Ecology: Biology of Interactions. III-07. Productivity of Different Biomes

III-7. Productivity of Different Biomes. To assess 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 III-7.1. Note: it presents data not on the net production of the entire community (which we discussed in the previous paragraph), but on the 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 either consumed by heterotrophs or removed beyond their boundaries, for example, by water flows. If none of these conditions are met, the amount of unused production in the biogeocenosis will increase, leading to autotrophic succession (see the next section). Table III-7.1. Data on biomass and net primary productivity of major biomes (in terms of dry organic matter).

Biomes	Area	Biomass, g/m²2	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
7.1	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 ocean (70.8% of the planet)		10	152	55
Total for the globe		333	170	170

III-7. Productivity of different biomes
To assess 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 III-7.1. Note: it presents data not on the net production of the entire community (which we discussed in the previous section), but on net primary production — the production of plants. The overwhelming part of this production is consumed by heterotrophs. Equilibrium in climax terrestrial communities is possible only because all primary production is either consumed by heterotrophs or is carried beyond their boundaries, for example, with water flows. If neither of these conditions is met, the amount of unused production in the biogeocenosis will increase, leading to autotrophic succession (see the next section).
Table III-7.1. Data on biomass and net primary productivity of major biomes (in terms of dry organic matter)

Thus, net primary production of land per year is 110–120 billion tons of dry organic matter, and of the ocean — 50–60 billion tons. Approximately, one can say that the ocean provides about 1/3 of our planet's production while occupying approximately 2/3 of its area. Note how the productivity of different types of biomes is linked to their biomass. The most productive biomes, for both land and ocean, are those with maximum biomass. However, the biomass of terrestrial ecosystems is much higher than that of marine ones. This is due to the fact that large plants with a significant amount of support and conducting tissues predominate on land.
Over most of the land area, productivity is limited by water shortages; in the ocean, by the lack of biogenic elements. The productivity of terrestrial ecosystems decreases from the tropics to the temperate latitudes and further towards the poles. For marine habitats, the dependence of productivity on geographical location is more complex, since currents and routes of nutrient movement significantly influence productivity. In arctic areas, land productivity is low due to the brevity of the photosynthesis period and the cold, while ocean productivity is relatively high. Circumpolar sea areas are often quite productive due to the good solubility of gases in cold water. In the tropical belt, much of the land is occupied by deserts, and the open ocean is low in productivity, but there are also particularly productive habitats — reefs, mangrove thickets, estuaries, bogs, and rainforest.
The maximum production recorded in the course of research (7000 g/m² per year) was observed in two habitats: in tropical shallow sea waters overgrown with vegetation, and in intensive cultivation of sugar cane in the Hawaiian Islands. The difference between these data and those shown in Table III-7.1 is due to the fact that the table gives average, not maximum, productivities for particular biomes.
By the way, we can now answer the exercise posed in the previous section. In the dark bottle, photosynthesis does not proceed (no light), only respiration occurs. The decrease in oxygen in the dark bottle is a measure of respiration: C0–Cb~R, where R (respiration) — respiration. In the light bottle, not only respiration but also photosynthesis occurs. For example, if the amount of oxygen in the light bottle has increased, this means that photosynthesis has produced enough oxygen to sustain respiration, with some excess. Therefore, the measure of photosynthesis of the planktonic community is the sum of the oxygen increase in the light bottle and its decrease in the dark bottle: (Cw–C0)+(C0–Cb)~P, where P (production) — production.