Soil compaction restricts root development and resource acquisition, limiting tree establishment and productivity. Michelia macclurei is a valuable timber species that may encounter compacted soils in subtropical forestry. This study screened plant growth stimulator formulations for improving M. macclurei seedlings performance under a defined moderately compacted-soil condition. An L9 (34) orthogonal array experiment was conducted using potassium indole-3-butyric acid (IBA-K), sodium naphthaleneacetate (NAA-Na), potassium fulvic acid, and thiamine hydrochloride. Several formulations improved multiple growth and physiological traits. Among the tested treatments, T8 (50 mg·L−1 IBA-K, 40 mg·L−1 NAA-Na, and 300 mg·L−1 Thiamine hydrochloride) achieved the highest PCA-based composite score and ranked above the commercial rooting agent under the tested conditions. Compared with the untreated control, T8 increased shoot and root biomass by 185.74% and 227.87%, respectively, and increased shoot and root P concentrations by nearly 300% to 1.78 g·kg−1 and 232.99% to 1.95 g·kg−1, respectively. T8 also improved root morphology and photosynthetic traits and increased antioxidant enzyme activities, accompanied by lower malondialdehyde content. Intrinsic water-use efficiency did not differ significantly among treatments, while none of the PGS formulations significantly altered the root-to-shoot biomass ratio relative to the untreated control. Notably, these seedling responses occurred without detectable changes in the measured bulk-soil physical properties. Main-effect analysis indicated that NAA-Na was associated with responses across a relatively broad range of physiological domains within the tested formulation space. Overall, T8 was the highest-ranked formulation tested and represents a promising candidate for improving early M. macclurei seedling performance under the compacted-soil conditions examined.

Aims Restoring soil structure through stable aggregate formation is essential for reclaiming soils on abandoned rare earth element (REE) mine sites. Sludge amendment may improve soil aggregation, but its use is constrained by potential heavy metal (HM) risks. This study examined whether plant–sludge co-application can balance soil structure improvement with HM risk mitigation. Methods A pot experiment was conducted to evaluate the effects of sludge amendment and seven plant configurations on soil aggregation, aggregate-associated binding agents, functional groups, enzyme activities and HM availability in a REE mine soil. Results Sludge amendment and plant cultivation jointly promoted macroaggregate formation and aggregate stability. Among all treatments, sludge combined with Heptapleurum arboricola (S-H) was most effective, increasing water-stable macroaggregates by 30.72% and reducing aggregate destruction by 82.70% compared with the unamended control. High-aggregation treatments showed greater accumulation of soil organic matter, polysaccharides and glomalin-related soil protein, together with enrichment of O–H functional groups. Mantel tests and random forest analysis indicated that carbon fractions were the dominant drivers of aggregate stability, followed by organic binding agents and enzyme activities. Although sludge amendment alone increased total and DTPA-extractable Cu, Zn and Ni, plant cultivation reduced metal availability and alleviated the associated risk. Comprehensive evaluation identified S-H as the optimal treatment. Conclusion Co-applying sludge with suitable plant species can enhance soil aggregation while mitigating HM risks, providing a feasible strategy for REE mine soil restoration.

The application of sewage sludge (SS) to forest soils offers a valuable waste management solution, but heavy rainfall can significantly alter heavy metal (HMs) transport pathways, destabilize soil aggregates, and accelerate erosion, thereby enhancing pollution risks to water bodies. This study examines how different rainfall intensities (60, 90, 120, and 150 mm·h⁻¹) influence the migration of six HMs (Ni, Cd, Pb, Cr, Cu, Zn) in SS-amended subtropical forest soils, focusing on their distribution in surface runoff, interflow, and sediment. Through nine simulated rainfall experiments, we found that SS amendment elevated HMs concentrations across three migration pathways, with sediment accounting for over 91.0 % of cumulative HMs transport. As rainfall intensity rose from 60 to 150 mm·h⁻¹ , the mass proportion of < 0.05 mm aggregates decreased by 48.1-58.6 %, while that of ≥ 0.25 mm aggregates increased by 12.1-23.7 %. Under extreme rainfall (≥120 mm·h⁻¹), the comprehensive ecological risk from the three HMs transport pathways was "moderate", primarily attributable to sediment and Cd. However, when rainfall intensity was below 150 mm·h⁻¹ , the risks associated with runoff and interflow were negligible. Although SS application reduced interflow and sediment loss, it heightened HMs pollution, driven largely by Cd and fine aggregates. These findings underscore the importance of sediment-bound HMs dynamics, particularly Cd, in guiding the safe use of SS in subtropical forests under increasing rainfall intensity.

