Effect of Monocrotophos and Quinalphos on Soil Population and Nitrogen-Fixing Activity of Azospirillum sp.

The effects of monocrotophos and quinalphos on population and nitrogen-fixing activity of Azospirillum sp.in four agricultural soils were determined in a laboratory study.Concentrations of the two insecticides up to a 5 kg ha^(-1)level were either stimulatory or innocuous to the popula- tion of Azospirillum in the soils.Four successive applications of the insecticides to soils resulted in a significant increase in the population density.Cultures of Azospirillum sp.,isolated from insecticide-treated soils,exhibited greater nitrogen-fixing activity.Three consecutive subcultur- ings of the isolates from insecticide-treated soils had no effect on their nitrogen-fixing activity.1989 Academic Press,Inc.

Tropical forest canopies and their relationships with climate and disturbance： results from a global dataset of consistent field-based measurements

Background： Canopy structure, defined by leaf area index （LAI）, fractional vegetation cover （FCover） and fraction of absorbed photosynthetically active radiation （fAPAR）, regulates a wide range of forest functions and ecosystem services. Spatially consistent field-measurements of canopy structure are however lacking, particularly for the tropics. Methods： Here, we introduce the Global LAI database： a global dataset of field-based canopy structure measurements spanning tropical forests in four continents （Africa, Asia, Australia and the Americas）. We use these measurements to test for climate dependencies within and across continents, and to test for the potential of anthropogenic disturbance and forest protection to modulate those dependences. Results： Using data collected from 887 tropical forest plots, we show that maximum water deficit, defined across the most arid months of the year, is an important predictor of canopy structure, with all three canopy attributes declining significantly with increasing water deficit. Canopy attributes also increase with minimum temperature, and with the protection of forests according to both active （within protected areas） and passive measures （through topography）. Once protection and continent effects are accounted for, other anthropogenic measures （e.g. human population） do not improve the model. Conclusions： We conclude that canopy structure in the tropics is primarily a consequence of forest adaptation to the maximum water deficits historically experienced within a given region. Climate change, and in particular changes in drought regimes may thus affect forest structure and function, but forest protection may offer some resilience against this effect.

Analysis of the Efficacy and Safety of Recombinant Tissue Plasminogen Activator for Chinese Patients over 80 Years of Age with Acute Ischemic Stroke： A Pilot Study

Dear Editor,Recombinant tissue plasminogen activator（rt-PA）remains the only proven therapy for acute ischemic stroke patients who meet the selection criteria for treatment[1–3].A small number of studies have investigated the efficacy of rt-PA for elderly stroke patients in Japanese and Caucasian populations[4,5].According to the American Heart Association/American Stroke Association Guidelines,

Core activated sludge communities are influenced little by immigration:Case study of a membrane bioreactor plant

Microbial immigrants arriving with influent wastewater may influence activated sludge(AS)ecosystems.However,the extent to which immigration impacts AS communities is still debated.To explore the intensity of immigration impact,we used sequencing technology to track the raw wastewater and AS communities from a membrane bioreactor plant over a 12-month period.We first distinguished core populations from peripheral ones in both raw wastewater and AS based on their occurrence frequency and abundance.The results showed that core OTUs(≥80%occurrence frequency)made up a large fraction(>90%)of total sequences,while peripheral OTUs composed the majority of all detected OTUs but merely occupied a few sequences.A significant difference in core communities between the influent and AS was found,as well as between the compositions of core and peripheral populations.Additionally,the persistent functional bacteria of AS,although not numerically dominant,accounted for 96.24%of the total sequences related to nutrient turnover,suggesting the presence of a small number of longstanding and core functional bacteria in the AS ecosystem.Importantly,64%of the 5188 OTUs in AS,which accounted for 91.51%of the sequences,exhibited positive growth rates,which suggested that their apparent abundances were due to growth within the plant,not from immigration.Taken together,these results demonstrated that the impact of influent populations on core AS communities was limited.Overall,this work provides quantitative insights into the impact of immigration,which is expected to advance our understanding of the AS community assembly.