Forest Soils: Difference between revisions

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{{Uncurated}}
==Introduction==
==Introduction==
Forests represent the 31% of the total land area and support more than 1.6 million people around the world. At the same time, forests are important because they are home of 80% of the terrestrial biodiversity which include plants, animals and microorganisms [http://wwf.panda.org/about_our_earth/about_forests|[1]]. The interactions of the terrestrial biodiversity are integrated in the food web process. Those processes include the transfer of energy, community interactions and nutrient cycling. These process are also linked with abiotic factors as soil, water and climate and determine the productive characteristic of each niche.  
Forests represent the 31% of the total land area and support more than 1.6 million people around the world. At the same time, forests are important because they are home of 80% of the terrestrial biodiversity which include plants, animals and microorganisms [http://wwf.panda.org/about_our_earth/about_forests]. The interactions of the terrestrial biodiversity are integrated in the food web process. Those processes include the transfer of energy, community interactions and nutrient cycling. These process are also linked with abiotic factors as soil, water and climate and determine the productive characteristic of each niche.  


The most common soil definition is "Soils as a media for plant growth" [[#Reference|[2]]]. However, soils have several functions that determine the ecological roles in the environment:
The most common soil definition is "Soils as a media for plant growth" [[#References |[2]]. However, soils have several functions that determine the ecological roles in the environment:
 
[[Image:forest_trees_soil_leaf_litter_mulch_lg.jpg|thumb|310px|right|Forest and litter http://globalwarming-arclein.blogspot.com/2012/06/forests-and-global-warming.html]]


*Recycling system for nutrients and organic waste
*Recycling system for nutrients and organic waste
*Modifier if the atmosphere
*Modifier of the atmosphere
*Habitat for soil organisms
*Habitat for soil organisms
*Engineering medium
*Engineering medium
*System for water supply and purification
*System for water supply and purification


Soil formation is a pedogenic and biogeochemical process that is dependent of the translocation, biocycling and transformation of materials deposited and degraded by microorganisms on the uppers soil layer. These processes are developed along time and space, and have as final product the formation of soils with different physical and chemical characteristics.


Soil formation is a pedogenic and biogeochemical process that is determined by space and time, and depends of the translocation, biocycling and transformation of materials deposited and degraded by organisms on the uppers soil layers. These processes are developed along time and space, and have as final product the formation of soils with different physical and chemical characteristics.
The early soil classification made by the USDA on 1938, classified forest soils in the Zonal soil Order, as Pedalfers [http://geowords.com/p_/soils/pedalfers.htm] , that are soils with the following suborder:
 
*Soils of forest-grassland transition
*Vegetation
*Terrestrial organism interaction
*Climate.
 
The early soil classification made by the USDA on 1938, classified forest soils in the Zonal soil Order, as Pedalfers, that are soils with the following suborder:
*Soils of forest-grassland trnasition
*Light-colored podzolized soils of timberland regions
*Light-colored podzolized soils of timberland regions
*Lateritic soils of forested warm-temperature and tropical regions.
*Lateritic soils of forested warm-temperature and tropical regions.


The Soil Science Society of America does not have a specific definition about forest soils. However, Comerford (2006) defined forest soils as a soil that has been developed under forest cover, or a forest that has been disturbed but once was covered by forest vegetation [[#References|[3]]].
The Soil Science Society of America does not have a specific definition about forest soils. However, Comerford (2006) defined forest soils as a soil that has been developed under forest cover, or a forest that has been disturbed but once was covered by forest vegetation [[#References|[3]]].
Line 28: Line 24:
==Physical environment==
==Physical environment==


The physical characteristics observed in forest soils, are determined by the soil formation factors:
===Soil Formation===
*Climate
The physical characteristics observed in forest soils, are determined by the soil formation factors:climate, organisms, parent material, time
*Organisms
and relief.
*Parent Material
*Time
*Topography


===Climate===
The process mentioned above, determine the type of soil that will be formed. For forest soils in particular, the principal characteristic is the development of an organic layer on the soil surface, usually referred as forest floor [http://en.wikipedia.org/wiki/Forest_floor]. This particular horizon contains fresh organic materials from dead plants and animals, that are easily degraded by microorganisms, especially by bacteria and fungi. This layer is represented with the letter "O" that means organic, due to the accumulation of organic mater.As the soil depth increase, the availability of organic matter decreases, having as result a more mineral soil layer. However, the thickness of each layer varies depending of the topography, vegetation and parental material in which the forest has been established.
====Tropic Forest====
====Temperate Forest====


Describe the physical and chemical characteristics of the environment, using as many sections/subsections as you require. If it is appropriate, you can divide the physical and chemical attributes of the environment into separate sections. Look at other topics available in MicrobeWiki. Which involve processes similar to yours? Create links where relevant.  
The transformation and translocation of organic and inorganic material by physical and chemical process along the soil profile, are the basic processes for the soil formation.


