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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]

Purpose: Poor structure, nutrient deficiency, and acidification are core factors restricting the reclamation of rare earth mining wasteland soil (REMWS). Sewage sludge, bagasse, and molybdenum tailings, all of which need proper disposal, have great potentials in REMWS reclamation. The goal of this study was to explore the remediation effect on rare earth mining wasteland soil with the combined application of sewage sludge compost (SSC), bagasse, and modified molybdenum tailings (MMT). Materials and methods: SSC (T1), SSC + bagasse (T2), and SSC + bagasse + MMT (T3) were applied in REMWS as amendments in a 4-month pot experiment, and their effects on REMWS properties and heavy metals (HMs) toxicity were tested with Eucalyptus urophylla, which grows fast, resists environment stress, and is a promising plant in REMWS reclamation. Results: The application of SSC (T1) improved REMWS fertility, but increased Cu, Zn, Cd, and Ni contents in soil and E. urophylla seedlings, and inhibited E. urophylla growth. Bagasse application (T2) alleviated growth inhibition and further addition of bagasse + MMT (T3) significantly improved E. urophylla growth. Moreover, T3 improved soil physical properties, organic carbon content, pH, and reduced soil HMs bioavailability and plant HMs content as compared to T1 and T2. Structural equation modeling results revealed that plant nutrient accumulation increased plant HMs accumulation, the latter inhibited plant nutrient accumulation in turn, and soil pH played a key role in retarding HMs uptake and improving E. urophylla growth and nutrients uptake. Conclusion: These results suggested that the combined application of SSC, bagasse, and MMT is an effective approach for REMWS amelioration and land disposal of solid waste resources. [ABSTRACT FROM AUTHOR]

Landscape plants have great potentials in heavy metals (HMs) removal as sewage sludge compost (SSC) is increasingly used in urban forestry. We hypothesize that woody plants might perform better in HMs phytoremediation because they have greater biomass and deeper roots than herbaceous plants. We tested the differences in growth responses and HMs phytoremediation among several herbaceous and woody species growing under different SSC concentrations through pot experiments. The mixing percentage of SSC with soil at 0%, 15%, 30%, 60, and 100% were used as growth substrate for three woody (Ficus altissima Bl., Neolamarckia cadamba (Roxb.) Bosser, and Bischofia javanica Bl.) and two herbaceous (Alocasia macrorrhiza (L.) G. Don and Dianella ensifolia (L.) DC) plants. Results showed that the biomass, relative growth rate, and nutrient uptake for all plants increased significantly at each SSC concentration compared to the control; woody plants had higher biomass and nutrient use efficiency than herbaceous plants. All plants growing in SSC-amended soils accumulated appreciable amounts of HMs and reduced the contents of HMs present in the substrates. The woody plants were generally more effective than herbaceous plants in potentials of HMs phytoextraction, but A. macrorrhiza showed higher bioconcentration and translocation of Cu and Zn and D. ensifolia had higher bioconcentration and translocation of Cd than woody plants. The optimal application concentrations were 30% or less for woody plants and 15% for herbaceous plants for plant growth and ecological risk control, respectively. Intercropping suitable woody and herbaceous landscape plants in urban forestry might have promising potentials to minimize the ecological risks in the phytoremediation of SSC. [ABSTRACT FROM AUTHOR]

The ecological effects of eucalypt plantations (EPs) have garnered increasing attention. To understand their effect on soil quality at a landscape scale, and to determine whether soil quality parameters differ due to different stand types, we evaluated soil characteristics in twenty-one groups of EPs, Pinus massoniana Lamb. plantations (PMPs) and natural broadleaved forests (NBFs) across Guangdong Province, China. Both the physical characteristics of soil hydrology and the properties of soil nutrients in A and B horizons were determined. Results showed that, compared to NBFs, EPs and PMPs produced a shallower litter layer, reduced canopy density, higher soil bulk density, significantly lower total porosity, non-capillary porosity, total water volume, and hygroscopic water in the A horizon (P < 0.05). Moreover, total N, available K, and soil organic carbon (SOC) in EPs and PMPs were significantly lower than in NBFs. EPs and PMPs did not differ significantly in N, P or K content, but PMPs had significantly lower SOC and boron in the A horizon than EPs. Low pH and poor capacity to buffer acidification generally occurred in all cover types. Both EPs and PMPs showed a decline in soil properties relative to NBFs, but EPs and PMPs exhibited no significant difference. These results indicate that actions are needed to ameliorate the potential negative effects on soil quality in forestry plantations. [ABSTRACT FROM AUTHOR]

