Effects of experimental warming on soil microbial communities in two contrasting subalpine forest ecosystems,eastern Tibetan Plateau,China

Soil microbial communities are primarily regulated by environmental temperature. Our study investigated the effects of global warming on soil microbial community composition as measured via phospholipid fatty acid （PLFA） analysis and soil chemical characteristics in relation to soil depth in a dragon spruce plantation and a spruce-fir-dominated natural forestin the Eastern Tibetan Plateau. Opentop chambers were utilized to increase the soil and air temperature. Soil samples were collected from the o-10 cm, 10-20cm, and 20-30 cm layers after a 4-year warming. Our results showed that the soil microbial community and the contents of TC （Total carbon）, TN （Total nitrogen）. NO3-. and NH4＋ responded differently to warming in the two contrasting forests, especially at the 0-10 cm soil depth. Warming increased soil microbial biomass at the 0-20 cm depth of soil in natural forest but reduced it at the o-lo cm depth ofsoil in the plantation. In contrast, the TC and TN contents were reduced in most soil layers of a natural forest but increased in all of the soil layers of the plantation under warming conditions. This result suggested that the effects of warming on soil microbial community and soil C and N pools would differ according to soil depth and forest types; thus, the two contrasting forests would under go differing changes following the future climate warming in this region.

Membrane fouling behavior and microbial community succession in a submerged membrane bioreactor treating harbor oily wastewater

A membrane bioreactor （MBR） was established for treating harbor oily wastewater. It showed good removal performance for chemical oxygen demand （COD）, oil content, suspended solids （SS）, and other pollutants. However, serious membrane fouling occurred. It was recognized that the extracellular polymeric substances （EPS） accumulated on the membrane surface, especially the proteins, were of great importance for the transmembrane pressure （TMP） increment and membrane fouling. The MBR was optimized via improving aeration rate and reducing the ratio of Ar/Ad （At and Ad are the cross-sectional areas of the riser and the downcomer of the MBR）. The increasing rate of TMP was slowed, indicating that the optimization strategy could effectively mitigate membrane fouling. Microbial community evolution was monitored and analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis （PCR-DGGE）, cloning, and sequencing of 16S ribosomal ribonucleic acid （rRNA） fragments. Results revealed that low community shift occurred during the whole operational period. Geobacter sp. and Rhodocyclales sp., which have also been identified by other studies in a petroleum refinery wastewater MBR or an infiltration basin receiving highway runoff, dominated in the MBR system throughout. Comamonas sp. was thought to accommodate the lower aeration rate in this study, while Rhodocyclales sp. preferred the higher aeration rate. In addition, during the operational time under high organic loading rate, a few species were present in abundance, and may have been responsible for the good removal performance at this time.