Movement response of Collembola to the excreta of two earthworm species: Importance of ammonium content and nitrogen forms

Several studies reported variable effects of earthworms on microarthropod density and variety. The present study tests the attraction of seven collembolan species belonging to four families, to the excreta of two earthworm species belonging to two families and two ecological categories, Aporrectodea giardi and Hormogaster elisae. Our objectives were (1) to better understand the impact of earthworms on the composition and density of Collembola communities, and (2) to dissect mechanisms involved in the attraction. Experiments were performed in Petri dishes containing two half-disks of filter paper, one with earthworm excreta, i.e. casts or a mix of mucus and urine, and the other with natural soil aggregates or water, respectively. Collembola were introduced half-way between the two half-disks and their number was counted on each half-disk and compared over 140 min. The content of ammonium in casts and mucus-urine of both earthworm species was analyzed to determine whether it altered the responses of Collembola faced with different types of earthworm excreta. The behaviour of Collembola varied strongly among the seven collembolan species, and with type of excreta and earthworm species. Six collembolan species were attracted to the mucus and urine of at least one earthworm species. The mucus-urine mixture of A. giardi, with low ammonium content, was generally more attractive than that of H. elisae, which was even repulsive in some cases, probably because of high levels of ammonium. The attraction to casts of the two earthworm species was less frequent and more variable. Folsomia candida was neither attracted to the casts nor to the mucus and urine of any earthworm species. Therefore, (1) earthworm species with different ecology, and different nitrogen excretion pathway impact differently the behaviour of collembolan species belonging to the same family or arising from the same habitat, and (2) variations in the sensitivity to ammonium among collembolan species partially explain the variable response of Collembola to earthworm excreta.     

Impacts of habitat disturbance on termites and soil water storage in a tropical Australian savanna

This study examines changes in the abundance and diversity of soil macroinvertebrate taxa and soil water storage across different disturbance treatments in a tropical savanna woodland in northern Australia. Nine plots representing three habitat disturbance treatments (uncleared savanna woodland; 25-year-old regrowth following past clearing; cleared areas) were sampled for macrofauna using soil pits in April 2003. Sub-surface soil moisture (0-0.4 m) was measured at 0.1 m intervals over the 2002/2003 wet season. Termites represented 55% of total individuals sampled. Abundance of soil macrofauna was greatest in uncleared plots and lowest in cleared plots, with the latter treatment also having the lowest taxon diversity. Mean abundances of termites, earthworms and ants were greatest in uncleared treatment plots. Five termite species from four genera were present, with Microcerotermes nervosus constituting 47% of termite species identified. Of the wood-, grass- and polyphagous-feeding termites present, wood-feeding species were restricted to uncleared treatment plots and grass-feeders to regrowth treatment plots. A shift in termite nesting habits from epigeal to hypogeal was observed from uncleared to cleared treatments. Soil water storage was lowest in the dry season and highest during the monsoon, and varied significantly across habitat disturbance treatments at the start and end of the wet season. Cleared plots were least effective in the capture of the first wet season rains, and uncleared treatment plots showed the greatest capacity to retain soil water during the transition from wet to dry season. The negative effects of habitat disturbance on soil water storage may have been partially mediated by the observed changes in soil macrofauna, especially termites.     

Effects of earthworms on soil enzyme activity in an organic residue amended rice–wheat rotation agro-ecosystem

The effect of earthworms on soil hydrolases (protease, urease, invertase, and alkaline phosphatase) and dehydrogenase activities was investigated in maize residue amended rice–wheat rotation agro-ecosystem. Experimental plots in the rotation had five treatments, i.e. incorporation or mulching of maize residues with or without added earthworms and an untreated control. The application of maize residues to soil without earthworms significantly enhanced the five soil enzyme activities compared with the control treatment during rice and wheat cultivation. The presence of earthworms further significantly enhanced protease activity in the soils with both incorporated and mulched maize residues during two cultivation seasons, but only significantly increased alkaline phosphatase activity in the soil with incorporated maize residue during the rice cultivation season. Invertase activity was significantly enhanced by the presence of earthworms in the soil with maize residue incorporation during two cultivation seasons. There were no changes in dehydrogenase activity when earthworms were present. Additionally, the five enzyme activities in earthworm casts were significant higher than those in the surrounding soil, especially dehydrogenase and invertase activities. Whatever the treatment, the values obtained for the enzyme activities in both soil and casts, except for dehydrogenase activity in earthworm casts, were significantly higher under wheat than those in rice-cultivated soil. These results indicate that the presence of earthworms strongly affected soil enzyme activities, depending on the method of organic residue application, and the enhanced enzyme activities of earthworm casts probably contributed to the surrounding soil enzyme activities.     