[Objective]To identify efficient and low-risk application methods of municipal sludge for im-proving soil structure at a rare earth element mining-disturbed site.[Method]A stratified incubation experi-ment was conducted by mixing municipal sludge with soil from a rare earth element mining-disturbed site.An L9(3⁴)orthogonal design was employed,involving four factors:sludge form(including 100％dried sludge,100％dewatered sludge,or a 50％dried+50％dewatered sludge mixture),water addition level(including 15％,20％,or 25％by volume),sludge application rate(including 10％,20％,or 30％by volume),and incubation time(in-cluding 30,60,or 90 d).Un-amended mining soil served as the control(CK).The effects of different treatments on soil aggregation and the bioavailability of heavy metals were analyzed.[Result]In the upper layer of the soils amended with mixed sludge,the proportions of>2 mm macroaggregates obtained through dry-and wet-sieving ranged from 23.93％-37.53％and 15.28％-25.80％,respectively.These represented a significant increase of 60.76％-157.94％and 120.17％-271.76％compared to the CK.The mean weight diameter(MWD)of the soil un-der dry-and wet-sieving conditions also increased significantly by 10.53％-34.21％and 20.48％-55.42％,re-spectively.The treatments exhibiting relatively better soil aggregation effects were the T6 treatment(application of 30％mixed sludge with 15％water,incubated for 60 d)and the T7 treatment(application of 30％dried sludge with 25％water,incubated for 90 d).Their Fourier Transform Infrared Spectroscopy(FTIR)spectra showed dif-ferences in characteristic peaks at 3 406 cm⁻¹(N-H),2 960-2 853 cm⁻¹(aliphatic C-H),1 655 cm⁻¹(C=O),and 1 384 cm⁻¹(C-H)compared to other treatments.Sludge application led to an increase in the concentrations of DTPA-extractable Cu,Zn,and Ni in the soil;however,the heavy metal concentrations in the T7 treatment were not significantly different from those in the unamended mining soil.Based on a comprehensive evaluation using a membership function analysis for both soil aggregation and heavy metal content,the top three treatments were the T6 treatment,the T7 treatment,and the T9 treatment(application of 10％mixed sludge with 20％wa-ter,incubated for 90 d).Main effect analysis indicated that sludge application rate and incubation time had a significant impact on soil aggregation.All four factors including sludge form,water addition level,sludge appli-cation rate,and incubation time had significant effects(P<0.05)on the bioavailability of soil heavy metals,with their combined interactions contributing 85.3％to 98.2％to the total variance.[Conclusion]The co-application of sludge promotes soil aggregation in REE mining-disturbed soil,but the effect is primarily influenced by the sludge application rate and incubation time.In this study,the co-application under the T7 condition-30％(by volume)dried sludge and 25％(by volume)water,followed by a 90-day incubation-can promote soil aggrega-tion in rare earth element mining-disturbed soil efficiently,with low heavy metal risk.The findings of this re-search are expected to provide a reference for the effective improvement of soil structure in mining-disturbed sites and the resource utilization of municipal sludge.

