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Soil aggregates are the key functional units of soil ecosystems which are essential to biogeochemical cycling and plant growth. However, it remains unclear how fertilization regimes influence soil aggregation, associated resources, and microbial distribution among aggregates, as well as the potential subsequent impacts for other abiotic and biotic processes. For this, a long-term maize cropping field experiment was conducted in the subtropical region of China under four fertilization treatments: no fertilizer, chemical fertilization, organic fertilization, and chemical plus organic fertilization. Additionally, we classified soil aggregates into large macro-aggregates (>2 mm), small macro-aggregates (0.25–2 mm), and micro-aggregates (<0.25 mm) and compared soil nutrients, enzyme activities, and microbial communities of each aggregate fraction and bulk soil as well as crop productivity and plant carbon (C), nitrogen (N), and phosphorus (P). Results showed that long-term organic fertilization (1) increased soil C, N, and P contents within macro-aggregates, while increased bacterial and fungal biomass within all three aggregate size fractions, (2) increased N-acquiring enzyme activity, C:P, and N:P enzyme ratios but decreased phosphatase activity and C:N enzyme ratio regardless of aggregate fractions, and (3) promoted crop productivity but decreased plant C:N, C:P, and N:P ratios compared with chemical fertilization. Additionally, the fungi:bacteria ratio and phosphatase activity decreased, but the gram-positive to gram-negative bacterial ratio, C-acquiring enzyme activity, C:N and C:P enzyme ratios increased with decreasing aggregate size. The partial least squares models confirmed that macro-aggregates had strong effects on crop performance while micro-aggregates was the main determinant of microbial community. Taken together, long-term organic fertilization promotes soil functioning and crop productivity via increasing the proportion of soil macro-aggregates. • Aggregates with different sizes played distinct roles in soil functioning. • Organic fertilization increased crop productivity by promoting macro-aggregation. • Macro-aggregates is an important resource of nutrients promoted plant growth. • Resources in micro-aggregate were conducive to microbial utilization. • Microorganisms in micro-aggregates were C-limited. [ABSTRACT FROM AUTHOR]

Nitrogen (N) deposition poses a threat to terrestrial biodiversity and ecosystem functioning globally. However, little is known concerning how the structure and function of litter fauna communities will respond in this context. Here, a gradient of N deposition (0, 20, and 40 kg N ha−1 yr−1) was simulated in a subtropical forest of southwestern China, to assess the potential effects of increased N deposition on the trophic structure and functioning of fauna communities in decomposing leaf litters of three main subtropical plant functional groups covering a total of 18 species: six evergreen broadleaf, six deciduous broadleaf, and six coniferous trees. We found that N addition shifted the trophic structure of fauna communities in decomposing litter, and different fauna feeding guilds showed distinct response patterns. Specifically, N addition increased the abundance of predators, decreased the abundance of omnivores, while detritivores were less affected. Compared to deciduous broadleaf and coniferous litters, evergreen broadleaf litter had less complex structure of fauna communities, but it decomposed slower. Further, structural equation modeling (SEM) showed that N addition increased litter decomposition in part via changing the trophic structure of fauna communities, with a positive correlation between predators and detritivores being associated with higher decomposition. As omnivores often exhibit top-down pressure on all other trophic guilds in (sub-)tropics, our observed shifts in trophic structure and litter decomposition might be partly due to the N addition-induced declines in omnivorous ant population. Future studies should investigate the role of bottom-up and top-down forces between detritivores, predators, and omnivores in driving litter decomposition. Collectively, our findings suggest that (i) N deposition consistently shifts the trophic structure of fauna communities across litter types, and (ii) such a shift further translate into changes in the functioning of subtropical forest ecosystems. [Display omitted] • In subtropical forests, distinct fauna feeding guilds responded differently to N addition. • These dissimilar response patterns caused a shift in the litter food web. • Such a shift in the litter food web had a knock-on effect on changes in litter decomposition. • Specifically, N addition promoted litter decomposition via increasing the abundances of predators and detritivores. [ABSTRACT FROM AUTHOR]

Global increases in the intensity and frequency of wildfires are driving major changes in soil organic matter (SOM) characteristics, including soil dissolved organic matter (DOM). As the most crucial component of SOM, soil DOM plays a pivotal role in the carbon cycle and regulates the environmental fate of contaminants through its versatile reactivities, including electron-donating capacity (EDC). However, it is still being determined how wildfire influences key characteristics of soil DOM and subsequent effects on EDC in forest soils. Thus, we conducted our study to fill this gap with the forest soils of Jinyun Mountain Nature Reserve of China, which experienced an unprecedented wildfire event in 2022. The results from optical characterization, high-performance size-exclusion chromatography (HPSEC), and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) showed decreasing molecular weight but elevating nitrogen-containing molecular formulas of soil DOM in the burned soils. This could be attributed to the Maillard reaction and microbial re-colonies. Additionally, wildfires increased the condensed aromatics and lignin components in soil DOM. In the burned soils, we observed increasing EDC of soil DOM, which accounts for an increase in lignin-derived phenolic components. Overall, the findings of this study demonstrate that eco-disturbances, such as wildfires, induce alterations in the properties of DOM, leading to variations in its reactivity and potentially influencing the fate of environmental pollutants beyond carbon dynamics alone. Thus, incorporating the dynamic properties of soil DOM, particularly in the context of climate change, can enhance the assessment of risks associated with contaminants in soil and water, providing valuable insights., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)