Effects Of Mowing Disturbance And Saline-Alkali Stress On Spatial Expansion Of Leymus Chinensis Clones With Different Densities

In recent years,the increasing degree of soil salinization has attracted wide attention.It is understood that the Songnen Plain is one of three major saline-alkali soil distributions in the world,of which the western Jilin Province is very serious areas.As a dominant species in the region,Leymus chinensis(Trin.)Tzvel.is a salt-tolerant rhizomatous clonal plants.It has a great advantage on the possession of space resources with strong vegetative reproductive ability.But the L.chinensis meadow has been degraded under the disturbance of historical reasons coupled with human factors,for example,blind reclamation,excessive grazing and so on.There are a large number of alkali-patches consisting of salt-tolerant plants(Chloris virgata Sw.,Artemisia anethifolia Web.)in the area,and the halophyte community is expanding year by year.The L.chinensis patches gradually go to fragmentation.It has great scientific significance to understand the process and mechanism of salinization of grassland by studying and revealing the spatial expansion strategy of L.chinensis.Based on the Grime plant selection theory(C-S-R triangle),disturbance,stress and competition are the main driving forces that affect the spatial expansion of clonal plants.In this study,the whole process that expanding from L.chinensis grassland to saline-grassland of L.chinensis was simulated by pot experiment.Revealing the influence of mowing disturbance(no mowing,mowing),density control(high or low density)and saline-alkali stress(high or low saline-alkali stress)on the space expansion potential ability(number of rhizome,average root length,average spacer length of rhizome),fecundity(average tiller number,average tiller ratio,the ratio of tiller number)and planting ability(the multiply of ramets number and average distance).The main results were as follows:(1)L.chinensis clones showed a spatial expansion behavior that was active in spreading to new plaques(saline-alkaline plaques),regardless of whether they were confronted with density constraints,mowing disturbance or saline-alkali stress.(2)The effect of mowing disturbance on the space expansion potential ability of L.chinensis was following: the mowing significantly reduced the number of rhizome to saline-alkali stress area,while the effect of mowing disturbance on the length of spacer was related to saline-alkali stress and density control,mowing disturbances increased the length of spacer under the condition of high salinity-high density;The effects of mowing on the fecundity were mainly in the number of buds(P < 0.05).Mowing disturbances reduced the number of rhizome buds.Despite mowing disturbances had no significant effect on the planting ability of L.chinensis,but significantly increased the average expand distance.(3)The effect of saline-alkali stress on average spacer length of space expansion potential ability,but which were depended on the density control and mowing.Only under low density-mowing and high density-no mowing,the length of spacers were increased in the low saline-alkali stress habitat;While under the condition of high density-mowing disturbance,the length of spacer was significantly increased in high saline-alkali stress.The fecundity and planting ability have no significant effect,but saline-alkali stress significantly affected the number of ramets and depended on the density constraints background.(4)The effect of density control on the length of the spacer space expansion potential ability,depending on saline-alkali stress conditions and mowing disturbances: under the low salt-alkali stress and mowing interference conditions,the low density constraints increased the spacers' length.The density control had a significant effect on the fecundity and planting ability after development.The results showed that the plant with low density had high tiller rate and planting ability.In addition,the effects of mowing disturbance,density control and saline-alkali stress on the space expansion potential ability,fecundity and planting ability for L.chinensis clones were different.In the overall analysis,mowing disturbance is the most important factor for affecting the spatial expansion.Saline-alkali stress is the weakest factor for influencing the spatial expansion.But we can't determine whether the weak effect of saline-alkali stress come from the low stress intensity.Specific analysis,mowing interference will stimulate the plant to expand the space,and the cost is reducing the potential breeding population and other underground components;Reducing the density constraints will not affect the clonal plant in the space development.But low density will enhance the reproductive capacity of clonal plants and survival capacity,thereby enhancing its ability to expand to the new plaque;And salt-alkali stress is often coupled with the density control and mowing interference: in the low density,low salt-alkali stress and mowing habitat,the spatial development potential ability of clones was the strongest.