| Due to the large use of chemical fertilizer and fossil fuel combustion,the global atmospheric nitrogen deposition increases year by year,and the grassland ecosystem may be slowly transformed from nitrogen limitation to other nutrients limitation.There is synergism between nitrogen and phosphorus in plant metabolism.The effect of phosphorus on plant nutrient concentration is related to N addition.In this study,three steppe types(meadow grassland,typical grassland,desert grassland)in Inner Mongolia were selected as the research objects to study the effects of nitrogen and phosphorus addition on grassland biomass,root-shoot ratio,species diversity and productivity,soil,leaf and root C,N,P and stoichiometric ratio in different Steppe types.The main conclusions are as follows:(1)Based on the analysis of the species distribution and composition of the grassland community families in the three grassland types,Gramineae,Compositae and Leguminosae were the main families,and the species richness index decreased with the concentration of nitrogen or phosphorus,which was followed by desert grassland >meadow grassland > typical grassland.For species diversity index,the Shannon Wiener index of three grassland types was much higher than Simpson index and Pielou index,and the size of Simpson index and Pielou index was similar,and showed similar trend.The species richness index showed a significant negative correlation(P < 0.05)with the annual average temperature and the monthly average temperature in the growth season,and a significant or extremely significant positive correlation with the annual precipitation(P < 0.05)and the monthly precipitation in the growth season(P < 0.01).(2)The above ground biomass of meadow steppe and desert steppe community was significantly increased by the experiment of nitrogen and phosphorus addition,and the above ground biomass increased with the higher nitrogen application concentration,but the above ground biomass of typical steppe community was not significantly affected(P > 0.05)N and P increased the underground biomass of typical grassland and desertgrassland,but decreased slightly(P > 0.05).(3)There was a positive correlation between N addition level and biomass of grassland community in three different grassland types,and plant biomass was also significantly affected by annual rainfall and drought index.There was no significant correlation between the aboveground biomass,the underground biomass and the total biomass of grassland communities in three different grassland types.N and P addition also had a certain difference(P < 0.05)in each biomass of grassland type area,and the spatial distribution of underground,underground/above ground and total biomass had the most significant difference.(4)The soil organic carbon and total nitrogen of 0-10 cm and 10-30 cm were not significantly affected by nitrogen addition.The C:N of 0-10 cm and 10-30 cm soils in typical steppe type areas showed a trend of rising first and then declining,while the C:N of other types of soils remained basically unchanged,which had no significant effect on the C:N of soils in general;the C:P and N:P of 0-10 cm soils in meadow steppe type areas decreased,while the C:P and N:P of 0-10 cm and 10-30 cm soils in other types areas showed an upward trend.(5)Under the condition of nitrogen addition,the correlation between the elements of C,N and P in leaves and roots is relatively weak,and the correlation between leaves and roots is relatively significant.Under the treatment of nitrogen addition,the correlation between C and N of leaves and roots in three grassland types was strong,and the correlation between the stoichiometric ratio of each element was relatively weak.Under the treatment of phosphorus addition,the overall correlation of typical grassland was weak,while the correlation between meadow grassland and desert grassland was significant. |
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