===Soil Genesis===
[[Image:Soil_profile_in_mature_forest.jpg|thumb|310px|right| Alfisol soil profile of a mature forest http://www.omrisk.unito.it/abstract/index.html]]
The development of forest soils is similar to any other soil type. It consists on layers or horizon that has been developed along time due to the parent material, water, and the decomposition of organic material, all these factors, affected by the climate.  


A particular characteristic of forest soils is the develop of an organic layer on the soil surface, usually referred as forest floor [http://en.wikipedia.org/wiki/Forest_floor [4]]. This layer is represented with the letter "O" that means organic, due to the accumulation of organic mater. This particular layer contains fresh organic materials that are easily degraded by microorganisms, especially by bacteria and fungi.
===Soil Organic Matter===
The most important role of the vegetation on soil, is the accumulation of organic matter. The tree leaves represent the most important source of carbon in the soil. The type of vegetation is also an important factor because it affects the soil acidity. For example, litter from conifer trees require more time to be decomposed, having as result a slow recycling of nutrients. On the other hand, litter from deciduous trees are easily decomposed due that they contains more less strong carbon bonds, that microorganisms can brake faster. As result, microorganisms release organic acids, that promote the soil formation by the desegregation of rocks. This process requires time, and at the long term, it will determine the thickness of the soil horizons and the fertility of the forest soil.


As the soil depth increase, the availability of organic matter decreases, having as result a more mineral soil layer. However, the thickness of each layer varies depending of the topography, vegetation and parental material in which the forest has been established. Some examples of these characteristics are...
===Climate===
 
Temperature and precipitation regimes have a direct impact on the forest vegetation, decomposition rate and soil formation process.
Forest soils are usually stratified by the accumulation of organic matter and the intemperism of the parental material
====Ultisol====
====Alfisol====
====Spodosol====


===Vegetation===
====Tropic Forest Soils====
Vegetation usually acelerate plant nutrient uptake. By doing this, it affect the biogeochemical process that occurs on the soil.
Soils formed under high temperature and precipitation rates from volcanic parent material are usually characterized for having a fragile nutrient cycle. In fact, tropical forest soils have high clay content and lower soil organic matter accumulation. A good example of these, are the [[Tropical Rainforest]] which usually have low pH and low plant nutrient due to the translocation of clay particles that carried non acid cations into the soil. Some examples of these soils are the Ultisols [http://en.wikipedia.org/wiki/Ultisols] and Oxisols [http://www.cals.uidaho.edu/soilorders/oxisols.htm].


==Chemical environment==
====Temperate Forest Soils====
C/N ratio determine the bacteria community distribution in the soil. Carbon quality tend to be an important component of the microbial communities distribution. Johnson (2001)[[https://wiki.usask.ca/download/attachments/293273780/Effects+of+Forest+Harvesting+on+C+and+N+soil+storage.pdf |[7]]] studied different forest management and their effect on the C and N soil storage. The results shown that saw-log forest removal tend to increase the C/N ratio in soil at the short term. This process is due to the rapid incorporation of small size carbon material into the soil, that allow microorganisms to decompose the carbon molecules and release the excess of nutrients to the soil. In this way, soil fertility increased until the carbon source is depleted.


