What is decomposed organic matter

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Access to higher quality images can also be provided on request. Your gateway to a wide range of natural resources information and associated maps. In a study from the northern hemisphere Cornelissen et al. The major role of climate on litter decomposition was also demonstrated by Garcia-Palacios et al.

Stimulation of litter decomposition by temperature increase has furthermore been reported from marine environments Kelaher et al. Despite the recognition of temperature as one of the main drivers of litter decomposition on regional scale, no significant difference between tropical, temperate and cold climate areas was reported when litter decomposition rates were compared in a meta-analysis covering studies of litter decomposition rates in streams Zhang et al.

There is a general positive linear relationship between plant decomposition rates and nutrient concentrations Enriquez et al. Also the carbon quality of the litter influence the decomposition rates and a substrate containing high concentration of more labile carbon as cellulose and hemicellulose decompose faster compared to substrates with high content of resilient carbon compounds as lignin Chapin et al.

This influence of litter quality on decomposition rates has been reported from marine environments Apostolaki et al. Also Boyero et al. Global scale studies from terrestrial ecosystems have also pointed at litter quality as a main driver of litter decomposition Heim and Frey, ; Cornwell et al. A recent study used standardized litter substrate, e. Another factor influencing litter decomposition rate in terrestrial surface ecosystems is the presence of detritivores Garcia-Palacios et al.

Their influence has been investigated using exclusion experiments and detritivore effects on decomposition rate seem most important on a regional scale Wall et al. In the marine environment lower rates of decomposition were observed at more sheltered sites Costa et al.

This effect though was also a result of less mechanical impact. The invertebrates also play a significant role in litter decomposition in streams Graca, When shredders are present in streams, the exclusion of them using mesh bags reduced considerably the litter mass loss. This pattern was further described in a global study by Boyero et al.

This observation of increased abundance of detritivores in streams toward higher latitude was not evident when synthesized across a bigger but less standardized data set Shah et al. Furthermore, the functional diversity of decomposer organisms stimulates the decomposition in terrestrial as well as aquatic ecosystems Dang et al. Caves are per definition natural underground spaces where humans can fit, and are extended to other voids of the underground hydrogeological network Lauritzen, Caves develop mostly in karst limestone rocks , where the chemical and mechanical interaction with water promotes its development, or in volcanic rocks, where the lava flow or lava retraction forms volcanic caves Kempe, The environmental conditions of caves differ from the surface ecosystems, regarding temperature and humidity conditions Lauritzen, The diurnal and seasonal variation of temperature is less pronounced in caves compared to the surface and the humidity is higher Jones and Macalady, ; Lauritzen, The total darkness characterizing caves prevents photosynthesis, and with the exception of chemolitho autotrophically based caves Sarbu et al.

Therefore, subterranean ecosystems depend on organic matter transport from the surface to maintain heterotrophic productivity Culver, ; Poulson and Lavoie, Organic matter contains both carbon and nutrient elements, and it comes into caves from allochthonous sources, such as water percolation, or floating into the cave, transport by wind, movement of animals in and out e. The volume of organic matter input and the form in which it enters into the caves is dependent on the connection to the surface Poulson and Lavoie, and the influx in general is sporadic with high temporal variation Simon, , and often slow, hence the majority of caves are oligotrophic Jones and Macalady, Organic matter is transported into caves as particulate or dissolved organic matter, of which dissolved organic carbon is an important component Simon et al.

It reaches caves by percolating water Simon et al. Organic carbon in dissolved form is potentially an important source of carbon in cave ecosystems, as it is the case in surface ecosystems Chapin et al.

Organic matter in particulate form also penetrates into the hyporheic zone Stegen et al. Transport of particulate organic matter into caves happens mostly in the form of movement of living animals or plant litter, and in-growth of roots Simon, The cave formation i. The cave environment is characterized by environmental constrains that entail dramatic changes in all life forms, and many species have evolved worldwide to be cave exclusive Christiansen, Globally, species diversity in caves is limited, as well as their abundance.

A cave biodiversity hotspot is considered when it has more than 25 species of terrestrial or aquatic cave animals Zagmajster et al. Trophic chains in caves are considered simplified: communities lack photosynthetic primary producers and are typically represented by invertebrates adapted to live in subterranean ecosystems with all their life-cycle in the underground, and by an active microbial biomass with an important biogeochemical activity Mammola et al.

Compared to surface ecosystems, decomposition in caves and their contributing role to the ecosystem carbon cycle and the net ecosystem CO 2 emission Figure 1 remains poorly studied. The main source of organic matter in caves originates from plant material such as litter from surface Humphreys, , supplemented by carrion Braack, and animal droppings as guano Hamilton-Smith, As described in the previous section surface organic matter decomposition is controlled by abiotic factors such as temperature, water availability and lack of light alongside with biotic factors such as substrate quality and decomposer community.

