Study On Phytolith-occluded Carbon Sink Of Belowground Rhizome And Trunk In Key Monopodial Bamboo Species Across China

Phytoliths are silicified features that form as a result of biomineralization within cell wall,lumen,or intercellular space of plants.During the formation of phytolith,some organic carbon?C?nearly with a proportion of 0.1%to 6%can be occluded in plant tissues,which has been well known as Phytolith occluded organic carbon?PhytOC?.Being considered as a long-term stable organic carbon pool in terrestrial ecosystems,PhytOC occupies an important part of the global C sink.Bamboo is a typical phytolith-accumulator within the family of gramineae,occupying about 3.20×10⁷ hm² around the world and known as a very important forest resource.Currently,bamboo forests cover an area of about6.73×10⁶ hm² in China,of which more than 85%are monopodial bamboo stands.In addition with the strong capacity of silicon enrichment,bamboo is also characterized by its rapid growth and large biomass.Recent studies have demonstrated that bamboo plants contribute greatly to PhytOC sink in forests based on their aboveground biomass.However,little is known about the contribution of belowground trunk and rhizome of bamboo to the PhytOC stock.In this study,eight typical monopodial bamboo species that widely distributed across China were selected,and both trunk and rhizome of bamboo with varying ages were collected.The contents of phytolith in the plant samples were extracted by using microwave digestion method,and the contents of PhytOC were determined with alkali solution spectrophotometry.Our main results and conclusions are as follows:?1?The belowground biomass including trunk and rhizome accounted for 39.41%of the total biomass on average,in which the belowground biomass of Phyllostachys prominens?PP?accounted for 74.91%,followed by Phyllostachys praecox?PPP?,Pleioblastus amarus?Keng?Keng f.?PAKK?,Phyllostachys glauca McClure?PGM?with a proportion of 50%.This result indicates that the belowground biomass of the key monopodial bamboo species is huge and the potential of carbon sink of underground part should not be ignored.?2?There were great variations in belowground Phytolith and PhytOC contents of monopodial bamboo among different bamboo species.The Phytolith contents ranged from 20.30 g·kg^-1 to 45.62g·kg^-1 across the eight species,with the order of PPP>PGM>BPM>PHO>PAMK>PP>PHMP>PAKK and the PhytOC contents ranged from 0.48 g·kg^-1 to 1.77 g·kg^-1 following the order of PPP>PHMP?PHO>PAKK>PGM>PAMK>BPM>PP.?3?The contents of Phytolith and PhytOC in the underground parts of 8 monopodial bamboo species were mainly distributed in the rhizome,which accounted for 69.48⁹9.45%of the total belowground pools.The PhytOC contents of rhizome in all the bamboo species accounted for more than80%of the total underground pools with the exception of PHO.The proportions of PHMP,PP,PAMK and PGM were even more than 95%.?4?The PhytOC stocks of the belowground parts of 8 monopodial bamboo species accounted for5.55⁵6.76%of total stocks of whole biomass with an average of 23.36%.There were great variations in the PhytOC stocks of the belowground biomass among the eight monopodial bamboo species.The PhytOC stocks of the belowground biomass of PHMP held for 94.84%of total stocks among the 8 bamboo species.Taking the mean value(14.60 kg·hm^-2)of PhytOC stock in of belowground biomass across 8 species and China's current monopodial bamboo area,we estimated that the total belowground PhytOC stocks of monopodial bamboo in China is 1.01×10⁵ t·C,which is equivalent to 3.69×10⁵ t CO₂ would be sequestered in belowground phytoliths of Chinese monopodial bamboo forests.?5?The rhizome biomass of PPP increased gradually with increasing plantation year.The contents of Si and PhytOC were higher in the two-year-old PPP rhizome than those in the one-year-old,whereas decreased significantly in the rhizome of three-year-old PPP.There were neither significant differences in the contents of C concentration in phytolith and PhytOC among PPP with different plantation year,nor the stocks of Si and PhytOC among different plantation year.Nevertheless,the three-year-old PPP had the highest mean PhytOC stock in rhizome due to its high C concentration in phytolith and rhizome biomass.In conclusion,our results show that the belowground biomass of bamboo represent a great PhytOC stock,and should not be overlooked in future studies in order to better quantify the PhytOC sequestration capacity.