International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.6, 267-276 http://ecoevopublisher.com/index.php/ijmec 271 4 Driving Factors of Grassland Decomposition Process 4.1 Quantity and quality of fallen debris Litter, as the main substrate in the decomposition process, its quantity and quality directly affect the rate of nutrient release. The larger the quantity, the stronger the micro-environmental protection received during the initial decomposition, and the better the water retention capacity. When the quantity decreases, the exposure of fallen leaves is high, and the increase in light and wind erosion makes the early decomposition slower. In terms of the quality of litter, the chemical composition of herbaceous plants varies significantly. Gramineous plants: The litter usually has a high fiber content, a large C/N ratio, and a relatively slow decomposition rate. Leguminous plants: They have a high nitrogen content and a low lignin content, and their decomposition rate is relatively fast. Semi-shrub plants: They have a high degree of lignification, a large residual proportion, and significant limitations in later decomposition. The composition changes of grassland plant communities will thus lead to the overall migration of litter mass. Grazing, burning and fertilization often indirectly affect the litter cycling pattern by changing species dominance. 4.2 Soil Microbial community: the core of decomposition and nutrient transformation Microorganisms are the core drivers of grassland decomposition and nutrient cycling. Fungi, bacteria and actinomycetes respectively undertake different decomposition functions. Fungi are good at decomposing refractory substances such as lignin and are the main force in the later stage of decomposition. Bacteria prefer easily decomposable substrates, such as cellulose and soluble organic matter. Actinomycetes have a strong metabolic capacity in dry and high-temperature environments. However, the activity of grassland microorganisms is significantly restricted by moisture, and the alternating dry and wet conditions lead to frequent fluctuations in their activity. After rainfall, microorganisms rapidly resume growth, triggering "pulse-like" carbon-nitrogen mineralization, a phenomenon that is widespread in temperate and semi-arid grasslands. Human activities that change the way land is used can also cause a reorganization of the microbial community structure. For example, long-term application of nitrogen fertilizer may lead to an increase in the proportion of bacteria and a relative decrease in fungi, thereby affecting the carbon turnover rate. 4.3 The participation of soil animals Soil animals change the physical structure of litter through activities such as gnawing, crushing, digging holes and excreting, increasing the contact area with microorganisms and thus accelerating decomposition. Its main functions are reflected in: large soil animals (such as earthworms) promoting the formation of aggregates and enhancing soil aeration and water infiltration. Medium-sized animals (jumping insects, mites), break up litter and regulate the distribution of microorganisms on the surface of the litter. Micro-animals (nematodes, protozoa) prey on microorganisms to form "micro-food webs", accelerating the recycling of nitrogen and carbon. The relative composition of soil animals varies significantly among different types of grasslands. The animal diversity in arid grasslands is low, resulting in the decomposition process being more dependent on microbial drive. The functions of moist grassland animals are relatively complete, and the decomposition pathways are more diverse (Dipman and Meyer, 2019). 4.4 Climatic factors: The limiting effects of temperature and precipitation Temperature and moisture are the most important environmental factors for the decomposition of grasslands. Temperature affects metabolic rate, while moisture determines microbial activity and substrate accessibility. In arid grasslands, rainfall events often have sudden "activation effects", which can increase soil respiration and nitrogen mineralization by 2 to 5 times in the short term. Long-term climate change also has a profound impact on the decomposition process: warming up and increasing the rate of surface decomposition, but it may cause instability in the deep soil carbon pool. Intensified drought reduces microbial activity and hinders the degradation of litter. The temporal distribution of precipitation changes, affecting the frequency of the dry-wet cycle and thereby altering the intensity of pulse-type decomposition (Hou et al., 2022).
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