Hojeong Kang

An enzymic 'latch' on a global carbon store

A shortage of oxygen locks up carbon in peatlands by restraining a single enzyme.

Export of dissolved organic carbon from peatlands under elevated carbon dioxide levels

Peatlands represent a vast store of global carbon. Observations of rapidly rising dissolved organic carbon concentrations in rivers draining peatlands have created concerns that those stores are beginning to destabilize. Three main factors have been put forward as potential causal mechanisms, but it appears that two alternatives—warming and increased river discharge—cannot offer satisfactory explanations. Here we show that the third proposed mechanism, namely shifting trends in the proportion of annual rainfall arriving in summer, is similarly unable to account for the trend. Instead we infer that a previously unrecognized mechanism—carbon dioxide mediated stimulation of primary productivity—is responsible. Under elevated carbon dioxide levels, the proportion of dissolved organic carbon derived from recently assimilated carbon dioxide was ten times higher than that of the control cases. Concentrations of dissolved organic carbon appear far more sensitive to environmental drivers that affect net primary productivity than those affecting decomposition alone.

Phosphatase and arylsulphatase activities in wetland soils: annual variation and controlling factors

Abstract Phosphatase and arylsulfatase activities were measured in three wetland soils (bog, fen and swamp) in North Wales, UK over 12 months. The fen site (85–176 nmol g −1 min −1 ) showed the highest phosphatase activity of the three, whilst there was little difference between the arylsulphatase activities of the fen (4–14 nmol g −1 min −1 ) and the swamp (5–16 nmol g −1 min −1 ). For both enzymes, the lowest activity was observed in the bog site (20–61 nmol g −1 min −1 for phosphatase; 1–3 nmol g −1 min −1 for arylsulphatase). Hydrogen ion concentration was a dominant controlling factor for the phosphatase activities in all sites. Waterlogging and low temperature seem to restrict enzyme activities in the fen and the swamp sites, as both factors showed significant correlations with the enzyme activities. No temporal relationships between the enzyme activities and the inorganic nutrient concentrations were detected. However, a negative relationship between phosphatase activity and phosphate content was discernable, when compared on a spatial basis.

Enzyme activities in constructed wetlands: Implication for water quality amelioration

Wetlands have been widely applied for water quality amelioration. Enzymatic analysis was applied in a study of decomposition in constructed wetlands. We hypothesise that soil enzyme activities would be lower in wetland sediment than adjacent upland and that the lower soil enzyme activities are partly responsible for the water quality amelioration. Four soil enzyme activities (β-glucosidase, β-N-acetylglucosaminidase, phosphatase, and arylsulfatase) and microbial activity (electron transport system activity) were measured across a transect from a upland soil to a wetland sediment in two constructed wetland sites in the USA. Along with the activities, hydrochemistry was determined in inflow and outflow of the wetlands. In both wetlands, the enzyme activities in the sediments were significantly lower than the adjacent upland soils. For hydrochemistry, significant decreases were observed in phosphate and nitrate concentrations in outflow water compared to inflow water. However, there were no significant changes in other anions (F-, Cl-, SO42- . For dissolved organic carbon, it seems that the wetlands would be a source rather than a sink. The results suggest that the enzymatic approach represents a valuable method to assess decomposition processes in wetland sediments, and that characteristically low enzyme activities in the sediments may be important in the water quality amelioration function.

Effects of biochar addition on greenhouse gas emissions and microbial responses in a short-term laboratory experiment.

Biochar application to soil has drawn much attention as a strategy to sequester atmospheric carbon in soil ecosystems. The applicability of this strategy as a climate change mitigation option is limited by our understanding of the mechanisms responsible for the observed changes in greenhouse gas emissions from soils, microbial responses, and soil fertility changes. We conducted an 8-wk laboratory incubation using soils from PASTURE (silt loam) and RICE PADDY (silt loam) sites with and without two types of biochar (biochar from swine manure [CHAR-M] and from barley stover [CHAR-B]). Responses to addition of the different biochars varied with the soil source. Addition of CHAR-B did not change CO and CH evolution from the PASTURE or the RICE PADDY soils, but there was a decrease in NO emissions from the PASTURE soil. The effects of CHAR-M addition on greenhouse gas emissions were different for the soils. The most substantial change was an increase in NO emissions from the RICE PADDY soil. This result was attributed to a combination of abundant denitrifiers in this soil and increased net nitrogen mineralization. Soil phosphatase and N-acetylglucosaminidase activity in the CHAR-B-treated soils was enhanced compared with the controls for both soils. Fungal biomass was higher in the CHAR-B-treated RICE PADDY soil. From our results, we suggest CHAR-B to be an appropriate amendment for the PASTURE and RICE PADDY soils because it provides increased nitrogen availability and microbial activity with no net increase in greenhouse gas emissions. Application of CHAR-M to RICE PADDY soils could result in excess nitrogen availability, which may increase NO emissions and possible NO leaching problems. Thus, this study confirms that the ability of environmentally sound biochar additions to sequester carbon in soils depends on the characteristics of the receiving soil as well as the nature of the biochar.

Effects of elevated CO2 on fen peat biogeochemistry.

Effects of elevated atmospheric CO2 concentration on northern peatland biogeochemistry was studied in a short-term experiment. Eight intact soil cores (11-cm diameter x 40-cm depth) with Juncus and Festuca spp. were collected from a calcareous fen in north Wales. Half of the cores were incubated under 350 ppm CO2 concentration, whilst the other four cores were maintained at 700 ppm CO2. After a 4-month incubation, significantly higher biomass (root + shoot + algal mat) was determined under elevated CO2 conditions. Higher emissions of N2O and CO2, and higher concentration of pore-water DOC (dissolved organic carbon) were also observed under elevated CO2. However, no significant differences were found in CH4 emission or soil enzyme activities (beta-glucosidase, phosphatase, and N-acetylglucosaminidase) in the bulk soil. Overall, the results suggest that elevated CO2 would increase the primary productivity of the fen vegetation, and stimulate N2O and CO2 emissions as a consequence of an enhanced DOC supply from the vegetation to the soil microbes.

