腐殖酸对农田土壤磷素吸附行为的影响研究

土壤有机腐殖酸类物质具有巨大的比表面积和表面活化基团,在土壤污染物和养分的吸附、利用和转化过程中起着重要作用。该研究选取5种中国典型农区土壤,采用增加和减少有机腐殖酸类物质含量的方法,设置不同含量梯度,利用振荡平衡法来定量研究不同腐殖酸含量对磷素吸附特性的影响,并对其利用Freundlich、Langumuir和Temkin方程来进行定量化拟合分析研究,试图定量探讨有机腐殖酸类物质对磷素吸附行为的影响。研究结果表明:Freundlich、Langumuir和Temkin这3种方程均可对磷素吸附特征进行拟合,但拟合相关性以Freundlich最好,对于不同土壤而言,对磷素吸附拟合方程的适应性,以Freundlich方程对黑土和红土最好,塿土和黑垆土次之,潮土最差。加入腐殖酸明显地减少土壤对磷素的吸附量和吸附速率。腐殖酸对于土壤磷素有一定的活化激发作用,无论是增加还是减少腐殖酸时,黑土和红土对磷素的最大吸附量变化比例不是很大,而塿土和黑垆土变化最大,可以减少50%～60%左右,而潮土次之。腐殖酸可作为土壤P素增效剂,改善肥料物理性状,提高其稳定性和有效性,尤其是在黄土高原石灰性土更为有效。     

作物秸秆碳在土壤中分解和转化规律的研究

采用14C标记秸秆,在大田和实验室的研究结果表明,秸秆的分解速率主要取决于C/N比。施入土壤后,土壤微生物迅速增加,尤其是细菌。秸秆降解首先形成非结构物质,其中大部分转化为富里酸,进而转化为胡敏酸。分解产物对土壤腐殖质的更新,从腐殖质表面官能团或分子断片开始,逐步进行。非结构物质可与腐殖酸的单个分子产生交联作用,在一定条件下,交联的复合分子可进入腐殖质分子核心的成分中。腐殖酸单个组分在土壤中的转化和重新分配,仅仅与腐殖质表面官能团的反交换过程密切相关。粘土矿物选择性吸附胡敏酸,而且优先吸附胡敏酸中低分子成分。     

土著菌群与蚯蚓肠道菌群共享核心物种协同抵御灭蚁灵胁迫研究

摘 要：灭蚁灵是一类高毒性的有机氯农药，当灭蚁灵通过直接或间接的人为途径进入到土壤生态环境系统后，会对生物体产生显著的毒害作用。土著菌群与蚯蚓肠道菌群都是对外源农药极其敏锐的感知受体，然而，它们对于抵御灭蚁灵毒害作用的微生物响应机制尚不清楚，值得探究。因而，本研究采集实际场地中不同梯度浓度（0~27.7 mg/kg）灭蚁灵污染土壤，设置蚯蚓土培实验，采用高通量测序技术，分析蚯蚓肠道菌群和土著菌群的结构和功能；通过MetagenomeSeq分析、LEfSe（Linear Discriminant Analysis Effect Size）分析和随机森林（Random Forests）分析以及网络分析，识别其核心类群。发现：1）灭蚁灵胁迫下蚯蚓肠道菌群相较之土著菌群的结构、组成受到的扰动更显著（p < 0.05）；2）不同梯度灭蚁灵胁迫下，蚯蚓肠道菌群和土著菌群组合存在稳定的核心物种，主要为气单胞菌属（Aeromonas）、黄杆菌属（Flavobacterium）、盖勒氏菌属（Gallerella）、微枝形杆菌属（Microvirga）、地杆菌属（Pedobacter）、亨氏菌（Ramlibacter）、Zavarzinella；3）这些核心种群在互作网络的平均度中心性、紧密中心性、特征向量中心性分别为136.72、0.44、0.52，均高于非核心种群的对应指标（91.52、0.42、0.33），表明核心种群具有更高的网络连通性，且此类核心种群具有碳氮转化和农药降解能力，说明蚯蚓肠道菌群和土著菌群可以通过共享核心物种与其它微生物联系紧密，具备发挥农药降解代谢的潜在功能，实现协同抵御土壤中灭蚁灵胁迫。本研究结果可为探明土著菌群与蚯蚓肠道菌群共享核心物种在抵御土壤中有机氯农药毒害作用的协同机制，提供新的科学认识。     

