Molecular Soil Biology 2024, Vol.15, No.1, 37-45 http://bioscipublisher.com/index.php/msb 38 2 Types of Dung Decomposers 2.1 Microbial decomposers (bacteria, fungi) Microbial decomposers, including bacteria and fungi, are essential for breaking down organic matter in dung. These microorganisms facilitate the mineralization process, converting organic nutrients into inorganic forms that plants can absorb. For instance, specific strains of bacteria in the rhizospheric soil, known as plant growth-promoting rhizobacteria, are used as biofertilizers to enhance soil fertility and suppress pests and pathogens (Pathma et al., 2019). Additionally, the microbial communities in earthworm digestive tracts contribute significantly to nutrient cycling by decomposing organic matter and enhancing soil microbial activity (Medina-Sauza et al., 2019). 2.2 Invertebrate decomposers (earthworms, dung beetles) Invertebrate decomposers such as earthworms and dung beetles also play a vital role in dung decomposition and nutrient cycling. Earthworms, for example, mix soil layers and incorporate organic matter into the soil, which improves soil structure and fertility. They also influence soil microbial communities, which in turn affect soil processes and plant growth (Medina-Sauza et al., 2019; Ahmed and Al-Mutairi, 2022; Li et al., 2022). Dung beetles, on the other hand, break down dung and incorporate it into the soil, enhancing nutrient availability. Different species of dung beetles vary in their efficiency, with some species like Sulcophanaeus imperator being more effective in incorporating nitrogen and phosphorus into the soil (Jones et al., 2018; Evans et al., 2019; Maldonado et al., 2019). 2.3 Role of different decomposers in nutrient cycling Both microbial and invertebrate decomposers are integral to nutrient cycling. Microbial decomposers break down complex organic compounds into simpler forms, making nutrients available for plant uptake. For example, earthworm activity enhances denitrification and increases soil nutrient availability, indirectly promoting plant growth (Medina-Sauza et al., 2019; Li et al., 2022). Invertebrate decomposers like dung beetles accelerate the decomposition process, leading to quicker nutrient release and improved soil fertility. The activity of dung beetles has been shown to increase soil nutrients in the topsoil, which is crucial for plant growth (Evans et al., 2019; Maldonado et al., 2019; Ma et al., 2023). 3 Mechanisms of Dung Decomposition 3.1 Breakdown of organic matter The breakdown of organic matter in dung is a complex process primarily driven by microbial and invertebrate decomposers. Microorganisms, including bacteria and fungi, play a crucial role in the initial stages of decomposition by breaking down complex organic compounds into simpler molecules. This microbial activity is essential for the recycling of nutrients and the formation of soil organic matter (SOM) (Soares and Rousk, 2019; Hicks et al., 2021). Invertebrates, such as earthworms and other soil fauna, further contribute to this process by physically fragmenting the dung and enhancing microbial access to organic substrates (Griffiths et al., 2021). The interaction between these decomposers ensures a continuous and efficient breakdown of organic matter, ultimately supporting soil fertility and plant growth (Griffiths et al., 2021; Sun and Ge, 2021). 3.2 Enzymatic activities involved Enzymatic activities are central to the decomposition of dung, with various enzymes produced by both microbial and invertebrate decomposers. Microorganisms secrete a range of enzymes, including cellulases, proteases, and lipases, which degrade cellulose, proteins, and lipids, respectively (Hicks et al., 2021; Raczka et al., 2021). These enzymes facilitate the conversion of complex organic compounds into simpler forms that can be assimilated by microbes and plants. Invertebrates also contribute to enzymatic decomposition through their digestive enzymes, which break down organic matter as it passes through their digestive systems (Griffiths et al., 2021). The combined enzymatic activities of microbes and invertebrates accelerate the decomposition process and enhance nutrient availability in the soil (Pimentão et al., 2019; Konschak et al., 2021).
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