Rainfall does not impair particulate matter accumulation on peri-urban field crops, but improves photosynthetic activity at UV exposure

Abstract

Anthropogenic aerosol pollution has intensified in (semi)-urban environments. Plant surfaces can accumulate a part of these aerosol particles in the terrestrial ecosystem. The deposition of aerosols on plant surfaces is a continuous process and is expected to be especially high in peri-urban agricultural environments. However, the deposited aerosols can be washed off by rain, or re-suspended by wind/rainfall, and rainfall is projected to increase due to climate change in some regions. In this study, we investigated how climate change, i.e. rainfall, affects the particles’ deposition on field crops and how UV radiation can influence crop-particulate pollution interaction with respect to the photosynthetic, and antioxidant activity and their effects on plant health of the economically important cereal crop barley grown at field conditions near a peri-urban environment. Firstly, we quantified leaf surface particle accumulation and their elemental ionic concentration in ambient and rain-exclusion environments. Secondly, we observed the photosynthetic and antioxidant activity responses under UV and rain exclusion environments. Barley, having hydrophobic (water repelling) and narrow leaves, accumulated 0.5–1.0 μg (Na+, K+,Ca2+, Cl−) per square centimeter leaf area, whereas other measured ions (Mg2+, SO42−, NO3−, PO43−) were less than 0.3 μg cm−2, and rainfall itself added a part of ions besides particles wash-off. Thus, about 19 rain events (>5 mm d−1 precipitation, 5 times) did not affect long-term ionic mass accumulation on barley leaves. Aerosol accumulation at no rainfall and UV-exclusion reduced plant growth (i.e. plant height) by 20%. The results presented here suggest that leaf surface microstructures, area and foliage topography can affect aerosol accumulation irrespective of rainfall due to continuous deposition of aerosols. Rainfall can induce positive interactions between aerosol particles and crops at field condition, whereas aerosol accumulation together with UV exclusion during a rain-free season can affect their interaction negatively and impair plant growth.