在土壤中的蚯蚓种群的分析
English
Condividere
Panoramica
资料来源： 玛格丽特工人和金伯利弗莱-Depaul 大学实验室
用芥末，可以直接从土壤深处没有景观干扰或毒性采样地龙蒺藜蚯蚓的种群。蚯蚓然后可以计算数据和统计分析使用条形图和学生氏 t-检验。
多个物种的蚯蚓 （尤其是那些从亚目 Lumbricina） 有创蔓延在整个北美和南美，监测蚯蚓的种群是环境科学家，关键技术。充满异国情调的蚯蚓可以发现在几乎每一片土地上，大规模的和在地球上几乎每一个生态系统中，何时何地这些物种成为创一直国际环境研究的一个重点。1
生态入侵通常通过直接影音、 危害，或以其他方式造成本土物种的灭亡而降低了生物多样性的生态系统。作为生态系统工程师，创蚯蚓物种改变养分循环通过有机物质的分解速率上表层的土壤，在植物的根系矿井为营养。地龙物种都有灭绝本机蚯蚓物种和已被证明增加速效氮浓度和入侵土壤中氮的速率。2在一个正反馈循环，加速的水平的氮反过来使系统更好客是适应高水平的氮相比，天然植物物种的入侵植物物种和将胜过了土著人的现象被称为”入侵崩溃”。创蚯蚓物种蚯蚓（欧洲蚯蚓） 和入侵植物物种鼠李属 cathartica （欧洲沙棘） 提出了一种入侵危机关系。3
Principi
Procedura
Risultati
Sampling site 1 was a managed park, which sees significant disturbances such as aeration and fertilizers. Sampling site 2 was an unmanaged area, which sees no human interferences. As shown in Figure 1, site 1 has a higher density of earthworm populations, likely due to the increased hospitability due to human disturbances. However, site 1 also has higher variability of sampling, indicating the earthworm population may not be as consistently dense as the average suggests.
Figure 1. Bar graph displaying population results from each collection site.
Applications and Summary
Invasive species are a major threat to biodiversity. Exotic earthworms (eg: Lumbricus terrestris) and European buckthorn (Rhamnus cathartica) have been implicated as part of an “invasional meltdown” occurring in mid-western United States wooded communities. An invasional meltdown is the process where one invasion of a species facilitates the invasion of others. Thus, the rate of loss of ecological health can greatly accelerate as one invasive species makes way for additional ones. As undesired Rhamnus populations currently account for over 90% of vegetative cover in Illinois, the role of Lumbricus populations in landscape management has become critical to understanding and predicting Rhamnus invasion on managed land. Landscape disturbance tends to facilitate Lumbricus invasion and sampling for Lumbricus populations can be an indicator of vulnerability of land areas to likely invasion. Comparing samples of Lumbricus populations can help land management to know where more intensive methods are needed to maintain intended plant diversity and prevent invasion of Rhamnus.
Riferimenti
- Belote, R.T., Jones, R.H. Tree leaf litter composition and nonnative earthworms influence plant invasion in experimental forest floor mesocosms. Biological Invasions. 11, 1045-1052 (2009).
- Costello, D.M., Lamberti, G.A. Non-native earthworms in riparian soils increase nitrogen flux into adjacent aquatic ecosystems. Oecologia. 158, 499-510 (2008).
- Nuzzo, V.A., Maerz, J.C., Blossey, B. Earthworm invasion as the driving force behind plant invasion and community change in northeastern north American forests. Conserve Biol.23, 4. 966-974 (2009).
Trascrizione
The monitoring of earthworm populations is vital to environmental scientists, as invasive exotic earthworms can be found in nearly every ecosystem on the planet. Ecological invasion typically lowers biodiversity of an ecosystem by directly outcompeting, endangering, or contributing to the extirpation, or local extinction, of native species.
