Ecology: the Biology of Interactions. 3.07. Productivity of Different Biomes
Net primary production on land per year is 110–120 billion tons of dry organic matter, and in the ocean 50–60 billion tons. Roughly speaking, the ocean provides about one-third of the planet’s production while occupying about 70% of its surface...
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3.06. Ecosystem Productivity and its Measurement
D. Shabanov, M. Kravchenko. Ecology: Biology of Interactions Section 3. Biogeocenology and Ecology of Communities
3.08. Successions. Basic Concepts
3.07. Productivity of Different Biomes To estimate the productivity of the Earth, it was necessary to divide its surface into different types of natural and artificial ecosystems, study the productivity of each of these types, and then obtain a global productivity estimate. The most characteristic (though far from all) results of this work are presented in Table 3.7.1. Note: it provides data not on the net production of the entire community (which we discussed in the previous paragraph), but on net primary production — the production of plants. The vast majority of this production is consumed by heterotrophs. Equilibrium in climax terrestrial communities is possible only because all primary production is consumed by heterotrophs (or removed beyond their limits, for example, by water flows). Table 3.7.1. Data on biomass and net primary productivity of major biomes (in terms of dry organic matter)
Biomes
Area
Biomass, g/m2
Production, g/m2 per year
Total, billion t/year
Tropical rainforest
11,4 %
45 000
2 200
37,4
Seasonal tropical forest
5,0 %
35 000
1 600
12,0
Deciduous forest
4,7 %
30 000
1 200
8,4
Steppe
6,0 %
1 600
600
5,4
Deserts
16,1 %
20
3
0,07
Lakes and rivers
1,3 %
20
250
0,5
Cultivated land
9,3 %
1 000
650
9,1
Total for land (29.2% of the planet)
12 300
773
115
Open ocean (pelagial)
92,1 %
3
125
41,5
Continental shelf
7,4 %
10
360
9,6
Algae beds and reefs
0,15 %
2 000
2 500
1,6
Upwelling zones
0,1 %
20
500
0,2
Estuaries
0,35 %
1 000
1 500
2,1
Total for the ocean (70.8% of the planet)
10
152
55
Total for the globe
333
170
170
Thus, the net primary production of land per year is 110–120 billion tons of dry organic matter, and that of the ocean is 50–60 billion tons. Approximately, it can be said that the ocean provides about 1/3 of our planet's production, while occupying about 2/3 of its area. Note how the productivity of different biome types is related to their biomass. The most productive biomes, both on land and in the ocean, are those with maximum biomass. However, the biomass of terrestrial ecosystems is much higher than that of marine ecosystems. This is because large plants with a significant amount of supporting and conductive tissues predominate on land. On a larger land area, productivity is limited by water scarcity, and in the ocean, by nutrient scarcity. The productivity of terrestrial ecosystems decreases from the tropics to temperate latitudes and further to the poles. For marine habitats, the dependence of productivity on geographical location is more complex, as productivity is significantly influenced by currents and nutrient transport pathways. In Arctic regions, land productivity is low due to the short photosynthetic period and cold, while ocean productivity is relatively high. Often, the polar seas turn out to be quite productive due to the good solubility of gases in cold water. In the tropical zone, most of the land is occupied by deserts, and the open ocean is unproductive, but there are also particularly productive areas – reefs, mangrove thickets, estuaries, swamps, and rainforests. The maximum production recorded during the studies (7000 g/m2 per year) was observed in two locations: in tropical shallow marine areas overgrown with vegetation, and in intensive sugarcane cultivation in the Hawaiian Islands. The difference between these data and those presented in Table 3.7.1 is due to the fact that the table shows averaged, not maximum, productivities for the respective biomes. By the way, it is now possible to answer the question posed in the previous section. In a dark bottle, photosynthesis does not occur (there is no light), only respiration occurs. The decrease in oxygen in the dark bottle is a measure of respiration: C0–Cb~R (where R (English respiration) is respiration). In a light bottle, not only respiration but also photosynthesis occurs. For example, if the amount of oxygen in a light bottle increased, it means that photosynthesis produced enough oxygen to support respiration, and some additional amount. Thus, the measure of plankton community photosynthesis is the sum of the increase in oxygen in the light bottle and its decrease in the dark bottle: (Cw–C0)+(C0–Cb)~P, where P (English production) is production.
3.06. Ecosystem Productivity and its Measurement
D. Shabanov, M. Kravchenko. Ecology: Biology of Interactions Section 3. Biogeocenology and Ecology of Communities
3.08. Successions. Basic Concepts