Xiaohua Fu

Organic carbon accumulation capability of two typical tidal wetland soils in Chongming Dongtan, China

We measured organic carbon input and content of soil in two wetland areas of Chongming Dongtan (Yangtze River Estuary) to evaluate variability in organic carbon accumulation capability in different wetland soils. Observed differences were investigated based on the microbial activity and environmental factors of the soil at the two sites. Results showed that the organic carbon content of wetland soil vegetated with Phragmites australis (site A) was markedly lower than that with P. australis and Spartina alterniflora (site B). Sites differences were due to higher microbial activity at site A, which led to higher soil respiration intensity and greater carbon outputs. This indicated that the capability of organic carbon accumulation of the site B soils was greater than at site A. In addition, petroleum pollution and soil salinity were different in the two wetland soils. After bio-remediation, the soil petroleum pollution at site B was reduced to a similar level of site A. However, the culturable microbial biomass and enzyme activity in the remediated soils were also lower than at site A. These results indicated that greater petroleum pollution at site B did not markedly inhibit soil microbial activity. Therefore, differences in vegetation type and soil salinity were the primary factors responsible for the variation in microbial activity, organic carbon output and organic carbon accumulation capability between site A and site B.

Variability of soil organic carbon reservation capability between coastal salt marsh and riverside freshwater wetland in Chongming Dongtan and its microbial mechanism

Two representative zones in Chongming Dongtan which faced the Yangtze River and East China Sea respectively were selected to study the variability of soil organic carbon (SOC) reservation capability between coastal wetland and riverside wetland in the Chongming Dongtan wetland as well as its mechanism by analyzing soil characteristics and plant biomass. The results showed the SOC content of riverside wetland was only 48.61% (P = 0.000 < 0.05) that of coastal wetland. As the organic matter inputs from plant litter of the coastal wetland and riverside wetland were approximately the same, the higher soil microbial respiration (SMR) of riverside wetland led to its lower SOC reservation capability. In the riverside wetland, the high soil microbial biomass, higher proportion of beta-Proteobacteria, which have strong carbon metabolism activity and the existence of some specific aerobic heterotrophic bacteria such as Bacilli and uncultured Lactococcus, were the important reasons for the higher SMR compared to the coastal wetland. There were additional differences in soil physical and chemical characteristics between the coastal wetland and riverside wetlands. Path analysis of predominant bacteria and microbial biomass showed that soil salinity influenced beta-Proteobacteria and microbial biomass most negatively among these physical and chemical factors. Therefore the low salinity of the riverside area was suitable for the growth of microorganisms, especially beta-Proteobacteria and some specific bacteria, which led to the high SMR and low SOC reservation capability when compared to the coastal area.

Matching Different Inorganic Compounds as Mixture of Electron Donors to Improve CO2 Fixation by Nonphotosynthetic Microbial Community without Hydrogen

The dominant bacteria in nonphotosynthetic microbial community (NPMC) isolated from the ocean were identified by PCR-DGGE. The results revealed that the dominant microorganisms in cultures of NPMC differed when Na(2)S, Na(2)S(2)O(3), and NaNO(2) were used as the electron donor to reduce CO(2). These findings implied that different microorganisms in the NPMC respond to different inorganic compound as suitable electron donor, indicating that matching of Na(2)S, Na(2)S(2)O(3), and NaNO(2) may provide mixed electron donors that increase the ability of NPMC to fix CO(2). Accordingly, the central composite response surface method (RSM) was used to predict the optimal concentration and match of Na(2)S, Na(2)S(2)O(3), and NaNO(2) as mixed electron donors to improve CO(2) fixation efficiency under aerobic and anaerobic conditions without hydrogen. The results indicated that 0.46% NaNO(2), 0.50% Na(2)S(2)O(3), and 1.25% Na(2)S were the optimal match under aerobic conditions, while 1.04% NaNO(2), 1.07% Na(2)S(2)O(3), and 0.98% Na(2)S were the optimal match under anaerobic conditions. Under these conditions, the fixed CO(2) by NPMC was determined to be 387.51 and 512.57 mg/L, respectively, which obviously exceeded those values obtained prior to optimization (5.94 and 7.14 mg/L, respectively), as well as that obtained when hydrogen was used as the electron donor (91.60 mg/L).

