N deposition is a key factor affecting the composition and function of soil microbial communities in wetland ecosystems. Previous studies mainly focused on the effects of N deposition in the soil during the growing season (summer and autumn). Here, we focused on the response of the soil microbial community structure and function in winter. Soil from the Sanjiang Plain wetland, China, that had been treated for the past 11 years by using artificial N deposition at three levels (no intervention in N0, N deposition with 4 g N m⁻² yr⁻¹ in N1, and with 8 g N m⁻² yr⁻¹ in N2). Soil characteristics were determined and the bacterial composition and function was characterized using high-throughput sequence technology. The N deposition significantly reduced the soil bacterial diversity detected in winter compared with the control N0, and it significantly changed the composition of the bacterial community. At the phylum level, the high N deposition (N2) increased the relative abundance of Acidobacteria and decreased that of Myxococcota and Gemmatimonadota compared with N0. In soil from N2, the relative abundance of the general Candidatus_Solibacter and Bryobacter was significantly increased compared with N0. Soil pH, soil organic carbon (SOC), and total nitrogen (TN) were the key factors affecting the soil bacterial diversity and composition in winter. Soil pH was correlated with soil carbon cycling, probably due to its significant correlation with aerobic_chemoheterotrophy. The results show that a long-term N deposition reduces soil nutrients in winter wetlands and decreases soil bacterial diversity, resulting in a negative impact on the Sanjiang plain wetland. This study contributes to a better understanding of the winter responses of soil microbial community composition and function to the N deposition in temperate wetland ecosystems.

Using the static chamber–gas chromatography method, this study investigates the flux characteristics of CO₂, CH₄, and N₂O in the soils of three typical island-like forests in the Sanjiang Plain during the growing season (May to September), as well as their relationships with environmental factors. The results indicate that the soils of the Broadleaf mixed forest, Quercus mongolica forest, and Betula platyphylla forest act as emission sources for CO₂ and N₂O, with average fluxes of 433.92, 452.41, and 358.17 μg·m⁻²·h⁻¹ for CO₂ and 12.48, 13.02, and 10.51 μg·m⁻²·h⁻¹ for N₂O, respectively. The differences among forest types are not significant. All three forest types serve as sinks for CH₄, with average fluxes of −22.52, −23.29, and −0.76 μg·m⁻²·h⁻¹. The Betula platyphylla forest has a significantly weaker absorption intensity compared to the other types (p < 0.01). The measured environmental factors collectively explain 66.58% of the variability in greenhouse gas fluxes in the island-like forests, with soil temperature, soil moisture, and total nitrogen content being the main influencing factors in the region. Rising temperatures favor the emission of CO₂ and N₂O and the absorption of CH₄ in all three forest types. Increased soil moisture inhibits the absorption of CH₄ in the Broadleaf mixed forest and Quercus mongolica forest, while higher levels of alkali-hydrolyzed nitrogen enhance the N₂O flux in the Quercus mongolica forest. Soil organic carbon and soil pH significantly influence only the greenhouse gas fluxes of the Betula platyphylla forest.

Shrub invasion affects plant growth and soil physicochemical properties, resulting in soil microbiota metabolic pathway changes. However, little is known about the shrub expansion intensity of microbial metabolic pathway processes. In this study, we used metagenome sequencing technology to investigate changes in soil microbial C and N metabolic pathways and community structures, along with different shrub invasion intensities, in the Sanjiang Plain wetlands. Different shrub invasion intensities significantly affected the soil microbial composition (β diversity), with no significant effect on the α diversity compared to CK. AN, pH, and TP were the major factors influencing the microbial community’s structures. Compared to CK, the shrub expansion intensity did not significantly affect C fixation and central metabolism but significantly reduced methanogenesis, which involves the CO₂-to-methane transition that occurs in methane metabolism, and denitrification, the nitrite to nitric oxide (nirK or nirS) transition that occurs in N metabolism. This study provides an in-depth understanding of the biogeochemical cycles of wetland ecosystems in cold northern regions undergoing shrub invasion.