The Lumbricus terrestris species of European earthworm, also called the nightcrawler, is extremely common in North America, but is not native. As a result, it has greatly extirpated native earthworm species. Lumbricus terrestris alters the cycling of nutrients through decomposition of organic matter in the upper layers of soil, where plant roots mine for nutrients, thereby changing the soil layer structure. In addition, the organic debris layer, containing much of the decomposing material that provides nutrients, is completely lost.
These invasive worms also increase the available nitrogen concentration in invaded soils. In turn, the changing soil layers and high levels of nitrogen make the soil more hospitable to invasive plant species, such as the European Buckthorn, which are more adapted to high levels of nitrogen as compared to native plant species. This phenomenon is known as “invasional meltdown.”
The invasional meltdown resulting from invasion of the European earthworm and exotic plants like the European buckthorn is of key concern because it is dramatically decreasing the diversity of forest plant life in North America.
This video will demonstrate the monitoring of European earthworms in various park areas in order to assess their vulnerability for buckthorn invasion.
To determine earthworm populations in invaded areas, worms are directly extracted from soil using a capsaicin solution.
In this experiment, capsaicin is extracted from spicy mustard and poured directly onto the soil in an area defined by a pre-sized square, or quadrat. It then penetrates through the soil matrix to where the earthworms reside.
The capsaicin solution causes irritation to mucous membranes in the earthworm. Earthworms react to the irritation by moving to the soil surface to escape the capsaicin solution. After surfacing, earthworms are collected and the population density analyzed.
The following experiment will demonstrate the extraction of earthworms from soil, and their population analysis.
First, prepare the capsaicin solution at least 24 h in advance by weighing 38 g of ground oriental hot mustard, and transferring it to a plastic container with a cap. Add 100 mL of tap water to the plastic container containing mustard. Secure a cap on the container, and shake vigorously until all of the mustard is dissolved in the water.
Let the solution sit for 24 h for maximum capsaicin extraction from the mustard. When the capsaicin extraction is complete, dilute the mustard solution with 4 L of water in an 8-L water carrier. Shake the mustard solution several times to mix, and transfer it into the water carrier. Rinse any residual mustard using the diluted solution.
Seal the water carrier cap, and ensure that the valve is in the “OFF” position. Invert the water carrier three times to mix evenly. Prepare one container of capsaicin solution for each testing site.
Proceed to the sampling site with a quadrat and the water carrier containing diluted mustard solution. Also bring three sampling cups per site. They should be labeled appropriately for three replicates per sampling site.
Place the quadrat randomly on the ground in a cleared spot. Clear away the brush, leaves, and mulch as much as possible to clearly expose the soil. Mix the dilute solution again, and then switch the cap valve to the ON position.
Pour approximately a third of the diluted mustard solution within the quadrat, concentrating the majority of the liquid at the center of the quadrat area. If the soil becomes saturated and forms pools, stop pouring, and wait until pooled solution infiltrates the soil before continuing.
Observe the quadrat area closely for 5 minutes, looking for earthworm appearance. Be sure to look directly under the sides of the quadrat.
Wait for all earthworms to emerge from the soil within the quadrat area, and then collect them with forceps. After 5 minutes, close the sample cup and proceed to the next sampling site.
Repeat the collection steps for all sampling sites. Return to each site and perform 3 replicates per site. Count the number of earthworms collected for each sample, and then calculate the mean and standard deviation for each collection site.
Create a bar graph to compare the average earthworm population densities between collection sites. Use the standard deviation to create the error bars. Site one is a managed park, and is therefore more hospitable to earthworm populations due to disturbances such as aeration and fertilizers. Site two is unmanaged, and is therefore less hospitable to earthworm populations.
Exotic earthworms and European buckthorn have been implicated as part of an “invasional meltdown” occurring, especially in the mid-western United States. Tracking earthworm populations can help to elucidate relationships between the two invasional species and enable researchers to develop methods to prevent further spreading.
You’ve just watched JoVE’s introduction to the extraction and analysis of earthworm populations. You should now understand the principles of earthworm extraction from soil, and the comparison between sampling sites. Thanks for watching!
