| AimsAs one of the important ecosystems on land,forests support a high level of biodiversity.As an important part of the forest ecosystem,mycorrhizal fungi in the soil can form a symbiotic relationship with most plants and promote species coexistence and diversity maintenance.Most of the plants in the forest community are arbuscular mycorrhizal(AM)or ectomycorrhizal(ECM)associated woody plants,and the plants in Ericaceae also occupy certain advantages in the understory of subtropical forests.However,there have been few previous studies on ericoid mycorrhizal(ERM)associated woody plants in forest communities,and there have been fewer comparative studies on AM,ECM and ERM woody plants.Woody plants associated with different mycorrhizal fungi have different capacities for plant nutrient uptake and pathogen defense,which may lead to large differences in spatial distribution among these woody plants.However,there is little research on the differences in spatial patterns and dynamics of different mycorrhizal woody plants.At the same time,plants of the same mycorrhizal type can exchange and absorb water and nutrients through the common mycorrhizal networks,thus can promote the coexistence of woody plants associated with the same mycorrhizal type.However,it is still unclear whether there is a stronger positive interspecific association between woody plants associated with the same mycorrhizal type than between woody plants associated with different mycorrhizal types.In addition,the existence of heterogeneous individuals within a certain range(neighborhood)around an individual usually alleviates the strength of conspecific negative density dependence(CNDD)and promotes the survival of focal individuals.Since the intensity and direction of impacts vary by different mycorrhizal woody plant neighbors,different effects of these heterospecific mycorrhizal neighbors will be masked if all heterospecific individuals are mixed together.Therefore,it is necessary to group heterospecific individuals according to their mycorrhizal symbionts.At the same time,it is not clear how different heterospecific mycorrhizal woody plant neighbors affect the survival and growth of saplings and adults,and whether this influence will affect the species diversity and forest carbon sink rate.Therefore,this study used data from a secondary evergreen broad-leaved forest in the central subtropics to analyze the differences and dynamic changes in the spatial patterns and interspecific associations of AM,ECM and ERM woody plants,as well as the different effects of density dependence on saplings and adults of these woody plants with different mycorrhizal types,in order to further understand the role of different mycorrhizal fungi in plant population regeneration,interspecific interaction,species diversity maintenance and community dynamics.MethodsBased on dynamic plot data of 9 ha of subtropical secondary evergreen broad-leaved forest in Wuyanling National Nature Reserve,Zhejiang Province,eastern China,the dynamic changes and differences in spatial patterns and interspecific associations of different mycorrhizal woody plants were analyzed using the paired correlation function g(r)and the significance test method for the dynamic changes of point patterns.At the same time,the generalized linear mixed-effects model was used to analyze the effects of the conspecific density and heterospecific density grouped by symbiont mycorrhizal types on different tree life stages of different mycorrhizal woody plants.Results(1)Among different mycorrhizal woody plants,the size-class structure of AM woody plants has always maintained an increasing type.Although the mortality ratio of AM woody plants reached 14.39%,its recruitment ratio was also the highest,2.11%.The size-class structure of ERM woody plants still maintained an increasing type,and the mortality ratio was the lowest,7.76%.The size-class structure of ECM woody plants has changed from an increasing type to a stable type,with the highest mortality ratio of 16%,and the lowest recruitment ratio of 0.35%.The mortality ratio of deciduous tree species was higher than that of evergreen tree species,and the recruitment ratio was lower than that of evergreen tree species in all types of mycorrhizal woody plants.The recruitment of deciduous tree species was relatively difficult.(2)The significant differences among different mycorrhizal woody plants showed that AM woody plants had the lower degree of aggregation,and the average relative variation ratio of their patterns was less than 0,meaning that their spatial pattern became more random after 5 years.However,ERM woody plants had a higher degree of aggregation,and the average relative variation ratio of their pattern was greater than 0,meaning that their spatial patterns became more aggregated after 5 years.Compared with AM woody plants,the degree of aggregation of ECM woody plants and ERM woody plants decreased faster with the increase of the number of individuals.(3)Compared with interspecific associations between other mycorrhizal woody plants,there were higher positive associations between ERM woody plants or ECM woody plants,but the average relative variation ratio of their interspecific associations was less than 0,meaning that their interspecific associations became more negative after 5 years.The positive associations between AM woody plants were weaker,but the average relative variation ratio of interspecific associations was greater than 0,meaning that their interspecific associations became more positive after 5 years.The positive associations between different mycorrhizal woody plants were weak,and the average relative variation ratios were low.(4)Compared with other mycorrhizal woody plants at the same growth stage,ECM saplings and AM adults experienced stronger CNDD.Heterospecific ECM density had a stronger positive effect on the survival and growth of AM and ERM individuals,while heterospecific AM or ERM density had a negative effect on the growth of individuals.Species diversity and average relative growth rate(RGR)first increased and then decreased with the increase of the basal area(BA)ratio of ECM to AM woody plants.ConclusionsThis study showed that due to the different physiological and biochemical properties of AM,ECM and ERM mycorrhizal fungi,there are significant differences in the spatial pattern,interspecific association and their dynamic changes of AM,ECM and ERM woody plants.The variation of CNDD makes different mycorrhizal woody plants have different regulatory effects on species diversity at different growth stages.Since the intensity and direction of impacts on plant growth and survival varied greatly with heterospecific AM or ECM neighbors,manipulating the appropriate proportion of AM and ECM woody plants will play an important role in maintaining species diversity and increasing the average RGR.This study is helpful to understand the nonnegligible roles of different mycorrhizal fungi in community assembly and dynamics,and provides new ideas for improving forest carbon sink rates and protecting biodiversity in the context of global change. |
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