接种蚯蚓和食细菌线虫对红壤性状及花生产量的影响

通过温室花生盆栽试验研究了接种有益土壤动物(蚯蚓和食细菌线虫)对旱地红壤生物学性质(微生物生物量碳氮、基础呼吸、微生物熵、脲酶和酸性磷酸酶活性)、土壤速效养分(碱解氮和速效磷)及花生产量的影响.试验包含4个处理:不接种处理(CK)、仅接种蚯蚓(E)、仅接种食细菌线虫(N)、联合接种蚯蚓和食细菌线虫(EN).结果表明:①蚯蚓和食细菌线虫均提高了土壤微生物生物量碳氮的含量,线虫对微生物生物量碳的贡献大于蚯蚓.②除花生成熟期的接种蚯蚓处理外,接种蚯蚓和食细菌线虫后土壤基础呼吸均有所增加,且食细菌线虫的影响也大于蚯蚓.③除花生结荚期无显著性差异外,蚯蚓和食细菌线虫均极显著提高了土壤脲酶和酸性磷酸酶活性(P＜0.05).④蚯蚓和食细菌线虫均能增加土壤速效磷和碱解氮含量.⑤接种蚯蚓和食细菌线虫后花生产量的增幅为17％～ 20％.总之,在4个花生生长时期,相对于不接种的对照处理,接种蚯蚓和食细菌线虫能明显改善红壤性状并最终提高花生产量.     

蚯蚓对土壤碳氮循环关键过程的影响及其机制研究进展

蚯蚓作为典型的大型土壤动物,对土壤结构和功能的形成具有重要的影响,被称作土壤生态系统工程师。国内外关于蚯蚓对土壤理化性质、土壤微生物群落组成、有机质分解和土壤矿化等方面的研究较多,但其对土壤碳、氮循环关键过程的系统总结较少。本文总结了蚯蚓通过摄食、挖洞、产生蚓粪及促进团聚体形成等活动对土壤碳氮循环产生的直接影响,及对微生物活性产生的间接影响;系统总结了蚯蚓对土壤有机质分解、碳氮矿化和反硝化的影响及其机制。在全球变化背景下,未来应更加重视建立定量模型评估蚯蚓对土壤有机碳库的影响,系统研究蚯蚓与微生物以及其他驱动因子相互作用对碳氮循环关键过程的影响,与人类活动相结合开展多因素、多水平研究。研究方法上应综合应用同位素和分子生物学等研究手段,并结合室内控制与长期野外模拟试验。     

木质素与蚯蚓对黑麦草生物量及土壤微生物群落的影响

采集农田土壤,设置添加木质素和蚯蚓不同组合处理的黑麦草盆栽试验,在测定植物生物量的基础上,结合定量PCR、高通量测序等方法,研究木质素和蚯蚓及其联合作用对土壤细菌、真菌群落的影响。结果显示:木质素显著降低了黑麦草的生物量,而蚯蚓能够缓解木质素的抑制作用,促进黑麦草生长。木质素明显抑制了土壤细菌、真菌数量,并改变群落结构,以Sphingomonadaceae、Methylophilaceae为标志的降解细菌和担子菌等潜在降解真菌显著富集;单一加入蚯蚓对土壤微生物的影响相对较小,木质素和蚯蚓组合处理显著提高细菌、真菌数量,改变上述降解微生物的丰度。这些结果表明,木质素降低土壤微生物数量,并可能通过其自身降解释放的酚类化感物质抑制植物生长,对土壤生态系统健康产生不利影响;蚯蚓与木质素联合处理影响土壤中木质素降解微生物组成,微生物数量与植物生物量均表现增加趋势,蚯蚓有利于土壤中木质素的微生物代谢,并为植物生长提供更多的养分。本研究为农田生态系统木质素资源化利用提供了科学依据。     

