| Arbuscular mycorrhizal(AM)fungi are ubiquitous in terrestrial ecosystems,which can increase plant nutrients uptake and affect ecosystem nutrient cycles.However,the role of AM fungi in regulating the development of individual plant and community characters is still not clear.To test the effect of AM fungi on plant phenology,community structure,and ecosystem stability under global change,a 4-year field experiment was conducted in Songnen grassland to simulate global warming and nitrogen(N)deposition with and without AM fungi by using benomyl.The results will reveal the importance of AM fungi in the process of the aboveground and belowground ecosystem adapting global change.Besides,the results will also provide a theoretical basis for explaining and evaluating the mechanism and potential of AM fungi on the development of the individual plant,community structure,and community stability under global change in grassland.The main results are as follows:(1)Plant phenology among years was different and relied on time and amount of rainfall.Plant heading time,flowering time,fruiting time,and seed maturing time were delayed as the start of the rainy season delayed over years.Plant heading phase,flowering phase,fruiting phase,and reproductive duration depended on both time and amount of rainfall among the growing season.Reproductive phenology of early flowering plants and late flowering plants moved towards the middle of the growing season.Warming accelerated flowering and fruiting of L.chinensis,shortened heading phase of L.chinensis;N addition shortened flowering phase,fruiting phase and reproductive duration of L.chinensis;Suppression of AM fungi delayed heading time,flowering time,fruiting time of L.chinensis,shortened heading phase,and fruiting phase of L.chinensis.Warming prolonged heading phase of P.tenuiflora;N addition did not affect the phenology of P.tenuiflora;Suppression of AM fungi delayed heading time and shortened heading phase and reproductive duration of P.tenuiflora.Warming did not affect phenology of P.australis;N addition advanced heading time,flowering time,and fruiting time of P.australis,N addition also prolonged flowering phase and fruiting phase of P.australis;Suppression of AM fungi advanced heading time and prolonged flowering phase and reproductive duration of P.australis.These results showed that the effect of warming and N addition on plant phenology depended on life-history strategy and root characteristics.The effect of AM fungi on plant phenology depended on mycorrhizal dependency with promoting effect on reproduction of high mycorrhizal dependency plant and delaying reproduction of low mycorrhizal dependency plant.AM fungi decreased temporal overlap of phenology and competition for resources,offered more niches for plant species,thus maintained biodiversity.Interactive effect of warming and N addition advanced fruiting time of L.chinensis,shortened heading phase,flowering phase,and reproductive duration.The interactive effect of warming and suppression of AM fungi shortened the heading phase of L.chinensis but did not affect the flowering phase and reproductive duration.When AM fungi were suppressed,warming plus N addition advanced seed maturing time of L.chinensis.The promoting effect of N addition on seed maturing time of P.australis was dampened by warming.(2)Warming did not affect plant species richness,plant species evenness,and plant species diversity,but decreased plant species net losses,plant species lost rate,and plant species net change in richness;N addition decreased plant species richness;suppression of AM fungi decreased plant species richness and plant species diversity bud did not affect plant species evenness,also,increased plant species net losses and plant species lost rate but decreased plant species net gains.The structural equation model(SEM)showed that suppression of AM fungi directly decreased plant species richness and indirectly decreased plant species richness by decreasing plant species net gains associated with hyphal length density.Moreover,hyphal length density can directly enhance plant species richness.Coverage and density of dominant plant species were stable and not sensitive to warming and N addition;interactive effect of warming and N addition promoted coverage and density of common plant species;coverage and density of rare species were sensitive to N addition but not warming.Suppression of AM fungi increased coverage and density of dominant plant species,decreased that of common plant species,but had little effect on the coverage and density of rare plant species.The coverage and density of main plant species in the community also changed differently under these treatments.Warming increased coverage and density of C.virgata,decreased that of P.tenuoflora;interactive effect of warming and N addition increased coverage and density of P.tenuiflora and S.viridis,decreased that of A.scoparia;Suppression of AM fungi increased coverage and density of P.australis,decreased that of C.virgata,S.viridis,A.anethifolia,and A.scoparia.(3)Warming and N addition did not affect aboveground productivity,but suppression of AM fungi increased aboveground productivity;the interactive effect of N addition and suppression of AM fungi increased aboveground productivity.Warming did not affect aboveground biomass of dominant plant species,common plant species,and rare plant species,decreased that of P.tenuiflora.N addition had no effect on the biomass of dominant plant species,common plant species,rare plant species,and main plant species.Suppression of AM fungi increased biomass of dominant plant species,which decreased that of common plant species,and did not affect the biomass of rare plant species.In addition,suppression of AM fungi increased the biomass of L.chinensis,P.tenuiflora and P.australis,decreased that of S.viridis,A.anethifolia and A.scoparia.The interactive effect of warming and N addition increased the biomass of S.viridis and C.virgata.The interactive effect of warming and suppression of AM fungi decreased biomass of P.tenuiflora and C.virgata.Warming decreased community stability and dominant species stability;N addition did not affect community stability but decreased dominant species stability;suppression of AM fungi decreased community stability and dominant species stability.Community asynchrony was not affected by treatments,while rare species asynchrony was decreased with warming,and common species asynchrony was decreased with suppression of AM fungi.SEM showed that warming and suppression of AM fungi decreased community stability through decreasing the richness of AM fungi and dominant species stability.N addition and suppression of AM fungi decreased community stability through mycorrhizal colonization.In addition,while N addition also decreased community stability through decreasing dominant plant species stability,due to a direct positive effect it did not overall reduce community stability.Higher AMF richness was associated with higher plant species asynchrony,higher temporal mean,and lower temporal standard deviation(s.d.)of productivity while higher stability of dominant plant species was associated with higher temporal s.d.of productivity,thus explaining how the decrease in AMF richness or dominant plant species stability in responses to global change reduced community stability.Higher mycorrhizal colonization increased community stability through increasing temporal mean of productivity.These results showed that the presence of AM fungi promote community stability under the global change context.Meanwhile,both dominant species stability and community asynchrony are important in stabilizing the ecosystem.In summary,warming and N addition had a different effect on plant phenology,community structure and composition,and community stability.Warming and N addition increased temporal overlap of phenology,decreased phenological complementarity,and increased resource competition.N addition decreased plant species richness and warming decreased community stability.AM fungi decreased temporal overlap of phenology,increased phenological complementarity and offered more niches for the plant.AM fungi increased plant species richness through plant species' net gains.AM fungal richness and mycorrhizal colonization increased community stability.These results showed that AM fungi are important in mitigating the negative effect of global change for the grassland ecosystem. |
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