Document: CHA-3-59-101

Effects of experimentally excluding foliar fungal plant disease on a grassland ecosystem: linking belowground production and allocation to leaf longevity and photosynthetic capacity.

MITCHELL, C.E.*

University of Minnesota, St. Paul MN 55108 USA ¹

Abstract:
To test the effects of plant disease on ecosystem processes, I chemically excluded foliar fungal plant pathogens from replicated plots of late-successional grassland using a fungicide spray. Fungicide treatment significantly reduced the percent leaf area infected by fungi by about an order of magnitude relative to unsprayed control plots. Fungicide treatment significantly increased root production by 34%, and generally increased aboveground production by 5-10%, although significance varied. Three years of fungicide treatment significantly increased standing root mass by 47%, and significantly increased root to shoot ratio from 1.6 to 2.3. At this time, total ecosystem carbon was 8%, but not significantly, greater in the fungicide treated plots. Fungicide treatment significantly increased soil respiration by 16%. Direct effects of the fungicide on the plants do not explain these results; in a companion greenhouse experiment, the only direct effect of the fungicide was to reduce root to shoot ratio in one subdominant species. Rather, these effects may be explained by increased leaf longevity and carbon gain under disease exclusion. Fungicide treatment significantly increased leaf longevity by 27% for the dominant species, Andropogon gerardi, and increased leaf longevity of three subdominant species by 4-32%, but not always significantly. Fungicide treatment significantly increased Andropogon maximum net photosynthetic rate by 32%. This study suggests that, by reducing leaf longevity and photosynthesis, ambient levels of foliar fungal disease strongly limit belowground plant allocation in this ecosystem.

Keywords: carbon storage, plant disease, plant allocation

This abstract is being presented at: 1:45 PM in session:
Oral Session #52: Carbon Storage in Ecosystems.