| Hulun Buir grassland is an important part of grassland in North China,and it is also an important ecological barrier in northern of Chian.Hulun Lake is the largest freshwater lake in the Hulun Buir area,plays a vital role in the balance of the grassland ecosystem of Hulun Lake area.In recent years,with the global warming,overgrazing,excessive grass and other human activities,the grassland degradation in Hulun Lake is becoming increasingly serious,and the resulting reduction,grassland desertification,salinization,and biodiversity reduction.Therefore,research on grassland vegetation in Hulun Lake area has important academic value to explore the dynamic changes of grassland ecosystem in the northern area of our country,and has important significance for the ecological protection in Hulun Buir Grassland.The types and structure of typical grassland vegetation in the Hulun Lake area were investigated and observed in the field.Combined with the local climate and weather station data,the LI-6400 photosynthetic system was used to measure photosynthesis characteristics of dominant species in different grassland vegetation.The changes of vegetation coverage in 1991-2010 were analyzed using remote sensing data.Through the above research,the following results were obtained:(1)The vegetation of the Hulun Lake area is mainly composed of Gramineae,Compositae.The community composition is relatively complex,and vegetation diversity is higher,which vegetation richness in Stipa baicalensis grassland and Stipa grandis grassland was relatively high.The ecological types is mainly perennial plants with the characteristics of semi-arid vegetation types.(2)According to the study of the floristic geographical elements of vegetation,the results showed that the world distribution,was the main element of plant family and the north temperate distribution was the main element of plant genus in 5 types of grassland vegetation.The types of geographical elements in Stipa Baicalensis grassland was the most,and the structure of species composition was relatively complex and the adaptability was strong.(3)Based on the analysis of plant diversity index,the results showed the species richness of Stipa Baicalensis and Stipa grandis grassland was relatively high,and the diversity index was the highest.(4)There were some differences in the aboveground biomass of vegetation in 5 types of grassland.The vegetation biomass of Stipa grandis grassland was highest,Leymus chinensis grassland and Stipa Baicalensis grassland were relatively high and Artemisia frigida grassland was relatively low.(5)In the study of photosynthetic characteristics of dominant species,the photosynthetic ability of Artemisia frigida was stronger.Its photosynthetic efficiency was the highest,respiration rate was weak,and the response of photosynthesis was sensitive to light.The observation and simulation of light adaptation curve showed that the coefficient of determination R2 had reached more than 0.97,which indicated that the model had better fitting effect.(6)The results of dynamic changes of vegetation showed that the change of vegetation coverage degree was obvious and the water area was gradually decreased from 1991 to 2010.The medium-high grade of vegetation coverage was the highest,up to 35.95%in 1991.The medium grade of vegetation coverage was the highest,up to 59.16%in 1995.The water area decreased from 3270 km2 in 1991 to about 2780 km2 in 2010,which had a certain impact on the local vegetation,and showed that the ecological environment was relatively weak. |
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