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Plant and soil elemental C:N:P ratios are linked to soil microbial diversity during grassland restoration on the Loess Plateau, China
No full textPlant and soil elemental ratios of carbon (C), nitrogen (N) and phosphorus (P) play a central role in shaping the composition and structure of microbial communities. However, the relationships between plant and soil elemental C:N:P ratios and microbial diversity are still poorly understood. Here, we evaluated the effects of C:N:P ratios in plant-soil systems on microbial diversity in a chronosequence of restored grasslands (1, 5,10,15, 25, and 30 years since restoration) on the Loess Plateau. We found that C and N concentrations, C:N and C:P ratios in leaf, root, soil and microbial biomass, bacterial and fungal diversity (Shannon-Wiener index) gradually increased with year since grassland restoration. Microbial C:N:P ratios ranged from 17.8:4.5:1 to 24.3:6.6:1, and C:P ratio increased from 17.8:1 at the 1-year site to 24.3:1 at the 30-year site, indicating the increasing P limitation for soil microorganisms during grassland development. Soil microbial diversity increased with root, soil, and microbial C and N concentrations, and decreased with P concentration (p < 0.05). Structural equation modeling indicated that soil and microbial C:N and N:P ratios had the greatest influences on soil bacterial and fungal diversity, and elemental C:N:P ratios had a greater effect on soil fungal than bacterial diversity. Our findings emphasize the importance of elemental C:N:P ratios on soil microbial diversity, which is critical for formulating policies for sustainable biodiversity conservation in terrestrial ecosystems. (c) 2021 Published by Elsevier B.V
Records of fire and its controls on coastal plain of Laizhou Bay, China since 5000 years
No full textDisentangling fire and its controls over thousands of years ago is a major challenge in the study of paleofires. In this paper, we synthesize sedimentary charcoal and black carbon from the coastal plain of Laizhou Bay, China to improve our ability to reconstruct fire history in the past 5000 years, and to assess the controls of fire using principal component analysis and multiple regression approach. The results show that there were three distinct fire episodes at the intervals of 5300-5100 yr BP., 1190-1060 yr BP., and 300-0 yr BP., based on the Changyi (CY) profile. A large-scale fire episode was synchronous with a rapid climate variability that occurred 5300 yr BP., which had frequent drought and cold epoch. High fluxes of black carbon and charcoal were closely related to mass migration and the use of fire for land reclamation from 1190 to 1060 yr BP. Subsequently, anthropogenic biomass burning for cereal cultivation has reached a higher level over the past 300 years. However, between 4600 and 4000 yr BP. the shifts in the frequency of high-magnitude floods and climate aridity consequently resulted in the decline of fire-episode frequency and the abandonment of the late Neolithic settlements in the study region.
Therefore, climate is still a prerequisite factor for fire occurrence on the southern coast of Laizhou Bay in the past 5000 years. A rapid climate variability was not only responsible for various fire patterns, but also could affect human settlements and the mode of production during middle-late Holocene. In the past 1000 years, human land use has been a more important control of fire. However, temperature has become one of the evidently identified controls of fire across the study area in recent decades. To synthesize the methods of Principal Component Analysis and Multiple Regression Analysis with multi-proxy evidence is necessary for us to better understand fire and its controls on coastal plain of Laizhou Bay at the region
Accumulation of aeolian sediments around the Tengger Desert during the late Quaternary and its implications on interpreting chronostratigraphic records from drylands in north China
No full textChronostratigraphic records in the drylands of north China provide essential archives to reveal the dynamic connections between climate changes and behaviours of aeolian systems. This study presents a detailed investigation of aeolian sediment accumulation around the Tengger Desert during the late Quaternary, comprising of grain-size characteristics and sources, sediment types and burial ages, and potential responses to external and localised forces. A combination of previously published chronostratigraphic records and 91 newly dated optically stimulated luminescence (OSL) samples collected from multiple sites covering a wide region of the south margin of the desert are used to constrain the accumulation of aeolian sediments during the late Quaternary. The prevailing strong near-surface winds at 22-19 ka, 18-14 ka, 13-10 ka, and 3-0 ka are found to be in anti-phase relation with the strength of the East Asia summer monsoon (EASM). The widespread attenuation