The subterranean domain influences the abiotic and biotic factors, and hence the decomposition rates and main drivers in caves may differ from what is observed at the surface. A large variability between decomposition rates k d values is observed across caves Table 1. This reflects differences between cave temperatures, degree-days, aquatic lotic and lentic systems and terrestrial compartments of caves, connectivity and distance to the surface, and even more pronounced between the use of different types of organic matter i.

Lower rates were reported from decomposing red maple leaves in a cave stream, independent of the mesh size of the litter bag Venarsky et al. Surprisingly, this normalization for temperature reveals equal decomposition rates k dd of the very different substrates Sorbus aucuparia and Mus musculus in fine mesh.

In general, however, animal tissue is more easily decomposed than plant tissue such as leaves, due to lower carbon to nitrogen ratio in the former Chapin et al. This is in line with what is observed when comparing the substrates in the coarse mesh bags, the decomposition rates k dd are almost a factor 20 smaller for S. This suggests an important role of invertebrates for the rate of animal tissue, e.

This discussion is though based on a limited number of observations. Despite the high difference in degree-days between the two studies using Quercus alba Brussock et al. Though decomposition rates k d for same leaf species has been studied at surface ecosystems, only few studies concern a direct comparison of cave decomposition rate with the decomposition rate at the surface Brussock et al.

Therefore, it is impossible to uncover clear, general patterns based on the present findings. Because caves are dependent on organic matter from the outside and the temperature partially reflects that of the surface, there might be a link between decomposition rates, despite the higher humidity and the more constant temperature inside the cave compared to the surface. Common to all previous studies is the lack of standardization of methods to study decomposition rates.

Methods vary in terms of substrate, incubation time, sites, availability of the substrate to invertebrates, temperature and calculation of decay rates, which can be standardized to degree-days Table 1.

Although previous studies debate influence of local drivers of decomposition, a general comparison between values and understanding the driving factors of decomposition in caves is currently challenged by the methodological variability across studies. Organic matter quality was pointed out as an important driver of decomposition in the terrestrial compartments within caves Hills et al. This was assessed for differences in litter quality after 3 months of incubation, observing a higher mass loss and decomposition rate of Acer pseudoplatanus leaves with high specific leaf area compared to Eucalyptus spp.

At the cave entrance the higher mass loss of A. A higher accumulation of invertebrates was also associated with a high-quality substrate in rat carrion packages, compared to the invertebrate assemblage in packages of leaf litter Schneider et al. It is likely that invertebrates also stimulate decomposition in terrestrial areas of caves, similar to observations in cave streams Venarsky et al. The importance of invertebrates as drivers of litter decomposition in terrestrial cave ecosystems might be very dependent on the site-specific invertebrate abundance, and may differ between cave areas.

This match observations of similar mass loss of leaf litter in the twilight zone and the deepest parts of the cave Hills et al. This was the case in both studies, despite of a higher occurrence of invertebrates at the entrance and twilight zone compared to the deepest cave zone. This shows that invertebrate occurrence per se does not explain the variation of the decomposition rates between cave areas. Presumably the deep cave microbial litter decomposition is stimulated by environmental factors such as high humidity and stable temperature which turns out to be some of the drivers of local litter decomposition in terrestrial surface ecosystems Gonzalez and Seastedt, ; Garcia-Palacios et al.

Investigations of the climatic influence on terrestrial cave decomposition are to our knowledge lacking. As is the case in the terrestrial compartments of caves, and at the surface, in cave waters litter quality influences decomposition rates. Higher decomposition rates were measured for high quality corn litter compared to red maple of lower quality in a cave stream Venarsky et al. This is in contrast to surface data from a mountain stream in which Alnus leaves were processed faster than leaves of Sorbus Galas, , In cave streams Quercus leaf litter and wood appeared to have comparable rates of decomposition, most likely because the Quercus leaf litter was of low quality and the Quercus wood is a veneer with high surface area: volume ratio Simon and Benfield, The role of invertebrates in the decomposition process in cave waters has been investigated in some detail.

Venarsky et al. A lab study reported an increase of microbial respiration in the presence of the effective leaf shredder, Gammarus minus Kinsey et al. The influence of organic matter abundance has also been suggested to influence the rate of decomposition in cave water, but correlations of environmental organic matter and decomposition rates of added litter Simon and Benfield, ; Venarsky et al. Cave connectivity to the surface influenced the decomposition rate of oak litter.

Cave streams with larger openings are well connected to the surface water, have a higher input of organic matter, and its invertebrate communities have higher abundance of surface taxa and relatively high decomposition rates Simon and Benfield, This was found in comparison to disconnected cave streams that had less organic matter, less surface taxa and lower rates of oak litter decomposition Simon and Benfield, The relationship between the organic matter content in caves and decomposition rates seem complex to disentangle and might be influenced by the stimulation of the organic matter abundance in the cave invertebrate community rather than by the organic matter content itself Simon and Benfield, The ambient cave organic matter content had little effect on the observed decomposition rate of carrion Huntsman et al.

