Ch 21: Movement of Elements in Ecosystems

Ecologists commonly determine the rate of nutrient regeneration through weathering by quantifying nutrient inputs and outputs from a watershed.

A watershed is an area of land that drains into a single stream or river. In a watershed, the rate of weathering is estimated by measuring the net movement of several highly soluble nutrients, such as calcium (Ca 2+ ), potassium (K+ ), sodium (Na + ), and magnesium (Mg 2+ ). These nutrients easily leach out of the soil and move into streams, where their concentrations can be measured as the stream leaves the watershed.

This reaction is accomplished by bacteria such as Pseudomonas denitrificans.

Additional chemical reactions under anaerobic conditions in soils and water subsequently convert nitric oxide to nitrous oxide (N2O) and then to nitrogen gas, thereby completing the nitrogen cycle

Ice cores contain ice that has been formed as far back as 500,000 years ago

After determining the age of different ice core layers, each layer is melted, which allows the release of trapped air bubbles of which the concentration of CO2 can be measured

The rate of weathering was highest in the southwest region of the province, probably because of regional differences in temperatures, precipitation, and soil conditions.

Although weathering of bedrock provides nutrients to terrestrial ecosystems, it is a very slow process. Therefore, primary production largely depends on rapid regeneration of nutrients from decomposition, a process that breaks down organic matter into smaller and simpler chemical compounds and is conducted primarily by bacteria and fungi.

When phosphate ions enter terrestrial ecosystems, they can be either bound strongly to the soil or taken up by plants and passed through the terrestrial food web.

Animal excretions and the decomposition of all terrestrial organisms release phosphorus back to the soil. Excess phosphorus that is not bound to the soil or taken up by plants either moves across the surface of the land during a rainstorm as runoff or leaches from the soil. When soil erosion occurs, the phosphorus that is bound to the soil is carried away with the eroding soil particles. In either case, the phosphorus can be carried to a variety of aquatic ecosystems.

Denitrification is necessary for breaking down organic matter in oxygendepleted soils and sediments.

However, as you can see from the above reaction, it produces nitrogen gas (N2 ). Since N2 cannot be taken up by producers, the denitrification process causes nitrogen to leave the waterlogged soils and aquatic ecosystems in the form of a gas.

The industrial production of fertilizers that improve crop productivity converts nitrogen gas to either ammonia or nitrates.

Like all nitrogen fixation, this process requires a great deal of energy and is powered mostly by the combustion of fossil fuels. The manufacture of nitrogen fertilizer has developed into such a large commercial endeavor that fixation conducted by humans now exceeds the nitrogen fixation that occurs through all natural processes.

phosphorus, sometimes in combination with excess nitrates, contributes to algal blooms that cause dead zones where rivers empty into oceans.

This phenomenon happens in locations around the world. An increase in the productivity of aquatic ecosystems is called eutrophication. An increase in the productivity of aquatic ecosystems caused by human activities is called cultural eutrophication.

In most rivers, lakes, and oceans, organic matter sinks to the bottom and accumulates in deep layers of sediments.

While some nutrients are recycled in the surface waters when animals excrete waste or when microbes in the surface water decompose organic matter, most organic matter sinks to the sediments. As a result, most nutrients must come from the sediments, although they will return slowly to the productive surface waters.

The decomposition process of leaves in a stream is similar to the process on land.

As the leaves settle onto the bottom of the stream, the first stage is the leaching of soluble compounds, followed by the shredding of the leaves into smaller pieces by invertebrates such as amphipods, isopods, and larval caddisflies. At the same time that leaves are being shredded, fungi and bacteria are working to decompose the leaves much as they do on land. Given the similar processes in both the terrestrial and stream ecosystems, it is perhaps not surprising that the rate of leaf decomposition depends on the temperature of the water and the chemical composition of the leaves. To determine the rate at which leaves decompose in streams, aquatic ecologists follow a protocol that is similar to the protocol used by terrestrial ecologists.

As nitric oxide enters the atmosphere from combustion, it reacts with water in the air to form nitrates, which then fall to the ground during precipitation events.

Because nitrogen is often a limiting nutrient, we would expect the addition of nitrates to affect a variety of ecosystems. Over the years, there have been numerous investigations into whether adding nitrogen to terrestrial ecosystems in North America affects productivity and species richness. These study sites, which range north to south from Alaska to Arizona and west to east from California to Michigan, were recently compiled in an effort to determine whether their results showed a general pattern.

