Search

Periodic natural disturbances shape the mosaic character of many landscapes and influence the distribution and abundance of organisms. In this study, we tested the effect of ice storm-induced treefall gaps on ground-dwelling beetle assemblages in different-aged successional stands of subtropical broad-leaved forest in southeastern China. We evaluated the relative importance of gap-phase microhabitat type (within gap, gap edge, and interior shaded) within different stand ages (regenerating stands and mature stands) as determinants of changes in beetle diversity and community structure. At 18 replicate sites sampled during 2009-2010, no significant differences were found in species richness and the abundances of the most common beetle species captured in pitfall traps among the three gap-phase microhabitat types, but the abundances of total beetles, as well as fungivorous and phytophagous species groups, were significantly lower in gap microhabitats than in interior shaded microhabitats in mature stands. Beetle assemblage composition showed no significant differences among the three microhabitat types, and only the fauna of gap plots slightly diverged from those of edge and shaded plots in mature stands. Cover of shrubs and stand age significantly affected beetle assemblage structure. Our results suggest that beetle responses to gap-phase dynamics in early successional forests are generally weak, and that effects are more discernible in the mature stands, perhaps due to the abundance responses of forest-specialist species. [ABSTRACT FROM AUTHOR]

Ancient manganese (Mn) deposits are primarily characterized by the presence of Mn(II) carbonates that likely formed by the diagenetic reduction of precursor Mn(IV) oxides. As such, Precambrian sedimentary Mn deposits have been used as a line of evidence for the evolution of oxygen in Earth's surface environments. However, recent studies have shown that these Mn(II)-carbonates have the ability to directly accumulate within anoxic water columns, where free oxygen does not play a role in their formation. This alternative pathway casts uncertainty on the robustness of using ancient Mn deposits to constrain the redox fabric of the past marine water columns. Here, we investigate the Wafangzi Mn and Fe ore deposit from the 1.45 billion-year-old Tieling Formation, North China. The deposit contains Mn(II,III) mineral phases (hausmannite, braunite) as inclusions, or unreacted residues, trapped within Mn(II) carbonate (Ca-rhodochrosite). Some nodules and oolites of Mn(II) and Fe(II)-carbonate phases are also present and display a banded structure with concentric rings. Mn(III) oxide (manganite) is present in a paragenetic assemblage along with hematite and replacement textures with braunite. The negative carbon isotope composition (δ13C, –7‰ to –4‰) from Mn(II) carbonate samples in the Wafangzi Mn deposit which are distinct from that of contemporaneous seawater (~0‰), along with petrographic and speciation analyses, collectively suggest that the Mn(II,III)- and Fe(II)-bearing mineral phases formed through the diagenetic reduction of primary Mn(IV)/Fe(III) minerals coupled to the oxidation of organic matter. Therefore, the Wafangzi Mn deposit suggests the presence of sufficiently oxygenated marine waters, overlying anoxic ferruginous deeper waters with a transitional manganous water layer that could have driven the redox cycling of Mn, Fe, and C. Given the contemporaneous economic Mn deposits in the 1.45 Ga Ullawarra Formation in Western Australia, our findings imply the existence of a transient, and perhaps widespread, pulsed oxygenation event in the mid-Proterozoic oceans. [ABSTRACT FROM AUTHOR]

