Deuterium Content in Organic Material of Hosts and Their Parasites
399
Due to this close dependence of the holoparasite with its host as far as
organic material is concerned, it is not surprising that there is no statistical
difference in the (513C values between host and parasite.
As expected, there is a clear difference in the (513C value of the hosts with
C 3 and C 4 photosynthesis, as well as with their corresponding parasites (in
both cases p < 0.001). Surprisingly, there is a statistically highly significant
(p < 0.001) difference in the deuterium content of the organic material of
the host and its holoparasite: the parasite is always considerably richer in
deuterium. We discuss this phenomenon later in more detail.
In these pairs of host plants and holoparasites there is a strong correlation
between the (513C and (5D values both within the host plants (K = 0.672) and
within the parasites (K = 0.635): those richer in 13C are also richer in
deuterium. It is remarkable that the correlation coefficients are so similar in
both cases.
19.2.3 Isotope Contents of Mistletoes (Hemiparasites) and Their Hosts
Mistletoes are considered to be hemiparasites, since they are able to perform considerable photosynthesis. As far as is known, they have C3 photosynthesis. Recently, several experimental data indicate that mistletoes (at
least in special cases) also obtain a considerable amount of organic material
from their hosts (d. Ehleringer et al. 1985; Marshall and Ehleringer 1990;
Schulze et al. 1991). Since mistletoes feed on the xylem of their hosts, this
organic material must be in the transpiration stream.
As a consequence, mistletoes on C 4 - or CAM hosts can have (513C values
different from normal C 3 values (d. Schulze et al. 1991).
In Table 19.3 the (513C and (5D values of a large number of mistletoes
and their hosts from two mistletoe-rich regions (Australia and Africa +
Madagascar) are given. It can be seen that - as expected - the (513C values of
mistletoes growing on CAM plants in Africa are significantly less negative
(13C-richer) (average -17.4 ± 4.46%0) than the ones growing on C 3 hosts
(average -25.4 ± 2.07).
As was mentioned and explained earlier (Ehleringer et al. 1985; Ullmann
et al. 1985; Ziegler 1986; Schulze et al. 1991), the mistletoes have in
practically every case more negative (513C values than their hosts (p < 0.001
in any case). This mirrors the higher Cj (intercellular CO 2 concentration)
over the whole vegetation period of the parasites with their higher degree of
stomatal opening and their consequently higher transpiration. The average
of the (513C in the C3 hosts in Australia is -26.50/00 (± 1.65), while that of
the mistletoes is -28.5 (± 1.3). The corresponding values for the African/Madagascar species are -23.8 (± 4.22) and -26.7 (± 2.9), respectively.
The (513C values of the African CAM species show an average of -17.4%0
(± 4.46), and those of associated mistletoes average -24.10/00 (± 3.74).
399
Due to this close dependence of the holoparasite with its host as far as
organic material is concerned, it is not surprising that there is no statistical
difference in the (513C values between host and parasite.
As expected, there is a clear difference in the (513C value of the hosts with
C 3 and C 4 photosynthesis, as well as with their corresponding parasites (in
both cases p < 0.001). Surprisingly, there is a statistically highly significant
(p < 0.001) difference in the deuterium content of the organic material of
the host and its holoparasite: the parasite is always considerably richer in
deuterium. We discuss this phenomenon later in more detail.
In these pairs of host plants and holoparasites there is a strong correlation
between the (513C and (5D values both within the host plants (K = 0.672) and
within the parasites (K = 0.635): those richer in 13C are also richer in
deuterium. It is remarkable that the correlation coefficients are so similar in
both cases.
19.2.3 Isotope Contents of Mistletoes (Hemiparasites) and Their Hosts
Mistletoes are considered to be hemiparasites, since they are able to perform considerable photosynthesis. As far as is known, they have C3 photosynthesis. Recently, several experimental data indicate that mistletoes (at
least in special cases) also obtain a considerable amount of organic material
from their hosts (d. Ehleringer et al. 1985; Marshall and Ehleringer 1990;
Schulze et al. 1991). Since mistletoes feed on the xylem of their hosts, this
organic material must be in the transpiration stream.
As a consequence, mistletoes on C 4 - or CAM hosts can have (513C values
different from normal C 3 values (d. Schulze et al. 1991).
In Table 19.3 the (513C and (5D values of a large number of mistletoes
and their hosts from two mistletoe-rich regions (Australia and Africa +
Madagascar) are given. It can be seen that - as expected - the (513C values of
mistletoes growing on CAM plants in Africa are significantly less negative
(13C-richer) (average -17.4 ± 4.46%0) than the ones growing on C 3 hosts
(average -25.4 ± 2.07).
As was mentioned and explained earlier (Ehleringer et al. 1985; Ullmann
et al. 1985; Ziegler 1986; Schulze et al. 1991), the mistletoes have in
practically every case more negative (513C values than their hosts (p < 0.001
in any case). This mirrors the higher Cj (intercellular CO 2 concentration)
over the whole vegetation period of the parasites with their higher degree of
stomatal opening and their consequently higher transpiration. The average
of the (513C in the C3 hosts in Australia is -26.50/00 (± 1.65), while that of
the mistletoes is -28.5 (± 1.3). The corresponding values for the African/Madagascar species are -23.8 (± 4.22) and -26.7 (± 2.9), respectively.
The (513C values of the African CAM species show an average of -17.4%0
(± 4.46), and those of associated mistletoes average -24.10/00 (± 3.74).