Using a static chamber-gas chromatography method, we investigate the characteristics of soil CO₂, CH₄, and N₂O fluxes and their relationships with environmental factors during the growing season in four typical Larix gmelinii forests (moss–Larix gmelinii forest, Ledum palustre–Larix gmelinii forest, herbage–Larix gmelinii forest, and Rhododendron dauricum–Larix gmelinii forest) in the Greater Khingan Mountains. Our results show that all four forest types are sources of CO₂ emissions, with similar average emission fluxes (146.71 mg·m⁻² h⁻¹–211.81 mg·m⁻² h⁻¹) and no significant differences. The soil in the moss–Larix gmelinii forest emitted CH₄ (43.78 μg·m⁻² h⁻¹), while all other forest types acted as CH₄ sinks (−56.02 μg·m⁻² h⁻¹–−28.07 μg·m⁻² h⁻¹). Although all forest types showed N₂O uptake at the beginning of the growing season, the N₂O fluxes (4.03 μg·m⁻² h⁻¹–5.74 μg·m⁻² h⁻¹) did not differ significantly among the four forest types for the entire growing season, and all acted as sources of N₂O emissions. The fluxes of CO₂, CH₄, and N₂O were significantly correlated with soil temperature and soil pH for all four forest types. Multiple regression analysis shows that considering the interactive effects of soil temperature and moisture could better explain the changes in greenhouse gas emissions among different forest types. The average Q₁₀ value (8.81) of the moss–Larix gmelinii forest is significantly higher than that of the other three forest types (3.16–3.54) (p < 0.05), indicating that the soil respiration in this forest type is more sensitive to temperature changes.

To investigate the effects of long-term elevated atmospheric CO₂ (eCO₂) on the distribution and stability of soil aggregates and microbial characteristics in wetland soils and to reveal the mechanisms by which eCO₂ influences soil organic carbon (SOC) sequestration, a multi-temporal-scale eCO₂ control experiment was conducted in the Sanjiang Plain wetland with treatments at ambient CO₂ concentration (AC), 550 ppm, and 700 ppm CO₂. Soil aggregate fractionation, phospholipid fatty acid (PLFA) analysis, and redundancy analysis (RDA) were used to analyze changes in aggregate size distribution, stability indices (MWD, GMD), microbial biomass, and community structure. The results showed that eCO₂ significantly affected aggregate size distribution. Both short- and long-term exposure to low-concentration eCO₂ reduced the proportion of large aggregates. Over time, the proportion of silt and clay particles increased, while microaggregates decreased. Although CO₂ concentration did not directly affect MWD and GMD, long-term eCO₂ significantly reduced soil aggregate stability. Microbial biomass and diversity were not sensitive to CO₂ concentration but decreased significantly with prolonged exposure. In contrast, microbial community structure was significantly affected by both CO₂ level and exposure duration. RDA indicated that, under short-term eCO₂, aggregate fractions were positively correlated with microbial biomass, whereas, under medium- and long-term treatments, they were positively correlated with soil physicochemical properties. Macroaggregates were positively correlated with aggregate stability, while microaggregates and silt–clay fractions were negatively correlated—a relationship that strengthened with longer eCO₂ exposure. Thus, long-term eCO₂ altered soil aggregate structure and microbial communities, ultimately influencing SOC stability. These findings provide data and theoretical support for predicting soil carbon stability and ecosystem functioning in wetlands under climate change.

Waterlogging restricts root-zone oxygen availability and can impair seedling growth and leaf quality in mulberry. Root-zone aeration may reduce waterlogging injury, but its effects on root anaerobic metabolism, photosynthesis, oxidative stress, and leaf functional quality have not been well integrated. In this study, Morus alba L. ‘Longsang No. 1’ seedlings were subjected to four treatments: normal moisture without aeration (CK), normal moisture with intermittent root-zone aeration (RA), waterlogging without aeration (WL), and waterlogging with intermittent root-zone aeration (WL+RA). Waterlogging was maintained with a water layer 1–2 cm above the substrate surface, and root-zone aeration was supplied using an air pump and microporous aeration stones for 30 min every 4 h. Root-zone dissolved oxygen, growth traits, root activity, root fermentative indicators, root and leaf oxidative injury, gas exchange, chlorophyll fluorescence, antioxidant enzyme activities, and leaf quality-related traits were measured after 14 d of treatment. Waterlogging decreased root-zone dissolved oxygen from 6.62 to 1.69 mg L⁻¹. It also reduced plant height, total leaf area, shoot and root dry weight, root activity, Pn, Fv/Fm, Y(II), and ETR. In contrast, WL increased ADH and PDC activities, lactate and ethanol contents, MDA, H₂O₂, electrolyte leakage, and NPQ. Leaf 1-DNJ, polysaccharides, total phenolics, total flavonoids, DPPH, ABTS, and FRAP were also reduced under WL. Intermittent aeration increased root-zone dissolved oxygen to 4.64 mg L⁻¹ under waterlogging and partially alleviated many of these changes. WL+RA showed higher growth, root activity, photosynthetic performance, PSII photochemical efficiency, antioxidant enzyme activities, and leaf functional quality than WL. These results indicate that intermittent root-zone aeration was associated with better mulberry seedling performance under waterlogging, together with changes in root-zone oxygen status, fermentation metabolism, photosynthesis, oxidative balance, and leaf quality.