Research On Phytolith Carbon Sequestration In Bamboo And Its Relationship With Species And Lithology

Phytolith-occluded carbon (PhytOC), one of the most stable carbon forms, represents up to82%of organic carbon in some soils and sediments. The phytoliths have huge potential of biogeochemistcalcarbon sequestration, thus play a crucial role in the control and regulation of the global climate. Bamboo,a typical Si-accumulator, has a global area of2.2×107ha, occupying about1%of the total global forestdistribution area. Bamboo forest plays an important role in global carbon cycle and global climatechange.This study selected leaf and soil samples of bamboo ecosystems in Lin’an, Anji, and Xinchang,Zhejiang, China. The phytoliths within bamboo leaves were extracted with microwave digestion andWalkley-Black method. Possible extraneous organic materials of phytoliths were removed andexamined with0.8mol L-1potassium dichromate. The purposes of this study are to provide scientificreferences for the regulation of phytolith C sink and to improve understanding of the role of bamboophytolith in the terrestrial C cycle by analyzing the variation of phytolith and PhytOC contents indifferent bamboo species.The phytolith content in leaves of the75bamboo species ranged significantly from4.28%to16.42%, with a mean of9.59%. There was a significant variation in the phytolith content of bambooleaves from different genera. The phytolith content in the leaves of Sasa was significantly higher thanthat of other genera. There was no obvious variation in the phytolith content of bamboo leaves fromdifferent subtribes, bambuseaes and bambusataes. According to the PhytOC content of phytoliths andaverage ANPP of bamboo leaf litters, it is estimated that the flux of phytolith carbon sequestration frombamboo is0.028–0.108t CO2ha–1yr–1, with a mean of0.063t CO2ha–1yr–1. Taking China’s currentbamboo area of7.2×106ha and global bamboo area of22×106ha and the mean bamboo PhytOCproduction flux of0.063t CO2ha–1yr–1, about0.45Tg and1.4Tg CO2each year would be sequesteredin phytolith of the bamboo forest system of China and world, respectively. Assuming an expansion rate(3%) of bamboo area each year and the mean (0.063t CO2ha–1yr–1) of the PhytOC production flux inbamboo, then at least2.8Tg CO2from the atmosphere would be sequestered in bamboo phytolithsglobally by2050; and taking the highest PhytOC production flux,4.7Tg CO2would be sequestered inbamboo phytoliths globally. Therefore, it may be possible to significantly increase bamboo phytolith carbon sink by both increasing the bamboo area and selecting high phytolith-content bamboo species(Pleioblastus kongosanensis, Phyllostachys ventricosa cv. huangganlucao, Phyllostachys sulphureaviridisulcata and Phyllostachys ventricosa cv. luganhuangcao), significantly suggesting that bambooforests may play a positive role in the regulation and control of global climate change.The dry weight of PhytOC content among the35bamboo species belonging to three differentmorphologies was0.07–0.42%. However, the average contents of phytoliths (7.69–11.09%) andPhytOC (0.17–0.21%) in leaf litter decreased in the following order: clustered≈mixed> scatteredbamboo. The PhytOC production flux among the three morphological types of bamboo decreases in theorder: clustered bamboo (0.050t CO–1––12hayr–1)≈mixed bamboo (0.049t CO2ha1yr)> scatteredbamboo (0.038t CO2ha–1yr–1). Based on these data and taking the mean PhytOC production flux ofthree morphological types of bamboo, the current rate of C sequestration within phytoliths (PhytOC) inChinese bamboo is about0.293Tg CO–2yr1,75%,3%and22%of which is contributed from scattered,mixed and clustered bamboo, respectively. Taking the production flux (0.180t CO2ha–1yr–1) of PhytOCand the dubled area, the phytoliths of global bamboo would be expected to sequester at least7.92TgCO2yr–1from the atmosphere in2050. However, the study of effect of management practices (e.g.,rock-powder amendment and organic mulching) on bamboo phytolith carbon sequestration is stillrequired to enhance the bamboo phytolith C sequestration potential of reducing the concentration ofgreenhouse gases in the atmosphere.Studies on PhytOC content distribution within moso bamboo (Phyllestachys pubescens) ofdifferent ages and lithologies revealed that the contents of phytolith and PhytOC in older bamboo weregenerally higher than those in the younger. The PhytOC content of dry mass basis within moso bambooin four sites of different lithologies was0.07%—0.20%and decreased as: granodiorite (0.20%)﹥granite (0.16%)﹥basalt (0.13%)﹥shale (0.07%). Based on the data, it is estimated that PhytOCflux varies significantly among the four sites from0.001to0.065t CO2ha-1yr-1and decreased in thefollowing order: granodiorite (0.065t CO-12hayr-1)﹥granite (0.050t CO2ha-1yr-1)﹥basalt (0.040t CO2ha-1yr-1)﹥shale (0.023t CO2ha-1yr-1). This may be caused by different lithologies and thedegree of weathering, with a varied SiO2content of the parent rock. According to the moso bambooplanting area (4.8×106ha), we estimate that0.005—0.311Tg CO2yr-1from atmosphere would be sequestered by moso bamboo phytolith. Assuming the same PhytOC flux (0.065t CO2ha-1yr-1) anddouble area of moso bamboo stands (9.6×106ha),0.622Tg CO2yr-1would be sequestered in mosobamboo phytoliths of China in2050.There is a positive correlation between PhytOC content in leaves and phytolith content withinmoso bamboo of different ages and lithologies. In addition, a strong positive correlation exists betweenthe PhytOC content in leaves and the PhytOC content in phytolith. Thus, the results indicate that thephytolith carbon sequestration depends on not only the efficiency and ability of C encapsulation inphytoliths, but also the quantity of Si (phytolith) in bamboo. Consequently, some measures (e.g., theexpanding of bamboo area, the selection of bamboo species with high phytolith and PhytOC content)may significantly increase the bamboo phytolith carbon sink. However, the efficiency and cost of eachmeasure and its application to different regions also need to be further studied.