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Efectos en la densidad de poblacin de nematodos del suelo en la abundancia y los niveles de nitrgeno
Human population density effects on soil nematode abundance and nitrogen levels
This study investigates the effects on human population density on soil properties and
found significant effects in nematode abundance and soil nitrogen levels. Five locations with differing human population densities around Monteverde, Costa Rica were chosen for soil sampling to conduct chemical tests and microfauna extractions. Chi square test (p = 0.02) prove that the differing soil location caused changes in nematode abundance, and a regression between nematode abundance and soil nitrogen (R square = .96) proved a strong relationship between the two. From this study we can see the impacts of human disturbance on levels of nitrogen and nematode abundance within our soil systems.
En este estudio investigue los efectos de la densidad poblacional en las caractersticas del suelo y encontr una correlacin entre la abundancia de nematodos y los niveles de nitrgeno en el suelo. Se escogieron cinco lugares para hacer muestras del suelo con diferentes densidades poblacionales cerca de Monteverde, Costa Rica con el fin de hacer un anlisis qumico y hacer extracciones de micro fauna.
Text in English.
Densidad de poblacin
Poblacin de nematodos
Suelos--Contenido de nitrogeno
Tropical Ecology 2009
Ecologa Tropical 2009
t Monteverde Institute : Tropical Ecology
Human population density effects on soil nematode abundance and Nitrogen levels Sarah Hulick Agricultural Sciences, College of Agriculture and Life Sciences, Cornell University ABSTRACT This study investigates the effects on human population density o n soil properties and found significant effects in nematode abundance and soil nitrogen levels. Five locations with differing human population densities around Monteverde, Costa Rica were chosen for soil sampling to conduct chemical tests and microfauna e xtractions. Chi square test (p = 0.02) prove that the differing soil location caused changes in nematode abundance, and a regression between nematode abundance and soil nitrogen (R square = .96) proved a strong relationship between the two. From this stud y we can see the impacts of human disturbance on levels of nitrogen and nematode abundance within our soil systems. RESUMEN En este estudio investig los efectos de la densidad poblaccional en las caractersticas del suelo y encontr una correlacin entr e la abundancia de nemtodos y los niveles de nitrgeno en el suelo. Cinco lugares con diferentes densidades poblacionales cerca de Monteverde, Costa Rica fueron escogidos para muestras de suelo con el fin de hacer anlisis qumico y extracciones de microf auna. Encontramos diferencias en los sitios en la abundancia de nemtodos y esas diferencias se correlacionaban con la cantidad de nitrgemo en el suelo. En este estudio podemos observar la relacin entre el impacto antropognico, el nitrgeno y la abundan cia de nemtodos en los sistemas de suelos tropicales. INTRODUCTION A true understanding of the soil system is our first step towards understanding the central link between the physical climate and biogeochemical systems, and is therefore the future of understanding humans' effects on the earth. (Yaalon 2000) Before we can understand humans' effects globally we must first understand how anthropogenic changes are already affecting the soil system. With 6.6 billion people in the world and that number incre asing daily it is important to understand the effects of human population density on soil quality. It is already known that urban areas can change abiotic climatic factors such as increasing carbon dioxide and temperature (George et al. 2009). These chang es cause one to wonder what other abiotic and biotic differences are occurring. Human altered ecosystems are under investigated even though are increasing in extent and impact
worldwide. Soils provide the services of filtering and regulating water, nutrien ts, and other dissolved and dispersed compounds for ecosystem and human use (Yaalon 2000). Humans have abused these resources and now need to protect them. Protection starts with acknowledging and understanding the effects of human disturbance on our soils Soil nematodes are integral to soil systems and are small worm like organisms, which are present in almost all soil ecosystems. They interact with plants and other microfauna to regulate decomposition and nutrient release to plants (Colman et al 1984). Nematodes provide many other ecosystem services including maintenance of soil structure, carbon sequestration, bio control of pests and diseases, soil detoxification and nutrient cycling (Kimenju et al 2005). Several studies have found effects of differ ent land and soil use intensity on nematodes abundance and diversity. Nematode diversity decreases with intensity of land use and increased human interference leaving natural forests with the highest nematode abundance (Kimenju et al ., 2005). Within agric ultural systems high input, intensively managed systems have lower soil fauna abundance and diversity. (Bardgett et al 1998) (Bagayoko et al 2000). Nutrient cycling is one of the important ecosystem services that soils provide. The nitrogen (N) cycle f lux rates and pools are often controlled by locally edaphic environmental condition whereas nitrogen sources are more global in nature (Russell Anelli et al. 2004). Fluxes and pools control how much nitrogen is available in the soil for plant use (Russell Anelli et al. 2004). The environmental mobility and pollution threat from nitrogen runoff