Earthworm functional groups are related to denitrifier activity in riparian soils

Riparian buffers, located in the transition zone between terrestrial and aquatic ecosystems, are a hotspot for nitrogen (N) removal through denitrification. Earthworms are abundant in riparian buffers and may enhance denitrification. This study investigated earthworm demographics of three earthworm functional groups (anecic, epigeic, and endogeic) and denitrifier activity in temporarily flooded and non-flooded riparian soils from April to October 2012 in southern Quebec, Canada. Nine earthworm species, mostly endogeic, were found in the temporarily flooded soil, while only six earthworm species were found in the non-flooded soil. On average, there were 11.7 times more earthworms with 12.4 times greater biomass (P<0.05) found in the temporarily flooded soil than in the non-flooded soil. The denitrification enzyme activity (DEA) was of similar magnitude in temporarily flooded and non-flooded soils, with temporal variation associated with rainfall patterns. Endogeic earthworm biomass was positively correlated (P<0.05) with DEA, while epigeic earthworm biomass was positively correlated (P<0.05) with 16S rRNA gene copies and nosZ gene copies from bacteria, indicating an association between earthworm functional groups and denitrifier activity in riparian soils. Stepwise multiple regressions showed that DEA in riparian soils could be predicted using soil moisture, inorganic N concentration, and earthworm functional groups, suggesting that endogeic and epigeic earthworms contributed to denitrifier activity in riparian soils.     

Can commercial mulches be reservoirs of invasive earthworms? Promotion of ligninolytic enzyme activity and survival of Amynthas agrestis (Goto and Hatai, 1899)

Amynthas agrestis is an exotic, invasive earthworm in North America that has been associated with horticulture settings as well as damage to forest soil. An experiment was conducted to find out whether A. agrestis, an earthworm commonly found in mulches in Vermont, stimulates ligninolytic enzymes in the presence of commercial wood mulches. Mesocosms filled with a sandy loam soil were topped with either spruce, cedar or pine mulch. Half of the mesocosms received juvenile A. agrestis, the other half did not. After 7 weeks soils were analyzed for phenoloxidase and peroxidase activity. Most A. agrestis survived and developed into adults during the incubation period. Significantly greater phenoloxidase activity was detected in soils with A. agrestis than without earthworms. Mean (standard deviation) phenoloxidase activities in the presence of A. agrestis were 0.15 (±0.10), 1.14 (±0.46), 2.71 (±0.98) μmol g⁻¹ h⁻¹ for pine, spruce and cedar respectively, and 0.012 (±0.023), 0.25 (±0.25), 0.78 (±0.45) μmol g⁻¹ h⁻¹ in the absence of A. agrestis. There was significantly greater peroxidase activity for the pine and spruce treatment when earthworms were present. Mean peroxidase activities were 0.47 (±0.21), 0.94 (±0.29), 1.20 (±0.77) μmol h⁻¹ g⁻¹ soil for pine, spruce and cedar, respectively for soils with A. agrestis and 0.15 (±0.10), 0.37 (±0.10), 0.63 (±0.30) μmol h⁻¹ g⁻¹ soil in the absence of earthworms. The increased ligninolytic activity in combination with successful maturation of juveniles into adult A. agrestis suggests that mulch can be habitat for these invasive earthworms. This finding is supported by a survey of master gardeners in Vermont and New Hampshire 20% of whom reported to have seen these earthworms mainly in their gardens and mulched beds.     

Removal of an invasive shrub (Chinese privet: Ligustrum sinense Lour) reduces exotic earthworm abundance and promotes recovery of native North American earthworms

This study investigated the possibility of a facilitative relationship between Chinese privet (Ligustrum sinense) and exotic earthworms, in the southeastern region of the USA. Earthworms and selected soil properties were sampled five years after experimental removal of privet from flood plain forests of the Georgia Piedmont region. The earthworm communities and soil properties were compared between sites with privet, privet removal sites, and reference sites where privet had never established. Results showed that introduced European earthworms (Aporrectodea caliginosa, Lumbricus rubellus, and Octolasion tyrtaeum) were more prevalent under privet cover, and privet removal reduced their relative abundance (from >90% to ∼70%) in the community. Conversely, the relative abundance of native species (Diplocardia michaelsenii) increased fourfold with privet removal and was highest in reference sites. Soils under privet were characterized by significantly higher pH relative to reference plots and privet removal facilitated a significant reduction in pH. These results suggest that privet-mediated effects on soil pH may confer a competitive advantage to European lumbricid earthworms. Furthermore, removal of the invasive shrub appears to reverse the changes in soil pH, and may allow for recovery of native earthworm fauna.     

