Bacterial Communities of Forest Soils along Different Elevations: Diversity, Structure, and Functional Composition with Potential Impacts on CO2 Emission.

Soil bacteria are important components of forest ecosystems, there compostion structure and functions are sensitive to environmental conditions along elevation gradients. Using 16S rRNA gene amplicon sequencing followed by FAPROTAX function prediction, we examined the diversity, composition, and functional potentials of soil bacterial communities at three sites at elevations of 1400 m, 1600 m, and 2200 m in a temperate forest. We showed that microbial taxonomic composition did not change with elevation (p = 0.311), though soil bacterial α-diversities did. Proteobacteria, Acidobacteria, Actinobacteria, and Verrucomicrobia were abundant phyla in almost all soil samples, while Nitrospirae, closely associated with soil nitrogen cycling, was the fourth most abundant phylum in soils at 2200 m. Chemoheterotrophy and aerobic chemoheterotrophy were the two most abundant functions performed in soils at 1400 m and 1600 m, while nitrification (25.59% on average) and aerobic nitrite oxidation (19.38% on average) were higher in soils at 2200 m. Soil CO2 effluxes decreased (p < 0.050) with increasing elevation, while they were positively correlated (r = 0.55, p = 0.035) with the abundances of bacterial functional groups associated with carbon degradation. Moreover, bacterial functional composition, rather than taxonomic composition, was significantly associated with soil CO2 effluxes, suggesting a decoupling of taxonomy and function, with the latter being a better predictor of ecosystem functions. Annual temperature, annual precipitation, and pH shaped (p < 0.050) both bacterial taxonomic and functional communities. By establishing linkages between bacterial taxonomic communities, abundances of bacterial functional groups, and soil CO2 fluxes, we provide novel insights into how soil bacterial communities could serve as potential proxies of ecosystem functions.

The potential risks and exposure of Qinling giant pandas to polycyclic aromatic hydrocarbon (PAH) pollution.

Rapid industrialization and urbanization have created a substantial urban-rural gradient for various pollutants. The Qinling Mountains are highly important in terms of biodiversity, providing habitat for giant pandas, which are endemic to China and are a widely recognized symbol for conservation. Whether polycyclic aromatic hydrocarbon (PAH) exposure risks regarding in situ animal conservation zones are affected by environmental pollution or even enhanced by the mountain-trapping effect requires further research. Our group carried out a large-scale investigation on the area ranging from Xi'an to Hanzhong across the giant panda habitat in the Qinling Mountains by collecting atmosphere, soil, bamboo, and fecal samples from different sites over a two-year period. The total toxicity of atmospheric PAHs and the frequencies of soil PAHs above effect range low (ERL) values showed a decreasing trend from urban areas to the central mountains, suggesting a distance effect from the city. The proportions of total 5- and 6-ring PAHs in the atmosphere were higher in the central mountainous areas than in the urban areas, while this difference was reversed in the soil. Health risk assessments showed that the incremental lifetime carcinogenic risks (ILCR) of PAH exposure by bamboo ingestion ranged from 2.16 × 10-4 to 3.11 × 10-4, above the critical level of 10-4. Bamboo ingestion was the main driver of the PAH exposure risks. The concentration difference between bamboo and fecal samples provided a reference for the level of PAHs absorbed by the panda digestive system. Since the Qinling Mountains possess the highest density of giant pandas and provide habitats to many other endangered animal and plant species, we should not ignore the probability of health risks posed by PAHs. Monitoring the pollution level and reducing the atmospheric emissions of toxic pollutants are recommended actions. Further detailed research should also be implemented on pandas' health effects of contaminant exposure.

Activity pattern study of Asiatic black bear (Ursus thibetanus) in the Qinling Mountains, China, by using infrared camera traps.

