CO₂ enrichment and soil type additively regulate grassland productivity.

Area of Science:

• Ecology
• Plant Science
• Environmental Science

Background:

• Atmospheric CO2 enrichment typically enhances grassland aboveground net primary productivity (ANPP).
• The magnitude of this ANPP-CO2 response varies across ecosystems.
• Soil properties influence ANPP but their role in modifying the CO2 response is understudied.

Purpose of the Study:

• To investigate the impact of soil type on the ANPP response to elevated CO2 in perennial C3/C4 grasslands.
• To determine if soil type and CO2 interactively or additively affect grassland ANPP.
• To assess the mechanisms driving changes in ANPP under elevated CO2.

Main Methods:

• Field experiment over 10 years in Texas, USA.
• Utilized three soil types: sandy loam, silty clay, and clay.
• Applied a gradient from subambient to elevated atmospheric CO2 concentrations.

Main Results:

• Contrary to predictions, CO2 and soil type additively influenced ANPP.
• A CO2 increase of 250 μl l-1 elevated ANPP by 170 g m-2 across all soil types.
• Increased clay content (10% to 50%) reduced ANPP by 50 g m-2.
• Elevated CO2 primarily increased ANPP directly, with a secondary effect from species succession favoring C4 tallgrass Sorghastrum nutans.

Conclusions:

• Grassland ANPP is significantly enhanced by elevated CO2 through direct physiological effects and species succession.
• The positive impact of CO2 enrichment on grassland productivity is consistent across soils with differing physical properties.
• Soil type did not modify the ANPP-CO2 relationship, indicating additive effects.