Understanding Microbes Helps Explain Nutrient Cycling

The turfgrass sites were found to be bacterially dominated and particularly abundant in gram positive bacteria — the stress tolerators. This result confirmed what Karp and Nelson (2004) found for soil (push-up) putting greens. The relative dominance of gram positive bacteria is somewhat unique to turfgrass. Typically, this level of community dominance by gram positive bacteria is found in extreme climates. Previous research on the microbial diversity of prairies found that arbuscular mycorrhizal fungi dominate prairies followed by gram negative bacteria.

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The turfgrass soils tested had a wide range in physical and chemical properties. Bulk density ranged from 0.7 grams per cubic centimeter. (g/cm3) to 1.4 g/cm3, organic matter from 2 percent to 18 percent, and there was a great diversity of soil texture as shown by the large ranges in sand and clay content of the soils. Regression analysis was performed to see how the microbial functional groups were affected by soil properties. Soil texture, organic matter, bulk density and soil pH had very little effect on the individual functional groups and the total microbial biomass.

However, of the functional groups, saprophytic fungi were most sensitive to changes in soil properties and were found to increase in abundance as organic matter increased, and decrease in abundance as clay content increased. The gram positive bacteria also increased in abundance with increasing organic matter, although the relationship between these two variables was fairly weak. While no strong linear correlations were found among functional groups and soil properties, a statistical technique known as principle component analysis discovered some significant interactions between the microbial community and soil properties. Principle component analysis can be thought of as a diversity index, which determines a unique fingerprint for each microbial community. In short, the results from this analysis confirm that microbial communities are indeed influenced by the properties of their soil habitats, although the differences do not break down as simply as the above mentioned functional groups.

The results of this research serve somewhat as a census of the microbial community in turfgrass systems, defining the species demographic and the corresponding labor force of the population as well as the influence of soil properties.

While this research does not directly suggest how these population dynamics can improve turf quality, it provides a starting point to move that direction.

Dan Lloyd is a graduate student/research fellow in the soil science department at the University of Wisconsin-Madison. Doug Soldat and Teri Balser are UW-M faculty members. You can reach Lloyd at dtlloyd@wisc.edu.

REFERENCES

Alig, R., Kline, J., and M. Lichtenstein. 2004. Urbanization on the US landscape: looking ahead in the 21st century. Landscape and Urban Planning 69: 219-234.

Craig, N.M. 2007. Exploring biotic and social aspects of rain gardens in Dane County, Wisconsin. M.S. Thesis: University of Wisconsin-Madison, Madison, WI.

Karp, M.A., and E.B. Nelson. 2004. Bacterial communities associated with creeping bentgrass in soil and sand root zones. USGA Turfgrass and Environ. Res. Online. 3(24):1-19.

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