Plant Phytolith Carbon Sequestration Potential And Its Relationships With Climate In Inner Mongolia Grassland

Phytolith is amorphous silicon（SiO₂·nH₂O）deposited in plant cell wall,cell cavity or intercellular space.As a component of biological silicon,phytolith plays an important role in the geochemical life cycle of silicon.Phytolith is fixed with a certain amount of organic carbon（0.1%-6.0%）during its formation,which is called phyt OC.Phytolith has stable structure,high temperature resistance,corrosion resistance and other characteristics,and can exist in soil for a long time.Therefore,phytolith carbon is an important part of the global carbon sink that can exist stably for a long time,and it is of great significance to slow down the increase of atmospheric CO₂concentration.Due to the large area of grassland,the dominant grasses have high carbon content in phytolith and phyt OC,which has become the focus of research on phyt OC sink in recent years.However,there is still a lack of systematic research on the relationship between phytolith and phyt OC accumulation and environmental factors in grassland.We sampled grassland plants and determined their phytolith and phyt OC contents in the temperate zone of Inner Mongolia along a climate gradient,and calculated their its reserves,and analyzes their changes in relation with climate and soil factors.We aimed at understanding the mechnisms of plant phytolith formation,and to provide more basis for accurately estimating phyt OC sequestration potential.The main research conclusions are as follows:1.With the increase of climate humidity（decrease of aridity）,the phytolith content of Leymus chinensis,the dominant plant widely distributed in the steppe grassland,increased significantly.That is,its phytolith content was positively correlated with precipitation（P<0.05）,negatively correlated with annual mean temperature（P<0.05）,but not correlated with soil property indicators.There was no significant correlation between phytolith content and climatic factors in mixture of 4 Stipa plants(Stipa kelmenzii,S.krylovii,S.gandis and S.baicalensis,which were substituted with each other on the climatic gradient.Significant correlations between phytolith and phyt OC contents and climatic factors were neither detected in two species of Cleistogenes（C.songolica and C.squarrosa）.2.On the climate gradient,plant community aboveground productivity increased with the increase of precipitation,but plant water use efficiency（PUE）decreased.The increase of phytolith content in L.chinensis with precipitation may reflect the decrease of plant water use efficiency;that is,plants use more water per unit dry matter production,so more phytolith is absorbed and deposited.The fact that no significant correlation between phytolith of the 4 Stipa species（or 2Cleistogenes species）and climatic factors,might be related to the different water use or silicon biological processes of the these substitution species along climate gradient.3.At the plant community level,the plant communities of desert steppe,typical steppe and meadow steppe are distributed in turn with the increase of climate humidity,and the phyt OC of plant community increases with the increase of climate humidity.The phytolith and phyt OC content were positively correlated with annual average precipitation（P<0.01）.The results showed a significant positive correlation with aboveground biomass and a negative correlation with the annual average temperature（P<0.01）.The phyt OC content was high in typical steppe.4.The phytolith and phyt OC varied with soil properties.They were negatively correlated with soil p H（P<0.05）,positively correlated with soil total carbon and total nitrogen（P<0.05）,and positively correlated with the content of available silicon in soil（P<0.05）.The research has deepened the understanding of the phytolith accumulation in grassland plants,and the relationship between phytolith production and environmental factors,which is of greatsignificance for accurately estimating the phyt OC sequestration potential in grasslands.