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What Are Photosynthesis and Respiration? - dummies

Organic Matter Stability
Stability is the measure of how rapidly carbon is altered in OM. Some organic matter is extremely stable. Diamonds and graphite are pure carbon, but a diamond will not change its composition for thousands of years. There are three basic facets of OM stability. If mixed with the soil, will OM take nutrients away from plants? If stacked, will OM heat up? If left on the soil surface, will OM create odors, draw flies, or invite larger animals to feed?
We have already shown how C:N ratio is used to predict immobilization in soil. A direct method to predict autoheating ability of solid manure or compost is to place a sufficient quantity of material into an insulated container, add water to bring moisture content to approximately 50 percent, and measure temperature rise in the container after one day. A step by step procedure to use this method is given in OSU Factsheet, BAE-1761, The Icebox Test: an Easy Method to Determine Autoheating Potential of Compost and Byproduct Materials.
Putrescibility is a measure of a waste’s ability to release noxious odors and attract flies. The general definition of a non-putrescible waste is that it cannot undergo “significant biological transformation.” Decomposing animal bodies undergo a huge transformation from muscle protein to soil organic matter. Composted manure is non-prutescible because it lies at a much lower energy state. First, the animal removed energy from the feed before it was excreted. Then, microorganisms removed more energy from the manure during composting. We generally rely on other indirect measures, such as the ability of the material to autoheat to determine the putrescibility of wastes. It is difficult to predict the autoheating potential of OM — especially with liquids. Therefore, the energy level of OM, as measured as resipiraiton rate, is usually used to indirectly measure putrescibility.
The Solvita™ compost stability test is a commercial product that uses respiration and ammonia volatilization rates to estimate stability. The mass of CO2 and NH3 released by a compost sample in an airtight container is measured using standard color changing panels. Organic matter stability is determined by consulting standard charts (Figure 4).

Organic Matter in the Environment
Soil Environment
The OM content of soil affects moisture holding capacity, nutrient holding capacity, and particle aggregation. Soil OM supplies nutrients to the soil environment. Think of soil OM as a pool. The OM pool is constantly being built up and broken down through chemical and biological action. Decomposition of the pool releases CO2 and plant nutrients. Manure is sometimes given the euphemism “organic nutrients.” This is because land application of manure adds both OM and nutrients to the soil. Plant materials (in particular plant roots) also add to the soil OM pool. Adding inorganic nutrients (chemical fertilizer) increases soil OM by increasing plant growth.
Soil microorganisms use the energy as well as the nutrients stored in OM to reproduce and grow. When OM is added to the soil, soil microorganisms respond to the input of energy by growing and reproducing. If the soil OM pool contains more nutrients than the microorganisms need, nutrients are released for plant uptake. If the soil is deficient in nutrients, microorganisms will either not grow or they will take nutrients from the soil to digest the OM.
The process of microorganisms removing nutrients from the soil is called immobilization. Immobilization’s effect on soil fertility is usually temporary, but can be devastating to plant growth. When a high carbon, low nutrient material such as wheat straw or saw dust is added to the soil, soil microorganisms remove nutrients from the soil in order to digest the high carbon material. They are basically robbing nutrients from plants. Eventually, the microorganisms use up the available digestible energy, die, and release the nutrients stored in their bodies to the soil.
Since nitrogen is the most limiting nutrient for plant growth, the amount of organic matter to nutrients is expressed as the ratio of carbon to nitrogen, or C:N ratio. As a general rule of thumb: materials with C:N 20 immobilize soil nutrients for some time after they are added.
The nutrient and moisture holding ability of soil OM is related to the amount of nearly completely decomposed material or humus in the pool. The other benefits of organic matter, aggregation and release of nutrients, are related to the actively decomposing portion of the pool. Healthy soils require a constant replenishing of the OM pools to remain productive.
Aqueous Environments
The oxygen supply is much more difficult to maintain in aqueous compared to terrestrial or soil environments. Oxygen must dissolve into water before it can be useful. If animals or microorganisms use DO faster than it can be replaced, O2 is depleted and aerobic organisms die.
One way DO is depleted occurs when excess plant nutrients in the water cause the primary producers (algae, plankton, aquatic plants) to flourish. During the day, primary producers pump O2 into the water, at night they remove O2. If nighttime removal outpaces daytime replenishment, DO is depleted. This process, called eutrophication, takes place in lakes, reservoirs, and estuaries, often far downstream from where the nutrients were introduced.
A second method of O2 depletion occurs when secondary producers (the decomposers) remove O2 faster than it can be replaced. Excess OM is usually the cause of this sudden flourishing of decomposers. Dissolved oxygen depletion due to microbial blooms happens close to the source of OM addition. This is why the OM content is usually the limiting factor of wastewater discharge to streams.

