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Soil phosphorus (P) is a vital nutrient that controls wetland productivity and ecological functions. However, the effects of soil P forms on P availability during wetland degradation are relatively unknown. We selected differently degraded marshes, including non‐degraded marsh (NDM), lightly degraded marsh (LDM), moderately degraded marsh (MDM), and heavily degraded marsh (HDM), to research the changes in soil P forms by sequential chemical extraction and its regulation on P availability in the Zoige Plateau, China. The results showed that compared with the 0–30 cm soil layers of NDM, the main changes in total P concentration were a significant increase of 31.6%–44.2% in LDM and MDM, and the available P concentration increased by 28.7%–76.2% in LDM and MDM but decreased by 4.0%–47.5% in HDM with a lower P activation coefficient. Marsh degradation increased the concentration of soil dicalcium phosphates, P occluded in iron hydroxides, and organic P from the entire profile by 46.7%–137.7%, 31.7%–49.3%, and 78.1%–82.1%, respectively, while it decreased that of iron oxide surface adsorbed P and apatite P by 17.2%–32.2% and 15.3%–27.8%, respectively. Soil available P was mainly related to organic P and P non‐occluded in iron oxide minerals, which might also be a non‐negligible direct source of available P. The transformation from apatite P to organic P was an important regulatory mechanism of P availability in soils during marsh degradation. This study revealed the transformation trajectory of soil P forms owing to soil desiccation accompanied by plant community changes and overgrazing during alpine marsh degradation, and the risk of P limitation in HDMs with low soil available P. For degraded marsh restoration, some measures for improving P availability should be implemented in the future, such as grazing exclusion and the application of organic fertilizer. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) is an important environmental heavy metal and one of the main soil pollutants in southwest China and even the Yangtze River Basin because of its toxicity to plants and humans. To clarify the potential of Euryops pectinatus L. and Gardenia jasminoides J. and the mechanism they use to remediate Cd-contaminated soil, a soil pot experiment with 0, 5, 10, 20, and 40 mg kg−1 of Cd was used to investigate the accumulation characteristics, subcellular distribution, chemical forms, and the antioxidative defense systems of the two ornamental plants. When the concentration of Cd was below 40 mg kg−1, it promoted the growth of E. pectinatus shoots, and the tolerance index (TI) was >1. However, 20–40 mg kg−1 Cd significantly inhibited the growth of G. jasminoides, and the TI was <1. The shoots of both varieties accumulated more Cd than the roots, and the E. pectinatus shoots accumulated more Cd (1.45 mg plant−1) than those of G. jasminoides (0.71 mg plant−1). The Cd in E. pectinatus and G. jasminoides was primarily distributed in the soluble fraction (52.83–68.97%) and cell walls (44.62–54.98%), respectively. Higher proportions of Cd bound to NaCl and acetic acid (HAc) in E. pectinatus (55.32–73.44%) than in G. jasminoides (42.94–61.58%), while the inorganic and water-soluble proportions of Cd bound in the opposite manner. E. pectinatus maintained high activities of antioxidant enzymes under Cd treatments, and its levels of malondialdehyde (MDA) and relative electrical conductivity (REC) were comparable to those of the control. Nonetheless, G. jasminoides had low levels of activity of antioxidant enzymes, but its levels of MDA and REC were significantly higher than those of the control under the 20–40 mg kg−1 Cd treatment. Therefore, both types of plants have a strong ability to tolerate and accumulate Cd, which makes them suitable for the remediation of Cd-polluted soil. However, E. pectinatus is more effective at remediating Cd and tolerant to it than G. jasminoides. These plants utilize different mechanisms to detoxify Cd. [ABSTRACT FROM AUTHOR]

