The in situ chemical immobilization method reduces the activity of heavy metals in soil by adding chemical amendments. It is widely used in farmland soil with moderate and mild heavy metal pollution due to its high efficiency and economy. However, the effects of different materials depend heavily on environmental factors such as soil texture, properties, and pollution levels. Under the influence of lead–zinc ore smelting and soil acidification, Cd is enriched and highly activated in the soils of northwestern Guizhou, China. Potato is an important economic crop in this region, and its absorption of Cd depends on the availability of Cd in the soil and the distribution of Cd within the plant. In this study, pot experiments were used to compare the effects of lime (LM), apatite (AP), calcite (CA), sepiolite (SP), bentonite (BN), and biochar (BC) on Cd accumulation in potatoes. The results showed that the application of LM (0.4%), AP (1.4%), and CA (0.4%) had a positive effect on soil pH and cations, and that they effectively reduced the availability of Cd in the soil. In contrast, the application of SP, BN, and BC had no significant effect on the soil properties and Cd availability. LM, AP, and CA treatment strongly reduced Cd accumulation in the potato tubers by controlling the total ‘flux’ of Cd into the potato plants. In contrast, the application of SP and BN promoted the migration of Cd from the root to the shoot, while the effect of BC varied by potato genotype. Overall, calcareous materials (LM, CA, and AP) were more applicable in the remediation of Cd-contaminated soils in the study area.

The karst area has become a high-risk area for Cadmium (Cd) exposure. Interestingly, the high levels of Cd in soils do not result in an excessive bioaccumulation of Cd in rice. Carbonate rock dissolution ions (CRIs) could limit the accumulation and translocation of Cd in rice. CRIs can become a major bottleneck in the remediation and management of farmlands in karst areas. However, there is limited research on the effects of CRIs in soils on Cd accumulation in rice. The karst area of lime soil (LS) and the non-karst areas of yellow soil (YS) were collected, and an external Cd was added to conduct rice cultivation experiments. Cd and CRIs (Ca²⁺, Mg²⁺, CO₃²⁻/HCO₃⁻, and OH⁻) in the rice–soil system were investigated from the grain-filling to maturity periods. The results showed that CRIs of LS were significantly higher than that of YS in different treatments. CRIs of LS were 2.05 mg·kg⁻¹ for Ca²⁺, 0.90 mg·kg⁻¹ for Mg²⁺, and 42.29 mg·kg⁻¹ for CO₃²⁻ in LS. CRIs could influence DTPA Cd, resulting in DTPA Cd of LS being lower than that of YS. DTPA Cd of YS was one to three times larger than that of YS. Cd content in different parts of rice in YS was higher than that of LS. Cd in rice grains of YS was one to six times larger than that of LS. The uptake of Cd from the soil during Filling III was critical in determining rice Cd accumulation. CRIs in the soil could affect Cd accumulation in rice. Ca²⁺ and Mg²⁺ had significant negative effects on Cd accumulation of rice at maturity and filling, respectively. CO₃²⁻/HCO₃⁻ and OH⁻ had significant negative effects on DTPA Cd in soil.

