Combined effects of acids and ammonium on functional pathway and microbial structure during organics methanization were investigated by stable isotopic method and quantitative PCR. The results showed ...that the stress from acids and ammonium was synergetic, resulted in different inhibition for acetoclastic and hydrogenotrophic methanogenesis and syntrophic acetate oxidation, leading to pathway shift. Methane production from acetate was affected more by acetate than by ammonium until the ammonium concentration reached 6–7 g-N/L. When the ammonium concentration exceeded 6 g-N/L, ammonium inhibition was strengthened by the increased concentration of acetate. At a low acetate concentration (50 mmol/L), acetoclastic methanogenesis dominated, regardless of ammonium concentration. At higher acetate concentrations (150 and 250 mmol/L) and at low-medium ammonium levels (1–4 g-N/L), acetate was mainly degraded by acetoclastic methanogenesis, while residual acetate was degraded by a combination of acetoclastic methanogenesis and the syntrophic reaction of syntrophic acetate oxidization and hydrogenotrophic methanogenesis with the latter dominating at 250 mmol/L acetate. At high ammonium levels (6–7 g-N/L), the degradation of acetate in the 150 mmol/L treatment was firstly through a combination of acetoclastic methanogenesis and the syntrophic pathway and then gradually shifted to the syntrophic pathway, while the degradation of acetate in the 250 mmol/L treatment was completely by the syntrophic pathway.
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► Methanogenetic pathway shifted at the synergetic stress of acid and ammonium. ► Acetoclastic methanogenesis wasn't inhibited by 1–7 g-N/L ammonium at 0.05 M acids. ► Syntrophic acetate oxidization was inhibited by high levels of 6–7 g-N/L ammonium. ► Methanosarcinaceae shifted methanogenic pathway depending on the combined stress. ► Soluble microbial products accumulated at 0.25 M acids and 6–7 g-N/L ammonium.
The spatial heterogeneity on a regional scale of forest biomass is caused by multiple biotic and abiotic factors. However, the contributions of biotic and abiotic factors to the spatial heterogeneity ...of forest biomass remain unclear. Based on the data of the National Forest Continuous Inventory (NFCI), digital elevation model (DEM), and meteorological data of Guizhou Province in 2015, we studied the spatial heterogeneity of the aboveground forest biomass in Guizhou province and evaluated the contribution rates of its influencing factors using Moran’s I, semivariogram, distance-based Moran’s eigenvector maps (dbMEMs), and variance partitioning. The results showed that the forest biomass in Guizhou province had strong spatial heterogeneity. Biotic and abiotic factors explained 34.4% and 19.2% of the spatial variation in forest biomass, respectively. Among the biotic factors, the average height of the stand had the greatest influence on forest biomass, while annual precipitation had the greatest influence on forest biomass among abiotic factors. Spatial factors only explained 0.7% of the spatial variation of forest biomass, indicating that the contribution of spatial factors can be explained by some measured abiotic factors. This study provided an effective approach to understand the underlying mechanisms of spatial allocation of forest biomass.
•We proposed a practical method to estimate the seasonal variations of LAI in mixed evergreen–deciduous forests.•We assessed the accuracy of optical methods to estimate the seasonal changes of ...LAI.•We evaluated the relative contributions of different sources of errors to optical LAI measurements.
Leaf area index (LAI), a critical parameter used in process models for estimating vegetation growth, can be measured through litterfall collection, which is usually referred to as a direct method. This method has been demonstrated to be applicable to deciduous forests, but few studies have used this method for estimating seasonal variations of LAI in mixed evergreen–deciduous forests. In this study, we proposed a practical method to estimate the seasonal variation of LAI directly by combining leaf emergent seasonality and litterfall collection (defined as LAIdir) in a mixed broadleaved-Korean pine (Pinus koraiensis) forest (BK), a Korean pine plantation (KP), a spruce–fir valley forest (SV), and a secondary birch (Betula platyphylla) forest (SB). In this direct method, the seasonal variation of LAI in a mixed forest can be quantified by tracking leaf growth and fall patterns throughout the growing season for each major evergreen and deciduous species. Using the LAIdir as a reference, we validated optical LAI (effective LAI, Le) measurements through a digital hemispherical photography (DHP) and the LAI-2000 instrument. We also explored the contribution of major sources of errors to optical LAI, including woody-to-total area ratio (α), clumping index (ΩE), needle-to-shoot area ratio (γE) and automatic exposure (E). We determined that DHP Le significantly (P<0.05) underestimated LAIdir from May to November by 48–64% in BK, KP and SV but overestimated LAIdir by 7% on average in SB. Similarly, LAI-2000 Le also significantly (P<0.05) underestimated LAIdir by an average of 27–35% in BK, KP and SV but overestimated LAIdir by 22% on average in SB. The relative contribution of E to the error in DHP Le is larger than other factors, and the γE was the largest relative contributor to the underestimation of LAI by LAI-2000. The results from our study demonstrate that seasonal variations of LAI in mixed evergreen–deciduous forests can be optically estimated with high accuracy (85% for DHP and 91% for LAI-2000), as long as accurate corrections are made to the various factors mentioned above. These close agreements between direct and optical LAI results also suggest that the direct method developed in this study is useful for tracking the seasonal variation of LAI in mixed forests.
