| 1. |
- Chen, Hong, et al.
(författare)
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PKU-3 : An HCI-Inclusive Aluminoborate for Strecker Reaction Solved by Combining RED and PXRD
- 2015
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 137:22, s. 7047-7050
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Tidskriftsartikel (refereegranskat)abstract
- A novel microporous aluminoborate, denoted as PKU-3, was prepared by the boric acid flux method. The structure of PKU-3 was determined by combining the rotation electron diffraction and synchrotron powder X-ray diffraction data with well resolved ordered Cl- ions in the channel. Composition and crystal structure analysis showed that there are both proton and chlorine ions in the channels. Part of these protons and chlorine ions can be washed away by basic solutions to activate the open pores. The washed PKU-3 can be used as an efficient catalyst in the Strecker reaction with yields higher than 90%.
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| 2. |
- Hao, Qian, et al.
(författare)
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Holocene carbon accumulation in lakes of the current east Asian monsoonal margin: Implications under a changing climate
- 2020
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Ingår i: Science of the Total Environment. - : Elsevier. - 0048-9697 .- 1879-1026. ; 737, s. 1-13
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Tidskriftsartikel (refereegranskat)abstract
- Carbon (C) present in lake sediments is an important global sink for CO2; however, an in-depth understanding of the impact of climate variability and the associated changes in vegetation on sediment C dynamics is still lacking. A total of 13 lakes were studied to quantify the influence of climate and vegetation on the reconstructed Holocene C accumulation rate (CAR) in lake sediments of the modern East Asian monsoonal margin. The corresponding paleoclimate information was assessed, including the temperature (30–90°N in the Northern Hemisphere) and precipitation (indicated by the δ18O of the Sanbao, Dongge, and Hulu caves). The Holocene vegetation conditions were inferred by pollen records, including arboreal pollen/non-arboreal pollen and pollen percentages. The results showed that the peak CAR occurred during the mid-Holocene, coinciding with the strongest period of the East Asian summer monsoon and expansion of forests. Lakes in the temperate steppe (TS) regions had a mean CAR of 13.41 ± 0.88 g C m−2 yr−1, which was significantly greater than the CARs of temperate desert (TD) and highland meadow/steppe (HMS; 6.76 ± 0.29 and 7.39 ± 0.73 g C m−2 yr−1, respectively). The major influencing factor for the TS sub-region was vegetation dynamics, especially the proportion of arboreal vegetation, while temperature and vegetation coverage were more important for the HMS. These findings indicate that C accumulation in lake sediments is linked with climate and vegetation changes over long timescales; however, there was notable spatial heterogeneity in the CARs, such as opposing temporal changes and different major influencing factors among the three sub-regions during the mid-Holocene. Aridification and forest loss would decrease C storage. However, prediction of C accumulation remains difficult because of the spatial heterogeneity in CARs and the interaction between the CAR and various factors under future climate change conditions.
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| 3. |
- Hao, Qian, et al.
(författare)
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Soil silicon fractions along karst hillslopes of southwestern China
- 2022
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Ingår i: Journal of Soils and Sediments. - : Springer Nature. - 1439-0108 .- 1614-7480. ; 22, s. 1121-1134
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Tidskriftsartikel (refereegranskat)abstract
- Purpose The karst region in southwestern China is undergoing soil erosion and rocky desertification. The different silicon (Si) fractions along the hillslopes in this mountainous region could benefit plant growth and alleviate the ecological deterioration. However, extensive distribution of carbonate rocks may lead to limited plant available Si. The mountainous terrain in karst region also leads to more Si output, which seriously affects the biogeochemical cycle of Si in this area. Yet, the soil Si fractions in the karst region have not been fully evaluated. Methods Soil profiles and their corresponding plants were sampled from two typical karst mountains in Guizhou, China. The different fractions of non-crystalline Si in soil, accounting for the most important pool for Si availability to plants, were analyzed by the improved sequential chemical extraction and Si concentrations in plants grown in this region were also measured. Results The concentration and storage of non-crystalline Si were higher at lower slopes (storage was 2.44, 2.73, and 3.25 kg center dot m(-2) for upper, middle, and lower slopes, respectively) than other slope positions. Grasses dominated at lower slopes and contained significantly higher Si (mean +/- SD: 14.42 +/- 6.63 mg center dot g(-1)) than trees and shrubs (1.94 +/- 1.78 and 1.29 +/- 1.00 mg center dot g(-1), respectively), which were primarily distributed on upper slopes. However, Si concentrations of the same plant species in different slope positions had no significant correlation with soil acid Na acetate-Si, the Si regarded as directly available for plants. Conclusions This study suggests that plant species and soil properties have a significant impact on the soil Si distribution of hillslopes in karst region. Soil erosion may decrease non-crystalline Si concentrations in soils and impair Si uptake in grasses, which need to be considered in ecosystem management in this region.
