Molecular Soil Biology 2026, Vol.17, No.1, 12-25 http://bioscipublisher.com/index.php/msb 21 6.3 Coupling relationship between microbial network structure and methane production flux When discussing the network structure and flux together, the value lies not merely in answering "are these microorganisms present", but rather it is closer to "how are they combined and together pushing the process forward". Some empirical studies across Asian paddy fields have depicted the co-occurrence relationships among methanogenic archaea as network links. The results revealed that many topological features were closely related to methane emissions, and they also had a prominent explanatory power among a variety of influencing factors (Zhou et al., 2019). Therefore, the network itself can be regarded as a kind of system-level "process intensity signal". If placed within the AWD framework, this link can be described more straightforwardly: Irrigation first alters Eh and substrate supply, and subsequently, methanogenic archaea, synthetic nutrient bacteria, methane-oxidizing bacteria, and iron/nitrate reduction-related groups change their relative positions; the previously "tight anaerobic chain" structure may be disrupted, and the network is more like multiple processes running simultaneously and with clearer modules, and finally, the net CH₄flux decreases (Banerjee et al., 2018). Co-occurrence is not equivalent to actual interaction, but if the changes in the network and functional genes, metabolic pathways, and flux changes align in direction, it can still be used for mechanism explanations and even as a connection point for predictive modeling. 7 Case Study: Empirical Analysis of the AWD Model in Typical Subtropical Rice Fields 7.1 Background of the case area and irrigation management practices This article takes a field trial of the "safe AWD" in the subtropical rice area of South China as the case background. The trial was conducted at the Agricultural Science Research Institute Experimental Station in Guangzhou, Guangdong Province, with the location roughly at 113°20′E, 23°08′N. The area has a typical subtropical humid monsoon climate. The study was carried out in both the early and late seasons, comparing treatments such as AWD15, AWD30, continuous flooding, and the commonly used irrigation methods by farmers (Carrijo et al., 2017). Water levels and water potentials in the fields were continuously recorded, and methane fluxes were regularly monitored. Crop yields and water productivity were also evaluated. In terms of management practices, the "safe AWD" approach is actually quite intuitive: a perforated pipe is inserted in the field to observe the water level. When the water level drops to about −15 cm below the field surface, water is then pumped to the shallow water layer. This threshold is basically consistent with the "15 cm rule" promoted by IRRI, aiming to help farmers make repeatable irrigation decisions using a simple method (Lampayan et al., 2015). The significance of this case lies in that it not only compares different irrigation methods, but also focuses on water conservation, yield, and methane emission reduction, providing a real field background for further discussion of microbial mechanisms. 7.2 Reconstruction of microbial network and changes in methane emission From the results of methane emissions, this experiment in Guangzhou provided a relatively clear conclusion: With the production remaining basically unchanged or with very little variation, the AWD treatment significantly reduced CH₄emissions, while the water productivity also improved (Carrijo et al., 2017). The most notable result was that AWD15 and AWD30 tended to be in a lower methane emission range compared to the common irrigation methods used by farmers (FP), and the water-saving effect and improvement in water utilization efficiency were also more significant. Regarding the microbial mechanism, another type of evidence comes from comparative studies of different water management methods. For example, a macro-genomic study comparing continuous flooding (FI), alternate wetting and drying (AI, i.e. AWD), and another intermittent irrigation (RI) found that under water-saving irrigation conditions, the relative abundance of groups related to methane production would decrease, and the co-occurrence network structure would also undergo significant changes; at the functional level, the enrichment degree of genes related to methane metabolism decreased, while the pathways related to nitrification and carbohydrate decomposition were enhanced (Figure 6) (Zhang et al., 2021). When the field flux results and these multi-omics evidence are considered together, a relatively consistent explanation can be obtained: The re-oxidation process brought by AWD would weaken the network connections centered on the methane-producing food web, and at the same time, more modules related to the oxidation process would become active, reducing the overall intensity of methane generation and emission from the system structure.
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