Seed germination and seedling emergence of four tree species of southern China in response to acid rain

Abstract

Acid rain has become a major concern due to increasing atmospheric pollution, particularly in China. We investigated whether acid rain inhibits the germination of seeds and subsequent emergence of seedling of four tree species from southern China: Cunninghamia lanceolata, Fokienia hodginisi, Pinus massoniana and Phoebe zhennan by simulating acid rain with pH of 2.5, 3.5, 4.5 and 5.5. We hypothesized that the inhibitory effect of acid rain on germination of seeds and emergence of seedling varies between species and the degree of acidity. A solution of 1 N H2SO4 and 1 N HNO3 in the ratio of 10–1 was prepared and diluted to four pH levels, and seeds were supplied with solutions of these pH values and distilled water as control and tested for germination in a controlled growth chamber. The results revealed that simulated acid rain of pH 2.5 adversely affected the germination capacity of F. hodginisi and P. zhennan; while all acid solutions significantly increased germination of P. Massoniana; but had no effect on germination of C. Lanceolata seeds. Strong acid solution (pH of 2.5) adversely affected elongation of radicle and hypocotyl as well as fresh and dry weights of radicle and hypocotyl of tender seedlings. The result demonstrated that seedling emergence is more sensitive than seed germination to simulated acid rain, and germination of conifer species are less sensitive than broad leaved species to simulated acid rain. As a whole, acid rain of pH of 3.5 is the threshold level and acid rain below this value will have a detrimental effect on seed germination and seedling emergence.