The study of activity patterns is important for understanding the capacity of animals for adapting their behavior based on their habitat conditions. Among bears, daily activity patterns are considered to be strongly influenced by regional climate conditions. We monitored the activity patterns (active vs. inactive) of the Asiatic black bear (Ursus thibetanus) using infrared camera traps (from May 2013 to November 2016) in the Qinling Mountains, China. We used 125 photos, with 19,132 camera days from 55 camera locations. Based on relative independent capture (RIC), bears were found to be intensively active during June (5.86 ± 1.05 SE), July (8.45 ± 2.74), September (14.83 ± 6.13), and October (8.70 ± 3.43), with activity levels gradually decreasing beyond October. After this decline, activities eventually come to a halt when the bears enter in hibernation. We found that their hibernation period was shorter in the Qinling bears, with only 3 months of denning from January to March. Based on their daily patterns, bears were predominantly active during the daytime both in spring (70.83 ± 35.41%) and summer (52.09 ± 28.89%), but more active at twilight during autumn (51.12 ± 42.88%). We assumed that food preferences and food availability (due to warmer regional climatic conditions) might be responsible for such deviations in daily and monthly activity patterns.

Characteristics of heavy metal concentrations and risk assessment for giant pandas and their habitat in the Qinling Mountains, China.

High concentrations of heavy metals in the environment threaten the quality of ecosystems and the health of human beings and animals. Giant panda (Ailuropoda melanoleuca), which is endemic to China and a global conservation icon, has the largest density in the Qinling Mountains. This paper investigated the spatiotemporal variation of heavy metal concentrations in soil (N = 44) at the regional scale with three zones of urban areas, mountain edges, and central mountains, the temporal variation of heavy metal concentrations in three bamboo species (N = 19) and two types of feces (N = 10), and assessed the ecological risk and health risk for giant pandas and their habitat in the Qinling Mountains. The results showed that the median concentrations of studied eight heavy metals mercury (Hg), arsenic (As), copper (Cu), manganese (Mn), zinc (Zn), chromium (Cr), lead (Pb), and cadmium (Cd) in soil exceeded the background values of Shaanxi Province except Pb. The median concentrations of Hg, Zn, Cr, Pb, and Cd in bamboo surpassed the reference standard (RS) of national food safety limits in vegetables for human intake, but the concentration of Zn was within the nutrient range in the bamboo plants. Heavy metals were enriched more in feces of captive than the wild giant pandas, which illustrated either higher ingestion or lower digestibility for captive giant panda. Ecological risk assessment of soil by the geo-accumulation index (Igeo) and risk index (RI) showed strong pollution by Hg and moderate pollution by Cd. Health risk assessment by the hazard index (HI) showed a potential to strong risk for giant pandas exposed to Pb, As, and Hg. In addition, the concentrations of heavy metals in feces showed a higher exposure risk for captive giant pandas than wild giant pandas. We suggest that attention should be paid to and all effective measurements should be taken for reducing the emission of Hg, As, Pb, and Cd in the study area.

Impacts of burial by sediment on decomposition and heavy metal concentrations of Suaeda salsa in intertidal zone of the Yellow River estuary, China.

Three one-off burial treatments were designed in intertidal zone of the Yellow River estuary to determine the effects of sediment burial on decomposition and heavy metal levels of Suaeda salsa. Sediment burial showed significant effect on decomposition rate of S. salsa. With increasing burial depth, Cu, Zn, Cd and Co levels generally increased, while Cr and Mn levels decreased. Except for Zn, Mn, Cd and Co, stocks of Pb, Cr, Cu, Ni and V in S. salsa among burials were greatly different. The S. salsa in three burials was particular efficient in binding V and Co and releasing Pb, Zn and Cd, and, with increasing burial depth, stocks of Cr, Cu, Ni and Mn shifted from accumulation to release. In future, the eco-toxic risk of Pb, Cr, Cu, Zn, Ni, Mn and Cd exposure might be serious as the strong burial episodes occurred in S. salsa marsh.

Decomposition and heavy metal variations of the typical halophyte litters in coastal marshes of the Yellow River estuary, China.

