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。     

Stable isotope N and C labelling of different functional groups of earthworms and their casts: A tool for studying trophic links

Earthworms (Oligochaeta: Lumbricidae) have substantial effects on the structure and fertility of soils with consequences for the diversity of plant communities and associated ecosystem functions. However, we still lack a clear understanding of the functional role earthworms play in terrestrial ecosystems, partly because easy-to-use methods to quantify their activities are missing. In this study, we tested whether earthworms and their casts can be dual-labelled with ¹⁵N and ¹³C stable isotopes by cultivating them in soil substrate amended with ¹⁵N ammonium nitrate and ¹³C-glucose. Additionally, we also wanted to know whether (i) earthworms from different functional groups (soil-feeders vs. litter-feeders) and their casts would differ in their incorporation of stable isotopes, (ii) if enrichment levels are higher if the same amount of isotopes is applied in one dose or in staggered doses, and (iii) if isotopic enrichment in casts changes when they are stored in a conditioning cabinet or in a pot filled with soil placed in a greenhouse. Our findings show the feasibility of dual-labelling tissues and casts of both litter-feeding (Lumbricus terrestris) and soil-feeding (Aporrectodea caliginosa) earthworms using the same method. The advantage of this method is that earthworms and their casts can be labelled under realistic conditions by cultivating them for only four days in soil that received a one-time addition of commercially available stable isotopes instead of offering labelled plant material. In earthworms, the isotopic enrichment remained at a stable level for at least 21 days; labelled casts could be stored for at least 105 days without significantly decreasing their isotopic signals. This simple and efficient method opens new avenues for studying the role of these important ecosystem engineers in nutrient cycling and their functional relationships with other organisms.     

Impact of soil engineering by two contrasting species of earthworms on their dispersal rates

By burrowing galleries and producing casts, earthworms are constantly changing the structure and properties of the soils in which they are living. These changes modify the costs and benefits for earthworms to stay in the environment they modify. In this paper, we measured experimentally how dispersal behaviour of endogeic and anecic earthworms responds to the cumulative changes they made in soil characteristics. The influence of earthworm activities on dispersal was studied in standardised mesocosms by comparing the influence of soils modified or not modified by earthworm activities on earthworm dispersal rates.The cumulative use of the soil by the earthworms strongly modified soil physical properties. The height of the soil decreased over time and the amount of aggregates smaller than 2 mm decreased in contrast to aggregates larger than 5 mm that increased. We found that: (i) earthworm activities significantly modified soil physical properties (such as bulk density, soil strength and soil aggregation) and decreased significantly the dispersal rates of the endogeic species, whatever the species that modified the soil; (ii) the decreasing in the dispersal proportion of the endogeic species suggests that the cost of engineering activities may be higher than the one of dispersal; (iii) the dispersal of the anecic species appeared to be not influenced by its own activities (intra-specific influences) or by the activities of the endogeic species (inter-specific influences). Overall these results suggest that the endogeic species is involved in a process of niche construction, which evolved jointly with its dispersal strategy.     

Crop diversification increases soil extracellular enzyme activities under no tillage: A global meta-analysis

Conservation agriculture with three management principles has been widely adopted to alleviate the current global agricultural soils facing threats such as soil erosion and nutrient loss. However, unclear understanding of rational crop rotation and the lack of global quantitative assessment limit our deeper insight into soil nutrient cycling under conservation agriculture. Considering the important role of soil extracellular enzyme activities (EEAs) on soil nutrient cycling, a meta-analysis with 3238 observations was conducted on the effects of no tillage (NT) and legumes incorporation into rotation system (LRS) on soil EEAs. NT significantly increased the activities of C-acquiring, N-acquiring, P-acquiring, and oxidative enzymes by 18.3%, 17.4%, 7.1%, and 14.0%, respectively, while LRS significantly increased only P-acquiring enzymes. The combination of NT and legume cultivation had no significant effect on EEAs. In contrast, crop diversity had a positive effect on the NT-induced increase in EEAs. In addition, the extent of NT-induced changes varied depending on other factors. Through further analysis, we clarified the important factors affecting NT-induced changes in EEAs, such as climatic conditions, soil properties, and agronomic practices at the experimental sites. Overall, our findings provide insights into the understanding of the mechanisms of conservation agriculture impacts on the soil nutrient cycling.     

