Plant photosynthesis is the source of energy for most organisms on earth and plant biomass supports complex consumer foodwebs composed of a wide array of organisms including fungal pathogens, insect herbivores, and mammalian herbivores. In turn, these consumers can alter the productivity, diversity, and composition of the plant communities on which they depend. Many studies have the effects of examined individual groups of consumers through the use of herbivore fencing or insecticides, however few studies manipulate these groups in a single experiment. To quantify and compare the effects of multiple consumer groups, we established two experiments (E244 and E245) in 2008 that use insecticides, fungicides, and fences to manipulate the presence of insects, soil fungi, foliar fungi, or vertebrate herbivores. These experiments are conducted in two settings: an experiment that manipulates plant richness and composition and a natural, old field community. The first experiment (E244) is nested within 32 BigBio plots (E120) such that the fungicide and insecticide treatments are crossed with plant community diversity. The second experiment (E245) is conducted in an old field and has an additional treatment (unfenced, or fenced to exclude vertebrate herbivores). In 2019, we added a nutrient addition treatment to the old field plots (E245) at the subplot scale to quantify the interactions between nutrient supply and food web composition.
In both experiments, we apply treatments and measure NDVI weekly to bi-weekly throughout the growing season in all plots. We annually harvest biomass of each plant species, determine plant species diversity, and sample root biomass in all 253 experimental plots.
from: Borer, E. T., Lind, E. M., Ogdahl, E. J., Seabloom, E. W., Tilman, D., Montgomery, R. A., & Kinkel, L. L. (2015; Nov) Food-web composition and plant diversity control foliar nutrient content and stoichiometry. Journal of Ecology, 103(6), 1432 <last_page> 1441. doi:10.1111/1365-2745.12461
In 2008, we established experimental food-web manipulation subplots nested within 41 E120 experimental plots to examine the role of different components of the grassland food web in modifying ecosystem functions. In these 1.5 x 2 m subplots, we manipulated the presence of insects, soil fungi and foliar fungi by applying fungicides and insecticides alone and in combination on a fortnightly basis. The food-web manipulation treatments were crossed with plant community diversity for a total of five food-web manipulation treatment subplots (control, soil fungicide, foliar fungicide, insecticide and all combined) that were randomly assigned to locations within each of the 41 plant diversity plots (5 x 41 = 205 food-web manipulation subplots).
The grassland food web was manipulated using commonly applied agricultural pesticides. To control foliar fungi, we applied Quilt (Syngenta Crop Protection, Inc., Greensboro, NC, USA), a combination of azoxystrobin (7.5%) and propiconazole (12.5%), every other week from the beginning of the growing season through mid-September. Azoxystrobin inhibits fungal mitochondrial respiration, stopping spore production, germination and mycelial growth of fungi; propiconazole inhibits fungal demethylation, stopping cellular growth. Because these chemicals differ in action, their joint application reduces the likelihood of fungal adaptive resistance. Soil fungi were controlled via monthly application throughout the growing season (late-April until mid-September) of Ridomil Gold SL (Syngenta Crop Protection, Inc.), a soil drench fungicide containing mefenoxam (45.3%). Mefenoxam inhibits ribosomal RNA synthesis in many soil-inhabiting fungi, stopping mycelial growth and spore formation. We reduced insects in the subplots via application of the insecticide Marathon II (OHP, Inc., Mainland, PA, USA; 21.4% imidacloprid), every other week through the growing season. One to two times each growing season, malathion was applied instead of Marathon II to reduce the possibility for adaptation by the local insect populations to insecticide. Both of these chemicals are broad-spectrum insect neurotoxins; imidacloprid is a neonicotinoid compound, whereas malathion is an organophosphate insecticide. The class of fungicidal compounds used in this study (Triazoles) has been shown not to induce changes in the growth, height or leaf area of wild grasses; less is known of their effects on non-agricultural legumes. Similarly, work examining the insecticides used in this study suggests minimal direct effects on plant growth, and there is no evidence for non-target effects of pesticide treatments on other components of the food web, e.g. fungicides on insect communities.
Foliar fungi and plant diversity drive ecosystem carbon fluxes in experimental prairies
M Kohli, JA Henning, ET Borer, L Kinkel, EW Seabloom
Ecology Letters 24 (3), 487-497
Stability of grassland production is robust to changes in the consumer food web
M Kohli, ET Borer, L Kinkel, EW Seabloom
Ecology letters 22 (4), 707-716
Food webs obscure the strength of plant diversity effects on primary productivity
EW Seabloom, L Kinkel, ET Borer, Y Hautier, RA Montgomery, D Tilman
2017 Ecology letters 20 (4), 505-512