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one of the important problems in global change, elevated ultraviolet-B (UV-B) radiation induced by the depletion of stratospheric ozone layer has received more and more attentions around the world. Field experiment with barley was conducted to investigate the effects of elevated UV-B radiation on microbial biomass carbon and nitrogen in rhizosphere and nonrhizosphere soil. The experiment was designed with two UV-B radiation levels, i.e., elevated (E, simulating 25% stratospheric ozone depletion) and ambient (A, control), and performed at the Station of Agricultural Meteorology, Nanjing University of Information Science and Technology, Nanjing, China. Compared with the control, elevated UV-B radiation significantly depressed shoot biomass by 13.2-42.6% and root biomass by approximately 50% from jointing to ripening stage. Elevated UV-B radiation significantly increased microbial biomass C and N in nonrhizosphere soil in most cases, but significantly decreased microbial biomass C and N in rhizosphere soil. Further researches are needed to elucidate whether the above findings are connected with the changes in composition and amount of root exudates induced by elevated UV-B radiation, which can mainly affect the dynamics of soil microbial biomass. [ABSTRACT FROM AUTHOR]

Analyses of regional carbon sources and sinks are essential to assess the economical feasibility of various carbon sequestration technologies for mitigating atmospheric CO2 accumulation and for preventing global warming. Such an inventory is a prerequisite for regional trading of CO2 emissions. As a U.S. Department of Energy Southeast Regional Carbon Sequestration Partner, we have estimated the state-level terrestrial carbon pools in the southeast and south-central US. This region includes: Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina, Tennessee, Texas, and Virginia. We have also projected the potential for terrestrial carbon sequestration in the region. Texas is the largest contributor (34%) to greenhouse gas emission in the region. The total terrestrial carbon storage (forest biomass and soils) in the southeast and south-central US is estimated to be 130 Tg C/year. An annual forest carbon sink (estimated as 76 Tg C/year) could compensate for 13% of the regional total annual greenhouse gas emission (505 Tg C, 1990 estimate). Through proper policies and the best land management practices, 54 Tg C/year could be sequestered in soils. Thus, terrestrial sinks can capture 23% of the regional total greenhouse emission and hence are one of the most cost-effective options for mitigating greenhouse emission in the region. [ABSTRACT FROM AUTHOR]

Red soils, one of the typical agricultural soils in subtropical China, play important roles in the global carbon budget due to their large potential to sequester C and replenish atmospheric C through soil CO2 flux. Soil CO2 emission was measured using a closed chamber method to quantify year-round soil flux and to determine the contribution of soil temperature, dissolved organic carbon (DOC) and soil moisture content to soil CO2 flux. Soil flux was determined every 10 d during the experiment from August 1999 to July 2000, at the Ecological Station of Red Soil (the Chinese Academy of Sciences). In addition, diurnal flux measurements for 24 hr were made on August 5 and November 5, 1999 during this experiment. The average soil fluxes from 2 hr measurements between 9:00 and 11:00 can be regarded as the representative of daily averages. Soil CO2 fluxes were generally higher in summer and autumn than in winter and spring, averaged 7.16 and 0.86 g CO2 m-2 d-1 for the former and latter two seasons, and had a seasonal pattern more similar to soil temperature and DOC than soil moisture. The annual soil CO2 flux was estimated as 1.65 kg CO2 m-2 yr-1. Regressed separately, the reasons for soil flux variability were 86.6% from soil temperature, 58.8% from DOC, and 26.3% from soil moisture, respectively. Regressed jointly, a multiple equation was developed by the above three variables that explained 85.2% of the flux variance, but only soil temperature was the dominant factor affecting soil flux, with significant partial correlation coefficient (r2 = 0.804, p ≤ 0.05), through stepwise regression analysis. Based on the exponential equation using soil temperature, the predicted fluxes were calculated and were essentially equal to the measured ones throughout the experiment. No significant difference was detected between the predicted average and the measured one. The exponential relationship describing the response of soil CO2 flux to the changes in soil temperature should accurately predict soil CO2 flux from red soils in subtropical China. [ABSTRACT FROM AUTHOR]

Body size determines individuals' life history and metabolic rates and thus, regulates community-level dynamics. However, whether body size mediates community co-occurrences and stability, especially in complex communities across different microbial trophic levels, remains unknown. Here, we investigate whether body size determines the co-occurrence pattern and stability of microbial communities across local, regional, and continental scales in the paddy soil ecosystems. Soil samples were collected from rice paddy fields at multiple spatial scales, and soil microbial communities were subsequently sequenced. The microorganisms were then divided into different groups based on taxonomic information at phylum/subphylum level, and the average body size of each microbial group was identified based on propagule size from documented literature. We examined the relationships between microbial body size and various community traits such as potential migration rate, co-occurrence pattern, cohesion, and community stability. Our results consistently showed that the small-sized microorganisms such as bacteria had significantly higher niche breadth, niche overlap and migration rate at various spatial scales. We found that microbial body size is consistently negatively correlated to negative co-occurrences and community stability. Our results, for the first time, put microbial body size into a broader community ecology framework, and contribute to a greater understanding of how microbial taxa with different body sizes would respond to future changes and perturbations. [ABSTRACT FROM AUTHOR]

Land application of intensive swine farm wastewater has raised serious environmental concerns due to the accumulation and microbially mediated transformation of large amounts of swine wastewater organic C (SWOC). Therefore, the study of SWOC mineralization and dynamics of wastewater microorganisms is essential to understand the environmental impacts of swine wastewater application. We measured the C mineralization of incubated swine wastewaters with high (wastewater H) and low (wastewater L) organic C concentrations. The dynamics of bacteria metabolic profile and community structure were also investigated. The results showed that SWOC mineralization was properly fitted by the two-simultaneous reactions model. The initial potential rate of labile C mineralization of wastewater H was 46% higher than that of wastewater L, whereas the initial potential rates of recalcitrant C mineralization of wastewaters H and L were both around 23 mg L-1 d-1. The bacterial functional and structural diversities significantly decreased for both the wastewaters during SWOC mineralization, and were all negatively correlated to specific UV absorbance (SUVA254; P < 0.01). The bacteria in the raw wastewaters exhibited functional similarity, and both metabolic profile and community structure changed with the mineralization of SWOC, mainly under the influence of SUVA254 (P < 0.001). These results suggested that SWOC mineralization was characterized by rapid mineralization of labile C and subsequent slow decomposition of recalcitrant C pool, and the quality of SWOC varied between the wastewaters with different amounts of organic C. The decreased bio-availability of dissolved organic matter affected the dynamics of wastewater bacteria during SWOC mineralization. [ABSTRACT FROM AUTHOR]