Nutrient Distribution and Cycling
265
Principal component 2 (17% of the variance) was positively related to Ca
and Mg increments in foliage, and negatively related to P increment in
branches+boles and litterfall P. The three holm oak stands appeared centered
(i.e. scores near zero) on component 2. Principal component 3 (9% of the
variance) was positively related to Ca, Mg and K increment in branches +
boles, and negatively related to P increment in foliage and litterfall P. The
three holm oak stands score moderately high in component 3.
Principal component 2 seems to be related to base cation demand for foliage production, while component 3 seems related to base cation demand for
woody production. Both components suggest an antagonism between P nutrition and base-cation richness, at least when the effects of overall nutrient
richness (component 1) are removed.
18.7 Nutrient Use Efficiency
Nutrient cycling data can give insight into the nutrient use efficiency (NUE)
at the stand level. Among the many definitions of NUE, we have chosen that
of Berendse and Aerts (1987) because they split the concept into two biologically meaningful components which can vary independently of each other:
A, the nutrient productivity or amount of annual production per unit of nutrient contained in the vegetation (g g-l year-I); and 1IL, the mean residence
time of the nutrient in the vegetation (year). The overall NUE is the product
of both components (A x 1IL; g g-l), and gives the amount of production per
unit of nutrient in the vegetation, integrated over the lifetime of this nutrient
unit. Again, we have restricted ourselves to the aboveground NUE since the
available fine root data were not enough for this purpose. For these aggrading holm oak forests we computed the mean residence time of nutrients in
the aboveground biomass as the nutrient pool in this biomass divided by the
aboveground nutrient return. Nutrient productivity is higher at Montseny
than at Prades for all five major nutrients (Fig. 18.3a), the highest relative
difference being for P. This higher nutrient productivity is mostly a reflection
of the higher aboveground net primary production at Montseny. Probably,
the higher rainfall there allows for better returns in terms of carbon gain of
each gram of nutrient invested in biomass. Mean residence time, which is
positively related to NUE, is much higher at Prades than at Montseny for N
and P, and somewhat higher for Ca (Fig. 18.3b). Two facts account for the
higher mean residence time of Nand P in the aboveground biomass at
Prades: (1) the higher mean concentrations of Nand P in the biomass at
Prades, themselves reflecting either a more concentrated soil solution under
a drier climate or a lesser dilution by growth; and (2) a higher return of N
and P in litterfall (and for P also in canopy leaching) at Montseny, resulting
largely from the higher production of flowers and fruits at Montseny, at least
during the respective study periods.
265
Principal component 2 (17% of the variance) was positively related to Ca
and Mg increments in foliage, and negatively related to P increment in
branches+boles and litterfall P. The three holm oak stands appeared centered
(i.e. scores near zero) on component 2. Principal component 3 (9% of the
variance) was positively related to Ca, Mg and K increment in branches +
boles, and negatively related to P increment in foliage and litterfall P. The
three holm oak stands score moderately high in component 3.
Principal component 2 seems to be related to base cation demand for foliage production, while component 3 seems related to base cation demand for
woody production. Both components suggest an antagonism between P nutrition and base-cation richness, at least when the effects of overall nutrient
richness (component 1) are removed.
18.7 Nutrient Use Efficiency
Nutrient cycling data can give insight into the nutrient use efficiency (NUE)
at the stand level. Among the many definitions of NUE, we have chosen that
of Berendse and Aerts (1987) because they split the concept into two biologically meaningful components which can vary independently of each other:
A, the nutrient productivity or amount of annual production per unit of nutrient contained in the vegetation (g g-l year-I); and 1IL, the mean residence
time of the nutrient in the vegetation (year). The overall NUE is the product
of both components (A x 1IL; g g-l), and gives the amount of production per
unit of nutrient in the vegetation, integrated over the lifetime of this nutrient
unit. Again, we have restricted ourselves to the aboveground NUE since the
available fine root data were not enough for this purpose. For these aggrading holm oak forests we computed the mean residence time of nutrients in
the aboveground biomass as the nutrient pool in this biomass divided by the
aboveground nutrient return. Nutrient productivity is higher at Montseny
than at Prades for all five major nutrients (Fig. 18.3a), the highest relative
difference being for P. This higher nutrient productivity is mostly a reflection
of the higher aboveground net primary production at Montseny. Probably,
the higher rainfall there allows for better returns in terms of carbon gain of
each gram of nutrient invested in biomass. Mean residence time, which is
positively related to NUE, is much higher at Prades than at Montseny for N
and P, and somewhat higher for Ca (Fig. 18.3b). Two facts account for the
higher mean residence time of Nand P in the aboveground biomass at
Prades: (1) the higher mean concentrations of Nand P in the biomass at
Prades, themselves reflecting either a more concentrated soil solution under
a drier climate or a lesser dilution by growth; and (2) a higher return of N
and P in litterfall (and for P also in canopy leaching) at Montseny, resulting
largely from the higher production of flowers and fruits at Montseny, at least
during the respective study periods.