Impact of land management of soil bacterial diversity at Thonghaphum District, Kanchanaburi Province

Abstract

Variations in soil properties and bacterial diversity in soil samples were noted for different land management, namely a chemically-intensive farm, an organic farm, and a forest at Thongphaphum District, Kanchanaburi Province. Significant differences in soil physical factors (soil moisture and pH) and nutrients (organic matter, organic carbon, total nitrogen, and available phosphorus contents) were found in sampling sites. Soil texture among three sites was classified as sandy loam. Forest had significantly higher organic matter and nutrient content than other sites. The analysis of soil bacterial community structure showed that the bacterial communities obtained from soils in 3 different sites were dominated by the r-strategist bacteria. No significant difference was found in bacterial numbers in both between sites and seasons, however, the colony forming unit (CFU) values were positively correlated with soil pH and soil nutrients. Ecophysiological index (EPI) values were not significantly different between sites and seasons. Despite no change in numbers of bacteria and EPI, there may be changes in bacterial function relating to land management. Finally, impacts of land management on bacterial diversity were analyzed. Total soil DNA were isolated from soil collected from 3 sites. The 16S rDNA was amplified with universal bacterial primers and cloned into plasmid vectors. Seventy clones were obtained. Phylogenetic analysis based on partial sequences (~379 bp) established with the neighbor-joining method and bootstrapped at 1,000 replications revealed the presence of major and minor groups that fell into several of the established lines of bacteria. Most of the clones belonged to the unidentified uncultured bacteria (57.14%) Moreover, Alpha (8.57%), Beta (2.86%), and Gamma (7.14%) Proteobacteria, Firmicutes (12.86%), Actinobacteria (8.57%), Bacteriodes (1.43%), and Planctomycetes (1.43%) were also found in this study. The majority of the clones (62.86%) had sequences that were 1-15% different from those current databases and 14.29% of the clones differed by more than 15% in sequence from the database. The results suggest that these Thongphaphum-derived clones are very diverse in phylogeny, and that many probably reflect new genera or families. From the results of bacterial diversity, different land management could affect the bacterial diversity because there were large numbers of unique phylotypes in each site. Although there was no significant difference between bacterial community structures among sites, it does not mean the land management practices have no impact to bacterial diversity. Furthermore, impacts of land management are also related to other factors, such as chemicals remaining in the area; and long-term studies should be implemented to examine absolute changes caused by land management.