The effective utilization of crop straw can contribute to sustainable agricultural development. However, how different straw return methods regulate soil fertility and rice yield via bacterial communities in karst paddy fields remains elusive. This field study investigated five straw return treatments [deep plowing (PD); rotary tillage with incorporation (RTM); field rapid composting, (FRC); no-till mulching (NT); and bioreactor (BR)] and a blank control CK (no straw return, fertilizer only) on soil physicochemical properties, bacterial community structure, and rice yield, combined with 16S rRNA sequencing technology. Results indicate the following: (1) all straw incorporation treatments significantly increased soil organic matter (SOM) and nutrient content ( p < 0.05), NT and BR treatments increased soil organic matter (SOM) by 38.2 and 36.4%, respectively, compared to CK, while total nitrogen increased by 42.1 and 48.4% with NT; (2) although RTM treatment did not achieve the highest SOM accumulation, it yielded the highest rice yield of 30.37 kg/plot (a significant increase of 13.2% compared to CK), revealing that yield is jointly regulated by soil physicochemical properties and bacterial communities; (3) straw return treatments did not significantly affect bacterial α-diversity (intergroup differences in Shannon index and Chao1 index, p > 0.05), but significantly influenced β-diversity, symbiotic network structure, and community assembly processes. BR treatment formed a complex and stable microbial network structure, while NT exhibited a highly modular community structure (modularity = 0.66); (4) bacterial community assembly under straw return was dominated by deterministic processes, with homogenous selection accounting for 45 and 42% in NT and BR treatments, respectively, significantly higher than CK (28%, p < 0.05); (5) pathwise linear structural equation modeling (PLS-SEM) confirmed that TN (path coefficient 0.97, p < 0.001) and bacterial β-diversity (path coefficient 0.83, p < 0.001) were the most critical factors influencing rice yield. This study elucidates the mechanisms by which different straw return methods drive soil functions by reshaping bacterial community assembly and interaction networks. It provides theoretical support for optimizing straw return technologies in karst paddy fields, such as applying RTM for “yield-priority” scenarios and NT for “Rapid fertilization” scenarios.

Acid mine drainage (AMD) causes environmental pollution that affects many countries with historic or current mining industries. The eco-remediation system (RW) which combined surface floating wetlands and bottom anaerobic sediments (SFW-BAS) was selected for AMD-contaminated lakes (AMDW). Meanwhile, AMDW and nature aquatic ecosystems (NW) were set as the control groups, respectively. The parameters, including pH, Eh, Fe, Mn, SO₄²⁻, and the degradation rate of the native dominant plant litter were investigated to assess the effects of remediation. The results showed that the average of pH, Eh, and EC, was 2.73, 484.08 mv, and 2395.33μs·cm⁻¹, respectively. The average content of SO₄²⁻, Fe, Mn, Cu, Zn, and Pb was 2190mg·L⁻¹, 40.2mg·L⁻¹, 4.6mg·L⁻¹, 249.2μg·L⁻¹, 1563μg·L⁻¹, and 112.9μg·L⁻¹, respectively. The degradation rate of plant litters in AMDW ranged from 14.5 to 22.6. However, RW ultimately improved the water quality and the degradation of litters. RW has a good effect on buffering the acidity, ranging from 3.96 to 7.41. The pH of RW (6.14) is close to that of NW (7.41). The average content of SO₄²⁻, Fe, Mn, Cu, Zn, and Pb was 2071mg·L⁻¹, 3.4mg·L⁻¹, 2.4mg·L⁻¹, 85.3μg·L⁻¹, 607.4μg·L⁻¹, and 47.8μg·L⁻¹, respectively, which showed good pollutant removal performance. The degradation rate of plant litters in RW ranged from 27.8 to 32.6. Therefore, RW can be used to remediate AMDW.

Carbonate rock dissolution (CRD) in karst areas generates abundant ions, which contribute significantly to nitrogen (N) transformation in paddy ecosystems. However, little is known about the microbial mechanisms by which CRD ions (Ca²⁺, Mg²⁺, HCO₃⁻/CO₃²⁻, and OH-) regulate N balance. In this experiment, rice pot studies were conducted using karst soil (S1), karst soil with removed carbonate minerals (S2), non-karst soil (S3), and non-karst soil with additional carbonate minerals (S4). The effects of CRD on N-metabolizing microorganisms and functional genes in N metabolism were investigated using metagenomic sequencing technology. Six N metabolism pathways, including N fixation, nitrification, denitrification, dissimilatory nitrate reduction to ammonia (DNRA), assimilatory nitrate reduction to ammonia (ANRA), and complete nitrification (comammox) were revealed. Compared with S3, the relative abundance of the denitrification module (M00529) in S1 clearly increased by 1.52%. Additionally, compared to S3, the relative abundance of the complete nitrification (comammox) module (M00804) in S4 decreased by 0.66%. Proteobacteria and Anaeromyxobacter were significant contributors to variations in N metabolism. Key factors that influenced variations in N metabolism included Ca²⁺, Mg²⁺, and pH. This study explored the effects of CRD on N-metabolizing microorganisms and functions, which was of great significance to the N cycle in karst paddy ecosystems.