Purpose: Chinese fir ( Cunninghamia lanceolata (Lamb.) Hook) is an important native tree species in China. Consecutive cropping traditionally occurs in Chinese fir plantations (CFPs), but this practice has resulted in productivity declines in subsequent rotations. This study was designed to better understand the change of soil properties in the continuous cropping CFPs. Materials and methods: We investigated soil pH, soil organic matter (SOM), and nutrient contents in different soil layers and in rhizosphere soil (RS) and non-rhizosphere soil (NRS) under CFPs of different ages and in different rotations. Results and discussion: In the upper (0-20 cm) soil layer, soil pH decreased, while SOM increased, beneath mature CFPs with consecutive rotations. Total nitrogen (TN), available potassium, and available phosphorus contents in the upper soil layers did not differ significantly with consecutive rotations. Soil pH in RS was significantly lower than in NRS under mature plantations of the third rotation. Soil organic matter, TN, and available nitrogen did not differ between RS and NRS. Available phosphorus in RS was consistently lower than in NRS, and was highly deficient in the third rotation. Conclusions: We conclude that no severe soil nutrient degradation occurred in the continuous cropping CFPs examined in this study, with soil acidification and phosphorus deficiency being two primary problems observed. [ABSTRACT FROM AUTHOR]

WRKY transcription factors play important roles in responses to environmental stress stimuli. Using a genome-wide domain analysis, we identified 287 WRKY genes with 343 WRKY domains in the sequenced genome of Brassica napus, 139 in the A sub-genome and 148 in the C sub-genome. These genes were classified into eight groups based on phylogenetic analysis. In the 343 WRKY domains, a total of 26 members showed divergence in the WRKY domain, and 21 belonged to group I. This finding suggested that WRKY genes in group I are more active and variable compared with genes in other groups. Using genome-wide identification and analysis of the WRKY gene family in Brassica napus, we observed genome duplication, chromosomal/segmental duplications and tandem duplication. All of these duplications contributed to the expansion of the WRKY gene family. The duplicate segments that were detected indicated that genome duplication events occurred in the two diploid progenitors B. rapa and B. olearecea before they combined to form B. napus. Analysis of the public microarray database and EST database for B. napus indicated that 74 WRKY genes were induced or preferentially expressed under stress conditions. According to the public QTL data, we identified 77 WRKY genes in 31 QTL regions related to various stress tolerance. We further evaluated the expression of 26 BnaWRKY genes under multiple stresses by qRT-PCR. Most of the genes were induced by low temperature, salinity and drought stress, indicating that the WRKYs play important roles in B. napus stress responses. Further, three BnaWRKY genes were strongly responsive to the three multiple stresses simultaneously, which suggests that these 3 WRKY may have multi-functional roles in stress tolerance and can potentially be used in breeding new rapeseed cultivars. We also found six tandem repeat pairs exhibiting similar expression profiles under the various stress conditions, and three pairs were mapped in the stress related QTL regions, indicating tandem duplicate WRKYs in the adaptive responses to environmental stimuli during the evolution process. Our results provide a framework for future studies regarding the function of WRKY genes in response to stress in B. napus. [ABSTRACT FROM AUTHOR]