The concentrations of C, Pb, Cr, Cu, Zn, Ni and Mn were determined in decomposing litters of Phragmites australis, Suaeda salsa and Suaeda glauca in three plots of the Yellow River estuary to investigate the variations of metal stocks. Results showed that the decomposition rates significantly differed among species (p < 0.05), in the order of S. glauca (0.002010 d(-1)) > S. salsa (0.000814 d(-1)) > P. australis (0.000766 d(-1)). The concentrations of Cu and Zn in the three litters (particularly S. glauca) generally showed increasing tendency, while those of Pb, Cr, Ni and Mn exhibited different temporal variations. Compared to P. australis and S. salsa, the key mechanisms affecting the variation of metals in S. glauca might be more complex. In most periods, Pb stocks in P. australis, S. salsa and S. glauca, Zn stocks in S. salsa and S. glauca, and Cr, Ni and Mn stocks in P. australis and S. glauca were lower than the initial ones, implying that release exceeded incorporation. Comparatively, Zn stocks in P. australis, Cr, Ni and Mn stocks in S. salsa and in particular Cu stocks in the three litters were generally positive, evidencing incorporation of these metals in most sampling times. The three halophytes were particular efficient in binding Cu and releasing Pb, indicating that the potential eco-toxic risk of Pb exposure might be serious. This study emphasized the strong influences of key biotic (litter types, carbon/metal ratios and activities of microbial organisms) and abiotic variables (salinity, sediment resuspension induced by tidal inundation and passive sorption onto recalcitrant organic fractions) on metal cycling in coastal marshes of the Yellow River estuary.

[Contribution of different processes in wetland soil N2O production in different restoration phases of the Yellow River estuary, China].

By using the method of time-space mutual substitution, the contribution of different processes in wetland soil N2O production was studied in the un-restoration wetland (R0), restoration wetland since 2007 (R2007) and restoration wetland since 2002 (R2002) of the Yellow River estuary to evaluate the effectiveness of the restoration projects. Results showed wetland soil total N2O production had a significant difference in different restoration phases, but the N2O release was the main source. The N2O production in restoration wetland was higher than that in un-restoration wetland. The N2O production wss mainly due to the nitrification and nitrifier denitrification processes, while the denitrification process had great weakening effects on N2O production, which was closely related to the physical and chemical properties of wetland soils in different restoration phases. The non-biological processes made greater contributions to N2O production and these were mainly due to that iron was reductive, while the Yellow River estuary was an area of highly active iron. Although N2O production in wetland soils was the results of biological processes combined with non-biological processes in different restoration phases, non-biological processes had larger influences and should be paid a special attention. There were different influences on wetland soil processes generating N2O between temperature and water content, indicating responses of soil microbial activities to temperature and water content were different. In addition, the N2O production contents ranged from 0.37 +/- 0.08 nmol x (kg x h) (-1) to 9.75 +/- 7.64 nmol x (kg x h) (-1) in marshes of the Yellow River estuary, which was slightly higher than those in the S. alterniflora wetland soils of the Min River estuary, but significantly lower than those in the C. malaccensis wetland soils of the Min River estuary, the grassland soils and the aerobic forest soils. We found that the long-term implements of ecological restoration project in the Yellow River estuary obviously promoted N2O production, so we should consider two factors of landscape restoration and weakening greenhouse gases in the next wetland restoration project.

Spatial and temporal variations of nitrous oxide flux between coastal marsh and the atmosphere in the Yellow River estuary of China.