An overview of some tillage impacts on earthworm population abundance and diversity — implications for functioning in soils

Conflicting reports in the literature on the effects of tillage on earthworms are reviewed in the light of their roles in agro-ecosystem functioning. Tillage can change the abundance (by 2–9 times) as well as the composition (diversity) of earthworm populations. The actual impact is dependent on soil factors, climatic conditions and the tillage operations but hitherto this information was seldom provided in research reports. The declines in earthworm population often reported in conventionally tilled soils are associated with undesirable changes in the soil environmental conditions resulting from excessive tillage. Different species of earthworm respond differently to tillage. While the abundance of the deep burrowing species (anecic) tends to decline under tillage, particularly under deep ploughing, endogeic species can actually increase in number especially when there is increased food supply. Under conservation tillage systems, earthworms can potentially play a more important role than under conventional tillage in the functioning of the farming systems because of their abilities to modify the soil physical environment and nutrient cycling. However, adoption of conservation tillage does not automatically result in an optimal earthworm population in terms of abundance and diversity. There are opportunities to introduce more beneficial species to improve the ecological performance of agro-ecosystems. More research is needed to fully understand the ecology of different earthworm species, their interactions and their potential roles in promoting more sustainable farming systems.     

塔里木沙漠公路防护林区土壤微生物的立地条件效应

通过分析来源于塔克拉玛干沙漠腹地防护林地的土壤样品,揭示了不同立地条件下防护林土壤微生物的差异及对土壤环境因子的响应规律,主要结论如下:(1)不同立地条件下土壤微生物活性差异极显著,呈现沙垄基部>沙垄中部>沙垄顶部>板结平沙地>流沙地的规律,而土壤深度间微生物数量表现为10～20cm>20～35cm>0～10cm,差异不明显。(2)三种微生物对环境因子的响应有所差异,细菌与土壤总孔隙度、含水量有显著正相关关系,与全K含量显著负相关;放线菌与全P、全K和全盐含量明显负相关,与全N正相关;真菌与全K、全盐含量负相关,与有机质含量和孔隙度大小正相关。(3)土壤不同深度范围内土壤因子对微生物活性的影响程度不同,0～10cm土层主要取决于有机质和N素含量;而土壤盐分状况和孔隙结构对10～20cm微生物较为重要;20～35cm土层中微生物需要满足一定养分供应和土壤结构。因此,土壤微生物对不同立地条件下土壤环境条件响应不同,微生物种群数量表现出一定差异,最终可能影响到微生物在土壤养分转化和促进土壤发育中的作用。     

Exotic earthworms alter soil microbial community composition and function

Exotic earthworms can profoundly alter soil carbon (C) and nitrogen (N) dynamics in northern temperate forests, but the mechanisms explaining these responses are not well understood. We compared the soil microbial community (SMC) composition (measured as PLFAs) and enzyme activity between paired earthworm-invaded and earthworm-free plots in northern hardwood forests of New York, USA. We hypothesized that differences in SMCs and enzyme activity between plots would correspond with differences in soil C content and C:N ratios. Relative abundance of several bacterial (mostly gram-positive) PLFAs was higher and that of two fungal PLFAs was lower in earthworm compared to reference plots, largely because of earthworm incorporation of the organic horizon into mineral soil. In surface mineral soil earthworms increased arbuscular mycorrhizal fungi (AMF) and gram-positive bacterial PLFAs, and decreased fungal (mostly saprotrophic) and several bacterial (gram-negative and non-specific) PLFAs. Earthworms also increased the activities of cellulolytic relative to lignolytic enzymes in surface mineral soil, and the relationships between enzyme activities and components of the SMC suggest a substrate-mediated effect on the SMC and its metabolism of C. A highly significant relationship between components of the SMC and soil C:N also suggests that earthworms reduce soil C:N through functional and compositional shifts in the SMC. Finally, changes in AMF abundances were linked to phosphatase activity, suggesting that earthworms do not necessarily inhibit P-acquisition by AMF-associated plants in our study system. We conclude that the combined influence of earthworm-related changes in physical structure, accessibility and chemistry of organic matter, and relative abundance of certain groups of fungi and bacteria promote C metabolism, in particular by increasing the activities of cellulolytic vs. lignolytic enzymes.     

