PARENT SESSION
Oral Session # 93: Vegetation Change and Response.
Presiding: B Parry Hecht
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 105.
Experimental scale and precipitation modify effects of N-deposition on a plant pathogen.
Strengbom, Joachim*,1, 2, Englund, Göran1, Ericson, Lars1, 1 Department of Ecology and Environmental Science, Umeå, Sweden, Sweden2 Present address: Department of Forest Resources, St. Paul, Minnesota, USA
ABSTRACT- When logistical and financial factors limit the spatial scale used in ecological experiments, it is important to know how such simplifications affect the generality of the results. Increased disease incidence on bilberry (Vaccinium myrtillus) of the parasitic fungus Valdensia heterodoxa has previously been found to play a key role for N-induced changes in species composition changes in boreal forests in Sweden. The fungus mediates vegetation changes by defoliating the dominant species V. myrtillus. This enables the grass Deschampsia flexuosa to increase in abundance. We studied the potential effect of a spatial scale-dependent interaction between the parasite and V. myrtillus in a N fertilization experiment in northern Sweden. Plot sizes included in the experiment were 1, 10, 100 and 1000 m2. Disease incidence by the fungus was, on average, higher in large plots with high N treatment than in small plots with low N treatment. The difference in disease incidence between small and large plots increased between 1998 and 2000. Potential mechanisms that may cause the observed scale dependence include a) scale-dependent dispersal of the fungus and b) a combination of scale-dependent heterogeneity in soil moisture and a nonlinear growth function of the fungus. Disease incidence during 1996-2000 showed a strong positive correlation to summer precipitation and high precipitation enhanced the effect of nitrogen. Climate models suggest that global warming will lead to increased summer precipitation in Northern Scandinavia. Thus an important implication of our result is that global climate change may enhance positive effects of N-deposition on the incidence of the pathogen and, indirectly, on plant species composition. Most certainly, spatial scale-dependence also exists in a large number of other experiments and a greater awareness of this issue may be needed in order to enable accurate predictions.
Key words: Parasitic fungus, Spatial scale-dependence, Vegetational change, Nitrogen addition