Important Role In Global Cycling Research Articles

Belowground biomass of alpine shrublands across the northeast Tibetan Plateau.

Although belowground biomass (BGB) plays an important role in global cycling, the storage of BGB and climatic effects on it are remaining unclear. With data from 49 sites, we aimed to investigate BGB and its climatic controls in alpine shrublands in the Tibetan Plateau. Our study showed that the BGB (both grass‐layer and shrub‐layer biomass) storage in the alpine shrublands was 67.24 Tg, and the mean BGB density and shrublands area were 1,567.38 g/m2 and 4.29 × 104 km2, respectively. Shrub layer had a larger BGB stock and accounted for 66% of total BGB this area, while only 34% was accumulated in the grass layer. BGB of the grass layer in the Tibetan Plateau shrublands was larger than that of Tibetan alpine grasslands, indicating that shrubland ecosystem played a critical importance role in carbon cycle on the Tibetan Plateau. The BGB in the grass layer and shrub layer demonstrated different correlations with climatic factors. Specifically, the effects from mean annual temperature on shrub‐layer BGB were not significant, similarly to the relationship between mean annual precipitation and grass‐layer BGB. But shrub‐layer BGB had a significantly positive relationship with mean annual precipitation (p < .05), while grass‐layer BGB showed a trend of decrease with increasing mean annual temperature (p < .05). Consequently, the actual and potential increases of BGB varied due to different increases of mean annual precipitation and temperature among different areas of the Tibetan Plateau. Therefore, in the warmer and wetter scenario, due to contrary relationships from mean annual precipitation and temperature on shrub‐layer BGB and grass‐layer BGB, it is necessary to conduct a long‐term monitoring about dynamic changes to increase the precision of assessment of BGB carbon sequestration in the Tibetan Plateau alpine shrublands.

Chloromethane formation and degradation in the fern phyllosphere

Chloromethane (CH3Cl) is the most abundant halogenated trace gas in the atmosphere. It plays an important role in natural stratospheric ozone destruction. Current estimates of the global CH3Cl budget are approximate. The strength of the CH3Cl global sink by microbial degradation in soils and plants is under discussion. Some plants, particularly ferns, have been identified as substantial emitters of CH3Cl. Their ability to degrade CH3Cl remains uncertain. In this study, we investigated the potential of leaves from 3 abundant ferns (Osmunda regalis, Cyathea cooperi, Dryopteris filix-mas) to produce and degrade CH3Cl by measuring their production and consumption rates and their stable carbon and hydrogen isotope signatures. Investigated ferns are able to degrade CH3Cl at rates from 2.1 to 17 and 0.3 to 0.9μggdw−1day−1 for C. cooperi and D. filix-mas respectively, depending on CH3Cl supplementation and temperature. The stable carbon isotope enrichment factor of remaining CH3Cl was −39±13‰, whereas negligible isotope fractionation was observed for hydrogen (−8±19‰). In contrast, O. regalis did not consume CH3Cl, but produced it at rates ranging from 0.6 to 128μggdw−1day−1, with stable isotope values of −97±8‰ for carbon and −202±10‰ for hydrogen, respectively. Even though the 3 ferns showed clearly different formation and consumption patterns, their leaf-associated bacterial diversity was not notably different. Moreover, we did not detect genes associated with the only known chloromethane utilization pathway “cmu” in the microbial phyllosphere of the investigated ferns. Our study suggests that still unknown CH3Cl biodegradation processes on plants play an important role in global cycling of atmospheric CH3Cl.

DGGE diversity of manganese mine samples and isolation of a Lysinibacillus sp. efficient in removal of high Mn (II) concentrations

Manganese contamination has become a serious environmental problem in the world and bacterial removal plays an important role in global cycling of manganese. In this study, microorganism distribution within samples from a manganese mine was analyzed with PCR-DGGE technology. The results suggested that Manganese oxidizing bacteria (such as Bacillus, Hyphomicrobiaceae and Erythrobacter) were dominant in the soil. In addition, a Lysinibacillus sp. Isolate, strain MK-1, revealed robust growth at high Mn(II) concentrations up to 1 mM. At that concentration, 55.94% of added Mn(II) was oxidized and 36.23% of the Mn(II) was adsorbed by MK-1(total manganese removal reached 94.67%) after 7 days of culturing. By measuring its metabolic process, the great role of biological adsorption was found. Additionally, the spectroscopic result demonstrated that Mn(III) was an intermediate during the biological oxidation process. These findings increase the knowledge of biological manganese removal mechanisms and show some potentials to the operation of manganese treatment.

