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Burning Reduces Nematode Abundance in Reconstructed Prairies Burning reduces nematode abundance in reconstructed prairies EVIE KENEPP Biology Department, Grinnell College, PO Box 805, Grinnell, IA 50112, USA Introduction community upon death (Freckman and Baldwin, 1990). Their effect on Nematodes are one of the most plant production is less numerous and diverse groups of conclusive and depends highly on organisms. They have an intricate the interaction between specific relationship with the soil plant and nematode species: some ecosystem (Freckman & Baldwin, plants are resistant to nematode 1990; Ingham, 1994). Nematodes are invasion, while others are microscopic worms that vary in tolerant of high numbers of size, but most are less than 4 mm nematodes feeding in or on their in length (Freckman and Baldwin, roots (Freckman and Baldwin, 1990). There are six 1990). classifications of nematodes, It is important to know the based on their feeding habits: impact of nematodes on prairie endoparasites, ectoparasites, ecosystems so they can be properly microbivores, and fungivores, managed. Smolick (1974) estimated omnivores and predators, which that root-feeding nematodes play a unique role in soil food consumed as much plant material as webs (Freckman and Virginia, 1997; cattle in a Colorado grassland Ingham, 1994). Plant-feeding ecosystem (as cited in Freckman nematodes affect primary plant and Virginia, 1989). Ingham and production by feeding on roots and Detling (1984) found that in seed heads. Other types of grassland ecosystems, nematode nematodes affect nutrient cycling herbivory decreased plant and decomposition by feeding on production from 6-13% (as cited in fungi, bacteria and microfauna. Freckman and Virginia, 1989). A (Freckman & Baldwin, 1990; high population of root-feeding Freckman & Virginia, 1997). nematodes combined with other Due to the diversity of species management techniques that reduce and feeding habits, nematodes have aboveground living plant material both negative and positive effects (biomass) could affect the success on the soil ecosystem (Freckman & of prairie restoration efforts. Baldwin, 1990). Negative effects Mow and burn treatments disturb include transmission of diseases, the natural cycles of the prairie crop loss and reduction of ecosystem but in the long run tend beneficial soil organisms. to have positive effects on However, nematodes also feed on tallgrass growth (Hulbert, 1988). pathogenic organisms, a positive Disturbances increase nutrient effect. Nematodes are rich sources loss from ecosystems (Molles, of nutrients because they store 1999), and nematodes are highly most of their energy as biomass, dependent on the nutrients in soil which is returned to the soil organic matter (Freckman and Baldwin, 1990). I determined The data confirms my expectation nematode abundance in burned and that nematode populations were mowed plots in order to examine highest in the control plots and the effects of these management lowest in the combination burned practices. I hypothesized that and mowed plots, but the variation nematode populations will be in abundance was not significant greatest in untreated plots, and (p = 0.659; Figure 1). Contrary decrease in burned and mowed to my expectations, there was no plots, with the lowest populations significant difference between the in plots that received both the mean nematode counts of mowed and burn and mowing treatment. unmowed plots (p = 0.152). However, there was a significantly Methods lower mean number of nematodes in the burned plots than in unburned CERA has fire and mowing plots, regardless of mowing experimental tall grass prairie treatment (p = 0.034; Figure 1). plots. There were originally 20 There was no significant plots in the experiment, but the interaction between the burn and southern half of plots 19 and 20 mow treatments. were not usable (J. Brown, pers. comm). Half of the plots (9) have Discussion been burned every spring since 1997, and the other nine plots While the nematode populations have been left unburned since were lower in the mowed, burned 1997. Five of the burned plots and and combination plots than in the four of the unburned plots were control plots, the difference was mowed in late June 1999 (Appendix only significant between burned A). To determine the affect of and unburned plots. Mowing mowing and burning on nematode treatments did not enhance the abundance, I took a random soil effects of burning on nematode samples from the 18 usable abundance. experiment plots. The differences between the On November 9, 1999, I took 100 disturbances caused by mow and cc soil cores at 0-25 cm depth in burn techniques could explain why four plots, and on November 16, mowing had no significant effect 1999, I took 100 cc soil cores at on nematode abundance, while 0-25 cm depth in the other 14 burning did. Burning clears the plots. All samples were stored in prairie of litter, leaving the a refrigerator until the nematodes topsoil exposed to solar heat were extracted and counted. I used (Hulbert, 1969). In contrast, the sieve extraction (Handoo, et. mowing covers