The Impact of Natural and Anthropogenic Stressors

on Soil Mite Communities

 

  

A Preliminary Report Written by:

Kathleen Lansaw

Submitted to the Bridges to the Future Program

 

 

 

  

Abstract

            This study was conducted to determine the effect of natural and anthropogenic stressors on soil mite communities in South Central New Mexico.  I would then determine if soil mites can be used as bioindicators of stress on the soil.  This study  tests the impact of two stressors, fire and winter livestock grazing, on the soil mites.  The objectives of this  study are to determine 1)  whether  winter livestock grazing  decreases the diversity and populations of soil mites,  2)  to determine if fire decreases the diversity and populations of soil mites,  and 3)  to see whether the combination of fire and winter livestock grazing effects the populations and diversity of the soil mites.  The experimental hypotheses  state that each stressor  will decrease the populations and diversity of the soil mites, and the combination of two stressors will further decrease the density and populations of the soil mites.  This study is incomplete pending the identification of the soil mites and does not include any results.

 

Introduction

            Interest in anthropogenic stressors on soil ecosystems has increased in the past ten years.  Many ecologists are attempting to determine the impact of humans on natural and urban ecosystems.  Some of the major impacts on deserts include cattle grazing and grass fires.  Soil mites have been shown to be affected by human activities.  Mites are important in the biological fertility of  soils. (Elkins, 1980)  This is accomplished by decomposing organic matter in the soil by breaking it down both mechanically and biologically.  There is a relationship between the soil mites and the  microorganisms in the soil.  Predacious mites feed on the bacteriophagic nematodes during the early stages of litter decomposition.  During the middle stages of litter decomposition the fungivorous mites and nematodes appear, causing the fungi population to decrease.  After the fungi have been destroyed, other predacious mites  and feed on the fungivores (both mites and nematodes).   Thus  during the cycle of litter decomposition  mites regulate the populations of  different microorganisms in the soil  (Dindal, 1980).   They also help create humus in the soil by performing the afore mentioned functions (Elkins, 1980).  The purpose of this study is to determine the effect the stressors have on  populations and diversity of soil mites.  My experimental hypotheses states if  one stressor decreases the soil mite population, then two stressors will decrease it even more.

           

Methods and Materials

            The study site  is located in the northern Chihuahuan Desert on the USDA - ARS Jornada Experimental Range in the Jornada del Muerto Basin in southern New Mexico, 37 km NNE of Las Cruses, Doña Ana County, New Mexico.  This study site is used for many different experiments mainly under the supervision of Dr. Whitford of the EPA, New Mexico State University.

            The experimental design, created by Dr. Whitford, consists of a compete randomized block with six plots per block (Fig. 1).  In three of the plots within each block the shrubs have been removed, and in the other three plots shrubs have been left intact.   One “shrub removed” plot and one “shrub intact” plot have been cattle grazed  in the winter, and one “shrub removed” plot and one “shrub intact” plot have been grazed in the summer.  The two remaining plots are the controls, and have not been grazed.  The treatments have been assigned at  random as the main effects  in each of the blocks.  Subplots (within each plot) measuring 3m x 5m  have been assigned the following subtreatments at random: burn, nutrient depletion (the tying up of nutrients in the soil by the application of glucose), burn and nutrient depletion control, winter rainout, summer rainout, and rainout control (Fig. 2).  The only plots I am using  for the purpose of my study are the winter grazed plots with the shrubs intact and the nongrazed plots with the shrubs intact.  The subplots I am interested in are the burned plots and the fire and nutrient depletion control plots.

            The specific disturbances and treatments on the study site I am using are environmental (fire) and anthropogenic (livestock winter grazing).  The fire treatment was done in 1993 - 1996. The livestock winter grazing is continuous every winter for a period of twenty - four hours and with 40 head of cattle; therefore, there is only the twelve month recovery period between the grazing treatments.

