COS 243-6 - Fine-scale spatial-structure of a generalist soil-borne plant pathogen in an untilled grassland

Background/Question/Methods

Soil-borne pathogens can readily infect host species and spread throughout an ecological community potentially altering plant abundances and ecosystem functioning; however, most of what we know of these effects comes from agricultural systems. For example, Macrophomina phaseolina is a generalist soil-borne fungal plant pathogen, but its spatial distribution and role in natural communities is nearly unknown. In this preliminary work, we quantified the fine-scale, spatial patterns of M. phaseolina and potential associations with soil and plant variables at two spatial scales in an untilled tallgrass prairie in central Kansas. At the coarse scale, we collected plant and soil samples at 1 m intervals within a 15x15 m grid. We then inoculated 10 g of each soil sample onto selective media and enumerated the colony forming units (CFU) to determine the inoculum density of M. phaseolina per gram of soil. Subsequently we located a fine-scale grid (1.4x1.4 m) centered at the interface between high and low M. phaseolina densities detected the year prior and enumerated inoculum density at 7 cm intervals.

Results/Conclusions

We found high variability in the inoculum density of M. phaseolina varying from 0-8.8 CFU/g of soil at the coarse scale and 0-9.1 CFU/g of soil at the fine scale. Heat maps suggested that ‘hot spots’ occurred within the sampled areas at both scales, but spatial statistics revealed no evidence of spatial aggregation at either scale. We found negative correlations between inoculum density and soil carbon, nitrogen, and organic matter, but these relationships were weak. Likewise, there was little evidence for a clear correlation between the plant community and inoculum density. Our intensive spatial sampling demonstrates M. phaseolina can obtain high inoculum densities within prairie, yet these patterns appear unconnected with obvious environmental variables. However, further work is needed to determine how temporal variability may contribute to the relationships with key environmental factors and to determine the influence of such pathogens in native habitats.