土壤腐殖酸对毒死蜱水解的影响

土壤腐殖酸的VIS-UV光谱特征和E465/E665的测定结果表明,各种土壤腐殖酸的VIS-UV吸收曲线相似,但吸收峰强度和E465/E665差异较大,进而推得它们的腐殖化程度排序为:紫色潮土腐殖酸>中性紫色土腐殖酸>酸性紫色土腐殖酸>腐殖土腐殖酸,说明它们在组成上有共同的本性,但结构和性质差异较大。在此基础上,研究它们对毒死蜱水解的影响。结果表明,不同来源土壤腐殖酸均促进了毒死蜱的水解,但它们的影响程度有明显的差异。对于腐殖化程度最低的腐殖土腐殖酸,浓度为120mg L-1时,对毒死蜱水解的促进作用最大,而随着腐殖酸浓度的增大,促进作用却越来越弱;而对于其它三种样品,腐殖酸溶液对毒死蜱水解的促进作用随着腐殖酸浓度增大而加强,其中以腐殖化程度较低的酸性紫色土的促进作用较为明显。可见,毒死蜱的水解速率与土壤腐殖酸的浓度和腐殖化程度有关。其中,腐殖酸腐殖化程度的影响机理主要与腐殖酸的酸性和腐殖酸的吸附—催化作用有关,其具体作用机理有待于进一步从定性和定量方面去研究,以更好地指导毒死蜱农药的合理施用和污染土壤的修复。     

不同土壤腐殖酸对辛硫磷水解的影响

各种试验土壤腐殖酸的紫外吸收曲线相似,但吸收峰强度和E 465/E 665值差异较大,腐殖酸的腐殖化程度由大至小排序为：紫色潮土HA〉黄壤HA〉中性紫色土HA〉酸性紫色土HA,说明它们组成相似,结构和性质有差异。在此基础上,研究它们对辛硫磷水解的影响。结果表明,不同来源土壤腐殖酸均阻碍辛硫磷的水解,但它们的影响程度有明显的差异。腐殖酸溶液浓度越大,辛硫磷水解速率越慢,相同腐殖酸浓度下以腐殖化程度较高的紫色潮土的作用最大。初步说明辛硫磷的水解速率与土壤腐殖酸的浓度和腐殖化程度有关。     

土壤有机碳稳定性及其影响因素

土壤有机碳库在全球碳循环中起着重要作用。利用文献资料,阐明土壤有机碳稳定性理论及其影响因素。土壤有机碳稳定性指土壤有机碳在当前条件下抵抗干扰和恢复原有水平的能力。它是由土壤的理化性质所决定的,是自然因素和人为因素共同作用的结果。土壤有机碳的降解包括生物降解作用和物理化学降解作用等,生物降解作用是主要的过程。把土壤有机碳库分成活性碳库、慢性碳库、惰性碳库,能较好地与土壤微生物的生物降解过程相对应。构建土壤有机碳稳定性概念模型,能更系统地理解有机碳在土壤中的稳定机制。     