土壤酶学硏究进展

土壤酶学是研究土壤酶活性及其相关特性的科学,是一门介于土壤生物学和生物化学之间的边缘交叉学科。土壤酶在土壤生态系统的物质循环和能量流动方面具有主要的作用。本文综述了土壤酶学发展简史、土壤酶的来源、分类、功能及分布特征等,总结了土壤理化性质、施肥、放牧、土壤微生物、施用稀土元素、草地生长年限、不同土地利用和耕作方式及其他因素对土壤酶活性的影响,对于加深理解生态系统中的物质循环、土壤酶的生态重要性以及土壤生态系统退化机理有重要作用。最后,结合本项目组的研究对土壤酶学的研究前景进行了展望。     

蚯蚓活动对生态滤池土壤酶活性的影响

通过构建蚯蚓生态滤池和无蚯蚓对照生态滤池的实验,研究了蚯蚓活动对生态滤池土壤酶活性(蔗糖酶、脲酶、碱性磷酸酶)的影响以及酶活性的季节动态变化特征。研究结果表明,在0~20 cm的基质层,三种土壤酶活性随土壤深度的增加而减少;蚯蚓活动对生态滤池的基质酶活性有促进作,蔗糖酶和脲酶活性在蚯蚓作用下得到显著的提高,而碱性磷酸酶对蚯蚓活动的响应仅限于5~10 cm基质层;在试验期内,生态滤池内的蚯蚓数量及生物量受温度及土壤湿度的影响表现出较大的季节波动:夏季最高,春季冬季相对较高,秋季最低;三种土壤酶活性表现为相似的季节变化规律:秋季活性最高,而秋季和夏季的酶活性高于春季和冬季。蚯蚓活动对生态滤池基质土壤蔗糖酶活性和脲酶显著的促进作用,并间接影响了其对生活污水污染物去除效果。     

Earthworm impacts on soil organic matter and fertilizer dynamics in tropical hillside agroecosystems of Honduras

Earthworms are important processors of soil organic matter (SOM) and nutrient turnover in terrestrial ecosystems. In agroecosystems, they are often seen as beneficial organisms to crop growth and are actively promoted by farmers and extension agents, yet their contribution to agroecosystem services is uncertain and depends largely on management. The Quesungual slash-and-mulch agroforestry system (QSMAS) of western Honduras has been proposed as a viable alternative to traditional slash-and-burn (SB) practices and has been shown to increase earthworm populations, yet the effect of earthworms on soil fertility and SOM in QSMAS is poorly understood. This study examined the role of Pontoscolex corethrurus in QSMAS by comparing their influence on aggregate-associated SOM and fertilizer dynamics with their effects under SB and secondary forest in a replicated field trial. Both the fertilized QSMAS and SB treatments had plots receiving additions of inorganic ¹⁵N and P, as well as plots with no inorganic N additions. Earthworm populations were manipulated in field microcosms at the beginning of the rainy season within each management treatment via additions of P. corethrurus or complete removal of existing earthworm populations. Microcosms were destructively sampled at harvest of Zea mays and soils were wet-sieved (using 53, 250 and 2000 μm mesh sizes) to isolate different aggregate size fractions, which were analyzed for total C, N and ¹⁵N. The effects of management system were smaller than expected, likely due to disturbance associated with the microcosm installation. Contrary to our hypothesis that earthworms would stabilize organic matter in soil aggregates, P. corethrurus decreased total soil C by 3% in the surface layer (0-15 cm), predominantly through a decrease in the C concentration of macroaggregates (>250 μm) and a corresponding depletion of C in coarse particulate organic matter occluded within macroaggregates. Earthworms also decreased bulk density by over 4%, but had no effect on aggregate size distribution. Within the two fertilized treatments, the QSMAS appeared to retain slightly more fertilizer derived N in smaller aggregate fractions (<250 μm) than did SB, while earthworms greatly reduced the recovery of fertilizer N (34% decrease) in both systems. Although management system did not appear to influence the impact of P. corethrurus on SOM or nutrient dynamics, we suggest the lack of differences may be due to artificially low inputs of fresh residue C to microcosms within all management treatments. Our findings highlight the potential for P. corethrurus to have deleterious impacts on soil C and fertilizer N dynamics, and emphasize the need to fully consider the activities of soil fauna when evaluating agroecosystem management options.     

