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Consumer effects on plant community structure, biomass, and decomposition

Project Abstract: 
Plants have many natural enemies that can have top-down effects on plant diversity, plant species relative abundance, and ecosystem processes such as productivity and decomposition. These natural enemies include insect herbivores, mollusks, and foliar fungal pathogens. Critically, the effects of insect herbivores, mollusks and fungal pathogens are most often studied in isolation, so our understanding of their interactive effects on plant community composition and ecosystem function is limited. Furthermore, we know even less about whether above ground natural enemies have effects on belowground processes such as decomposition. To address these research gaps, I will work within the BugNet experiment where insects, mollusks, and fungal pathogens are factorially excluded from using biocides. I will quantify exclusion effects on plant diversity, above ground biomass, and decomposition by employing a standardized method of estimating decomposition using tea bags. By factorially excluding insect herbivores, mollusks, and fungal pathogens, this work will improve our understanding of the role of each taxa in structuring plant communities, and whether they can also affect below ground ecosystem functions.
Investigators: 
Status of Research Project: 
Years Active: 
2022 to 2024
Research sites: 
Methods: 
The experimental BugNet site is located in the UV field at UMBS. This site is organized in three blocks, each of which contains eight experimental plots. All experimental plots are 5 × 5 meters, with a distance of at least one meter between each plot. There are three replicates per treatment, making 24 plots total. Insect herbivores, mollusks, and fungal pathogens are factorially excluded using multiple biocides. I will exclude insect herbivores by spraying Lambda-Cyhalothrin, a broad-spectrum insecticide commonly used in herbivore exclusion experiments. To exclude mollusks, I will spread ferric phosphate molluskicide pellets. To exclude foliar fungi, I spray a mixture of azoxystrobin and difenoconazole which inhibit fungal respiration and fungal cell membrane synthesis, respectively. I will apply the biocides that exclude insect herbivores, mollusks, and fungal pathogens at the beginning of the growing season and then every 5 weeks until the end of the growing season. At the end of the growing season, I will quantify plant community composition and biomass. I will identify all plant species present in a 1-m2 subplot at the southwest corner of each 5 x 5 m plot and estimate the percent cover of each species. In a 20 × 50 cm strip within each 1-m2 subplot, I will remove all above ground plant biomass at soil level. I will separate plant species by plant functional group, dry at 60ºC for 72 hours, and weigh dried biomass. I will estimate decomposition in each treatment using the tea bag index protocol outlined by Keuskamp et al. 2013. In the southeast corner of each 5 × 5 m plot, I will bury one bag of Lipton green tea (EAN: 87 22700 05552 5) and one bag of Lipton rooibos tea (EAN: 87 22700 18843 8). Prior to burying, I will estimate the initial weight of the tea by weighing each tea bag and then subtracting the weight of an empty tea bag. I will bury each tea bag 8-cm deep in the soil and mark the location with at flag, also leaving the labelled tea bag tag visible above the soil to aid in retrieval. I will retrieve the tea bags after 90 days, remove any soil particles on the exterior of the tea bag, and dry the tea bags for 48 hours at 70ºC. After drying, I will weigh each tea bag and subtract the weight of an empty bag to determine tea weight following burial in the soil. Using the amount of weight the tea lost, I will calculate a decomposition curve to estimate decomposition rate in each experimental treatment. References Keuskamp, J. A., Dingemans, B. J., Lehtinen, T., Sarneel, J. M., & Hefting, M. M. (2013). Tea Bag Index: a novel approach to collect uniform decomposition data across ecosystems. Methods in Ecology and Evolution, 4(11), 1070-1075.