Effects of Stand Age and Environmental Factors on Soil Phytolith-Occluded Organic Carbon Accumulation of Cunninghamia lanceolata Forests in Southwest Subtropics of China

The area of Cunninghamia lanceolata forests in China is expansive, the soil PhytOC(phytolith-occluded organic carbon) stock of Cunninghamia lanceolata forests is a vital carbon reservoir on the global scale. Soil from the Cunninghamia lanceolata forests was collected, and the soil physicochemical indexes and phytoliths and PhytOC content were measured to explore the accumulation characteristics of PhytOC in the 0-10, 10-20, and 20-30 cm soil layers at different stand ages. The results are as follows: (1) soil phytolith content (11.98-32.60 g<middle dot>kg(-1)), PhytOC content (0.48-1.10 g<middle dot>kg(-1)), PhytOC/TSOC (1.90%-6.93%), soil PhytOC stock (0.446-1.491 t<middle dot>hm(-2)), and mature forest > middle-aged forest > Huitou-sha forest > young forest. The soil PhytOC accumulation was significantly affected by stand age. Huitou-sha is not an advantageous afforestation way of Cunninghamia lanceolata. (2) the soil physicochemical properties and stand conditions had significant effects on soil PhytOC accumulation. High-silicon, carbon-rich, acidic soil environment and appropriate thinning are conducive to phytolith formation and PhytOC sequestration. (3) the accumulation potential of soil PhytOC in the Cunninghamia lanceolata forest is relatively large, and its importance as a forest carbon sink cannot be ignored. Soil PhytOC stock in Cunninghamia lanceolata forests of different stand ages will lay a foundation for accurate estimation of forest carbon sink.