Earthworm bioturbation stabilizes carbon in non-flooded paddy soil at the risk of increasing methane emissions under wet soil conditions

Studies on earthworms in rice-based ecosystems tend to focus on some pest species, while the potential of these important soil engineers for beneficially affecting carbon storage and cycling is widely ignored. We carried out a microcosm experiment to quantify the impact of the tropical earthworm Pheretima sp. on the C turnover in paddy soils under different conditions of water saturation and N fertilization. The soil was sampled at the lowland farm of the International Rice Research Institute (Philippines). In the absence of earthworms, soil respiration showed a distinct hump-shaped maximum at intermediate levels of water saturation (4-fold higher than in hand-dry soil) and increased 1.5-fold with increasing amounts of N fertilization. Amounts of CH₄ emitted, in contrast, were small at low to moderate soil humidity and became very high under conditions of water saturation (80-fold higher than hand-dry soil). No response to nitrogen addition was observed. Earthworms suppressed both the respiration maximum at intermediate saturation levels (by a factor of 1.4) and the stimulating impact of N fertilization (1.7-fold at maximum fertilizer level). On the other hand, earthworms strongly increased CH₄ release under conditions of high water saturation (3-fold). No consistent response of the soil microflora (bacterial abundance, soil enzymes) to earthworm activity could be established. Our findings suggest that the stabilization of soil organic C via earthworm bioturbation is confined to the range of soil humidity that allows high activity of Pheretima sp. Under conditions of intensive agriculture, the stabilizing effect of the worms may even be augmented by the fact that they offset the positive effect of N fertilization on microbial respiration. Earthworms may thus play a vital role in reducing the CO₂ flush from paddy soils after the conversion to non-flooded crops such as aerobic rice or maize. Acceleration of methane emission in very humid soils nevertheless points to a certain risk that is associated with increasing earthworm abundance in production systems that are still exposed to temporary flooding during the wet season.     

西双版纳热带雨林次生林的生物养分循环

本文获得了西双版纳热带雨林，砍伐后２块处于恢复演替阶段不同年代的次生林的生物量、生长量、年凋浇物量及它们的主要营养元素含量、对土壤养分状况的影响、以及土壤微生物状况和土壤生化活性等一系列资料。阐明了次生林生物物质和养分吸收、积累和归还的特点及对土壤养发状况的影响，研究了土壤微生物对凋落物的分解作用，从而对热带雨林次生林的生物养分循环作了一初步的探讨，为热带森林生态系统研究奠定了基础。研究表明：１．     

Influence of heavy metals on the functional diversity of soil microbial communities