蚯蚓和基质种类对人工湿地植物根系特征及净化效果的影响

选择4种常见的人工湿地基质(沙、沙+土、有机质+沙、有机质+沙+土),研究加入蚯蚓后不同基质对黄菖蒲最长根长、根体积和基质总孔隙度及其净化CODMn能力的影响。结果表明,不同基质上黄菖蒲的最长根长、根体积存在差异,以有机质+沙基质上黄菖蒲的最长根长、根体积最大,而沙子基质上黄菖蒲的最长根长、根体积最小,两处理间存在显著差异(P<0.01)。加入蚯蚓能增加黄菖蒲的最长根长、根系体积、总孔隙度和CODMn的去除率。相关分析显示,黄菖蒲的最长根长、根体积与总孔隙度呈显著正相关(P<0.01),且根系体积、最长根长与CODMn去除率也呈显著正相关(P<0.01)。     

蚯蚓活动对铜尾矿废弃地土壤养分的影响

[目的]研究蚯蚓活动对铜尾矿废弃地土壤养分的影响,以期为利用土壤动物进行铜尾矿生态恢复提供参考。[方法]在室内恒温(20℃)条件下培养1个月,共设置8种处理进行试验。[结果](1)接种蚯蚓对土壤养分的影响强弱顺序依次为:有效磷有机质速效钾碱解氮,且随着蚯蚓密度的增加土壤养分的含量呈上升趋势;(2)添加秸秆后接种蚯蚓对铜尾矿废弃地土壤养分的影响强弱顺序依次为:有效磷碱解氮速效钾有机质,且随着蚯蚓密度的增加土壤养分的含量呈上升趋势;(3)接种蚯蚓且添加秸秆比仅接种蚯蚓对土壤养分的影响大,且影响速度表现为:有效磷速效钾碱解氮有机质。[结论]蚯蚓对铜尾矿废弃地土壤养分的恢复具有促进作用,蚯蚓密度越大影响作用越强。     

Technical Recommendations for the Update of the ISO Earthworm Field Test Guideline (ISO 11268-3) (5 pp)

Background, Aim and Scope   Background, Aims and Scope. The earthworm field test firstly was developed by the German Federal Biological Research Centre for Agriculture and Forestry (BBA) for testing of pesticides and later internationally standardised by the International Organization for Standardization (ISO) as a tool for characterizing soil quality. It is mainly used for the assessment of effects of pesticides on earthworms under field conditions. Growing experience has shown that the practical performance of the test can be improved. Main Features: In two meetings organised by the Federal Biological Research Centre for Agriculture and Forestry (Braunschweig, 2002) and later the German Federal Agency for Consumer Protection and Food Safety (Lille, 2005) an ad-hoc working group of experts from various countries and institutions discussed the practical performance and recommendations that should be taken into account in a revised draft following the current ISO guideline after the proposed revision has been approved by voting in the periodical review. Results: The outcome of the discussions and the background of the recommendations of the ad-hoc working group are briefly summarised in this paper. These are mainly methodological details in order to improve the test performance (e.g. by decreasing variability or increasing practicability). Discussion: These recommendations are proposed to be considered for the next update of the current ISO guideline. They should be seen as technical amendments still waiting for their approval by standardisation organisations. Conclusions: Although this method focuses on the assessment of effects of pesticides on earthworms, the recommendations will also be valuable for testing contaminated soils. The recommendations presented may also be a first step for splitting the current guideline into two fields of application, one for testing of chemicals and pesticides (i.e. within the scope of OECD) and another one for testing soil quality (i.e. within the scope of ISO). Perspectives: Nevertheless, there is still a major need for guidance concerning the interpretation of effects determined in such complex field tests.     

The influence of mineral and organic fertilisers on the growth of the endogeic earthworm Octolasion tyrtaeum (Savigny)

Endogeic earthworms play an important role in mobilisation and stabilisation of carbon and nitrogen in forest and arable soils. Soil organic matter is the major food resource for endogeic earthworms, but little is known about the size and origin of the organic matter pool on which the earthworms actually live. We measured changes in body mass of juvenile endogeic earthworms, Octolasion tyrtaeum (Savigny), in soils with different C and N contents resulting from different fertiliser treatments. The soil was taken from a long-term experiment (Statischer Düngungsversuch, Bad Lauchstädt, Germany). The treatments included (1) non-fertilised soil, (2) NPK fertilised soil, (3) farmyard manure fertilised soil and (4) NPK + farmyard manure fertilised soil. The soil was incubated in microcosms with and without one juvenile O. tyrtaeum for 80 days.Earthworm biomass decreased in non-fertilised soil by 48.6%, in NPK soil by 9.4%, but increased in farmyard manure soil by 19.7% and 42.8% (soil with additional NPK application). In farmyard manure treatments the biomass of bigger individuals decreased, but in smaller individuals it increased. In NPK fertilised soil without farmyard manure only small O. tyrtaeum increased in body mass, whereas in the non-fertilised soil all individuals decreased in body mass. Generally, soil respiration correlated positively with soil carbon content. Earthworms significantly increased soil respiration and nitrogen leaching and this was most pronounced in farmyard manure treatments. Microbial activity was generally higher in farmyard manure soil indicating that farmyard manure increases labile organic matter pools in soil. Also, biomass of earthworms and microorganisms was increased in farmyard manure soil. The presence of earthworms reduced microbial biomass, suggesting that earthworms feed on microorganisms or/and that earthworms and soil microorganisms competed for similar organic matter pools in soil. The results demonstrate that NPK fertilisation only is insufficient to sustain O. tyrtaeum, whereas long-term fertilisation with farmyard manure enables survival of endogeic species due to an increased pool of utilisable soil organic matter in arable soil.