[Effects of Biochar Application on Physicochemical Properties and Bacterial Communities of Microplastic-contaminated Calcareous Soil].

Microplastics are widely distributed in the soil environment, threatening the soil ecological environment system and changing soil physicochemical properties and microbial characteristics. Biochar is often used as a soil amendment to improve soil quality due to its special pore structure and good soil nutrient retention ability. However, the understanding of the effects and mechanisms of biochar application on the physicochemical properties and bacterial communities of microplastic-contaminated soils is still very limited. Therefore, a 21-day micro-soil culture experiment was conducted to analyze the effects of biochar application on physicochemical properties and bacterial community changes in soil contaminated with different concentrations of microplastics using 16S rRNA high-throughput sequencing technology. The results revealed that the application of biochar slowed down the decrease in nitrate nitrogen and Olsen-P contents in microplastic-contaminated soil and increased the total phosphorus content. Biochar addition increased the relative abundance of tolerant phylum such as Acidobacteriota, Actinobacteriota, and Bacteroidota in microplastic-contaminated calcareous soil. Proteobacteria, Acidobacteriota, and Actinobacteriota were the dominant bacteria of the soil bacterial community in each treatment on day 7 and day 21. Compared with that on day 7, the relative abundance of Proteobacteria and Firmicutes significantly decreased, and the relative abundance of Acidobacteriota, Actinobacteriota, Bacteroidota, Chloroflexi, and Myxococcota increased on day 21. Biochar application also increased the relative abundance of Lysobacter in microplastic-contaminated soils. This study demonstrated that the application of biochar increased microplastic-resistant bacteria, enhanced the stability of microplastic-contaminated soil, and slowed down the pollution of microplastics to the soil. Moreover, biochar had great potential to improve the quality of microplastic-contaminated calcareous soil.

[Diversity of Soil Eukaryotic Microbes in Different Succession Stages in Maolan Karst Forest of Guizhou].

As an indispensable part of the Maolan karst forest soil microorganisms, eukaryotic microbes play an important role in ecosystem material and energy flow. To investigate the composition and diversity of soil eukaryotic microbial communities under different succession stages in the Maolan karst forest, we explored the diversity and composition of soil eukaryotic microbes under four succession stages of primary forests (YSL), shrub forests (GML), bushes (GMC), and grassland (CD) via high-throughput sequencing (HTS) of the 18S rDNA. The results showed that the composition of soil eukaryotic microbial communities was similar in different succession stages under different classification levels. There was a significant difference in α diversity, Shannon, and Simpson's indices at different stages of succession as follows: YSL > GMC > GML > CD. The non-metric multidimensional scaling analysis showed that there were differences in the soil eukaryotic microbial community structure at different succession stages. The linear discriminant analysis effect size (LEfSe) analysis showed that the number of differential indicator species in YSL was higher than in GML, GML, and CD. The results of our study provide a theoretical basis for further research on soil eukaryotic microorganisms in different succession stages.

[Soil bacterial community characteristics under different microhabitat types on Maolan karst forest, Guizhou, Southwest China]. / è´µå·žèŒ‚å °å–€æ–¯ç‰¹æ£®æž—ä¸åŒå°ç”Ÿå¢ƒä¸‹åœŸå£¤ç»†èŒç¾¤è½ç‰¹å¾.

We analyzed the diversity, community composition and relative abundance of soil bacteria communities in five different types of microhabitats (included stone caverns, stone crevices, stone gullies, stone grooves, top-soils) in Maolan karst forest, Guizhou Province, China. Bacterial 16S rRNA V3-V4 variable regions were analyzed by high-throughput sequencing technique. We examined the effects of soil physicochemical factors on bacterial community structure. The results showed that 27 phyla, 64 classes, 128 orders, 242 families, 367 genera, and 704 species were detected in the soils from five types of microhabitats. Proteobacteria, Actinomycetes, Acidobacteria, Chlorofleixi and Nitrospirae were the dominant bacterial phyla. Actinomycetes was the dominant phyla in the microhabitats of top-stone cavern (0-10 cm), sub-stone cavern (10-20 cm), stone crevice, and stone groove. Acidobacteria was the dominant phyla in the top-soil (0-10 cm) and the sub-soil (10-20 cm). Proteobacteria was the dominant phyla in the top-stone gully (0-10 cm) and the sub-stone gully (10-20 cm). The highest soil bacterial Simpson index was found in stone crevice microhabitat, while the lowest was found in sub-soil (10-20 cm) microhabitat. Results from the LEfSe analysis showed that the number of distinct indicator species at the different levels of taxo-nomy was higher in the top-soil (0-10 cm), sub-soil (10-20 cm), sub-stone cavern (10-20 cm), and the stone groove than in the stone crevice, the top-stone gully (0-10 cm) and sub-stone gully (10-20 cm). The indicator phyla were Actinobacteria and Chlorofleixi in the sub-stone cavern (10-20 cm). The top-stone gully (0-10 cm) were characterized by the phyla of Proteobacteria and Tectomicrobia. The top-soil (0-10 cm) was featured by Acidobacteria, Verrucomicrobia and Latescibacteria. The sub-soil (10-20 cm) was dominated by Nitrospirae. There were no indicator species in stone groove, stone crevice, and sub-stone gully (10-20 cm). There was no indicator species in phylum to genus in top-stone cavern (0-10 cm). RDA and ABT analysis showed that soil organic matter, pH, and available phosphorus explained a large part of the variation regarding the responses of bacterial community to the changes in basic physicochemical factors in the soil.

