Nitrogen fertilisation influences low CO₂ effects on plant performance

Area of Science:

• Plant Science
• Environmental Science
• Biogeochemistry

Background:

• Low atmospheric CO2 concentrations have been prevalent throughout much of plant evolutionary history.
• Reduced CO2 can limit plant growth and affect physiological processes like photosynthesis and nitrogen assimilation.

Purpose of the Study:

• To investigate how nitrogen (N) availability modulates plant performance under low CO2 conditions.
• To assess the impact of different nitrogen forms (nitrate, ammonium, mixed) on plant responses to subambient CO2.

Main Methods:

• Cultivation of Elymus canadensis under ambient (~400 μmol mol-1) and subambient (~180 μmol mol-1) CO2 levels.
• Application of four distinct nitrogen treatments: nitrate only, ammonium only, and two mixed ratios of nitrate and ammonium.
• Measurement of biomass, photosynthetic rates, electron transport rates, stomatal index, and 15N isotope discrimination.

Main Results:

• Low CO2 decreased biomass in plants receiving full or nitrate-only N, but not in ammonium-only or mixed N treatments.
• Photosynthesis and electron transport rates were most negatively impacted by low CO2 in plants with full N supply.
• Low CO2 reduced stomatal index in mixed N plants, and altered 15N discrimination patterns across treatments, indicating N-dependent responses.

Conclusions:

• Nitrogen availability is a critical factor influencing plant responses to past low CO2 environments.
• The form of nitrogen impacts plant growth, physiology, and isotopic signatures under low CO2.
• These findings necessitate consideration of N availability when interpreting paleoecological data derived from plant traits and isotopes.