===Carbon cycle===
Forest soils developed under temperate climate, usually have higher organic matter because they have lower temperature which slow down the decomposition rate. However, these soils are highly weathered due to the seasonal temperature and precipitation rate along the year. Alfisols and Spodosols are the most common soils observed under these conditions. These soils are characterized by the accumulation of calcium carbonate and clay particles in deeper horizons, due to leaching nutrient from the parent material rocks and decomposition of litter which released strong organic acids that reduce the soil pH and with a CEC up to 35%.[[#References |[7]]].
===Nitrogen cycle===


==Microbial communities==
==Microbial communities==
===Fungi===
===Fungi===


The microbial community in forest soil is dominated by fungi. Due that most of the organic compounds in forest soils stayed on the soil surface and there is plenty oxygen, fungi communities are able to extend their filaments called hyphae. Fungi are more efficient than bacteria, in terms of decomposing organic compounds. In fact, 50% of the decomposed material is transformed in fungi tissue. The formation of hyphae is what improve soil fertility by the formation of humus.  
The microbial community in forest soil is dominated by fungi. Since most of the organic compounds in forest soils is located on the soil surface and there is plenty oxygen, fungi communities are able to extend their filaments called hyphae. Fungi are more efficient than bacteria, in terms of decomposing organic compounds. In fact, 50% of the decomposed material is transformed in fungi tissue and 94% of fungi have enzymes capable to degrade lignin, that is a important component of wood cells in trees (Sylvia, D., et al. 2005). The formation of hyphae on the forest floor, improves the plants nutrient uptake, because hyphaes have more surface area per volume than roots. (Perry,D. 1994). Which allow the plant to establish symbiotic relation with the fungi.
 
The relation of fungi organisms with forest soils, is important for the establishment of the vegetation. Sometimes, when forest restoration works are conducted, the tree planted is not able to growth, because the soil does not have the proper mycorrhizal [http://en.wikipedia.org/wiki/Mycorrhiza] community to interact with the plant. This is an example of the fragile and important connection between organisms in the environment.


===Bacterias===
===Bacteria===
Bacterias have an important role in the nutrient cycling. The distribution of bacterias in forest soils is mostly determined by vegetation and soil chemical characteristics. For example, the study conducted by Hackl, E.(2004), compared the bacterial communities on six forests under different pine and oak vegetation. The results shown that Gram-positive bacteria communities, especially actinomycetes, were more abundant under conifer forests than under oak coverage.  This results suggest that bacterial communities are adaptive to the soil chemistry [[#References|[4]]].
Bacterias have an important role in the nutrient cycling. The distribution of bacterias in forest soils is mostly determined by vegetation and soil chemical characteristics. For example, the study conducted by Hackl, E.(2004), compared the bacterial communities on six forests under different pine and oak vegetation. The results shown that Gram-positive bacteria communities, especially actinomycetes, were more abundant under conifer forests than under oak coverage.  This results suggest that bacterial communities are adaptive to the soil chemistry [[#References|[9]]].


==Microbial processes==
==Microbial processes==
What microbial processes define this environment? Describe microbial processes that are important in this habitat, adding sections/subsections as needed. Look at other topics in MicrobeWiki. Are some of these processes already described? Create links where relevant.


===Decomposition===
===Decomposition===
Microbial communities degrade most of the organic material that is settled on the forest soils. For these reason, most of forest soil have a fragile nutrient cycle. An example of these process can be seen when mature forest soil is disturbed, often the disturbance include, deforestation, fire and soil removal for agricultural activities. The first observation is that soil nitrate under natural conditions, does not represent a big part of the N pool, however, when is disturbed, nitrifier bacteria population increases, which increase soil fertility by the making nitrate more accessible for plants. That is one of the reason why poor farmers on the Tropics had adopt the slash and burn [http://www.forestsforever.org/climate2.html[5]] practice to enhance soil fertility. However, at the long range the soil fertility is depleted due to the disruption of the nutrient cycle.  
Microbial communities degrade most of the organic material that settled on the forest soils. The organic matter decomposition rate depends of physical factors, substrate quality and the type of microbial community. The degradation of certain compounds by specific bacterias, lead to a successional microbial community until all the substrate is completely decomposed.
 
Some saprophytic fungi and bacteria, are the the primary agents that induce decomposition. By the degradation of organic compounds as: cellulose, hemicellulose, pectin and lignin.(Sylvia,D. et al., 2005).
 
