Gas Exchange and Growth
167
Table 8.2 shows the effects of nitrogen supply in gas exchange characteristics of Eucalyptus globulus plants grown in 10-1 pots in the glasshouse
with nutrient addition rates allowing for a high relative growth rate (0.042 d- 1 )
and a low relative growth rate (0.023d- 1 ) (Pereira et al. 1992a). The higher
growth rates of the high N plants were proportional to nitrogen concentrations in the leaf tissues and to significantly higher rates of net photosynthesis
and photosynthetic capacity measured as O2 evolution at CO2 and light
saturation. Stomatal aperture was unaffected and therefore water use efficiency increased significantly with increasing N in the tissues. However,
the different growth rates were also related with differences in biomass
partitioning with an increase of ca. 48% in leaf area partitioning that resulted in a decrease (ca. 50%) in the root/shoot ratio after 56 days of
growth. High N also resulted in a slight increase (20%) in the cr. All this
resulted in a 34% increase in F in the high N plants. Similar morphological
effects were also found to be dominant by McDonald et al. (1986), who
showed that a reduction in the rate of nitrogen supply to birch seedlings
decreased growth mainly because it reduced more the allocation of assimilates to new leaf area than the rate of photosynthesis per leaf area. The
extra carbon in slow growing plants was accumulated as starch mainly in
leaves.
The results shown in Table 8.2 contrast with those reported by Pereira
et al. (1992a) for plants of the same species grown in the field with different rates of nutrients and water supply. In these, biomass production was
positively related to leaf area (see Table 8.1) but the leaf photosynthetic
capacity was higher in the control without fertilizers added (C) than in the
optimal nutrition trees (IL), as shown in Table 8.3. However, as shown by
the similar values of photosynthetic capacity expressed on a dry weight basis
(Pereira et al. 1992b) or in nitrogen or chlorophyll concentration (see Table
8.3), the differences in photosynthetic capacity on a leaf area basis (in the
first row of Table 8.3) result largely from differences in cr (see also Fig. 8.2).
Nevertheless, the differences between treatments in nitrogen content of leaf
tissues were modest and much smaller than in potted plants. The primacy of
partition of N to foliage growth rather than to inreased leaf photosynthetic
capacity on a leaf level in E. globulus (Pereira et al. 1992b) was also found
by Cromer and Jarvis (1990) in Eucalyptus grandis seedlings grown with
different nutrient addition rates under controlled laboratory conditions.
Low nitrogen supply reduces the rate of leaf expansion, final leaf size, and
specific leaf area, as well as the release ofaxilary buds and the accumulation
of starch (Dale 1982; Trewavas 1985; McDonald et al. 1986; Lambers et al.
1990; Pereira 1990; Fredeen et al. 1991; Schulze et al. 1991). Table 8.4
shows a clear loss of apical dominance (number of branches of higher orders
inserted in lower order ones) in E. globulus plants grown in the field with
high rates of nutrient supply (IL) in comparison to rain-fed controls without
fertilizers added (C). This effect of high N was largely responsible for the
increase in L and in growth rate in eucalyptus (see Table 8.1). It is possible
167
Table 8.2 shows the effects of nitrogen supply in gas exchange characteristics of Eucalyptus globulus plants grown in 10-1 pots in the glasshouse
with nutrient addition rates allowing for a high relative growth rate (0.042 d- 1 )
and a low relative growth rate (0.023d- 1 ) (Pereira et al. 1992a). The higher
growth rates of the high N plants were proportional to nitrogen concentrations in the leaf tissues and to significantly higher rates of net photosynthesis
and photosynthetic capacity measured as O2 evolution at CO2 and light
saturation. Stomatal aperture was unaffected and therefore water use efficiency increased significantly with increasing N in the tissues. However,
the different growth rates were also related with differences in biomass
partitioning with an increase of ca. 48% in leaf area partitioning that resulted in a decrease (ca. 50%) in the root/shoot ratio after 56 days of
growth. High N also resulted in a slight increase (20%) in the cr. All this
resulted in a 34% increase in F in the high N plants. Similar morphological
effects were also found to be dominant by McDonald et al. (1986), who
showed that a reduction in the rate of nitrogen supply to birch seedlings
decreased growth mainly because it reduced more the allocation of assimilates to new leaf area than the rate of photosynthesis per leaf area. The
extra carbon in slow growing plants was accumulated as starch mainly in
leaves.
The results shown in Table 8.2 contrast with those reported by Pereira
et al. (1992a) for plants of the same species grown in the field with different rates of nutrients and water supply. In these, biomass production was
positively related to leaf area (see Table 8.1) but the leaf photosynthetic
capacity was higher in the control without fertilizers added (C) than in the
optimal nutrition trees (IL), as shown in Table 8.3. However, as shown by
the similar values of photosynthetic capacity expressed on a dry weight basis
(Pereira et al. 1992b) or in nitrogen or chlorophyll concentration (see Table
8.3), the differences in photosynthetic capacity on a leaf area basis (in the
first row of Table 8.3) result largely from differences in cr (see also Fig. 8.2).
Nevertheless, the differences between treatments in nitrogen content of leaf
tissues were modest and much smaller than in potted plants. The primacy of
partition of N to foliage growth rather than to inreased leaf photosynthetic
capacity on a leaf level in E. globulus (Pereira et al. 1992b) was also found
by Cromer and Jarvis (1990) in Eucalyptus grandis seedlings grown with
different nutrient addition rates under controlled laboratory conditions.
Low nitrogen supply reduces the rate of leaf expansion, final leaf size, and
specific leaf area, as well as the release ofaxilary buds and the accumulation
of starch (Dale 1982; Trewavas 1985; McDonald et al. 1986; Lambers et al.
1990; Pereira 1990; Fredeen et al. 1991; Schulze et al. 1991). Table 8.4
shows a clear loss of apical dominance (number of branches of higher orders
inserted in lower order ones) in E. globulus plants grown in the field with
high rates of nutrient supply (IL) in comparison to rain-fed controls without
fertilizers added (C). This effect of high N was largely responsible for the
increase in L and in growth rate in eucalyptus (see Table 8.1). It is possible