Abstract: Plants can recover their ability in capturing particulate matter (PM) deposited on leaf surface through the washing of rainfall. In this study, six evergreen plant species (Osmanthus fragrans, Pittosporum tobira, Ligustrum lucidum, Photinia serrulata, Magnolia grandiflora, and Pinus bungeana) were selected to investigate the washoff effects, retention threshold, and the relationships between rainfall and washoff efficiency under two rainfall intensities (60 and 90 mm·h^-1) and different duration (0, 5, 10, 15, 20, 30, 45, 60 min). The PM deposited on leaf surface were classified into three size fractions: PM>10 (particles intercepted by 10  μm membrane), PM_2.5-10 (particles pass through 10  μm membrane and intercepted by 2.5  μm membrane), and PM_2.5 (particles pass through 2.5  μm membrane). The results showed that rainfall can remove most of the PM and its size fractions deposited on leaf surfaces. The elution rate ranged from 54.55% to 95.07%, 49.83% to 96.00%, 63.15% to 93.63% and 75.80% to 91.84% for PM, PM>10, PM_2.5-10 and PM_2.5, respectively. The elution rates of PM and PM>10under the rainfall intensity of 90 mm·h^-1 were higher than those of PM_2.5-10 and PM_2.5. Rainfall intensity had significant effects on the elution rates of PM>10, but with no effects on PM_2.5-10 and PM_2.5. The threshold of retaining PM and PM>10 for the six species ranked as (from large to small): P. bungeana>L. lucidum>M. grandiflora>P. serrulata>P. tobira>O. fragrans. The washoff efficiency increased sharply at the beginning of rainfall, and then increased very slowly. The rainfall and particulate matter washoff efficiency were well correlated. As rainfall increased, the PM washoff efficiency increased logarithmically. The PM washoff efficiency increased rapidly within 30 minutes, and then increased in a very low speed.

Key words: microbial biomass carbon, black soil, no tillage, ridge tillage.