[Investigation of Soil Fungal Communities and Functionalities within Karst Paddy Fields].

Fungi are important drivers of soil biogeochemical cycles. However, the characteristics of fungal community structures and functional groups within karst area (KA) soils remain understudied. Top soil samples were collected from paddy fields within a KA and non-karst area (NKA) containing red soil, in the Maocun karst experimental site of Guilin. The fungal community structure was analyzed via high-throughput sequencing, and FUNGuild was used to predict the function of fungi. The average relative abundance of Mucormycota in KA was 4.87%, which was significantly lower than that in NKA (29.92%); The average relative abundance of Mortierellomycetes in KA was 3.36%, which was significantly lower than that in NKA (29.15%). However, in KA, the average relative abundances of Glomeromycetes, Chytridiomycetes, and Exobasidiomycetes were 0.91%, 0.98%, and 0.23%, respectively, significantly higher than those in NKA (0.47%, 0.28%, and 0.04%). In KA, the average relative abundances of Ramophialophora and Emericellopsis were 2.39% and 1.25%, respectively, significantly higher than those in NKA (0.05% and 0.09%). However, the average relative abundance of Mortierella was 3.04% in KA, which was lower than that in NKA (28.34%). KA contained 32 dominant OTUs, including OTU141, 99, and 192. There was more connectivity between OTU69 (Emericellopsis terricola) and OTU138 (Westerdykella globosa) with the cation exchange capacity (CEC), exchangeable Ca2+, and total phosphorus (TP) in the correlation network. In KA, the average abundances of symbiotroph and pathotroph-saprotroph fungi were 1.29% and 1.50%, respectively, significantly higher than those in NKA (0.08% and 0.09%). The average abundance of the saprotroph-symbiotroph fungi in KA was 10.81%, which was significantly lower than that in NKA (63.69%). In KA, dung saprotroph-wood saprotroph fungi were dominant, with an abundance of 9.73%, whereas in NKA, endophyte-litter saprotroph-soil saprotroph-undefined saprotroph fungi were dominant, with an abundance of 45.93%. The above results suggest that the soil factors of KA, such as CEC, exchangeable Ca2+, and TP, alter the structures and functions of fungi.

[Comparison of Soil Bacterial Community Structure Between Paddy Fields and Dry Land in the Huixian Karst Wetland, China].

In order to explore the effect of land-use change on soil bacteria in wetland systems, the topsoil (0-20 cm) of a natural wetland (NW), paddy field (PF), and dry land (DL) were collected in the Huixian karst wetland. The α-diversity, species composition, and abundance of soil bacterial communities were analyzed using high-throughput sequencing. The effect of environmental factors on bacterial community structure was also examined. The results showed that the soil bacteria in the Huixian karst wetland can be divided into 49 phyla and 145 classes. The Shannon index of bacteria in the PF was significantly higher, and the Simpson index of bacteria in the NW is significantly lower, than in the other two land-use types. The dominant phyla (operational taxonomic units, OTUs>1%) in the NW were Proteobacteria (52.15%), Actinobacteria (15.16%), and Acidobacteria (8.80%); the dominant phyla in the PF were Proteobacteria (45.79%), Acidobacteria (17.20%), and Chloroflexi (11.75%); the dominant phyla in the DL were Proteus (51.42%), Acidobacteria (15.51%), and Chloroflexi (7.43%). The dominant classes (OTUs>1%) in the NW were α-Proteobacteria (17.98%), ß-Proteobacteria (13.72%), and Actinobacteria (13.13%); the dominant classes in the PF were Acidobacteria (14.35%), ß-Proteobacteria (13.37%), and δ-Proteobacteria (12.02%); the dominant classes in the DL were α-Proteobacteria (19.44%), Formobacteria (13.30%), and Acidobacteria (13.03%). Among the dominant OTUs (>0.3%), the dominant genera of in the NW were Sphingomonas (OTU2, 59), Micromonospora (OTU5, 24 and 50487), Gemmatimonas (OTU1), and Tenotrophomonas (OTU8); the dominant genera in the PF were Lysobacter (OTU4 and 115) and Aquabacterium (OTU33); the dominant genera in the DL were Sphingomonas (OTU85, 157 and 2916), Rhodanobacter (OTU19 and 52), and Penlobacterium (OTU60). A heatmap showed that there were significant differences in soil bacterial community structure among the three land-use types. Redundancy analysis showed that pH, soil organic carbon (SOC), total nitrogen (TN), alkali-hydrolyzable nitrogen (AN), exchangeable Mg2+, exchangeable Ca2+, soluble organic carbon (DOC), and available phosphorus (AP) were the main factors that affected the bacterial community structure in the Huixian karst wetland. These results indicate that changes in land-use types have significantly shaped the structure of soil bacterial communities in this area.

[Soil nutrient accumulation and its affecting factors during vegetation succession in karst peak-cluster depressions of South China].

Taking the typical karst peak-cluster depressions in Huanjiang County of northwest Guangxi as the objects, and by using the method of replacing time with space, an analysis was made on the dynamic changes of top soil (0-15 cm) nutrients and their dominant controlling factors during the process of vegetation succession. With the positive succession of vegetation (herb-shrub-secondary forest-primary forest), the soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) contents increased significantly, with the soil SOC, TN, and TP increased from 29.1 g x kg(-1), 2.48 g x kg(-1), and 0.72 g x kg(-1) in herb community to 73.9 g x kg(-1), 8.10 g x kg(-1), and 1.6 g x kg(-1) in primary forest, respectively, which indicated that the positive succession of vegetation was helpful to the soil nutrient accumulation. The soil cation exchange capacity (CEC) had close relationships with the soil SOC and TN, being the primary controlling factor for the accumulation of the soil C and N. The litter P content, C/P ratio, and N/P ratio were the major factors controlling the P accumulation in the topsoil. The litters higher P content and N/P ratio and smaller C/P ratio were helpful for the P accumulation. Topographic indices (slope, aspect, and rock exposure ratio) had little effects on the soil nutrients.