Super-resolution three-dimensional (3D) optical microscopy has incomparable advantages over other high-resolution microscopic technologies, such as electron microscopy and atomic force microscopy, in ...the study of biological molecules, pathways and events in live cells and tissues. We present a novel approach of structured illumination microscopy (SIM) by using a digital micromirror device (DMD) for fringe projection and a low-coherence LED light for illumination. The lateral resolution of 90 nm and the optical sectioning depth of 120 μm were achieved. The maximum acquisition speed for 3D imaging in the optical sectioning mode was 1.6×10(7) pixels/second, which was mainly limited by the sensitivity and speed of the CCD camera. In contrast to other SIM techniques, the DMD-based LED-illumination SIM is cost-effective, ease of multi-wavelength switchable and speckle-noise-free. The 2D super-resolution and 3D optical sectioning modalities can be easily switched and applied to either fluorescent or non-fluorescent specimens.
The spread of coronavirus disease 2019 (COVID-19) around the world has put a heavy burden on human society and is also a great challenge facing medical staff. This study aimed to assess the ...difficulties faced by health care personnel (HCP) in using personal protective equipment (PPE) in clinical practice during the COVID-19 outbreak in Wuhan, China. One hundred twenty medical staff from the First Affiliated Hospital of Chongqing Medical University presented to the Wuhan First Hospital to provide medical assistance, from whom 20 HCP volunteered to participate in a focus group discussion attended by infection control nurse leaders. Participants' responses and discussions were recorded, and the content was analyzed for themes. Observed difficulties included inappropriate PPE sizes, the design of the PPE and its complexity of use, doubts related to the quality and effectiveness of PPE, potential risks during doffing, space layout between clean and contaminated area, and poor comfort with PPE use. Other factors, such as the support environment, management, processes, preparedness, HCP, and equipment can also have a positive or negative impact on the use of PPE. Future efforts to optimize PPE use should focus on strengthening training for HCP using real items for increasing compliance with standardized protocols, improving PPE design, and performing further research on the risks, benefits, and best practices of PPE use.
•We investigated the background influence on remotely sensed LAI estimates.•We detected the relationship between understorey and overstorey LAI.•We obtained more accurate overstorey and understorey ...LAI values using field methods.•We explored how interference and management have influenced the forests LAI.
The presence of understorey vegetation is a recognised problem that limits the accuracy of the satellite-estimated forest leaf area index (LAI). To detect the influence of the understorey, the relationships between the effective overstorey LAI (Leo), gap fraction, effective understorey LAI (Leu) and remote sensing were explored in five forest types: a mixed broadleaved-Korean pine (Pinus koraiensis) forest (BKPF), a spruce-fir valley forest (SVF), a secondary birch (Betula platyphylla) forest (SBF), a Korean pine plantation (KPP) and a Dahurian larch (Larix gmelinii) plantation (DLP) in northeastern China. Leo and Leu were obtained from hemispherical photographs of temporary sample plots. By examining these relationships, we determined that the remote sensing spectral signal was influenced by both the understorey and the gap fraction. In particular when Leo was smaller than 2.5, the understorey substantially influenced the remotely sensed LAI estimates. The relationships between Leo and remote sensing information and between Leo and Leu were both strengthened by considering the effect of gap fraction, although the latter relationship was still poor compared to that of the former. To further explore the relationships between effective and “true” LAI in different forests, “true” overstorey LAI values based on litter collection and hemispherical photographs in permanent sample plots and “true” understorey LAI values through harvesting in temporary sample plots were also determined. The effective LAI of both the overstorey and understorey exhibited good agreement with the “true” LAI. Leo underestimated Lto by 53.7%, 35.1%, 14.6%, 43.9% and 36.0% for BKPF, SVF, SBF, KPP and DLP, respectively. Both Leo and Leu varied less than Lto in different forest types. Our study demonstrates that the remote sensing of biophysical properties of the canopy layer in the forested part of this region is hindered by the dominant role of the understorey with the gap fraction in the spectral signal, and different formats of LAIs have different responses to the degree of disturbance in the forests.
