Performing Department
Biological Sciences
Non Technical Summary
Soil health is central to the goal of producing healthy high-yield crops. Soil nutrients can be replaced seasonally from the breakdown of plant and animal material, but in conventional agroecosystems, these nutrients are removed from the system during harvest. This necessitates the commercial input of fertilizers that can cause detrimental ecosystem off-balance of nutrient flow. Research has shown that decomposing carcasses of large grazing animal replace nutrients in the soil, but no research has focused on the nutrient pulses that may leach into soil from the decaying carcasses of small animal. Further, there is very little understanding of how soil-dwelling insects that use carcasses as a resource, such as Nicrophorus burying beetles, may also cycle nutrient from carcasses back into the soil. This project will: 1) quantify the spatial and temporal occurrence of vertebrate carcasses, 2) determine whether animal carcasses contribute measurable macronutrients to soil, 3) determine whether necrophilous insect behaviors contribute to soil nutrient cycling, and 4) describe the change in microbial community abundance and structure associated with carcass decomposition and utilization.
Animal Health Component
0%
Research Effort Categories
Basic
75%
Applied
25%
Developmental
(N/A)
Goals / Objectives
Soil health is central to the goal of producing healthy high-yield crops. Annual and long-term cycling of organic material, minerals, and other nutrients contributes to the overall growth rate and primary productivity of natural and crop vegetation, which then contributes to health and productivity of the trophic cascade. As farmers become more attuned to environmentally responsible farming practices, they are seeking solutions for increasing crop yield in a way that preserves the nutrient richness of soil without the use of costly and potentially hazardous anthropogenic inputs.The contribution to soil health of organic material and nutrients from plant material is well established. But, little is known regarding the contribution of organic material and nutrients from animal materials in the form of decaying carcasses. In fact, studies of nutrients emanating from carcasses are virtually absent from the agroscience literature, despite evidence from predatory-prey ecological literature showing carcasses can modulate heterogeneity in soil macronutrients, soil microbes, and plant quality (Bump et al., 2009; Danell et al., 2002; Melis et al. 2007). Entomological studies of the presence of invertebrates at carcass sites have revealed a biodiverse and temporally segregated cascade of necrophilous scavengers, but there is a dearth of studies investigating the nutrient cycle and resulting surge of plant growth that may result when soil-dwelling insects utilize small carcasses as a food and/or reproductive resource. While this interaction is assumed to occur, the scale at which necrophilous insect breakdown carrion and return nutrient to the soil is unknown.This project will focus on the role of small animal carcasses as a primary source of soil organic material and macronutrients, and on the role that soil-dwelling necrophilous insects and microbes play in cycling these nutrients from the carcass into the soil structure. Specifically, this project will address the following questions:How do small vertebrate carcasses contribute to overall soil health?How do necrophilous insects facilitate the cycling of nutrients from carcasses into the soil?This project will utilize field experiments and laboratory analysis to investigate these questions at the alpha level. Experiments will establish these data from three different agroecosystem contexts. These contexts include nutrient cycling in an organic farming pasture, a commercially supplemented row-crop farm, and a minimal-input farmed forestry plot. The results from this project will help New England producers understand the importance of small animals and soil-dwelling insects in agroecosystems, and may serve as an incentive for maintaining suitable cover habitat surrounding farmed plots. Further, this project will provide preliminary data describing the role of microorganisms in the carcass-microbe-soil interaction cascade, and will be the first project to examine these interactions in the context of New England agroecosystems.Soil health is central to the goal of producing healthy high-yield crops. Soil nutrients can be replaced seasonally from the breakdown of plant and animal material, but in conventional agroecosystems, these nutrients are removed from the system during harvest. This necessitates the commercial input of fertilizers that can cause detrimental ecosystem off-balance of nutrient flow. Research has shown that decomposing carcasses of large grazing animal replace nutrients in the soil, but no research has focused on the nutrient pulses that may leach into soil from the decaying carcasses of small animals. Further, there is very little understanding of how soil-dwelling insects that use carcasses as a resource, such as Nicrophorus burying beetles, may also cycle nutrient from carcasses back into the soil. This project will:Objective 1: Quantify the spatial and temporal occurrence of vertebrate carcassesObjective 2: Determine whether animal carcasses contribute measurable macronutrients to soilsObjective 3: Determine whether necrophilous insect behaviors contribute to soil nutrient cyclingObjective 4: Describe the change in microbial community abundance and structure associated with carcass decomposition and utilizationReferences:Bump, J., Peterson, R. & Vucetich, J. (2009). Wolves modulate soil nutrient heterogeneity and foliar nitrogen by configuring the distribution of ungulate carcasses. Ecology 90(11): 3159-3167.Danell, K., Berteaux, D., & Brathen, K. (2002). Effect of muskox carcasses on nitrogen concentration in tundra vegetation. Artic 55(4): 389-392.Melis, C., Selva, N., Teurlings, I., Skarpe, C., Linnell, J., & Andersen, R. (2007). Soil-vegetation nutrient response to bison carcasses in Bialowieza Primeval Forest, Poland. Ecological Research 22(3): 807-813.
