Abstract
Acid rain pollution is one of the serious environmental problems in China.It is also one of the reasons behind the aggravated pollution situation in the northern regions of the country.Large areas suffering from the continued occurrence of strong acid rains are at risk for serious threats to the health of terrestrial ecosystems.Plants above and below the ground are seriously affected by acid rain,because they are the main receptors of acid pollution.The impacts of acid rain on plants specifically affect their growth and root systems.Therefore,studies on growth and bleeding sap amount of root of typical tree species in reaction to acid rains in northern China have important theoretical and practical values.These can help us understand the effects of acid rain on forest community and vegetation restoration.Quercus mongolica Fisch.ex Ledeb.is one of the main species of deciduous broad-leaved forests in northern China,and is the main associated tree species of pines in temperate coniferous forests.Thus,in the present work,we chose one-year-old Q.mongolica seedlings to study the effects of simulated acid rain on plant growth,biomass,and bleeding sap amount of root.From June to September 2011,Q.mongolica seedlings were exposed to 12 simulated acid rain treatments of 4 different acidities(severe,moderate,slight and control) that are delivered by 3 types of rainfalls(natural rainfall in summer,and increased or decreased amounts by 30%,respectively).Simulated acid rains were applied to the seedlings on a weekly basis.The results demonstrate that an increase of 30% acid rain rainfall significantly raised the biomass and leaf numbers,promoted height growth,and increased bleeding sap amount of root of Q.mongolica seedlings.However,growth and biomass accumulation of Q.mongolica seedlings were slightly influenced by acid rain acidity,such that when acidity increased the bleeding sap amount of root became significantly lower.Furthermore,the root systems of the Q.mongolica seedlings were damaged by the high acidity of simulated acid rain.Compared with other treatments,in the treatment with an increase of 30% in severe acid rain rainfall,Q.mongolica seedlings exhibited significantly higher height levels,grew more leaf numbers,and accumulated more biomass.Based on our estimations,the stimulation of seedling growth and the acceleration of biomass accumulation were caused by the increased concentration of soil N,which came from the added NO-3 in acid rain.The acid rain also served as a fertilizer,thereby promoting the growth of Q.mongolica seedlings.Relative to acidity,acid rain rainfall had greater impact on Q.mongolica seedlings,however,no interaction between two factors was found.In conclusion,Q.mongolica showed resistance and adaptability to acid rain.Thus,they can be considered as pioneer and constructive plant species for use in the recovery of regions suffering from acid rain.
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