Promoting soil structure is considered an essential prerequisite for abandoned mine land restoration. Sewage sludge (SS) has the potential to improve soil structure. However, traditional SS application to improve soil structure requires a lot of SS, potentially exacerbating heavy metal (HM) contamination. To find an effective way to improve abandoned rare-earth mine land soil (ARLS) aggregation, we wall-broke SS and conducted an L9 (34) orthogonal design soil incubation experiment with four factors, including SS form (wall-breaking dewatered or composted SS, WBSS), water addition volume, volume ratio of WBSS to soil, and incubation time, and evaluated their effects on aggregation ability and HM availability in ARLS. The results showed that WBSS addition improved ARLS aggregation by increasing the percentage of >2 mm water-stable aggregates (by 4.53%-187.23%), mean weight diameter (by 19.18%-58.90%), and geometric mean diameter (by 23.81%-95.24%) not only in the WBSS-mixing layer but also the layer without mixed with WBSS but under the WBSS-mixing layer. These aggregate characteristic indicators positively correlated with organic matter content. Adding WBSS under a suitable condition (20% wall-breaking mixed SS or composted SS addition, 100 or 150 mL water addition, and incubation for 30 or 60 days) could produce high cementing substances (hydroxyl and carboxyl groups and mineral-associated organic carbon) but release low content of active HM. Treatment of 20% wall-breaking mixed SS addition, 150 mL water addition, and incubation for 30 days had the highest subordinate function values of aggregation ability. This treatment was more suitable for safely improving mining soil aggregation than other treatments. These results suggested that wall-breaking SS addition with suitable conditions had the potential to improve the mining soil structure.

[Objective]To investigate the effects of drought stress on the growth and physiological characteristics of Chukrasia tabularis,and reveal the physiological response mechanism of C.tabularis seedlings to adapt to drought environments.[Method]Taking half-year-old C.tabularis seedlings as the research subjects,four treatments were set up:Light drought(65%-70%of field water capacity),moderate drought(50%-55%of field water capacity),severe drought(35%-40%of field water capacity),and control(80%-85%of field water capacity).The growth indicators,photosynthetic parameters,and physiological characteristics of C.tabularis seedlings were measured.[Result]Moderate and severe drought significantly reduced the plant height growth,leaf width,leaf length and leaf area of C.tabularis seedlings(P<0.05),while light drought promoted root growth.The root length(1103.24 cm)and root volume(2.53 cm3)were significantly higher than those of the control(P<0.05).With the increase of stress intensity,the net photosynthetic rate,stomatal conductance,intercellular CO2 concentration,transpiration rate,and chlorophyll content of C.tabularis seedlings all showed a trend of first increasing and then decreasing,reaching the maximum values under light drought.The proline content reached the maximum value under severe drought,significantly higher than that in the control(P<0.05).The contents of soluble protein and malondialdehyde(MDA),as well as the activities of peroxidase(POD)and superoxide dismutase(SOD)in all drought treatment groups were not significantly different from those in the control.[Conclusion]A field water capacity of 65%-70%facilitates root growth,biomass accumulation,and enhances photosynthetic efficiency in C.tabularis seedlings,indicating that appropriate drought is generally advantageous for the growth of C.tabularis seedlings.

Abstract Sewage sludge (SS) application to forest plantation soils as a fertilizer and/or soil amendment is increasingly adopted in plantation forest management. However, the potential risks of SS-derived heavy metals (HMs) remain a concern. Many factors, including woodland slope may affect the risks, but the understanding of this issue is limited. This research evaluated the HMs migration via surface runoff, interflow, and sediments when SS was applied in woodlands of varying slopes. We conducted indoor rainfall simulations and natural rainfall experiments to clarify the effect of slope on the migration of HMs via runoff (including surface and interflow) and sediments. In the simulated rainfall experiment, HMs lost via sediments increased by 9.79–27.28% when the slope increased from 5° to 25°. However, in the natural rainfall experiment, when the slope of forested land increased from 7° to 23°, HMs lost via surface runoff increased by 2.38% to 6.13%. These results indciate that the surface runoff water on a high slope (25°) posed high water quality pollution risks. The migration of HMs via surface runoff water or interflow increased as the steepness of the slope increased. The total migration of Cu, Zn, Pb, Ni, Cr and Cd via sediment greatly exceeded that via surface runoff and interflow. Particles ≤ 0.05 mm contributed the most to the ecological risks posed by sediments. Cd was the main source of potential ecological risks in sediments under both experimental conditions.

