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Leaf litter decomposition in agroforestry systems
1. Leaf litter decomposition in agroforestry system
Submitted by:-
S.S.R Tripathy
o1SAF/16
2nd year MSc. Forestry
2. Leaf litter:-
Litter fall, plant litter, leaf litter, tree litter, soil litter, or duff, is dead plant material, such
as leaves, bark, needles, twigs, and cladodes; that have fallen to the ground. This
detritus or dead organic material and its constituent nutrients are added to the top layer
of soil, commonly known as the litter layer or O horizon ("O" for "organic").
Leaf litter can be a critical element of soil. Leaving leaves to decompose replenishes
soil by releasing carbon, nitrogen, phosphorus and other inorganic compounds. The
decomposition process can also foster interesting forms of life, like fungus, which often
thrive in decaying leaf material.
Leaf litter also helps to retain moisture and regulate temperature. This is important in
cold regions where organisms live under leaf litter during the winter, and where plants
can receive some protection from extreme temperatures under a blanket of leaves.
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5. LEAF LITTER DECOMPOTION
• Decomposition is a multistage process initiates with leaching by water liberating soluble
carbon compounds. Another early process is physical breakup or fragmentation of the
plant material into smaller bits which have greater surface area for microbial
colonization and attack.
• In smaller dead plants, this process is largely carried out by the soil invertebrate fauna,
whereas in the larger plants, primarily parasitic life-forms such as insects and fungi play
a major breakdown role and are not assisted by numerous detrivore species.
• Following this, the plant detritus (consisting of cellulose, hemicellulose, microbial
products, and lignin) undergoes chemical alteration by microbes. Different types of
compounds decompose at different rates.
• This is dependent on their chemical structure. For instance, lignin is a component of
wood, which is relatively resistant to decomposition and can in fact only be decomposed
by certain black-rot fungi.
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• Wood decomposition is a complex process involving fungi which transport nutrients
to the nutritionally scarce wood from outside environment. Because of this
nutritional enrichment the fauna of saproxylic insects may develop and in turn
affect dead wood, contributing to wood decomposition and nutrient cycling in the
forest floor.
• Lignin is one such remaining product of decomposing plants with a very complex
chemical structure causing the rate of microbial breakdown to slow. Warmth
determines the speed of plant decay, with the rate of decay increasing as heat
increases, i.e. A plant in a warm environment will decay over a shorter period of
time.
• In most grassland ecosystems, natural damage from fire, insects that feed on
decaying matter, termites, grazing mammals, and the physical movement of animals
through the grass are the primary agents of breakdown and nutrient cycling, while
bacteria and fungi play the main roles in further decomposition.
7. LEAF LITTER DECOMPOTION PROCESS
• Generally speaking there are two processes of leaf litter decompotion:
1.ANAEROBIC (without oxygen) decomposition
2. AEROBIC (with oxygen) decomposition and stabilization
8. Anaerobic decomposition
• Anaerobic decomposition takes place in nature, as in the decomposition of the
leaf litter at the bottom of marshes and in buried leaf litter to which oxygen
does not have access. Intensive reduction of leaf litter is usually accompanied
by disagreeable odours of hydrogen sulphide and reduced organic compounds
which contain Sulphur, such as mercaptans (any Sulphur-containing organic
compound).
• Organic compounds break down by the action of living organisms that do not
require air in the normal sense. These organisms use nitrogen, phosphorus, and
other nutrients to live and to develop cell protoplasm, but they reduce the
organic nitrogen to organic acids and ammonia.
• The carbon from the organic compounds which is not utilized in the cell
protein is liberated mainly in the reduced form of methane (CH4). A small
portion of carbon may be respired as carbon dioxide (C02).
9. 2. AEROBIC (with oxygen) decomposition and stabilization:-
• When leaf litter decompose in the presence of oxygen, the process is called
“aerobic.” The aerobic process is most common in nature. For example, it takes
place on ground surfaces such as the forest floor, where droppings from trees and
animals are converted into a relatively stable humus. There is no accompanying
bad smell when there is adequate oxygen present.
• In aerobic decomposition organisms which use oxygen, feed upon the leaf litter.
They use the nitrogen, phosphorus, some of the carbon, and other required
nutrients. Much of the carbon serves as a source of energy for the organisms and is
burned up and respired as carbon dioxide (C02).
• carbon serves both as a source of energy and as an element in the cell protoplasm,
much more carbon than nitrogen is needed. Generally about two-thirds of carbon
is respired as C02, while the other third is combined with nitrogen in the living
cells. However, if the excess of carbon over nitrogen (C:N ratio) in organic
materials being decomposed is too great, biological activity diminishes. Several
cycles of organisms are then required to burn most of the carbon.
11. Factors affecting leaf litter fall:-
• Although decomposition is predominantly a microbial process, soil and leaf litter
invertebrates enhance leaf litter decomposition by physically breaking up the organic
material and stimulating microbial activity (Anderson et al. 1983, Berg and
McClaugherty 2014).
• Globally, the relative importance of this faunal effect is known to increase with
increasing total precipitation and minimum temperature (Garcıa-Palacios et
al.2013). Locally, the faunal effect is determined by the composition, abundance, and
activity of the soil fauna, which in turn are partially dependent on the abiotic micro-
environment, in particular the temperature and moisture content of the litter (Gonza
lez and Seastedt 2001).
• However, the contribution of invertebrates to decomposition also varies with litter
quality, with a larger effect reported for more rapidly decom- posing litter (Yang and
Chen 2009, Handa et al. 2014).
• Abundance of the soil and litter invertebrate fauna also varies seasonally and may
be partially responsible for seasonal dynamics in litter decomposition rates (Seastedt
and Crossley 1980).
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• Decomposition rates also vary seasonally, as a consequence of changes in litter
temperature and moisture (Rozema et al. 1999, Rigobelo and Nahas 2004, Eviner
et al. 2006), resulting in higher wet season mass loss across a range of forest types
(Bernhard Reversat 1982, Seastedt et al. 1983, Torres et al. 2005).
• Low precipitation can limit leaching of the dissolved organic material from the
litter, as well as reducing the activity of decomposers (Rigobelo and Nahas 2004).
De- composer activity may also be affected by the seasonal differences in
substrate supply and quality (Schmidt et al. 2007).
• In addition, microbial communities are specific to the different stages of
decomposition, because the chemical composition and physical properties of litter
changes over the course of decomposition (Griffith and Boddy 1990, Berg and
McClaugherty2014).
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• Fast growing trees like eucalyptus can produce very high quantities of litter
(Binkerly et al., 1992; Tokay and Singh, 1993).
• Litter fall is generally low before the rise of green crown that commences
around canopy closure. It can be seasonal or continuous (Wedderburn and
Carter, 1999) depending on species (deciduous or evergreen) and climate.
• Eucalyptus litter fall often peaks in summer in both plantations (George and
Varghese, 1990; Toky and Singh, 1993) and in native forests (Ashton, 1975;
Attiwii et al 1996).