In tropical regions, lack of moisture-damage-resistant fillers in flexible pavements poses significant challenges for infrastructure development and maintenance. Hence, this study examined sawdust ash (SDA) for such purposes. SDA is abundant as agricultural waste in rice-producing countries like India and China. Durability assessment of SDA-enriched bituminous concrete (BC) against moisture damage is considered as state-of-art in this investigation. To implement this study, numerous laboratory tests were carried out. First, the Marshall test was carried out to estimate the optimal bitumen content (OBC) and several Marshall properties, including Marshall volumetric properties. After that, a modified Marshall immersion test, energy loss ratio test, ultrasonic pulse velocity (UPV) test, indirect tensile strength test (ITS), resilient modulus ratio test, and rutting resistance test were done to execute this investigation. Furthermore, the morphological characteristics of the studied filler were investigated by atomic force microscopy (AFM). The experimental result shows that the 8% SDA-enriched BC mix may be applied in low-volume roads in tropical regions like India with 86.94% structural integrity for the presence of ample amounts of calcium oxide (CaO), silicon oxide (SiO2), ferric oxide (Fe2O3), and higher loss on ignition value in that ash. Moreover, the results have shown that the mixes containing 8% SDA perform exceptionally well against moisture damage with the highest energy loss ratio (63.27%) and dynamic modulus (12.1 MPa) after 14 days of immersion. Similarly, this type of mix delivers the highest tensile strength ratio (96.27%) and resilient modulus ratio (89.21%), with minimum rutting depth (9.55 mm), and performs not only in terms of moisture resistance but also in its ability to withstand rutting deformation significantly. These results make it a promising choice for asphalt pavements, to mitigate the detrimental effects of both rutting and moisture on the overall durability and longevity of the road. [ABSTRACT FROM AUTHOR]

Changes in tree species composition are one of the key aspects of forest succession. In recent decades, significant changes have occurred in the tree species composition of subtropical forests in China, with a decrease in coniferous trees and an increase in broad-leaved trees. This study focuses on Zhejiang Province, located in the subtropical region of China, and utilizes seven inventories from the National Continuous Forest Inventory (NCFI) System spanning 30 years (1989-2019) for modeling and analysis. We categorized tree species into three groups: pine, fir, and broadleaf. We used the proportion of biomass in a sample plot as a measure of the relative abundance of each tree species group. A novel nonlinear difference equation system (NDES) model was proposed. A NDES model was established based on two consecutive survey datasets. A total of six models were established in this study. The results indicated that during the first two re-examination periods (1989-1994, 1994-1999), there was significant fluctuation in the trend of tree species abundance, with no consistent pattern of change. During the latter four re-examination periods (1999-2004, 2004-2009, 2009-2014, 2014-2019), a consistent trend was observed, whereby the abundance of the pine group and the fir group decreased while the abundance of the broad-leaved group increased. Moreover, over time, this pattern became increasingly stable. Although the abundances of the pine group and the fir group have been steadily declining, neither group is expected to become extinct. The NDES model not only facilitates short-term, medium-term, and even long-term predictions but also employs limit analysis to reveal currently obscure changing trends in tree species composition. [ABSTRACT FROM AUTHOR]

Crop phenology indicators provide essential information on crop growth phases, which are highly required for agroecosystem management and yield estimation. Previous crop phenology studies were mainly conducted using coarse-resolution (e.g., 500 m) satellite data, such as the moderate resolution imaging spectroradiometer (MODIS) data. However, precision agriculture requires higher resolution phenology information of crops for better agroecosystem management, and this requirement can be met by long-term and fine-resolution Landsat observations. In this study, we generated the first national maize phenology product with a fine spatial resolution (30 m) and a long temporal span (1985–2020) in China, using all available Landsat images on the Google Earth Engine (GEE) platform. First, we extracted long-term mean phenological indicators using the harmonic model, including the v3 (i.e., the date when the third leaf is fully expanded) and the maturity phases (i.e., when the dry weight of maize grains first reaches the maximum). Second, we identified the annual dynamics of phenological indicators by measuring the difference in dates when the vegetation index in a specific year reaches the same magnitude as its long-term mean. The derived maize phenology datasets are consistent with in situ observations from the agricultural meteorological stations and the PhenoCam network. Besides, the derived fine-resolution phenology dataset agrees well with the MODIS phenology product regarding the spatial patterns and temporal dynamics. Furthermore, we observed a noticeable difference in maize phenology temporal trends before and after 2000, which is likely attributable to the changes in temperature and precipitation, which further altered the farming activities. The extracted maize phenology dataset can support precise yield estimation and deepen our understanding of the future agroecosystem response to global warming. The data are available at 10.6084/m9.figshare.16437054 (Niu et al., 2021). [ABSTRACT FROM AUTHOR]

