The Species Diversity And Community Assembly Of Arbuscular Mycorrhizal Fungi In Qilianshan Mountains On A Northwest-facing Slope And A Southeast-facing Slope

Slope aspect not only modifies microclimate and soil-forming processes,but also significantly influences biogeographical patterns of species and multiple ecosystem functions across terrestrial landscapes.Although the effect of slope aspect on vegetation has been extensively studied,its influences on belowground microbial communities has not been widely examined.It is well accepted that belowground microbes are abundant,various and closely related to aboveground biota,and they are important in energy flow and substance circulation processes.Understanding microbial biogeography and the underlying mechanisms provides important information which can assist in improving our predictions for ecosystem dynamics and functions.These improvements will assist scientific management decisions under continuously changing environments.In this study,we investigated arbuscular mycorrhizal(AM)fungal communities,a group of functionally important root-associated microorganisms,in an alpine ecosystem on a northwest-facing slope(NS)and a southeast-facing slope(SS)along a steep environmental gradient.Ecological processes structuring the fungal communities were inferred according to phylogenetic patterns and species abundance distributions.The main results are listed below.1.The microclimate(light intensity,soil temperature and soil moisture)and soil properties(soil fertility index and p H)were strikingly different between SS and NS.Light intensity and soil temperature recorded significantly higher values on SS than on NS.Soil moisture was also recorded to be nearly six times lower on SS than on NS.Soil fertility index was significantly higher on NS,although p H was lower.There was no significant difference in concentration of soil available P between the two slopes.Moreover,the plant compositions on different slopes were significantly different and the aboveground net primaryproductivity(ANPP)and plant species richness had declined dramatically from NS to SS.The changing microclimate and soil properties can strongly regulate the species diversity and community composition of vegetation,and the extremely different water availability on different slopes should be the primary factor determining the plant community distribution.2.Thirty-two distinct AM fungal virtual taxa(VTs)were identified,predominantly belonging to the genus Glomus.The change of slope aspect from SS to NS recorded a significant decline in AM fungal richness,resulting in a marked loss of Glomus VTs and the dominance of Rhizophagus.As shown on the NMDS plots,both VT and phylogenetic composition of AM fungal communities between SS and NS were well separated,a finding which was verified by PERMANOVA outputs.Variation partition analysis showed that the local environment was the major factor accounting for the variations,being followed by plant species community,and that geographical distance was a minor contributing factor.Comparison between the effects of environmental and plant parameters on the fungal community compositions indicated that soil moisture had the strongest effect on AM fungal communities and significant effects of soil temperature,p H and light intensity were also detected.3.AM fungal communities were phylogenetically clustered on SS and random on NS,suggesting that the central process structuring communities shifted from a niche-dominated filter to the combination of competitive exclusion and a niche filter.Similarly,AM fungal species abundance distribution showed the best fit with the Lognormal model on SS and the Zipf-Mandelbrot model on NS,indicating that community dynamics on both slopes were also in accordance with niche-based mechanisms.We believe that this study is the first to analyze fungal phylogenetic structure to explore principal ecological processes in assembling AM fungal communities on different slopes.Based on an increase in information provided by phylogenetic composition,it is essential that future investigations merge the phylogenetic information of the belowground communities,thereby helping to formulate a better understanding about the mechanisms behind community distribution patterns.