Microbial communities of Lumbricus terrestris L. middens: structure, activity, and changes through time in relation to earthworm presence

Background, aim, and scope  Earthworms make a major contribution to decomposition in ecosystems where they are present, mainly acting in the drilosphere, that is, galleries, burrows, casts, and middens. Earthworm middens are hot-spots of microbial activity and nutrient dynamics and represent a suitable model for studying earthworm-mediated influences on soil microbial communities by alteration of the patch structure of the microbial environment. We studied the structure and activity of the microbial communities in the soil system formed by middens of Lumbricus terrestris and the soil below and surrounding them and the role of earthworms in maintaining these structures through time. Material and methods  We set up an experiment in which middens were either left (control) or removed from their original place (translocated) and left in a nearby area free of earthworm activity for 2 months. After 1 and 2 months we sampled middens, soil below them, and surrounding soil. We analyzed the phospholipid fatty acid (PLFA) profiles and measured respiratory fluxes of CO₂ and CH₄. Results  Microbial communities of middens clearly differed from those of soil below and surrounding soil samples, showing higher bacterial and fungal PLFAs (p < 0.0001 and p < 0.01, respectively); furthermore, changes in microbial communities were stronger in control middens than in translocated middens. Moreover, gram positive and negative bacterial PLFAs were greater in translocated than control middens (p < 0.0001 and p < 0.001, respectively), as well as total organic carbon (p < 0.001). Microbial activity was higher in middens than in soil below and surrounding soil samples both for CO₂ (p < 0.0001) and CH₄ (p < 0.0001). Discussion  Soil bioturbation by the earthworm L. terrestris was strong in their middens, but there was not any effect on soil below and surrounding soil. Microbial communities of middens maintain their biomass and activity when earthworms were not present, whereas they decreased their biomass and increased their activity when earthworms were present. Conclusions  Earthworms strongly enhanced microbial activity measured as CO₂ production in middens, which indicates that there are hot spots for soil microbial dynamics and increasing habitat heterogeneity for soil microorganisms. Moreover, our data strongly support the fact that the impact of this earthworm species in this soil is restricted to their middens and increasing soil heterogeneity. Recommendations and perspectives  Our data indicate that it is not clear if earthworms enhance or depress microbial communities of middens since the microbial activity increased, but did not modify their biomass and this was not dependent on soil organic C content. These results indicate no competence for C pools between this anecic earthworm and microorganisms, which has been found for other earthworm species, mainly endogeics. Conversely, they suggest some type of facilitation due to the release of additional nutrient pools in middens when earthworms are present, through the digestion of middens' material or the addition of casts produced from other food sources.     

Plant community impacts on the structure of earthworm communities depend on season and change with time

Declining plant diversity potentially threatens essential ecosystem functions driven by the decomposer community, such as litter decomposition and nutrient cycling. Currently, there is no consensus on the interrelationships between plant diversity and decomposer performance and previous studies highlighted the urgent need for long-term experiments.In the Jena Experiment we investigated the long-term impacts of plant community characteristics on the structure of earthworm communities representing key decomposers in temperate grassland. We repeatedly sampled plots varying in plant species richness (1-16 species), plant functional group richness (1-4 groups), and presence of certain plant functional groups (grasses and legumes) three, four, and six years after establishment of the experiment in spring and autumn.The results show that earthworm performance is essentially driven by the presence of certain plant functional groups via a variety of mechanisms. Plant productivity (root biomass) explained most of the detrimental grass impacts (decrease in earthworm performance), while beneficial legume effects likely were linked to high quality inputs of plant residues (increase in earthworm performance). These impacts depended on the functional group of earthworms with the strongest effects on surface feeding anecic earthworms and minor effects on soil feeding endogeic species. Remarkably, effects of plant community characteristics on the composition and age structure of earthworm communities varied between seasons. Moreover, plant diversity effects reported by a former study decreased and detrimental effects of grasses increased with time.The results indicate that plant community characteristics, such as declining diversity, indeed affect the structure of earthworm communities; however, loss of key plant functional groups is likely to be more important than plant species number per se. However, in frequently disturbed ecosystems plant species richness might be important for the recovery and resilience of belowground functions. Moreover, the results accentuate the importance of long-term repeated measurements to fully appreciate the impacts of plant community composition and diversity on ecosystem properties. Single point observations may be misleading and potentially mask the complexity of above-belowground interrelationships.     