Contrasted effects of simulated drought on the production and oxidation of methane in a mid-Wales wetland

Abstract Wetlands are a major contributor to the global CH 4 budget. Currently, there is a consensus view that drought restrains CH 4 emissions from wetlands, and that this arises due to a suppression of CH 4 production and stimulation of CH 4 oxidation under the more aerobic conditions that accompany lower water table levels. Our data confirm that under drought conditions, CH 4 production is lower (−73%, P P 4 oxidation during the drought, and in contrast, at the end of the simulation observed significantly less CH 4 oxidation in the drought treated system ( P

Identification of airborne bacterial and fungal community structures in an urban area by T-RFLP analysis and quantitative real-time PCR.

This study explores the characteristics of bacterial and fungal communities of total suspended particles (TSP) in the atmosphere by using various molecular methods. TSP samples were collected on a glass fiber filter at an urban location in the middle of the Korean Peninsula (Seoul) between middle autumn and early winter in 2007. From the aerosol samples, DNA could be extracted and DNA sequences were determined for bacteria and fungi. Terminal restriction length polymorphism (T-RFLP) analysis was applied to analyze the community structure of them. To estimate the concentration of DNA originating from bacterial and fungal communities, we used the quantitative real-time polymerase chain reaction (Q-PCR). Sequence analyses were also used to determine the identity of biological organisms. The number of bacteria and fungi in the air were between 5.19x10(1) and 4.31x10(3) cellsm(-3) and from 9.56x10(1) to 4.22x10(4) cellsm(-3), respectively and bacterium/fungus ratios ranged from 0.09 to 0.76 across the seven sampling dates. Most of the bacterial sequences found in our TSP samples were from Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes. The fungal sequences were characteristic for Ascomycota, Basidiomycota, and Glomeromycota which are known to actively discharge spores into the atmosphere. The plant sequences could be also detected. We found that large shifts in the community structure of bacteria and fungi were present in our TSP samples collected on different dates. The results demonstrated that in our TSP samples collected at the urban site; (1) there were very diverse bacterial and fungal groups including potential pathogens and allergens and (2) there were temporal shifts in both bacterial and fungal communities in terms of both diversity and abundances across an inter-seasonal period.

Exotic Spartina alterniflora invasion alters ecosystem–atmosphere exchange of CH4 and N2O and carbon sequestration in a coastal salt marsh in China

Coastal salt marshes are sensitive to global climate change and may play an important role in mitigating global warming. To evaluate the impacts of Spartina alterniflora invasion on global warming potential (GWP) in Chinese coastal areas, we measured CH4 and N2O fluxes and soil organic carbon sequestration rates along a transect of coastal wetlands in Jiangsu province, China, including open water; bare tidal flat; and invasive S. alterniflora, native Suaeda salsa, and Phragmites australis marshes. Annual CH4 emissions were estimated as 2.81, 4.16, 4.88, 10.79, and 16.98 kg CH4 ha(-1) for open water, bare tidal flat, and P. australis, S. salsa, and S. alterniflora marshes, respectively, indicating that S. alterniflora invasion increased CH4 emissions by 57-505%. In contrast, negative N2O fluxes were found to be significantly and negatively correlated (P < 0.001) with net ecosystem CO2 exchange during the growing season in S. alterniflora and P. australis marshes. Annual N2O emissions were 0.24, 0.38, and 0.56 kg N2O ha(-1) in open water, bare tidal flat and S. salsa marsh, respectively, compared with -0.51 kg N2O ha(-1) for S. alterniflora marsh and -0.25 kg N2O ha(-1) for P. australis marsh. The carbon sequestration rate of S. alterniflora marsh amounted to 3.16 Mg C ha(-1) yr(-1) in the top 100 cm soil profile, a value that was 2.63- to 8.78-fold higher than in native plant marshes. The estimated GWP was 1.78, -0.60, -4.09, and -1.14 Mg CO2 eq ha(-1) yr(-1) in open water, bare tidal flat, P. australis marsh and S. salsa marsh, respectively, but dropped to -11.30 Mg CO2 eq ha(-1) yr(-1) in S. alterniflora marsh. Our results indicate that although S. alterniflora invasion stimulates CH4 emissions, it can efficiently mitigate increases in atmospheric CO2 and N2O along the coast of China.

Characteristics of biochar derived from marine macroalgae and fabrication of granular biochar by entrapment in calcium-alginate beads for phosphate removal from aqueous solution.

In this work, granular biochar, Laminaria japonica-derived biochar (LB)-calcium alginate beads (LB-CAB), was successfully prepared by dropping a mixture of powder biochar and alginate solution into a calcium chloride solution for phosphate adsorption. Among different marine macroalgae derived biochars, LB exhibited the best performance, showing a phosphate removal rate of 97.02%, which was attributed to its high Ca/P and Mg/P ratios. With increasing pyrolysis temperature up to 600°C, the physicochemical properties of LB became suitable for adsorbing phosphate. Experimental results of kinetics and equilibrium isotherms at different temperatures (10-30°C) showed that the phosphate adsorption process is endothermic and is mainly controlled by external mass transfer and the intraparticle diffusion rate. The maximum adsorption capacity was found to be 157.7mgg(-1) at 30°C, as fitted by the Langmuir-Freundlich model, which is higher than capacities of other powder form of biochars.