Ecosystem water fluxes for two grasslands in elevated CO₂: a modeling analysis

Area of Science:

• Ecology
• Environmental Science
• Climate Science

Background:

• Combining CO2 field experiment data with climate data is crucial for long-term ecological predictions.
• Ecosystem predictions require accounting for inherent differences in productivity and leaf area index (LAI) independent of CO2 effects.
• Long-term CO2 experiments are not feasible, necessitating modeling approaches.

Purpose of the Study:

• To model the effects of elevated carbon dioxide (CO2) and climate variability on ecosystem water fluxes.
• To investigate how grassland productivity and leaf area index (LAI) influence the response to CO2 and climate variations.
• To assess the impact of CO2 on water movement, transpiration, and drainage in different grassland types.

Main Methods:

• Utilized long-term weather records and field data from the Jasper Ridge CO2 experiment.
• Modeled ecosystem water fluxes using 10-year weather data (1985-1994).
• Compared water flux simulations between sandstone (higher productivity) and serpentine (lower productivity) grasslands.

Main Results:

• Sandstone grasslands showed significantly higher transpiration (approx. 30%) than serpentine grasslands (approx. 10%) under elevated CO2.
• Elevated CO2 increased soil drainage by 20% in sandstone, with minimal change in serpentine, despite similar biomass increases.
• Simulated water savings from elevated CO2 ranged from 54-76 mm in early-season transpiration for sandstone grasslands.

Conclusions:

• Grassland water budgets' response to CO2 is contingent on productivity, structure, rainfall patterns, and CO2-induced physiological changes.
• Higher productivity and LAI in grasslands amplify the effects of elevated CO2 on water budgets.
• In low LAI systems, significant physiological changes may not drastically alter total ecosystem water budgets.