Introduction

Decomposition can be considered the inverse process of production, because it is a metabolic degradation of organic matter (such as plant residues, animal tissues, and microbial material) into simple organic and inorganic compounds. Decomposition is essentially a process of breakdown of the carbon skeleton existing in the organic compounds with consequent liberation of energy. Decomposition is an important component in global carbon budget; without decomposition, the atmospheric CO2 pool could be depleted literally in one decade based on the current annual rates of net photosynthesis (without considering the effect of biological feedbacks). Moreover, soil organic matter is one of the largest and most dynamic reservoirs of carbon in the global carbon cycle. The carbon stored in soil organic matter is 2400 petagrams (Pg, 1015g), which is about twice as much the amount stored in vegetation (550 Pg) and atmosphere (750 Pg), together. A better understanding of processes involved in the dynamics of soil organic matter is crucial to predict future changes in atmospheric CO2 concentrations. Decomposition and the subsequent mineralization are also an indispensable process for sustaining life on Earth, as they are the only processes enabling massive recycling of chemical elements in the biosphere. Most nutrients cycle from an inorganic form in the soil solution to vegetation and back to the soil solution through decomposition and subsequent mineralization. Mineralization is the conversion of nutrients and other substances from an organically bound form to a water-soluble inorganic form. Decomposition and mineralization are closely related processes. In fact, mineralization is often considered as part of the decomposition process; however, decomposition does not always lead to mineralization. Decomposition is associated with carbon cycling whereas mineralization is with nutrient cycling. Part of decomposition processes such as fragmentation and chemical alteration could be classified as mineralization, if inorganic nutrients or other simple bases (e.g., NH3, (PO4)3~ ) are lost from the complex organic compounds during these processes. Mineralization is a vital process in ecosystem dynamics since most plant essential nutrients (such as nitrogen, phosphorus, and sulfur) are made available to plant uptake through the process of mineralization (Figure 1).

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