of aeolian activity occurred between 7 and 3 ka. The accumulation of aeolian sediments during the past 250 ka has been controlled by multiple factors, including wind, aridity, sediment availability, and preservation capacity. We demonstrate that the interpretation of chronostratigraphic records is significantly affected by the number of available records, which emphasises the importance of sampling at multiple sites. The synchronous accumulation of aeolian sand and sandy loess at certain periods and the significant overlapping of volume percentage distributions at certain grain-size intervals between the two types of sediments indicate that their responses to external forces may not be independent and that the palaeoclimatic significance of sandy loess accumulated in the desert-loess transition zone requires a reassessment. (C) 2021 Elsevier Ltd. All rights reserved
In-vitro oxidative potential and inflammatory response of ambient PM2.5 in a rural region of Northwest China: Association with chemical compositions and source contribution
No full textOverproduction of reactive oxygen species (ROS) induced by atmospheric particles and subsequent inflammatory responses are considered as one of the most important pathological mechanisms with regard to the adverse effects of air pollution exposure. In this study, fine particulate matter (PM2.5) samples were collected at a rural site in Guanzhong Basin, Northwest China, in both summer (August 3-23, 2016) and winter (January 5-February 1, 2017). Then, human bronchial epithelial BEAS-2B cells were exposed to the PM2.5, cultured for 24 h, and then assayed for particle-induced ROS and three inflammatory factors (tumor necrosis-alpha (TNF-alpha), interleukin-6 (IL-6), and interferon-gamma (IFN-gamma)) in vitro. The oxidative potential (OP) induced by winter PM2.5 samples was higher than that induced by summertime samples, whereas inflammatory values showed contrasting seasonal variations. Both OP and inflammatory factors were significantly correlated with most chemical compounds in winter, but not in summer, which was thought to be related mainly to the higher contribution from secondary aerosols formed during the warm season. Source apportionment results showed secondary aerosols formation have significant contribution to OP of PM2.5 in both seasons, but the dominant oxidation processes is different. Secondary nitrates-related process was the major contributors regulating the OP in winter; however, secondary sulfates formation were mainly responsible for the ROS responses in summer. For primary emission, biomass burning, rather than coal emission or vehicle exhaust, was the significant source for OP of PM2.5 in winter. In most cases, the source contribution of each inflammatory factor was similar to that of the ROS. Our results highlighted the significant health risk of atmospheric aerosols from biomass burning in the rural regions of Guanzhong Basin, Northwest China
Efficacy of rice husk biochar and compost amendments on the translocation, bioavailability, and heavy metals speciation in contaminated soil: Role of free radical production in maize (Zea mays L.)
No full textThe present study investigated the effectiveness of rice husk biochar (RHB) and chicken manure compost (CMC) amendments (T1: Control, T2: 2% RHB, T3: 2% CMC, T4: 1% RHB + 1% CMC) on the potential mobility of heavy metals (HMs) and the growth of maize plants in contaminated soil. Results indicated that the potential mobile fraction of Cr (44.43%), Ni (29.93%), and Zn (44.68%) accounted for T2, whereas Cu (69.33%) and Pb (34.38%) for T4 of their total amount. Amending the soil resulted in a significant increase in maize growth and biomass production, whereas T4 showed an increment of 156% in fresh maize weight. While root biomass was highest with T2 treatment, which increased fresh and dry weight by 35% and 90%. The bioaccumulation factor (BF) and Translocation factor (TF) were less than one indicating that the low content of HMs accumulation in roots from soil and slight transferred to shoot (edible tissues). The results of electron paramagnetic resonance (EPR) revealed the generation of hydroxyl radical (center dot OH) as reactive oxygen species (ROS) in root and shoot of maize seedling. The X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectrum confirmed the complexation and the adsorption of HMs as prominent mechanisms owing to their complexation with hy-droxyl, carbonyl and carboxyl groups. The results indicate that the RHB and CMC, especially their combination can be used effectively for the remediation of HMs by reducing their toxicity and bioavailability in food matrices and soils
Soil pH changes in a small catchment on the Chinese Loess Plateau after long-term vegetation rehabilitation