To investigate the spatial and seasonal variations of nitrous oxide (N2O) fluxes and understand the key controlling factors, we explored N2O fluxes and environmental variables in high marsh (HM), middle marsh (MM), low marsh (LM), and mudflat (MF) in the Yellow River estuary throughout a year. Fluxes of N2O differed significantly between sampling periods as well as between sampling positions. During all times of day and the seasons measured, N2O fluxes ranged from -0.0051 to 0.0805 mg N2O m(-2) h(-1), and high N2O emissions occurred during spring (0.0278 mg N2O m(-2) h(-1)) and winter (0.0139 mg N2O m(-2) h(-1)) while low fluxes were observed during summer (0.0065 mg N2O m(-2) h(-1)) and autumn (0.0060 mg N2O m(-2) h(-1)). The annual average N2O flux from the intertidal zone was 0.0117 mg N2O m(-2) h(-1), and the cumulative N2O emission throughout a year was 113.03 mg N2O m(-2), indicating that coastal marsh acted as N2O source. Over all seasons, N2O fluxes from the four marshes were significantly different (p < 0.05), in the order of HM (0.0256 ± 0.0040 mg N2O m(-2) h(-1)) > MF (0.0107 ± 0.0027 mg N2O m(-2) h(-1)) > LM (0.0073 ± 0.0020 mg N2O m(-2) h(-1)) > MM (0.0026 ± 0.0011 mg N2O m(-2) h(-1)). Temporal variations of N2O emissions were related to the vegetations (Suaeda salsa, Phragmites australis, and Tamarix chinensis) and the limited C and mineral N in soils during summer and autumn and the frequent freeze/thaw cycles in soils during spring and winter, while spatial variations were mainly affected by tidal fluctuation and plant composition at spatial scale. This study indicated the importance of seasonal N2O contributions (particularly during non-growing season) to the estimation of local N2O inventory, and highlighted both the large spatial variation of N2O fluxes across the coastal marsh (CV = 158.31%) and the potential effect of exogenous nitrogen loading to the Yellow River estuary on N2O emission should be considered before the annual or local N2O inventory was evaluated accurately.

Fluxes of nitrous oxide and methane in different coastal Suaeda salsa marshes of the Yellow River estuary, China.

The spatial and temporal variations of the fluxes of nitrous oxide (N(2)O) and methane (CH(4)) and associated abiotic sediment parameters were quantified for the first time across the coastal marsh dominated by Suaeda salsa in the Yellow River estuary during 2009/2010. During all times of day and the seasons measured, N(2)O and CH(4) fluxes from coastal marsh ranged from -0.0147 mg N(2)O m(-2) h(-1) to 0.0982 mg N(2)O m(-2) h(-1) and -0.7421 mg CH(4) m(-2) h(-1) to 0.4242 mg CH(4) m(-2) h(-1), respectively. The mean N(2)O fluxes in spring, summer, autumn and winter were 0.0325 mg N(2)O m(-2) h(-1), 0.0089 mg N(2)O m(-2) h(-1), 0.0119 mg N(2)O m(-2) h(-1) and 0.0140 mg N(2)O m(-2) h(-1), and the average CH(4) fluxes were -0.0109 mg CH(4) m(-2) h(-1), -0.0174 mg CH(4) m(-2) h(-1), -0.0141 mg CH(4) m(-2) h(-1) and -0.0089 mg CH(4) m(-2) h(-1), respectively, indicating that the coastal marsh acted as N(2)O source and CH(4) sink. Both N(2)O and CH(4) fluxes differed significantly between times of day of sampling. N(2)O fluxes differed significantly between sampling seasons as well as between sampling positions, while CH(4) fluxes had no significant differences between seasons or positions. Temporal variations of N(2)O emissions were probably related to the effects of vegetation (S. salsa) during summer and autumn and the frequent freeze/thaw cycle of sediment during spring and winter, while those of CH(4) fluxes were controlled by the interactions of thermal conditions and other abiotic factors (soil moisture and salinity). Spatial variations of N(2)O and CH(4) fluxes were primarily affected by soil moisture fluctuation derived from astronomic tide, sediment substrate and vegetation composition. N(2)O and CH(4) fluxes, expressed as CO(2)-equivaltent (CO(2)-e) emissions, showed that N(2)O comprised the principal part of total calculated CO(2)-e emissions during spring and winter, while the contributions of CH(4) could not be ignored during summer and autumn. This study highlights the importance of seasonal N(2)O and CH(4) contributions, particularly during times of significant CH(4) consumption. For the accurate up-scaling of N(2)O and CH(4) fluxes to annual rates, a careful sampling design at site-level is required to capture the potentially considerable temporal and spatial variations of N(2)O and CH(4) emissions.

[Spatial distribution characteristics of Fe and Mn contents in the new-born coastal marshes in the Yellow River estuary].