create an imperative for scientists to better understand how to optimize nitrogen from organic sources ( Hofman et al. 2004). Nematodes and therefore less disturbed areas create a better environment for natural nitrogen cycling. For various natural ecosystems including forests, soil micro fauna contribute approximately 30% of nitrogen mobilization (Verhoef et al 1990). The nitrogen cycle naturally has "leaks" where n itrogen is lost from a location, this happens through erosion, leaching, and denitrification (Russell Anelli et al. 2004). These losses are offset by biological fixation of N and addition of N fertilizers (Russell Anelli et al. 2004). Having nematodes pr esent in the system increases likelihood of biological fixation and increased levels of available nitrates. I believe that human population densities are affecting soil chemistry and microfauna in soils in the Monteverde area. Understanding changes in t he soil system is imperative to providing sustainable and healthful soils for the future. The purpose of this study is to explore the effects of human population density on soil chemistry and microfauna abundance levels, with a concentration on fluctuation s of nitrate and nematode abundance. METHODS Study Sites I studied soil samples from five locations within the Puntarenas Province in Costa Rica between April 18 th 2009 and May 9 th 2009. Locations were chosen based on their proximity to Monteverde and t heir relative human population densities to one another (Masters 2009). In order from least to most populated they are: (1) Monteverde Biological Station Cloud Forest; (2) Canitas; (3) Cerro Plano; (4) Santa Elena; (5) City of
Puntarenas. Location 1 was ta ken from just below marker 227 on the trail above the Ocotea tree. Location 2 was taken from the front yard of Socorro Arguedas Torres, between the house and cattle pasture. Location 3 was from the back yard of Sabores heladeria. Location 4 was taken from the front yard of Luna Look Inn and location 5 was taken from a man made roadside planting in front of the bus station on the bay side of the city. At each soil extraction location I measured a 16 meter square plot and then took eight 15 cm long by two c m wide soil cores using an auger randomly placed within the plot. The soil cores were then homogenously mixed together to form the composite sample. The sample was brought to the lab where I performed microarthropod and nematode extractions and complete c hemical analysis within 24 hours. Microarthropod Sampling I used the Berlese Tullgren method and 50 g of soil from each sample for microarthropod extraction. This includes using a 40 watt light above the funnel containing the sample to decrease moisture and increase temperature. The temperature gradient causes the microarthropods to move downward seeking moisture where they eventually fall out of the funnel into a beaker of alcohol where I could collect and count them. I used 4 layers of window size scre en to work as the barrier between soil and beaker. The samples were allowed to sit for 6 days before species richness and abundance counts were made. Nematode Sampling I used a variation on the Baermann Funnel technique for collecting nematode samples. I set up a funnel with 50 grams of soil wrapped in panty hose and then filled the funnel with water, fully covering the sample. The bottom of the funnel was plugged with a rubber stopper, instead of the usual rubber hose. The nematodes can only swim downwar ds and aggregate in the bottom of the stopped funnel where after 1 day I uncorked the stopper and took nematode abundance counts. (Extracting Nematodes 2009) Soil Chemistry Variables The chemical tests performed were: pH, Nitrate nitrogen, potassium, hum us, aluminum and manganese from the model STH series soil test kit by LaMOTTE, and phosphorus from the 5934 LaMOTTE kit. Instructions on how to perform each test are provided in the kits. Data was analyzed using Chi Squared Tests and Regressions. RESUL TS Soil location had a statistically significant difference on nematode abundance (chi squared p = 0.01979221 and x = 11.69230769). Data for arthropod species counts and arthropod abundance were not statistically significant (respectively p = 0.65035963 and p = 0.109721562). There is a strong relationship between nematode abundance and nitrogen measurements. R square = .955707, Prob > F = .0040, F Ratio = 64.7302; Figure 1. Monteverde, location 1, was the only location with no human disturbance and had much higher levels of nitrogen and nematode abundance than other locations (Table 1). Humus
only showed presence in the locations with the two lowest human population densities (Locations 1 and 2; Table 1). The only location with measurable phosphorus lev els was Puntarenas (5), with the most human disturbance (Table 1). TABLE 1. Comparing soils based on location Monteverde (1) Canitas (2) Cerro Plano (3) Santa Elena (4) Puntarenas (5) pH 6.6 6.3 7.2 6.6 7.4 Phosphorus lbs/acre trace trace trace trace 25 Nitrogen lbs/acre 100 15 10 10 10 Potassium lbs/ acre 110 125 50 120 180 Humus low low 0 0 0 Aluminum ppm 10 10 10 8 12 Manganese ppm 0 0 0 0 0 Nemotode abundance 12 4 4 2 4 Arthropod species 8 8 12 12 7 Arthropod abundance 12 12 17 17 14 R 2 = 0.9557 0 2 4 6 8 10 12 14 0 20 40 60 80 100 120 Nitrogen lbs/acre Nemotode abundance count FIGURE 1. Nemotode abundance and Nitrogen concentration have a positive correlation. Highest amounts of both found in the Monteverde Forest, location 1. R egression was preformed and the Rsquare = .955707 and the Prob > F = .0040. DISCUSSION Nematode abundance is affected by human population density, or more likely human presence at all. In the Monteverde location there were three times more nematodes fou nd than in any other location, it is likely this result is due to the undisturbed and pristine
