Effect On The Bacterial Diversity From Exotic Larix Kaempferi In Xiaolongshan National Forest Soil

The exotic tree species have been used to restore forest coverage over China and the world. Most previous studies focused on the affects of the exotic species on plant and animal community structure and original biodiversity and the exotic herbal plants were further found to affect the subsoil microbial diversity and function.However,few was made on how the exotic tree species influenced the local soil bacterial biomass or community structure.This study reported the changes of soil characteristics and soil bacterial diversity between the introduced exotic-fast-growth tree species Japan Larch(Larix kaempferi),the original native pine species (Pinus tabuliformis)and the naturally restored secondary forests.Main results are summarized as following.1.Except JL-11(11-year of Japan Larch,pH 7.06),the soils of all remaining samples were acid:the highest one was CP-10(11-year of Chinese Pine),reaching 6.98,and lowest one was CP-7(7-year of Chinese Pine),only 5.51.Significant discrepancy(P＜0.05)was also found in soil water holding capacity between different samples:the highest one was NS-60(60-year of secondary forest),reaching 37.07%,and lowest one was CP-7(7-year of Chinese Pine),only 22.31%.The discrepancy of water holding capacity depended on the soil characteristics of sampling sites:it increased with the forest age growth in three different forest stands.The soil total N and organic contents increased significantly in the Japan Larch if compared with the other two types of stands:the highest one was JL-11(11-year Japan Larch),reaching 11.86%, higher than the average 3.67%of 8,11,18,30 year-old pine stands.2.The PCR-DGGE banding patterns suggested that the main bacterial populations were different between the exotic species and two other stands soils.Based on the presence and the intensity of each band in its profile of each samples,the Shannon-Weaver diversity index(H) was calculated to reflect species richness of the bacterial community:the secondary forest soils have higher bacterial diversity and NS-30(30-year of secondary forest)was the highest (3.03±0.02).All diversity indexes from Japan Larch are lower although JL-30(30-year Japan Larch)has relatively high values between 2.76 and 2.93.The bacterial diversity of the pine soils was between those of the other two forest soils.3.Higher similarities of bacterial community composition were observed within Japan Larch forests of various ages than those in the other two stands,as demonstrated by principal component analysis(PCA)and UPGMA method analysis.Band sequences revealed that the soil bacterial in Xiaolongshan belonged to three divisions,Proteobacteria,CFB and high G+C, among which the most dominant bacterial group was Proteobao(?)eria(a-,β-,γ-).The results suggested that introduced exotic species Japan Larch had effected the soil characteristics and bacterial community structure,made it different significantly with those in two other stands.The exotic species Japan Larch in Xiaolongshan national forest could effect the local soil enverionment.But whether this effect may change the local soil ecosystem,or the mechanism of the possibility for this change,was still unknown and need to be studied further more.