Increased PM levels influence leaf conductance and modify transpiration dynamics, altering groundwater levels in IGP India.

Aerosols affect the worldwide plant environment in both beneficial and harmful ways. Despite its potential importance, its direct influence on plant–water interactions is little known. Tomato plants were grown in ambient urban air, filtered air, and severely polluted air following precise exposure procedures. While measuring transpiration rate and stomatal density, leaf hydration kinetics, microscopic leaf wetness creation, and aerosol deposition patterns were also assessed.

The experiment was conducted from August 2025 in three plant-growing chambers at IIT Delhi. Temperature and RH were the same. At plant level, plants were exposed to natural daylight (up to 1500 µmol m⁻² s⁻¹). Leaf dust deposition was monitored. Every other day, elevated chambers were sprayed with dust, while HEPA filters cleaned air in filtered chambers. PM2.5 deposition on leaves ranges from 50 µg/cm² to 600 µg/cm² for HEPA filter-equipped and increased PM conc. chambers, respectively. During the monitoring period, PM2.5 levels at several locations in the area averaged 150-600 µgm⁻³.Net photosynthesis, stomatal conductance, and transpiration rate were measured in real time using LI-COR 6400XT.

The mass accumulated on leaves was 10 to 12 times more in the elevated PM chamber. Fresh leaves from plants grown under reduced, ambient, and elevated chamber conditions were collected, affixed to specimen holders using adhesive Leit tabs, and analysed using environmental scanning electron microscopy. Stomatal density was seen to have risen (~170 per mm²) from the seedling stage. The minimum leaf conductance (gmin) was measured on leaflets. Photosynthetic rate increased from 14 µmol m⁻² s⁻¹ to 21 µmol m⁻² s⁻¹. The gmin is anticipated to rise when dust deposition on leaves increases. The rise in water uptake by plants suggests that phenomena such as hydraulic activation of stomata (HAS) or heat retention by deposited aerosols have intensified water loss, either through cooling themselves from the heat absorbed from excessive dust accumulation or by forming wicks into the leaves from the salts in the aerosols, thereby facilitating the escape of water from leaves into the environment through evaporation. The Fv/Fm ratio, a measure of photosynthetic efficiency, was maximised in the lowered chamber.

The impact of aerosols on plants is contingent upon their composition, species, and environmental conditions, affecting the movement of water via stomata and cuticular transpiration. Research indicates that ambient aerosol deposition in polluted urban environments elevates gmin, transpiration rates and modified stomatal density. Severity of impact increases pollution levels and hygroscopic aerosols due to extended exposure. Aerosol-induced water loss diminishes stomatal regulation, impairs drought resilience and water usage efficiency, and complicates carbon-water flow scaling. The increased transpiration rate leads to greater water consumption by plants, which might contribute to the depletion of groundwater levels in the IGP India. Additional investigation is required to elucidate the processes connecting aerosol deposition and stomatal response, considering their significance for global climate change.