Because environmental conditions are a key determinant for rates of decomposition, terrestrial ecosystems differ a great deal in their decomposition rates.

Comparative studies of temperate and tropical forests show that detritus in the tropics decomposes more rapidly because of warmer temperatures and higher amounts of precipitation. For example, we can compare the amount of dead plant matter on the forest floor—including leaves, branches, and logs—versus the total biomass of vegetation and detritus in a forest. The proportion of dead plant matter is about 20 percent in temperate coniferous forests, 5 percent in temperate hardwood forests, and only 1 to 2 percent in tropical rainforests. Of the total organic carbon in terrestrial ecosystems, more than 50 percent occurs in soil and litter in northern forests, but less than 25 percent occurs in tropical rain forests, where the majority of the organic matter exists in the living biomass.

One major way in which humans have altered the carbon cycle is through the extraction and combustion of fossil fuels.

During the past 2 centuries, extraction and combustion have been happening at an increasing rate to meet growing energy demands. Other forms of combustion by humans include burning land to prepare it for agriculture.

An example of this approach was recently reported for 21 small watersheds in the Canadian province of Quebec

Each watershed contained a small lake with a stream flowing out of the lake that drained the watershed. The watersheds were all forested and had little human activity, so the researchers assumed that nutrient movement was at equilibrium. Measurements were made of the amount of calcium, potassium, sodium, and magnesium entering each watershed through precipitation, the amount of each element present in the soil and bedrock, and the amount of each element coming out of the watershed in the stream that drained it. By knowing the inputs and outputs of a watershed, scientists were able to determine rates of bedrock weathering.

The rise in atmospheric CO2 is of great importance to humans because CO2 is a greenhouse gas that absorbs infrared radiation and radiates some of it back to Earth.

Having CO2 in the atmosphere helps keep our planet warm, but an excessive amount of CO2 and other greenhouse gases in the atmosphere will cause our planet to become much warmer than it has been in a very long time. We know that the mean temperature on Earth is now 0.8°C warmer than it was when the first temperature measurements were taken in the 1880s. While a mean increase of 0.8°C may not seem like much, we can find some dramatic changes in specific locations.

nitrogen fixation can also occur through abiotic processes.

For example, lightning provides a high amount of energy that can convert nitrogen gas into nitrate in the atmosphere. Similarly, combustion that occurs during wildfires or when fossil fuels are burned also produces nitrates. In both cases, nitrates, which are suspended in the air after combustion, fall to the ground with precipitation.

Bacteria and fungi play an important role in decomposition because they help convert organic matter into inorganic nutrients.

Fungi play a special role because the hyphae of fungi can penetrate the tissues of leaves and wood that large detritivores and bacteria cannot penetrate on their own. If you have ever walked through a forest, you may have seen the fruiting bodies of many different fungi, including the impressive shelf fungi that emerge from the sides of dead logs

Before human activities began dramatically altering the environment, the production of usable forms of nitrogen through the process of fixation was approximately offset, on a global scale, by the loss of usable nitrogen through denitrification.

However, during the last 3 centuries, and especially during the past 50 years, human activities have nearly doubled the amount of nitrogen put into terrestrial ecosystems. These activities include combustion of fossil fuels that add nitric oxide to the air, production of nitrogen fertilizers, and planting nitrogenfixing crops.

As you can see, CO2 concentrations in the atmosphere during the past 400,000 years have varied a great deal, from about 180 to 300 ppm.

However, since 1800, as humans increasingly burned fossil fuels, CO2 concentrations have increased exponentially to the current value of 405 ppm. This means that the current concentration of CO2 in our atmosphere is 35 percent higher than the highest concentrations that existed during the past 400,000 years.

In terrestrial ecosystems, nutrients regenerate close to the location, where they are taken up by producers.

In aquatic ecosystems, however, most nutrients regenerate in sediments, which are often far below the surface waters that contain dominant producers, such as phytoplankton. In addition, in terrestrial ecosystems, aerobic decomposition is most common, whereas decomposition in the sediments and deep waters of aquatic ecosystems is typically anaerobic, which is considerably slower.

When phosphate ions enter aquatic ecosystems, they are taken up by producers and enter the food web in a manner that is similar to the terrestrial food web.

