Principal Investigators:
Louise E.
Jackson, Department of Vegetable Crops, University of California, Davis,
CA 95616
Dennis E. Rolston,
Department, of Land, Air and Water Resources, University of California, Davis,
CA 95616
Collaborating Investigator:
Mark R. Stromberg, Hastings Natural History Reservation, Carmel Valley, UC Berkeley
Duration of project: 2 years
How does plant species composition affect soil C dynamics and
C storage in grasslands with different management histories? We focus on plants
with different rooting attributes and their contribution to soil C retention
in grasslands with different vegetation and past tillage history: annual grassland,
restored native perennial grassland, recently-tilled soil, and undisturbed grassland
soil with no plants present. These management treatments were initiated several
years ago at the UC Hastings Reserve in Monterey County. Plantings of an annual
legume and a deep-rooted non-leguminous annual will be made in each grassland
treatment. We hypothesize that: 1) Plant C is less likely to be retained as
soil C in grassland soils with a past history of tillage than in undisturbed
grasslands due to lack of physical protection. 2) Large inputs of root-derived
C result in greater retention of older soil C due to reliance of microbes on
freshly deposited material. 3) Plant species that produce 'recalcitrant' root
litter increase soil C storage, especially in deep zones with little soil microbial
activity. And, 4) linkages between plant and microbial community structure can
increase the potential for retention of soil C and N. Seasonally, we will conduct
soil profile analysis of C pools in roots and various organic matter fractions,
C mineralization activity, and soil CO2 concentrations and efflux
to be used to model CO2 production in situ. A field experiment
with 13C/15N-labelled amino acids will provide activity and fate measurements
in situ. In a microcosm experiment with large intact cores of soil from the
field, aboveground parts of plants will be labeled with foliar application of
13C/l5N-labelled urea. The C and N in rhizodeposits from living plants will be
assessed, and related to the timing of plant growth and development. After plant
senescence, fates of root and litter C and N will be determined. Based on these
experimental outcomes, we will suggest management scenarios to enhance C storage
in California grasslands.