11.3 Flux Analysis by
14
C Addition
In recent years, global warming caused by anthropogenic increases in CO 2 has
become a critical problem, and it should be noted that aquatic ecosystems participate
deeply as places of CO 2 sources and sinks. However, elucidating the mechanisms of
this participation is difficult because natural ecosystems are comprised of a great
variety of organisms, with complicated interactions existing between many of them,
and various environmental parameters are also related in a complex way. Therefore,
to control the environmental parameters, experimental ecosystems using model
ecosystems, which are simplified so as not to affect the behavior of the system,
have become essential. Here, radioactive carbon (
14 C) was added to the microcosm
subsystem containing Chlorella vulgaris (producer), Cyclidium glaucoma (consumer), and Pseudomonas putida (decomposer), and the rate of carbon flux was
examined by measuring the
14
C quantity taken in by each constituent microbe. The
compartmentalization of the constituent microbes of the microcosm subsystem was
fractionated by Cyclidium glaucoma + Chlorella vulgaris and Pseudomonas
putida + dissolved matter with a 2.0 μm diameter filter, Cyclidium glaucoma and
Chlorella vulgaris + Pseudomonas putida + dissolved matter with a 5.0 μm diameter
filter, and microbes + dissolved matter with a 0.2 μm diameter filter.
The RI of the constituent microbes in the microcosm was examined, and the
carbon flux after the addition of NaH
14 CO 3 was calculated over time. The uptake of
carbon of each microbe was determined using the rate of increase in the RI of each
microbe until 30 minutes after chemical addition. As a result, the RIs were 2227 Bq/
pop/hr. in Chlorella vulgaris, 254.25 Bq/pop/hr. in Pseudomonas putida, and
45.019 Bq/pop/hr. in Cyclidium glaucoma. Therefore, when Chlorella vulgaris
took in carbon as a carbonate or carbonate ion, Pseudomonas putida took in the
products of metabolism, and Cyclidium glaucoma took in carbon from prey, the RI
was calculated as 1 for Chlorella vulgaris, 0.1 for Pseudomonas putida, and 0.02 for
Cyclidium glaucoma; the flux decreased by approximately 1/10 whenever it passed
through each trophic level in the microcosm food chain. The value of 1/10 corresponds to 10 times the formula of energy flow in the natural ecosystem, and it was
determined that the microcosm can serve as a functional model of natural
ecosystems.
11.4 Phosphate Addition
The effects of phosphorus concentrations on aquatic microcosms were evaluated in
terms of microbial population dynamics and the photosynthetic activity, which is the
starting point of material flux. Microcosms that consisted of Chlorella vulgaris,
Pseudomonas putida, and Cyclidium glaucoma were incubated using media that
contained various concentrations of KH 2 PO 4 . At 14–16 days after incubation began,
[
14 C]-sodium bicarbonate was added to each microcosm, and then the microbial
11 A Subsystem Microcosm Verification of the Microcosm N-System
197
14
C Addition
In recent years, global warming caused by anthropogenic increases in CO 2 has
become a critical problem, and it should be noted that aquatic ecosystems participate
deeply as places of CO 2 sources and sinks. However, elucidating the mechanisms of
this participation is difficult because natural ecosystems are comprised of a great
variety of organisms, with complicated interactions existing between many of them,
and various environmental parameters are also related in a complex way. Therefore,
to control the environmental parameters, experimental ecosystems using model
ecosystems, which are simplified so as not to affect the behavior of the system,
have become essential. Here, radioactive carbon (
14 C) was added to the microcosm
subsystem containing Chlorella vulgaris (producer), Cyclidium glaucoma (consumer), and Pseudomonas putida (decomposer), and the rate of carbon flux was
examined by measuring the
14
C quantity taken in by each constituent microbe. The
compartmentalization of the constituent microbes of the microcosm subsystem was
fractionated by Cyclidium glaucoma + Chlorella vulgaris and Pseudomonas
putida + dissolved matter with a 2.0 μm diameter filter, Cyclidium glaucoma and
Chlorella vulgaris + Pseudomonas putida + dissolved matter with a 5.0 μm diameter
filter, and microbes + dissolved matter with a 0.2 μm diameter filter.
The RI of the constituent microbes in the microcosm was examined, and the
carbon flux after the addition of NaH
14 CO 3 was calculated over time. The uptake of
carbon of each microbe was determined using the rate of increase in the RI of each
microbe until 30 minutes after chemical addition. As a result, the RIs were 2227 Bq/
pop/hr. in Chlorella vulgaris, 254.25 Bq/pop/hr. in Pseudomonas putida, and
45.019 Bq/pop/hr. in Cyclidium glaucoma. Therefore, when Chlorella vulgaris
took in carbon as a carbonate or carbonate ion, Pseudomonas putida took in the
products of metabolism, and Cyclidium glaucoma took in carbon from prey, the RI
was calculated as 1 for Chlorella vulgaris, 0.1 for Pseudomonas putida, and 0.02 for
Cyclidium glaucoma; the flux decreased by approximately 1/10 whenever it passed
through each trophic level in the microcosm food chain. The value of 1/10 corresponds to 10 times the formula of energy flow in the natural ecosystem, and it was
determined that the microcosm can serve as a functional model of natural
ecosystems.
11.4 Phosphate Addition
The effects of phosphorus concentrations on aquatic microcosms were evaluated in
terms of microbial population dynamics and the photosynthetic activity, which is the
starting point of material flux. Microcosms that consisted of Chlorella vulgaris,
Pseudomonas putida, and Cyclidium glaucoma were incubated using media that
contained various concentrations of KH 2 PO 4 . At 14–16 days after incubation began,
[
14 C]-sodium bicarbonate was added to each microcosm, and then the microbial
11 A Subsystem Microcosm Verification of the Microcosm N-System
197