Wen Yang

Background: Enzymatic stoichiometry reflects microbial relative resource limitations by linking microbial nutritional demands with soil nutrient availability, yet how plant invasion-induced changes in vegetation, soil properties, and microbial communities modulate these limitations and metabolic efficiency remains undetermined. Here, we employed enzymatic stoichiometry and vector modeling to assess microbial relative resource limitations in invasive Spartina alterniflora salt marsh in comparison to those in bare flat and in native Suaeda salsa and Phragmites australis salt marshes, and systematically linked these limitations to microbial carbon (C) and nitrogen (N) use efficiencies (CUE and NUE, respectively) across coastal wetland ecosystems of eastern China. Results: Our analyses showed predominant phosphorus (P) limitation of soil microbial metabolism in bare flat and native S. salsa and P. australis salt marshes, contrasting with dual C-P co-limitation observed in invasive S. alterniflora salt marsh. S. alterniflora invasion intensified microbial P limitation compared with bare flat, while simultaneously inducing the most pronounced C limitation among all plant communities. The microbial C limitation induced by S. alterniflora invasion drove reductions in microbial CUE, whereas microbial NUE increased, establishing an antagonistic relationship between these metabolic efficiencies. Microbial resource constraints and nutrient use efficiencies (CUE/NUE) in soils were coordinately controlled by plant traits, soil properties, and microbial attributes. Partial least squares path modeling analysis identified soil organic C (SOC) chemical fractions (e.g., aromatic C, alkyl C, dissolved organic C) as predominant positive drivers of microbial C limitation and NUE, while simultaneously suppressing microbial CUE. Simultaneously, plant traits were identified as the foremost contributor to microbial P limitation, followed by microbial attributes as the second-most influential positive factor. Conclusions: This study revealed that S. alterniflora invasion fundamentally shifted microbial nutrient limitation from predominant P limitation in bare flat and native salt marshes to dual C-P co-limitation, while simultaneously inducing the strongest microbial C limitation among all communities. This invasion-induced microbial C limitation drove a reduction in microbial CUE but an enhancement of NUE. SOC accumulation increased with decreasing microbial CUE following S. alterniflora invasion, a tradeoff potentially linked to divergent nutrient limitations across ecosystems. This study provided empirical evidence for microbially-mediated soil C sequestration mechanisms underlying plant invasion-induced ecosystem transformations.

Plant secondary succession is a very effective approach for the rejuvenation of degraded ecosystems. In order to comprehend alterations and driving mechanisms of soil bacterial communities under secondary succession of old-field and reveal their subsequent impacts on the decomposition and accumulation of soil organic carbon (SOC) and nitrogen (SON), we investigated changes in soil bacterial communities following ~160 years of old-field succession on the Loess Plateau of China through analyses of quantitative polymerase chain reaction (qPCR) and Illumina MiSeq DNA sequencing of 16S rRNA genes. Our results revealed that subsequent to secondary succession of old-field, soil bacterial abundance progressively increased, while bacterial richness and diversity significantly decreased. Principal component analysis and Bray–Curtis similarity index showed that bacterial community composition gradually shifted following old-field succession. Specifically, the relative abundances of Proteobacteria, Rokubacteria, and Verrucomicrobia progressively increased, while Actinobacteria and Firmicutes slightly decreased following old-field succession. The most enriched of Proteobacteria (e.g., Rhizobiales, Xanthobacteraceae, Gammaproteobacteria, Bradyrhizobium, Rhizobiaceae, and Mesorhizobiur) were found in a climax forest, while Chloroflexi and Gemmatimonadetes had the lowest relative abundances. Further, the most enriched members of Actinobacteria, including Geodermatophilaceae, Frankiales, Blastococcus, Micrococcales, Micrococcacea, Propionibacteriales, Nocardioidaceae, Nocardioide, and Streptomycetaceae, were exhibited in the farmland stage. Our results suggested that secondary succession of old-field greatly modified soil bacterial communities via the transformation of soil nutrients levels, altering plant biomass and soil physiochemical properties. Soil bacterial community composition was transformed from oligotrophic groups to copiotrophic Proteobacteria following old-field succession, which may promote SOC and SON accumulation through increasing the utilization of labile organic carbon (C) and nitrogen (N), while decreasing decomposition of recalcitrant organic C and N from the early- to late-successional stages.

