Soil Organic Carbon Chemical Functional Groups under Different Revegetation Types Are Coupled with Changes in the Microbial Community Composition and the Functional Genes

Organic management pattern improves microbial community diversity and alters microbial network structure in karst tea plantation

Soil microbiomes play a crucial role in enhancing plant growth, health, and overall agricultural productivity. Nevertheless, the influence of distinct agricultural management practices on the microbial diversity and community structure within tea (Camellia sinensis) plantations has remained enigmatic. This study postulates that organic agricultural management models can enhance microbial diversity and optimise the microbial community structure within tea plantations, indirectly augmenting soil fertility and tea quality. We employed metagenome technology and conducted molecular ecological network analysis to explore the impact of organic management, pollution-free management, and conventional management on the microbial network structure of tea plantation soil in Weng'an County in the southwestern karst region. Soils subjected to organic management exhibited a higher relative abundance of soil microbial and carbohydrate-active enzyme functional genes than those subjected to other management regimes. Additionally, the relative abundance and diversity of dominant bacteria and keystone species were notably higher under organic management than under the other management regimes. Correlation analysis showed that soil microorganisms were closely related to soil fertility and tea quality, respectively. One-way analysis of variance and the structural equation modelling results showed significant variability in soil fertility under the three agricultural management modes and that soil fertility and soil microbial diversity had a direct impact on tea quality (P > 0.05). In conclusion, this study underscores the profound impact of management modes on microbial diversity and community structure within tea plantations. These management practices alter the soil microbial network structure and potential function, ultimately regulating the microecological dynamics of the soil community in tea plantations.

Bacterial community regulation of soil organic matter molecular structure in heavy metal-rich mangrove sediments

Heavy metals (HMs) profoundly impact soil carbon storage potential primarily through soil carbon structure. The association between HM content and soil carbon structure in mangrove sediments remains unclear, likely due to the involvement of microorganisms. In this study, surface sediments in the Futian National Mangrove Nature Reserve were sampled to investigate the chemical structure of soil organic carbon (SOC), the molecular composition of dissolved organic matter (DOM), and potential interactions with microorganisms. HMs, except for Ni, were positively correlated with soil carbon. HMs significantly reduced the alkyl C/O-alkyl C ratio, aromaticity index, and aromatic C values, but increased the labile carboxy/amide C and carbonyl C ratio in SOC. HMs also increased DOM stability, as reflected by the reduced abundance of labile DOM (lipids and proteins) and increased proportion of stable DOM (tannins and condensed aromatics). Bacteria increased the decomposition of labile DOM components (unsaturated hydrocarbons) and the accumulation of stable DOM components (lignins) under HM enrichment. In addition, the association between the bacterial groups and DOM molecules was more robust than that with fungal groups, indicating bacteria had a more significant impact on DOM molecular composition. These findings help in understanding the molecular mechanisms of soil carbon storage in HM-rich mangroves.

Characterization of an In-Situ Soil Organic Carbon (SOC) via a Smart-Electrochemical Sensing Approach

Soil is a vital component of the ecosystem that drives the holistic homeostasis of the environment. Directly, soil quality and health by means of sufficient levels of soil nutrients are required for sustainable agricultural practices for ideal crop yield. Among these groups of nutrients, soil carbon is a factor which has a dominating effect on greenhouse carbon phenomena and thereby the climate change rate and its influence on the planet. It influences the fertility of soil and other conditions like enriched nutrient cycling and water retention that forms the basis for modern 'regenerative agriculture'. Implementation of soil sensors would be fundamentally beneficial to characterize the soil parameters in a local as well as global environmental impact standpoint, and electrochemistry as a transduction mode is very apt due to its feasibility and ease of applicability. Organic Matter present in soil (SOM) changes the electroanalytical behavior of moieties present that are carbon-derived. Hence, an electrochemical-based 'bottom-up' approach is evaluated in this study to track soil organic carbon (SOC). As part of this setup, soil as a solid-phase electrolyte as in a standard electrochemical cell and electrode probes functionalized with correlated ionic species on top of the metalized electrodes are utilized. The surficial interface is biased using a square pulsed charge, thereby studying the effect of the polar current as a function of the SOC profile. The sensor formulation composite used is such that materials have higher capacity to interact with organic carbon pools in soil. The proposed sensor platform is then compared against the standard combustion method for SOC analysis and its merit is evaluated as a potential in situ, on-demand electrochemical soil analysis platform.

