Soil Biology & Biochemistry最新文献

Coastal wetlands, being a multifaceted and crucial global ecosystem, are facing significant impacts from diverse environmental alterations, particularly soil salinization. Concurrently, the escalation of extreme climate events, such as global warming, presents complex challenges for the protection and restoration efforts. Previous researches concerning microbial communities in the context of climate with continous line numbering change have predominantly concentrated on their structural aspects, with limited attention given to establishing relationships between community structure and functional attributes. In this study, a two-year investigation was conducted on conventional coastal wetland ecosystems, considering variations in salinity and seasonal temperature. Utilizing high-throughput 16S rRNA sequencing, isotope technology, and other methods to explore the bacterial community, nitrogen cycling functional groups, and nitrogen reduction process. This research aims to assess the holistic impacts of significant global environmental changes on microbial communities. The results suggest that salinity, acting as an environmental filter, has a significant impact on the microbial community composition. It leads to a decrease in species abundance, an increase in deterministic processes and the nesting of community succession, while also reducing the stability of microbial ecological networks. The mechanism by which soil salinity impacts bacterial communities involves three main aspects: direct effects, positive climate regulation, and negative regulation of soil properties. Surprisingly, soil salinity exerts a mild inhibitory influence on microbial functional genes and metabolic activity. The primary factors involved in the nitrogen reduction process include electron donors/acceptors, types of nitrogen sources, and organic carbon. The three processes are interconnected due to the impact of environmental factors and signal transmission among microbial populations. This study offers a novel scientific framework for the rehabilitation and enhancement of saline-alkali coastal ecosystems in the face of impending global changes. It achieves this by investigating the varied response patterns exhibited by microbial communities and ecological functional metabolism under salinity-induced stress.

Mitigation of N₂O emissions, a potent greenhouse gas, remain challenging due to knowledge gaps in plant-mediated nitrogen (N) transformation pathways, which limits ability to identify optimal approaches for efficient N utilization. We set up mesocosms with barley, Italian ryegrass, and barley in combination with Italian ryegrass to assess role of cover crop in N₂O emission mitigation. Soil emitted N₂O was collected simultaneously from the pots with plants at three growth stages: namely, vegetative, canopy expansion, and grain filling. The gas sample N₂O contents, N in microbial biomass (MBN), mineral N content, and phospholipid fatty acid (PLFA) analysis in soils were determined at the three growth stages. Cumulatively, highest N₂O was emitted from soil under Italian ryegrass (0.056 mg N g⁻¹ soil) followed by barley (0.0051 mg N g⁻¹ soil) and the least under barley and Italian ryegrass combination (0.0014 mg N g⁻¹ soil). The high emissions under Italian ryegrass occurred at vegetative stage due to high reactive N availability. Strong emissions were observed at canopy expansion stage under barley and were linked to access to the large mineral N proportion redistributed to the lower depth as depicted by highest MBN (0.025 mg N g⁻¹ soil) and decreased extractable N (0.0068 mg N g⁻¹ soil). The high emissions under barley correlated with high fungal/bacterial ratio, pointing towards a fungal role in the emissions. The least soil N₂O emissions under barley and Italian ryegrass combination were accompanied by elimination of variations induced by the plant growth stages. Absence of 18:2ω6,9 fungal PLFA biomarker under barley and Italian ryegrass combination indicates a potential inhibition and corresponds with reduced N₂O emissions. Together, these results broaden our understanding on how plant-soil interactions drives N₂O emissions processes and improves our ability to identify optimal plant-based emission mitigation approaches.

Extended exposure to acid rain has vastly limited soil microbial activity with the consequences for soil carbon (C) storage, but less is known about the microbial responses within soil aggregates that to some extent determine soil C stabilization. Here, we investigated the main microbial group compositions and the relevant potential enzyme activities within different soil aggregates sizes (microaggregates (<250 μm), small macroaggregates (250–2000 μm), and microaggregates (>2000 μm)) in a subtropical forest with decade-long simulated acid rain (SAR) treatments. Four SAR treatments were set by irrigating plots with water of different pH values (i.e., 3.0, 3.5, 4.0, and 4.5 as a control). Results showed that the SAR treatment significantly inhibited microbial activities, specifically decreasing both bacterial and fungal abundances, leading to declines in C-degrading potential enzyme activities. Conversely, potential enzyme activities related to phosphorus (P) and nitrogen (N) mineralization as well as the enzyme stoichiometry for P/N ratio significantly increased under the SAR treatment. The SAR treatment showed no significant differences in microbial abundance across the three soil aggregate sizes. However, it had a more pronounced effect on potential enzyme activities in their optimal aggregate sizes, such as hydrolytic enzymes like β-glucosidase in macroaggregates and oxidases like phenol oxidase and peroxidase in microaggregates. Overall, C-degrading potential enzyme activities were more strongly decreased in the microaggregates than in macroaggregates, and the distribution in aggregates was significantly altered, transforming from large to small sizes under the SAR treatment, which together may boost SOC stabilization and accumulation. Additionally, our findings indicate that prolonged acid rain also caused soil nutrient limitation and imbalance, particularly for P, in subtropical forests. This study highlights the importance of soil aggregate size in regulating microbial responses to acid rain, which should be integrated into ecosystem models to predict soil biogeochemical cycles under future climate conditions.

