| The grassland in the Qinghai-Tibet Plateau is degraded and the area of available grassland is reduced,and the traditional grazing in cold and warm season is no longer suitable for the development of animal husbandry.Therefore,in this study,the four seasons grassland which grazed in spring(Poa pratensis cv.Qinghai supplementary sowing grassland),summer grassland(swamp meadow),autumn grassland(steppe meadow)and winter grassland(Poa pratensis cv.Qinghai cultivated grassland)were took as research object.To provide basic data for optimizing the allocation of grass and livestock resources and rational utilization of grassland resources.The vegetation characteristics of the four seasons grassland were researched,and the annual changes of vegetation productivity,forage carbon,nitrogen,phosphorus and forage nutrition were analyzed as well as the soil condition of the four seasons grassland was evaluated from the soil-microbial level.The main results are as follows:1.The composition of vegetation community structure of four seasons grassland is different,in which the important value of edible forage(Gramineae + Cyperaceae)is winter pasture(96.61)>spring pasture>(91.98)>autumn pasture(80.62)> summer pasture(68.00).The important value of miscellaneous grass is summer pasture(30.41)>spring pasture(18.10)>autumn pasture(16.91)>winter pasture(7.44).There significant differences were found in vegetation diversity,dominance and evenness index among different pasture.The above-ground biomass of vegetation showed an inverted "N" seasonal variation trend,in which the above-ground biomass in summer was lower than that in the other three seasons pasture.The seasonal change of forage carbon content in four seasons pasture reached the maximum in October,but the change of carbon content in each grassland was different.the carbon content in winter pasture showed the lowest value in March,while that in summer,autumn and winter pasture showed the minimum value from May to June.The nitrogen content in each grassland varied in an "inverted V" trend in different months,and the maximum value were found in June.The seasonal variation range of phosphorus content in each grassland was lower than that of carbon and nitrogen,and reached the maximum around July,and the seasonal variation of phosphorus content in each grassland was not consistent.The plant growth of summer pasture is mainly limited by phosphorus,while that of spring and autumn pasture is limited by nitrogen.2.The crude protein(CP)content of forage grass in the four seasons pasture showed an "inverted V" change trend.It showed a slow upward trend from January to April,increased rapidly from May to June,and reached the maximum in June.There were different among different pasture during the grazing period.The crude fat in each pasture showed a "N" change trend,with a peak in July and August,and showed differences in different grazing period.On the other hand,the(CF)content showed a V-shaped trend,and the(CF)content of each grassland showed the lowest value in the peak growing season.The content of crude ash and nitrogen free extract shows an irregular monthly change trend.3.The soil water content,nitrate nitrogen,available phosphorus,total nitrogen and organic carbon in summer pasture were significantly higher than those in other pastures(P<0.05).There was no significant difference in soil physical and chemical properties except total phosphorus between winter and spring pasture.The activities of urease and invertase were the highest in autumn grassland,the lowest in winter pasture and the highest in summer pasture,which were significantly higher than those in other three seasons pasture(P<0.05).The soil microbial biomass carbon,nitrogen and phosphorus of summer pasture were significantly higher than those of other pasture(P<0.05),followed by autumn pasture,and there was no significant difference between spring and winter pasture.High-throughput sequencing showed that the OTUs of bacteria in four seasons pasture was significantly higher than that of fungi,and the OTUs in summer pasture was lower than that in other three seasons pasture.PCo A analysis showed that there were significant differences in soil microbial community composition among different pasture.Correlation analysis showed that bacteria were not associated with vegetation factors,fungi were significantly associated with vegetation,while bacteria and fungi were significantly associated with soil physical and chemical properties. |
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