Carbon Sequestration Potential And Different Land Use Impacts Of Phytolith-occluded Carbon Production In The Steppe

The rapid increase in atmospheric CO2 and global surface temperature since the advent of the Industrial Revolution has motivated many scientists to investigate methods that can securely sequestrater atmospheric CO2.Terrestrial biogeochemical carbon(C)sequestration is among the most promising approaches to reduce the speed of rapidly rising atmospheric carbon dioxide(CO2)concentrations and thus mitigate impacts of climate change.The Phytolith-occluded organic carbon production and its potential in carbon sequestration had recently emerged as a focus in the search for the methods to mitigate the climate change.Phytolith-occluded organic carbon(Phyt OC)is an inert form of organic carbon that is bio-sequestered within plants and accumulated in soils after plant decomposition.As Phyt OC has a long residual time in soil(on a millennial scale),it plays an important role in carbon bio-sequestration from a long-term perspective,which can off-set the increase in atmospheric carbon dioxide concentration.The grassland ecosystems cover about one fifth of the world’s land surface,and the dominate species are all silicon-enrechment,so they have a great potential for carbon sequestration.However,the research on the Phyt OC production in grassland is very limited,with only some rough estimation of Phyt OC production based on the above-ground net productivity(ANPP),and not at all evaluated in grassland plant roots(BNPP,below-ground net productivity).In addition,the impacts of grassland utilization,such as animal grazing,mowing and enclosure,on Phyt OC production have not yet been assessed,and grassland types is various,which Phyt OC production are still unstudied.As the BNPP is generally around 10-times greater than the ANPP in semi-arid grassland,we speculated that grassland BNPP had a significant contribution to total Phyt OC production in grassland.The grassland use has profound impacts on grassland species composition(which has different Phyt OC contentand productivity),and that land use through animal grazing and mowing would affect grassland Phyt OC production.Based on the differences in the composition and productivity of plants of different grassland types affected by environmental factors,we speculated that the carbon content of plant decreaded with the climate drought,and the productivity of grassland was lower than that of wet grassland,and the carbon production flux of Phyt OC would be lower.The present study,we determined the ANPP,BNPP and the Phyt OC production of major plant species of the main grassland vegetation types in Inner Mongolia and of different utilization grasslands in typical degraded steppe,such as grazing,mowing,short-time enclosure and long-time enclosure.Thus we can(1)upscale the results at the representative grassland sites to grassland regions to quantify the carbon sequestration potential via Phyt OC production in grassland regions,(2)evaluated the long-term effects of land use change on Phyt OC production for the development of grassland management systems,and(3)determined total Phyt OC production flux under varying conditions,and established the relations between Phyt OC production with climate and soil factors.In this study,the main dominant species of communities in different types of grasslands and different utilization modes of grasslands in Inner Mongolia were slected to explore the accumulation characteristics and distribution rules of phytoliths in different parts of different species,and calculate the carbon content of phytoliths,in order to estimate the carbon production flux of above-ground and underground phytoliths in the grassland plant communities.The main conclusions are as follows:1)The Phyt OC concentration of major steppe species was significantly(p < 0.05)higher in belowground(0.67 g kg-1)than aboveground biomass(0.20 g kg-1)and that the belowground net primary productivity(BNPP)was 8-15 times of the aboveground net primary productivity(ANPP).Consequently,the Phyt OC stock in belowground biomass(12.50 kg ha-1)was about 40 times of that in aboveground biomass(0.31 kg ha-1),and Phyt OC production flux from BNPP(8.1-15.8 kg ha-1 yr-1)was 25-51 times of that from ANPP.Our results indicated that BNPP played a dominant role in the Phyt OC production in grassland ecosystems.2)The Phyt OC content of dominant plant under different utilization grasslands(grazing,long-term enclosure,short-term enclosure and cutting grass)varied substaitially and we found that the Phyt OC content of communities of different utilizations ranged from 0.08-0.20 g kg-1 and 0.18 to 0.66 g kg-1 in above and belowground,but the aboveground biomass of livestock grazing and mowing grasslands had a tendency to reduce,whereas the underground biomass increased.Consequently compared to the enclosed grasslands,livestock grazing and mowing grasslands did not reduce the grassland Phyt OC production.3)The phytolith concentration and Phyt OC concentration in aboveground and belowground parts of dominant plants ranged from 4.23 g kg-1 to 126.01 g kg-1 and from 0.23 g kg-1 to 3.63 g kg-1.The phytolith occluded organic carbon was from 0.66% to 28.96%,which was lower in grass and sedge families(p<0.05).The drier climate and lower p H,the Phyt OC content was higher in community level.However,the belowground net primary productivity was lower in drier steppe,resulting lower Phyt OC produce flux.Different steppe types had significant effects on the Phyt OC production potential in grassland ecosysterm.We suggested that potential phytolith C sequestration of grasslands maight be at least one order of magnitude greater than the previous estimation based on ANPP only.Our results emphasized the need for more research on phytolith and Phyt OC distribution and flux in both above and below ground plant parts when quantifying the phytolith C sequestration.