Symbiotic Adaptation Of Plant And AM Fungi To Environmental Change Along Tibetan Altitudinal Gradients

Predicting the response of plants to environmental change is a great challenge for ecologists and requires a deeper understanding of the importance of biotic and abiotic interactions in mountain ecosystem.Symbioses may be important mechanisms of plant adaptation to their environment.The process of co-adaptation varies spatially among populations such that evolutionary mosaics of symbiotic function can arise from geographic differences in the environment.The degree to which geographic mosaics of symbioses are caused by variation in the biotic or abiotic environment is not well-understood.We conducted field investigation,controled reciprocal inoculation and field reciprocal transplantation experiments to learn how biotic(plant and fungal)and abiotic(temperature and elevation environment)variation affected the performance of plant and AM fungi association in Mount Segrila.Results are as follows:(1)A field investigation of the performance of plant community and their associated AM fungi was conducted along an elevation gradient(3273-4546 m)on the west slope of Mount Segrila.Plant biomass and AM fungal colonization both showed unimodal pattern.Further analysis showed that no significant relationship existed between plant biomass and AM fungal abundance,while the shoot P concentration was positively correlated with AM fungal abundance.SEM model showed elevation and temperature significantly influenced shoot biomass,shoot P concentration and AM fungal colonization in root and soil.(2)The reciprocal inoculation experiment was conducted to identify the possible interactions among plants,inoculum and temperature conditions,and to test whether local adaptation or foreign advantage existed in the symbionts under contrasting temperature conditions.Evidence of local adaptation of plant growth was found only under the high-elevation temperature condition(8-15 C),with no consistent local versus foreign effect found in AM fungal performance.The origin of either the plant or the inoculum relative to the temperature was important in explaining symbiotic function.Specifically,when inoculum and temperature were sympatric but allopatric to the plant,poor adaptation by the plant to the novel environment was clearly found under both temperature conditions.Further analysis found that the symbiotic function was inversely related to fungal diversity under the low-elevation temperature condition(14-21 C).(3)Plants were grown in a dual-compartment system with a hyphal mesh separating roots of Carex capillacea from roots of the host species(Aster himalaicus),avoiding direct root competition.The host plants Aster himalaicus in the system ensured the present of an active AM fungal network.Microscopy analyses revealed that the host plant increased the infecting of C.capillacea root tissues(increased by 13.87%at most).The effect of hyphal networks on the growth of C.capillacea varied with the inoculums type,the indigenous inoculum caused growth depressions in C.capillacea,while no significant effect of Funneliformis mosseae on the growth of C.capillacea.(4)Using reciprocal transplantation experiments we tested the performance of two plant species(P.atrodentata and A.himalaicus)and AM fungal associations and their interactions in response to environmental change at sites of contrasting elevations.The results showed a clear home advantage of symbionts in most cases,except for the fungal performance of P.atrodentata originating from the high elevation site and plant growth of A.himalaicus from the low elevation site.Interestingly,in the two populations from the high elevation site no local advantage in plant growth was found when the AM fungi were inhibited by benomyl treatment.In conclusion,the geographic origin of plants and AM assocations and environment(temperature)conditions were important in explaining plant growth and symbiotic function in controled reciprocal inoculation and field reciprocal transplantation experiments.Specifically,home advantage in symbiotic function was found easily in stress conditions.The AM fungi was important in mediating the plant responses to the environmental change,little local advantage in plant growth was found when the AM fungi were inhibited by benomyl treatment.These findings highlight the need for taking both biotic and abiotic interactions especially plant-AM fungal interactions occurring at local scale into account in the prediction of plant responses to global environmental change.