environment of the forest. There does not seem to be a relationship between human disturbance from density and nematode abundance, because the only significant d ifference seen is in the forest versus all other locations. It seems as though the factor that effects nematode abundance is more likely to be the presence of any human disturbance, not differing levels of population. Arthropod abundance counts were not related to human population density. From what I viewed when taking abundance counts, there were very few insects that were found in more than one sample. Most of the locations had unique insects species showing the changes within the samples were enough t o change the mixture of arthropods found there, but not necessarily abundance levels. There is a strong relationship between nematode abundance and nitrogen in the soil. Both of these soil characteristics thrive in undisturbed locations and are therefore both high in the Monteverde cloud forest, and low in all other locations (Table 1). This strong relationship is obviously due to the importance of nematodes in nitrogen sequestration (Coleman et al 1984; Verhoef and Brussaard 1990; Yeates 1999; Kimenju et al 2005). The amount of nematodes in the soil can offer great insight into how much nitrogen will be available. Humus was found only in the Monteverde forest (1) and in Canitas (2), the two locations with the lowest human population densities. Humic mat erial is one of the pools of available nitrogen in soils (Russell Anelli et al 2004) and thus explains why humic matter is found simultaneously with nitrogen. Furthermore, these two locations had the most above ground plant biomass including tree cover, w hich is most likely a contributor to the humic matter found in the soils in these locales. The only measurable amounts of phosphorus (P) I found was in Puntarenas. These were not unusually high levels, but were higher than all other soil samples, which I think can be contributed to two concepts. Puntarenas is an area where many rivers are merging and entering into the Nicoyan Gulf, because of this the chances of phosphorus run off from agriculture further up stream are increased greatly. Higher concentrati ons of P in water, from run off, generally contribute to higher P levels in soils since P molecules are bound to soil particles (Urbanization/water quality: Phosphorus. 2009). Another possible reason for these increased levels of P is because of great incr ease of human population density from the other locations. Much phosphorus in our soils is from cleaning detergents, and with a densely populated area like Puntarenas, there are increased detergents per unit of soil causing levels of soil P to increase (Ur banization/water quality: Phosphorus. 2009). From this study we can learn further about nematode sensitivity towards human disturbance, and more about the important relationships between nematodes and nitrogen levels. Furthermore, we start to delve into th e world of urban soils to discover things like decreases in humic content and increases in phosphorus. For further studies I would suggest that human population density not be used as the method of measurable change and to use some form of human disturbanc e instead. Additionally, I feel a study in the future would benefit from added replications, for more data to base the statistics from. I think the extremely high Rsquare value (.96) for the Nitrogen and nematode abundance relationship is a little biased b ecause of my small data set. Another experiment with replications could help ensure an accurate Rsquare value is known for this relationship.
ACKNOWLEDGEMENTS Thank you to everyone who helped me with the completion of this project. Thank you Alan Maste rs, Anjali Kumar, Pablo Allen Monge, Yi men Araya, and Moncho Calderon. Thank you to the people who let me use their property for taking soil samples: Monteverde Biological Station, Socorro Arguedas Torres, Sabores, Luna Look Inn in Santa Elena, and the C ity of Puntarenas. Thank you Yi men for your patience and help with statistics. Thank you to Jonathan Russell Anelli of Cornell University Department of Crop and Soil Science for responding to my questioning e mails. Thank you to the CIEE Tropical Ecology and Conservation program for providing this opportunity. _____________________________________________________________ LITERATURE CITED Bagayokol, M. A. Buerkert, G. Lung, A. Bationo, and V. Romheld. 2000. Cereal/legume rotation effects on cereal grow th in Sudano Sahelian West Africa: soil mineral nitrogen, mycorrhizae and nemotodes. Plant and Soil 218: 103 116 Bardgett, R. D. and Cook, R. 1998. Functional aspects of soil animal diversity in agricultural grasslands. Applied Soil Ecology 10(3), 263 276 Coleman, D.C., C.V. Cole, and E.T. Elliot. 1984. Decomposition, organic matter turnover, and nutrient dynamics in agroecosystems. In: R. Lowrance, B.R. Stinner and G.J. House (Eds.), Agricultural Ecosystems. Unifying Concepts. Wiley, New York, pp. 83 440. "Extracting Nematodes from Soil with a Baermann Funnel." 2009. Iowa State Plant Pathology 8 Apr. 2009
http://ga.water.usgs.gov/edu/u Verhoef, H.A. and Br ussaard, L. 1990. Decomposition and nitrogen minieralization in natural and agro ecosystems: the contribution of soil animals. Biogeochemistry 11: 175 211 Yaalon, D. H. 2000. Down to earth. Nature 407: 301 Yeates, G.W. 1999. Effects of plants on nematode community structure. Annu. Rev. Phytopathol. 37:127 49.