Profile Changes in the Soil Microbial Community When Desert Becomes Oasis.

The conversion of virgin desert into oasis farmland creates two contrasting types of land-cover. During oasis formation with irrigation and fertilizer application, however, the changes in the soil microbial population, which play critical roles in the ecosystem, remain poorly understood. We applied high-throughput pyrosequencing to investigate bacterial and archaeal communities throughout the profile (0-3 m) in an experimental field, where irrigation and fertilization began in 1990 and cropped with winter wheat since then. To assess the effects of cultivation, the following treatments were compared with the virgin desert: CK (no fertilizer), PK, NK, NP, NPK, NPKR, and NPKM (R: straw residue; M: manure fertilizer). Irrigation had a greater impact on the overall microbial community than fertilizer application. The greatest impact occurred in topsoil (0-0.2 m), e.g., Cyanobacteria (25% total abundance) were most abundant in desert soil, while Actinobacteria (26%) were most abundant in oasis soil. The proportions of extremophilic and photosynthetic groups (e.g., Deinococcus-Thermus and Cyanobacteria) decreased, while the proportions of R-strategy (e.g., Gammaproteobacteria including Xanthomonadales), nitrifying (e.g., Nitrospirae), and anaerobic bacteria (e.g., Anaerolineae) increased throughout the oasis profile. Archaea occurred only in oasis soil. The impact of fertilizer application was mainly reflected in the non-dominant communities or finer taxonomic divisions. Oasis formation led to a dramatic shift in microbial community and enhanced soil enzyme activities. The rapidly increased soil moisture and decreased salt caused by irrigation were responsible for this shift. Furthermore, difference in fertilization and crop growth altered the organic carbon contents in the soil, which resulted in differences of microbial communities within oasis.

Heavy metal contamination in a typical mining town of a minority and mountain area, South China.

This study was conducted in Dachang, a small mining town in Gaungxi Zhuang Autonomous Region in southern China. A total of 23 farmland soil samples and two atmospheric samples of particulate matter less than 10 microns (PM(10)) were collected in this town. ICP-MS was used to analyze for 20 elements in each of the samples. All of the samples contained some level of heavy metals. The most commonly detected heavy metals detected in the soil samples were: Cd (up to 29.0 mg kg(-1)), As (up to 776 mg kg(-1)), Sb (up to 36.8 mg kg(-1)), Pb (up to 582 mg kg(-1)), Zn (up to 1379 mg kg(-1)) and Cu (up to 156 mg kg(-1)), Mn (up to 1476 mg kg(-1)). The PM(10) content in air samples exceeded the Chinese standard by nearly ten-fold. The most commonly detected heavy metals detected in the PM(10) atmospheric samples were Cd (up to 210 mg kg(-1)), As (up to 15239 mg.kg(-1)), Sb (up to 445 mg kg(-1)), Pb (up to 8053 mg kg(-1)), Zn (up to 13151 mg kg(-1)) and Cu (up to 673 mg kg(-1)), Mn (up to 2826 mg kg(-1)), Mo (up to 120 mg kg(-1)). All of these heavy metals are associated with significant human health effects ranging from reduced intelligent quotients (IQs) in children (cf. Pb) to cancer (e.g., Cd and As). Müller Geo-accumulation Index (Igeo) and enrichment factor (EF) were used to assess the findings. The results to the two assessments showed the same ranking: Cd > As > Sb > Pb > Zn > Cu > Mn, which would imply that the particulate matter in ambient air was the source of the contamination in the soil. The correlation analysis supported this inference. Upon further examination, ore transportation through the town was identified as the most likely source of contamination. Therefore, steps should be taken to improve the management of the ore transportation in order to protect the farmland and the health of the residents.