Elevated CO₂ and nitrogen availability have interactive effects on canopy carbon gain in rice

Area of Science:

• Agricultural Science
• Plant Physiology
• Environmental Science

Background:

• Rising atmospheric carbon dioxide (CO2) concentrations and nitrogen (N) availability are key factors influencing plant growth and productivity.
• Understanding these factors' effects on crop canopies is crucial for predicting agricultural yields in a changing climate.
• Rice (Oryza sativa) is a globally important staple crop, making its response to environmental changes a significant research area.

Purpose of the Study:

• To investigate the interactive effects of elevated CO2 and varying nitrogen availability on rice canopy structure, leaf area index (LAI), and canopy photosynthesis.
• To quantify how changes in CO2 and nitrogen influence key physiological and structural parameters of the rice canopy.
• To compare experimental findings with model predictions regarding canopy responses.

Main Methods:

• Rice was cultivated under ambient and elevated CO2 conditions using Free-Air CO2 Enrichment (FACE) technology.
• Two levels of nitrogen availability were applied to the rice plants.
• Measurements included leaf area, leaf N content, light-saturated photosynthesis (Pmax), apparent quantum yield, and net daily canopy photosynthesis.

Main Results:

• Elevated CO2 enhanced light-saturated photosynthesis rates and apparent quantum yields.
• CO2 elevation reduced total leaf N content but did not affect LAI, leading to an 8% decrease in average leaf N content.
• Leaf area index significantly increased with nitrogen availability, consistent with model predictions.
• Canopy photosynthesis showed a stronger response to leaf N under elevated CO2, indicating an N × CO2 interaction.

Conclusions:

• There is a significant interactive effect between nitrogen availability and elevated CO2 on rice canopy carbon gain.
• Increased nitrogen availability enhances canopy photosynthesis under elevated CO2 by increasing leaf area index, which amplifies the positive effects of higher quantum yields.
• These findings highlight the complex interplay of nutrient and CO2 dynamics in determining crop productivity and carbon sequestration potential.