In well-oxygenated waters, phosphorus binds readily with calcium and iron ions and precipitates out of water to become part of the sediments. Thus, marine and freshwater sediments act as phosphorus sinks by continually removing phosphorus from the water. Under low-oxygen conditions, iron tends to combine with sulfur rather than phosphorus, so phosphorus remains more available in the water. Over time, the phosphate that precipitates down to ocean sediments is converted into calcium phosphate rocks, and the phosphorus cycle begins again.

over time calcium phosphate (Ca(H2PO4 )2 ) precipitates out of ocean water and slowly forms sedimentary rock.

Later, some of this rock is uplifted by geologic forces. Exposed rocks experience weathering, which causes them to slowly release phosphate ions. Phosphate rocks are also mined for phosphate that is used in fertilizers and in a variety of detergents.

In terrestrial ecosystems, 90 percent of all plant matter produced in a given year is not consumed directly by herbivores but is ultimately decomposed.

Many plants resorb some of the nutrients from their leaves before the leaves are dropped. The aboveground dead plant biomass, combined with the organic matter of dead animals and animal waste, drops onto the soil surface where nutrients are leached. Here, decomposition is primarily aerobic, and plant roots and their associated mycorrhizal fungi have ready access to the nutrients that are released by the decomposers.

The process of converting atmospheric nitrogen into forms producers can use is known as nitrogen fixation.

Nitrogen fixation converts nitrogen gas into either ammonia (NH3 ), which is rapidly converted to ammonium (NH4 + ), or into nitrate (NO3 − ). The compound that is formed depends on whether nitrogen fixation occurs by organisms, lightning, or the industrial production of fertilizers.

Some organisms are able to convert nitrogen gas into ammonia.

Nitrogen fixation occurs in some species of cyanobacteria, in some free-living species of bacteria such as Azotobacter, and in mutualistic bacteria such as Rhizobium that live in the root nodules of some legumes and other plants. Nitrogen fixation is an important source of required nitrogen, especially for early-succession plants colonizing habitats that have little available nitrogen. The process of nitrogen fixation requires a relatively high amount of energy, which nitrogen-fixing organisms obtain either by metabolizing organic matter from the environment or by acquiring carbohydrates from a mutualistic partner.

A large pool of nitrogen gas (N2 ) exists in the atmosphere, where it comprises 78 percent of all atmospheric gases.

Nitrogen moves through five major transformations: nitrogen fixation, nitrification, assimilation, mineralization, and denitrification.

Producers can take up nitrogen from the soil or water as either ammonium or nitrates.

Once producers take up nitrogen, they incorporate it into their tissues, a process known as assimilation. When primary consumers ingest producers, they can either assimilate nitrogen from the producers or excrete it as waste. The same process occurs again with secondary consumers. Animal waste, as well as the biomass of dead producers and consumers, is broken down by scavengers, detritivores, and decomposers. The fungal and bacterial decomposers break down biological nitrogen compounds into ammonia.

Determining the rate of weathering can be difficult because bedrock often exists far below the surface of the soil.

One solution has been to measure the nutrients that enter a terrestrial ecosystem from precipitation and the nutrients that leave an ecosystem by leaching out of the soil and into a stream.

Carbon can also be buried as organic matter before it fully decomposes

Over millions of years, some of this organic matter is converted to fossil fuels such as oil, gas, and coal. The rate of carbon burial is slow, and it is offset by the rate of carbon released into the atmosphere by the weathering of limestone rock and during volcanic eruptions. Because the process of sedimentation and burial can lock up carbon for millions of years, carbon moves through these pools very slowly.

These high-latitude regions contain large deposits of frozen peat, which is a mixture of dead sphagnum moss and other plants.

Peat thaws and decomposes more easily with warmer temperatures. Because peat decomposes under anaerobic conditions, the decomposition produces methane, which is a greenhouse gas. This means that the rise in temperatures due to increased atmospheric CO2 causes the release of additional greenhouse gases from the decomposing peat that exacerbate the problem.

The process of nutrient regeneration in sediments of aquatic ecosystems helps us understand many patterns of ecosystem productivity.

