不同饲养密度对鳝苗的生长性能研究

本试验以水蚯蚓作为饵料,研究了60日龄鳝苗不同密度下的增重、存活率及饵料转化率。试验分3个密度组,其对应的密度分别为2000尾/m2、3000尾/m2、4000尾/m2,每个密度组设4个平行;试验时间为30d。结果表明:在本试验条件下,3个密度组鳝苗的增重率、存活率随着密度的增大呈下降趋势,而其饵料系数随着密度增大而增大;其中在4000尾/m2的密度下,鳝苗的增重率最低,仅为1.12±0.13;饵料系数最高,为5.71±1.37。     

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.     

接种蚯蚓对潮土氮素矿化特征的影响

在室内恒温（20℃）培养，间歇破坏性采样（于培养后第2、6、13、20、27、41、55天采样）的条件下，研究蚯蚓活动对土壤中氮素矿化特征的影响。共设置4个处理：（1）对照处理-不接种蚯蚓不添加秸秆（S）；（2）仅接种蚯蚓不添加秸秆处理（E）；（3）不接种蚯蚓仅添加秸秆处理（O）；（4）接种蚯蚓并添加秸秆处理（0E）。结果表明：在整个培养时期中，仅接种蚯蚓处理（E）的土壤铵态氮和硝态氮含量均较对照处理（S）有显著提高（P〈0．05），分别较同期对照处理（S）高出0．54-5．71倍和0．04-2．01倍；接种蚯蚓添加秸秆处理（OE）的土壤中的铵态氮含量较同期仅添加秸秆处理（0）增高了0．42-7．26倍，并达到显著性差异（P〈0．05），但两处理的硝态氮含量无显著性差异（P〉0．05）。从整体水平来看，无论是否添加秸秆，接种蚯蚓处理（E，OE）的土壤矿质氮水平均较相应的对照处理（S，O）有显著提高（P〈0．05），到培养55d时，分别增加了1．93倍和2．36倍。仅接种蚯蚓处理（E）的土壤氮素矿化速率和累积矿化速率较对照处理（S）有显著提高（P〈0．05）；添加秸秆后，无论是否接种蚯蚓，土壤累积矿化速率均为负值，表现为对土壤矿质氮的净固定，而从土壤氮素矿化速率的变化来看，前期的各个时间段中主要表现为矿质氮的净固定，后期逐渐表现为一定程度的矿化。此外，仅接种蚯蚓处理（E）的全氮含量除了培养2d外，其他培养时期均与对照处理（S）有显著差异（P〈0．05），到培养55d时，其全氮含量较同期对照处理（S）增高了6．55％。相关性分析结果表明，在仅接种蚯蚓处理（E）中，培养前后蚯蚓鲜重的减少量与土壤全氮含量之间存在极显著正相关（P〈0.01），根据一元线性方程将蚯蚓损失的鲜重换算为蚯蚓体损失的氮量后发现，在整个培养期中蚯蚓体本身排泄的氮大约占土壤全氮含量增加量的百分比为42％-100％。     

Isotopic detection of recent photosynthate carbon flow into grassland rhizosphere fauna

In this study, we measured the incorporation of recent photosynthate-C inputs into active rhizosphere fauna (earthworms, enchytraeids, mites and collembolans) in an upland grassland soil under natural environmental conditions. This was achieved by means of a ¹³CO₂ pulse-chase experiment made during the growing season, followed by a 20-day dynamic sampling of soil fauna for ¹²C/¹³C analysis by IRMS. The effect of post-¹³C labelling defoliation (cutting) on fauna ¹²C/¹³C ratios was also examined.Results showed that earthworms made up over 93% of the extracted fauna biomass, while mites, collembolans and enchytraeids together accounted for less than 7%. All fauna groups showed evidence of tracer ¹³C in their tissues within a week of ¹³CO₂ pulse labelling in both control and cut treatments. Cutting significantly increased the amount of tracer ¹³C entering the organisms (P=0.0002). Similarly, the fauna group also had a significant effect (P=0.0001). Time did not have any effect on fauna ¹³C content between groups as differences were only significant at the last sampling occasion. The interaction time×animal group, however, had a significant effect (P=0.0054).Collembolans accounted for most of the tracer ¹³C measured within the fauna biomass, i.e. mean±standard deviation of 44.78±12.75% and 44.29±14.69% of fauna ¹³C in control and cut treatments, respectively. Mites and earthworms contained between 22.13% and 28.45%, and enchytraeids less than 6% of the tracer ¹³C. We conclude that, during the growing season, there was a rapid incorporation of recent photosynthate-C into rhizosphere mesofauna. This carbon transfer was most significantly increased by defoliation in mites and collembolans (P<0.01). These results provide evidence that soil foodweb carbon dynamics are not solely underpinned by detrital decomposition but are also affected by short-term plant rhizodeposition patterns.     