The environmental risks of migration of heavy metals (HMs) following applications of sewage sludge (SS) to forest soils are garnering increased attention. Plant litter at the forest floor may modify HM migration pathways through impacts on soil aggregates and water/soil erosion; however, HM migration responses to plant litter are poorly understood. The aim of this study was to determine the effects of plant litter cover on HMs migration, and water and soil erosion following the application of SS to subtropical forest soils. Effects of addition of SS along and SS plus plant litter at 0.75 or 1.5 kg m(-2) on the migration of cadmium, chromium, copper, nickel, lead, and zinc in surface runoff, soil interflow, and sediments were quantified across nine simulated rainfall events in a laboratory experiment and following natural intense rain events in a field experiment. Addition of SS elevated HM concentrations in surface runoff by 38.7 to 98.5%, in soil interflow by 48.3 to 312.5%, and in sediment by 28.5 to 149.4 %, and increased the production of sediment aggregates <0.05 mm that led to greater cumulative migrations of HMs in surface runoff and sediment; sediment accounted for 89.5 % of HM migrations. Addition of plant litter reduced cumulative migration of HMs by 87.1-97.27 %; however, the higher rate of plant litter led to a decrease in surface runoff and sediment yield, and an increase in soil interflow. Addition of plant litter shifted the main pathway of HM migration from sediment to surface runoff and soil interflow. The potential ecological HM risk index was "low" for each treatment. We found consistency in HM concentrations and migrations via surface runoff between the field and laboratory experiments. Overall, the addition of plant litter with SS mitigated soil erosion and reduced total migration of HMs, resulting in a 88.7-97.3 % decrease in the ecological risk index of the six HMs. We conclude that the addition of plant litter may provide a management strategy for the mitigation of HM risks to environmental safety for the disposal of SS in subtropical forest systems.

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.

Heavy metals (HMs)-induced iron (Fe) deficiency severely inhibits plant growth and thus hampers phytoremediation and revegetation in HMs-contaminated soil. We conducted a 12-month pot experiment to investigate the effects and mechanisms of co-planting on altering plant HM-induced Fe deficiency. The landscape tree Ilex rotunda was co-planted with Ficus microcarpa and Talipariti tiliaceum in sludge-amended soil. The responses of I. rotunda growth, ele-ments uptake, and rhizosphere microbial community and metabolites were analyzed. The addition of sludge increased cadmium (Cd), zinc (Zn), and nickel (Ni) uptake and induced Fe deficiency-induced chlorosis in I. rotunda. This chlo-rosis was exacerbated when I. rotunda was co-planted with F. macrocarpa due to the increase in the abundance of sul-fate reduction or Fe immobilization-associated bacteria and the relative level of isoprenyl alcohol and atropine in I. rotunda rhizosphere but the decrease in the contents of soil diethylenetriaminepentaacetic acid Fe (DTPA-Fe) (-16.19 %). Co-planting with T. tiliaceum or F. macrocarpa and T. tiliaceum decreased the contents of total or DTPA Zn/Cd/Ni in the soil while increased the contents of soil DTPA-Fe by 13.24 % or 11.34 % and the abundance of mi-crobes which contributed to immobilizing HMs or activating Fe reduction, and then alleviated the chlorosis and the growth inhibition of I. rotunda. These results provide a new perspective on the phytoremediation and revegetation of HMs-contaminated soil.

挖掘农林专业课程中家国情怀元素,并将其有机融入专业课程教学过程,巧妙而有效地开展"课程思政",是协助思政课推进农林专业爱国情怀教育的重要途径.在农林专业中推进爱国情怀教育,需要抓住自尊和自信在学生情感形成中的作用,注重隐性引导、由感性生发理性和知行合一.

Urban greening produces a large amount of garden waste, and the pyrolysis of garden waste into biochar is an effective waste management technology. Biochar has a large specific surface area and soil remediation ability. However, the knowledge about the co-recycling of sewage sludge and garden waste biochar to improve the growth of Monstera deliciosa needs to be highlighted. Therefore, we conducted a pot experiment by applying Ficus altissima litter-derived biochar (FB) at rates of 0, 1.5, and 3.0% (w/w, CK, FB1.5, and FB3) in soil amended with sewage sludge at 50% (w/w), to improve the soil properties, and further analyzed the effects of FB on growth and heavy metals (HMs) uptake of landscape plant M. deliciosa. Results showed in comparison with control setups, the addition of 3% FB treatment in sewage sludge amended soil improved the soil properties and significantly increased M. deliciosa dry weight (86.75%), root: shoot ratio (73.23%), N (99.44%), P (116.13%), K (124.40%), Pb (78.81%), and Cu (159.01%) accumulation respectively. In summary, FB3 treatment achieved the best effects in promoting plant growth and soil remediation. These findings revealed that sewage sludge and garden waste biochar could be recycled as amendments for poor acid soils under restoration, a sustainable development path for urban waste disposal.

