| In this study,three grassland types in Inner Mongolia were used as research objects to study the differences in the response of biomass,stoichiometry and carbon and nitrogen distribution of grassland communities to nitrogen and phosphorus addition under different climatic conditions.The theoretical basis and suggestions for the restoration and treatment of degraded grassland are provided,and the scientific basis and basic data for the accurate analysis and prediction of grassland carbon source and sink change and carbon budget in the background of nitrogen deposition are provided.The main conclusions are as follows:(1)The community structure and species composition of grassland in Inner Mongolia are relatively simple.The distribution of species,families and species is dispersed.The species diversity and community productivity show a trend of decreasing first and then increasing along the northeast-southwest transect.There is no significant difference in species diversity index among the three grassland types(P>0.05),while the productivity of meadow steppe community is significantly higher than that of typical steppe and desert steppe.The results of correlation analysis show that climate factors and soil conditions have significant effects on the species diversity and productivity of natural vegetation in Inner Mongolia.The productivity of grassland community was positively correlated with species richness and diversity index.(2)Nitrogen and phosphorus addition promoted grassland community biomass(aboveground and underground biomass and total biomass)at all stations in Inner Mongolia grassland,and the proportion of biomass change increased first and then decreased with the level of nitrogen and phosphorus addition.The above-ground biomass of meadow(8.22%~38.44%)and desert grassland(14.72%~54.38%)was higher than that of typical grassland(4.18%~19.18%).The response of underground biomass to nitrogen and phosphorus addition was smaller than that of aboveground biomass.Among them,N addition promoted the underground biomass of meadow steppe(6.99%~27.32%)and typical steppe(22.9%~41.83%)higher than that of desert steppe(2.29%~18.28%),and promoted the total biomass of typical steppe(3.81%~21.20%)and desert steppe(10.98%~35.15%)higher than that of meadow steppe(1.18%~10.93%).The effects of different P addition levels on underground biomass and total biomass of typical steppe(24.72% ~ 53.84%;5.58% ~ 27.38%)and desert steppe(27.94% ~ 49.49%;17.21% ~ 41.19%)were higher than those of meadow steppe(-1.39% ~ 19.72%);-8.82%~11.41%).The above-ground biomass of grassland communities along the longitude gradient was positively correlated with nitrogen and phosphorus addition level and rainfall,while the belowground biomass and total biomass were positively correlated with phosphorus addition level and drought coefficient,all of which were negatively correlated with temperature.(3)At the community level,the increase of N/P ratio in desert steppe(4.03%~22.04%)was higher than that in meadow steppe(-0.48%~10.93%)and typical steppe(-0.38%~14.51%)at different N addition levels,while the change ratio of C/N and C/P in community was not significantly different among the three steppe types.With the increase of nitrogen application level,N/P of community in meadow steppe and desert steppe increased gradually,C/N of community decreased gradually,but the change trend of C/P of community was not significant(P>0.05),while the stoichiometric ratio of each site in typical steppe did not change significantly.The change trend of soil stoichiometric ratio of different soil layers was similar.The C/N of 0-10 cm and 10-30 cm soils in three grassland types showed a downward trend with the N addition level,while the N/P of soils increased first and then decreased,while the C/P of soils showed no significant change trend(P>0.05).The C/N ratio of three grassland types had little difference under different P addition levels,while the C/P(-41.31%~19.99%)and N/P(-43.16%~27.72%)decreased the most in desert steppe,while the meadow steppe and typical steppe were close.With the increase of phosphorus application level,community C/N increased gradually,while community C/P and N/P decreased gradually.C/P and N/P in 0-10 cm and 10-30 cm soil of three grassland types decreased significantly with P addition level,but C/N did not change significantly with P addition level(P>0.05).(4)Nitrogen and phosphorus addition could enhance the carbon and nitrogen pools of grassland community biomass under longitude gradient,and the change proportion of carbon and nitrogen pools of grassland community biomass increased with the increase of nitrogen and phosphorus addition level.The promotion ratio of aboveground biomass carbon and nitrogen pools in typical grassland was weaker than that in meadow and desert steppe,while the change ratio of belowground biomass carbon and nitrogen pools and total biomass carbon and nitrogen pools in meadow and typical steppe was higher than that in desert steppe.The promotion ratio of aboveground biomass carbon and nitrogen pool in desert steppe was higher than that in meadow and typical steppe,and the promotion ratio of belowground biomass carbon and nitrogen pool and total biomass carbon and nitrogen pool in typical steppe was higher than that in meadow and desert steppe.The effects of different nitrogen and phosphorus levels on soil carbon and nitrogen pools in different soil layers were weaker,and the change ratio of soil carbon and nitrogen pools in different soil layers in desert steppe was smaller than that in meadow and typical steppe.Under different nitrogen and phosphorus levels,the aboveground living carbon pool/root carbon pool of grassland community in meadow steppe decreased the most,while the aboveground living nitrogen pool/root nitrogen pool in desert steppe increased the most.Carbon and nitrogen in meadow steppe increased more than those in typical steppe and desert steppe at different levels of N addition.Under different P levels,the N allocation between aboveground living organisms and soil in desert steppe increased the most,while that between root system and soil in meadow steppe increased the most. |
PDF Full Text Request