Project Methods
Objective 1: Quantify the spatial and temporal occurrence of vertebrate carcassesLittle work has been done to quantify the temporal and spatial distribution of naturally occurring small vertebrate carcasses in local landscapes. In fact, survey protocol for census of small animal carcasses is absent from the literature. Therefore, a three-year study will be conducted at three agro-ecosystems: the UNH Woodman farm, the organic dairy, and at UNH forest sites to develop a first-ever method for quantifying the occurrence of carcasses that could provide a reproductive resource for Nicrophorus species. Carcass presence will be surveyed from Jun-Sept, which is the active season of Nicrophorus beetles. Surveyors will canvas four cardinal-direction 10 m transects at each field site. Since carcasses are an ephemeral and sought-after resource, transects will be surveyed twice per week. We will also document the genus of any insects present on the carcasses. I will examine inter-site variation in carcass abundance using GLM in R statistical software, using survey site as the predictor and carcass quantity as the response, testing the null prediction that carcass abundance will not vary between sites.Objective 2: Determine whether animal carcasses contribute measurable macronutrients to soilNicrophorus beetles will be captured at UNH field sites using above-ground pitfall traps baited with aged meat. Wild-caught males and females will be breed in the lab, and F1 males and females will be maintained in the laboratory on a 14:10 day:night light cycle in individual containers until field experiments begin. Beetles will be fed organic vertebrate organ meat and given water via moistened paper towel, ad libitum.At each field site, researchers will set three grid plots of three experimental treatments. Each grid plot will contain six 1 m replicate exclosures of each of the following treatments: 1) the control, 2) carcass only, and 3) carcass with Nicrophorus breeding (total n=18 for three grid plots per field site).For carcass only experimental plots, a 35 g mouse carcass will be placed in the center of the 1 m x 1 m grid plot. Soil samples for Day 0 will be collected prior to placement of the carcass, and the preparation will be covered with mesh cloth and secured in place with metal stakes. This method ensures that predatory scavengers cannot access the carcass, but that abiotic environmental conditions that impact brood success (rainfall, temperature, and light level), remain constant. Carcass with Nicrophorus breeding experimental plots will be established similarly, along with the introduction of an F1 lab-reared male and female Nicrophorus beetle (N. orbicollis or N. marginatus). The aluminum mesh cover also captures eclosing brood offspring, allowing pertinent brood data (number of offspring, time to eclosure, sex ratio of the brood, offspring size, etc.) to be recorded.Because the typical breeding period for Nicrophorus beetles is 45 day, soil samples will be collected from three plots of each treatment from each grid at three temporal intervals: Day 0, Day 22, and Day 45. Samples will be collected using a 2 cm diameter corer from the soil surface, and at 30 cm, and at 45 cm to allow for analysis of conditions on the surface where the carcass was deposited, at the approximate depth of carcass burial, and at a depth below the carcass. Soil will be measured for enzyme activity (as a proxy for microbial activity), inorganic N, organic carbon, organic nitrogen, and pH. Enzyme assays will follow established protocol. Soil inorganic N, measured as concentrations of NO3- and NH4+, be determined colorimetrically according to the Hach packet (Loveland, CO, USA). Depending on soil type and aggregate size, we will utilize OC and ON methods that are appropriate for analysis, such as determination of total soil C and N using a Costech elemental analyzer (Costech ECS 4010; Costech Analytical Technologies Inc, Valencia, CA, USA). Soil pH will be determined spectrophotometrically using a method that extracts nitrate and ammonium, reacts each in a series of reductions, and forms a color reaction. Data from this 3x3 factorial design will be evaluated using Generalized Linear Mixed Model (GLMM) techniques, examining differences in soil nutrient concentrations over time across three sites in three conditions, testing the hypothesis that carcass decomposition alone will result in increases in available N and C, decreases in pH, and increases in soil microbial biomass and activity.Objective 3: Determine whether necrophilous insects contribute to soil nutrient cyclingThe method for determining this interaction will be conducted as outlined above utilizing the soil samples collected from the control plots (grey) and the plots in which Nicrophorus breedings are active (green) (see Fig. 1). Here I test the hypothesis that carcass burial and processing by Nicrophorine burying beetles will result in increases in available N but not C, decreases in soil pH, and increases in soil microbial biomass and activity.Objective 4: Describe the change in microbial community abundance and structure associated with carcass decomposition and utilizationTo quantify microbial respiration in each treatment and at each agro-use site, 30 cm and 45 cm depth soil sample will be placed in jars and capped with rubber septa-fitted lids. CO2 concentration will be measured from air headspace using an LI-820 infrared CO2 analyzer (Licor Biosciences, Lincoln, NE). Microbial biomass C and N will be measured according to the fumigation/extraction. Microbial community structure and diversity associated with carcass and soil will be determined using next-generation sequencing of the V6 hypervariable region of 16S rRNA gene. We note that our focus will be on bacterial communities only, the best characterized microbial taxon studied to date. DNA from soil samples will be extracted using MoBio PowerSoil DNA Isolation kits (Qiagen, Carlsbad, CA). We will use amplicon-based targeting of 16S rRNA for each sample and sequencing libraries will then be prepared, pooled, and sequenced on an Illumina HiSeq2500 (San Diego, CA) at UNH's Hubbard Genome Center. Sequence data will be analyzed using QIIME to determine various measures of species diversity. Our analyses of soil microbial communities follow the overall methodologies of the Earth Microbiome Project, which has rigorously tested these methods for assessing microbial diversity and composition in soils worldwide. Microbial biomass and community structure data will also be analyzed using a full factorial Generalized Linear Mixed Model (GLMM) design, testing the hypothesis that carcass burial by burying beetles will result in a lower abundance but greater taxonomic diversity than carcass decomposition alone. Digitized field notes, spreadsheets, and other data will be stored in hard copy and digital format on lab computers and external hard drives, as well as on my lab cloud hosting platform. Molecular data will be stored at -80°C, and sequence data archived according to standard protocol through NCBI SRA archives.Microbial community samples will be assayed during four distinct timeframes of carcass utilization: 1) before contact with adult beetles, 2) following burial and carcass preparation by adult beetles, 3) during larval feeding stages, and 4) following larval dispersal pre-pupation. Negative control samples will be sampled from carcasses that have not come into contact with adult beetles, but that are exposed to the same environmental conditions as treatment samples.