Phytolith Occluded Carbon Pools And Stability And Their Regulation Mechanism In Typical Bamboo Plantations

Phytolith-occluded carbon(Phyt OC)long-term accumulation in soil is a stable carbon sink and can play an important role in the regulation of the global climate.The distribution and storage of soil Phyt OC depend on the balance between plant Phyt OC input and soil Phyt OC output.However,the effects of abiotic and biotic factors,such as phytolith stability,soil properties and management practices,as well as the vegetation types present at a site,on the plant Phyt OC input and soil Phyt OC output remain largely unknown.As a typical silicon-enriched plant in gramineae,bamboo plants have a high potential for Phyt OC sequestration and are well represented and of high research value for Phyt OC studies.In this paper,we study the effects of bamboo species and organs,soil physical fractions,parent types,plantation ages and soil depths,application of silicon fertilizer and biochar,and management intensities on the Phyt OC concentration and its stability through a combination of sampling,field and laboratory experiments to reveal the factors and mechanisms affecting the soil Phyt OC balance with typical bamboo plantations.The main findings are as follows.(1)The change of silicon and C concentrations in Boric-acid Base buffer by bamboo species was more evident in 15 and 30 days than in 0.5,1,3 and 7 days.Bamboo species significantly influenced the carbon concentration in leaf phytolith,?10?m and>10?m phytolith concentration,soil Phyt OC concentration,and mass-normalized alkaline stable phytolith.In addition,mass-normalized alkaline stable phytolith was positively(R~2=0.13)correlated with>10?m phytolith,while negatively(R~2=0.16)correlated with?10?m phytolith.Further,the structural equation model revealed that soil Phyt OC driven by carbon concentration in leaf phytolith(P<0.001),>10?m phytolith(P<0.001),and mass-normalized alkaline stable phytolith(P<0.05)varied with bamboo species.The selection of bamboo species,i.e.,Moso bamboo(Phyllostachys edulis),with high Phyt OC production and stability,can be used as a representative bamboo species for further study.(2)The organ,source and soil physical fractions significantly affected the phytolith concentration,chemical composition of phytolith and alkali-stabilized phytolith.Leaves,branches and rhizomes increased phytolith solubility,instead of stems.The phytolith solubility decreased with the following order:leaves>litters>soils.The solubility of the phytolith in heavy fraction organic matter(HFOM)was lower than that of the phytolith in light fraction organic matter(LFOM),while surface of the HFOM-phytolith is rougher with more etching pits.The phytolith solubility was significantly linearly negatively correlated with silicon concentration in phytolith(R~2=0.27),but not with the carbon concentration in phytolith.(3)The parent types significantly affected the leaf Phyt OC concentration,instead of leaf phytolith solubility.The parent type significantly affected soil phytolith solubility in0-10 and 10-30 cm soil layers,but did not affect the Phyt OC concentration in both soil layers.Both the concentrations of plant Phyt OC(R~2=0.34)and 0-10 cm soil Phyt OC(R~2=0.34)were significantly positively correlated with 0-10 cm soil available silicon concentration.The best subset selection linear regression and least angle linear regression revealed that soil available silicon is a major driver in soil phytolith solubility.(4)The Phyt OC concentrations in the bamboo plants and 0-10 cm soil increased with increasing silicon fertilizer addition,regardless of biochar application.Biochar addition increased the soil Phyt OC pool size,as well as the LFOM-and HFOM-Phyt OC fractions,regardless of silicon fertilizer application.The silicon fertilizer with biochar application increased soil phytolith solubility.Soil Phyt OC was correlated with the concentration of soil organic nitrogen(R~2=0.32),SOC(R~2=0.51),p H(R~2=0.28),and available silicon(R~2=0.23).Furthermore,silicon fertilizer application increased plant and soil Phyt OC by increasing soil available silicon.Moreover,biochar application increased soil Phyt OC concentration in LFOM-Phyt OC and the unstable fraction of Phyt OC.(5)The Phyt OC concentration in LFOM increased with increasing stand age in the0-10 and 10-30 cm but not in the 30-60 and 60-100 cm.HFOM-Phyt OC concentrations with the same soil layer increased over time with increased plantation age.The increase was more significant in the surface soil than in the deeper soils.Long-term planting of Moso bamboo forests increased the soil Phyt OC pool size,as well as the LFOM-and HFOM-Phyt OC fractions.The LFOM-(R~2=0.32)and HFOM-Phyt OC(R~2=0.35)concentrations were positively correlated with soil organic carbon concentrations.The HFOM-Phyt OC(R~2=0.06)concentration was positively correlated with that of water-soluble silicon.(6)Intensive management increased Phyt OC production mainly due to increased forest productivity;increased Phyt OC storage in the heavy fraction but decreased its storage in the light fraction of organic matter,resulting in the lack of effect on soil Phyt OC storage;increased the rate of dissolution of phytolith and the loss of Phyt OC in runoff;and promoted Phyt OC sequestration in the soil-plant system,mostly in the plants,due to the greater rate of Phyt OC production than the rate of loss,respectively,as compared to extensive management.The above researchers revealed that genotype(bamboo species),physiological characteristics(organs),soil properties,management practices and phytolith self-attribute affect the Phyt OC stability and thus affect the soil Phyt OC pools and its distribution in physical fractions in bamboo forests.