| Human disturbance such as mowing is an important factor of grassland degradation.Therefore,it is an urgent task to establish a scientific and reasonable rotation mowing system to protect and restore the inherent structure and function of typical grassland.With Inner Mongolia Xilingol typical stipa grandis grassland community as the research object,and on the basis of comprehensive survey on soil and vegetation,this study designs a variety of mowing systems,and arrange the experimental treatment area to simulate the different intensity of anthropogenic interference to carry out the research on the functional structure of the grassland community and species diversity,the relationship between species and ecological niche,the plants and stoichiometric characteristics of soil nutrients of the stipa grandis community in different mowing rules.With the 17 years continuous observation data,the dynamic evolution process of community structure characteristics of the stipa grandis grassland community in different mowing rules has been analyzed,and the succession track and trend of the steppe community has been explored,as well as the corresponding changes in soil characteristics.The main conclusions are as follows:(1)Mowing would lead to the decrease of community height and aboveground biomass of the stipa grandis grassland community,and the community height and aboveground biomass are negatively correlated with mowing frequency.Mowing could promote the density in the steppe community,and the annual mowing has the greatest effect on the promotion of the community density.In addition to the height and individual character index,mowing is beneficial to the maintenance of the density and biomass of stipa grandis,and to the increase of the density of cleistogenessquarrosa,but has an opposite effect on the density and biomass of leymus chinensis.Under different mowing rules,there are significant differences in population distribution and species diversity of the stipa grandis grassland community.Under mowing treatment,stipa grandis is the dominant species in the community,but under non-mowing control treatment,leymus chinensis becomes the dominant species in the community,and the advantages are significantly enhanced.Reasonable mowing is helpful to improve the species richness of the community,but non-mowing control treatment is more beneficial to the restoration of species diversity.(2)Mowing significantly increases the overall community correlation,resulting in the instability of community structure and function,and the correlation of the same species to different mowing systems is somewhat different.High frequency mowing can significantly reduce the stability of the community,and enclosure treatment can help to improve the stability of the community,in which the grassland community is relatively stable under non-mowing control treatment.The niche width of plant species under mowing treatment is higher than that under enclosure treatment,and the higher the mowing frequency is,the wider is the niche width of plant species.Mowing increases the mean value of niche overlap and competition among plant species.There is a positive correlation between niche overlap index and niche width of plant species.When the niche width of species pairs is large,the niche overlap index is relatively high,and vice versa.(3)Mowing is helpful to improve species richness of the stipa grandis steppe community,and the promoting effect of high frequency and low frequency mowing is more obvious,while medium frequency mowing is relatively weak.Cumulative mowingdecreases the species diversity and evenness of the community,and short-term high-frequency mowing can lead to unbalance of community species.(4)Under different mowing systems,the evolution process of the sipa grandis steppe community in the 17 years can be divided into three stagesrespectively.Cutting twice a year,the community types were stipa grandis plus cleistogenes squarrosa and leymus chinensis in the first stage(2001-2006),stipa grandis plus leymus chinensis and carex korshinskyi in the second stage(2007-2012),and stipa grandis plus carex korshinskyi and leymus chinensis in the third stage(2013-2017).Cutting once a year,the community types were stipa grandis plus leymus chinensis and cleistogenes squarrosa in the first stage(2001-2006),stipa grandis plus carex korshinskyi and leymus chinense in the second stage(2007-2012),and stipa grandis plus leymuschinenseand carex korshinskyiin the third stage(2013-2017).Cutting twice every three years,the community types were stipa grandis plus cleistogenes squarrosa and leymus chinensis in the first stage(2001-2006),stipa grandis plus leymus chinensis and carex korshinskyi in the second stage(2007-2010),and stipa grandis plus carex korshinskyi and leymus chinensis in the third stage(2011-2017).Cutting once every two years,the community types were stipa grandisplus leymus chinensis and cleistogenes squarrosa in the first stage(2001-2004),stipa grandis plus leymus chinense and carex korshinskyi in the second stage(2005-2011),and stipa grandis plus leymus chinense,carex korshinskyi and agropyron michnoiin the third stage(2012-2017).Under non-mowing control treatment,the community types were stipa grandis plus leymus chinensis,cleistogenes squarrosa and carex korshinskyi in the first stage(2001-2003),stipa grandis plus leymus chinense,agropyron michnoi and carex korshinskyi in the second stage(2004-2009),and leymus chinense plus stipa grandis,agropyron michnoi and achnatherum sibiricum in the third stage(2010-2017).(5)High frequency mowing reduces the content of soil organic matter to a certain degree,and rational mowing can increase the content of soil organic matter to some extent,where the effects of annual mowing are more obvious.Mowing reduces the content of total nitrogen and available phosphorus in soil,but increases the content of available nitrogen and total phosphorus in soil.The contents of organic matter,total nutrient,and available nutrient in soil generally decrease with the deepening of soil layer.Mowing increases the content of total nitrogen in plants to some extent,and the effect of low-frequency mowing is more obvious.Mowing may decrease the content of total phosphorus in plants,the higher the frequency,the higher is the effect.(6)There is a significant positive correlation between the current soil water storage and aboveground biomass of plants at different soil depths of 0-40 cm.There is an obvious linear relationship between the aboveground biomass of dominant species and available nutrients in soil.Community height,density,aboveground biomass,groundlitter have a significant positive correlation with total nitrogen in soil,and ground litter and soil availablephosphorus present a significant positive correlation.Community density and total potassium in soil have a significant negative correlation relationship.Community height,aboveground biomass,ground litter and soil organic matters show a strong positive correlation,and such a strong positivecorrelation can also be seen between community height,ground litter and total potassium. |
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