Effects of submicron ammonium sulfate particles on the growth and yield of komatsuna (Brassica rapa L. var. perviridis)

The aim of this study was to determine the effects of submicron ammonium sulfate (AS) particles on komatsuna (Brassica rapa L. cv. Hakkei) plants. First, we optimized a leaf-washing method to measure the amount of AS particles deposited on the leaf surface of the plants. Then, we used this method to determine the retention time of particles deposited on the leaf surface of the plants. We also investigated the effects of AS particles on the growth and yield of the plants. Almost all the AS particles deposited on the leaf surface were removed within 1 min washing time with ultrapure water, and ion leaching from the leaf was relatively slow but continuous during the leaf-washing procedure. On the basis of these results, we determined that 1 min was a suitable washing time to remove most of the AS particles while minimizing the influence of ion leaching from the leaf. The amount of particulate SO42− deposited on the leaf surface decreased over time, probably because AS particles deposited on the leaf surface deliquesced, allowing ions such as SO42− in the deliquescence solution to be absorbed into the leaf. The plants were grown and exposed to AS particles for 16 days in naturally lit phytotrons. The daily mean increase in the concentration of SO42− in PM2.5 by the exposure to AS particles was 22.5 μg m−3 in the phytotrons. The growth and yield of the plants were significantly reduced by the exposure to AS particles. The exposure to AS particles did not affect the leaf concentrations of nitrogen and chlorophyll, but significantly reduced stomatal conductance. Therefore, stomatal closure is one of the reasons for the AS particle-induced reductions in the growth and yield of komatsuna plants.