Three soil types-Calcaric Phaeozem, Eutric Cambisol and Dystric Lithosol-in large container pots were experimentally contaminated with heavy metals at four different levels (light pollution: 300 ppm Zn, 100 ppm Cu, 50 ppm Ni, 50 ppm V and 3 ppm Cd; medium pollution: twofold concentrations; heavy pollution: threefold concentrations; uncontaminated control). We investigated the prognostic potential of 16 soil microbial properties (microbial biomass, respiration, N-mineralization, 13 soil enzymes involved in cycling of C, N, P and S) with regard to their ability to differentiate the four contamination levels. Microbial biomass and enzyme activities decreased with increasing heavy metal pollution, but the amount of decrease differed among the enzymes. Enzymes involved in the C-cycling were least affected, whereas vartous enzyme activities related to the cycling of N, P and S showed a considerable decrease in activity. In particular, arylsulfatase and phosphatase activities were dramatically affected. Their activity decreased to a level of a few percent of their activities in the corresponding unpolluted controls. The data suggest that aside from the loss of rare biochemical capabilities-such as the growth of organisms at the expense of aromatics (Reber 1992)-heavy metal contaminated soils lose very common biochemical propertities which are necessary for the functioning of the ecosystem. Cluster analysis as well as discriminant analysis underline the similarity of the enzyme activity pattern among the controls and among the polluted soils. The trend toward a significant functional diversity loss becomes obvious already at the lowest pollution level. This implies that concentrations of heavy metals in soils near the current EC limits will most probably lead to a considerable reduction in decomposition and nutrient cycling rates. We conclude that heavy metal pollution severely decreases the functional diversity of the soil microbial community and impairs specific pathways of nutrient cycling.Dedicated to Professor J. C. G. Ottow on the occasion of his 60th birthday     

土壤微生物影响土壤健康的作用机制研究进展

土壤健康是农业可持续发展的中心主题。土壤微生物参与土壤生态功能、环境功能和免疫功能协同驱动土壤生命系统运转，是维持土壤健康的核心与关键。了解不同微生物介导的土壤健康调控机制对有效利用这些核心微生物维持和改善土壤健康至关重要。本文围绕微生物参与调节土壤碳循环、养分循环，改变土壤结构、抑制植物病虫害、污染控制等主要生物过程系统梳理了微生物在调控土壤健康中的重要作用，以及微生物作为土壤健康的敏感指标对土壤健康的指示与预警作用。强调未来应加强驱动土壤健康特定功能以及多个生物过程的核心微生物组信息数据库挖掘、构建与生产应用研究，为定向利用微生物改善农业土壤生态系统功能、维持土壤健康以及保障土壤可持续发展提供科学依据。     

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...     

Nest-mounds of the yellow meadow ant (Lasius flavus) at the “Alter Gleisberg”, Central Germany: Hot or cold spots in nutrient cycling?

Nests of the yellow meadow ant (Lasius flavus) occur at high densities in grasslands worldwide. Although many studies have shown that L. flavus nests influence soil nutrient contents, little is known about their effect on soil nutrient cycling rates. The aim of this study was to examine the role of nest-mounds inhabited by L. flavus as potential ‘hot spots’ for soil nutrient cycling. Six pairs of nest-mounds and control soils were selected at a grassland site at the plateau of the Alter Gleisberg (Thuringia, Central Germany). L. flavus significantly modified the soil environment within the nest. In comparison to the control soils, nest-mounds were characterized by slightly higher soil temperatures during the summer months. In addition, we found that nests were related to decreased potential C mineralization rates and increased potential net N mineralization rates. Nest-mound soil exhibited lower amounts of SOC, hot-water extractable DOC and DN, and higher concentrations of leachable DOC and DN. Moreover, ants promoted the enrichment of base cations in the nest. Differences in the soil environment between nests and control soils were possibly a result of the burrowing activity of ants, soil mixing, accumulation of aphid honeydew, and decreased plant-derived nutrient inputs into the nest-mound soil. In conclusion, L. flavus nest-mounds had a significant but element dependent effect on the soil nutrient cycling and may represent cold spots for C cycling and hot spots for N cycling. Thus, L. flavus nests increase the spatial heterogeneity of soil properties and create unique micro-sites within grassland ecosystems.     