The relative toxicities of insecticides to earthworms of the Pheretima group (Oligochaeta)

An artificial soil test was used to determine the LC50 values of carbaryl, chlorpyrifos, imidacloprid, cyfluthrin and fipronil against earthworms of the Pheretima group. For a 24-h interval, carbaryl was the most toxic to earthworms (LC50 = 77 mg kg-1), followed by imidacloprid (155 mg kg-1), cyfluthrin (351 mg kg-1), chlorpyrifos (390 mg kg-1) and fipronil (> 8550 mg kg-1) as the least toxic. For the 48-h and 7-day intervals, imidacloprid was the most toxic to earthworms (LC50 = 5 mg kg-1 and 3 mg kg-1 respectively), followed by carbaryl (16 mg kg-1; 9 mg kg-1), cyfluthrin (128 mg kg-1; 110 mg kg-1), chlorpyrifos (330 mg kg-1; 180 mg kg-1) and the least toxic was fipronil (> 8550 mg kg-1 both intervals). The surface application rates required to achieve these values are compared with the rates recommended for the control of turfgrass pests.     

土壤环境质量铅镉基准值的研究综述

综述了分别用生物环境效应试验和土壤生态地球化学方法研究铅镉基准值的特点和进展。探讨了土壤生态地球化学，地球化学以及生态毒理学研究者对铅镉土壤环境质量基准值的研究思路。比较了国内外在确定铅镉基准值时存在的差异。列举了针对不同口的制订铅镉基准值的研究现状。为完善现有土壤环境质量标准提供了基础资料。     

不同饵料对大口鲇苗种生长速度的影响

为观察不同饵料对大口鲇鱼苗生长速度的影响,采用不同时期进行不同饵料的投喂试验.结果:孵化出5d的鱼苗以喂水蚤较好;鱼苗达到3～5cm后,分别投喂鱼浆和水蚯蚓,以投喂水蚯蚓生长速度较快.     

蚯蚓及其在环境保护上的应用Ⅲ.蚯蚓在处理有机废弃物和生活污水上的应用

蚯蚓具有吞食有机物质,并将其以颗粒状排出的功能。通过与微生物的协同作用,蚯蚓可以明显加速有机物质的分解过程。因此,蚯蚓分解处理这一利用蚯蚓处理城市生活垃圾和农业有机废弃物的新技术发展起来了。蚯蚓过滤处理是另一项利用蚯蚓处理城市生括污水的新技术。在这项技术中．蚯蚓清除过滤器中堵塞的孔道,加速有机物质的分解,并通过颗粒状的蚓粪促进硝化-脱氮过程。本文主要介绍蚯蚓在环境保护上这两项应用技术,同时指出土壤生物多样性在环境保护上的重要性。     

丘陵坡地油茶林下新型生态种养模式研究与实践

充分利用茶林间隙土地实施种养立体开发,对丘陵坡地水土保持以及促进农民增收、创收具有重要意义。以湖南应用技术学院农林科技学院丘陵坡地的千亩油茶林为试验基地,通过油茶林下利用牛粪、羊粪养殖蚯蚓和土鸡,探索与实践了一种“茶—蚓—禽”种养结合新型生态模式,对丘陵坡地油茶林下间隙养殖蚯蚓的技术参数和实际效果进行介绍,旨在利用丘陵坡地资源发展林下经济,提高立体综合利用效率,对解决当前丘陵坡地油茶种植普遍存在的前期投入大、产出低、树间土地利用少等现实问题,以及发展丘陵坡地区域经济具有重要的现实意义。     

Earthworms influenced by reduced tillage,conventional tillage and energy forest in Swedish agricultural field experiments

Abstract

We compared earthworm density, depth distribution and species composition in three soil cultivation experiments including the treatments ploughless tillage and mouldboard ploughing. Sampling was done in September 2005 and for one experiment also in 1994. By yearly sampling 1995–2005, earthworms in an energy forest of Salix viminalis were compared with those in an adjacent arable field. Sampling method was digging of soil blocks and hand sorting and formalin sampling in one cultivation experiment. Both methods were used in the energy forest and arable land comparison.

In two soil cultivation experiments, highest abundances or biomass were found in ploughless tillage. Earthworm density was higher in the upper 10 cm, especially in the ploughless tillage. Earthworm density was significantly higher in the energy forest than in the arable field. Formalin sampling revealed c. 36% of the earthworm numbers found by digging in the energy forest and gave almost no earthworms in the arable field. In all treatments with soil cultivation, species living and feeding in the rhizosphere and soil dominated. One such species, Allolobophora chlorotica, was more abundant under mouldboard ploughing than ploughless tillage. Lumbricus terrestris, browsing on the surface and producing deep vertical burrows, was more common in the ploughless tillage. Species living and feeding close to the soil surface were almost only found in the energy forest, which had not been soil cultivated since 1984.

The findings support earlier studies pointing out possibilities to encourage earthworms by reduced soil cultivation. This is one of the first published studies that followed earthworm populations in an energy forest plantation during several years. Explanation of earthworm reactions to management and environmental impacts should be done with consideration of the ecology of species or species groups. Earthworm sampling by formalin must always be interpreted with caution and calibrated by digging and hand-sorting sampling.