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| 4. |
- He, Chunmei, et al.
(författare)
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A new vegetation index combination for leaf carotenoid-to-chlorophyll ratio : minimizing the effect of their correlation
- 2023
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Ingår i: International Journal of Digital Earth. - : Informa UK Limited. - 1753-8947 .- 1753-8955. ; 16:1, s. 272-288
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Tidskriftsartikel (refereegranskat)abstract
- The ratio of leaf carotenoid to chlorophyll (Car/Chl) is an indicator of vegetation photosynthesis, development and responses to stress. However, the correlation between Car and Chl, and their overlapping absorption in the visible spectral domain pose a challenge for optical remote sensing of their ratio. This study aims to investigate combinations of vegetation indices (VIs) to minimize the influence of Car-Chl correlation, thus being more sensitive to the variability in the ratio across vegetation species and sites. VIs sensitive to Car and Chl variability were combined into four candidates of combinations, using a simulated dataset from the PROSPECT model. The VI combinations were then tested using six simulated datasets with different Car-Chl correlations, and evaluated against four independent datasets. The ratio of the carotenoid triangle ratio index (CTRI) with the red-edge chlorophyll index (CIred-edge) was found least influenced by the Car-Chl correlation and demonstrated a superior ability for estimating Car/Chl variability. Compared with published VIs and two machine learning algorithms, CTRI/CIred-edge also showed the optimal performance in the four field datasets. This new VI combination could be useful to provide insights in spatiotemporal variability in the leaf Car/Chl ratio, applicable for assessing vegetation physiology, phenology, and response to environmental stress. Trial registration:Clinical Trials Registry India identifier: CTRI/.
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| 5. |
- He, Chunmei, et al.
(författare)
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PROSPECT-GPR : Exploring spectral associations among vegetation traits in wavelength selection for leaf mass per area and water contents
- 2023
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Ingår i: Science of Remote Sensing. - 2666-0172. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Leaf mass per area (LMA) and equivalent water thickness (EWT) are key indicators providing information on plant growth status and agricultural management, and their retrieval is commonly done through radiative transfer models (RTMs) such as the PROSPECT model. However, the PROSPECT model is frequently hampered by the ill-posed problem as a consequence of measurement and model uncertainties. Here, we propose a wavelength selection method to improve the inversion of EWT and LMA by integrating PROSPECT with a machine learning algorithm (Gaussian process regression (GPR); PROSPECT-GPR for short). The GPR model conducted sorting of wavelengths and the PROSPECT-D was used to determine the optimal number of characteristic wavelengths. The results demonstrated that the estimation of EWT (R2 = 0.80; RMSE = 0.0021) and LMA (R2 = 0.71; RMSE = 0.0021) using the proposed wavelengths and PROSPECT inversion all exhibited superior accuracy in comparison with those from previous studies. The efficacy of PROSPECT-GPR in exploring the spectral linkage among vegetation traits was demonstrated by selecting wavelengths associated with leaf structure parameter N and EWT (1368 nm) that turn out to contribute to the estimation of LMA. The findings lay a strong foundation for understanding the spectral linkage among vegetation traits, and the proposed wavelength selection method provides valuable insights for selecting informative spectral wavelengths for RTMs inversion and designing future remote sensors.
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| 6. |
- Xia, Shaopan, et al.
