Research On Silicon Distribution And Phytolith Carbon Sequestration Of Grassland Ecosystem

Phytoliths are silicified features resulting from the deposition of microscopic Si in the intraand extra-cellular structures in living plant tissues.About 1%–6% of organic carbon?C?can be occluded in phytoliths during plant growth,and is referred to as phytolith-occluded carbon?PhytOC?.PhytOC can be accumulated in soil or in sediment after plant decomposition for millions of years being protected by phytoliths.Grasslands represent nearly one third of China's land area.Due to the large area,high net primary productivity?NPP?,and high Si concentration of grassland ecosystems,it may have a great potential on phytolith occluded carbon.Therefore,it is necessary to research the potential of PhytOC and the regulating mechanisms of phytolith C sink of grassland ecosystems.This study selected Xixi wetlands,degraded grasslands,and Setaria viridis under different habitats and sampled the plant and soil samples in grasslands.And then use lithium metaborate fusion-dilute nitric acid dissolution,microwave digestion and Walkley-Black method to analyze silicon?Si?distribution of different plants,and variation of phytoliths and phytolith-occluded-carbon?PhytOC?content within different plants.Investigatingly seasonal accumulation of phytoliths in plants of Xixi Wetland,the response of phytolith content and phytolith carbon sink potential of degraded grasslands ecosystem to nitrogen application,which provide scientific references for the regulation mechanisms of carbon?C?sequestration of phytolith in grasslands ecosystems.According to the research on the seasonal accumulation of phytoliths and PhytOC in plants of Xixi Wetland,we found that the variability of phytolith contents,and PhytOC content of different tissues of Cortaderia selloana?TS?and Triarrherca sacchariflora?CS?for each month from May to October following trends: leaf > stem and sheath > leaf.The content of phytoliths of plant tissues generally peaked in July and decreased over the following months.Similarly,in most tissues the C contents of phytoliths and PhytOC contents were also higher at the early plant growth stages than at later growth stages.The decrease of PhytOC contents in all tissues near the end of the plant growing season indicates that part of the phytolith-Si may be transported to plant roots or the soil during the plant senescence.Therefore,traditional measures such as regulating harvest time of wetland plants for economic and environmental purposes could significantly enhance the potential of phytolith C sequestration in wetlands.The application of nitrogen?N?changed the phytolith content in degraded grasslands.The phytolith contents were in the range 0.98% to 2.94%.The phytolith content increased slightly?2.25%–2.94%?from 0 N m^-2 year^-1 to 10 N m^-2 year^-1,but decreased markedly?0.98%–1.53%?at the higher N application levels(30 to 50 N m^-2 year^-1).What is more,N application increased the PhytOC production flux in the extremely degraded grassland from 0.003 to 0.021 t CO₂ ha^-1 year^-1 and the flux increased with the level of N fertilization peaking in the 20 g N m^-2 year^-1 treatment at 700% of the control flux,but decreased at higher N doses.Assuming half of China's grasslands are fertilized with N to recover from degradation and the phytolith C sequestration flux of degraded grasslands amended with N is half of the 700% increase,the potential of phytolith C sequestration in China's grasslands could be increased at least 60%.This study demonstrates that optimization of nutritional supply is a promising approach to increase long-term phytolith C sequestration in degraded grasslands.According to silica contents and above-ground net primary production?ANPP?,the accumulation fluxes of silica in Setaria viridis under different habitats was obtained,with the following trend: No tree bank > hillside fields > bank with tree shade > grasslands.The accumulation fluxes of silica under the two habitats of roadside and artificial buildings were lowest.With the habitats changes,the silica content and ANPP changed significantly.Among all the habitats,the silica content,ANPP and accumulation fluxes of silica in Setaria viridis highest under the habitats of No tree bank.