Molecular Soil Biology 2026, Vol.17, No.1, 12-25 http://bioscipublisher.com/index.php/msb 14 dries, oxygen begins to diffuse in, and some reduced states are re-oxidized. The Eh gradually increases, and nitrification also intensifies. Sometimes, processes such as iron reduction may be more active than methane production for a period of time. This often delays or suppresses methane generation. Field observations can also show similar changes. For example, in some typical paddy fields in Hunan, the Eh is usually relatively low during the long irrigation stage after transplanting, but once the field is left dry or exposed to the sun, the Eh rises quickly (Yang et al., 2019). For farmers, there is a relatively intuitive reference method for operation: insert a perforated pipe in the field to observe the water level. When the water level drops to about −15 cm below the field surface and then re-irrigate. This relatively gentle drying method is considered to be neither likely to cause obvious water stress nor conducive to balancing yield, water saving, and emission reduction. 2.3 Complexity of microbial networks and ecological stability hypothesis The relationship between "complexity" and "stability" in ecology has been debated for a long time. The model proposed by May in the early days already pointed out a problem: if the interactions in the system are random, then an increase in scale and connectivity does not necessarily mean greater stability. Therefore, it is necessary to be cautious when simply equating "more complex networks" with "more stable systems". When looking at the soil microbial network from this perspective, under disturbances such as changes in the water cycle, such as alternate wetting and drying irrigation, the network structure is likely to be re-adjusted (Hernandez et al., 2021). Some strictly anaerobic nodes, such as groups related to methane production, may have reduced connections or even withdraw, while nodes related to oxidation processes, nitrogen cycling, or iron cycling may become more prominent. As a result, the system sometimes shows more obvious modules and key nodes may become more concentrated or more dispersed. Based on this idea, a testable hypothesis can be proposed: In subtropical paddy fields, compared to continuous flooding, alternate wetting and drying irrigation may weaken the connectivity of the co-occurrence network centered on methane-producing groups, while increasing the degree of modularization and functional differentiation, making the system more structurally resilient under water disturbance, and this change often shows a consistent trend with the decrease in methane flux (Figure 1) (Banerjee et al., 2019). Figure 1 Alpha diversity indices and community composition of root fungal communities across conventional (Conv), no-till (NT), and organic (Org) farming systems. OTU richness (a), Sheldon evenness (b), and Shannon–Weaver index (c) were calculated from the rarefied fungal OTU table. Same lowercase letter indicates no statistically significant (P < 0.05) difference between farming systems. d Stacked bar chart showing the relative abundance of various orders of wheat root fungal communities (Adopted from Banerjee et al., 2019)
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