[[Image:forest_fungi.jpg|thumb|400px|right| Fungi decomposition http://summitcountyvoice.com/2012/08/20/morning-photo-a-few-more-fungi/1-191/]]
 
===Carbon Cycle===
 
The microbial biomass composes less than 35 of the total organic carbon in soils (Schlesinger, W., 1997). In natural or undisturbed forest ecosystems, the decomposition rate humus is lower than an agricultural field. This process is due to the low management which reduce the respiration process that is part of the metabolism of some bacteria and fungi. However, depending of the the substrate quality, carbon compounds can be break down by the enzymatic action of microorganisms. That is the reason why in forest soils, the decomposition of leaf litter produces high quantities of dissolved organic carbon compounds and 5 to 40% of the total C losses may occur by leaching. However, less carbon is lost by soil erosion. This important processes reduce the decomposition rate and storage carbon in the soil
 
C/N ratio determine the bacteria community distribution in the soil. Carbon quality tends to be an important component of the microbial communities distribution. Johnson (2001)[[https://wiki.usask.ca/download/attachments/293273780/Effects+of+Forest+Harvesting+on+C+and+N+soil+storage.pdf 10]] studied different forest management and their effect on the C and N soil storage. The results shown that saw-log forest removal tend to increase the amount of carbon and nitrogen in the soil at the short term. This process is due to the rapid incorporation of small size carbon material into the soil, which allow microorganisms to decompose the carbon molecules and release the excess of nutrients to the soil. The abundance of carbon is taken by microbes which at the same time helps to the immobilization the nitrogen in the soil.


====C/N ratio===
===Nitrogen Cycle===


====Carbon Cycle====
Nitrogen in soils is linked with the amount of soil organic matter, which contained around 5% of nitrogen (Brady and Weil, 2010). These organic nitrogen is not accesible for plants, that is why microbes decomposed the organic material to smaller pieces which later are release as ammonium. The process of consuming organic material and releasing inorganic compounds is called mineralization. However, in natural forest soils, this process take longer and usually is carried by a limited microbial community due to the low organic nitrogen available. That is why soil nitrogen is not considered a major N pool.


===Subsection 2===
However, when the soil is disturbed, nitrifier bacteria population increases, which increase soil fertility by the making nitrate more accessible for plants. That is one of the reason why poor farmers on the Tropics had adopt the slash and burn [http://www.forestsforever.org/climate2.html] practice to enhance soil fertility. However, at the long range the soil fertility is depleted due to the disruption of the nutrient cycle.


==Current Research==
==Current Research==


Enter summaries of recent research here--at least three required
===Conversion of the Amazon rainforest to agriculture results in biotic homogenization of soil bacterial communities===
This study is focused on how the land use change from a Tropical Rainforest to an agricultural land will impact the microbial communities. After, the deforestation and shift in the soil land use, the phylogenetic characteristic of the bacteria communities increases, but at the same time their diversity decrease along the area. The researchers suggest that microbial communities should be taken in consideration before change the land used in order to avoid losing the biodiversity within. [http://www.pnas.org/content/early/2012/12/26/1220608110.abstract 12]
 
===Soils in newly forested areas store substantial carbon that could help offset climate change===
The increase in the emissions of CO<2> to the atmosphere, and high interest about climate change. These two particular situations are leading to the development of new alternatives for carbon sequestration. The new initiatives proposed includes the reforestation of non-forested areas. Researchers from the University of Michigan explain that non-forested areas area capable to sequester the double amount of CO<2> than areas that are or had some forest vegetation. [http://ns.umich.edu/new/releases/21340-soils-in-newly-forested-areas-store-substantial-carbon-that-could-help-offset-climate-change 13].
 
===Impacts of elevated N inputs on north temperate forest soil C storage, C/N and net N-mineralization===
This study is focused on the impact of forest soil disturbance and the effect of several N application rates. The main idea is that nitrogen influences the carbon storage in the soil. So by changing the soil chemistry, the researchers found that under N application increase the soil carbon and mineralization rate. However, it decrease the C/N ratio. As conclusion, at the long term the C/N and N mineralization depends of the addition of nitrogen along time. At the short term, the changes are due to the organic matter decomposition rate and to the stabilization of the plant community.


==References==
==References==
Brady, N., and Weil, R. (2010). "Elements of the nature and properties of soils". Third Edition. Pearson Education Inc.
Buol, S., Southard, R., Graham, R., and McDaniel, P.(2003)."Soil Genesis and classification". 5th Edition. Blackwell Publishing Company.


[Sample reference]
Comerford, B. (2005). "Forest Soil. Encyclopedia of Soil Science", Second Edition.