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.

为探讨不同原料生物炭对污泥-土壤混合基质理化性质和在该基质中种植的园林植物生长的影响,采用盆栽试验,以污泥和土壤(质量比1∶1)混合物为栽培基质(CK),研究污泥生物炭(SB)、凋落物生物炭(LB)和水稻秸秆生物炭(RB)添加(按照基质质量的4.5％添加)对基质理化性质、有效态重金属含量以及蓝花草(Ruellia simplex)生长的影响.结果表明:与CK(基质中不添加生物炭)相比,3种生物炭均降低基质容重,提高总孔隙度和毛管持水量,对基质pH影响不显著.SB显著增加基质全P含量,降低速效P含量,LB显著提高有机质、全N、全P、碱解N、速效K含量,降低速效P含量,RB显著提高全P、全K、速效P、速效K含量.对于有效态重金属,SB显著降低有效态Cd、Pb、Cu、Zn、Ni含量,而LB和RB仅显著降低有效态Cu含量.3种生物炭均显著促进蓝花草根系生长及对N、K的吸收,SB还显著提高蓝花草地上部生物量及对P的吸收.模糊隶属函数显示,对基质改良和植物生长影响的综合评价排序为SB>LB>RB>CK.综上,在污泥园林利用中添加污泥生物炭、凋落物生物炭和水稻秸秆生物炭均可有效提升土壤质量,促进园林植物生长,其中污泥生物炭的综合改良效果最佳.

为了解粤北英德白沙稀土矿迹地周边农田土壤重金属的生态和风险情况,采集当地农田土壤样品45份,测定Cd、Cr、Cu、Pb、Hg、As的含量,利用单因子污染指数评价法、内梅罗污染指数评价法、Hakanson潜在生态风险指数法评价该区域重金属的污染程度.结果表明,农田土壤Pb、Cd的平均值是广东省土壤背景值2.12倍、1.47倍,Pb的土壤样品中有64％超过重金属风险筛选值.由单因子污染指数可知,Pb属中等污染,Cd属轻污染,Hg属警戒线污染,Cu、Cr、As属安全等级;由内梅罗综合污染指数可知,土壤整体属于轻度污染水平.通过Hakanson潜在生态风险评价结果可知,Cd具有中等生态风险,Cu、Pb、Cr、As、Hg为低生态风险,土壤整体处于低生态风险水平.各种评价结果表明英德白沙稀土矿迹地周边农田土壤存在一定生态风险,Pb和Cr是农田土壤污染风险的主要贡献因子,需引起相关部门重视或采取一定的土壤污染风险管控措施.

[目的]分析表施和混施污泥对鹅掌藤Schefflera arboricola根系生长和重金属吸收的影响,深入认识污泥施用对园林植物根系生长的影响,为污泥在园林中安全利用提供借鉴.[方法]采用根箱试验,观测不施、表施和混施 10％(w)污泥对常见园林植物鹅掌藤的不同土层根系形态及土壤pH和电导率动态变化的影响,分析根组织密度、根密度和重金属含量,拟合土壤pH、电导率、根系重金属含量与根长的关系.[结果]与不施污泥相比,混施污泥明显抑制鹅掌藤根长、根表面积和根密度增长;而表施污泥显著增加鹅掌藤 0～20 cm土层的总根长、根体积和根密度.处理 240 d后,混施污泥处理的 0～20 与 20～40 cm土层总根长分别为不施污泥的 66.37％和51.51％,而表施污泥处理分别为不施污泥的 115.43％和 98.66％.最大总根长、根体积和根密度均出现在表施污泥的 0～20 cm土层,最大根干质量和根组织密度出现在表施污泥的污泥层.混施污泥显著提高了土壤pH和电导率以及植株重金属含量,不同土层根系Cd、Zn、Cu和Ni含量分别是不施污泥的 2.32～11.70 倍.线性回归拟合分析表明,不施和表施污泥处理的 0～20 cm土层鹅掌藤原位扫描总根长均与原位测定土壤pH呈极显著正相关(P＜0.001),鹅掌藤总根长与根系Cd、Zn、Cu和Ni含量均呈极显著负相关(P＜0.001).[结论]表施 10％(w)污泥可以提高土壤pH并促进鹅掌藤根系生长.混施 10％(w)污泥显著增加不同土层根系重金属含量,进而抑制鹅掌藤根系生长.

