毛竹(Phyllostachys heterocyela‘Pubescens’)凭借其独特的生长特性极易扩张进入周边的常绿或针阔混交森林群落并取而代之。菌根减弱假说对毛竹林扩张导致周边林分枯亡并抑制林下幼苗更新的机制进行了解释,即毛竹林的成功扩张是由于毛竹蔓延引起森林群落的菌根系统紊乱,使宿主植物与菌根真菌的共生关系受到干扰,进而影响了宿主植物的分布与更新。该研究以浙江省西天目山国家自然保护区为研究区域,对菌根减弱假说进行了检验。通过在毛竹一针阔混交林交接区沿毛竹扩张方向设置毛竹纯林、竹-林过渡带、针阔混交林3种类型的样带,选取在针阔混交林、竹.林过渡带同时存在的6种优势乔灌树种——杉木(Cunninghamia lanceolata)、枫香树(Liquidambar formosana)、青冈(Cyclobalanopsis glauca)、柳杉(Cryptomeria fortunei)、江浙山胡椒(Lindera chienii)、毛柄连蕊茶(Camellia fraterna),测定这6个树种在两样带中的菌根侵染频率和强度,检测在毛竹林扩张中周边森林群落菌根的响应,同时对比了毛竹在毛竹纯林和竹-林过渡带菌根感染率和强度的变化,检验该假设。实验结果表明:1)针阔混交林和竹.林过渡带的主要树种菌根都具有较高的菌根侵染频率(〉95%),且不同林分间林木的侵染频率无显著差异(p〉0.1);2)在竹.林过渡带杉木和江浙山胡椒的丛枝菌根侵染强度较针阔混交林明显增加(p〈0.1);3)毛竹的丛枝菌根侵染频率和强度远低于其他针阔树种,且在扩张前后没有显著变化(p〉0.1)。实验结果否定菌根减弱假说。
Aims Phyllostachys heterocycla 'Pubescens', through its unique growth feature, is easy to encroach on, and re- place surrounding evergreen broad-leaved forests or coniferous and broad-leaved mixed forests rapidly. The ex- pansion leads to coniferous and broadleaved tree species withering and dying gradually, and inhibits the forest regeneration. Mycorrhizal weakening hypothesis suggests that expansion ofP. heterocycla 'Pubescens' would in- terrupt the original mycorrhizal associations and causes the subsequence dieback of the forests. This study was to investigate the changes of mycorrhiza along a bamboo forest, bamboo-forest transition, mixed forest transect to examine the hypothesis. Methods A transect, perpendicular to the bamboo expansion direction, went through P. heterocycla 'Pubescens' forest (PPF), bamboo-forest transition (BFT), coniferous and broad-leaved mixed forest (CBF), and were sampled in the Tianmu Mountain National Reserve, Zhejiang Province. Six dominant tree and shrub species (Cunningha- mia lanceolata, Liquidambar formosana, Cyclobalanopsis glauca, Cryptomeria fortune, Lindera chienii, Camel- liafraterna) existing in both CBF and BFT, were chosen for collecting their root tips for measuring the frequency and intensity of arbuscular mycorrizal (AM) colonization for AM species, and frequency of ectomycorrhizal (EM) colonization for EM species. The AM colonization frequency and intensity of P. heterocycla 'Pubescens' in PPF and BFT were also measured and compared. Important findings 1) Before and during the encroachment of P heterocycla 'Pubescens', frequency of the my- corrhizal fungi root colonization of the six tree species were very high (〉95%), and there was no significant difference between CBF and BFT (p 〉 0.1); 2) In BFT, intensity of the AM fungi root colonization of Cunning- ham& lanceolata and Liquidambarformosana increased significantly than those in CBF (p 〈 0.1); 3) The fre- quency and intensity of the AM fungi r