[http://wwf.panda.org/about_our_earth/about_forests/|[1]]
Hackl, E., Zechmeister-Boltenstern, S., Bodrossy, L., and Sessitsch, A.(2004). "Comparison of Diversities and Composition of Bacterial      Populations Inhabiting Natural Forest Soils".  Appl. Enviro. Microbiol. 70(9):5057-5065. Web: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC520910/


[2][Soil Genesis and classification 2003. 5th Edition. Blackwell Publishing Company]
Johnson,D., and Curtis, D. (2001). "Effects of forest management on soil C and N storage:meta analysis". Forest Ecology and Management 140:227-238. Web: https://wiki.usask.ca/download/attachments/293273780/Effects+of+Forest+Harvesting+on+C+and+N+soil+storage.pdf


[3][http://en.wikipedia.org/wiki/Forest_floor]
Nave, L., Vance, E., Swanston,C., and Curtis, P. (2009). Impacts of elevated N inputs on north temperate forest soil C storage, C/N and net N-mineralization J. Geoderma. 153: 231-240.


[4][Comerford, B., 2005. Forest Soil. Encyclopedia of Soil Science, Second Edition]
Perry, D. (1994). Forest Ecosystems. First Edition. The Johns Hopkins University Press. pp 429.


[5][http://www.forestsforever.org/climate2.html]
Rodriguez, J., Pellizari, V., Mueller, R., Baek, K., Jesus, E., Paula, F., Mirza, B., Hamaoui, G., Tsai, S., Feigl, B., Tiedje, J., Bohannan., B., and Nusslein, K. (2013). "Conversion of the Amazon rainforest to agriculture results in biotic homogenization of soil bacteria communities". PNAS 110:988-993. Web: http://www.pnas.org/content/early/2012/12/26/1220608110.abstract.


Schlesinger, W. (1997). "Biogeochemestry: An analysis of global change". Second Edition. Elsevier.


[http://www.ncbi.nlm.nih.gov/pmc/articles/PMC520910/ Hackl, E., Zechmeister-Boltenstern, S., Bodrossy, L., and Sessitsch, A. "Comparison of Diversities and Composition of Bacterial Populations Inhabiting Natural Forest Soils". '' Appl Enviro Microbiol''. 2004 September; 70(9):(5057-5065)|[4]]
Sylvia, D., Fuhrmann, J., Hartel, P., and Zuberer, D.(2005). "Principles and applications of soil microbiology" Second Edition. Person Education Inc.


[https://wiki.usask.ca/download/attachments/293273780/Effects+of+Forest+Harvesting+on+C+and+N+soil+storage.pdf Johnson,D., and Curtis, D.(2001)Effects of forest management on soil C and N storage:meta analysis. Forest Ecology and Management 140: 227-238 |[7]]
WWF: http://wwf.panda.org/about_our_earth/about_forests/


[http://ijs.sgmjournals.org/cgi/reprint/50/2/489 Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "''Palaeococcus ferrophilus'' gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". ''International Journal of Systematic and Evolutionary Microbiology''. 2000. Volume 50. p. 489-500.]


Edited by Tito Lavaire, a student of Angela Kent at the University of Illinois at Urbana-Champaign.
Edited by Tito Lavaire, a student of Angela Kent at the University of Illinois at Urbana-Champaign.


<!-- Do not edit or remove this line -->[[Category:Pages edited by students of Angela Kent at the University of Illinois at Urbana-Champaign]]
<!-- Do not edit or remove this line -->[[Category:Pages edited by students of Angela Kent at the University of Illinois at Urbana-Champaign]]

Latest revision as of 21:53, 22 April 2013

This student page has not been curated.

Introduction

Forests represent the 31% of the total land area and support more than 1.6 million people around the world. At the same time, forests are important because they are home of 80% of the terrestrial biodiversity which include plants, animals and microorganisms [1]. The interactions of the terrestrial biodiversity are integrated in the food web process. Those processes include the transfer of energy, community interactions and nutrient cycling. These process are also linked with abiotic factors as soil, water and climate and determine the productive characteristic of each niche.

The most common soil definition is "Soils as a media for plant growth" [2. However, soils have several functions that determine the ecological roles in the environment:

  • Recycling system for nutrients and organic waste
  • Modifier of the atmosphere
  • Habitat for soil organisms
  • Engineering medium
  • System for water supply and purification

Soil formation is a pedogenic and biogeochemical process that is dependent of the translocation, biocycling and transformation of materials deposited and degraded by microorganisms on the uppers soil layer. These processes are developed along time and space, and have as final product the formation of soils with different physical and chemical characteristics.

