Experiment at restored perennial grassland, Hastings Reserve

Martin Potthoff, Kerri Steenwerth and Louise Jackson

Restoring native perennial bunchgrasses in California's non-native annual grassland has been notoriously difficult. The only successful method has been to use agricultural techniques such as tillage and herbicide for two to three years to control exotic annuals before seeding with native perennials. The field area of this project is the UC Hastings Natural History Reservation in the foothills of the Santa Lucia Mountains in Upper Carmel Valley. The study site is located on a level area that was farmed between 1865 and 1937. From 1937 to 1996, the site was annual grassland. Different management treatments are established for grasslands. Now, after 5 years, these treatments have been in place long enough to provide meaningful data on soil microbial and soil chemical properties. There are three field management types:

• tilled annual grassland that has been plant-free for 5 years using tillage and Round-up^TM herbicide
• annual grassland
• 3-year old restored perennial grassland that was created after tilling annual grassland and planting with the native bunchgrasses, Nassella pulchra and Elymus glaucus.

The investigations include field experiments as well as lab experiments. The work is addressing the following questions: Is the microbial carbon turnover different in an annual and in a perennial grassland, and how does it affect CO2 loss and soil C retention? Is there an effect on the productivity, microbial C turnover, and soil C retention in restored bunchgrass grassland associated with the winter legume annual, Lupinus bicolor ? Are there differences between the litter qualities and the decomposer activity of grassland types, caused by vegetation and management? The performance of the project work will include a classical litter bag approach, a application of the bait-lamina test, and determinations of the vertical distribution of soil CO2. Moreover, we will apply stable isotope techniques for 13C to investigate the fate of plant derived carbon in the soil system.

References

Pothoff, M., K.L. Steenwerth, L.E. Jackson, R.E. Drenovsky, K.M. Scow, R.G. Joergensen, 2006. Soil microbial community composition as affected by restoration practices in California grassland. Soil Biology and Biochemistry 38:1851-1860. P

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