【Objective】To explore the effects of different addition amounts of litter biochar on the growth， heavy metal absorption and accumulation of Ruellia simplex planted in the sludge + soil mixed matrix （mass ratio 1∶1）， and provide a reference for the resource utilization of municipal sludge and garden waste.【Method】A pot experiment was conducted to analyze the effects of adding 0% （CK）， 1.5% (F 1.5 )， 3% (F 3.0 ) and 4.5% (F 4.5 ) of litter biochar on the growth， root morphology， physiology， nutrient and heavy metal uptake and accumulation of Ruellia simplex.【Result】Compared with CK， F 1.5 significantly increased plant height， root biomass， shoot biomass and whole plant biomass. The plant biomass decreased gradually with the increase of biochar addition， and the biomass of F 4.5 was significantly lower than that of CK， showing the characteristic of "low promotion and high inhibition". The total root length， root surface area， average diameter and root volume of Ruellia simplex reached the maximum in F 1.5 treatment， and all of them gradually decreased with the increase of biochar addition. Among all treatments， the contents of soluble protein and malondialdehyde （MDA） in roots of F 1.5 were the lowest， and the content of superoxide dismutase （SOD） was the highest. The SOD contents of roots showed a downward trend with the increase of biochar addition， while the change trends of soluble protein and MDA contents were opposite. Compared with CK， all treatments increased the uptakes of N， P， and K of R. simplex shoots and roots to different degrees， reduced the contents of Cd and Cu in R. simplex plant to different degrees， and increased the Pb and Ni contents. The accumulative amounts of N， P， K， Cd， Cu， and Pb in R. simplex plant showed a downward trend with the increase of biochar addition， and the accumulative amounts of N， P， K， Cd， Cu， Pb and Ni treated with F 1.5 were significantly higher than those of CK.【Conclusion】The addition of 1.5% litter biochar significantly promoted R. simplex growth， the absorption and accumulation of Pb， Cu， Cd and Ni， but excessive addition would inhibit plant growth and affect the repair effect of substrate. Therefore， the applied amount of biochar should be controlled reasonably in the practical application process.

Woodland utilization is a promising disposal method for sewage sludge (SS). However, the potential risk of heavy metals (HMs) transport with runoff must be considered. Among the various factors influencing HMs loss, SS application methods (Holing application, HA; Broadcasting and mixing application, BM; Broadcasting application, BA) are likely to cause significant effects by altering soil erosion and soil aggregates. This study aimed to determine how SS application methods affect HMs loss, soil aggregates erosion, and how they are related. Accordingly, the losses of HMs in surface runoff, interflow, and sediment were quantified during six simulated rainfalls. The results demonstrated that all methods reduced surface runoff, but BA was the most effective. Additionally, BA significantly reduced the total sediment yield and the total proportion of the <0.05 mm fraction aggregates. Moreover, BA had the smallest cumulative losses of Pb and Cd through surface runoff and Cu, Pb, and Cd through sediment. Sediment was the most important pathway for HMs loss, through which over 76.56 % of HMs were lost. In BA, the <0.05 mm fraction aggregates had the lowest HMs load, whereas in other treatments had the highest (54.33 %-80.33 %). The potential ecological risk coefficient of Cd was beyond "moderate" in all the pathways of BM and "high" in the interflow of each SS treatment. Nonetheless, when the multi-elements were evaluated collectively, the potential ecological risk index for each SS treatment was categorized as "low". Overall, BA not only reduced soil erosion but also posed no risk of HMs pollution. It should be noted that the loss of Cd in the interflow had a great impact, while the <0.05 mm fraction aggregates played a significant role in the HMs load. Thus, the current study not only provides an effective approach for the environmentally safe disposal of SS but also proposes a scientific method for the application of SS in woodlands.

PurposePoor 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 methodsSSC (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.ResultsThe 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.ConclusionThese 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.