Carbon sequestration and stress resilience potential of select dominant tropical tree species of Indian subcontinent under combined elevated CO2, O3, and climate stress.

During the last two decades, a number of research outcomes have vetted possible plant responses to elevated CO2 (eCO2) and other climate stressors in temperate trees and agricultural crops. However, such climate change repercussions (elevated CO2, O3, temperature, and drought) on tropical trees, especially on dominant trees of the Indian subcontinent, remain largely unexplored. This study investigates the productivity of selected species (Pongamia pinnata, Ficus benghalensis, Azadirachta indica, and Syzygium cumini) under three experimental settings, 1) Combined Stress Condition (SC) - Carbon dioxide (CO2): 700 ppm, ozone (O3): 70 ppb, temperature: 1.5 to 2°C, and drought: 20% under Open Top Chamber days; 2) Chamber Condition (CC) - species were tested in the OTC without stress treatments; 3) Ambient Conditions (AC) - species were maintained under Ambient Conditions (AC). Under all the above three conditions, the following key parameters, viz., photosynthetic rate, stomatal conductance, transpiration, carbon stock, chlorophyll content, proline, phenol, and soil organic carbon, were monitored throughout the experimental period (90 days) at specific intervals. Results of the experimental study revealed that the mean photosynthesis rate of the selected saplings in SC was found to be low when compared to AC and CC. Furthermore, under SC, the carbon stock of selected saplings decreased significantly in the four species but at different magnitudes during the post stress stage: 59% in Pongamia pinnata; 39% in Ficus benghalensis; 13% in Azadirachta indica, and 1% in Syzygium cumini. Notably, Syzygium cumini and Azadirachta indica demonstrated comparatively greater stress tolerance. These findings explicitly demonstrate the climate resilience potential of Syzygium cumini, and this could be attributed to the enhanced phenol synthesis and Mono Dehydro Ascorbate radical production. In the wake of climate extremes, potential use of these tree species may strengthen sustainable forestry.