Shallow oceans are more productive, in part, because the sediments are much closer to the surface waters and can therefore regenerate nutrients to the surface water more quickly through decomposition. The upwelling of water from the deep sediments to the surface brings nutrients from the site of regeneration to the site of algal productivity. In addition, some of the most productive regions of the ocean occur at the upwelling of water along the coasts of continents, where currents draw deep, nutrient-rich water up to the surface

Evaporation of water occurs from bodies of water, soil, and plants that experience evapotranspiration.

Solar energy provides the energy for the process of evaporation and evapotranspiration, which changes water from a liquid to a gas in the form of water vapor. There is a limit to the amount of water vapor that the atmosphere can contain. As additional water continues to evaporate, the water vapor in the atmosphere condenses into clouds that ultimately create precipitation in the form of rain, hail, sleet, or snow.

When precipitation drops from the atmosphere, it can take several paths

Some precipitation falls directly onto the surface of aquatic ecosystems and the rest falls onto terrestrial ecosystems. Water that falls onto terrestrial ecosystems can travel along the surface of the ground or it can infiltrate the ground, where it is either absorbed by plants or moves deeper into the ground and becomes part of the underlying groundwater. The surface runoff and some of the groundwater will eventually find their way back into water bodies, thereby completing the cycle. Precipitation that falls on land either runs off along the surface or infiltrates the soil. In the soil, this water may evaporate, be taken up by plants, or enter groundwater. Excess water ultimately returns to the ocean.

weathering is the physical and chemical alteration of rock material near Earth's surface.

Substances such as carbonic acid in rainwater and organic acids produced by the decomposition of plant litter react with minerals in the bedrock and release various elements that are essential to plant growth.

Stratification happens in temperate and tropical lakes when the surface waters are warmed by the summer sunlight, while the deeper waters stay cold and dense.

Such stratification does not happen in polar lakes because their surfaces never become warm enough. In estuaries and oceans, stratification of the water happens when an input of less dense freshwater from rivers or melting glaciers is positioned above a layer of the denser ocean saltwater. Occasionally, stratified aquatic ecosystems experience periods of vertical mixing. For example, temperate lakes in the spring and fall experience changes in the temperature of surface waters that eventually match the temperature of the deeper waters. When the temperatures become equal, spring and fall winds that blow along the surface of the lakes cause the entire lake to mix. Mixing can also happen in oceans. In areas where the surface water is less salty than the deep water, sunlight can slowly cause the surface waters to evaporate and leave the salt behind. At some point, the surface water becomes saltier than the deeper water and the surface water sinks, thereby causing the ocean water to circulate.

The vertical mixing of water from the sediments to the surface can be hindered whenever surface waters have a different temperature and therefore a different density than that found in deep waters.

The vertical mixing can affect primary production in two opposing ways: it can bring the deep, nutrient-rich water to the surface where phytoplankton can use it; but it can also carry phytoplankton down to the deep water, where they will die because of the low light conditions. When phytoplankton die, primary production may shut down in the deep water and little primary production will occur in the nutrient-rich waters at the surface.

Carbon dioxide is also exchanged between aquatic ecosystems and the atmosphere

The exchange occurs in both directions at a similar magnitude, which means there is little net transfer over time. when CO2 diffuses from the atmosphere into the ocean, some of it is used by plants and algae for photosynthesis and some is converted to carbonate (CO3 2- ) and bicarbonate ions (HCO3 - ). The carbonate ions can then combine with calcium in the water to form calcium carbonate (CaCO3 ). Calcium carbonate has a low solubility in water, so it precipitates out of the water and becomes part of the sediments at the bottom of the ocean. Over millions of years, the calcium carbonate sediments that accumulate in the ocean bottoms, combined with the calcium carbonate skeletons from tiny marine organisms, can develop into massive sources of carbon in the form of rocks known as dolomite and limestone. Humans mine dolomite and limestone for use in making concrete and fertilizer as well as for numerous industrial processes.

The movement of water through ecosystems and atmosphere, known as the hydrologic cycle, is driven largely by evaporation, transpiration, and precipitation

The largest pool of water, approximately 97 percent of all water on Earth, is found in the oceans. The remaining water exists in lakes, streams, rivers, wetlands, underground aquifers, and soil

Water cycles through Earth's biosphere with no net loss or gain over the long term.

Therefore, any change in one part of the water cycle influences the other parts. For example, in large developed areas, construction materials such as roofing and paved parking lots are impervious to water infiltration. The amount of water that can percolate into the soil is significantly reduced, and we see an increase in surface runoff. Less water is able to infiltrate the soil for plants to use or to replenish the groundwater that many people rely on for drinking water. An increase in surface runoff also increases soil erosion.

