Research Of Response Mechanisms Of Soil Seed Banks Of Alpine Grassland To Environmental Factors Changes In The Eastern Qinghai-Tibetan Plateau

The underlying mechanism of the effects of environmental factors changes on plant communities is an important scientific question in the community ecology.Most of previous studies have focused on the impact of environmental changes on the species composition and structure of above-ground plant communities,but few studies have been conducted on the response mechanism of the potential plant community buried underground—soil seed bank to environmental changes.The soil seed bank can reduce the risk of population extinction through the ‘storage effect’ in a certain area,and play an important buffering effect after the ecosystems were disturbed.In addition,soil seed bank play an important role in the regeneration of plant communities and the maintenance of species diversity.All environmental factors affect the soil seed bank will ultimately have an effect on species composition,structure and function of the plant community,thus it has a great scientific significance to study the response of the soil seed bank to environmental changes,especially in the fragile alpine ecosystem on the Qinghai-Tibet Plateau,which is extremely sensitive to environmental changes.Therefore,our research located in the alpine region of the eastern Qinghai-Tibet Plateau,and the typical alpine meadow and wetland ecosystems in this region as the main research object,using large-scale field investigation,manipulated experiments,and multiple statistical analysis methods to study the response mechanisms of the soil seed bank size(species diversity and seed density)and species composition,as well as the role of the soil seed bank in the regeneration of the above-ground plant community to the of altitude(temperature and precipitation),light,and grazing intensity change in the Qinghai-Tibet Plateau.The results and conclusions of our research will provide theoretical support and scientific basis for the alpine ecosystem protection,management and restoration on the Qinghai-Tibet Plateau under global climate change and the disturbance of human activities.The main results are as follows.1.Along the altitude gradient(3158-4002 m),the increase in the mean annual precipitation(MAP)directly reduced the species richness and seed density of soil seed bank in alpine meadow;the mean annual temperature(MAT)and mean annual precipitation indirectly reduced the species richness of the soil seed bank through reduced the species richness of above-ground plant community.Although mean annual precipitation and mean annual temperature increased the availability of available nitrogen,available phosphorus and total phosphorus,these factors had no significant effects on the above-ground plant community and soil seed bank,indicating that precipitation was the main factor to affect soil seed bank rather than temperature with the altitude increase,climatic factors did not indirectly affect the soil seed bank by changing the soil environmental factors.2.Species composition of the soil seed bank and the above-ground plant community has a significant difference at different altitude levels in the alpine meadow in the eastern Qinghai-Tibet Plateau;further analysis revealed that the similarity index between the soil seed bank and the above-ground plant community decreased with altitude,and the relationship significantly decreased with the precipitation increase,but the temperature had no significant effect on it.It showed that the contribution of the soil seed bank to the regeneration of the plant community gradually weaken with altitude,and this process was controlled by precipitation,but not temperature.3.Only the species richness and seed mass(community weighted average)of soil seed bank significantly increased under medium light and full light treatments with the succession in an abandoned farmland on subalpine meadows.The seed density of soil seed bank significantly decreased under different light treatments(full light,medium light,and low light)with the plant community succession.The species composition of the soil seed bank had significant differences in the early and late,the middle and late succession under different light treatments.4.As the light intensity increased(from low to medium,and to high light),the species richness germinated from soil seed bank significantly increased only in the late succession stage,the seed density significantly increased in the early and middle succession,and the seed mass significantly decreased in the middle and late succession in an abandoned farmland on the subalpine meadows.The species composition of the seed bank had a significant difference only in the late stage of succession under different light treatments.It showed that both abiotic(light)and biotic(seed mass)factors affected the replenishment/regeneration of the soil seed bank.The regeneration of small seeds in the soil seed bank was inhibited by low light under low light conditions in the late succession stage.The balance of the stochastic and deterministic process of plant communities with the succession gradient was determined by the regeneration process of the soil seed bank,and this process depended on the availability of light(light intensity).5.The above-ground plant communities and the species diversity and abundance of soil seed banks showed non-linear response to grazing disturbance at different degradation levels of alpine wetlands.The species richness and seed density of the transient seed bank decreased and then increased with the increase of grazing disturbance,while the persistent seed bank showed the opposite trend.Compared with the above-ground plant community,the species composition of the persistent seed bank and the transient seed bank had no significant difference during the degradation process of alpine wetland.6.The similarity between the species composition of persistent/transient seed bank and the above-ground plant community also showed a nonlinear response to grazing disturbance,while the species composition of the persistent seed bank was more similar to the above-ground plant community.It showed that persistent seed bank has a greater role than transient seed bank on the regeneration of above-ground plant community in the degradation process of alpine wetland.However,whether transient or persistent soil seed bank,is limited under the potential restoration of seed banks in vegetation restoration,when the intensity of grazing disturbance exceeded the threshold,the soil seed bank will gradually deplete.