[Effects of Chinese prickly ash orchard on soil organic carbon mineralization and labile organic carbon in karst rocky desertification region of Guizhou province].

Taking 5-year-old Chinese prickly ash orchard (PO-5), 17-year-old Chinese prickly ash orchard (PO- 17), 30-year-old Chinese prickly ash orchard (PO-30) and the forest land (FL, about 60 years) in typical demonstration area of desertification control test in southwestern Guizhou as our research objects, the aim of this study using a batch incubation experiment was to research the mineralization characteristics of soil organic carbon and changes of the labile soil organic carbon contents at different depths (0-15 cm, 15-30 cm, and 30-50 cm). The results showed that: the cumulative mineralization amounts of soil organic carbon were in the order of 30-year-old Chinese prickly ash orchard, the forest land, 5-year-old Chinese prickly ash orchard and 17-year-old Chinese prickly ash orchard at corresponding depth. Distribution ratios of CO2-C cumulative mineralization amount to SOC contents were higher in Chinese prickly ash orchards than in forest land at each depth. Cultivation of Chinese prickly ash in long-term enhanced the mineralization of soil organic carbon, and decreased the stability of soil organic carbon. Readily oxidized carbon and particulate organic carbon in forest land soils were significantly more than those in Chinese prickly ash orchards at each depth (P < 0.05). With the increasing times of cultivation of Chinese prickly ash, the contents of readily oxidized carbon and particulate organic carbon first increased and then declined at 0-15 cm and 15-30 cm depth, respectively, but an opposite trend was found at 30-50 cm depth. At 0-15 cm and 15-30 cm, cultivation of Chinese prickly ash could be good for improving the contents of labile soil organic carbon in short term, but it was not conducive in long-term. In this study, we found that cultivation of Chinese prickly ash was beneficial for the accumulation of labile organic carbon at the 30-50 cm depth.

[Effects of land use and abandonment on soil labile organic carbon in the Karst region of southwest China].

Effects of land use and land abandonment on labile organic carbon (LOC) in whole soils and different aggregate sizes were studied by sampling analysis of the soils in some typical land uses of the Karst region, southwest China. Results showed that the content and degree of dispersion of labile organic carbon decreased with soil depth, and the content of LOC was highly significant (P < 0.01) in 0-10 cm than in 10-20 cm and 20-30 cm. In the 0-10 cm soil layer, the content of LOC distribution in different aggregates was higher in the < 0.25 mm size, while no obvious changes of LOC among aggregates were found in the 10-20 cm and 20-30 cm depths. In different land use patterns, the LOC was the highest in paddy whether in whole soils or aggregates, followed by shrub, and the lowest in abandoned 3 years grassland. Within-between principal component analysis showed that the accumulation characters between land use and LOC were in the order of paddy > shrub > abandoned 15 years grassland = dry land > abandoned 3 years grassland, the content of LOC increased by 20.3% as compared to dryland, and had reached 80% of the content of shrub in abandoned 15 years grassland at the 0-10 cm depth, indicating that at the early stage of land abandonment, the natural recovery of carbon is relatively slow, while with the abandonment time increase, the carbon sink effect gradually appear.

[Relationships between soil and rocky desertification in typical karst mountain area based on redundancy analysis].

Redundancy analysis (RDA) was employed to reveal the relationships between soil and rocky desertification through vegetation investigation and analysis of soil samples collected in typical karst mountain area of southwest Guizhou Province. The results showed that except TP, TK and ACa, all other variables including SOC, TN, MBC, ROC, DOC, available nutrients and basal respiration showed significant downward trends during the rocky desertification process. RDA results showed significant correlations between different types of desertification and soil variables, described as non-degraded > potential desertification > light desertification > moderate desertification > severe desertification. Moreover, RDA showed that using SOC, TN, AN, and BD as soil indicators, 74.4% of the variance information on soil and rocky desertification could be explained. Furthermore, the results of correlation analysis showed that soil variables were significantly affected by surface vegetation. Considering the ecological function of the aboveground vegetation and the soil quality, Zanthoxylum would be a good choice for restoration of local vegetation in karst mountain area.

[Variation of soil organic carbon under different vegetation types in Karst Mountain areas of Guizhou Province, southwest China].

This paper studied the variation characteristics of soil organic carbon (SOC) and different particle sizes soil particulate organic carbon (POC) in normal soil and in micro-habitats under different vegetation types in typical Karst mountain areas of southwest Guizhou. Under different vegetation types, the SOC content in normal soil and in micro-habitats was all in the order of bare land < grass < shrub < forest, with the variation range being 7.18-43.42 g x kg(-1) in normal soil and being 6.62-46.47 g x kg(-1) and 9.01-52.07 g x kg(-1) in earth surface and stone pit, respectively. The POC/MOC (mineral-associated organic carbon) ratio under different vegetation types was in the order of bare land < grass < forest < shrub. Under the same vegetation types, the POC/MOC in stone pit was the highest, as compared to that in normal soil and in earth surface. In the process of bare land-grass-shrub-forest, the contents of different particle sizes soil POC increased, while the SOC mainly existed in the forms of sand- and silt organic carbon, indicating that in Karst region, soil carbon sequestration and SOC stability were weak, soil was easily subjected to outside interference and led to organic carbon running off, and thus, soil quality had the risk of decline or degradation.