Foraging by deep-burrowing earthworms degrades surface soil structure of a fluventic Hapludoll in Ohio

The presence of deep-burrowing earthworms can affect soil structure and infiltration, therefore influencing agricultural productivity. We investigated the effects of deep-burrowing earthworm species on soil structure at the surface of chisel-plowed or ridge-tilled cropping systems in Pike County, OH, planted to corn (Zea mays L.). Earthworm populations were experimentally manipulated in field enclosures by adding predominantly deep-burrowing Lumbricus terrestris L., or leaving enclosures unmodified in each tillage system. In 1995, after 2 years of bi-annual additions, we measured surface residue cover, dry sieved aggregates (DSA)- and water-stable aggregates (WSA), and carbon and nitrogen concentration of aggregates by size class, in each treatment combination. Also, in 1998, we used tension infiltrometry to examine crusting effects at the soil surface among earthworm treatments in the chisel-plow treatment. Earthworm additions yielded increased density and biomass of L. terrestris than ambient controls, and to a greater extent in the ridged corn–soybean (Glycine max L. Mess.)–wheat (Triticum aestivum L.) (CSW) than corn–soybean (CS) rotation. Percentage residue cover in CS cropping decreased with earthworm additions. Earthworm additions decreased the geometric mean weight diameter (GMWD) of DSA and WSA in chisel-plow treatment compared to no additions. Earthworm additions influenced carbon-to-nitrogen (C/N) ratios for smaller DSA and WSA. Water-stable aggregate C/N decreased with size class. The overall effect of earthworm additions was an increase in deep-burrowing earthworms, a decrease in surface residue cover, and more pronounced crusting, which decreased mesopore conductivity.     

蚯蚓活动对稻麦轮作系统中土壤微生物量碳的影响

在建立6 a的稻麦轮作田间小区试验中,研究了2001年稻季至2004年麦季(共6季)蚯蚓活动对土壤微生物量碳(MBC)的影响。本研究设计了秸秆施用方式(混施或表施)×蚯蚓(接种或剔除)以及对照共5个处理,各3个重复。实验结果表明:在该生态系统中,无论采用何种秸秆施用方式,蚯蚓活动均能显著提高土壤MBC(p<0.05)。秸秆的施用会减弱同年内土壤MBC在麦季成熟期高于稻季的趋势,而蚯蚓的作用使该差异变得更显著(p<0.05)。在0~5 cm土层中,蚯蚓对MBC的积极作用在秸秆混施时比表施更明显,在5~10 cm土层中则相反,而在10~20 cm土层中的作用效果基本一致。     

What happens to earthworm casts in the soil? A field study of carbon and nitrogen dynamics in Neotropical savannahs