Soil microorganisms are primary decomposers driving carbon and nutrient cycling in terrestrial ecosystems. One prevailing view is that fungi, rather than bacteria, play a predominant role in litter decomposition. However, the roles of bacteria and factors that restrict their activity during decomposition remain unclear. We hypothesized that the limiting activity of bacterial decomposers is associated with litter size beyond chemical quality. To address this gap, we conducted a 180-d decomposition microcosm experiment to investigate the effect of fragment size (large, 1–2 mm; middle, 0.18–0.28 mm; small, <0.07 mm) of oak and pine litters on bacterial or fungal decomposition. Bacterial and fungal decomposition were accelerated with fragment size decrease, suggesting that an interface effect existed between microbial decomposers and litter. Generally, the decomposition ability of bacteria was more sensitive to changes in fragment size compared to fungi. Fungi resulted in faster decomposition of large fragments than bacteria. For small oak litter fragments, bacteria showed faster decomposition than fungi, whereas the opposite was true for small pine litter. Therefore, the decomposition dominance of bacteria and fungi was regulated by fragment size and influenced by the chemical quality of litter, especially the lignin:N ratio. The contrasting decomposition dominances of bacteria versus fungi were likely attributed to filamentous fungi penetrating litter interiors and forming mycelial bridges between scattered litters. Bacteria resided on litter surfaces and even formed biofilms. Consistent with the findings of the microcosm experiment, the proportion of small fragments was greater in the fresh litter layer than in the decomposed layer in the field, and greater in the pine forest than in the oak forest, suggesting the fresh, large, and low-quality litter was preferentially fragmented by fungi. Consequently, the dominance of fungi and bacteria during litter decomposition in the conventional view should be revisited considering the litter size.

The impact of human-induced nitrogen (N) enrichment on microbial diversity has been extensively studied, with two main hypotheses proposed: soil N availability and soil acidification. However, the specific roles of these two hypotheses and their environmental preferences on soil bacterial and fungal communities are not fully understood. By conducting two independent experiments (a 16-year N and a 6-year acid addition) in a temperate semi-arid grassland, we tested the responses of soil microbial attributes (e.g., richness and relative abundance) at various levels (community, phylum/class, and phylotype) to N and acid addition. At the community level, our results showed that both N and acid addition had a negative effect on the richness of the whole, dominant, and rare bacterial communities; N enrichment only decreased the richness of the dominant fungal community, while acid addition decreased the richness of the whole, dominant, and rare fungal communities. By categorizing the microbial attributes into nine environmental preferences based on their responses to N and acid addition, we found that most bacterial phyla were associated with low N availability and high pH preferences, while most fungal classes had other environmental preferences. Most dominant bacterial phylotypes were linked to low N availability and high pH preferences, while most dominant fungal phylotypes were associated with other environmental preferences and high pH preferences. Conversely, most rare bacterial and fungal phylotypes were linked to other environmental preferences. Our experiments revealed that the decline in bacterial richness caused by N enrichment was predominantly due to their sensitivity to soil acidification, while fungal richness remained largely unaltered. By pinpointing distinct microbial attributes at different levels in response to N and acid addition, our findings could potentially forecast how soil microorganisms will react to future global N deposition.

Biofilm and planktonic prokaryotic communities were studied using a glass fibre filter as trapping material immersed in field soil at different times of the year (January, April, July, September) and incubated there for different periods (3, 6, 9, 12 months). The composition of biofilm and planktonic communities fluctuated over time, likely shaped by succession processes and varying environmental factors. This highlights soil biofilms as dynamic structures whose microbial community differs from that of soil plankton. Additionally, quantification of the biofilm-to-plankton 16S rRNA gene copy number ratio indicated that soil prokaryotes occur mainly as biofilm components.

The afforestation of tropical forests plays an important role in mitigating climate change. Exploring the impacts of nitrogen (N) and phosphorus (P) deposition on earthworm communities is significant for understanding the contributions of tropical forests to global change. A 14-year field experiment simulating N and P deposition at a station with 50-year-old tropical plantations was conducted. We found that the pantropical widespread exotic earthworm species Pontoscolex corethrurus was dominant, and it did not respond to exogenous N input. Moreover, P addition only increased the abundance of P. corethrurus after 14 years. Similarly, neither N addition nor P addition changed the stoichiometric traits of P. corethrurus. However, over the past decade, the abundance, biomass, and carbon (C), N, and P concentrations in the tissues of P. corethrurus have increased. A strong positive correlation between P. corethrurus population size and soil gram-negative (G⁻) bacteria biomass was observed, suggesting that P. corethrurus may benefit from the soil bacterial channel. This study ascertained that non-natural tropical lands may be resistant to N and P deposition in terms of earthworm related belowground processes, which would be helpful for fully understanding plant-soil biota feedback and their contributions to tropical plantation development and the mitigation of global climate change.

Over recent decades, there has been a noticeable change in vegetation diversity accompanied by increased plant productivity in tundra systems of the High-Arctic, leading to elevated carbon and nutrient inputs into the soil. This shift can alter microbial community composition and activity in these ecosystems. In this study, we aimed to identify genes transcribed by active microorganisms and compare their expression in unamended and amended soils with labile carbon and/or nitrogen compounds. We also assessed gene expression differences in tundra soils with varying edaphic characteristics (upslope vs. downslope sites). We amended soils with either glycine or cellulose or left them unamended (i.e., control) for 7 days of incubation, and we isolated and sequenced RNA using Illumina technology. Whereas we observed only a weak transcriptional response after cellulose addition, the glycine addition significantly influenced transcriptional patterns, with upregulation of carbon- and nitrogen-cycling genes. Notably, microbial taxa from the Pseudomonadaceae and Micrococcaceae families showed the most pronounced response to glycine, indicating a shift of the communities towards copiotrophic organisms. This response was consistent across the two soil types, suggesting a common impact on microbial community activity. These findings suggest that an increase in carbon and nitrogen inputs could substantially affect microbial functioning in High-Arctic tundra soils, with potential implications for ecosystem dynamics under global warming.