Science Experiments on Environmental Education and Biology

08. Respiration pdf | Biology Notes for IGCSE 2014

The dependence of respiration on photosynthetic substrate supply and temperature: Integrating leaf, soil and ecosystem measurements

Organic Matter (OM) plays a large role in the environment. The OM content of soil affects nutrient retention, water holding capacity, and the soil’s ability to provide nutrients for plant growth. The OM content of wastewater discharged to a stream determines how much oxygen is available for fish to breathe. This Fact Sheet defines OM in byproduct materials, and shows how the many different measures of OM are used to predict the material’s behavior in the environment.

AB - Interactions between photosynthetic substrate supply and temperature in determining the rate of three respiration components (leaf, belowground and ecosystem respiration) were investigated within three environmentally controlled, Populus deltoides forest bays at Biosphere 2, Arizona. Over 2 months, the atmospheric CO2 concentration and air temperature were manipulated to test the following hypotheses: (1) the responses of the three respiration components to changes in the rate of photosynthesis would differ both in speed and magnitude; (2) the temperature sensitivity of leaf and belowground respiration would increase in response to a rise in substrate availability; and, (3) at the ecosystem level, the ratio of respiration to photosynthesis would be conserved despite week-to-week changes in temperature. All three respiration rates responded to the CO2 concentration-induced changes in photosynthesis. However, the proportional change in the rate of leaf respiration was more than twice that of belowground respiration and, when photosynthesis was reduced, was also more rapid. The results suggest that aboveground respiration plays a key role in the overall response of ecosystem respiration to short-term changes in canopy photosynthesis. The short-term temperature sensitivity of leaf respiration, measured within a single night, was found to be affected more by developmental conditions than photosynthetic substrate availability, as the Q10 was lower in leaves that developed at high CO2, irrespective of substrate availability. However, the temperature sensitivity of belowground respiration, calculated between periods of differing air temperature, appeared to be positively correlated with photosynthetic substrate availability. At the ecosystem level, respiration and photosynthesis were positively correlated but the relationship was affected by temperature; for a given rate of daytime photosynthesis, the rate of respiration the following night was greater at 25 than 20°C. This result suggests that net ecosystem exchange did not acclimate to temperature changes lasting up to 3 weeks. Overall, the results of this study demonstrate that the three respiration terms differ in their dependence on photosynthesis and that, short- and medium-term changes in temperature may affect net carbon storage in terrestrial ecosystems.

LabBench Activity Dissolved Oxygen and Aquatic Primary Productivity

AB - Terrestrial ecosystems currently offset one-quarter of anthropogenic carbon dioxide (CO2) emissions because of a slight imbalance between global terrestrial photosynthesis and respiration. Understanding what controls these two biological fluxes is therefore crucial to predicting climate change. Yet there is no way of directly measuring the photosynthesis or daytime respiration of a whole ecosystem of interacting organisms; instead, these fluxes are generally inferred from measurements of net ecosystem-atmosphere CO2 exchange (NEE), in a way that is based on assumed ecosystem-scale responses to the environment. The consequent view of temperate deciduous forests (an important CO2 sink) is that, first, ecosystem respiration is greater during the day than at night; and second, ecosystem photosynthetic light-use efficiency peaks after leaf expansion in spring and then declines, presumably because of leaf ageing or water stress. This view has underlain the development of terrestrial biosphere models used in climate prediction and of remote sensing indices of global biosphere productivity. Here, we use new isotopic instrumentation to determine ecosystem photosynthesis and daytime respiration in a temperate deciduous forest over a three-year period. We find that ecosystem respiration is lower during the day than at night - the first robust evidence of the inhibition of leaf respiration by light at the ecosystem scale. Because they do not capture this effect, standard approaches overestimate ecosystem photosynthesis and daytime respiration in the first half of the growing season at our site, and inaccurately portray ecosystem photosynthetic light-use efficiency. These findings revise our understanding of forest-atmosphere carbon exchange, and provide a basis for investigating how leaf-level physiological dynamics manifest at the canopy scale in other ecosystems.

Students could design a poster explaining the difference between photosynthesis and respiration, and how both processes are vital to sustaining an ecosystem.

Terrestrial ecosystems currently offset one-quarter of anthropogenic carbon dioxide (CO2) emissions because of a slight imbalance between global terrestrial photosynthesis and respiration. Understanding what controls these two biological fluxes is therefore crucial to predicting climate change. Yet there is no way of directly measuring the photosynthesis or daytime respiration of a whole ecosystem of interacting organisms; instead, these fluxes are generally inferred from measurements of net ecosystem-atmosphere CO2 exchange (NEE), in a way that is based on assumed ecosystem-scale responses to the environment. The consequent view of temperate deciduous forests (an important CO2 sink) is that, first, ecosystem respiration is greater during the day than at night; and second, ecosystem photosynthetic light-use efficiency peaks after leaf expansion in spring and then declines, presumably because of leaf ageing or water stress. This view has underlain the development of terrestrial biosphere models used in climate prediction and of remote sensing indices of global biosphere productivity. Here, we use new isotopic instrumentation to determine ecosystem photosynthesis and daytime respiration in a temperate deciduous forest over a three-year period. We find that ecosystem respiration is lower during the day than at night - the first robust evidence of the inhibition of leaf respiration by light at the ecosystem scale. Because they do not capture this effect, standard approaches overestimate ecosystem photosynthesis and daytime respiration in the first half of the growing season at our site, and inaccurately portray ecosystem photosynthetic light-use efficiency. These findings revise our understanding of forest-atmosphere carbon exchange, and provide a basis for investigating how leaf-level physiological dynamics manifest at the canopy scale in other ecosystems.

