Interactive effects of elevated CO2, warming, and altered water availability are being studied in a constructed ecosystem with plants typical of an old-field system (including C3 and C4 grasses, forbs, and legumes).
The hypotheses and research approach are built around four general predictions:
- The response of an old-field community to elevated [CO2] and increased air temperature will be mediated by the availability of soil water;
- Community composition and production will be driven by interactions between the component taxa and their individual and combined responses;
- Ecosystem-level responses will depend on the interactions between above- and below-ground processes; and
- A mechanistic understanding will be necessary to explain the responses to temperature and the net ecosystem response to the multiple factor interactions and feedbacks.
Specific hypothese include:
- Warming will have negative effects on productivity because of increased evapotranspiration, but this effect will be moderated by elevated CO2, which will tend to reduce transpiration.
- Increased soil temperatures will stimulate N mineralization and availability, thereby enhancing aboveground productivity.
- Increases in temperature that remove temperature constraints on plant growth may simply advance the growing season and plant phenology with no net change in production, or may lengthen the growing season and thereby increase production
- Plant community composition will be governed by functional group response to resource availability and interactions between functional groups.
- The responses of growth and activity of arbuscular mycorrhizae of old-field plants to environmental perturbations are predictable from changes in carbon allocation below ground.