| Overgrazing and unreasonable utilization of grassland generally result in the decrease in,the dominance of high-quality herbage such as Leymus chinensis.The proportion of poisonous plants(i.e.Stellera chamaejasme L.)which can release allelopathic substances through their root exudates increases year by year,with the influence on seed germination and seedling growth of neighboring plants.At present,a large number of studies carried out on poisonous plants in degraded grasslands focus on the content of secondary metabolites released by them,and the efficacy of insecticides.However,there are few studies on their effects on the endophyte communities of neighboring plants.In order to explore the physiological and ecological response,including the change of endophytic community composition for the dominant plants,this study choose the Songnen grassland advantages of L.chinensis as the research object.The methods include the field in-situ sampling,potted control experiment and high-throughput sequencing technology.Further study,the effects of S.chamaejasme and drought stress on the L.chinensis were analyzed.Potted experiment was conducted to treat L.chinensis with different concentrations of S.chamaejasme water extract(original solution,dilution 20 times,the control)and water conditions(sufficient soil moisture,20-25%;and drought stress,10-15%).In the field,the samples were set according to three levels of density of S.chamaejasme(density of S.chamaejasme higher than 40 refers high density(H),density of S.chamaejasme less than 20 is low density,that is(L),no S.chamaejasme(N),).The main results are as follows:(1)The plant number,net photosynthetic rate,transpiration rate and stomatal conductance of L.chinensis increased after original solution treating,when water was sufficient.Under drought stress,there was no significant effect on the growth and physiological indexes of L.chinensis,because original solution reduced the malondialdehyde content in L.chinensis and weakened the damage to L.chinensis cells.Therefore,the original solution can promote the growth index and physiological index of L.chinensis with sufficient water.However,drought stress weakened the promoting effect of original solution on the growth and physiological indexes of L.chinensis.Besides,the results of subordination function analysis showed that the drought resistance of L.chinensis was gradually enhanced with the increase of the concentration of S.chamaejasme water extract under drought stress,that is,the drought resistance of L.chinensis was the strongest in the original solution.(2)Under the same water condition,the diversity and richness of endophytic bacterial community of L.chinensis with the original solution were lower than CK.Without the original solution,the water had no significant influence on the diversity and richness of the endophytic bacterial community in L.chinensis.the endophytic bacterial richness in L.chinensis in the group with sufficient water was significantly higher than that in the drought stress group with the same original solution treating.That indicates that original solution treating could inhibit the diversity and richness but increase the influence of soil moisture on the bacterial community richness in L.chinensis.Moreover,proteobacteria after the original solution treating demonstrates higher the relative abundance than CK but the relative abundance of actinomycetes shows opposite result with the same water treating.In the field in situ experiments,the increase of the density of S.chamaejasme can improve the endophytic bacterial richness of L.chinensis,and significantly increase the relative abundance of proteobacteria and decrease the relative abundance of bacterial.These results showed that both the density and soil water conditions could change the bacterial community diversity and the relative abundance of certain bacterial groups in L.chinensis.(3)L.chinensis in the well-watered group showed significantly higher the endophytic fungal community richness than that in the drought stressed group.However,there was no significant difference in the endophytic fungal community richness of L.chinensis in the water-rich group and the drought-stressed group.In other words,the effect of water on the community richness of endophytic fungi in L.chinensis was weakened by the application of the original solution.The relative abundance of ascomycetes of L.chinensis in the group with sufficient water was significantly lower than that,but the relative abundance of basidiomycetes was not significantly different from that in the drought stress group.Besides,there was no significant difference in the relative abundance of ascomycetes between the original solution and the drought stressed group,while the basidiomycetes exhibits significantly higher the relative abundance than the drought stressed group.The application of original solution weakened the promoting effect of drought stress on ascomycetes and enhanced the inhibiting effect of drought stress on basidiomycetes.In the field in situ experiments,the richness of endophytic fungi in L.chinensis increased following the increase of the density of S.chamaejasme significantly.However,the increasing relative abundance of ascomycetes of L.chinensis results the decreasing relative abundance of basidiomycetes.These results show that the effect of rhizomorph on the community structure of endophytic fungi in L.chinensis is related to the soil water content.(4)Soil physical and chemical factors show a great impact on the firmicutes of endophytic bacteria,and a slight impact on the ascomycetes of endophytic fungi in L.chinensis,while the results in the field in situ experiment were contrary.Microbial biomass carbon and total nitrogen content of soil physical and chemical factors had a great impact on the endophytic bacterial community of L.chinensis,and the content of available phosphorus show the same influence.The results showed that the contents of carbon,nitrogen and phosphorus in soil were the main environmental factors affecting the change of endophytes in L.chinensis.Based on the above results,the original solution can improve the drought resistance of L.chinensis.The growth index,physiological index and endophytic bacterial community of L.chinensis were significantly affected by the level and soil moisture.Moreover,the functional groups of endophytes in L.chinensis were also changed due to the presence of rhizoides.The relative abundance of the dominant bacteria of endophytic bacteria and endophytic fungi in L.chinensis was increased and the community diversity was decreased in the presence of rhizoides.This study started from the influence of poisonous plants on the change of endophytic community of L.chinensis,analyzed the internal factors of poisonous plants affecting the growth of adjacent plants,provided a new perspective for us to understand the function and role of poisonous plants in grassland ecosystem,and provided a theoretical reference for the degradation and restoration of degraded grassland in the north. |
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