Background: This study aimed to assess brain oxygenation status and cerebral autoregulation function in subjects with cognitive dysfunction. Methods: The Montreal Cognitive Assessment (MoCA) was applied to divide the subjects into three groups: cognitive impairment (Group CI, 72.50 ± 10.93 y), mild cognitive impairment (Group MCI, 72.02 ± 9.90 y), and normal cognition (Group NC, 70.72 ± 7.66 y). Near-infrared spectroscopy technology and a non-invasive blood pressure device were used to simultaneously measure changes in cerebral tissue oxygenation signals in the bilateral prefrontal lobes (LPFC/RPFC) and arterial blood pressure (ABP) signals from subjects in the resting state (15 min). The coupling between ABP and cerebral oxyhemoglobin concentrations (Δ [O2Hb]) was calculated in very-low-frequency (VLF, 0.02–0.07 Hz) and low-frequency (LF, 0.07–0.2 Hz) bands based on the dynamical Bayesian inference approach. Pearson correlation analyses were used to study the relationships between MoCA scores, tissue oxygenation index, and strength of coupling function. Results: In the interval VLF, Group CI (p = 0.001) and Group MCI (p = 0.013) exhibited significantly higher coupling strength from ABP to Δ [O2Hb] in the LPFC than Group NC. In the interval LF, coupling strength from ABP to Δ [O2Hb] in the LPFC was significantly higher in Group CI than in Group NC (p = 0.001). Pearson correlation results showed that MoCA scores had a significant positive correlation with the tissue oxygenation index and a significant negative correlation with the coupling strength from ABP to Δ [O2Hb]. Conclusion: The significantly increased coupling strength may be evidence of impaired cerebral autoregulation function in subjects with cognitive dysfunction. The Pearson correlation results suggest that indicators of brain oxygenation status and cerebral autoregulation function can reflect cognitive function. This study provides insights into the mechanisms underlying the pathophysiology of cognitive impairment and provides objective indicators for screening cognitive impairment in the elderly population. [ABSTRACT FROM AUTHOR]

Understanding the spatio-temporal variations of temperature and precipitation in the arid and semiarid region of China (ASRC) is of great significance for promoting regional eco-environmental protection and policy-making. In this study, the annual and seasonal spatio-temporal patterns of change in average temperature and precipitation and their influencing factors in the ASRC were analyzed using the Mann-Kendall test, linear tendency estimation, accumulative anomaly and the Pearson's correlation coefficient. The results showed that both annual average temperature and average annual precipitation increased in the ASRC during 1951–2019. The temperature rose by about 1.93°C and precipitation increased by about 24 mm. The seasonal average temperature presented a significant increase trend, and the seasonal precipitation was conspicuous ascension in spring and winter. The spatio-temporal patterns of change in temperature and precipitation differed, with the southwest area showing the most obvious variation in each season. Abrupt changes in annual and seasonal average temperature and precipitation occurred mainly around the 1990s and after 2000, respectively. Atmospheric circulation had an important effect on the trends and abrupt changes in temperature and precipitation. The East Asian summer monsoon had the largest impact on the trend of average annual temperature, as well as on the abrupt changes of annual average temperature and precipitation. Temperature and precipitation changes in the ASRC were influenced by long-term and short-term as well as direct and indirect anthropogenic and natural factors. This study identifies the characteristics of spatio-temporal variations in temperature and precipitation in the ASRC and provides a scientific reference for the formulation of climate change responses. [ABSTRACT FROM AUTHOR]

