Ecological Stoichiometry And Stable Carbon Isotope Characteristics In Agro-pastoral Ecotone Grasslands Of Northern China

Ecological stoichiometric characteristics in agro-pastoral ecotone are of great significance for understanding element cycles,vegetation growth and soil nutrients condition in grasslands.Meanwhile,stable carbon isotope characteristics of plants can provide environmental information during plant growth.Due to the interference of climate change and human activities,ecological environment problems such as vegetation degradation and soil desertification have appeared in agro-pastoral ecotone of northern China.Therefore,it is necessary to understand plant growth and soil nutrients from the perspective of ecological stoichiometry.In this study,we analyzed the content,storage,stoichiometric ratio of carbon（C）,nitrogen（N）,phosphorus（P）and silicon（Si）in plant and soil,and the stable carbon isotope characteristics of plants in the northern agro-pastoral ecotone.The relationships between these indicators and environmental factors were analyzed.The above studies can provide scientific reference for improving the ecological environment in this region.The main results and conclusions are as follows:（1）The contents of soil organic carbon（SOC）,total nitrogen（TN）,total phosphorus（TP）and total silicon（TSi）are 4.513 g kg^–1,0.586 g kg^–1,0.358 g kg^–1 and181.7 g kg^–1,respectively.Soil C:N,C:P and N:P are 7.67,11.88 and 1.56,respectively.These indexes are all lower than the average value of China,and N is more deficient than P.The contents and storages of SOC,TN and TP are reduced with the decrease of vegetation cover.Compared with high cover（HC）,the storages of SOC and TN in low coverage（LC）decrease by more than 50%,and the storages of TP also decrease by more than 20%,while the contents and storages of total silicon（TSi）show no significant changes.（2）There are significant differences in element stoichiometric characteristics among plants of different functional groups.Based on the analysis of plants N:P,our results show that the Gramineae（14.0）are limited by N and P,the Legumes（16.3）are limited by P,and the Compositae（11.6）and Chenopodiaceae（12.6）are limited by N.In this study,Si contents of Gramineae,Compositae and Chenopodiaceae show significant positive correlations with N contents,but no significant correlation with P contents.Affected by species composition,Si contents are negatively correlated with N and P contents on the whole plants.Climate factors can influence the stoichiometric characteristics of plant elements,and mean annual precipitation has a greater influence than mean annual temperature.（3）The averageδ¹³C values of C₃（–30.19±1.31‰）and C₄（–25.04±1.27‰）phytoliths are significantly lower than C₃（–26.94±0.88‰）and C₄（–14.44±0.94‰）plants.The correlation between plantsδ¹³C values and altitude and temperature in this study area are greater than that of precipitation.In addition,the C,P and Si contents of C₄ plants are significantly correlated with theδ¹³C,while the C₃ plants not.It shows a significant positive correlation between theδ¹³C of C₄ phytolith and theδ¹³C of plants,which may provide reference for the reconstruction of ¹³CO₂ in the ancient atmosphere.However,theδ¹³C shows no correlation between C₃ plants and phytoliths.