Study On Phytolith-occluded Carbon In Soil Under Important Forest Kinds

Phytolith is the soil soluble silicon(H4Si O4) absorbed by plant roots. In the transpiration of plant, Si is precipitated in the cell, or the cell wall, which forms solid amorphous particles through the self-silicification of plants. In the process of the formation of Phytolith, there will be part of the organic carbon wrapped in Phytolith and this part of the organic carbon is called Phytolith-occluded organic carbon(Phyt OC). Phyt OC protected by the phytolith is resistant to exterior weathering and corrosion. Then Phyt OC can be stably for long time in the soil and thus becomes one of the important, long-term(thousand years) fixation carbon mechanisms in terrestrial soil.The distribution of subtropical forests in China is very broad, vegetation types are very rich. Moso bamboo stands, Chinese fir stands, broadleaf stands, and conifer-broadleaf stands are the main forest types. Therefore, the understanding of Phyt OC stocks and long-term carbon sequestration potential in the soils derived from different lithology under different forest types in subtropical China is very necessary. In this paper, different lithology(rhyolite, sandshale, and tuff) soils under different forest types were selected as study object to compare to the effects of different lithology and forest types on phytolith and Phyt OC contents and discuss the distribution characteristics of soil. Phyt OC in the soil profiles. We also estimated total stocks of soil Phyt OC under different forest types. The main results of this study are as follow:The effects of forest types on the contents of phytoliths and organic carbon in phytolith in the soils: There are no significant differences in Phytolith contents in the soils under different forest types. The Phytolith contents in the soils different forest types ranged from 11.28 g kg-1 to 14.58 g kg-1 in which the highest content was obtained from Moso bamboo stands. The contents of organic carbon in phytolith under the soils different forest types ranged from 12.43 g kg-1 to16.15 g kg-1. The total Phyt OC stocks in 0-30 soil depths under 4 forest stands decreased in the order: broadleaf stands(1.22×107 t C) > Chinese fir stands(6.45×106 t C) > Moso bamboo stands(3.07×106 t C) >conifer-broadleaf stands(0.69×106 t C).The effects of lithology on the contents of phytoliths and Phyt OC in the soils: The contents of phytoliths in the soils derived from rhyolite, sandshale, and tuff were 15.54~19.62, 7.94~11.77, and 7.46~14.02 g kg-1, respectively. The phytolith content in the soil derived from rhyolite was much greater(p<0.05) than that from tuff under Moso bamboo stands. The phytolith content in the soil derived from rhyolite was much greater(p<0.05) than that from sandshale and tuff under other three forest stands. The Phyt OC contents in the soil derived from rhyolite was much greater(p<0.05) than that from sandshale and tuff in all the forest types.The distribution characteristics of soil Phyt OC and Phyt OC/TOC in the soil profiles: For the four forest stands, the changes in phytolith and Phyt OC contents in the soils with soil depths were different: the phytolith content in the soils under Moso bamboo stands decreased with soil depths, but the decrease was the greatest in 60~100cm soil depth; the decrease in the phytolith contents in 30-60cm soil depth under Chinese fir stands and in 0-30 cm soil depths under broadleaf and conifer-broadleaf stands were the greatest. The changes in Phyt OC contents in the soils with soil depth under Moso bamboo and Chinese fir stands were greater than that under broadleaf and conifer-broadleaf stands. The ratios of Phyt OC/TOC in the soils under the four forest stands increased sharply with soil depths.