Aims: Mangrove ecosystems play an important role in mitigating climate change with their capacity to sequester and store carbon. Mangrove can store larger amount of carbon in their soil than any other tropical forests in the same latitude. The coastline is a highly dynamic environment, mangroves can develop at the mudflat with stands of different ages paralleling the shoreline. Hence, this study aimed to assess the role of mangrove growth on ecosystem carbon stock. Methods: Four sites, including natural mangrove stands with different ages (15, 45 and 80-yr-old) and mudflat were selected. Vegetation biomass and the soil carbon content from 0 to 100 cm were analyzed. Results: Ecosystem carbon stocks (including biomass carbon stocks and 0–100 cm soil organic carbon stocks) of 15-yr-old, 45-yr-old and 80-yr-old stands are 171.57 t ha−1, 274.53 t ha−1 and 380.72 t ha−1,respectively, and are 1.76, 2.82 and 3.91 times higher, than that of the bare mudflat ecosystem (111.23 t ha−1). Moreover, the vegetation carbon stocks in 15-yr-old, 45-yr-old and 80-yr-old forest stands account for 33.78%, 17.74%, and 12.33% of the ecosystem carbon density, respectively. The annual accumulation rates of the ecosystem carbon stocks are 3.61 t ha−1, 3.43 t ha−1 and 2.78 t ha−1 for 15-yr-old, 45-yr-old and 80-yr-old stands, respectively. Conclusions: The mangrove stand characteristics and its soil properties were changed with the mangrove ages. The contribution of vegetation biomass carbon stock to ecosystem carbon stock increased along the chronology, while the soil showed the opposite pattern. The annual accumulation rate of ecosystem carbon stocks decreased along the chronology. [ABSTRACT FROM AUTHOR]

Green tide algal blooms occur worldwide, especially in China's Yellow Sea, and have caused serious damage to local ecological environments and economies. As a dominant agent of green tides, the green macroalga Ulva has caused widespread concern. In this study, phylogenetic clades were constructed among related Ulva species isolated from Pyropia rafts at six sites over 1.5 years based on internal transcribed spacer (ITS) and tufA sequences. In addition, traditional observation ploidy methods and flow cytometry methods were used to analyse continuous change in the biphase and sex ratios of Ulva species and to assess the changes in phase advantages over time. The results showed that the perennial Ulva populations on rafts mainly consisted of Ulva flexuosa and Ulva prolifera, and the biphasic dominance of the attached Ulva populations changed with the seasons: sporophytes were predominant mainly in winter and spring, and gametophytes were predominant mainly in summer and autumn. At the same time, there were some differences in gametophyte and sporophyte frequencies (mainly sporophyte biased) compared to the null model prediction of a √2:1 ratio, while the sex ratio of male and female gametophytes remained 1:1 throughout the year. Our results indicate the presence of both phases of bloom-forming species of Ulva in green tides year round, and that multiple generations coexist and grow continuously. [ABSTRACT FROM AUTHOR]

An unresolved question of temperate forests is how pioneer tree species persist in mature forests. In order to understand the responsible mechanisms, we investigated a near‐climax mixed temperate forest dominated by Betula albosinensis in the Qinling Mountains of China. Through establishing four 50 m × 50 m plots, we examined the canopy disturbance characteristics and its effects on tree recruitments. We further test the intra‐ and interspecific effects on the recruitment of B. albosinensis. The obtained data demonstrated canopy disturbance was frequent but most small‐sized. The canopy gaps are caused mainly by adult B. albosinensis by snapping. The regeneration of coexistent tree species shows a distinct preference for gap size. B. albosinensis were clumped at the juvenile stage and small scales. B. albosinensis juveniles were positively associated with B. utilis juveniles and negatively associated with the conspecific and B. utilis large trees. In addition, B. albosinensis juveniles showed negative associations with contemporary other tree species. Our results suggested that canopy disturbance caused by canopy trees and gap partitioning among the coexistent tree species are important for the persistence of the mixed forest. As a main gapmaker, B. albosinensis appear to develop a self‐perpetuating life‐history trait and allow them to persist. [ABSTRACT FROM AUTHOR]