Large detritivores, including millipedes, earthworms, and wood lice, also play an important role in decomposition.

These animals can consume 30 to 45 percent of the energy available in leaf litter, but they consume a much lower fraction of the energy available in wood. The importance of large detritivores is twofold; they decompose organic matter directly and they macerate organic matter into smaller pieces of detritus, which have a greater surface-area-to-volume ratio. This gives bacteria and fungi more surfaces on which to act and increases the rate of decomposition.

producers use photosynthesis in terrestrial and aquatic ecosystems to take CO2 from the air and water and to convert it to carbohydrates.

These carbohydrates are used to make other compounds, including proteins and fats. The carbon that is locked up in producers can then be transferred to consumers, scavengers, detritivores, and decomposers. All these trophic groups experience respiration, which releases CO2 back into the air or water.

Another process in the nitrogen cycle is nitrification, which converts ammonium to nitrite (NO2 - ) and then converts nitrite to nitrate (NO3 - )

These conversions release much of the potential energy that is contained in ammonium. Each step is carried out by specialized bacteria and archaea in the presence of oxygen. In terrestrial and aquatic ecosystems, the conversion of ammonium to nitrites is carried out by Nitrosomonas and Nitrosococcus bacteria, whereas the conversion of nitrites to nitrates is carried out by Nitrobacter and Nitrococcus bacteria. Although nitrites are not an important nutrient for producers, plants can take them up and use them

From the 1940s to the 1990s, household detergents contained phosphates to improve their cleaning effectiveness.

These detergents became part of the wastewater that traveled through public sewage systems, ultimately emptying into rivers, lakes, and oceans. People began to realize that these detergents significantly increased phosphorus in waterways, which contributed to eutrophication and dead zones. In 1994, the United States banned phosphates in laundry detergents after several states had already done so. In 2010, 16 states banned phosphates in dishwashing detergents. In 2011, the European Union agreed to similar restrictions on phosphates in laundry and dishwasher detergents to help reduce the problems of cultural eutrophication and dead zones.

Because nitrates produced by nitrification are quite soluble in water, they readily leach out of soils and into waterways, where they settle in the sediments of wetlands, rivers, lakes, and oceans

These sediments are typically anaerobic. Under anaerobic conditions, nitrates can be transformed back into nitrites, which are then transformed into nitric oxide (NO)

When nitrogen was added in the form of nitrates and ammonium, all sites experienced an increase in primary productivity

This confirmed that nitrogen was a limiting resource at all sites. However, the sites differed in the proportion of species that were eliminated over time In addition to differences in temperature and soil among the sites, they found that the sites with the largest increases in productivity experienced the largest reduction in species richness. Adding nitrogen to these communities commonly caused a few plant species to grow very large and to dominate the community. These large plants shaded the lesscompetitive smaller plants, which caused the smaller species to decline. These results demonstrate that the increases in nitrogen in the environment due to human activities can reduce the species diversity of ecosystems.

For example, in the Great Plains of the United States, a large supply of groundwater, known as the Ogallala aquifer, extends from South Dakota to Texas

This groundwater supplies about 30 percent of all water used for irrigation in the United States and provides drinking water for 82 percent of the people who live in the region. However, the extraction of this water has exceeded its rate of replenishment, and scientists are concerned that this critical supply of water for industry, households, and irrigation could run out sometime during this century

These differences in litter decomposition rates mean that tropical forests have a much larger proportion of the total organic matter in living vegetation than in detritus.

This has important implications for tropical agriculture and conservation. For example, when tropical forests are cleared and burned, a large fraction of the nutrients are mineralized by burning and by subsequent high rates of decomposition. Together, these processes create an abundance of nutrients during the first 2 to 3 years of crop growth, but any surplus nutrients not taken up by the crops quickly leach away. Traditionally, tropical areas burned for agricultural fields would be farmed for 2 to 3 years and then left to undergo natural succession for 50 to 100 years to rebuild the fertility of the soil. However, many regions have human populations that are too dense to allow rotation of agriculture into different areas over several decades. Without rotation, the soils cannot replenish their nutrients and the fertility of the land rapidly degrades.

Terrestrial ecosystems constantly lose nutrients because many are leached out of the soil and transported away in streams and rivers.

