Molecular Soil Biology 2024, Vol.15, No.1, 37-45 http://bioscipublisher.com/index.php/msb 39 3.3 Interaction between microbial and invertebrate decomposers The interaction between microbial and invertebrate decomposers is a synergistic relationship that enhances the efficiency of dung decomposition. Invertebrates, such as earthworms and detritivores, physically break down dung into smaller particles, increasing the surface area available for microbial colonization and activity (Griffiths et al., 2021; Sun and Ge, 2021). This physical fragmentation by invertebrates facilitates microbial access to organic substrates, promoting microbial growth and enzymatic activity (Pimentão et al., 2019; Griffiths et al., 2021). Additionally, the presence of invertebrates can influence the composition and diversity of microbial communities, further affecting the decomposition process (Raczka et al., 2021; Mason et al., 2023). This interaction between decomposers not only accelerates the breakdown of organic matter but also contributes to the formation of stable soil organic matter, which is crucial for soil health and plant growth (Fanin, et al., 2021; Griffiths et al., 2021; Raczka et al., 2021) (Figure 1). Figure 1 The fate of plant matter through the decomposition process (Adopted from Griffiths et al., 2021) Image caption: This can be conceptualised as removing different layers of an onion. The initial stages of decomposition involve leaching and multiple organisms (microbial and invertebrate) that can digest simple compounds: carbohydrates, peptides and fats (the red layer of the onion). After this stage multiple organisms can catabolise lignocellulose (the yellow and green parts of the onion). This can be microbes alone, invertebrates alone (using endogenous cellulases, but generally not endogenous lignin-modifying enzymes), or a partnership between endogenous invertebrate cellulases and (mostly) gut symbiont cellulases (‘digestomes’). The result of these progressive decomposition processes is the creation of organic matter that becomes smaller in molecular size and is increasingly protected from further breakdown by interaction with mineral surfaces and incorporation into soil aggregates (Lehmann and Kleber (2015) defined here as stable or protected soil organic matter; the blue part of the onion). This protected organic matter is then consumed by a range of organisms, including microbes, soil-feeding termites, and endogeic earthworms. These soil-feeding invertebrates often break down clay-complexed peptides and are thought to be important sources of plant-available nitrogen, key bioavailable parts of the nitrogen cycle (Ji and Brune, 2005) (Adopted from Griffiths et al., 2021) 4 Impact on Soil Fertility 4.1 Nutrient release and availability (nitrogen, phosphorus, etc.) Dung decomposers, particularly dung beetles, play a crucial role in enhancing soil fertility by facilitating the release and availability of essential nutrients such as nitrogen (N) and phosphorus (P). Studies have shown that dung beetles incorporate significant amounts of nitrogen, ammonium, and phosphorus into the soil, which varies among species. For instance, the dung beetle Sulcophanaeus imperator was found to incorporate the highest quantities of organic matter, nitrogen, and phosphate into the soil, thereby improving nutrient cycling and soil fertility (Maldonado et al., 2019). Additionally, the application of dung beetles in soil has been shown to significantly increase the levels of magnesium and potassium, further contributing to soil nutrient status
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