No full textSoil pH is a fundamental parameter of soil chemical properties, and changes in soil pH (CIPs) alter hydrogeochemical processes in the Earth's critical zone. Afforestation has long been reported to change surface soil pH at the site scale or regional scale, while few studies have discussed the effects of afforestation and microtopography on soil pH at the catchment scale. We hypothesize that both afforestation and microtopography affect surface soil pH in a catchment. To test this hypothesis, two neighboring catchments in which one catchment was restored with natural vegetation and the other was afforested in 1954 were selected and surface soils were sampled. The soil pH, soil water content (SWC), total nitrogen (TN), soil organic and inorganic carbon (SOC and SIC) were analyzed for those soil samples. Moreover, trees coverage, LAI and grass cover were investigated in the two catchments. The results showed that over 60 years of afforestation in the catchment reduced the soil pH values at the depth of 0-80 cm in only the topography of the downhill gully, and the CIPs ranged from -0.02 to -0.15. In the topography of the upper hillslope, afforestation showed no significant impacts on soil pH. The reduction in soil pH in the gullies of the forestland catchment had a significant linear and negative relationship with TN and SOC. Moreover, microtopography showed significant impacts on soil pH. In the forestland catchment, the downhill gully showed lower soil pH values than those in the upper hillslope, while the opposite difference was detected in the grassland catchment. The high coverage of vegetation in the forestland gully and frequent gravity erosion in the grassland gully could explain the contrasting trends of soil pH differences between the two landforms in the catchment. The results of this study deepen our understanding of the effects of afforestation and catchment topography on soil pH and the related critical zone processes
Soil pH changes in a small catchment on the Chinese Loess Plateau after long-term vegetation rehabilitation
No full textSoil pH is a fundamental parameter of soil chemical properties, and changes in soil pH (CIPs) alter hydrogeochemical processes in the Earth's critical zone. Afforestation has long been reported to change surface soil pH at the site scale or regional scale, while few studies have discussed the effects of afforestation and microtopography on soil pH at the catchment scale. We hypothesize that both afforestation and microtopography affect surface soil pH in a catchment. To test this hypothesis, two neighboring catchments in which one catchment was restored with natural vegetation and the other was afforested in 1954 were selected and surface soils were sampled. The soil pH, soil water content (SWC), total nitrogen (TN), soil organic and inorganic carbon (SOC and SIC) were analyzed for those soil samples. Moreover, trees coverage, LAI and grass cover were investigated in the two catchments. The results showed that over 60 years of afforestation in the catchment reduced the soil pH values at the depth of 0-80 cm in only the topography of the downhill gully, and the CIPs ranged from -0.02 to -0.15. In the topography of the upper hillslope, afforestation showed no significant impacts on soil pH. The reduction in soil pH in the gullies of the forestland catchment had a significant linear and negative relationship with TN and SOC. Moreover, microtopography showed significant impacts on soil pH. In the forestland catchment, the downhill gully showed lower soil pH values than those in the upper hillslope, while the opposite difference was detected in the grassland catchment. The high coverage of vegetation in the forestland gully and frequent gravity erosion in the grassland gully could explain the contrasting trends of soil pH differences between the two landforms in the catchment. The results of this study deepen our understanding of the effects of afforestation and catchment topography on soil pH and the related critical zone processes
Assessment of the juvenile vulnerability of symbiont-bearing giant clams to ocean acidification
No full textOcean acidification (OA) severely affects marine bivalves, especially their calcification processes. However, very little is known about the fate of symbiont-bearing giant clams in the acidified oceans, which hinders our ability to develop strategies to protect this ecologically and economically important group in coral reef ecosystems. Here, we explored the integrated juvenile responses of fluted giant clam Tridacna squamosa (Lamarck, 1819) to acidified seawater at different levels of biological organization. Our results revealed that OA did not cause a significant reduction in survival and shell growth performance, indicating that T. squamosa juveniles are tolerated to moderate acidification. Yet, significantly reduced net calcification rate demonstrated the calcifying physiology sensitivity to OA, in line with significant declines in symbiont photosynthetic yield and zooxanthellae density which in turn lowered the amount of energy supply for energetically expensive calcification processes. Subsequent transcriptome sequencing and comparative analysis of differentially expressed genes revealed that the regulation of calcification processes, such as transport of calcification substrates, acid-base regulation, synthesis of organic matrix in the calcifying fluid, as well as metabolic depression were the major response to OA. Taken together, the integration of physiological and molecular responses can provide a comprehensive understanding of how the early life history stages of giant clams respond to OA and make an important leap forward in assessing their fate under future ocean conditions