To maintain a stable level of productivity, the loss of nutrients from an ecosystem must be balanced by an input of nutrients. For some nutrients, such as nitrogen, inputs come from the atmosphere. For most other nutrients, such as phosphorus, the inputs come from the weathering of bedrock beneath the soil.

In some habitats, such as the waterlogged sediments of swamps or marshes, oxygen is not available for respiration.

Under such anaerobic conditions, some species of archaea use carbon compounds for respiration.

phosphorus can only enter the atmosphere in the form of dust.

Unlike nitrogen, phosphorus rarely changes its chemical form and typically moves as a phosphate ion (PO4 3- ). Plants take up phosphate ions from soil or water and incorporate them directly into various organic compounds. Animals eliminate excess phosphorus in their diets by excreting urine containing either phosphate ions or phosphorus compounds that are converted into phosphate ions by phosphatizing bacteria.

Leaching removes 10 to 30 percent of soluble substances from organic matter, which includes most salts, sugars, and amino acids.

What remains behind are complex carbohydrates, such as cellulose, and other large organic compounds, such as proteins and lignin. Lignin determines the toughness of leaves and many of the structural qualities of wood. The lignin content of plants is a particularly important determinant of decomposition rate because it resists decomposition more than cellulose. However, some fungi and bacteria can break down cellulose and lignin. They secrete enzymes that break down the plant matter into simple sugars and amino acids that they then absorb. Some portion of the lignins, as well as other plant compounds that resist decomposition, may never break down in the surface soils but can form fossil fuels when buried for millions of years.

The rate of evaporation must balance the rate of precipitation or water would continually accumulate in one part of the cycle.

When we consider the hydrologic cycle on a global scale, we find that precipitation exceeds evaporation in terrestrial ecosystems, whereas evaporation exceeds precipitation in aquatic ecosystems. To help maintain an overall balance, the excess water that is evaporated from aquatic ecosystems is transported by the atmosphere and falls onto terrestrial ecosystems. At the same time, the excess water that falls on terrestrial ecosystems is transported in the form of runoff and groundwater into aquatic ecosystems.

A similar effect occurs when we reduce the amount of plant biomass in a terrestrial ecosystem, as occurs during logging.

Where there are fewer trees and other plants, much less precipitation is taken up by plant roots and subsequently released to the atmosphere through evapotranspiration. Consequently, the amount of surface runoff increases, which often causes severe soil erosion and flooding. Finally, when we pump out groundwater for irrigation or household use, we sometimes reduce the amount of groundwater at a rate that exceeds its replenishment.

Temperature increases can have numerous effects around the world, such as reducing the size of the polar ice sheets

altering the length of plant growing seasons, and changing the timing of plant and animal life histories

This process of converting nitrates into nitrogen gas is known as

denitrification

The rate of decomposition is also affected by the ratio of carbon and nitrogen in the organic matter.

differences in the stoichiometry of an organism's food can affect the consumption of the food and the number of consumers that can be supported by the food supply. In the case of decomposition, if the decomposers require high amounts of nitrogen, then low nitrogen availability in the organic matter can cause slower rates of decomposition.

Humans also alter the hydrologic cycle through activities that contribute to global warming

g. Scientists expect that as air and water temperatures rise, there will be an increase in the rate of water evaporation. An increase in the evaporation rate will cause water to move through the hydrologic cycle more quickly, potentially leading to an increased intensity of rain and snowstorms in various parts of the world.

The process of breaking down organic compounds into inorganic compounds is known as

mineralization

Phosphorus is a critical element for organisms because it is used in bones and scales, teeth, DNA, RNA, and ATP, a molecule involved in metabolism.

phosphorus is also a common limiting nutrient in aquatic and terrestrial ecosystems. For this reason, phosphorus is a component of most fertilizers manufactured to boost the growth of crops

breakdown of plant matter in a forest occurs in four ways:

soluble minerals and small organic compounds leach out of organic matter, large detritivores consume organic matter, fungi break down the woody components and other carbohydrates in leaves, and bacteria decompose almost everything.

Because plant growth and decomposition are biochemical processes, nutrient cycling between producers and decomposers in terrestrial ecosystems is influenced by

temperature, pH, and moisture. The rate of decomposition is also affected by the ratio of carbon and nitrogen in the organic matter.