• Ayah Khan

Decomposition served with tea


Organic Matter Decomposition (OMD) is an ecological process that involves physical and biological soil activities (Tisdall and OADES, 1982). A fundamental natural process, OMD produces vital soil nutrients. Initially found in plant tissue, residues are now located on the surface layer of soil and are composed of decaying remains of animal, microbial, and plant matter. Nutrients vital for flora and fauna survival are released into nearby soils during this process.

Compression facilitates recirculation, energy storage, nutrient flow, and carbon storage within an ecosystem. Decomposition is controlled by substrate and decomposition-agent availability and soil temperature (Gavazov 2010). As well as soil acidity and litter bag chemical properties, the decomposition rate depends on several other abiotic and biotic factors. Accordingly, decomposition rates vary over time and space. The biological tissue mass of litter decomposes over time, implying that a constant proportion of waste is being destroyed. There are three primary phases, each of which has a set duration:


Figure 1: showing all three phases of the organic matter decomposition (Chapin et al, 2002)


Phase 1: Leaching


Decomposition begins with the leaching of essential soluble components (e.g. organic acids) for microorganisms. The leaf senescence (autumn die-back) is the process of breaking down organic compounds in the leaf. Those compounds then travel to other parts of the plant. In water, leaching occurs when water-soluble and mineral ions dissolve. Concentrations of water-soluble products, such as sugar, are broken down. When organic matter is located in an area with high rainfall concentrations, mass loss is most significant during this phase ( Tukey, 1970 ).


Phase 2: Fragmentation


The outer layer of plant cells is comprised of lignin-impregnated cuticles (Figure 2). These walls protect plant tissue from microbial attack, but the second phase pierces them. This is the slowest stage, with a further 40-70% of original material being removed by the decomposition of organic matter. The second phase involves creating a fresher surface for microbial colonization, a process known as fragmentation. Agents of fragmentation include soil invertebrates (microfauna). It increases the proportion of litter masses accessible to microbial attack (Scheu and Wolters,1991).



Figure 2: showing the structure and components making a leaf.

Phase 3: Chemical alteration


The third phase may take a year; decaying activity in this phase occurs very slowly because the materials are relatively refractory (figure 3). Only 10% of the original plant tissue mass remains in this third phase. It occurs in bacteria and fungus; animal residue and litter are gradually decomposed and broken down until they are Soil Organic Matter (SOM). Chemical alterations occur by soil microbes such as fungi and bacteria. They account for approximately 80-90% of decomposer biomass (Bada, J.L. and Lee, C., 1977).


Figure 3: leaves before decomposing and after showing the final stage of decomposing.

Tea bags


Litter bags or tea bags (e.g. greens or rooibos tea bags) are a standard method of measuring decomposition by recording decomposition substrate mass loss (Cotrufo et al. 2009). Litter bags containing plant material are made of a perforated mesh-like material that allows microorganisms to break down plant litter. The bag prevents waste from being lost so a researcher or citizen-scientist can record weight changes. In the field, the tea bag will be buried in soil, allowing for measuring the mass loss over some time and increasing the resolution of decomposition measurements (Keuskamp et al., 2013). Before burial, the bas would be weighed; then, after it’s been buried, it will be considered again to measure the differences as well as taking photos of the original product within the bag and pictures taken after the fieldwork has concluded to see if physical appearance has changed as shown in figure 3, making it clear that phase 3 of the processes had occurred.


This measurement can then create a Tea Bag index (TBI), which follows the measures of mass loss after some time. This facilitates data comparison between soil types, ecosystems and biomes. This approach has several advantages:

  • Simplicity

  • Cost-efficiency (commercially available in stores as seen in figure 4)

  • Potential involvement in citizen science

A global map of soil decomposition could be constructed with geographical distribution, making comparison easier.


Figure 4: Tetrahedron-shaped synthetic tea bags used for Tea Bag Index (TBI) experiments (Keuskamp et al, 2013)

Bibliography


Bada, J.L. and Lee, C., 1977. Decomposition and alteration of organic compounds dissolved in seawater. Marine Chemistry, 5(4-6), pp.523-534.


Chapin, F.S., Matson, P.A. and Mooney, H.A., 2002. Terrestrial decomposition. Principles of terrestrial ecosystem ecology, pp.151-175.


Cotrufo, M.F., Del Galdo, I. and Piermatteo, D., 2009. 5 r Litter decomposition: concepts, methods and future perspectives. Soil carbon dynamics, p.76.


Keuskamp, J.A., Dingemans, B.J., Lehtinen, T., Sarneel, J.M. and Hefting, M.M., 2013. Tea Bag Index: a novel approach to collect uniform decomposition data across ecosystems. Methods in Ecology and Evolution, 4(11), pp.1070-1075.



Keuskamp, J.A., Dingemans, B.J., Lehtinen, T., Sarneel, J.M. and Hefting, M.M., 2013. Tea Bag Index: a novel approach to collect uniform decomposition data across ecosystems. Methods in Ecology and Evolution, 4(11), pp.1070-1075.


Scheu, S. and Wolters, V., 1991. Influence of fragmentation and bioturbation on the decomposition of 14C-labelled beech leaf litter. Soil Biology and Biochemistry, 23(11), pp.1029-1034.


Tisdall, J.M. and OADES, J.M., 1982. Organic matter and water‐stable aggregates in soils. Journal of soil science, 33(2), pp.141-163.


Tukey Jr, H.B., 1970. Leaching of substances from plants. Annu. Rev. Plant Physiol.;(United States), 21.