Inhibition of Spartina alterniflora growth alters soil bacteria and their regulation of carbon metabolism

The state of growth of invasive species has a significant impact on the microbial regulation of the soil carbon (C) cycle. This study focused on the growth of Spartina alterniflora treated with imazapyr in the Tiaozini wetland of Jiangsu Province, China. The changes in soil bacterial structure, bacterial C metabolic activity, soil C, and regulation mechanism of soil C metabolic activity by biotic and abiotic factors were investigated. The results showed that soil bacterial diversity eventually decreased significantly (p < 0.05) along with significant changes in microbial structure (p < 0.05). Significant changes in soil physicochemical properties due to S. alterniflora growth inhibition were the key factors affecting the changes in the soil bacterial taxa composition (p < 0.05). Abiotic factors showed a greater effect on metabolic activities related to C fixation and biosynthesis of bacterial taxa than biotic factors (self-regulation). Additionally, bacterial taxa regulated soil C emission and degradation to a greater extent than abiotic factors. This study provides important information for understanding the regulators of C cycling in coastal wetland soil during the control of S. alterniflora invasion by imazapyr; moreover, it provides a scientific basis for the government to establish a prevention and control policy for S. alterniflora invasion. Understanding the complex interplay between abiotic and biotic factors is essential for developing effective strategies to manage soil C and mitigate the impacts of climate change.

Metagenomics reveals the effect of long-term fertilization on carbon cycle in the maize rhizosphere

Long-term fertilization can result in the changes in carbon (C) cycle in the maize rhizosphere soil. However, there have been few reports on the impacts of microbial regulatory mechanisms on the C cycle in soil. In the study, we analyzed the response of functional genes that regulate the C fixation, decomposition and methane (CH₄) metabolism in maize rhizosphere soil to different fertilization treatments using metagenomics analysis. As the dominant C fixation pathway in maize rhizosphere soil, the abundance of the functional genes regulating the reductive citrate cycle (rTCA cycle) including korA, korB, and IHD1 was higher under the chemical nitrogen (N) fertilizer treatments [nitrogen fertilizer (N), compound chemical fertilization (NPK), the combination of compound chemical fertilizer with maize straw (NPKS)] than maize straw return treatments [maize straw return (S), the combination of phosphorus and potassium fertilizer with maize straw (PKS)]. The NPK treatment decreased the abundance of functional genes involved in 3-hydroxypropionate bicycle (3-HP cycle; porA, porB, and porD), which was one of the major C fixation pathways in soil aside from dicarboxylate-hydroxybutyrate (DC/4-HB cycle) and Calvin cycle. The abundance of functional genes related to C degradation was higher in S, PKS and NPKS treatments than N and NPK treatments, and chemical N fertilizer application had a significant effect on C degradation. The dominant Methanaogenesis pathway in maize rhizosphere soil, used acetate as a substrate, and was significantly promoted under chemical N fertilizer application. The functional genes that were related to CH₄ oxidation (i.e., pmoA and pmoB) were reduced under N and NPK treatments. Moreover, soil chemical properties had a significant impact on the functional genes related to C fixation and degradation, with SOC (r² = 0.79) and NO₃^--N (r² = 0.63) being the main regulators. These results implied that N fertilization rather than maize straw return had a greater influence on the C cycle in maize rhizosphere soil.