Optimization of electron donors to improve CO2 fixation efficiency by a non-photosynthetic microbial community under aerobic condition using statistical experimental design

To improve the CO(2) fixation efficiency of non-photosynthetic microbial community (NPMC) isolated from sea water under aerobic conditions without hydrogen, the concentration of inorganic compounds as electron donors and their ratios were optimized using response surface methodology design (RSMD). These results indicated that Na(2)S, followed by Na(2)S(2)O(3) and NaNO(2) enhanced the CO(2) fixation by NPMC and the efficiency was increased about 100%, 200% and 200%, respectively. Some interaction between NaNO(2) and Na(2)S(2)O(3), as well as between Na(2)S(2)O(3) and Na(2)S was observed. Central composite RSMD experimentation predicted that the optimal concentration of these inorganic compounds and their ratios was 0.457% NaNO(2), 0.50% Na(2)S(2)O(3) and 1.25% Na(2)S. Under these conditions, the fixed CO(2) was 105.76 mg/L, which obviously exceeded the amount before optimization, as well as that obtained using hydrogen as the electron donor. This indicates that the NPMC using the established electron donors system can effectively fix CO(2) without light and hydrogen gas under aerobic condition.

Salinity and nutrient contents of tidal water affects soil respiration and carbon sequestration of high and low tidal flats of Jiuduansha wetlands in different ways

Soils were collected from low tidal flats and high tidal flats of Shang shoal located upstream and Xia shoal located downstream with different tidal water qualities, in the Jiuduansha wetland of the Yangtze River estuary. Soil respiration (SR) in situ and soil abiotic and microbial characteristics were studied to clarify the respective differences in the effects of tidal water salinity and nutrient levels on SR and soil carbon sequestration in low and high tidal flats. In low tidal flats, higher total nitrogen (TN) and lower salinity in the tidal water of Shang shoal resulted in higher TN and lower salinity in its soils compared with Xia shoal. These would benefit β-Proteobacteria and Anaerolineae in Shang shoal soil, which might have higher heterotrophic microbial activities and thus soil microbial respiration and SR. In low tidal flats, where soil moisture was high and the major carbon input was active organic carbon from tidal water, increasing TN was a more important factor than salinity and obviously enhanced soil microbial heterotrophic activities, soil microbial respiration and SR. While, in high tidal flats, higher salinity in Xia shoal due to higher salinity in tidal water compared with Shang shoal benefited γ-Proteobacteria which might enhance autotrophic microbial activity, and was detrimental to β-Proteobacteria in Xia shoal soil. These might have led to lower soil microbial respiration and thus SR in Xia shoal compared with Shang shoal. In high tidal flats, where soil moisture was relatively lower and the major carbon input was plant biomass that was difficult to degrade, soil salinity was the major factor restraining microbial activities, soil microbial respiration and SR.

Response of cbb gene transcription levels of four typical sulfur-oxidizing bacteria to the CO2 concentration and its effect on their carbon fixation efficiency during sulfur oxidation

The variability in carbon fixation capability of four sulfur-oxidizing bacteria (Thiobacillus thioparus DSM 505, Halothiobacillus neapolitanus DSM 15147, Starkeya novella DSM 506, and Thiomonas intermedia DSM 18155) during sulfur oxidation was studied at low and high concentrations of CO2. The mechanism underlying the variability in carbon fixation was clarified by analyzing the transcription of the cbb gene, which encodes the key enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase. DSM 15147 and DSM 505 fixed carbon more efficiently during sulfur oxidation than DSM 506 and DSM 18155 at 0.5% and 10% CO2, which was mainly because their cbb gene transcription levels were much higher than those of DSM 506 and DSM 18155. A high CO2 concentration significantly stimulated the carbon fixation efficiency of DSM 505 by greatly increasing the cbb gene transcription efficiency. Moreover, the influence of the CO2 concentration on the carbon fixation efficiency of the four strains differed greatly during sulfur oxidation.

