[Variations of microbial biomass and hydrolase activities in purple soil under different cropping modes as affected by ginger planting].

This paper studied the variations of soil microbial biomass C, N, and P contents and soil hydrolase activities under different cropping modes, i.e., corn + sweet potato intercropping (CS), soybean mono-cropping (SM), continuous cropping of ginger (CG), and rice-milk vetch rotation (RM) , after ginger planting in the purple soil area at the lower reaches of Minjiang River. Ginger planting decreased the soil microbial biomass C, N and P contents significantly. The decrement of the soil microbial biomass C and N contents after ginger planting was lesser under CS and RM than under SM and CG, but the soil microbial biomass P content was in adverse. Ginger planting also decreased the soil acid phosphatase activity significantly, and the decrement was the greatest under CS but the least under RM. The soil invertase activity decreased significantly under CG, and the soil urease activity had a significant decrease under SM, CG and RM. After ginger planting, the soil urease and intervase activities under CS were higher, as compared with those under the other cropping modes.

Abundance and composition dynamics of soil ammonia-oxidizing archaea in an alpine fir forest on the eastern Tibetan Plateau of China.

Real-time qPCR and clone library sequencing targeting amoA genes were used to investigate the seasonal dynamics of an ammonia-oxidizing archaea (AOA) community in an alpine fir forest in western China. AOA were detected at all sampling dates, and there were significant variations in archaeal amoA gene copy numbers (7.63 × 10(5) to 8.35 × 10(8) per gram of dry soil) throughout the nongrowing season. Compared with ammonia-oxidizing bacteria (AOB), the AOA displayed a higher abundance on the majority of sampling dates during the freeze-thaw period. All of the AOA sequences fell within soil and sediment lineages and were affiliated with 7 clusters. Compared with the other clusters, cluster 1 was more sensitive to low temperature and was the dominant group in August. In contrast, cluster 3 dominated the AOA community in winter and probably represents a group of cold-adapted archaea. Redundancy analysis (RDA) revealed that the seasonality of the AOA community was mainly attributed to changes in soil temperature and nutrient availability (e.g., dissolved organic nitrogen and carbon). Our results indicate that AOA exist in frozen soils in the alpine coniferous forest ecosystem of the eastern Tibetan Plateau. Moreover, soil temperature may directly and (or) indirectly affect AOA abundance and composition and may further influence the soil N cycle during the winter.

[Effects of cadmium stress on the microbial biodiversity in purple soil and alluvial soil potted with a poplar (Populus deltoides x Populus nigra)].

Effects of current Cd contamination levels on microbial biodiversity were studied under the typical Cd contaminated soils in the Yangtze Basin. Purple soil and alluvial soil potted with a poplar (Populus deltoides x Populus nigra) were selected, and the culturable soil microbial amounts by flat method, microbial biomass and bacterial community structure by PCR-DGGE were investigated. Cd supplies significantly increased the culturable amounts of bacteria and actinomyces in purple soil, but decreased the culturable amounts of fungi and the content of microbial biomass N. Fingerprint of DGGE also showed that bacterial community structure have obviously changed under different Cd supplies. In contrast, the lower Cd supplies slightly increased the culturable amounts of bacteria and fungi in alluvial soil, but higher Cd supply treatment decreased the culturable amounts of bacteria, actinomyces and fungi, and the content of microbial biomass N. However, only a slight change was observed under different Cd supplies by DGGE fingerprint. Additionally, there were few effects of Cd supplies on the content of microbial biomass C in both purple soil and alluvial soil. The results provided basic data to understand the effects of present Cd contamination levels on soil microbial characteristics.