Balance between photosynthesis and respiration

Some of the carbon released by decomposition may be washed into rivers and the ocean. Some of it may be taken up by other living things for use in their life processes. Some of it maybe buried in sediments and, over long periods of time, converted to fossil fuels. The burial and conversion of carbon compounds to fossil fuels upsets the balance between photosynthesis and respiration because these processes remove the carbon from the cycle for such long periods of time. Some carbon is also removed from the cycle for longs periods of time when the shells of some small ocean-dwelling... 

Balance Between Photosynthesis and Respiration. We may consider a stationary state which involves photosynthetic production, P = dp/dt (rate of production of organic material) and heterotrophic respiration, R (rate of destruction of organic material) (Figure 3). We can characterize this steady state chemically by a simple stoichiometry ... 

A temporally or spatially localized disturbance of the balance between photosynthesis and respiration (Figure 3b,c) leads to chemical and biological changes which constitute pollution (5, 25, 26). For an open system, the steady state balance is characterized by... 

Alkalinity and buffer capacity Dissociation of ammonium ions to ammonia results in the production of hydrogen ions. Unless the water column or soils are well buffered, the medium can be acidified and the rate of ammonia volatilization can decrease. Thus, a water column with high alkalinity and calcium carbonate content can buffer the system and maintain high-pH conditions. Alkalinity is affected by the balance between photosynthesis and respiration by algae and submersed macrophytes in the water column. Ammonia volatilization losses are directly proportional to the alkalinity of the system. 

C02 compensation point reflects the balance between photosynthesis and respiration processes in the light (3 4), and... 

As used here, the term biosphere includes the total sum of living matter - plants, animals, and microbial biomass and the residnes of the living matter in the geological environment snch as coal and petrolenm. A fairly close balance exists between photosynthesis and respiration, although over the whole of geological time respiration has been exceeded by photosynthesis, and the energy derived from this is stored mostly in disseminated organic matter, and, of course, in coal and petroleum. 

Acid atmospheric deposition causes acidification of waters and soils if the neutralization of the acids by weathering is too slow. Biologically mediated redox processes are important in affecting the H balance. Among the redox processes that have a major impact on H" production and consumption are the synthesis and mineralization of biomass. Any uncoupling of linkages between photosynthesis and respiration affects acidity and alkalinity in terrestrial and aquatic ecosystems (Table 15.1). 

For example, in the carbon cycle consider the balance between terrestrial photosynthesis and respiration-decay. If the respiration and decay flux to the atmosphere were doubled (perhaps by a temperature increase) from about 5200 x 1012 to 10,400 x 1012 moles y-l, and photosynthesis remained constant, the CO2 content of the atmosphere would be doubled in about 12 years. If the reverse occurred, and photosynthesis were doubled, while respiration and decay remained constant, the CO2 content of the atmosphere would be halved in about the same time. An effective and rapid feedback mechanism is necessary to prevent such excursions, although they have occurred in the geologic past. On a short time scale (hundreds of years or less), the feedbacks involve the ocean and terrestrial biota. As was shown in Chapter 4, an increase in atmospheric CO2 leads to an increase in the uptake of CO2 in the ocean. Also, an initial increase in atmospheric CO2 could lead to fertilization of those terrestrial plants which are not nutrient limited, provided there is sufficient water, removal of CO2, and growth of the terrestrial biosphere. Thus, both of the aforementioned processes are feedback mechanisms that can operate in a positive or negative sense. An increased rate of photosynthesis would deplete atmospheric CO2, which would in turn decrease photosynthesis and increase the oceanic evasion rate of CO2, leading to a rise in atmospheric CO2 content. More will be said later about feedback mechanisms in the carbon system. 

Figure 15.6. Photosynthesis and respiration, (a) A well-balanced ecosystem may be characterized by a stationary state between photosynthetic production, P (rate of production of organic material) and heterotrophic respiration, R (rate of destruction of organic matter). Photosynthetic functions and respiratory functions may become vertically segregated in a lake or in the sea. In the surface waters the nutrients become exhausted by photosynthesis, (b) The subsequent destruction (respiration) of organism-produced particles after settling leads to enrichment of the deeper water layers with these nutrient elements and a depletion of dissolved oxygen. The relative compositional constancy of the aquatic biomass and the uptake (P) and release (R) of nutritional elements in relatively constant proportions (see equation 3) are responsible for a co-variance of carbon, nitrate, and phosphate in lakes (during stagnation period) and in the ocean an increase in the concentration of these elements is accompanied by a decrease in dissolved oxygen, (c, d) The constant proportions AC/AN/AP/AO2 typically observed in these waters are caused by the stoichiometry of the P-R processes.

Photosynthesis and respiration in living organisms are the reverse of each other and so the balance between the carbon dioxide and oxygen in the atmosphere is controlled by these two processes. 

The balance between relative rates of aerobic respiration and water movement were considered in Section 4.3.4. We saw that a subsurfece concentration minimum, the oxygen minimum zone (OMZ), is a common characteristic of vertical profiles of dissolved oxygen and is produced by in situ respiration. Waters with O2 concentrations less than 2.0 ppm are termed hypoxic The term anoxic is applied to conditions when O2 is absent. (Some oceanographers use the term suboxic to refer to conditions where O2 concentrations fall below 0.2 ppm but are still detectable.) As illustrated by Figure 4.21b, this water column is hypoxic in the OMZ. The dissolved oxygen concentrations are presented as % saturations in Figure 4.21c. With the exception of the mixed layer, the water column is undersaturated with respect to dissolved oxygen with the most intense undersaturations present in mid-depths. Surface supersaturations are the result of O2 input from photosynthesis and bubble injection. 

Interannual deviations from a long-term steady-state balance between respiration and photosynthesis are likely and thought to be caused by large-scale phenomena, such as ENSO events. 

NPP is the net carbon gain by vegetation over a particular time period— typically a year. It is the balance between the carbon gained by photosynthesis and the carbon released by plant respiration. NPP includes the new biomass produced by plants, the soluble organic compounds that diffuse or are secreted by roots into the soil (root exudation), the carbon transfers to microbes that are symbiotically associated with roots (e.g., mycorrhizae and nitrogen-fixing bacteria), and the volatile emissions that are lost from leaves to the atmosphere (Clark et al., 2001). 

Explain the relationship between respiration and photosynthesis. Why is the balance between these two processes important for living organisms ... 

A disturbance of the P-R (photosynthesis-respiration) balance results from vertical (lakes) or longitudinal (rivers) separation of P and R organisms. An unbalance between P and R functions leads to pollutional effects of one kind or another depletion of 0> if P < R or mass development of algae if production rates become larger than the rates of algal destruction by consumer and decomposer organisms (R < P). 

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