Biogeochemical Characteristics Of Carbon, Nitrogen, And Silicon In Grasslands, North China

The biogeochemical characteristics of carbon（C）,nitrogen（N）and silicon（Si）in grassland ecosystem have significant impacts on the function and evolution of grasslands.In the present research,we analyzed the content,storage and stoichiometric ratio of C-N-Si in plant-soil system of meadow steppe,typical steppe and desert steppe in Inner Mongolia.The correlations of these parameters with environmental factors were also investigated.This thesis elucidated the biogeochemical characteristics of C,N and Si and their response to environmental factors of grasslands in northern China aiming at providing scientific reference for the sustainable use of grasslands.Main results and conclusions are as follows:（1）The plant C（41.55±0.53%）,Si（0.84±0.03%）content in typical steppe was significantly lower than that in other two grassland types.The plant N content（2.53±0.51%）in desert steppe was the highest among three grassland types.The plant stable carbon isotope(δ¹³C)（-27.85±0.18‰）in meadow steppe was significantly lower than that in other two grassland types,but stable nitrogen isotope(δ¹⁵N)（5.29±0.07‰）was the highest.These findings suggest that there were significant differences in biogeochemical characteristics of plant C,N and Si among three grassland types.Temperature and precipitation were main factors contributing to these differences.（2）The value of plant C:N in meadow steppe（30.95±8.55）and typical steppe（21.31±10.79）was significantly higher than those in desert steppe（17.11±4.08）.The value of C:Si in typical steppe was significantly lower than that in other two grassland types.The value of plant N:Si in meadow steppe（0.07±0.03）was significantly lower than that in typical steppe and desert steppe.These results suggest that desert steppe plant had the highest efficiency of using N and meadow steppe had the highest absorption of Si_avail.（3）The soil organic carbon（SOC）and N in meadow steppe were the highest in topsoil,but SOC and N in typical steppe were the highest in deep soil.The distribution of organic carbon,N in different particle-sizes was:clay>silt>coarse sand>fine sand.The distribution of non-crystalline Si in soil showed the trend of amorphous Si>Fe/Mn-oxide Si>Si_avail>Oxidizable Si.The values of soilδ¹³C andδ¹⁵N in desert steppe were the highest.These results indicate that the biogeochemical characteristics of soil C,N and Si differed significantly among three grassland types.Climatic factors and soil texture are main reasons for these differences.（4）The value of soil C:N in meadow steppe（14.61±5.24）and typical steppe（13.21±1.37）was higher than that in desert steppe（8.13±0.35）,indicating that the mineralization ability of N in desert steppe was much stronger.The value of soil C:Si_availvail in meadow steppe（46.01±34.11）was the highest among three grassland types,suggesting that soil Si_avail in meadow steppe mainly came from the decomposition and conversion of amorphous silicon.The value of soil N:Si_avail in meadow steppe（2.70±1.39）and typical steppe（2.34±0.55）was significantly higher than that in desert steppe（1.32±0.11）,indicating that with the increase of soil moisture,the relative accumulation of soil N is greater than that of Si_avail.