Natural revegetation has been widely confirmed to be an effective strategy for the restoration of degraded lands, particularly in terms of rehabilitating ecosystem productivity and soil nutrients. Yet the mechanisms of how natural revegetation influences the variabilities and drivers of soil residing fungal communities, and its downstream effects on ecosystem nutrient cycling are not well understood. For this study, we investigated changes in soil fungal communities along with ~160 years of natural revegetation in the Loess Plateau of China, employing Illumina MiSeq DNA sequencing analyses. Our results revealed that the soil fungal abundance was greatly enhanced during the later stages of revegetation. As revegetation progresses, soil fungal richness appeared first to rise and then decline at the climax Quercus liaotungensis forest stage. The fungal Shannon and Simpson diversity indexes were the lowest and highest at the climax forest stage among revegetation stages, respectively. Principal component analysis, Bray–Curtis similarity indices, and FUNGuild function prediction suggested that the composition, trophic modes, and functional groups for soil fungal communities gradually shifted along with natural revegetation. Specifically, the relative abundances of Basidiomycota, Agaricomycetes, Eurotiomycetes, and ectomycorrhizal fungi progressively increased, while that of Ascomycota, Sordariomycetes, Dothideomycetes, Tremellomycetes, saprotrophic, pathotrophic, arbuscular mycorrhizal fungi, and endophyte fungi gradually decreased along with natural revegetation, respectively. The most enriched members of Basidiomycota (e.g., Agaricomycetes, Agaricales, Cortinariaceae, Cortinarius, Sebacinales, Sebacinaceae, Tricholomataceae, Tricholoma, Russulales, and Russulaceae) were found at the climax forest stage. As important carbon (C) sources, the most enriched symbiotic fungi (particularly ectomycorrhizal fungi containing more recalcitrant compounds) can promote organic C and nitrogen (N) accumulation in soils of climax forest. However, the most abundant of saprotrophic fungi in the early stages of revegetation decreased soil organic C and N accumulation by expediting the decomposition of soil organic matter. Our results suggest that natural revegetation can effectively restore soil fungal abundance, and modify soil fungal diversity, community composition, trophic modes, and functional groups by altering plant properties (e.g., plant species richness, diversity, evenness, litter quantity and quality), quantity and quality of soil nutrient substrates, soil moisture and pH. These changes in soil fungal communities, particularly their trophic modes and functional groups along with natural revegetation, impact the accumulation and decomposition of soil C and N and potentially affect ecosystem C and N cycling in the Loess Plateau of China.

Black Huangjiu (BH) is a traditional alcoholic beverage in China, which is very popular among people. The different methods (simultaneous inoculation, sequential inoculation), were applied to ferment BH in this study, which were investigated the changes in the composition of fungal communities and non-volatile flavor compounds (nVFCs) by high-throughput sequencing (HTS) and ultraperformance liquid chromatography–tandem mass spectrometer (UPLC MS/MS). The results showed that Rhizopus and Saccharomyces were the predominant fungal genera throughout fermentation, and 471 nVFCs were detected in BH after fermentation. Compared to that observed simultaneous inoculation, Rhizopus increased at the end of sequential fermentation, and the contents of the organic acids and their derivatives increased significantly [variable importance in the projection (VIP) > 1.0, p < 0.05, fold change (FC) > 2], while that of lipids and lipid-like molecules decreased significantly (VIP > 1.0, p < 0.05, FC < 0.5). Through the correlation analysis of 32 nVFCs with significant differences (VIP > 1.0, p < 0.05, FC >32 or < 0.03) and the community, it was found that lipids and lipid-like molecules (12) and organic acids and their derivatives (10) were significantly (p < 0.05) negatively correlated with Saccharomyces, but they were significantly (p < 0.05) positively correlated with Rhizopus. Compared with simultaneous inoculation, BH fermented by sequential inoculation, the taste was stronger, sweeter, mellow, and softer. Our findings provide information on nVFC dynamics and will aid in the selection of beneficial strains to improve BH quality.

Coastal reclamation seriously disturbs coastal wetland ecosystems, while its influences on soil microbial communities remain unclear. In this study, we examined the impacts of coastal reclamation on soil microbial communities based on phospholipid fatty acids (PLFA) analysis following the conversion of Phragmites australis wetlands to different land use types. Coastal reclamation enhanced total soil microbial biomass and various species (i.e., gram-positive bacterial, actinomycete, saturated straight-chain, and branched PLFA) following the conversion of P. australis wetland to aquaculture pond, wheat, and oilseed rape fields. In contrast, it greatly decreased total soil microbial biomass and various species following the conversion of P. australis wetland to town construction land. Coastal reclamation reduced fungal:bacterial PLFA, monounsaturated:branched PLFA ratios, whereas increasing gram-positive:gram-negative PLFA ratio following the conversion of P. australis wetland to other land use types. Our study suggested that coastal reclamation shifted soil microbial communities by altering microbial biomass and community composition. These changes were driven primarily by variations in soil nutrient substrates and physiochemical properties. Changes in soil microbial communities following coastal reclamation impacted the decomposition and accumulation of soil carbon and nitrogen, with potential modification of carbon and nitrogen sinks in the ecosystems, with potential feedbacks in response to climate change.