(författare)
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Distribution, sources, and decomposition of soil organic matter along a salinity gradient in estuarine wetlands characterized by C:N ratio, δ13C-δ15N, and lignin biomarker
- 2021
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Ingår i: Global Change Biology. - : John Wiley & Sons. - 1354-1013 .- 1365-2486. ; 27:2, s. 417-434
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Tidskriftsartikel (refereegranskat)abstract
- Despite increasing recognition of the critical role of coastal wetlands in mitigating climate change, sea‐level rise, and salinity increase, soil organic carbon (SOC) sequestration mechanisms in estuarine wetlands remain poorly understood. Here, we present new results on the source, decomposition, and storage of SOC in estuarine wetlands with four vegetation types, including single Phragmites australis (P, habitat I), a mixture of P. australis and Suaeda salsa (P + S, habitat II), single S. salsa (S, habitat III), and tidal flat (TF, habitat IV) across a salinity gradient. Values of δ13C increased with depth in aerobic soil layers (0–40 cm) but slightly decreased in anaerobic soil layers (40–100 cm). The δ15N was significantly enriched in soil organic matter at all depths than in the living plant tissues, indicating a preferential decomposition of 14N‐enriched organic components. Thus, the kinetic isotope fractionation during microbial degradation and the preferential substrate utilization are the dominant mechanisms in regulating isotopic compositions in aerobic and anaerobic conditions, respectively. Stable isotopic (δ13C and δ15N), elemental (C and N), and lignin composition (inherited (Ad/Al)s and C/V) were not completely consistent in reflecting the differences in SOC decomposition or accumulation among four vegetation types, possibly due to differences in litter inputs, root distributions, substrate quality, water‐table level, salinity, and microbial community composition/activity. Organic C contents and storage decreased from upstream to downstream, likely due to primarily changes in autochthonous sources (e.g., decreased onsite plant biomass input) and allochthonous materials (e.g., decreased fluvially transported upland river inputs, and increased tidally induced marine algae and phytoplankton). Our results revealed that multiple indicators are essential to unravel the degree of SOC decomposition and accumulation, and a combination of C:N ratios, δ13C, δ15N, and lignin biomarker provides a robust approach to decipher the decomposition and source of sedimentary organic matter along the river‐estuary‐ocean continuum.
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| 7. |
- Zhang, Xiaodong, et al.
(författare)
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Storage of soil phytoliths and phytolith-occluded carbon along aprecipitation gradient in grasslands of northern China
- 2020
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Ingår i: Geoderma. - : Elsevier. - 0016-7061 .- 1872-6259. ; 364, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- Climatic factors including mean annual precipitation (MAP) significantly influence the carbon (C) cycle interrestrial ecosystems and Earth overall. Phytolith-occluded carbon (PhytOC) is an important C sequestrationmechanism and as such plays a vital role in global long-term C sequestration. Understanding the spatialvariability in the storage of soil phytoliths and PhytOC and its relationship with climate is critical for evaluatingthe impact of global climate change on terrestrial ecosystem functions. However, little is known about theresponses of soil phytoliths and PhytOC to MAP in grassland ecosystems. This study sampled soil from 24natural, semi-arid steppe sites along a 2,500 km transect with a precipitation gradient of 243–481 mm yr−1 innorthern China. We investigated the influence of precipitation on the spatial distributions of soil phytoliths andPhytOC storage. Storage of soil phytoliths in bulk soil (0–100 cm depth) ranged from 21.3 ± 0.4 to88.4 ± 20.3 t ha−1 along the precipitation gradient. Amounts of soil phytoliths and PhytOC storage weresignificantly and positively correlated with MAP. Multiple regression analysis revealed that phytolith storage inbulk soil was best predicted by MAP (R = 0.5) and soil organic carbon (SOC, R = 0.4), with these two variablesaccounting for about 58% of the total variation observed. Considering the forecasted increase in MAP in theInner Mongolian steppe due to climate change, and the strong influence of MAP on the annual net primaryproductivity (ANPP) and related soil PhytOC input from litter decomposition in this region, we expect thatecosystem primary productivity will increase from deserts to meadow steppe and thereby promote soil PhytOCstorage. These findings have important implications for understanding the dynamics of soil phytoliths, andpredicting the impacts of global climate change on ecosystem functions and management practices in the EastAsian steppe ecosystems.
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