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9(l) Primary Productivity of Plants - Physical Geography


GCSE Physics – unit 1, unit 2 and unit 3. AQA

The response of respiration to temperature in plants can be considered at both short- and long-term temporal scales. Short-term temperature responses are not well described by a constant Q10 Of respiration, and longer-term responses often include acclimation. Despite this, many carbon balance models use a static Q10 of respiration to describe the short-term temperature response and ignore temperature acclimation. We replaced static respiration parameters in the ecosystem model photosynthesis and evapo-transpiration (PnET) with a temperature-driven basal respiration algorithm (Rdacclim) that accounts for temperature acclimation, and a temperature-variable Q10 algorithm (Q10var). We ran PnET with the new algorithms individually and in combination for 5 years across a range of sites and vegetation types in order to examine the new algorithms' effects on modeled rates of mass- and area-based foliar dark respiration, above ground net primary production (ANPP), and foliar respiration-photosynthesis ratios. The Rdacclim algorithm adjusted dark respiration downwards at temperatures above 18 °C, and adjusted rates up at temperatures below 5 °C. The Q10var algorithm adjusted dark respiration down at temperatures below 15 °C. Using both algorithms simultaneously resulted in decreases in predicted annual foliar respiration that ranged from 31% at a tall-grass prairie site to 41% at a boreal coniferous site. The use of the Rdacclim and Q10var algorithms resulted in increases in predicted ANPP ranging from 18% at the tall-grass prairie site to 38% at a warm temperate hardwood forest site. The new foliar respiration al gorithms resulted in substantial and variable effects on PnETs predicted estimates of C exchange and production in plants and ecosystems. Current models that use static parameters may over-predict respiration and subsequently under-predict and/or inappropriately allocate productivity estimates. Incorporating acclimation of basal respiration and temperature-sensitive Q10 have the potential to enhance the application of ecosystem models across broad spatial scales, or in climate change scenarios, where large temperature ranges may cause static respiration parameters to yield misleading results.

9(j) Introduction to the Ecosystem Concept

Interactions between photosynthetic substrate supply and temperature in determining the rate of three respiration components (leaf, belowground and ecosystem respiration) were investigated within three environmentally controlled, Populus deltoides forest bays at Biosphere 2, Arizona. Over 2 months, the atmospheric CO2 concentration and air temperature were manipulated to test the following hypotheses: (1) the responses of the three respiration components to changes in the rate of photosynthesis would differ both in speed and magnitude; (2) the temperature sensitivity of leaf and belowground respiration would increase in response to a rise in substrate availability; and, (3) at the ecosystem level, the ratio of respiration to photosynthesis would be conserved despite week-to-week changes in temperature. All three respiration rates responded to the CO2 concentration-induced changes in photosynthesis. However, the proportional change in the rate of leaf respiration was more than twice that of belowground respiration and, when photosynthesis was reduced, was also more rapid. The results suggest that aboveground respiration plays a key role in the overall response of ecosystem respiration to short-term changes in canopy photosynthesis. The short-term temperature sensitivity of leaf respiration, measured within a single night, was found to be affected more by developmental conditions than photosynthetic substrate availability, as the Q10 was lower in leaves that developed at high CO2, irrespective of substrate availability. However, the temperature sensitivity of belowground respiration, calculated between periods of differing air temperature, appeared to be positively correlated with photosynthetic substrate availability. At the ecosystem level, respiration and photosynthesis were positively correlated but the relationship was affected by temperature; for a given rate of daytime photosynthesis, the rate of respiration the following night was greater at 25 than 20°C. This result suggests that net ecosystem exchange did not acclimate to temperature changes lasting up to 3 weeks. Overall, the results of this study demonstrate that the three respiration terms differ in their dependence on photosynthesis and that, short- and medium-term changes in temperature may affect net carbon storage in terrestrial ecosystems.

Gerry Marten | Human Ecology - Ecosystem Services

Globally, patterns of primary productivity vary both spatially and temporally. The least productive ecosystems are those limited by and water like the deserts and the polar tundra. The most productive ecosystems are systems with high temperatures, plenty of water and lots of available soil nitrogen. Table 9l-1 describes the approximate average net primary productivity for a variety of ecosystem types.

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