Leaf area index (LAI) is an important variable in the study of forest ecosystem processes, but very few studies are designed to monitor LAI and the seasonal variability in a mixed forest using ...non-destructive sampling. In this study, first, true LAI from May 1(st) and November 15(th) was estimated by making several calibrations to LAI as measured from the WinSCANOPY 2006 Plant Canopy Analyzer. These calibrations include a foliage element (shoot, that is considered to be a collection of needles) clumping index measured directly from the optical instrument, TRAC (Tracing Radiation and Architecture of Canopies); a needle-to-shoot area ratio obtained from shoot samples; and a woody-to-total area ratio. Second, by periodically combining true LAI (May 1(st)) with the seasonality of LAI for deciduous and coniferous species throughout the leaf-expansion season (from May to August), we estimated LAI of each investigation period in the leaf-expansion season. Third, by combining true LAI (November 15(th)) with litter trap data (both deciduous and coniferous species), we estimated LAI of each investigation period during the leaf-fall season (from September to mid-November). Finally, LAI for the entire canopy then was derived from the initial leaf expansion to the leaf fall. The results showed that LAI reached its peak with a value of 6.53 m(2) m(-2) (a corresponding value of 3.83 m(2) m(-2) from optical instrument) in early August, and the mean LAI was 4.97 m(2) m(-2) from May to November using the proposed method. The optical instrument method underestimated LAI by an average of 41.64% (SD = 6.54) throughout the whole study period compared to that estimated by the proposed method. The result of the present work implied that our method would be suitable for measuring LAI, for detecting the seasonality of LAI in a mixed forest, and for measuring LAI seasonality for each species.
Pinus massoniana is the major afforestation and vegetation restoration tree in southern China, and it plays an important role in the sustainable development of plantations. However, long-term single ...planting of P. massoniana has resulted in the decline of soil quality and forest productivity, and a soil fertility assessment is urgently needed. We selected P. massoniana plantations of four age stages for plot investigation and sampling to determine the soil physicochemical properties, microbial diversity and composition, and enzyme activities at different soil depths. The results showed that soil total phosphorus (TP) and available phosphorus (AP) decreased with the increase of age, especially low C/N ratio and high C/P and N/P ratio in the 30-year and 36-year stands, leading to P limitation. Meanwhile, the bacterial Shannon index also decreased with the increase of age and was positively correlated with AP, NO3−-N, and pH. However, the fungal Shannon index decreased first and then increased with the increase of age; soil acid phosphatase (S-ACP) and urease activities showed a similar trend. Correlation analysis demonstrated that the increase of total organic carbon (TOC) and total nitrogen (TN) promoted the increase of fungal Shannon index, which was beneficial to the secretion of more enzymes. We found that soil physicochemical properties, microbial diversity, and enzyme activity decreased simultaneously when soil depths increased. Moreover, Acidobacteria and Basidiomycota were the most abundant bacterial and fungal communities, respectively, followed by Proteobacteria and Actinobacteria for bacteria and Ascomycota for fungi, and these microbial taxa were significantly affected by soil water content (SWC), TOC, AP, and C/P. In conclusion, this work reveals the potential correlation among soil physicochemical properties, microbial diversity and composition, and enzyme activities, and revealed potential correlations among them which will help to improve understanding of soil conditions and provide a reference for rational management of soil resources.
Focusing an annular laser beam can improve the axial trapping efficiency due to the reduction of the scattering force, which enables the use of a lower numerical aperture (NA) objective lens with a ...long working distance to trap particles in deeper aqueous medium. In this paper, we present an axicon-to-axicon scheme for producing parallel annular beams with the advantages of higher efficiency compared with the obstructed beam approach. The validity of the scheme is verified by the observation of a stable trapping of silica microspheres with relatively low NA microscope objective lenses (NA = 0.6 and 0.45), and the axial trapping depth of 5 mm is demonstrated in experiment.
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