Biogeochemical Interactions Between an Invasive Scarab ... · Biogeochemical Interactions Between...
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Biogeochemical Interactions Between an Invasive Scarab (Japanese beetle Popillia japonica Newman) and its Subterranean Environment Garrett Y. Price, Brittany F. Peterson, Michael E. Scharf, Matthew D. Ginzel, and Douglas S. Richmond Department of Entomology, Purdue University, West Lafayette, IN 47907 Abstract Introduction Objective Materials and Methods Results and Discussion Conclusion The goal of this project is to gain a better understanding of the interactions between invasive Japanese beetle (JB) larvae and their subterranean environment. In support of this goal, we quantified the impact of JB larvae on soil microbial activity and functional diversity. CO 2 flux in soil microcosms was measured in response to JB larval infestation to provide a surrogate measure of their impact on soil microbial activity. Coarse changes in microbial functional diversity were also examined using phospholipid fatty acid (PLFA) analysis. Findings support the idea that JB larvae cause significant and lasting changes to soil microbial diversity and activity by weakening soil fungal and protozoan populations and shifting remaining microbial populations in favor of bacteria. These changes resulted in increased microbial activity, potentially liberating larger amounts of CO 2 from the soil. Our results suggest that JB infestations may reduce soil organic matter and increase soil CO 2 emissions. Results also imply that interactions between JB larvae and the soil are, in part, microbially-mediated, which could have implications for pest management. Invasive species are a serious economic and ecological threat throughout the world. Although the ecological consequences of invasion by above-ground insects have been well documented, the impacts of invasive insects that spend the majority of their life underground have received much less attention. The ability of invasive soil insects to alter fundamental soil processes is poorly understood. Since its introduction almost a century ago, the Japanese beetle has managed to infest most of the Eastern United States (USDA, 2000). The Japanese beetle larva is a serious pest of turf (Fig. 1A) and ornamental crops where it feeds on the soil, thatch, and roots of turfgrass (Fig. 1B). In order to break down the relatively nutrient poor soil matrix, the larval hindgut is modified into a multi-lobed, bulbous microbe-rich, fermentation chamber where symbiotic microbes aid in digestions (Fig. 1C) (Crowson 1954, Egert et al 2005, Pittman et al 2008). In the case of the invasive earthworm Lumbricus terrestris, these gut microbial associates enhance decomposition of organic residues (Vinotha et al 2000), mobilize plant nutrients (Biswas 2014), direct earthworm foraging patterns, and facilitate chemical communication (Novo et al. 2013). Whether or not invasive soil insects like the Japanese beetle have similar impacts on the soil they infest remains unclear. To better understand interactions between an invasive soil insect and its subterranean environment by examining its effects on soil microbial activity and soil microbial community structure. Soil Microbial Activity CO 2 Flux - Microcosms with 60 g of clean field soil and either 0, 5, or 10 third instar larvae were left to incubate for 72 hours (Fig. 2). The larvae were then removed, and the microcosms sealed for 24 hours. Finally, a headspace gas sample was taken, and the CO 2 measured via gas chromatography-mass spectrometry against a set of standards. Microbial Functional Diversity In order to quantify the impacts of JB larvae on soil functional diversity, I processed samples from the microcosms used above. These samples were then analyzed using phospholipid fatty acid (PLFA) analysis in order to observe coarse changes to the microbial communities between treatments. Soil Microbial Activity Soil CO 2 flux was higher in soil that was previously infested by JB larvae with headspace CO 2 concentrations increasing linearly as larval density increased (Fig. 3A). This finding indicates that JB larval infestations may increase soil microbial activity even after larvae are no longer present. Microbial Functional Diversity There was a negative correlation between the functional diversity of microcosm soil and larval density (Fig. 3B). As the larval density increased, the ratio of protozoa (Fig. 3C) and fungi (Fig. 3D) to bacteria shifted in favor of bacteria. • CO 2 concentrations increased with larval density indicating an increase in soil microbial activity following infestation. • PLFA analysis showed a decrease in functional diversity with a shift towards bacteria as larval density increased. • Invasive soil insects could potentially alter soil microbial communities in ways that influence C-cycling and soil health Contact the Author: [email protected] R 2 =0.45 P=0.01 R 2 =0.38 P=0.03 R 2 =0.57 P<0.01 R 2 =0.35 P=0.04 References Cited: USDA/APHIS 2000. Managing the Japanese Beetle. A Homeowner’s Handbook. US Dept. Agric. Crowson, R.A. (1954) (Reprint 1967) The natural classification of the families of coleoptera. E. W. Classey, Middlesex. Egert, Markus, et al. "Structure and topology of microbial communities in the major gut compartments of Melolontha melolontha larvae (Coleoptera: Scarabaeidae)." Applied and environmental microbiology 71.8 (2005): 4556-4566. Pittman, Geoffrey W., et al. "“Endomicrobia” and other bacteria associated with the hindgut of Dermolepida albohirtum larvae." Applied and environmental microbiology 74.3 (2008): 762-767. Vinotha, S.P., K. Parthasarathi and L.S. Ranganathan: Enhanced phosphatase activity in earthworm casts is more of microbial origin. Curr. Sci., 79, 1158-1159 (2000). Biswas, Sreejata, Pulak Lahiri, and Satadal Das. "A study on the role of a close homologue of Bacillus cereus isolated from Metaphire posthuma on germination of gram" Journal of Global Biosciences ISSN 3.4 (2014): 708-713. Novo, Marta, et al. "Pheromone evolution, reproductive genes, and comparative transcriptomics in Mediterranean earthworms (Annelida, Oligochaeta, Hormogastridae)." Molecular biology and evolution (2013): mst074. Figure 1: (A) The damage caused by JB larvae on turfgrass is due to their preference for (B) feeding on the thatch-soil matrix. (C) To digest the nutrient-poor soil, they host microbes in their bulbous, multi-lobed hindgut. Figure 2: Microcosms of 0, 5, or, 10 3 rd instar larvae in 60 g of previously uninfested soil were established in order to measure soil microbial activity and the soil microbial community. Figure 3: (A) CO 2 concentration in headspace samples increased as larval density increased. (B) Functional microbial diversity decreased as the larval density increased. (C) The ratio of protozoa to bacteria shifted in favor of bacteria as larval density increased. (D) The ratio of fungi to bacteria also shifted in favor of bacteria as larval density increased. Acknowledgements: I’d like to thank Gabriel Hughes, Lauren Beebe, Alexandra Duffy, Danielle Craig, and Jasleen Kaur for technical assistance and the Daniel Center staff for letting me infest their turf and then surround it with an electric fence.
Transcript of Biogeochemical Interactions Between an Invasive Scarab ... · Biogeochemical Interactions Between...
Biogeochemical Interactions Between an Invasive Scarab (Japanese beetle Popillia
japonica Newman) and its Subterranean Environment
Garrett Y. Price, Brittany F. Peterson, Michael E. Scharf, Matthew D. Ginzel, and Douglas S. RichmondDepartment of Entomology, Purdue University, West Lafayette, IN 47907
Abstract
Introduction
Objective
Materials and Methods
Results and Discussion
Conclusion
The goal of this project is to gain a better understanding of theinteractions between invasive Japanese beetle (JB) larvae and theirsubterranean environment. In support of this goal, we quantified theimpact of JB larvae on soil microbial activity and functional diversity.CO2 flux in soil microcosms was measured in response to JB larvalinfestation to provide a surrogate measure of their impact on soilmicrobial activity. Coarse changes in microbial functional diversity werealso examined using phospholipid fatty acid (PLFA) analysis. Findingssupport the idea that JB larvae cause significant and lasting changes tosoil microbial diversity and activity by weakening soil fungal andprotozoan populations and shifting remaining microbial populations infavor of bacteria. These changes resulted in increased microbialactivity, potentially liberating larger amounts of CO2 from the soil. Ourresults suggest that JB infestations may reduce soil organic matter andincrease soil CO2 emissions. Results also imply that interactionsbetween JB larvae and the soil are, in part, microbially-mediated, whichcould have implications for pest management.
Invasive species are a serious economic and ecological threatthroughout the world. Although the ecological consequences ofinvasion by above-ground insects have been well documented, theimpacts of invasive insects that spend the majority of their lifeunderground have received much less attention. The ability of invasivesoil insects to alter fundamental soil processes is poorly understood.
Since its introduction almost a century ago, the Japanese beetle hasmanaged to infest most of the Eastern United States (USDA, 2000). TheJapanese beetle larva is a serious pest of turf (Fig. 1A) and ornamentalcrops where it feeds on the soil, thatch, and roots of turfgrass (Fig. 1B).In order to break down the relatively nutrient poor soil matrix, thelarval hindgut is modified into a multi-lobed, bulbous microbe-rich,fermentation chamber where symbiotic microbes aid in digestions (Fig.1C) (Crowson 1954, Egert et al 2005, Pittman et al 2008).