Assessing soil quality (SQ) of cropland is fundamental for food security and sustainable land management. However, there is limited information regarding SQ assessment on a national scale, which is vital to answer important SQ‐related questions in quantitative terms on that scale. Here, the SQ of cropland in China was assessed by constructing a minimum data set (MDS) from 23 soil physicochemical properties based on principal component analysis. The interaction roles and relative contributions of climate and topography on SQ was evaluated by a structural equation model. The MDS comprised eight indicators: proportion of silt, bulk density, total phosphorus, total potassium, available nitrogen, exchangeable calcium, chlorite, and vermiculite. The soil quality index (SQI) varied from 0.245 to 0.705 and showed a clear pattern of decreasing quality from the north to the south of the country. Of the total cropland area in China, the largest share (27.91%) was of soils of high quality, followed by those of moderate quality (24.63%), low quality (20.37%), very high quality (14.18%), and very low quality (12.91%). The north and the south differed significantly in terms of total potassium, exchangeable calcium, chlorite, and vermiculite, which are the four most important indicators of SQ. Climate and elevation explained about 2.2%–30.1% of the variation in SQ on the national and regional scales. These findings suggest that croplands in southern China will benefit from potassium and calcium fertilizers, which will contribute to enhance food security and promote sustainable land management in China. [ABSTRACT FROM AUTHOR]

Purpose: Phytoliths are microscopic particles of amorphous silica produced by plants that have vital importance for environmental change and carbon sequestration. This study investigated phytoliths and their morphotype assemblages, and phytolith-occluded carbon (PhytOC) along a marsh degradation gradient to clarify the significance of phytoliths for evaluating carbon sequestration dynamics during marsh degradation on the Zoige Plateau, China. Materials and methods: Soil samples from non-degraded marsh (NDM), lightly degraded marsh (LDM), moderately degraded marsh (MDM), and seriously degraded marsh (SDM) were collected. Soil phytolith shape and PhytOC were determined using heavy liquid suspension, microscope observations, and alkali-solution spectrophotometry. Results and discussion: The dominant phytolith morphotypes among the 15 identified in the soils from the differently degraded marshes were lanceolate, rectangular, and elongate, which originated from Poaceae and Cyperaceae. Soil phytolith morphotype assemblages show potential for studying past vegetation and climatic succession in alpine wetlands. The soil phytolith and PhytOC content exhibited no significant differences between the NDM and LDM samples. Compared with the NDM soil, phytolith content was significantly lower in the MDM (33.8–58.8%) and SDM (52.7–65.4%) soils, respectively, and PhytOC content was also significantly lower (by 31.0–57.1% and 47.5–74.4%, respectively). The soil phytolith and PhytOC content decreased significantly with soil depth, especially once the marsh has become moderately degraded. Conclusions: Alpine marsh degradation reduced the accumulation of soil PhytOC by decreasing the PhytOC input flux, thereby altering the long-term carbon sequestration mechanism of phytoliths in this alpine-marsh wetland ecosystem. [ABSTRACT FROM AUTHOR]

Complex and dynamic land-use patterns have been observed globally due to rapid urbanization and persistent human disturbance. Analyzing the effect of urbanization on carbon (C) stocks is a key step toward enhancing C sequestration and mitigating emissions of carbon dioxide. In a newly urbanized area of western Chengdu, China, we analyzed soil organic C (SOC), soil inorganic C (SIC) stocks down to 1 m, and aboveground vegetation C, and we discussed the effects of land use, density of construction and roads, and distance from the urban center on SOC and SIC density. The SOC, SIC stocks down to 1 m, and aboveground vegetation C stocks were 1.08 × 10 9 kg, 4.67 × 10 7 kg, and 1.58 × 10 7 kg, respectively. Our analyses of SOC and SIC density provided three results: (1) it was significantly higher in rural than in urban land-use types; (2) it tended to decrease as the density of construction and roads increased; and (3) it increased with distance far from the urban center. The results indicated that urbanization led to SOC and SIC loss in our study area. SOC and SIC loss will be alleviated by decreasing the construction and road density and increasing green space area. [ABSTRACT FROM AUTHOR]