Nutrient limitation status in a subtropical mangrove ecosystem revealed by analysis of enzymatic stoichiometry and microbial abundance for sediment carbon cycling

Mangrove ecosystem plays an important role in global cycling of nutrients. According to nutrient availability, microorganisms can optimize the allocation of C-, N- and P-degrading enzymes. Thus, in this study, enzymatic stoichiometry involved in C, N and P acquisition, and the microbial abundance were analysed in coastal mangrove sediments in two different seasons. Activities of β-1,4-glucosidase (GLU), N-acetyl-β-glucosaminidase (NAG), acid phosphotase (ACP) and phenol oxidase (PHO) were determined, and then applied to calculate the enzymatic C:N (GLU:NAG), C:P (GLU:ACP) and N:P (NAG:ACP) acquisition, respectively. Besides, GLU:PHO was applied as relative recalcitrance of sediment organic matter (SOM). The results showed the enzymatic stoichiometry and microbial abundance had strongly seasonal variations. Compared to other ecosystems, GLU:ACP and NAG:ACP ratios were largely lower, suggesting that sediments in this ecosystem might be microbial P-limitation. Moreover, the higher GLU:PHO ratio implied that SOM in this ecosystem might be more decomposable. Furthermore, the imbalance of nutrients for microbial abundance was revealed by the strong correlations relating sediment N:P to GLU:NAG, GLU:ACP, and GLU:PHO. On the other hand, microbial P limitation in this ecosystem may enhance C storage and sequestration because the higher C contents in sediments of March than November occurred with lower GLU:ACP and NAG:ACP ratios as well as bacterial abundance.

Inter-annual variation in growing season length of a tropical seasonal forest in northern Thailand

Tropical seasonal forests play an important role in global cycling of carbon, water and energy in terms of inter-annual variation in the growing season. We investigated year-to-year variations in the canopy duration and transpiration period as measures of growing season length using time series data of radiative transmittance and sap flux in a teak plantation in Thailand over a 3-year period. In 2001, leaf-out and tree transpiration commenced earlier than in 2002 and 2003 following exceptionally heavy rainfall in the late dry season, strongly suggesting that enhanced soil moisture advanced the timing of leaf unfolding and commencement of tree transpiration. The commencement of leaf-fall and decline in tree transpiration at the beginning of 2003 were late in coming in correlation with a prolonged rainy season. Declines in tree transpiration were directly controlled by soil moisture conditions at the beginning of the dry season, with time lags between the timing of leaf-fall and decline in tree transpiration. These results revealed that soil moisture conditions are a major determinant of large inter-annual variation in the growing season at this site. The variation in canopy duration and transpiration period in this study, from 2001 to 2004, spanned about 40 and 60 days, respectively. This was much larger than the inter-annual variations previously reported in temperate deciduous forests, implying a profound potential impact on surface energy balance and canopy-atmosphere water and carbon exchange on an annual time scale.

Maximum reservoir capacity of vegetation for persistent organic pollutants: Implications for global cycling

The concept of maximum reservoir capacity (MRC) or “equilibrium capacity ratio,” the ratio of the capacities of the vegetation and of the atmospheric mixed layer (AML) to hold chemical under equilibrium conditions, is applied to selected persistent organic pollutants (POPs) in vegetation in order to assess its importance for the global cycling of POPs. Vegetation is found to have a significant storage capacity, and because of its intimate contact with the atmosphere may play an important role in global cycling of POPs. The vegetation MRC is calculated for some representative PCB congeners (PCB‐28; −152; −180) at the global scale with a spatial resolution of 0.25° × 0.25°. It is shown to be comparable to that of the skin layer of the soil and to vary over many orders of magnitude, between compounds, locations, and time (seasonally/diurnally), depending on the vegetation type and on the temperature. The highest MRC values are observed in areas with low temperatures and coniferous forests (e.g., Siberia, Canada, Scandinavia), while the lowest values are typically located in warm and desert areas (e.g., Sahara). Large differences were also observed at the regional scale. Implications for the global cycling and long‐range atmospheric transport (LRAT) of POPs are discussed, including comparisons with soil and ocean MRCs, which will drive net transfers of POPs between media and regions.

Diversity of methanotroph communities in a basalt aquifer

Methanotrophic bacteria play an important role in global cycling of carbon and co-metabolism of contaminants. Methanotrophs from pristine regions of the Snake River Plain Aquifer (SRPA; Idaho, USA) were studied in order to gain insight into the native groundwater communities' genetic potential to carry out TCE co-metabolism. Wells were selected that were proximal to a TCE plume believed to be undergoing natural attenuation. Methane concentrations ranged from 1 to >1000 nM. Carbon isotope ratios and diversity data together suggest that the SRPA contains active communities of methanotrophs that oxidize microbially produced methane. Microorganisms removed from groundwater by filtration were used as inocula for enrichments or frozen immediately and DNA was subsequently extracted for molecular characterization. Primers that specifically target methanotroph 16S rRNA genes or genes that code for subunits of soluble or particulate methane monooxygenase, mmoX and pmoA, respectively, were used to characterize the indigenous methanotrophs via PCR, cloning, RFLP analysis, and sequencing. Type I methanotroph clones aligned with Methylomonas, Methylocaldum, and Methylobacter sequences and a distinct 16S rRNA phylogenetic lineage grouped near Methylobacter. The majority of clone sequences in type II methanotroph 16S rRNA, pmoA, and mmoX gene libraries grouped closely with sequences in the Methylocystis genus. A subset of the type II methanotroph clones from the aquifer had sequences that aligned most closely to Methylosinus trichosporium OB3b and Methylocystis spp., known TCE-co-metabolizing methanotrophs.