In the case of the invasive earthworm Lumbricus terrestris, these gutmicrobial associates enhance decomposition of organic residues(Vinotha et al 2000), mobilize plant nutrients (Biswas 2014), directearthworm foraging patterns, and facilitate chemical communication(Novo et al. 2013). Whether or not invasive soil insects like theJapanese beetle have similar impacts on the soil they infest remainsunclear.
To better understand interactions between an invasive soil insect andits subterranean environment by examining its effects on soil microbialactivity and soil microbial community structure.
Soil Microbial ActivityCO2 Flux - Microcosms with 60 g of clean field soil and either 0, 5, or 10third instar larvae were left to incubate for 72 hours (Fig. 2). The larvaewere then removed, and the microcosms sealed for 24 hours. Finally, aheadspace gas sample was taken, and the CO2 measured via gaschromatography-mass spectrometry against a set of standards.
Microbial Functional DiversityIn order to quantify the impacts of JB larvae on soil functional diversity,I processed samples from the microcosms used above. These sampleswere then analyzed using phospholipid fatty acid (PLFA) analysis inorder to observe coarse changes to the microbial communities betweentreatments.
Soil Microbial ActivitySoil CO2 flux was higher in soil that was previously infested by JB larvaewith headspace CO2 concentrations increasing linearly as larval densityincreased (Fig. 3A). This finding indicates that JB larval infestations mayincrease soil microbial activity even after larvae are no longer present.
Microbial Functional DiversityThere was a negative correlation between the functional diversity ofmicrocosm soil and larval density (Fig. 3B). As the larval densityincreased, the ratio of protozoa (Fig. 3C) and fungi (Fig. 3D) to bacteriashifted in favor of bacteria.
• CO2 concentrations increased with larval density indicating anincrease in soil microbial activity following infestation.
• PLFA analysis showed a decrease in functional diversity with a shifttowards bacteria as larval density increased.
• Invasive soil insects could potentially alter soil microbialcommunities in ways that influence C-cycling and soil health
Contact the Author: [email protected]
R2=0.45P=0.01
R2=0.38P=0.03
R2=0.57P<0.01
R2=0.35P=0.04
References Cited:USDA/APHIS 2000. Managing the Japanese Beetle. A Homeowner’s Handbook. US Dept. Agric.Crowson, R.A. (1954) (Reprint 1967) The natural classification of the families of coleoptera. E. W. Classey,
Middlesex.Egert, Markus, et al. "Structure and topology of microbial communities in the major gut compartments of
Melolontha melolontha larvae (Coleoptera: Scarabaeidae)." Applied and environmental microbiology 71.8(2005): 4556-4566.
Pittman, Geoffrey W., et al. "“Endomicrobia” and other bacteria associated with the hindgut of Dermolepidaalbohirtum larvae." Applied and environmental microbiology 74.3 (2008): 762-767.
Vinotha, S.P., K. Parthasarathi and L.S. Ranganathan: Enhanced phosphatase activity in earthworm casts is more ofmicrobial origin. Curr. Sci., 79, 1158-1159 (2000).
Biswas, Sreejata, Pulak Lahiri, and Satadal Das. "A study on the role of a close homologue of Bacillus cereusisolated from Metaphire posthuma on germination of gram" Journal of Global Biosciences ISSN 3.4 (2014):708-713.
Novo, Marta, et al. "Pheromone evolution, reproductive genes, and comparative transcriptomics in Mediterraneanearthworms (Annelida, Oligochaeta, Hormogastridae)."Molecular biology and evolution (2013): mst074.
Figure 1: (A) The damage caused by JB larvae on turfgrass is due to their preference for(B) feeding on the thatch-soil matrix. (C) To digest the nutrient-poor soil, they hostmicrobes in their bulbous, multi-lobed hindgut.
Figure 2: Microcosmsof 0, 5, or, 10 3rd instarlarvae in 60 g ofpreviously uninfestedsoil were establishedin order to measuresoil microbial activityand the soil microbialcommunity.
Figure 3: (A) CO2 concentration in headspace samples increased as larval densityincreased. (B) Functional microbial diversity decreased as the larval density increased.(C) The ratio of protozoa to bacteria shifted in favor of bacteria as larval densityincreased. (D) The ratio of fungi to bacteria also shifted in favor of bacteria as larvaldensity increased.
Acknowledgements: I’d like to thank Gabriel Hughes, Lauren Beebe, AlexandraDuffy, Danielle Craig, and Jasleen Kaur for technical assistance and the Daniel Centerstaff for letting me infest their turf and then surround it with an electric fence.
