Effect Of Disturbance By Plateau Pika On The Characteristics Of Belowground Bud Bank And Soil Seed Bank In Alpine Meadows

Plant propagule bank has been widely proven to be an indicator of the plant community’s self-renewing ability.Plant propagule bank included plant belowground bud bank and soil seed bank.The characteristics of belowground bud bank and soil seed bank may direct the trajectory of plant community succession in perennial grasslands.Plateau pika(Ochotona curzoniae)is a small common rodent herbivore of alpine meadow in the Qinghai-Tibetan Plateau(QTP),which can affect plant community composition and plant biomass results in varied outcomes of plant community succession.Changeable characteristics of the belowground bud bank and the soil seed bank driven by plateau pika disturbance may indicate the successional direction of the existing plant community and herald the potential plant community to some extent.Therefore,understanding the effect of disturbance by plateau pika and its intensity on characteristics of the belowground bud bank and soil seed bank,and the relationship between belowground bud bank,soil seed bank,and self-renewing ability of plant community may help explain why plateau pika disturbances often lead to improvement or deterioration of alpine meadows in the QTP.This study used a stratified and paired design to examine the effect of disturbance by plateau pika and its intensity on characteristics of belowground bud bank and seed bank,and to explore the relationship between belowground bud density,soil seed density,and environmental factors in the presence and absence of plateau pika,and clarify the effect of disturbance by plateau pika and its intensity on the contribution of belowground bud bank and soil seed bank on plant community biomass and plant species composition.This study will provide basic information on the relationship between disturbance by plateau pika and plant community succession.The main results are as follows:1.Disturbance by plateau pika increased the total belowground bud density through increasing rhizome bud density and root-sprouting bud density.Disturbance by plateau pika directly impacted total belowground bud density and altered the main environmental factors that control total belowground bud density in alpine meadows.This study showed that total belowground bud density and graminoid bud density in the presence of plateau pika were 49.41%and 63.04%higher than in the absence of plateau pika(P<0.05),respectively.Rhizome bud density and root sprouting bud density were lower in the absence of plateau pika than in the presence of plateau pika(P<0.05),whereas tiller bud density had no significant difference between in the presence and the absence of plateau pika.The percentage of rhizome bud density and root sprouting bud density on total belowground bud density were increased from 33.79%and 10.15%in the absence of plateau pika to 41.87%and 13.31%in the presence of plateau pika,respectively.The percentage of tiller bud density on total belowground bud density was decreased from 56.06%in the absence of plateau pika to 44.83%in the presence of plateau pika.Based on the structural equation model,disturbance by plateau pika directly affected total belowground bud density,graminoid bud density,rhizome bud density,and root-sprouting bud density,whereas did not directly affect tiller bud density.The disturbance by plateau pika altered the main environmental factors that control total belowground bud density and graminoid bud density.The main environmental factors that control total belowground bud density were soil total phosphorus concentration and plant rhizome biomass in the presence of plateau pika,and soil moisture and plant aboveground biomass in the absence of plateau pika.Graminoid bud density was controlled by soil total phosphorus content and plant rhizome biomass in the presence of plateau pika,whereas was determined by soil moisture and plant aboveground biomass in the absence of plateau pika.Disturbance by plateau pika altered the related environmental factors of tiller bud density,rhizome bud density,and root-sprouting bud density.Tiller bud density was related to soil organic carbon content,soil total nitrogen content,soil total phosphorus content,and soil C:N in the presence of plateau pika,whereas was related to soil bulk density in the absence of plateau pika.The related environmental factors of rhizome bud density were plant rhizome biomass and plant aboveground biomass in the presence of plateau pika,and plant rhizome biomass and soil available nitrogen content in the absence of plateau pika.Root-sprouting bud density was related to soil phosphorus content in the presence of plateau pika,whereas was related to soil organic carbon content and soil C:N in the absence of plateau pika.Total belowground bud density and graminoid bud density showed a downward parabola trend in response to increased disturbance intensity of plateau pika(P<0.05),and both had a threshold(inflection point)of 535 burrow entrances per ha.The different disturbance intensities of plateau pika did not affect tiller bud density,rhizome bud density,and root-sprouting bud density.2.Disturbance by plateau pika increased seed density at the end of seed rain,whereas had no effect on seed density in the early growing season;Disturbance by plateau pika altered the main environmental factors that control the soil seed density at the end of seed rain.Disturbance by plateau pika increased the seed density at the end of seed rain(P<0.05),whereas had no effect on the seed density in the early growing season.The seed density at the end of seed rain in the presence of plateau pika was 15.45%higher than in the absence of plateau pika.Disturbance by plateau pika had no impact on species of all seedlings from seed bank per plot both at the end of seed rain and in the early growing season.Disturbance by plateau pika increased the Margalef richness index and Shannon diversity index of the seed bank at the end of seed rain(P<0.05),whereas had no effect on the Margalef richness index,Shannon diversity index,and Pielou evenness index of the seed bank in the early growing season.Disturbance by plateau pika altered the main environmental factors that control seed density at the end of seed rain.The main environmental factors that determined seed density at the end of seed rain were soil moisture in the presence of plateau pika and no factors that controlled seed density at the end of seed rain in the absence of plateau pika.The Pielou evenness index of the seed bank at the end of seed rain increased linearly with the increasing disturbance intensity of plateau pika(P<0.05).However,the different disturbance intensities of plateau pika had no effect on seed density,species of all seedlings from seed bank per plot,Margalef richness index,or Shannon diversity index of seed bank both at the end of seed rain and in the early growing season and Pielou evenness index of the seed bank in the early growing season.3.Disturbance by plateau pika increased the contribution of the belowground bud bank to plant aboveground shoots and increased the similarity index between the soil seed bank in the early growing season and the plant community in the growing season.Disturbance by plateau pika increased the contribution of the belowground bud bank to the plant aboveground shoots from 65.08%in the absence of plateau pika to 76.80%in the presence of plateau pika(P<0.05).Disturbance by plateau pika increased the similarity index between soil seed bank in the early growing season and plant community in the growing season from 0.446 in the absence of plateau pika to 0.527 in the presence of plateau pika(P<0.05).The different disturbance intensities of plateau pika had no effect on the contribution from the belowground bud bank to the plant aboveground shoot and the similarity index between the soil seed bank in the early growing season and the plant community in the growing season.