Context: Rates, patterns, and consequences of urban expansion are drawing increasing attention globally because of their profound impacts on socioeconomics, human life, and the environment. Horizontal comparative studies across multiple cities over large geographic regions are rare. Objectives: We quantified and compared the magnitude and forms of urban expansion for China's 32 major cities, and examined the spatiotemporal evolution of urban growth and trajectory of patch structure formation. Methods: Multi-temporal Landsat data of circa 1978, 1990, 1995, 2000, 2005, and 2010, patch-based analyses, and urban growth metrics were used. Results: These 32 major cities have experienced extensive expansion during the study period. Leapfrogging was the dominant urban expansion form, followed by edge-expansion and infilling in the early time periods. Interestingly, the fractions of infilling, edge-expansion, and leapfrogging has gradually reached a quasi-equilibrium condition with a ratio of 2:4:4 (the number) and 2:5:3 (the area) during recent years. Patch analysis suggested that these cities evolved under a nationally-consistent converged urban patch structure regardless of city size, location, and history. The dynamics of urban growth in China corresponded well with its socioeconomic and political geography and the phased implementation of various regional and national policies. Conclusions: Our results generally supported the continuum of diffusion-coalescence urbanization process and a spatial self-organization of urban land patches during urbanization. More studies are needed to test the generality of urban growth hypothesis and examine the universality of converged urban patch structure across regions and countries and to understand their implications to city organization, metabolism, and evolution. [ABSTRACT FROM AUTHOR]

Key message: The gap dynamics in the studied secondary forest were comparable to those of other temperate forests; large openings were filled within 30 years by afforestation; large and medium gaps closed 30–40 years after they formed. Context: Gaps have important roles in forest regeneration and plant succession. However, it is difficult to determine gap dynamics over long time periods at regional scales. Aims: We studied how the dynamics of gaps and large openings (oversized "gaps") changed in a secondary temperate forest over 50 years. Methods: We computed the dynamic indices of gaps (16–3257 m2) and large openings (>3257 m2) using remote sensing techniques applied to six satellite images that were taken approximately every 10 years. Additionally, number-based gap closure ratios were calculated at each interval. Results: Gap dynamics were comparable in magnitude to those calculated for other temperate forests, and 60% and 53% of the large and medium gaps had closed within 30–40 and 20–30 years, respectively. The small gaps closed within 10 years, based on ground-level surveys, and 79.2% of large openings that existed in 1964 were covered by artificial forests in 1994. Conclusion: Gaps of different sizes closed within 40 years due to natural regeneration. Large openings had closed within 30 years via afforestation. These findings can be used for evaluating recovery status and for predicting succession times in secondary forest structures driven by gap formation. [ABSTRACT FROM AUTHOR]

This conference report gives a summary on the contributed papers and discussions presented at the 8th Asia-Pacific Transport Working Group Meeting held at the Engineering & Technical College of Chengdu University of Technology, Leshan, China, from 12 to 15 June 2018. The objective of the meeting is to develop a predictive understanding of the physical mechanisms responsible for particle, energy and momentum transport in magnetically confined plasmas. In order to achieve this objective, five technical working groups were organized under the headings: (A) edge/SOL turbulence and L-H/H-L transition, (B) core-edge turbulence coupling, and transport in high beta plasmas, (C) transport and turbulence in 3D magnetic topology, (D) interaction between energetic particles, MHD instabilities and turbulence, and (E) model reduction and experiments for validation. A summary of the selected significant progresses from the presentations in the five technical working groups is given. The Young Researchers Forum which was held in this meeting is described. [ABSTRACT FROM AUTHOR]

The aim of this study was to explore the effect of gap environmental factors on the plant population regeneration pattern in the Castanopsis kawakamii natural forest. We used the detrended canonical correspondence analysis (DCCA) method to study coupling relationships between species distribution in the regeneration layer and environmental factors. The results showed that: (1) The main environmental factors that influenced species distribution in the forest gaps and non-gaps were different, and the highest explanation rate of environmental factors was the soil temperature below the surface 10 cm (ST10); (2) The relationships between species distribution in the regeneration layer of the forest gaps and non-gaps were mainly restricted by environmental factors, given the environmental factors complied with the ecological niche hypothesis; and (3) For the endangered C. kawakamii population, there were positive and negative relationships between the environmental factors and the various species in the forest gaps and non-gaps, whilst the effects of such relationships were varied. Some management operations, including the creation of artificial gaps and adequate fertilization in the non-gaps, could more effectively promote the growth and regeneration of the C. kawakamii population. [ABSTRACT FROM AUTHOR]