溶液培养条件下腐殖酸对Cr(Ⅵ)微生物还原的影响

探明铬(Cr)的氧化还原作用机制对于深入认识其污染过程特征进而制订科学的防控措施有重要意义。本研究采用从山西大同风化煤、河南巩县褐煤和云南昆明滇池底泥中提取的腐殖酸(分别记为HAs、HAh、HAk),通过分别添加,以及共同添加葡萄糖和不同制备来源或不同浓度的腐殖酸,并接种水稻土悬液,研究了溶液培养条件下腐殖酸对Cr(Ⅵ)的微生物还原过程的影响。结果表明:在有充足碳源存在条件下腐殖酸能够发挥其电子传递作用促进Cr(Ⅵ)的微生物还原过程。腐殖酸促进Cr(Ⅵ)还原的作用随其添加浓度的升高而增强,腐殖酸浓度为0.02 g/L时其促进作用较微弱,而2.00 g/L时培养期间Cr(Ⅵ)的还原率达到95%以上。腐殖酸的结构组成差异对其作用于Cr(Ⅵ)的微生物还原过程有重要的影响,腐殖化程度相对较高的HAk和HAs对Cr(Ⅵ)的微生物还原的促进作用明显,HAk更因含有一定量的多糖或类多糖物质而加快了Cr(Ⅵ)微生物还原过程的发生时间,而HAh则对Cr(Ⅵ)的微生物还原的影响较小。     

Selective digestion of the proteinaceous component of humic substances by the geophagous earthworms Metaphire guillelmi and Amynthas corrugatus

Humic substances play a key role in the global carbon cycling and the sequestration of micropollutants in soil. The transformation of these substances by earthworms, the dominant soil macroinvertebrates of many terrestrial ecosystems, and the mechanisms involved are still obscure. We prepared two chemically identical humic model compounds that were specifically ¹⁴C-labeled either in the aromatic or the proteinaceous component, and added them to soil incubated with the geophagous earthworm species Metaphire guillelmi (anecic) and Amynthas corrugatus (endogeic). In the absence of the earthworms, both the aromatic and the proteinaceous components were mineralized at similarly low rates (5−8% after 9 days of incubation). In the presence of the earthworms, mineralization rate of the proteinaceous component was strongly stimulated (2-fold by M. guillelmi and 1.4-fold by A. corrugatus). The mineralization rate of the aromatic component was (slightly) stimulated (1.2-fold; P < 0.05) only by A. corrugatus. In all cases, the stimulated mineralization was accompanied by a transformation of radiolabeled humic acids to fulvic acids within the earthworm guts and by an incorporation of radiolabel into the earthworm tissues. Digestion of the proteinaceous component of humic acids by the earthworms was corroborated also by a decrease of extractable humic acids in fresh cast and a stimulated mineralization of soil nitrogen; in the case of M. guillelmi, the fresh cast contained sixfold more NH₄⁺ than the non-ingested soil. Our study provides direct evidence for the selective digestion of humic components by earthworms. Considering the ubiquity of geophagous earthworms and their large biomass, the alteration of the chemical structure of humic substances by the earthworms through their selective digestion of peptidic components may have significant impacts on the stability of humic substances and the bioavailability of micropollutants in soil.     

蚯蚓对土壤温室气体排放的影响及机制研究进展

土壤是温室气体的重要源和汇。蚯蚓是土壤物质循环的重要参与者,能够直接或间接影响土壤CO2、N2O和CH4等温室气体的产生和释放。蚯蚓呼吸产生的CO2,是土壤呼吸的重要组成部分;蚯蚓自身肠道、分泌液、消化物和排泄物等微环境促进反硝化过程释放N2O。蚯蚓还通过取食、掘穴、排泄等活动,改变土壤理化性质、微生物组成和活性及其他土壤动物的组成,影响地上植物生长,调节土壤分解、矿化、硝化、反硝化和甲烷生成及氧化等生态过程,间接影响土壤温室气体的排放。蚯蚓对土壤温室气体排放的影响逐渐受到重视,但目前研究仍以室内培养和单因子环境条件的模拟为主,缺少野外原位实验和多环境因子的交互实验研究。长期监测和同位素示踪技术,是深入探讨蚯蚓影响温室气体排放机制的重要手段。温室气体类型上,CO2和N2O是研究热点,CH4研究比较罕见。未来研究,应重视不同生态类群蚯蚓与土壤理化特征、微生物组成、其他类群土壤动物和地上植物间的交互作用,加强机制研究,并关注土壤污染环境下蚯蚓功能性状的变化;综合评价蚯蚓对土壤温室气体排放和土壤碳氮固定的影响,科学评估蚯蚓活动对土壤碳氮释放的促进或减缓作用。     