Leaf litter colonization by microorganisms in cave streams follows the pattern that is typical of surface streams Simon and Benfield, and the trophic community structure in many cave streams also appears similar to the surface community structure Simon et al.

Litter decomposition in cave streams is also to some extent comparable with the process in surface streams but slower rates of decomposition within cave streams have been observed Brussock et al. In the study by Galas et al. For instance, the lower amount of decomposer microbes of all successional stages Brussock et al. Specific conclusions about the major drivers of decomposition in caves and how these may differ from those on surface ecosystems are difficult to predict, based on the current level of knowledge, for two main reasons.

Primarily, all previous studies have a strong geographical bias. Data on decomposition rates and mass loss due to decomposition are only known from ten caves, located in Europe, North and South America, and Australia. Most of these were performed in the aquatic lotic and lentic compartment of caves while only three studies focused on the terrestrial compartments of caves, and, to our knowledge, no studies on organic matter decomposition have been performed in anchialine caves i.

The result shows a huge variation in decomposition rates, likely explained by several differences in the environmental conditions of caves, their connectivity to surface, and the impact of invertebrate activity in the process. Moreover, the variability among experimental conditions between studies complicates comparisons of results, and the possibility to reveal general patterns for decomposition below the ground.

But it is clear that there is considerable decomposition of organic matter in caves. Secondly, the lack of standard data among studies of decomposition in caves and at their correspondent surface is currently the major impediment to evaluate how differently the process occurs below ground compared to at the surface, and to understand if decomposition in caves follows the same patterns as at the surface, across biomes.

Despite of the lack of direct comparison, some surface decomposition rates k values for the same litter type are available in the literature, e. Methodological differences especially in the incubation and in mesh size, limit the use of this information to extrapolate general patterns. In the same way, the litter quality of the same species can differ depending on environmental factors Hansen et al. In caves the litter quality seems to be an important driver of decomposition and influences the decomposition rates Galas et al.

Instead, much of the organic material in a forest is tied up in the tree instead of being returned to the soil. What Are the Benefits of Organic Matter? Nutrient Supply Organic matter is a reservoir of nutrients that can be released to the soil. Each percent of organic matter in the soil releases 20 to 30 pounds of nitrogen, 4. The nutrient release occurs predominantly in the spring and summer, so summer crops benefit more from organic-matter mineralization than winter crops.

Water-Holding Capacity Organic matter behaves somewhat like a sponge, with the ability to absorb and hold up to 90 percent of its weight in water. A great advantage of the water-holding capacity of organic matter is that the matter will release most of the water that it absorbs to plants. In contrast, clay holds great quantities of water, but much of it is unavailable to plants. Soil Structure Aggregation Organic matter causes soil to clump and form soil aggregates, which improves soil structure.

With better soil structure, permeability infiltration of water through the soil improves, in turn improving the soil's ability to take up and hold water. Erosion Prevention This property of organic matter is not widely known. Data used in the universal soil loss equation indicate that increasing soil organic matter from 1 to 3 percent can reduce erosion 20 to 33 percent because of increased water infiltration and stable soil aggregate formation caused by organic matter.

Reduce or Eliminate Tillage Tillage improves the aeration of the soil and causes a flush of microbial action that speeds up the decomposition of organic matter. Tillage also often increases erosion. No-till practices can help build organic matter. Reduce Erosion Most soil organic matter is in the topsoil. When soil erodes, organic matter goes with it. Saving soil and soil organic matter go hand in hand. Usually, they can produce the appropriate enzyme to digest whatever material they find themselves on.

In addition, respiratory enzymes in the cell membrane make aerobic respiration possible as an energy source for compost bacteria. Since bacteria are smaller, less mobile and less complex than most organisms, they are less able to escape an environment that becomes unfavorable. A decrease in the temperature of the pile or a sharp change in its acidity can render bacteria inactive or kill them. When the environment of a heap begins to change, bacteria that formerly dominated may be decimated by another species.

The characteristically earthy smell of newly plowed soil in the spring is caused by actinomycetes, a higher form of bacteria similar to fungi and molds. Actinomycetes are especially important in the formation of humus. While most bacteria are found in the top foot or so of topsoil, actinomycetes may work many feet below the surface. Deep under the roots they convert dead plant matter to a peat-like substance. While they are decomposing animal and vegetable matter, actinomycetes liberate carbon, nitrogen and ammonia, making nutrients available for higher plants.