Inoculating maize fields with earthworms (Aporrectodea trapezoides) and an arbuscular mycorrhizal fungus (Rhizophagus intraradices) improves mycorrhizal community structure and increases plant nutrient uptake

Earthworms and arbuscular mycorrhizal fungi (AMF) are important macrofauna and microorganisms of the rhizosphere. The effect of the inoculation of soil with earthworms (Aporrectodea trapezoides) and mycorrhiza (Rhizophagus intraradices) on the community structure of mycorrhizal fungi and plant nutrient uptake was determined with split plots in a maize field. Maize plants were inoculated or not inoculated with AMF, each treated with or without earthworms. Wheat straw was added as a feed source for earthworms. Inoculating AMF significantly increased maize yield (p?<?0.05), and the yield was further enhanced by the addition of earthworms. Alkaline phosphomonoesterase activities, soil microbial biomass carbon (SMBC) and nitrogen (SMBN) increased with the addition of both earthworms and AMF. Soil inorganic N and available K were positively affected by earthworms, while available P showed a negative relationship with AMF. Treatment with both AMF and earthworms increased shoot and root biomass as well as their N and P uptake by affecting soil phosphomonoesterase and urease activities, SMBC, SMBN, and the content of available nutrients in soil. The applied fungal inoculants were successfully traced by polymerase chain reaction with novel primers (AML1 and AML2) which target the small subunit rRNA gene. The amplicons were classified by restriction fragment length polymorphism and sequencing. Moreover, field inoculation with inocula of non-native isolates of R. intraradices appeared to have stimulated root colonization and yield of maize. Adding earthworms might influence native AMF community, and the corresponding abundance increased after earthworms were inoculated, which has positive effects on maize growth.     

The combined effects of earthworms and arbuscular mycorrhizal fungi on microbial biomass and enzyme activities in a calcareous soil spiked with cadmium

Earthworms and arbuscular mycorrhizal fungi (AMF) are known to independently affect soil microbial and biochemical properties, in particular soil microbial biomass (SMB) and enzymes. However, less information is available about their interactive effects, particularly in soils contaminated with heavy metals such as cadmium (Cd). The amount of soil microbial biomass C (MBC), the rate of soil respiration (SRR) and the activities of urease and alkaline phosphatase (ALP) were measured in a calcareous soil artificially spiked with Cd (10 and 20 mg Cd kg⁻¹), inoculated with earthworm (Lumbricus rubellus L.), and AMF (Glomus intraradices and Glomus mosseae species) under maize (Zea mays L.) crop for 60 days. Results showed that the quantity of MBC, SRR and enzyme activities decreased with increasing Cd levels as a result of the elevated exchangeable Cd concentration. Earthworm addition increased soil exchangeable Cd levels, while AMF and their interaction with earthworms had no influence on this fraction of Cd. Earthworm activity resulted in no change in soil MBC, while inoculation with both AMF species significantly enhanced soil MBC contents. However, the presence of earthworms lowered soil MBC when inoculated with G. mosseae fungi, showing an interaction between the two organisms. Soil enzyme activities and SRR values tended to increase considerably with the inoculation of both earthworms and AMF. Nevertheless, earthworm activity did not affect ALP activity when inoculated with G. mosseae fungi, while the presence of earthworm enhanced urease activity only with G. intraradices species. The increases in enzyme activities and SRR were better ascribed to changes in soil organic carbon (OC), MBC and dissolved organic carbon (DOC) contents. In summary, results demonstrated that the influence of earthworms alone on Cd availability is more important than that of AMF in Cd-polluted soils; and that the interaction effects between these organisms on soil microorganism are much more important than on Cd availability. Thus, the presence of both earthworms and AMF could alleviate Cd effects on soil microbial life.     

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.     

A review of earthworm impact on soil function and ecosystem services

Biodiversity is responsible for the provision of many ecosystem services; human well‐being is based on these services, and consequently on biodiversity. In soil, earthworms represent the largest component of the animal biomass and are commonly termed ‘ecosystem engineers’. This review considers the contribution of earthworms to ecosystem services through pedogenesis, development of soil structure, water regulation, nutrient cycling, primary production, climate regulation, pollution remediation and cultural services. Although there has been much research into the role of earthworms in soil ecology, this review demonstrates substantial gaps in our knowledge related in particular to difficulties in identifying the effects of species, land use and climate. The review aims to assist people involved in all aspects of land management, including conservation, agriculture, mining or other industries, to obtain a broad knowledge of earthworms and ecosystem services.