秸秆施用下接种蚯蚓对农田土壤微生物特性的影响

在连续6年稻麦轮作系统中，研究不同秸秆施用方式下接种蚯蚓对土壤微生物生物量、活性（基础呼吸）及群落功能多样性（BIOLOG单一碳源利用指纹方法）的影响，试验设5个处理：对照（CK）、秸秆表施（M）、秸秆混施（I）、秸秆表施且接种蚯蚓（ME）、秸秆混施且接种蚯蚓（IE）。不同秸秆施用下接种蚯蚓均对土壤微生物生物量、微生物生物活性和群落碳源利用能力产生显著影响：两种秸秆施用方式下接种蚯蚓均增加微生物生物量；秸秆表施并接种蚯蚓导致微生物活性、碳源利用丰富度和多样性指数均降低，而在秸秆混施下则均升高；BIOLOG碳源利用分析结果表明在秸秆施用下接种蚯蚓后土壤的微生物群落组成发生明显变化。     

Digestion of peptidic residues in humic substances by an alkali-stable and humic-acid-tolerant proteolytic activity in the gut of soil-feeding termites

Previous feeding experiments have shown that soil-feeding termites (Termitidae: Termitinae) preferentially mineralize the peptidic component of synthetic humic acids, but nothing was known about the mechanism involved in digestion. Here, we studied the hydrolysis of humus-stabilized peptides in gut extracts of Cubitermes orthognathus by measuring the release of radiolabel from ¹⁴C-peptide-labeled synthetic humic acids. Gut extracts exhibited proteolytic activity over a wide pH range (from 4 to 12) with a maximum at about pH 8. The highest activity was located in the gut section containing the midgut and the extremely alkaline (up to pH 12) mixed segment. Chemical hydrolysis at in situ pH (up to pH 12) was negligible. Proteolytic activity in the hindgut fluid was generally relatively low, but alkaline proteases dominated in the anterior hindgut. When compared to other alkaline proteases, the proteolytic activity of gut extracts had a higher alkali-stability and tolerance to humic acids than subtilisin and an alkaline protease of Streptomyces griseus. Gut extracts also hydrolyzed the peptidic component of synthetic humic acids more efficiently than the commercial enzymes. Together with previous results, this study strongly supports the hypothesis that soil-feeding termites mobilize and digest the peptidic component of organic nitrogen in soil humic substances by a combination of proteolytic activities and extreme alkalinity in their intestinal tract.     

Earthworm activities and the soil system

Summary Earthworms find in soil the energy, nutrient resources, water and buffered climatic conditions that they need. According to the food resource they exploit and the general environmental conditions, earthworms can be grouped into different functional categories which differ essentially in morphology, size, pigmentation, distribution in the soil profile, ability to dig galleries and produce surface casts, demographic profiles and relationships with the soil microflora. Soil characteristics are both the determinant and the consequence of earthworm activities, since these animals greatly influence the functioning of the soil system. When present, they build and maintain the soil structure and take an active part in energy and nutrient cycling through the selective activation of both mineralization and humification processes. By their physical activities and resultant chemical effects, earthworms promote short and rapid cycles of nutrients and assimilable carbohydrates. Thus earthworms represent a key component in the biological strategies of nutrient cycling in soils and the structure of their communities gives a clear indication of the type of soil system that they inhabit.     

