Martin Potthoff, Kerri Steenwerth and Louise Jackson

When non-native annual grasslands in California are re-vegetated with native California perennial bunchgrasses, the soil microbial community composition of the restored sites bears more resemblance to annual grasslands than relict perennial grasslands, indicating slower recovery of soil vs. vegetation to the management transistion. Using tillage to reduce the seed bank of annual plants initially has little longer-term effect on soil microbial biomass and activity, compared to undisturbed annual grassland.

Restoring native perennial bunchgrasses in California's non-native annual grassland has been notoriously difficult. One 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 were established for grasslands:

• tilled annual grassland that has been plant-free for 5 years using tillage and Round-upTM 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.\

After 5 to 7 years, a series of field and lab experiments were conducted. The work addressed 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?


References


Potthoff, M., L. E. Jackson, S. Sokolow, and R.G. Joergensen. Responses of plants
     and microbial communities to litter addition and annual lupines in perennial
     California grassland restored with the bunchgrass, Nassella pulchra. In press,
     Restoration Ecology.

Jackson, L.E., M. Potthoff, K.L. Steenwerth, A.T. O’Geen, M.R. Stromberg, and K.M.
     Scow. 2007. Soil biology and carbon sequestration. Chapter 7. In: Ecology and
     Management of California Grasslands (Corbin, J., C. D’Antonio, and M.R.
     Stromberg, eds.). University of California Press, Berkeley, CA. pp. 107-118.
     ucce.ucdavis.edu/files/filelibrary/5472/43464.pdf

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.  ucce.ucdavis.edu/files/filelibrary/5472/28051.pdf

Pothoff, M., L.E. Jackson, K.L. Steenwerth, I.Ramirez, M.R. Stromberg, and D.E.
    Rolston, 2005. Soil biological and chemical properties in restored perennial
    grasslands in Califonia. Restoration Ecology 13:61-73.