They are found on every natural substrate, and the majority are aerobic and mesophilic. The reason bacteria tend to die rapidly as actinomycete populations grow in the compost pile is that actinomycetes have the ability to produce antibiotics, chemical substances that inhibit bacterial growth. Protozoa are the simplest form of animal organism. Even though they are single-celled and microscopic in size, they are larger and more complex in their activities than most bacteria.

A gram of soil can contain as many as a million protozoa, but a gram of compost has many thousands less, especially during the thermophilic stage. Protozoa obtain their food from organic matter in the same way bacteriado, but because they are present in far fewer numbers than are bacteria, they play a much smaller part in the composting process.

Fungi are many-celled, filamentous or single-celled primitive plants. Unlike more complex green plants, they lack chlorophyll, and, therefore, lack the ability to make their own carbohydrates.

Most of them are classified as saprophytes because they live on dead or dying material and obtain energy by breaking down organic matter in dead plants and animals. Like the actinomycetes, fungi take over during the final stages of the pile when the compost has been changed to a more easily digested form.

The larger organisms that chew and grind their way through the compost heap are higher up in the food chain and are known as physical decomposers. The following is a rundown of some of the larger physical decomposers that you may find in nearly any compost heap. Most of these creatures function best at medium or mesophilic temperatures, so they will not be in the pile at all times. Mites are related to ticks, spiders, and horseshoe crabs because they have in common six leg-like, jointed appendages.

They can be free-living or parasitic, sometimes both at once. Some mites are small enough to be invisible to the naked eye, while some tropical species are up to a half-inch in length. Mites reproduce very rapidly, moving through larval, nymph, adult and dormant stages. They attack plant matter, but some are also second level consumers, ingesting nematodes, fly larvae, other mites and springtails. The wormlike body of the millipede has many leg-bearing segments, each exceptthe front few bearing two pairs of walking legs.

The life cycles are not well understood, except that eggs are laid in the soil in springtime, hatching into small worms. Young millipedes molt several times before gaining their full complement of legs.

When they reach maturity, adult millipedes can grow to a length of 1 to 2 inches. They help break down plant material by feeding directly on it. Centipedes are flattened, segmented worms with 15 or more pairs of legs, 1 pair per segment. They hatch from eggs laid during the warm months and gradually grow to their adult size. Centipedes are third level consumers, feeding only on living animals, especially insects and spiders. The sowbug is a fat-bodied, flat creature with distinct segments.

In structure, it resembles the crayfish to which it is related. Sowbugs reproduce by means of eggs that hatch into smaller versions of the adults. Since females are able to deposit a number of eggs at one time, sowbugs may become abundant in a compost heap.

They are first level consumers, eating decaying vegetation. Both snails and slugs are mollusks and have muscular disks on their undersides that are adapted for a creeping movement. Snails have a spirally curved shell, a broad retractable foot, and a distinct head.

Slugs, on the other hand, are so undifferentiated in appearance that one species is frequently mistaken for half of a potato. Both snails and slugs lay eggs in capsules or gelatinous masses and progress through larval stages to adulthood.

Their food is generally living plant material, but they will attack fresh garbage and plant debris and will appear in the compost pile. It is well,therefore, to look for them when you spread your compost, for if they move into your garden, they can do damage to crops. Spiders, which are related to mites, are one of the least appreciated animals in the garden.

These eight-legged creatures are third level consumers that feed on insects and small invertebrates, and they can help control garden pests. Springtails are very small insects, rarely exceeding one-quarter inch in length. They vary in color from white to blue-grey or metallic and are mostly distinguished by their ability to jump when disturbed. They feed by chewing decomposing plants, pollen, grains, and fungi. The rove beetle, ground beetle, and feather-winged beetle are the most common beetles in compost.

Feather-winged beetles feed on fungal spores, while the larger rove and ground beetles prey on other insects as third level consumers.

Beetles are easily visible insects with two pairs of wings, the more forward-placed of these serving as a cover or shield for the folded and thinner back-set ones that are used for flying. Once grubs are full grown, they pass through a resting or pupal stage and change into hard-bodied, winged adults. Most adult beetles, like the larval grubs of their species, feed on decaying vegetables, while some, like the rove and ground beetles, prey on snails, insects, and other small animals.

The black rove beetle is an acknowledged predator of snails and slugs. Some people import them to their gardens when slugs become a garden problem. Ants feed on a variety of material, including aphid honeydew, fungi, seeds, sweets, scraps, other insects, and sometimes other ants. Compost provides some of these foods, and it also provides shelter for nests and hills.

They will remain, however, only while the pile is relatively cool. Ants prey on first level consumers, and may benefit the composting process by bringing fungi and other organisms into their nests. The work of ants can make compost richer in phosphorus and potassium by moving minerals from one place to another.

Many flies, including black fungus gnats, soldier flies, minute flies, and houseflies, spend their larval phase in compost as maggots. Adults can feed upon almost any kind of organic material. All flies undergo egg, larval, pupal, and adult stages.