Soil aggregates are essential to the long-term sequestration of soil organic carbon (SOC) in coastal wetlands. Coastal wetlands in China have undergone profound transformation by the invasion of Spartina alterniflora and subsequent aquaculture reclamation, but the effects on soil aggregates remain unclear. This study examined the distribution of soil aggregate size, stability and organic carbon content across 21 coastal wetlands in China that had undergone a similar transformation, from native mudflats (MFs) to S. alterniflora marshes (SAs), and subsequent conversion to aquaculture ponds (APs). The results showed that silt+clay was the dominant fraction of soil aggregates (78.7%–83.1%), followed by micro-aggregates (12.8%–13.9%) and macroaggregates (4.1%–6.6%). Transition from MFs to SAs led to an increase in macroaggregate and microaggregate contents and the aggregate stability index (MWD, MGD and DR0.25), but a reduction in silt+clay content. Subsequent conversion of SAs to APs led to a reduction in macroaggregate content and aggregate stability index, and an increase in silt+clay and microaggregate contents. Change from MFs to SAs increased SOC by 69.6% in the silt+clay fraction, 29.4% in the microaggregate fraction, and 22.4% in the macroaggregate fraction. Conversely, converting SAs to APs decreased SOC content by 11.4% in the silt+clay fraction and 16.3% in the macroaggregate fractions, but an 8.5% increase in the microaggregate fraction. The results underscore the crucial role of soil aggregate formation in sequestration and storage of SOC under varying land cover change scenarios.
Partitioning of soil organic matter for particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) is essential to understand carbon (C) storage under climate change, given their distinct properties and response to warming. The mechanisms underlying warming-induced changes in C pools in black soils (Mollisols) remain unknown, owing to the stability of C pools and the complexity of their associated microbial communities. This study elucidates POC and MAOC contents and their microbial controls in black soils along a mean annual temperature (MAT) gradient from 0.6 to 7.3 °C. The POC content (3.3–17 g kg−1) increased with MAT, while MAOC content (33–60 g kg−1) decreased, indicating accelerated C turnover with warming. Higher MAT shifted the bacterial communities from K- to r-strategies, aligning with increased POC content. The dominance of r-strategists facilitated rapid utilization and mineralization of organic compounds (e.g., mainly with low C/N ratio), reducing MAOC and increasing POC through sustained plant residue inputs. This shift towards r-strategists also corresponded with increased abundance of saprotrophic fungi and stronger bacteria–saprotrophic fungi associations. Warming in colder regions may release available organic matter that saprotrophic fungi preferentially utilize over plant residues to minimize energy expenditure, decreasing POC decomposition. Our findings suggest that integrating microbial r-/K-strategies help to elucidate these mechanisms and simplify the interpretation of temperature effects on the dynamics of two main functional pools of soil organic matter.
The functional traits of soil fauna are closely related to ecosystem functions. The gut microbiota, which can reflect environmental changes, may be associated with functional traits. Therefore, in this study, collembolan (Entomobrya proxima) was used to clarify the linkage response of specific gut taxa and traits under long-term urea exposure. A small amount of urea had positive effects on functional traits of E. proxima. Chao1 and Shannon indices of gut bacteria conditionally rare or abundant taxa (CRAT) gradually decreased under low and medium fertilizer, while increased under high fertilizer. Shannon index of abundant taxa (AT) showed a similar trend to that of CRAT except that the value of Shannon index was higher at high fertilizer than that of medium treatments. The structure and community assembly of CRAT changed significantly, and with the increase of urea addition amount, the dominant mechanism of community assembly changed from a deterministic process to a stochastic process. The niche width of AT and CRAT decreased. Relative abundance of some genera in AT and CRAT was closely related to functional traits. In conclusion, CRAT was more sensitive to urea than AT, had the potential to characterize functional traits of E. proxima, which will provide a basis for predicting the changes of soil animal traits and functions under the change of agricultural fertilizer strategy in the future.
Soil microbial alpha diversity is essential for driving ecosystem functions and processes. However, little is known about the beta-diversity affect community functions. Here, we combine distinct community inocula using the dilution-to-extinction approach with two wheat genotypes to study the effect of microbial diversity loss on rhizosphere community assembly processes, which are related to beta-diversity (between-habitat diversity), and the consequences for ecosystem functions within greenhouse experiment. Compared with alpha-diversity, the bacterial and fungal community beta-diversity are stronger predictors of ecosystem functions (organic matter degradation, phosphorus supply capacity and nitrogen supply capacity), plant genotypes regulated the relationship between microbial diversity and ecosystem functions, with ecosystem functions being significant link to microbial diversity under different wheat genotypes. Loss of microbial diversity decreased the abundance of Bacterial_ASV6 (Burkholderia) and increased Fungal_11 (Altemaria) within the restored rhizosphere soil. Null modeling analysis showed that the deterministic assembly processes are dominant in bacterial community and fungal high-diversity (alpha-diversity) community, associating with the change of specialized functions (organic matter degradation, phosphorus supply capacity and nitrogen supply capacity) that are correlated with microbial diversity and specific microbial taxa. In addition, these two species were key role for regulating to the network cohesion. Overall, our study pointed out that the regulation of community assembly by microbial diversity loss limits the development of soil ecological functions and weakens the stability of rhizosphere microbial network, highlighting the potential regulatory effect of microbial taxa distribution on microbial community stability and changes of specific ecological functions.
Hurricanes cause significant damage to tropical forests; however, little is known of their effects on decomposition and decomposer communities. This study demonstrated that canopy debris deposited during Hurricane Otto stimulated sequential changes in soil carbon (C) and nitrogen (N) components, and decomposer microbial communities over 5 years. The initial response phase occurred within 2 years post-hurricane and appeared associated with decomposition of the labile canopy debris, suggested by: increased DNA sequences (MPS) of the Acidobacterial community (as common decomposers of labile plant material), decreases in total organic C (TOC), increased biomass C, respiration, and
A comprehensive understanding of microbial biogeography is essential to elucidate the mechanisms that regulate microbial diversity and facilitate ecosystem functioning. Here, we present a standardised approach for microbial biogeography research, using the ‘6W principles’ of ‘Who’, ‘What’, ‘Where’, ‘When’, ‘Why’, and ‘How’, to provide a paradigmatic framework for its study. The ‘6W principle’ we developed aimed to address the six fundamental questions in microbial biogeographical researches, including the taxonomic and functional identity, abundance and diversity, distribution patterns, movement or evolutionary trajectory, driving factors, and future changes of microbial communities. Some key corresponding actions were suggested to promote the microbial biogeographical research such as constructing high-resolution taxonomic and functional annotation databases, developing absolute-quantitative high-throughput sequencing, increasing sampling coverage, establishing multidimensional time-series monitoring, developing unified theoretical frameworks and advanced biogeographical modelling approaches, and establishing long-term global networking experiments. We call on the community to jointly enrich the connotation and coverage of the 6W principle, in order to promote the further development and exploitation of microbial biogeography in the context of ongoing global change.