The spatial distribution characteristics of Fe and Mn contents in soils of nine different vegetation communities, located in the new-born marshes of the northern Yellow River estuary, were studied in May 2009. The results showed that the horizontal distributions of Fe and Mn contents showed an increasing tendency from Sparganiaceae-Potentilla supina marsh to bare flat. The vertical distribution characteristics of Fe and Mn contents in different marsh soils fluctuated significantly with the vegetation succession. The soil parent materials determined the Fe, Mn contents in the new-born marshes, and seawater, vegetations and soil fine particle also had important influences on their contents. Further analysis showed that Fe contents had significant positive correlation with Mn contents (P < 0.01). Fe, Mn contents also showed significant correlations with silt, clay, TN, NO3(-) -N and organic matter (P < 0.05), indicating that Fe and Mn had close relationships with nitrogen, and the contents of soil fine particles and organic matter were the dominant factors affecting the distribution of Fe and Mn in soils. In addition, the Fe contents ranged from 16.49 g x kg(-1) to 33.11 g x kg(-1) and the average was 22.54 g x kg(-1), which was close to the Fe contents in the tidal marshes of north Jiangsu, the Loess Plateau and the China soil background value, but slightly lower than those in the marshes of the Yangtse River estuary, the mangrove swamps and inland lake wetland. The Mn contents ranged from 305.87 mg x kg(-1) to 711.39 mg x kg(-1) and the average was 451.09 mg x kg(-1), which was lower than the Mn contents in the Loess Plateau and the China soil background value. Hydrology and Water Resources Survey Bureau of the Yellow River Estuary, Dongying 257091, China)

[Methane fluxes and controlling factors in the intertidal zone of the Yellow River estuary in autumn].

The characteristics of methane (CH4) fluxes from tidal wetlands of the Yellow River estuary were observed in situ with static-chamber and GC methods in September and October 2009, and the key factors affecting CH4 fluxes were discussed. From the aspect of space, the CH4 flux ranges in high tidal wetland, middle tidal wetland, low tidal wetland, bare flat are - 0.206-1.264, -0.197-0.431, -0.125-0.659 and -0.742-1.767 mg x (m2 x h)(-1), the day average fluxes are 0.089, 0.038, 0.197 and 0.169 mg x (m2 x h)(-1), respectively, indicating that the tidal wetlands are the sources of CH4 and the source function of CH4 differed among the four study sites, in the order of low tidal wetland > bare flat > high tidal wetland > middle tidal wetland. From the aspect of time, the ranges of CH4 fluxes from the tidal wetland ecosystems are -0.444-1.767 and - 0.742- 1.264 mg x (m2 x h)(-1), and the day average fluxes are 0.218 and 0.028 mg x (m2 x h)(-1) in September and October, respectively. The CH4 fluxes in each tidal wetland in September are higher than those in October except that the high tidal wetland acts as weak sink in September. Further studies indicate that the changes of environmental factors in the Yellow River estuary are complicated, and the CH4 fluxes are affected by multiple factors. The differences of CH4 fluxes characteristics among different tidal wetlands in autumn are probably related to temperature (especially atmospheric temperature) and vegetation growth status, while the effects of water or salinity condition and tide status on the CH4 flux characteristics might not be ignored.

Ascertainment-adjusted maximum likelihood estimation for the additive genetic gamma frailty model.

The additive genetic gamma frailty model has been proposed for genetic linkage analysis for complex diseases to account for variable age of onset and possible covariates effects. To avoid ascertainment biases in parameter estimates, retrospective likelihood ratio tests are often used, which may result in loss of efficiency due to conditioning. This paper considers when the sibships are ascertained by having at least two affected sibs with the disease before a given age and provides two approaches for estimating the parameters in the additive gamma frailty model. One approach is based on the likelihood function conditioning on the ascertainment event, the other is based on maximizing a full ascertainment-adjusted likelihood. Explicit forms for these likelihood functions are derived. Simulation studies indicate that when the baseline hazard function can be correctly pre-specified, both approaches give accurate estimates of the model parameters. However, when the baseline hazard function has to be estimated simultaneously, only the ascertainment-adjusted likelihood method gives an unbiased estimate of the parameters. These results imply that the ascertainment-adjusted likelihood ratio test in the context of the additive genetic gamma frailty may be used for genetic linkage analysis.