the soil with al., 1999; Appendix B) and the litter. A study of tropical soil modified centrifugation-flotation nematodes found that disturbances techniques (Jenkins, 1964; that expose topsoil to drying Appendix C) to separate the after the initial disturbance nematodes from the soil and count caused a decrease in nematode them. I used ANOVA to determine species richness (Bloemers, et. the effect of burning and mowing al., 1997). Soil exposure on the treatments on nematode abundance. burned prairie plots could account for the decrease in nematode Results abundance that did not occur on prairie plots covered by litter. There are a few reasons why nematode abundance, although it effects of mowing could have was not significantly lower than decreased abundance of certain the other plots. The burn nematode species, although the treatment occurred in early decrease was not significant. spring, while the mow treatment Plant-feeding nematodes are occurred in late June. Depending dependent on the health of the on how much growth occurred plant (Freckman and Baldwin, between the burn and mow 1990). While both burning and treatments, there could have been mowing affect the health of the a much smaller amount of litter plant, plots that are cleared of cover on the burn/mow plots than litter tend to regenerate more on the mow plots. A limited quickly; in other words, litter amount of litter cover could initially inhibits new plant stimulate nematode abundance in growth (Hulbert, 1969). A sudden some species. Nematode abundance change in the health of the plant, is influenced by soil organic without new growth, could possibly matter and litter quality cause plant-feeding nematodes to (Freckman and Virginia, 1989). decrease in abundance. An Plant litter decomposition is a overabundance of litter caused by major source of nutrient inputs in mowing could also introduce too soil ecology (Molles, 1999). many toxins into the soil and Bloemers, et. al. (1997) suggested decrease nematode abundance there could be a positive (Yeates, et. al. 1997). Thus, correlation between the amount of litter cover could both directly litter and abundance of primary and indirectly decrease abundance decomposers. As stated in the in different nematode species. introduction, microbivorous and The plots that received the fungivorous nematodes feed on burn/mow treatment had the lowest primary decomposers. We could None of the treatments increased nematode abundance over the Figure 1. A Comparison of Mean control group. Hence, fire and Populations in the Fire and M Experiments at CERA, ± 1 standar mowing management practices do not 100 90 appear to compound the negative 80 effects of nematodes on health of 70 the prairie. The multiple effects 60 Burn of burn and mow treatments affect 50 No Burn 40 different nematode species in 30 different ways. Burn treatments # of nematodes 20 were shown to significantly 10 decrease nematode abundance. It 0 would be interesting to see how Mow No Mow burn treatments affect the then expect microbivorous and different feeding groups and more fungivorous nematodes to increase specifically, different species. A in mowed prairie plots that were study of the interactions between also recently burned. Bloemers, particular plant and nematode et. al. (1997) found the inverse species under the constraints of of this to be true as well: in fire, for example, could provide tropical soils, the proportion of useful data about the effects of bacterial feeding nematodes burn treatments on plant-eating decreased as organic inputs to nematodes. While mow treatments soil decreased. at CERA showed no significant decrease in nematode abundance, Daniel L. Dindal (Ed). Soil evidence from other studies Biology Guide. John Wiley & suggest that different amounts of Sons, NY. litter cover could produce Freckman, Diana W. and Ross A. different effects in nematode Virginia. 1997. Low-Diversity abundance. Again, studies of the Antarctic Soil Nematode interactions of specific nematode Communities: Distribution and groups or species could provide Response to Disturbance. data that are more useful. It Ecology, 78(2): 363-369. would be of particular interest to Freckman, Diana W. and Ross A. study how microbivorous and Virginia. 1989. Plant-feeding fungivorous species react to Nematodes in Deep-Rooting Desert litter cover, and assess whether Ecosystems. Ecology, 70(6): they have positive or negative 1665-1678. effects on nutrient cycling and Handoo, Zafar A., Donna Ellington, plant health. and A. Morgan Golden. 10/10/99. Some Procedures for Collecting Acknowledgements and Preparing Nematodes for Study. The author would like to thank http://www.ianr.unl.edu/son/ Laura Makinen for her initial Hulbert, Lloyd C. 1969. Fire and development of this project; Brian litter effects in undisturbed Turner for his research assistance bluestem prairie in Kansas. and for contacting Tom Powers; Tom Ecology 50: 874-877. Powers for providing useful tips Hulbert, Lloyd C. 1988. Causes of and the sugar centrifugation fire effects in tallgrass method protocol; Professors Brown prairie. Ecology, 69(1): 46-58.
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