| This paper takes the Hulunbuir meadow steppe as sample plots and sets three mowing gradients,namely,the plot that mowing once a year(represented by 1G),the plot that mowing once for two years(represented by 2G)and the enclosure sample plot that will not be mowed for many years(represented by Y).In order to provide theoretical basis for the reasonable mowing and water utilization of the meadow steppe,Observe and analyze influences of different mowing frequencies on vegetation,water and soil of meadow steppe and the influences and changing rules of water characteristics during the whole growing seasons(spring-June,summer-July,autumn-August)through comparison with the enclosure sample plot.The findings of the research are as follows:(1)Compared with the plot that will not be mowed for many years,mowing lowers the height of the community;increases the density of the community and the density reaches the maximum while mowing once for two years and makes the biomass of the community in a deceasing trend.Among the heights of different plant communities,leymus chinensis and stipa baicalensis are comparatively dominating;while with no mowing,leymus chinensis bears the highest density of community and stipa baicalensis bears the lowest;leymus chinensis has the highest biomass of the community.Mowing lowers the importance value of sedge and artemisia laciniata of the community,increases the importance value of leymus chinensis and improves the importance value of fine pasture in the community.(2)The monthly changing trend of soil moisture is variant under different mowing frequencies.Mowing once for two years leads to the decline of soil moisture,however,it increases the soil moisture than mowing once a year and the soil moisture of lower-layer is higher than that of without mowing for years.Mowing increases the soil moisture of 10-60 centimeter soil layer in dry months and the soil moisture reaches the highest value while mowing once for two years.Mowing has no obvious influence on spatial distribution of the soil moisture.(3)In the growing seasons,community evapotranspiration is in rising trend from June to August.Mowing results in the increase of community evapotranspiration,and with the shortening of mowing intervals,community evapotranspiration is in declining trend.Meanwhile,under the condition of using the mowed grass,mowing a year then resting a year(mowing once for two years)is beneficial to the improvement of water-using efficiency.Therefore,mowing once a year has great influences on community water-using efficiency of grassland.(4)The influences of different mowing frequencies on photosynthesis:mowing makes the net photosynthetic rate(Pn),transpiration rate(Tr),intercellular C02 concentration(Ci),stomatal conductance(Gs)and water utilization efficiency higher than those of the compared enclosure sample plot.Meanwhile,the photosynthetic parameters of the plot that mowing once for two years are higher than those of the plot which is mowed once a year.(5)The influences of different mowing frequencies on chlorophyll fluorescence:measure chlorophyll fluorescence parameters of leymus chinensis and stipa baicalensis of different mowing frequenciesin natural conditions.Then compare the parameters and find that different mowing modes have obvious influences on chlorophyll fluorescence of plants.In the mowing condition,the initial fluorescence(FO),maximal fluorescence(Fm),maximal photochemical quantum yield of PS II(Fv/Fm),photochemical quenching coefficient(qP)and non-photochemical quenching coefficient(qN)of mowed plants increase greatly than those of the plants that without mowing for years;under mowing condition,chlorophyll fluorescence parametersof FO,Fm,Fv/Fm,qP,and qN of leymus chinensis and stipa baicalensis are all higher than those of the unmowed leymus chinensis and stipa baicalensis.Meanwhile,the chlorophyll fluorescence parameters of the plot that mowing once for two years are higher than those of the plot which is mowed once a year.(6)The influences of different mowing frequencies on stable carbon isotope:through the research on the composition change of stable carbon isotope under different mowing frequencies,the results indicate that the ?13 C value of leymus chinensis ranges from(-25.79 ± 0.05)to(-27.08±0.05)and the ?13 C value of stipa baicalensis ranges from(-26.76±0.05)to(-28.15±0.05).The 13C value of the plot that mowing once for two years are higher than that of the plot which is mowed once a year and the enclosure plot without mowing for years bears the lowest?13 C value. |
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