            The collections of soil mites from the subplots were taken in September 1997, January 1998, and May 1998.  These soil samples were extracted using an auger, and placed into prelabled recloseable plastic bags. Samples  were placed inside a small picnic cooler  used to help maintain soil temperature, then moved into a larger picnic cooler to be transported to the greenhouse at UTEP.  The soil mites were extracted using the modified Berlese - Tulgren funnel method (Edwards and Fletcher, 1971).  The materials needed for this method are:  1) one pound coffee cans painted black, 2) 60 watt light bulbs, 3) large funnels, and 4) film canisters filled with water.  The  bottoms of the coffee cans were removed and replaced with several layers of cheese cloth.  The lightbulbs were positioned 4 - 5 cm above the coffee cans and  the funnels were placed directly below the coffee cans and had the film canisters attached. The mites were then temporarily stored in 95% aqueous ethyl alcohol before being sorted into Taxa.  The mites were sorted using spot plates and a dissecting microscope.  Since the mites are extremely small and must be identified at least to family, they are mounted on microscope slides and observed under a  compound microscope at high magnification.  The  identifcation of  soil mites will be done using Mesostigmata (Krantz, 1978), Prostigmata (Kethley, 1990), Astigmata (Phillip, 1990), and Oribatid (Norton, 1990) keys.  It is possible that some of the specimens cannot be identified with the keys mentioned above.  In that case it may be necessary to seek the assistance from other acarologists.

 

Accomplishments

            As of July 28, 1998, I have completed the tasks of extracting and sorting the

mites from September 1997, January 1998, and May, 1998.  I have also assisted in compiling a key to the mites found in the Chihuahua Desert.  Furthermore, I have been asked on occasion to assist in the identification of mites from samples collected at other stressor sites.  I still need to mount, identify, and sort my data from the soil samples I have been working with.  Therefore, the only data included in this report is preliminary and not yet compete.  This information will; however, be included in my final report  to the Bridges to the Future Program.  The final report will be submitted in December of this year.   

 

ß                 BLOCK 1                    àß                     BLOCK 2                   àß                   BLOCK 3                    à 

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Figure 1.  A diagram of a plot.  The plot covers an area of 1/2 ha.  The shaded areas represent the plots used for this study.  (SUM - Summer grazed, WIN - Winter grazed, NON - Non grazed, INT - Shrubs intact, REM - Shrubs removed)

 

Figure 2.  Diagram of 6 subplots, each measuring 3m x 5m.  The shaded areas represent the blocks being used for this study.  (ROC - Rain out control, F&NDC - Fire and nutrient depletion control, ND - Nutrient depletion, ROS - Rain out summer, ROW - Rain out winter)

 

LITERATURE CITED

Dindal, Daniel L.  1990.  In: Soil Biology Guide.  (Editor) D. Krantz.  John Wiley & Sons.  583 - 803

Edwards, C.A., and K. E. Fletcher, 1971.  A comparison of extraction methods for terrestrial arthropods.  In: Methods of Study in Quantitative Soil Ecology: Population, Production and Energy Flow.  F. A. Davis Company.  Philadelphia, Pennsylvania.  pp. 150 - 181.

ELKINS, N. Z.  1980.  Predaceous Microarthropods as potential regulators of microbial grazing during litter decomposition in a Chihuahuan desert ecosystem. pp. 29 - 32.

 

Kethley, J.  1990.  “Acarina: Prostigmata (Acarina).”  Soil Biology Guide.  (Editor) D. Krantz. John Wiley & Sons Inc.  Syracuse, New York pp. 667 - 756.

Krantz, G. W.  1978.  A Manual of Acarology, (Second Edition).  Oregon State. Corvallis, Oregon pp. 92.

Norton, R. A.  1990.  “Acarina: Oribatid”.  In: Soil Biology Guide.  (Editor) D. Krantz.  John Wiley & Sons, Inc.  Syracuse, New York.  pp. 757 - 778.

 

Phillips, J. R.  1990.  “Acarina: Oribatid”.  In: Soil Biology Guide.  (Editor) D. Krantz.  John Wiley & Sons Inc.  Syracuse, New York pp. 757 - 778.

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