Different impacts of native and exotic earthworms on rhizodeposit carbon sequestration in a subtropical soil

Earthworms are known to regulate the sequestration of soil and leaf litter carbon (C). However, their impacts on the more accessible rhizospheric C, which represents a major energy source for soil food webs and an essential factor for C sequestration, are still unclear. Previous studies indicate that earthworms regulate the dynamics of SOC and leaf litter-C by increasing C accessibility to microbiota. However, in the case of labile rhizodeposit-C, microbiota might not require any pre-conditioning by earthworms and may rapidly metabolize most of this root-derived C. Consequently, potential pathways by which earthworms may affect the fate of rhizodeposit-C would be to regulate the biomass and/or activity of rhizosphere microbiota and, further, to mineralize/stabilize microbial products. A ¹³CO₂ labelling experiment was performed to determine the impacts of four different earthworm species on the fate of tree rhizodeposit-C in a subtropical soil. We hypothesized that endogeic earthworm species, representing primarily geophagous species, would closely interact with soil microbiota and sequester the microbially metabolized rhizodeposit-C more efficiently than epigeic and anecic earthworm species. We found that irrespective of ecological group affiliation, the three native earthworms did not affect rhizodeposit-C sequestration. In contrast, the exotic endogeic species stimulated the immobilization of rhizodeposit-C in the biomass of root-associated bacteria and/or arbuscular mycorrhizal fungi and, further, accessed the microbiota-metabolized rhizodeposit-C more efficiently. As a consequence, the exotic endogeic earthworm species transiently tripled rhizodeposit-C retention in soil. We propose that the weak linkages between native earthworms and rhizodeposits-related microbiota limit earthworm impacts on rhizodeposit-C sequestration. However, the exotic endogeic species Pontoscolex corethrurus may potentially alter rhizodeposit-C dynamics in invaded areas by shifting rhizosphere microbial community composition. This work highlights a distinct mechanism by which earthworms can regulate C dynamics and indicates a significant contribution of invasive earthworm species to belowground processes.     

Digestion and residue stabilization of bacterial and fungal cells,protein, peptidoglycan,and chitin by the geophagous earthworm Metaphire guillelmi

Microbial biomass is an important source of soil organic matter, which plays crucial roles in the maintenance of soil fertility and food security. However, the mineralization and transformation of microbial biomass by the dominant soil macrofauna earthworms are still unclear. We performed feeding trials with the geophagous earthworm Metaphire guillelmi using ¹⁴C-labelled bacteria (Escherichia coli and Bacillus megaterium) cells, fungal (Penicillium chrysogenum) cells, protein, peptidoglycan, and chitin. The mineralization rate of the microbial cells and cell components was significantly 1.2–4.0-fold higher in soil with the presence of M. guillelmi for seven days than in earthworm-free soil and 1–11-fold higher than in fresh earthworm cast material. When the earthworms were removed from the soil, the mineralization of the residual carbon of the microbial biomass was significantly lower than that in the earthworm-free soil, indicating that M. guillelmi affects the mineralization of the biomass in soil in two aspects: first stimulation and then reduction, which were attributed to the passage of the microbial biomass through the earthworm gut, and that the microorganisms in the cast could play only minor roles in the stimulated mineralization and residual stabilization of microbial biomass. Large amounts (8–29%) of radiolabel of the tested microbial biomass were assimilated in the earthworm tissue. Accumulation of fungal cells (11%) and cell wall component chitin (29%) in the tissue was significantly higher than that of bacterial cells (8%) and cell wall component peptidoglycan (15%). Feeding trails with ¹⁴C-lablled microbial cells and cell components provided direct evidence that microbial biomass is a food source for geophagous earthworm and fungal biomass is likely a more important food source for earthworms than bacterial biomass. Findings of this study have important implications for the roles of geophagous earthworms in the fate of microbial biomass in soil.     