Response of Soil Net Nitrogen Mineralization to a Litter in Three Subalpine Forests

Forest litter accumulation can regulate the soil microclimate and alter nutrient distribution, but the effects of litter quality and seasonal differences on soil nitrogen (N) mineralization are still uncertain. The effects of litter change on the rates of net N mineralization, nitrification, and ammonification were studied through in situ incubation experiments in coniferous, mixed, and broad-leaved forests in the eastern Qinghai–Tibetan Plateau. Two litter treatments were established, one to allow the litter to enter the soil normally (remain litter) and the other to prevent the litter from entering the soil (remove litter). Soil samples were collected at the freezing (FS), thawing (TS), early growing (EGS), late growing (LGS), and early freezing (EFS) seasons during the 1.5-year incubation period. Compared to coniferous forests, the effects of litter removal on the net ammonification, nitrification, and N mineralization rates were more pronounced in broad-leaved forests, mainly during the growing and thawing seasons. Structural equation modeling indicated that microbial biomass N (MBN) was a common factor affecting the net ammonification, nitrification, and N mineralization rates in the three forest soils. The coniferous forest microbial biomass carbon (MBC), mixed forest soil moisture, broad-leaved forest soil N concentration, and C:N ratio were the unique influencing factors of the different forest types. The results showed that the effect of litter distribution on the soil net N mineralization mainly depended on forest type and season, suggesting that the litter composition and productivity in different seasons and forest types may alter the soil N cycling processes in subalpine forest ecosystems.

Soil Organic Carbon Distribution and Its Response to Soil Erosion Based on EEM-PARAFAC and Stable Carbon Isotope, a Field Study in the Rocky Desertification Control of South China Karst

Ecological restoration plays an important role in enhancing carbon sequestration ability in karst areas, and soil organic matter is one of the main carbon reservoirs in karst key zones. The serious soil erosion in karst areas leads to the loss of soil organic matter (SOM). However, the distribution characteristics of SOM and its response mechanism to soil erosion in the process of rocky desertification control have rarely been reported. In this study, soil samples of five restoration types (abandoned land, AL; grassland, GL; peanut cultivated land, PCL; Zanthoxylum bungeanum land, ZBL; forest, FS) were collected in typical karst rocky desertification drainage, south China. By measuring soil organic carbon (SOC), dissolved organic carbon (DOC), and δ13Csoc values and combining with spectral tools, the distribution and isotopic composition of soil shallow organic carbon in definitized karst drainage was definitized and the response of DOM spectral characteristics to soil erosion was explored. The results showed that three kinds of fluorescence components were detected by fluorescence excitation emission matrix (EEM)-parallel factor analysis (PARAFAC), C1 and C2 were humus-like, and C2 was protein-like. Abandoned could be a more suitable control measure for enhancing SOC quality in the karst regions of south China. The variation trend of SOC content, δ13Csoc values, spectral indexes, and the distribution of fluorescence components from the midstream to downstream of the drainage indicated the soil redistribution. This study provides basic scientific data for karst rocky desertification control and for enhancing the soil carbon sequestration ability of karst.

Soil pH and Organic Carbon Properties Drive Soil Bacterial Communities in Surface and Deep Layers Along an Elevational Gradient

Elevational gradients strongly affect the spatial distribution and structure of soil bacterial communities. However, our understanding of the effects and determining factors is still limited, especially in the deep soil layer. Here, we investigated the diversity and composition of soil bacterial communities in different soil layers along a 1,500-m elevational gradient in the Taibai Mountain. The variables associated with climate conditions, plant communities, and soil properties were analyzed to assess their contributions to the variations in bacterial communities. Soil bacterial richness and α-diversity showed a hump-shaped trend with elevation in both surface and deep layers. In the surface layer, pH was the main factor driving the elevational pattern in bacterial diversity, while in the deep layer, pH and soil carbon (C) availability were the two main predictors. Bacterial community composition differed significantly along the elevational gradient in all soil layers. In the surface layer, Acidobacteria, Delta-proteobacteria, and Planctomycetes were significantly more abundant in the lower elevation sites than in the higher elevation sites; and Gemmatimonadetes, Chloroflexi, and Beta-proteobacteria were more abundant in the higher elevation sites. In the deep layer, AD3 was most abundant in the highest elevation site. The elevational pattern of community composition co-varied with mean annual temperature, mean annual precipitation, diversity and basal area of trees, pH, soil C availability, and soil C fractions. Statistical results showed that pH was the main driver of the elevational pattern of the bacterial community composition in the surface soil layer, while soil C fractions contributed more to the variance of the bacterial composition in the deep soil layer. These results indicated that changes in soil bacterial communities along the elevational gradient were driven by soil properties in both surface and deep soil layers, which are critical for predicting ecosystem functions under future climate change scenarios.