PLANT SPECIES COMPOSITION, SOIL BIOLOGY, AND CARBON STORAGE IN GRASSLANDS

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

Project Summary

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.