The early soil classification made by the USDA on 1938, classified forest soils in the Zonal soil Order, as Pedalfers [2] , that are soils with the following suborder:

  • Soils of forest-grassland transition
  • Light-colored podzolized soils of timberland regions
  • Lateritic soils of forested warm-temperature and tropical regions.

The Soil Science Society of America does not have a specific definition about forest soils. However, Comerford (2006) defined forest soils as a soil that has been developed under forest cover, or a forest that has been disturbed but once was covered by forest vegetation [3].

Physical environment

Soil Formation

The physical characteristics observed in forest soils, are determined by the soil formation factors:climate, organisms, parent material, time and relief.

The process mentioned above, determine the type of soil that will be formed. For forest soils in particular, the principal characteristic is the development of an organic layer on the soil surface, usually referred as forest floor [3]. This particular horizon contains fresh organic materials from dead plants and animals, that are easily degraded by microorganisms, especially by bacteria and fungi. This layer is represented with the letter "O" that means organic, due to the accumulation of organic mater.As the soil depth increase, the availability of organic matter decreases, having as result a more mineral soil layer. However, the thickness of each layer varies depending of the topography, vegetation and parental material in which the forest has been established.

The transformation and translocation of organic and inorganic material by physical and chemical process along the soil profile, are the basic processes for the soil formation.

Alfisol soil profile of a mature forest http://www.omrisk.unito.it/abstract/index.html

Soil Organic Matter

The most important role of the vegetation on soil, is the accumulation of organic matter. The tree leaves represent the most important source of carbon in the soil. The type of vegetation is also an important factor because it affects the soil acidity. For example, litter from conifer trees require more time to be decomposed, having as result a slow recycling of nutrients. On the other hand, litter from deciduous trees are easily decomposed due that they contains more less strong carbon bonds, that microorganisms can brake faster. As result, microorganisms release organic acids, that promote the soil formation by the desegregation of rocks. This process requires time, and at the long term, it will determine the thickness of the soil horizons and the fertility of the forest soil.

Climate

Temperature and precipitation regimes have a direct impact on the forest vegetation, decomposition rate and soil formation process.

Tropic Forest Soils

Soils formed under high temperature and precipitation rates from volcanic parent material are usually characterized for having a fragile nutrient cycle. In fact, tropical forest soils have high clay content and lower soil organic matter accumulation. A good example of these, are the Tropical Rainforest which usually have low pH and low plant nutrient due to the translocation of clay particles that carried non acid cations into the soil. Some examples of these soils are the Ultisols [4] and Oxisols [5].

Temperate Forest Soils

Forest soils developed under temperate climate, usually have higher organic matter because they have lower temperature which slow down the decomposition rate. However, these soils are highly weathered due to the seasonal temperature and precipitation rate along the year. Alfisols and Spodosols are the most common soils observed under these conditions. These soils are characterized by the accumulation of calcium carbonate and clay particles in deeper horizons, due to leaching nutrient from the parent material rocks and decomposition of litter which released strong organic acids that reduce the soil pH and with a CEC up to 35%.[7].

Microbial communities

Fungi

The microbial community in forest soil is dominated by fungi. Since most of the organic compounds in forest soils is located on the soil surface and there is plenty oxygen, fungi communities are able to extend their filaments called hyphae. Fungi are more efficient than bacteria, in terms of decomposing organic compounds. In fact, 50% of the decomposed material is transformed in fungi tissue and 94% of fungi have enzymes capable to degrade lignin, that is a important component of wood cells in trees (Sylvia, D., et al. 2005). The formation of hyphae on the forest floor, improves the plants nutrient uptake, because hyphaes have more surface area per volume than roots. (Perry,D. 1994). Which allow the plant to establish symbiotic relation with the fungi.

The relation of fungi organisms with forest soils, is important for the establishment of the vegetation. Sometimes, when forest restoration works are conducted, the tree planted is not able to growth, because the soil does not have the proper mycorrhizal [6] community to interact with the plant. This is an example of the fragile and important connection between organisms in the environment.

Bacteria

Bacterias have an important role in the nutrient cycling. The distribution of bacterias in forest soils is mostly determined by vegetation and soil chemical characteristics. For example, the study conducted by Hackl, E.(2004), compared the bacterial communities on six forests under different pine and oak vegetation. The results shown that Gram-positive bacteria communities, especially actinomycetes, were more abundant under conifer forests than under oak coverage. This results suggest that bacterial communities are adaptive to the soil chemistry [9].