Moisture conservation for rainfed wheat production with alternative mulches and conservation tillage in the hills of north-west India

In the hills of north–west India, maize (Zea mays L.)-wheat (Triticum aestivum L.) is the dominant cropping system. However, rainfed wheat suffers from lack of optimum moisture at sowing. Field experiments were conducted for 3 years on a silty clay loam (Typic Hapludalf) to evaluate the effectiveness of mulches and conservation tillage for rainfed wheat in mitigating this problem. The treatments were ten factorial combinations of five mulch-tillage practices and two nitrogen levels (N₆₀ and N₁₂₀ kg ha⁻¹). Mulch treatments consisted of application of 10 Mg ha⁻¹ (dry weight basis), to previous standing maize, of either wild sage (Lantana camara L.) or eupatorium (Eupatorium adenophorum Sprengel) in combination with either conventional or conservation (minium) tillage prior to wheat sowing. These alternative practices were compared to the conventional farmer practice of soil tillage after harvest of maize with no mulch. The application of these weed mulches to standing maize maintained friable soil structure owing to a five fold higher mean population of earthworms underneath mulch. Mulches resulted in 0.06–0.10 m³ m⁻³ higher moisture in the seed-zone when wheat was sown compared with the conventional farmer practice of soil tillage after maize harvest. Mulch-conservation tillage treatments favourably moderated the hydro-thermal regime for growing a wheat crop. The mean root mass density under these treatments at wheat flowering was higher by 1.27–1.40 times over the conventional farmer practice during the 3 year study. Conservation tillage holds promise because it does not require elaborate tillage and may ultimately reduce animal draught in the hilly regions. Recycling available organic materials having no fodder value coupled with conservation tillage may help enrich the soil environment in the long-term. The practice also offers gainful use of these obnoxious weeds that cause great menace in grass and forest lands in the region.     

Earthworm biomass response to soil management in semi-arid tropical Alfisol agroecosystems

Earthworms recorded during 1989–1993 across 15 soil management treatments, comprising three different tillagexthree organic amendments (bare, farmyard manure, and rice straw) and six perennial ley treatments, belonged to two endogeic species, Octochaetona phillotti (Michaelsen) and Lampito mauritii Kinberg, while in a nearby undisturbed natural revegetation area three species were found, including the above two and Octonochaeta rosea (Stephenson). The earthworm biomass showed significant temporal and spatial variations and was higher during the post monsoon period than in the early rainy season. No worm biomass was recorded during the dry season. In the tillage and organic amendment treatments, the biomass was drastically reduced from September 1989 to September 1991 after the application of carbofuran and some herbicides, and was significantly reduced during these two years compared to that of 1992. The maximum monthly earthworm biomass ranged between 2.5 and 17.9 g m^-2 across the treatments and increased several-fold in the nearby natural revegetation area (75.9 g m^-2). It significantly increased in perennial ley treatments compared to annual treatments with organic amendments. Thus the earthworm biomass varied significantly (P<0.01) across the 15 treatments, indicating discernible effects of soil management.Visiting Scientist (under the Rockefeller Foundation Environmental Research Fellowship in International Agriculture)     

蚯蚓对污染物的生物富集与环境指示作用

蚯蚓在陆地生态系统中具有十分重要的功能,是污染物从土壤到生物,进而向食物链更高营养级转移的重要环节。总结了蚯蚓对土壤污染物进行生物富集的途径：扩散作用和摄食作用;分析了土壤重金属和有机污染物在蚯蚓体内的生物富集规律和蚯蚓对污染胁迫的生理响应,提出利用蚯蚓体内的敏感生理生化指标作为生物标记物对污染土壤进行生态毒理诊断的新思路。     

Earthworm ecological groupings based on C analysis

We report the first use of ¹⁴C isotope analysis to investigate the ecological grouping of earthworms. Mature endogeic (Allolobophora caliginosa), mature epigeic (Lumbricus rubellus), and semimature anecic worms (A. longa) were collected in September 2002 from a woodland site at Lancaster, UK. Because anecic worms are known to have a variable feeding behaviour and can show dietary changes during ontogeny, additional immature and mature specimens of A. longa were also collected from the same site in January 2004. Epigeic earthworms showed the lowest radiocarbon concentration (0-3-years old), implying that they assimilated more recently fixed carbon than the anecic or endogeic earthworms. The age of carbon assimilated in mature anecic species (5-7-years old) was closer to that of endogeic species (5-8-years old) than to epigeics, suggesting that a greater proportion of older, more mineralised organic matter may form part of the diet of the anecic earthworms than previously thought. These results suggest that ¹⁴C approaches are useful in the study of the feeding behaviour of detritivorous animals by providing in situ information on the age of the carbon assimilated by the worms. This can then be related to their role in ecosystem functioning, particularly in carbon cycling.     

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.     

Variables controlling denitrification from earthworm casts and soil in permanent pastures

Summary Denitrification (using the acetylene block method) was determined in earthworm casts and soils from permanent, drained or undrained pasture plots fertilized with 0 or 200 kg N ha^-1 year^-1 as ammonium nitrate. Rates of N₂O production from soil cores were about three times higher from the fertilized than from the unfertilized plots while drainage had a relatively small effect. Denitrification rates from casts were 3–5 times higher than those from soil irrespective of the drainage treatment. Casts generally had higher NO _inf3 ^sup- , NH _inf4 ^sup+ , and moisture contents, and higher microbial respiration rates than soil. Rates of N₂O production were determined primarily by NO _inf3 ^sup- supply, secondarily by moisture; available C did not appear to limit denitrification in these pastures. Estimates of the potential contribution of casts to denitrification ranges from 10.1% of 29.3 kg ha^-1 year^-1 from the unfertilized, drained plot to 22% of 82.5 kg ha^-1 year^-1 from the fertilized undrained plot.