Spatial Characteristics Of Plant And Soil Nutrients In Inner Mongolia Grassland

Grassland accounts for about one third of the total land and provides vital production and services.Inner Mongolia grassland is a security barrier in northern China,and its vegetation growth is related to the ecological security in northern China.As indispensable nutrient elements for plant growth,carbon(C),nitrogen(N)and phosphorus(P)reflect the dynamic balance between soil nutrient supply and plant nutrient demand.The spatial pattern of plant and soil C,N,P status with changing environmental factors shows the response of plant-soil nutrient system to climate change,which can provide a theoretical basis for predicting plant adaptation and biogeochemical cycle under global climate change.However,there is still a lack of relevant research,which take plants and soil as a complete system,to compare the pattern of plant and soil C,N and P and their response to climate change.This study conducted a transect,which spans 3500 km,in the east-west in Inner Mongolia Autonomous.The field investigation and laboratory test were used to analyze the plant and soil nutrient status and the response of plant-soil nutrient pattern to the changing environmental factors.The main results are as follows:(1)The variation of plant nutrient elements along the environmental factors were different.The variation range of aboveground C,N,P concentrations,C:N,C:P and N:P ratios were 20.8-50.5%,0.748-3.07%,0.0703-0.278% 1.07-1.75,2.14-2.79 and0.52-1.21 respectively.And the coefficients of variation of plant C,N,P concentrations,C:N,C:P and N:P ratios were 8.98%,34.3%,28.2%,9.90%,5.52% and 18.3%respectively.The concentrations of plant C and N did not change with the change of mean temperature in the growing season(GST),while the concentration of P decreased with the increase of the GST.There was no significant correlation between plant C,P concentrations and precipitation in the growing season(GSP),while N concentration decreased with the increase of the GSP.The change of aridity did not cause the change of plant C and P concentrations,but the N concentration increased with the increase of aridity.The C:N and C:P ratios did not change with the GST,but the N:P ratios increased with the increase of the GST.Plant C:N and C:P ratios increased and decreased with the increase of the GSP,respectively.There was no significant correlation between plant C:P ratios and the GSP.The C:N and N:P ratios of plants decreased and increased with the increase of aridity respectively,and the C:P ratios did not change with the change of aridity.(2)Soil nutrient elements had different responses to environmental factors along the transect.The variation ranges of soil C,total N,total P concentrations,C:N,C:P and N:P ratios were 0.019-1.01%,0.007-0.786%,0.013-0.094%,0.004-0.729,0.047-1.340 and 0.074-1.390,respectively.The coefficients of variation of soil C,total N,total P concentrations,C:N,C:P and N:P ratios were 75.9%,80.6%,51.1%,82.5%,34.4% and 39.5% respectively.The concentrations of soil C and total N decreased with the increase of the GST,while the GST did not lead to the change of total P concentration.Compared with plants,the concentrations of soil C,total N and total P increased significantly with the increase of the GSP.The concentrations of soil C,total N and total P decreased with the increase of aridity.The soil C:N ratios increased with the increase of the GST,and the C:P and N:P ratios decreased with the increase of the GST.The soil C:N ratios did not change with the GSP.Soil C:P and N:P ratios increased with the increase of the GSP.The soil C:N ratios increased with the increase of aridity.Soil C:P and N:P ratios decreased with the increase of aridity.(3)The effects of soil nutrients on plant nutrients were different.There was no correlation between plant C and soil C,total N and total P.There was a significant negative correlation between plant N and soil C and total N,but there was no correlation with soil total P.There was no significant correlation between plant P and soil C,but a significant positive correlation with plant P and soil total N and total P was observed.There was a significant negative correlation between plant C:N and soil C:N.A significant positive correlation with soil C:P and N:P ratios(r=0.630)was found.And there was no significant correlation between plant C:P ratios and soil C:N,C:P and N:P ratios.There was a significant positive correlation between plant N:P and soil C:N ratios.And there was a significant negative correlation with soil C:P and N:P ratios.SEM analysis showed that the concentration of soil C and total P had no direct effect on the concentration of plant C and P.The above results indicated that the coupling pattern of plant soil nutrients may have changed under the climate change.Plant and soil nutrients have different response patterns to the changes of environmental factors,especially the plant N and soil N.they showed the opposite trend in the gradient of precipitation and aridity.Plant C:N and soil C:N ratios had the opposite trend in aridity gradient.And plant N:P and soil N:P ratios also had the opposite trend in temperature,precipitation and aridity gradient.Our results indicated that the plant nutrients may depend more on its nutrient utilization strategy,rather than the nutrient supply of soils.And the impact of soil nutrients on plants was often overwhelmed by macro climate change(temperature and drought).In addition,"dilution effect" and plant nutrient system regulated by demand may lead to the out-sync between plant and soil nutrients.However,the positive nutrient correlation between soils and plants in previous studies may be challenged under climate changes.In general,this study analyzed the changes of nutrients and their stoichiometric ratios of plants and soils under climate change,and explored the different response mechanisms of plant and soil nutrients to climate change.Our findings provided valuable information for nutrient cycling and the prediction of changes in plant-soil system in arid areas under global changes.It also provided a theoretical basis for revealing the nutrient adaptation mechanism of plants to climate change and the management of grassland ecology in Inner Mongolia grassland.