Research on Ca-Mg carbonate crystallization and phase transition regulated by microbial cells and extracellular polymeric substances (EPS) is significant for carbon sequestration, remediation of polluted soil and water, and synthesis of functional biomaterials. This study focused on the mineralogical transformation from amorphism to crystal, and interaction among cells, EPS, and minerals. By tracing the law of mineral growth and morphological evolution, the influences of cells and EPS on mineral formation were investigated. The results revealed that calcification and the template of rod-shaped cells of strain HJ-1 were the basis for the formation of dumbbell-shaped particles, and directional aggregation and differential growth were the keys to the development and stability of dumbbells. Cell participation had a noticeable impact on mineral prototypes, instead of determining the polymorphism. EPS contributed to aragonite formation and stability. The acidic amino acids or proteins in EPS were likely to cause an increase in MgCO₃ content in Mg-calcite. EPS promoted aggregation of particles and induced spherical formation. Exopolysaccharides and proteins were the main components of EPS that can affect carbonate mineralization. EPS could influence the morphology and polymorphism by providing nucleation sites, interacting with Mg²⁺, adsorbing or incorporating mineral lattices, and inducing particle aggregation.

Microbial mineralization of calcium–magnesium carbonate has been a hot research topic in the fields of geomicrobiology and engineering geology in the past decades. However, the formation and phase transition mechanism of calcium–magnesium carbonate polymorphs at different Mg/Ca ratios still need to be explored. In this study, microbial induced carbonate mineralization experiments were carried out for 50 days in culture medium with Mg/Ca molar ratios of 0, 1.5, and 3 under the action of Curvibacter sp. HJ-1. The roles of bacteria and the Mg/Ca ratio on the mineral formation and phase transition were investigated. Experimental results show that (1) strain HJ-1 could induce vaterite, aragonite, and magnesium calcite formation in culture media with different Mg/Ca molar ratios. The increased stability of the metastable phase suggests that bacterial extracellular secretions and Mg²⁺ ions inhibit the carbonate phase-transition process. (2) The morphology of bacteriological carbonate minerals and the formation mechanism of spherical minerals were different in Mg-free and Mg-containing media. (3) The increased Mg/Ca ratio in the culture medium has an influence on the formation and transformation of calcium–magnesium carbonate by controlling the metabolism of Curvibacter sp. HJ-1 and the activity of bacterial secretion.

Understanding the molecular-scale heterogeneity of dissolved organic matter (DOM) in tea plantation soils is essential for explaining regional differences in tea quality and mitigating contaminant risks. However, systematic studies on the structural characteristics of DOM in tea garden soils at different molecular weight scales and its binding behavior with pollutants remain limited. In this study, the molecular weight fractionation, structural composition, and arsenic (As) binding behavior of DOM in iron-rich red soils from three premium tea-growing regions of Huangshan City, China, were comprehensively investigated. An integrated spectroscopic approach was employed to analyze soil samples from Huangshan Mao Feng (Region 1, HSMF), Keemun Black Tea (Region 2, QMHC) and Taiping Houkui (Region 3, TPHK) plantations. The results revealed that the soil DOM exhibited high aromaticity (average SUVA₂₅₄ > 4.34 L·mg^-¹·m^-1) and was predominantly of microbial origin (fluorescence index > 1.9). Distinct regional patterns emerged: Region 2 exhibited the highest aromaticity (SUVA₂₅₄ = 4.75 ± 3.99 L·mg^-¹·m^-1) and a pronounced microbial signature in low-molecular-weight DOM (LMW-DOM, FI = 1.89 ± 0.87). Region 1 was characterized by highly humified, high-molecular-weight DOM (HMW-DOM, HIX = 8.64 ± 3.57). In addition, Region 3 displayed stronger allochthonous inputs (S_R = 1.13 ± 0.58). PARAFAC analysis revealed that protein-like substances accounted for approximately 60 % of the fluorescence intensity in Region 2's HMW-DOM, whereas humic-like components dominated in Region 1 and Region 3. Furthermore, two-dimensional correlation spectroscopy revealed distinct DOM-As binding sequences: humic acid-dominated in Region 1 (389 nm → 324 nm → 288 nm), protein-dominated in Region 2 (425 nm → 390 nm → 386 nm) and fulvic acid-dominated in Region 3 (370 nm → 410 nm → 280 nm). These findings demonstrate that the molecular composition of DOM, which is shaped by local agronomic practices, determines its environmental reactivity. This provides crucial insights for optimising the management of tea quality and controlling the mobility of contaminants.

Southwestern China is a critical biodiversity hotspot area, and many large hydroelectric projects have been established in the valleys in the region. Tree growth in the valleys will be affected by both regional climate and reservoir impoundment. However, it remains unknown whether the radial growth of trees in the valleys has a common response pattern to the regional climate, and it is also unclear whether the response of radial growth to reservoir impoundment can be detected. In this study, we developed tree-ring width chronologies of Pinus yunnanensis Franch. collected at 11 sites with vertical and horizontal gradients to three hydroelectric reservoirs in three riverine valleys in southwestern China. We analyzed the radial growth responses to the regional climate from 1986 to 2017 by correlation with instrumental meteorological data. Tree growth responses to reservoir impoundment were investigated through spatial and temporal comparisons using the change in the Euclidean distance and difference test. We also distinguished their responses at tree-ring sites without influenced by reservoir impoundment including two sites in the valleys and seven sites at high elevations. The results showed that the climate conditions in May and the dry season before the growth season significantly limit the radial growth in the valleys, which is different to that at high-elevation areas in southwestern China. Growth variations in the valleys are related to elevations and the trees in similar slopes positions exhibit similar responses. For trees in the low slope positions, both variance and mean values of radial growth are affected by reservoir impoundment. Trees at relatively low sites (i.e., sites M2, R2, L2), rather than the trees close to the reservoirs (i.e., sites M1, R1, L1), respond more sensitively to reservoir impoundment.

Calcium–magnesium (Ca–Mg) carbonates are among the most widely distributed carbonates in the Earth’s surface environment, and their formation mechanisms are of great significance for revealing geological environmental changes and carbon sequestration processes. In this study, the gas diffusion method was employed with L-glutamic acid, L-glycine, and L-lysine as nucleation templates for carbonate minerals to systematically investigate their regulatory effects on the mineralization of Ca–Mg carbonates. The results demonstrated that L-glycine, with the shortest length, was more conducive to forming aragonite, whereas acidic L-glutamic acid, which contains more carboxyl groups, was more beneficial for the structural stability of aragonite. The morphology of the Ca-Mg carbonate minerals became more diverse and promoted the formation of spherical and massive mineral aggregates under the action of amino acids. Moreover, the amino acids significantly increased the MgCO₃ content in Mg calcite (L-glutamic acid: 10.86% > L-glycine: 7.91% > L-lysine: 6.63%). The acidic L-glutamic acid likely promotes the dehydration and incorporation of Mg²⁺ into the Mg calcite lattice through the preferential adsorption of Mg²⁺ via its side-chain carboxyl groups. This study shows how amino acid functional groups influence Ca–Mg carbonate mineralization and provides insights into biogenic Mg-rich mineral origins and advanced mineral material synthesis.