Net primary productivity

Many estimates of total terrestrial net primary production are available, ranging between 45.5 Pg C/yr (Lieth, 1972) and 78 Pg/yr (Bazilevich et al., 1970). Ajtay ef oZ. (1979) have revised the various estimates and methods involved, they also reassess the classifications of ecosystem types and the extent of the ecosystem surface area using new data and arriving at a total NPP of 60 Pg C/yr. Gross primary production is estimated to be twice net primary production, i.e., 120 Pg C/yr. This implies that about 60 Pg C/yr are returned to the atmosphere during the respiratory phase of photosynthesis. It is well known that carbon dioxide uptake by plants follows daily cycles most plants take up CO2... 

The subsequent fate of the assimilated carbon depends on which biomass constituent the atom enters. Leaves, twigs, and the like enter litterfall, and decompose and recycle the carbon to the atmosphere within a few years, whereas carbon in stemwood has a turnover time counted in decades. In a steady-state ecosystem the net primary production is balanced by the total heterotrophic respiration plus other outputs. Non-respiratory outputs to be considered are fires and transport of organic material to the oceans. Fires mobilize about 5 Pg C/yr (Baes et ai, 1976 Crutzen and Andreae, 1990), most of which is converted to CO2. Since bacterial het-erotrophs are unable to oxidize elemental carbon, the production rate of pyroligneous graphite, a product of incomplete combustion (like forest fires), is an interesting quantity to assess. The inability of the biota to degrade elemental carbon puts carbon into a reservoir that is effectively isolated from the atmosphere and oceans. Seiler and Crutzen (1980) estimate the production rate of graphite to be 1 Pg C/yr. 

The two prime mechanisms of carbon transport within the ocean are downward biogenic detrital rain from the photic zone to the deeper oceans and advection by ocean currents of dissolved carbon species. The detrital rain creates inhomogeneities of nutrients illustrated by the characteristic alkalinity profiles (Fig. 11-9). The amount of carbon leaving the photic zone as sinking particles should not be interpreted as the net primary production of the surface oceans since most of the organic carbon is recycled... 

Ecosystem net primary production Combining ecology and remote sensing. Remote Sens. Environ. 51, 74-88. 

B. (1995). Monitoring seasonal and interannual variations of gross primary productivity, net primary productivity and net ecosystem productivity using a diagnostic model and remotely-sensed data, Tellus, Ser. B, 47,178-190. 

Malmstrom, C. M., Thompson, M. V., Juday, G. P., Los, S.O., Randerson, J. T. and Field, C. B. (1997). Interannual variation in global-scale net primary production Testing model estimates. Global Biogeo-chem. Cycles 11, 367-392. 

C. J. and Schloss, A. L. (1997). Equilibrium responses of global net primary production and carbon storage to doubled atmospheric carbon dioxide Sensitivity to changes in vegetation nitrogen concentration, Global Biogeochem. Cycles 11,173-189. 

The present average PO4 concentration of deep ocean water is 2.2 /rmol/kg. When a parcel of deep water is transported to the photic zone, this POi is completely incorporated into plants. Note that this assumes that net primary productivity is not limited by the availability of other micronutrients. In shortterm laboratory studies, this assumption is clearly not true in that it has been demonstrated... 

Van Cappellen, P. and Ingall, E. D. (1994). Benthic phosphorus regeneration, net primary production, and ocean anoxia A model of the coupled marine biogeochemical cycles of carbon and phosphoms. Paleoceanography 9,677-692. 

The plant species biomass of Boreal and Sub-Boreal Forest ecosystems accumulates a significant part of living matter of the whole planet. This value is about 700 x 106 tons of dry weight. The biomass per unit area of different Forest ecosystems varies from 100 to 300 ton/ha and even 400 ton/ha in the Eastern European Oak Forest ecosystems. The annual net primary productivity, NPP, varies from 4.5 to 9.0 ton/ha (Table 1). 

We can see from Table 4 that most of the Spruce Forest ecosystem biomass is accumulated in trees, with trunk mass predominating. The values of annual Net Primary Production (NPP) and litterfall production are more connected with needles. In living matter, the mass of moss and bush species makes up to 2-3% of the tree biomass, whereas in dead matter (litterfall), it is up to 10%. 

Table 10. Biomass and net primary productivity of the Tar Dry Desert ecosystem, India.

Mangrove ecosystems are an example of one of the most productive ecosystems of the World. The biomass pool is in excess of 100 ton/ha of dry matter and annual NPP varies from 10 to 30 ton/ha, including leaf litter production of 8-15 ton/ha. Using average data on annual net primary production and content of various elements, we... 

The depth of the mixed layer is important for two reasons. First, phytoplankton can be carried out of the photic zone and, hence, halt net primary production if the mixed layer is deeper than the photic zone. Second, the bottom of the mixed layer marks the upper limit to which density stratification in the thermocline inhibits upward vertical transport of nutrients. If the photic zone extends into the thermocline, phytoplankton... 

Table 1.3 Net primary production of wetlands compared with other ecosystems...

The soil contains organic matter which is humified to a varying extent and inputs of fresh organic matter are often much larger than in aquatic systems because of greater net primary productivity. The organic matter both provides substrates for microbial processes and participates in sorption and other reactions. 

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