this fact provides
little or no insight into alternative modes of foliar function. The apparent lack of
correlation between NRE and PRE is somewhat misleading, however, because in
fact tropical species are more efficient in resorbing phosphorus and temperate and
boreal species are more efficient in resorbing nitrogen, which would appear to
reflect latitudinal differences in soil availability of nitrogen relative to phosphorus
(Yuan and Chen 2009; Fig. 10.4 ). The NRE also is lower and PRE higher on average
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