Tree Biomass Sensitivity to Ozone Exposure: Insights From a Decade of Free-Air Experiments

Area of Science:

• Environmental Science
• Plant Physiology
• Forest Ecology

Background:

• Tropospheric ozone (O3) is a major air pollutant that negatively impacts forest ecosystems.
• Ozone exposure affects plant biomass, carbon allocation, and overall forest health.
• Understanding species-specific responses to ozone is crucial for predicting forest ecosystem changes.

Purpose of the Study:

• To assess the impact of ozone (O3) on biomass allocation in 17 woody taxa using free-air controlled exposure (FACE).
• To compare the effectiveness of flux-based metrics in quantifying ozone-induced biomass reductions.
• To investigate differences in ozone sensitivity and carbon allocation strategies between deciduous and evergreen species.

Main Methods:

• Utilized a decade of free-air controlled exposure (FACE) data from 17 woody species.
• Analyzed biomass responses (total, aboveground, belowground) in relation to ozone uptake (phytotoxic ozone dose, POD1).
• Evaluated flux-based metrics, including Leaf Index Flux (LIF), and their correlation with carbon allocation ratios (shoot-to-root ratio, S/R; leaf area ratio, LAR).

Main Results:

• Consistent biomass reductions (RTB, RTAB, RTBB) were observed with increasing ozone uptake (POD1).
• Deciduous species exhibited lower thresholds (CL4) and smaller ozone uptake increments (ΔPOD1) for biomass reduction compared to evergreen species.
• Ozone exposure altered carbon allocation, with negative correlations between POD1/LIF and S/R in deciduous species, and positive correlations with LAR and S/R in evergreens.

Conclusions:

• Flux-based metrics effectively quantify ozone-induced biomass losses, demonstrating higher sensitivity in deciduous species.
• Belowground biomass (roots) is the most vulnerable component to ozone exposure.
• Leaf habit influences carbon allocation strategies under ozone stress, necessitating species-specific considerations in ecological models.