The Response Of Arbuscular Mycorrhizal Fungal Community Under Japanese Cedar Forest To Bamboo Expansion And Forest Gap Formation In Lushan Mountain

Japanese cedar(Cryptomeria japonica)is one of the most important forest vegetation in Lushan National Nature Reserve,which has high ornamental and ecological values.Due to historical reasons,Japanese cedar afforested in 50 s was mainly existed as pure forest type.As growth extension,Japanese cedar was gradually disturbed by external factors(including biological factors such as moso bamboo(Phyllostachys heterocycla ‘Pubescens')expansion and abiotic factors such as forest gap formation),resulted in landscape patches appeared in pure Japanese cedar forest.Therefore,study about response of Japanese cedar to external interference is of great ecological significance to understand the forest landscape formation and maintain the Japanese cedar landscape integrity in the Lushan National Nature Reserve.In these processes,underground microbial communities might play important roles.As one important group of soil microbes,arbuscular mycorrhizal fungi(AMF)delievers multi-functions in plant growth,nutrient uptake and tolerance formation.In this study,a 454 high-throughput sequencing method was employed to study the response of arbuscular mycorrhizal fungal community under Japanese cedar forest to bamboo expansion and forest gap formation in Lushan mountain.Two experiments were set including moso bamboo expansion and forest gap formation.The moso bamboo expansion experiment included three kinds of interfaces: the bamboo pure forest,bamboo-cedar ecotone and Japanese cedar pure forest.In moso bamboo expansion experiment,we also had a anthropogenic cutting plot as intervention treatment.The forest gap experiment included the control plots(Japanese cedar pure forest)and the adjacent forest gap.The results are as follows:During the expansion process,OTU number in 0~10 and 10~20 cm soil depths were 63 and 59 in Japanese cedar plots,which increased to 74 and 72 in moso bamboo plots,respectively.Richness of soil AMF community in moso bamboo plots had significant improvements compared with Japanese cedar.The Shannon-Wiener,Simpson and Evenness indexes also showed increasing tendencies in expansion process,especially in bamboo-cedar ecotone.Higher soil AMF community richness and diversity indexes might be main reason resulted in successful expansion of moso bamboo to Japanese cedar.Soil AMF community was also changed,the relative abundance of Glomerales-uncultured showed a decreasing tendency and the Rhizophagus increased after moso bamboo expansion.This might be due to the inherent morphological characteristics and exudate components of moso bamboo root,which accompanied by soil AMF community function change.After remove moso bamboo from Japanese cedar plots,soil AMF community richness,diversity indexes and composition were all showed changing trends toward non-expansion field.It indicated that this soil AMF community variation was mainly caused by moso bamboo expansion.Forest gap decreased soil AMF community richness level,OTU number in 0~10 and 10~20 cm soil depths were 57 and 60 in closed stand of Japanese cedar,which decreased to 46 and 42 in forest gap of Japanese cedar,respectively.The Shannon-Weiner,Simpson and Evenness indexes also showed significant decrease in forest gap treatment.Our results indicated that there was no significant correlation between soil AMF community diversity and underground vegetation diversity,which might also due to the exudate variation between herbs and low shrubs in forest gap.In closed stand of Japanese cedar,soil AMF community richness and diversity indexes in 10~20 cm depth were higher than 0~10 cm depth,and those in forest gap treatment showed an opposite tendency,which might be due to the root vertical distribution of dominant plants in different treatments.Uncultured-Glomerales was the main dominated AMF group in control plot,which accounted for 49.05 % and 58.0 % in 0~10 and 10~20 cm soil,respectively.Archaeosporales was the main dominate AMF group in forest gap treatment,which might be due to its strong autotrophic ability.Soil AMF community composition variation in Lushan Mountain might be mainly caused by physiological and ecological characteristics of AM fungi itself.