Overexpression of OsPIN2 reduces Al-induced formation of reactive oxygen species, weakens lipid peroxidation and lignification, and thus enhances Al tolerance of rice seedlings.Al-induced cell rigidity is one of the symptoms of Al toxicity, but the mechanism by which plants tolerate this toxicity is still unclear. In this study, we found that overexpression of OsPIN2, an auxin transporter gene, could alleviate Al-induced cell rigidity in rice root apices. A freeze–thawing experiment showed that the Al-treated roots of wild-type (WT) plants had more damage in the epidermal and outer cortex cells than that found in lines overexpressing OsPIN2 (OXs), and the freeze-disrupt coefficient was 2-fold higher in the former than in the latter. Furthermore, Al could induce aberrations of the cell wall–plasma membrane interface, which was more prominent in the epidermal cells of the elongation zone of the WT. Overexpressed OsPIN2 reduced Al-induced formation of reactive oxygen species and weakened Al-induced lipid peroxidation and lignification in roots. Compared with WT, a 16.6–32.6% lower Al-triggered hemicellulose 1 accumulation was observed in root apices of OXs, and 17.4–20.5% less Al accumulated in the cell wall of OXs. Furthermore, overexpression of OsPIN2 ameliorated the Al inhibitory effect on basipetal auxin transport and increased Al-induced IAA and proton release. Taken together, our results suggest that by decreasing the binding of Al to the cell wall and Al-targeted oxidative cellular damage, OXs lines show less Al-induced damage. By modulating PIN2-based auxin transport, IAA efflux, and cell wall acidification, lines overexpressing OsPIN2 alleviate Al-induced cell rigidity in the rice root apex. [ABSTRACT FROM PUBLISHER]

Al-activated organic acid transporter genes ( ALMT and MATE) and plasma membrane H-ATPase gene ( PHA) are known to contribute to the regulation of organic acid secretion in several crops. However, it remains unclear how these genes interact to modulate organic acid exudation in the same plant species. In this study, Al-induced expression of genes ( GmALMT1, GmMATE1 and GmPHA1), secretion of organic acid and root elongation were characterized in soybean roots. Results indicated that treatment with 50 μM Al activated the expression of GmALMT1, GmMATE1 and GmPHA1, and the exudation of citrate and malate significantly in apical 5 mm region of soybean seedlings, but inhibited root elongation by 57.8 %. The highest malate exudation rate and the maximal expression of GmALMT1 and GmPHA1 were observed after 2 h of 50 μM Al treatment, while the corresponding values for citrate exudation rate and GmMATE1 expression occurred at 8 h. The exudation of malate and citrate contributed to but could not recover Al-triggered root elongation. A root-split experiment indicated that Al-activated gene expression, organic acid secretion and root growth inhibition required the direct contact of Al. The removal of shoots in soybean seedlings decreased Al-activated gene expression by 26.1-40.5 %, and secretion of organic acid by 14.7-40.2 %. Furthermore, shoot excision aggravated Al-inhibited root elongation, indicating the existence of other Al tolerance mechanism except the exudation of organic acid. These results suggested that Al-activated expression of GmPHA1-, GmMATE1- and GmALMT1-mediated exudation of malate and citrate, and shoots played an important role in Al toxicity resistance in soybean roots. [ABSTRACT FROM AUTHOR]

Silicate (Si) can enhance plant resistance or tolerance to the toxicity of heavy metals. However, it remains unclear whether Si can ameliorate lead (Pb) toxicity in banana ( Musa xparadisiaca) roots. In this study, treatment with 800 mg kg Pb decreased both the shoot and root weight of banana seedlings. The amendment of 800 mg kg Si (sodium metasilicate, NaSiO·9HO) to the Pb-contaminated soil enhanced banana biomass at two growth stages significantly. The amendment of 800 mg kg Si significantly increased soil pH and decreased exchangeable Pb, thus reducing soil Pb availability, while Si addition of 100 mg kg did not influence soil pH. Results from Pb fractionation analysis indicated that more Pb were in the form of carbonate and residual-bound fractions in the Si-amended Pb-contaminated soils. The ratio of Pb-bound carbonate to the total Pb tended to increase with increasing growth stages. Treatment with 100 mg kg Si had smaller effects on Pb forms in the Si-amended soils than that of 800 mg kg Si. Pb treatment decreased the xylem sap greatly, but the addition of Si at both levels increased xylem sap and reduced Pb concentration in xylem sap significantly in the Si-amended Pb treatments. The addition of Si increased the activities of POD, SOD, and CAT in banana roots by 14.2% to 72.1% in the Si-amended Pb treatments. The results suggested that Si-enhanced tolerance to Pb toxicity in banana seedlings was associated with Pb immobilization in the soils, the decrease of Pb transport from roots to shoots, and Si-mediated detoxification of Pb in the plants. [ABSTRACT FROM AUTHOR]