International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.6, 267-276 http://ecoevopublisher.com/index.php/ijmec 269 Soil animals: including earthworms, arthropods (such as jump worms, beetle larvae), nematodes and micro-arthropods (such as mites). They change substrate accessibility and microenvironment through fragmentation of litter, soil stirring, excrement release and food web interaction, promoting microbial degradation and nutrient recycling (Zheng et al., 2023). Microbial communities: Bacteria, fungi, actinomycetes and archaea form the biological basis for decomposition and mineralization. Fungi play a significant role in the decomposition of complex aromatic and lignin substances, while bacteria mainly deal with easily decomposable carbon sources. The structure and function of microbial communities are determined by soil moisture, temperature, pH and substrate supply, and are highly sensitive to disturbances such as dry-wet cycles and nitrogen deposition. Rhizosphere microorganisms and mycorrhizal fungi: Rhizosphere microorganisms enhance plants' adaptability to environmental stress by promoting nutrient absorption, altering root physiology, and defending against pathogens. Mycorrhizal fungi play a particularly crucial role in phosphorus absorption and the mitigation of drought stress. These functional groups form a complex interdependent network through the exchange of matter and energy, jointly supporting the productivity and stability of the grassland. 2.4 Ecosystem structure and energy flow characteristics The ecological structure of the grassland shows the characteristics of "strong underground and dynamic above-ground" : although the above-ground biomass fluctuates significantly within the seasons, the underground root system and soil organic matter constitute a long-term stable energy and material reservoir. Energy flow begins with photosynthetic capture, is transferred by herbivores to higher trophic levels, and is largely returned to the soil system through litter and manure input. Unlike forests, there is a high aboveground ratio variation in the energy distribution of grasslands: in drought years, more energy is stored in the form of root systems for use in adverse times. Energy flow is characterized by significant seasonality and impulsivity: the growing season is the peak of energy input, and rainfall pulses can activate photosynthesis and microbial mineralization in a short period of time, generating a strong "short-term pulse-long-term balance" feature. Disturbances (such as grazing or burning) play a dual role in energy flow: they rapidly release energy by consuming aboveground biomass and reshape the direction of matter flow, while also causing the system to experience phased high productivity or degradation - the long-term effects depend on the frequency and intensity of the disturbances. 3 The Nutrient Element Cycling Mechanism of the Grassland Ecosystem 3.1 Carbon cycle: dual control of vegetation-soil systems The carbon cycle of the grassland ecosystem is composed of processes such as plant photosynthesis, litter return, soil organic matter accumulation and mineralization, and carbon gas exchange (Bicharanloo et al., 2022). The carbon storage of grasslands is mainly concentrated in the underground part, and the proportion of root biomass and soil organic carbon in the total carbon pool can exceed 70%. This underground dominant carbon allocation model enables grasslands to have a certain recovery capacity under disturbances such as drought, fire and grazing. On the one hand, plants fix atmospheric CO₂ as organic matter through photosynthesis and input it into the soil in the form of root secretions, root renewal and ground litter. On the other hand, the decomposition of these organic substances by microorganisms can release CO₂ and dissolved organic carbon, thereby driving soil respiration. The annual net ecosystem carbon exchange capacity of grasslands is usually significantly affected by precipitation changes. Carbon absorption increases in humid years, while in dry years, the phenomenon of "carbon sourization" may occur. In addition, fire, changes in grazing intensity and soil erosion can alter the vegetation structure and the stability of the soil carbon pool, thereby affecting the long-term carbon balance. 3.2 Nitrogen cycle: the dominant role of microbial processes Nitrogen is a key element that limits the primary productivity of grasslands. The nitrogen cycle in grasslands mainly includes processes such as nitrogen fixation, mineralization, nitrification, denitrification, nitrogen
RkJQdWJsaXNoZXIy MjQ4ODYzNA==