Effects Of Mycorrhizal Fungi On Interspecific Competition Between Stipa Grandis And Cleistogenes Squarrosa Under Different Water Conditions

The change of precipitation pattern under climate change scenario is the main driving factor for the degradation of arid and semi-arid grassland ecosystems in China.The process of grassland degradation is intuitively shown as the changes of plant community structure and the replacement of dominant species,but essentially it is the outcome of inter-specific competition between different plant species under changing biotic and abiotic factors,which then drives the succession of community towards the direction of degradation.Therefore,the study of the effects of biotic factors(such as soil key microorganisms)and abiotic factors(such as precipitation)on the competition among different plant species is of great significance for understanding the process and mechanism of grassland degradation under future climate change in northern China.In typical steppe of Inner Mongolia,S.grandis is the dominant plant species when grassland succession reaches the climax community while C.squarrosa becomes more abundant when degradation process starts.Interspecific competition between two species often determines the direction of grassland community succession.Arbuscular mycorrhiza fungi(AMF)are one of the most important soil microbial groups that are symbiotic with grassland plants.Studies have shown that AMF plays a potentially important role in regulating plant competition and changing plant competition pattern.However,little is known about whether AMF could affect competitive relationship between S.grandis and C.squarrosa in the typical steppe of Inner Mongolia or how interspecific competition between these two species would respond to changes in precipitation patterns.In this study,we set up AMF inoculation pot experiment with S.grandis and C.squarrosa as the research objects,simulated different precipitation patterns by changing water conditions,to studied the influence of AMF on the competitive relationship between S.grandis and C.squarrosa,and the response of AMF-affected plant competition to changes in precipitation pattern,with a view to further understanding the ecological mechanism of the succession of typical grassland plant communities under future climate changes.The results are as follows:(1)The roots of S.grandis and C.squarrosa were substantially colonized by AM,and both plants were highly dependent on mycorrhizal.(2)AMF inoculation and water treatment significantly affected the growth of S.grandis and C.squarrosa.Under different water treatments,the plant height,leaf number and tiller number of the two plants were increased by AMF inoculation,and the above-ground biomass and total biomass of the two plants were significantly higher than that of non-AMF control.Under low water treatment,the plant height,leaf number and biomass of S.grandis were significantly decreased,and the tiller number and biomass of C.squarrosa were significantly decreased.(3)The root P content of S.grandis and C.squarrosa were affected by AMF inoculation,water treatment and planting ratio.For S.grandis,inoculation with AMF significantly reduced P content in roots under low and medium water conditions,but the effect of AMF inoculation under high water condition depended on the initial ratios of S.grandis and C.squarrosa planted in pots.For C.squarrosa,the influence of AMF inoculation on root P content depended on initial ratios of S.grandis and C.squarrosa seedlings under all three water treatments.(4)The analysis of interspecific competition between S.grandis and C.squarrosa showed that AMF inoculation,water content change and planting ratio all affected the direction and intensity of competition outcome between the two plants.Under low and high water conditions,AMF inoculation enhanced the interspecific competition between S.grandis and C.squarrosa.Under normal water conditions,AMF reduced the interspecific competition and therefore promoted plant coexistence.In conclusion,AMF can change the growth and biomass allocation of S.grandis and C.squarrosa under different water conditions and regulate the interspecific competition between their host plants.AMF plays an important role in the dynamics of plant community structure and diversity and the succession process of grassland ecosystem.Investigating the effects of AMF and water on the process and mechanisms of grassland community succession is important for us to further understand the response and adaptation of grassland ecosystems to future climate change.