• Marsh degradation reduced large-aggregate ratio and SOC content in aggregates. • Dominant aggregate size of SOC preservation decreased under marsh degradation. • SOC active functional groups in aggregates increased along degraded marsh gradient. • Marsh degradation weaken organic C stability and sequestration in soil aggregates. Alpine marsh wetlands in the Qinghai-Tibetan Plateau are ecological hotspots for global carbon (C) cycling in Central Asia; however, the soil C sinks are increasingly limited by marsh degradation. To assess the physical mechanisms by which changes in the soil C sequestration occur, the distribution and functional groups of soil organic C (SOC) in aggregates along a marsh degradation gradient on the Zoige Plateau in China were investigated using soil samples collected from differently degraded marshes. Our results showed that, beyond the state of light degradation, the large aggregate content decreased significantly by 31.1–55.2%, while the micro-aggregate content increased significantly by 23.1–93.1%. The SOC content in the aggregates decreased significantly by 39.1–84.8% and the dominant aggregate size for SOC preservation decreased to small or micro-aggregate. Marsh degradation also decreased the relative ratio of aliphatic-C while increasing that of alcohol and phenolic-C, and polysaccharide-C. Index I (relative decomposition of SOC in aggregates) was 73.5–429.0% higher for degraded marshes than for relatively pristine marsh (RPM), while Index Ⅱ (relative recalcitrance of SOC in aggregates) was 13.8–79.5% lower in comparison. Therefore, we concluded that marsh degradation probably reduces the organic C sequestration capacity of soil by increasing the decomposition of SOC in aggregates after both the dominant aggregate size for SOC preservation and aggregate stability decreased. This result represents the physical mechanism by which the decrease in SOC content occurs in response to marsh degradation in alpine regions. [ABSTRACT FROM AUTHOR]

Michelia champaca L. (Magnoliaceae) was cultivated in large scale for flowers as cosmetic raw materials, whereas the value of its leaves remains to be discovered. Our chemical study on the leaves yielded four new flavonol diglycosides, champaflavosides A-D (1-4), together with twenty-three known flavonoid glycosides (5-27). Their structures were determined by spectroscopic and chemical methods. Compounds 5-21 and 23-27 were not previously reported from the genus Michelia, and kaempferol 3-O-rutinoside (22) was obtained from this species for the first time. All the compounds were evaluated for antioxidant activity by four in vitro assays. Compounds 3-12 and 20 showed more potent 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity than l-ascorbic acid (l-AA). Compounds 2-23, 25, and 27 exhibited 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) radical cation scavenging activity superior to l-AA. The ferric reducing antioxidant powers (FRAP) of compounds 2-13, 17, and 19 were higher than l-AA. Further, eighteen compounds demonstrated cellular reactive oxygen species (ROS) scavenging activity, of which champaflavoside D (4), rhamnetin 3-O-neohesperidoside (8), quercetin 3-O-(6-O-E-p-coumaroyl)-neohesperidoside (9), and liquiritin (27) were more potent than curcumin. The results revealed that the renewable leaves of M. champaca are a rich source of flavonoids and antioxidants., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Potentially toxic element (PTE) pollution of urban soils has become the focus of social concern, but the differences of the sources, pollution levels and source-oriented human health risks (HHR) of PTE in urban soils among different urban intensity areas is rarely known. This study explored a comprehensive scheme that combined positive matrix factorization model and source-oriented assessment to quantitatively assess the priority pollution sources and HHR in urban soils from areas with different urbanization intensities. All the average values for PTE concentrations, except for Cr, were higher than their corresponding background values. The contributions made by the four sources (atmospheric deposition, agricultural activities, traffic activities, and natural sources) were relatively similar (22.29-29.89%) in the low urbanization intensity (LUI) area, whereas traffic activities and atmospheric deposition made the greatest contributions in the medium urbanization intensity (MUI) (29.12%) and the high urbanization intensity (HUI) (38.97%) areas, respectively. The geo-accumulation index results revealed that Cd was the most polluting element and the HUI area had the highest pollution levels. The content-oriented assessment of HHR demonstrated that the non-carcinogenic risks were acceptable, but the carcinogenic risks were unacceptable. According to the source-oriented HHR assessment, among the anthropogenic activities, atmospheric deposition contributed the most to carcinogenic risk of children in all areas, and atmospheric deposition, traffic activities and agricultural activities contributed the most to the carcinogenic risk of adults in HUI, MUI and LUI, respectively. This suggest that control measures need to be tailored to the appropriate urbanization intensity to effectively curb PTE pollution caused by anthropogenic activities., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)