Emission characteristics and formation mechanisms of PM2.5 and gases from different geological maturities coals combustion
No full textTo evaluate the influence of geological maturity on coal combustion pollutant emissions, six chunk coals and corresponding briquettes (volatile matter [VM] content from 8.0% to 39.9%) were selected for simulated residential combustion in a carefully designed chamber, and the formation mechanism involved was investigated. VM was revealed to have a nonlinear effect on the emission factors (EFs) of particulate matter with an aerodynamic diameter of <2.5 mu m (PM2.5), polycyclic aromatic hydrocarbons (PAHs), elemental carbon (EC), and organic carbon (OC), with the highest EFs observed in VM of 15.8% and 26.8%. Coal tar yield and air-supply from VM combustion in its initial stage was found to be a key factor influencing PM2.5 and PAH emissions when compared with the char combustion and burnout stages. The highest PM2.5 and PAH EFs were observed in coal with 15.8% VM. Additionally, significant amounts of hydrogen cyanide (HCN) were detected at stage 1 and were released as volatile-N through the pyrolysis of coal-N. N2O and NOx were also emitted through homogeneous gas-phase HCN reactions. However, only a small proportion of NOx was produced, indicating that the contribution of VM to HCN and N2O emissions is greater than that of NOx. In the char reaction stage (stage 2), char-N reacted with O-2 to form large amounts of NO, and the reaction length of the entire coal combustion process exhibited a positive relationship with coal maturity (correlation coefficient 0.69, p < 0.05), suggesting that the contribution of NO from char-N to overall NO emissions increased with the coal's geological maturity due to the increase in coal-N retention in char. Furthermore, coal briquetting was found to decrease the EFs of pollutants, which may be explained by an increase in MCE (modified combustion efficiency) and the conversion from coal tar to carbon and hydrogen. This study elucidated the effects of geological maturity on pollutant emissions from coal combustion and examined relevant underlying mechanism. These data can serve as the foundation for a clean coal project in China or other counties concerned with coal combustion emissions
The sedimentary succession of the last 2.25 Myr in the Bohai Strait: Implications for the Quaternary paleoenvironmental evolution of the Bohai Sea
No full textThe Bohai Strait connects the Bohai Sea with the Yellow Sea, allowing material and energy exchange between the seas. The sedimentary record in this region is important for reconstructing the Quaternary sea-level changes and environmental evolution in the Bohai Sea area; however, long sedimentary sequences with a reliable chronological framework from this area are scarce. We assessed the sedimentary characteristics, grain size, microfossils, accelerator mass spectrometry 14C ages and optically stimulated luminescence ages of core BHS01 from the Bohai Strait. From these and previous paleomagnetic results, new insights into regional sea-level changes and environmental evolution in the Bohai Strait over the last 2.25 Myr are obtained. The sedimentology and environmental proxies (benthic foraminifera and marine ostracods) indicate that the sedimentary environment of the area around core BHS01 was mainly dominated by fluvial-lacustrine deposits from 2.25 to 0.89 Ma, and subsequently by alternating marine and fluvial deposits. Comparative analyses of the chronological and sedimentary results of core BHS01 with previous drilling records in the eastern marginal seas of China revealed that the Quaternary initial marine transgression of the Bohai Sea occurred no later than 0.89 Ma (latest early Pleistocene) since Quaternary. The initial transgression presumably resulted from the partial subsidence and disintegration of the Miaodao Islands Uplift with sea-level rise during this period or slightly earlier. This result is generally consistent with the timing of the Quaternary regional marine transgressive processes of the Yellow and Bohai seas; thus, we propose a conceptual model in which the first marine transgression of the Yellow Sea and the Bohai Sea during the Quaternary occurred no later than 1.66 Ma and 0.89 Ma, respectively. This study provides new evidence for understanding the Quaternary sea-level changes and regional environmental evolution in the Bohai Sea