Earthworm activity affects soil aggregation and organic matter dynamics according to the quality and localization of crop residues—An experimental study (Madagascar)

Soil organic matter (SOM) plays a central role in the functioning of ecosystems, and is beneficial from agronomic and from environmental point of view. Alternative cultural systems, like direct seeding mulch-based cropping (DMC) systems, enhance carbon (C) sequestration in agricultural soils and lead to an increase in soil macrofauna. This study aimed at evaluating in field mesocosms the effects of earthworms on SOM dynamics and aggregation, as influenced by residue quality and management.In the highlands of Madagascar, buckets were filled with 2 mm-sieved clayey Inceptisol. The effects of earthworm addition (Pontoscolex corethrurus), residue addition (rice, soybean, and no addition), and localization of the residues (mulched or buried) were studied. After 5 months, soil from mesocosms with earthworms had significantly lower C concentration and higher proportion of large water-stable macroaggregates (>2000 μm) than those without earthworms, because of the production of large macroaggregates by earthworms. Earthworm effect on soil aggregation was greater with rice than with soybean residues. Casts (extracted from mesocosms with earthworms) were slightly enriched in C and showed significantly higher mineralization than the non-ingested soil (NIS), showing that at the time scale of our study, the carbon contained in the casts was not protected against mineralization. No difference in microbial biomass was found between casts and NIS.Complementary investigations are necessary to assess long-term effects of earthworm addition on SOM dynamics, the conditions of occurrence of physical protection, and the impact of earthworms on the structure of the microbial community.     

蔬菜连作对铜尾矿土壤中有机碳、腐殖质碳以及可溶性有机碳的影响

Carbon of humus acids （HSAC） and dissolved organic carbon （DOC） are the most active forms of soil organic carbon （SOC） and play an important role in global carbon recycling. We investigated the concentrations of HSAC, water-soluble organic carbon （WSOC）, hot water-extractable organic carbon （HWOC） and SOC in soils under different vegetation types of four copper mine tailings sites with differing vegetation succession time periods in Tongling, China. The concentrations of HSAC, WSOC, HWOC and SOC increased with vegetation succession. WSOC concentration increased with the accumulation of SOC in the tailings, and a linearly positive correlation existed between the concentrations of HSAC and SOC in the tailings. However, the percentages of HSAC and DOC in the SOC decreased during vegetation succession. The rate of SOC accumulation was higher when the succession time was longer than 20 years, whereas the speeds of soil organic matter （SOM） decomposition and humification were slow, and the concentrations of HSAC and DOC increased slowly in the tailings. The percentage of carbon of humic acid （HAC） in HSAC increased with vegetation succession, and the values of humification index （HI）, HAC/carbon of fulvic acid, also increased with the accumulation of HSAC and SOC in soils of the tailings sites. However, the HI value in the each of the tailings was less than 0.50. The humification rate of SOM was lower than the accumulation rate of SOM, and the level of soil fertility was still very low in the tailings even after 40 years of natural restoration.     

Impact of five different tillage systems on soil organic carbon content and the density,biomass, and community composition of earthworms after a ten year period

To assess the impact of different types of soil tillage on the density, biomass, and community composition of earthworms, a long-term field study was performed in which soils were tilled in different ways for ten years. This study included five different types of tillage: (i) plough, (ii) grubber, (iii) disc harrow, (iv) mulch sowing, and (v) direct sowing. At the end of the experiment the earthworm density, biomass, and community composition, and the SOC (soil organic carbon) content were determined. The results show that density, biomass, and community composition of earthworm populations varied in relation to the type of soil tillage used. The density of anecic earthworm species decreased when soils were managed by conventional ploughing, relative to reduced tillage practices, whereas conversely the density of endogeic species increased. Additionally, the varying types of soil tillage influenced the abundance and biomass of different earthworm species in different ways. The density of Aporrectodea caliginosa was positively influenced by ploughing, whereas Aporrectodea longa, Lumbricus castaneus, and Satchellius mammalis showed a positive relationship to the grubber and Allolobophora chlorotica to direct sowing. We attribute these changes to modifications in the vertical distribution of SOC and varying potentials for mechanical damage of earthworms by tillage. A decrease in tillage intensity modified the vertical SOC distribution in the topsoil and consequently revealed positive effects on earthworm biodiversity, thus sustaining soil functioning.