亚热带森林根系和菌根真菌调控凋落叶分解和主场效应

Roots and associated mycorrhizal fungi regulate leaf litter decomposition and home⁃field advantage in subtropical forests

根系向凋落物层生长是森林生态系统中存在的普遍现象,研究根系和菌根真菌如何调控凋落物分解对理解森林生态系统的养分循环具有重要意义。通过在亚热带楠木(丛枝菌根树种)和格氏栲(外生菌根树种)人工林中进行了2年的凋落物互换和菌根排除实验,研究根系及其共生菌根真菌如何影响森林凋落物的分解速率和主场效应。结果发现:经过720 d的分解,在楠木人工林中,根系的存在促使楠木和格氏栲凋落物的分解速度分别提高了29%和47%,而在格氏栲人工林中,根系存在对格氏栲凋落物分解无显著影响,但增加了楠木凋落物的分解速率。此外,楠木人工林中,有根和无根处理下凋落物分解均无主场效应,而格氏栲人工林凋落物仅在根系存在的情况下显示出负的主场效应。进一步发现格氏栲凋落物的负主场效应归因于楠木人工林凋落物层更大的腐生真菌丰度和更强的磷降解酶活性。结果表明,在亚热带不同菌根类型树种中,菌根真菌与腐生真菌的相互作用(拮抗或促进),很有可能通过影响磷降解酶的活性,进而影响凋落物的分解率和主场效应。

Plant litter decomposition is a basic process involved in terrestrial ecosystem carbon and nutrient cycling.Root dispersal into the litter layer is a common phenomenon in forest ecosystems.Existing studies on litter decomposition have primarily focused on the impact of climatic conditions,environmental factors,and litter quality on decomposition.However,investigations into the regulation of litter decomposition by roots and mycorrhizal fungi,as well as the home field effects(HFA),remain insufficient.We conducted a litter decomposition experiment with two treatments-reciprocal litter transplantation and root exclusion-in Phoebe zhennan(an arbuscular mycorrhizal tree species)and Castanopsis kawakamii(an ectomycorrhizal tree species)plantations in subtropical China.Over a period of 720 days,we found that the presence of roots increased the rate of litter decomposition in P.zhennan plantation.However,in the C.kawakamii plantation,the presence of roots had no significant effect on the rate of litter decomposition for C.kawakamii.Moreover,regardless of the presence or absence of roots and associated mycorrhizae,no HFA effect was observed for P.zhennan litter.Conversely,C.kawakamii litter exhibited a negative HFA effect solely in the presence of roots and mycorrhizae.This negative HFA effect for C.kawakamii litter may attribute to the higher saprophytic fungal abundance and phosphorus-degrading enzymes activity in the guest environment than in the home environment.Our findings suggest that the interaction between mycorrhizal and saprotrophic fungi may be a key factor in determining litter decomposition rates and the HFA effect through modification of saprophytic fungal abundance and P-acquiring enzyme activities in P.zhennan and C.kawakamii plantations.