In the Oxisols of the eastern plains of Colombia, the large native anecic earthworm Martiodrilus sp. is an abundant ecosystem engineer producing long-lasting casts and burrows. Casts deposited in the soil by this species have been estimated at several tonnes per hectare per year. The physical and chemical processes occurring in these casts have never been studied. In this study, we compared the dynamics of water content (WC), total C (C_tot), and available N (N_avail) contents, and the distribution in size of aggregates in ageing below-ground casts of this species and in the bulk soil. In a native herbaceous savannah and a sown grass/legume pasture (Brachiaria humidicola, Arachis pintoi, Desmodium ovalifolium and Stylosanthes capitata), fresh surface casts were experimentally injected into artificial burrows of 1 cm Ø and 10 cm depth and sampled at different dates during a total period of 120 days. The injection procedure used resulted in a 34% decrease in WC of the casts from the sown pasture and reduced the mean mass diameter (MMD) of the aggregates of casts from the savannah by 19%. Other properties were not significantly affected by the procedure.For injected casts in both grasslands, MMD and C_tot were stable during cast ageing while WC and N_avail were initially at levels several times higher than the bulk soil and decreased to similar bulk soil values with ageing. The C_tot was twice and one third higher in casts compared with the bulk soil in the pasture and the savannah, respectively. Overall means for cast MMD (8.3 and 7.4 mm) were twice as high as those in the bulk soil (3.8 mm) in the savannah and the pasture, respectively. However, MMD was not significantly different between the casts and the bulk soil in two occasions in the pasture. Available nitrogen (N_avail) in injected casts was initially greater than bulk soil levels, reaching maximum levels just after injection (116 and 93 mg kg⁻¹) and remained significantly greater during 1-2 weeks, in the savannah and the pasture, respectively. In conclusion, the tonnes of casts deposited in the soil profile by Martiodrilus sp. each year are likely to contribute greatly to plant nutrition and to the regulation of the soil structure. For each anecic earthworm species, the ecological impact of its below-ground casts is likely to be as important as its surface casts.     

Mechanisms of stabilization of earthworm casts and artificial casts

Summary Fresh casts were collected from the earthworm species Aporrectodea caliginosa, and artificial casts were also made. The casts were subjected to ageing, drying-rewetting, and sterilization by hexanol vapour. Clay dispersion was determined, as a measure of the lack of stability of the casts. Two soils were used, the topsoil of a recently reclaimed polder soil in the Netherlands and the topsoil from a South Australian duplex soil. For both soils the fresh worm casts had higher dispersible clay than the artificial casts. During ageing, both types of casts became more stable. There are strong indications that this was mainly due to changes on the surface of the casts. Fungi developed on the surface of 6-day-old worm casts made of Australian soil. This gave a higher stability to the casts compared to artificial casts of the same age without fungal growth. With both types of casts, hexanol inhibited fungal growth on the surface of the casts, reducing the stabilizing effect of ageing. The fungus did not develop on Dutch soil casts until after 42 days, and the development of a higher stability with age was also less marked than in the Australian soil. When the casts were subjected to a drying and rewetting cycle before analysis, they became much more stable than the casts that were analyzed wet. The drying-rewetting cycle removed most of the differences between the worm casts and the artificial casts, and also removed any effects of ageing.Dedicated to the late Prof. Dr. W. Kühnelt     

蚯蚓活动对土壤氮素矿化的影响

通过室内培养试验和田间长期定位试验,探讨了蚯蚓活动对土壤矿质氮的影响。发现蚯蚓对NH4+-N、NO3--N,以及矿质总氮(NH4+-N+NO3--N)均有显著影响,且加速了土壤氮素矿化。小区试验中,在2001年稻季和2003年麦季,蚯蚓活动显著提高了NO3--N和矿质总氮(p<0.05*),但在其他时期,未有显著影响。室内培养试验中,蚯蚓活动明显加速了氮素矿化。尤其在未施用秸秆时,蚯蚓处理后的硝态氮和矿质总氮明显增加,且累积净矿化量和净矿化率也有显著提高。     

No evidence of facilitation between invasive Rhamnus cathartica (European buckthorn) and invasive earthworms in west central Minnesota

Biological invaders are seen as a real and growing threat to biodiversity, and there is much interest in the role that positive interactions among invasive species may play in promoting further invasions. Both the invasive tree Rhamnus cathartica (European buckthorn) and invasive Eurasian earthworms are reported to alter forest dynamics across large parts of the northern portion of the eastern deciduous forest of North America. Some evidence suggests that the two invaders may be aided by mutual facilitation, and it has recently been hypothesized that interactions between the two organisms may form the basis of a larger multi-species “invasional meltdown.” We examined covariance among R. cathartica and earthworm distributions over a seven year period at six forested sites near the prairie-forest border in west central Minnesota and found no evidence to support facilitation. In fact, the correlation between R. cathartica and earthworm abundance and biomass was weak: 95% confidence intervals for Kendall's tau correlation coefficients in some cases indicated a negative association among the two organism types, often suggesting no association, and never allowing for a positive association greater than τ = 0.38. Individual earthworm species varied in their correlation with R. cathartica, but most correlations were negative and none were substantially positive. We thus suggest that the relationship between these invaders may be more complicated than previously thought and question whether earthworms and R. cathartica can be seen as the foundation of an invasional meltdown.     