Water Organic Pollution and Eutrophication Influence Soil Microbial Processes, Increasing Soil Respiration of Estuarine Wetlands: Site Study in Jiuduansha Wetland

Undisturbed natural wetlands are important carbon sinks due to their low soil respiration. When compared with inland alpine wetlands, estuarine wetlands in densely populated areas are subjected to great pressure associated with environmental pollution. However, the effects of water pollution and eutrophication on soil respiration of estuarine and their mechanism have still not been thoroughly investigated. In this study, two representative zones of a tidal wetland located in the upstream and downstream were investigated to determine the effects of water organic pollution and eutrophication on soil respiration of estuarine wetlands and its mechanism. The results showed that eutrophication, which is a result of there being an excess of nutrients including nitrogen and phosphorus, and organic pollutants in the water near Shang shoal located upstream were higher than in downstream Xia shoal. Due to the absorption and interception function of shoals, there to be more nitrogen, phosphorus and organic matter in Shang shoal soil than in Xia shoal. Abundant nitrogen, phosphorus and organic carbon input to soil of Shang shoal promoted reproduction and growth of some highly heterotrophic metabolic microorganisms such as β-Proteobacteria, γ-Proteobacteria and Acidobacteria which is not conducive to carbon sequestration. These results imply that the performance of pollutant interception and purification function of estuarine wetlands may weaken their carbon sequestration function to some extent.

Universally improving effect of mixed electron donors on the CO2 fixing efficiency of non-photosynthetic microbial communities from marine environments

The universality of improved CO₂ fixing upon the addition of mixed electron donors (MEDs) composed of Na₂S, NO₂(-), and S₂O₃(2-) to non-photosynthetic microbial communities (NPMCs) obtained from 12 locations in four oceans of the world was validated. The CO₂ fixing efficiencies of NPMCs were universally enhanced by MED compared with those obtained using H₂ alone as electron donor, with average increase of about 276%. An increase in microbial inoculation concentration could increase the net amount of CO₂ fixing to 853.34 mg/L in the presence of MED. NO₂(-) and S₂O₃(2-) may play the roles of both electron acceptor and electron donor under aerobic conditions, which may improve the energy utilization efficiency of NPMC and enhance the CO₂ fixation efficiency. The sequence determination of 16S ribosomal deoxyribonucleic acid (rDNA) from 150 bacteria of NPMC showed that more than 50% of the bacteria were symbiotic and there were many heterotrophic bacteria such as Vibrio natriegens. These results indicate that NPMC acts as a symbiotic CO₂ fixing system. The interaction between autotrophic and heterotrophic bacteria may be a crucial factor supporting ladder utilization and recycling of energy/carbon source.

Waste recombinant DNA: Effectiveness of thermo-treatment to manage potential gene pollution

Heating at 100 degrees C for 5-10 min is a common method for treating wastewater containing recombinant DNA in many bio-laboratories in China. In this experiment, plasmid pET-28b was used to investigate decay efficiency of waste recombinant DNA during thermo-treatment. The results showed that the decay half-life of the plasmid was 2.7-4.0 min during the thermo-treatment, and even heating for 30 min the plasmids still retained some transforming activity. Low pH promoted the decay of recombinant DNA, but NaCl, bovine serum albumin and EDTA, which existed in the most wastewater from bio-laboratories, protected DNA from degradation. Thus, the decay half-life of plasmid DNA may be longer than 2.7-4.0 min practically. These results suggest that the effectiveness of heating at 100 degrees C for treating waste recombinant DNA is low and a gene pollution risk remains when those thermo-treated recombinant DNAs are discharged into the environment. Therefore other simple and effective methods should be developed.

Effects of salinity on soil bacterial and archaeal community in estuarine wetlands and its implications for carbon sequestration: verification in the Yellow River Delta

ABSTRACT Soils from two typical tidal salt marshes with varied salinity in the Yellow River Delta wetland were analysed to determine possible effects of salinity on soil carbon sequestration through changes in soil microbiology. The mean soil respiration (SR) of the salt water–fresh water mixing zone (MZ) was 2.89 times higher than that of the coastal zone (CZ) (4.73 and 1.63 μmol m−2 s−1, respectively, p < .05), and soil dehydrogenase activity was the main microbial factor influencing SR. In addition to the higher soil microbial biomass, the MZ had more β-Proteobacteria than the CZ, as well as some specific bacteria with strong heterotrophic metabolic activity such as Pseudomonas sp. and Limnobacter sp. that might have led to its higher dehydrogenase activity and respiratory rates. Additionally, the CZ possessed more Halobacteria and Thaumarchaeota with the ability to fix CO2 than the MZ. Significantly lower soil salinity in MZ (4.25 g kg−1) was suitable for β-Proteobacteria, but detrimental for Halobacteria compared with CZ (7.09 g kg−1, p < .01), which might lead to the lower microbial decomposition capacity of soils in CZ. As a result, the CZ has a higher soil organic carbon content than the MZ.