Using growth analysis to interpret competition between a C₃ and a C₄ annual under ambient and elevated CO₂

Area of Science:

• Plant Ecology
• Physiological Ecology
• Weed Science

Background:

• Competition dynamics between C3 and C4 annual weeds are crucial for understanding plant community structure.
• Elevated atmospheric CO2 concentrations can alter plant growth and competitive interactions.

Purpose of the Study:

• To investigate the competitive interactions between Abutilon theophrasti (C3) and Amaranthus retroflexus (C4) under varying CO2 levels.
• To determine how elevated CO2 affects the growth, resource acquisition, and competitive success of these two weed species.

Main Methods:

• Detailed growth analysis, including leaf display and nitrogen uptake, was performed.
• Plants were grown individually and in competition under ambient and elevated CO2 conditions (500 and 700 μl l-1).
• Key physiological parameters such as leaf area ratio (LAR) and unit leaf rate (ULR) were analyzed.

Main Results:

• Competition reduced growth in both species, with Abutilon affected by decreased LAR and Amaranthus by decreased ULR.
• Amaranthus exhibited a higher nitrogen uptake rate and better below-ground resource competition than Abutilon.
• Elevated CO2 positively impacted Amaranthus biomass and relative growth rate (RGR), and to a lesser extent, Abutilon biomass.

Conclusions:

• Abutilon's initial size advantage was overcome by Amaranthus under elevated CO2, altering competitive outcomes.
• Elevated CO2 levels can shift the competitive balance between C3 and C4 weeds, favoring C4 species like Amaranthus.
• Understanding these responses is vital for predicting weed dynamics in future climate scenarios.