Microbial processes

Decomposition

Microbial communities degrade most of the organic material that settled on the forest soils. The organic matter decomposition rate depends of physical factors, substrate quality and the type of microbial community. The degradation of certain compounds by specific bacterias, lead to a successional microbial community until all the substrate is completely decomposed.

Some saprophytic fungi and bacteria, are the the primary agents that induce decomposition. By the degradation of organic compounds as: cellulose, hemicellulose, pectin and lignin.(Sylvia,D. et al., 2005).

Carbon Cycle

The microbial biomass composes less than 35 of the total organic carbon in soils (Schlesinger, W., 1997). In natural or undisturbed forest ecosystems, the decomposition rate humus is lower than an agricultural field. This process is due to the low management which reduce the respiration process that is part of the metabolism of some bacteria and fungi. However, depending of the the substrate quality, carbon compounds can be break down by the enzymatic action of microorganisms. That is the reason why in forest soils, the decomposition of leaf litter produces high quantities of dissolved organic carbon compounds and 5 to 40% of the total C losses may occur by leaching. However, less carbon is lost by soil erosion. This important processes reduce the decomposition rate and storage carbon in the soil

C/N ratio determine the bacteria community distribution in the soil. Carbon quality tends to be an important component of the microbial communities distribution. Johnson (2001)[10] studied different forest management and their effect on the C and N soil storage. The results shown that saw-log forest removal tend to increase the amount of carbon and nitrogen in the soil at the short term. This process is due to the rapid incorporation of small size carbon material into the soil, which allow microorganisms to decompose the carbon molecules and release the excess of nutrients to the soil. The abundance of carbon is taken by microbes which at the same time helps to the immobilization the nitrogen in the soil.

Nitrogen Cycle

Nitrogen in soils is linked with the amount of soil organic matter, which contained around 5% of nitrogen (Brady and Weil, 2010). These organic nitrogen is not accesible for plants, that is why microbes decomposed the organic material to smaller pieces which later are release as ammonium. The process of consuming organic material and releasing inorganic compounds is called mineralization. However, in natural forest soils, this process take longer and usually is carried by a limited microbial community due to the low organic nitrogen available. That is why soil nitrogen is not considered a major N pool.

However, when the soil is disturbed, nitrifier bacteria population increases, which increase soil fertility by the making nitrate more accessible for plants. That is one of the reason why poor farmers on the Tropics had adopt the slash and burn [7] practice to enhance soil fertility. However, at the long range the soil fertility is depleted due to the disruption of the nutrient cycle.

Current Research

Conversion of the Amazon rainforest to agriculture results in biotic homogenization of soil bacterial communities

This study is focused on how the land use change from a Tropical Rainforest to an agricultural land will impact the microbial communities. After, the deforestation and shift in the soil land use, the phylogenetic characteristic of the bacteria communities increases, but at the same time their diversity decrease along the area. The researchers suggest that microbial communities should be taken in consideration before change the land used in order to avoid losing the biodiversity within. 12

Soils in newly forested areas store substantial carbon that could help offset climate change

The increase in the emissions of CO<2> to the atmosphere, and high interest about climate change. These two particular situations are leading to the development of new alternatives for carbon sequestration. The new initiatives proposed includes the reforestation of non-forested areas. Researchers from the University of Michigan explain that non-forested areas area capable to sequester the double amount of CO<2> than areas that are or had some forest vegetation. 13.

Impacts of elevated N inputs on north temperate forest soil C storage, C/N and net N-mineralization

This study is focused on the impact of forest soil disturbance and the effect of several N application rates. The main idea is that nitrogen influences the carbon storage in the soil. So by changing the soil chemistry, the researchers found that under N application increase the soil carbon and mineralization rate. However, it decrease the C/N ratio. As conclusion, at the long term the C/N and N mineralization depends of the addition of nitrogen along time. At the short term, the changes are due to the organic matter decomposition rate and to the stabilization of the plant community.

References

Brady, N., and Weil, R. (2010). "Elements of the nature and properties of soils". Third Edition. Pearson Education Inc.

Buol, S., Southard, R., Graham, R., and McDaniel, P.(2003)."Soil Genesis and classification". 5th Edition. Blackwell Publishing Company.

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Edited by Tito Lavaire, a student of Angela Kent at the University of Illinois at Urbana-Champaign.