Earthworm populations in septic system filter fields and potential effects on wastewater renovation

Wastewater renovation in septic-system filter fields can be affected by preferential flow through soil macropores. Anecic earthworm species make deep vertical burrows that may reduce renovation by acting as preferential flow paths that decrease effluent contact with the soil matrix. On the other hand, endogeic earthworms make largely horizontal burrows that may enhance wastewater renovation by distributing the effluent over a larger area. Additionally, the moist, nutrient-rich environment in filter fields may increase earthworm populations by enhancing their survival. Therefore, our objectives were to determine earthworm numbers and biomass with distance from soil treatment trenches, and identify species present to estimate potential effects on wastewater renovation. Five septic systems were investigated. At each site, earthworm populations were measured using formalin extraction at 10 locations along each of three 7-m long transects perpendicular to the trenches. There were an average of 6.4 times more earthworms and 5.4 times more earthworm biomass within 1 m of the trench than in the background (3.5–7.0 m from the trenches) in 13 of the 15 transects. This suggests that earthworms may have a significant effect on the movement of effluent. Because only epigeic and endogeic species were observed, the potential for reduced renovation and groundwater contamination at these sites is likely low. This may not be the case in areas with large numbers of anecic earthworms.     

Dynamics of acetylcholinesterase activity recovery in two earthworm species following exposure to ethyl-parathion

In order for cholinesterase (ChE) activity to be used as an effective biomarker in earthworms, the time course of enzyme activity inhibition and recovery must be fully characterized. A laboratory experiment was carried out using parathion as a model organophosphorus pesticide at the recommended dose (1 mg kg⁻¹) and a 10 fold higher dose (10 mg kg⁻¹), on two earthworm species (Allolobophora chlorotica and Aporrectodea caliginosa). ChE activity and weight were measured every week for a 14 day period of exposure to parathion and then for 8 weeks in uncontaminated soil. After 3 days of exposure, the weight of both earthworm species had decreased by 10–15% compared to the control, regardless of the dose used. During the remainder of the exposure period, no differences were observed between the two doses for A. chlorotica; but A. caliginosa showed rapid weight recuperation for the lowest dose applied. After 28 days and over, the control and both exposed species of worms lost similar amounts of weight. ChE inhibition was measured during and after the exposure period. ChE inhibition followed a different time course for the two species investigated. A. chlorotica appeared less sensitive to parathion than A. caliginosa. In this latter species, ChE inhibition was rapid at close to 70% of the control after 3 days, for either dose, and reached 80–90% after 7 days exposure. While A. chlorotica exhibited the same pattern of inhibition for 10 mg kg⁻¹ of parathion, the inhibition process was slower for the recommended dose with 50% inhibition after 7 days of exposure and 70% after 14 days. ChE activity recovery, after transfer to uncontaminated soil, also followed a different pattern for the two species. After exposure to 1 mg kg⁻¹ parathion, ChE activity from A. chlorotica underwent a slow but constant recovery process to regain the control value after 8 weeks in unpolluted conditions. On the other hand, the ChE activity from A. caliginosa remained strongly inhibited. The differential susceptibility to parathion found in this study could be related to differences in the specificity of the total ChE activities between those two species.     

作物产量差研究与展望

作物实际产量与潜在产量间存在较大差距,地区间甚至同一地区不同田块间作物产量也存在显著差异,这种现象在世界范围内的农业生产中广泛存在.缩小该差距对于提高粮食产量,确保粮食安全具有重要意义.本文在阐述开展作物产量差研究重要性和必要性的基础上,从产量差的内涵、研究尺度的扩展及分析方法等方面介绍了目前国内外有关作物产量差的研究进展,并综述了作物生长模拟模型在产量差研究中的应用,最后分析了目前作物产量差研究中存在的问题和不足之处,并探讨了未来作物产量差研究的发展方向.     

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。