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This study conducted a large root box experiment with Schefflera arboricola monoculture, Neolamarckia cadamba monoculture, and co-planting of Schefflera arboricola and Neolamarckia cadamba. The dynamic changes in Cu, Zn, Cd, and Hg contents in fresh and litter leaves of Schefflera arboricola and Neolamarckia cadamba and their litter leaves yield were analyzed for three months (September, October, and November 2020) after the surface application of 2% (W/W) sewage sludge (SS). The relationship between the heavy metal contents of fresh and litter leaves and the changes in the heavy metal return amount in litter leaves were further analyzed. The results were as follows: (1) N. cadamba had significantly higher Cu contents in fresh and litter leaves than those of S. arboricola, while had significantly lower Zn and Cd contents than those of S. arboricola. (2) The fresh leaves of S. arboricola had the lowest Zn content and the highest Hg content in November. (3) The fresh leaves of monoculture and co-planting Neolamarckia cadamba had the highest Zn, Cd, and Hg contents in November. (4) The Hg content in the litter leaves of co-planting of N. cadamba increased significantly with the time of SS application, while those of Cu, Zn, and Cd contents showed no significance. (5) The Cd content in fresh leaves was significantly and positively correlated with the Hg and Cd contents of litter leaves in Schefflera arboricola in both September and November. (6) The highest yield of litter leaves and the highest return amount of Cu, Zn, Cd, and Hg in S. arboricola occurred one month after SS application (September), while those in Neolamarckia cadamba occurred two months after SS application (October). In summary, the application time of SS showed a greater effect on the heavy metal contents in fresh leaves of N. cadamba and Schefflera arboricola than those in litter leaves; there was a positive correlation between the Cd content in the fresh leaves and the Cd and Hg contents in the litter leaves of S. arboricola; the heavy metal pollution risk of the litter leaves of S. arboricola and Neolamarckia cadamba was easy to occur in one month (September) and two months (October) after SS application, respectively. This study provides a reference for safe SS utilization and reasonable litter disposal in the landscape.

Co-application of sewage sludge (SS) with biochar in landscape/forestry soil is a common strategy for enhancing soil fertility and reducing the bioavailability of potential toxic elements (PTEs) derived from SS, such as Cd, Pb, Cu, Zn, and Ni. However, due to variability of biochar quality and uncertainties in responses of different plant species, whether the co-application benefits the landscape/forestry plant system remains elusive. Here, we tested the effectiveness of three types of biochar (SS-derived biochar (SB), rice straw-derived biochar (RB), and litter-derived biochar (LB)), which were added to soil amended with SS at 50% (w/w) at rates of 1.5%, 3%, and 4.5% as growth media for the landscape plant Aglaonema modestum (A. modestum). We analyzed the substrate's physicochemical properties and assessed the alleviation of phytotoxicity by biochar application. A significant increase in the fertility index of substrate was observed in all the treatments with biochar addition. The addition of biochar reduced the potential mobility of PTEs while increasing their residual fraction in media. Nonetheless, it has been found that the addition of biochar has ineffective or even negative effects on A. modestum growth (height, biomass, root length) and nutrient absorption. Importantly, the reduction in root biomass and the increased activity of root antioxidant enzymes (SOD, POD, CAT, and MDA) indicate contamination stress of biochar on the roots of A. modestum. Toxic elements of concern—namely Cu, Cd, and Pb—were not significantly higher in tissues of A. modestum saplings planted in biochar-SS-amended soil. However, elevated levels of other elements that may pose toxicity concerns, such as Ni and Zn, increased in tissues at high biochar dosages. Based on the Entropy–Weight TOPSIS method, it was further confirmed that compared to the treatment without biochar, all treatments except for 3.0% LB application resulted in poorer A. modestum comprehensive growth. Our results emphasize the need for detailed research on the response of specific plants to biochar in specific environments, including plant adaptability and the unexplored toxicity of biochar, to understand the large variations and mechanisms behind these ineffective or negative effects before the large-scale co-utilization of SS and biochar in landscape/forestry soils. [ABSTRACT FROM AUTHOR]

Coastal blue carbon (C) ecosystems are recognized as efficient natural C sinks and play key roles in mitigating global climate change. Microbially driven C, nitrogen (N) and sulphur (S) cycles are crucial for ecosystem functioning, but how microorganisms drive C sink formation and C sequestration in coastal sediments remains unclear.In this study, we conducted a comprehensive analysis of amino sugars, C, N and S cycling genes/pathways and their associated taxa in coastal sediments of native (Cyperus malaccensis and Kandelia obovata) and alien (Spartina alterniflora and Sonneratia apetala) vegetation.Compared to the alien‐vegetated coastal sediment, the native‐vegetated coastal sediment had significantly (p < 0.05) higher microbial necromass C and higher functional potentials of chemoautotrophic C fixation, C degradation, methane cycling, N2 fixation, S oxidation and sulphate reduction. Also, our analysis of coastal sediment microbiomes showed that S oxidation could be coupled with C fixation and/or nitrate/nitrite reduction. S oxidation, C degradation and C fixation were found to be key functional pathways for predicting sediment microbial necromass C. Additionally, the sulphur‐oxidizing Burkholderiales metagenome‐assembled genomes (MAGs) were a key functional group that dominated chemoautotrophic C fixation in coastal sediments.These results suggested that chemoautotrophic S oxidizers, in particular Burkholderiales with a novel lineage, might be the key microbial group that dominates microbial necromass C formation in coastal sediments through microbial anabolism (C fixation);the coupling of microbially driven C, N and S cycling processes; and the deposition of microbially derived C. This study provides novel insights into the importance of chemoautotrophic S oxidizers for microbial necromass formation and shed new light on the microbial mechanism of C sink formation in coastal ecosystems, which also has important implications for enhancing C sequestration in coastal wetlands. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]