Study On PhytOC In Masson Pine(Pinus Massoniana Lamb.) Forest Ecosystem

Phytolith-occluded organic carbon（Phyt OC）in terrestrial plays an important role in long-term stable C sequestration and the regulation of the global climate due to its high resistance to decomposition.Masson pine（Pinusmassoniana Lamb）is the main coniferous tree species in China,which has a considerable volume,a wide distribution area and a great potential of phytolith carbon sink.We collected the different above-ground organs（leaves,branch,trunk）and Four soil depths（0-10cm,10-30cm,30-60cm,and 60-100 cm）samples from Masson pine forests with different ages which come from Jiande Forest Farm in Zhejiang Province.The phytoliths were extracted by microwave digestion method,and the Phyt OC contents were determined in the samples.We estimated phytolith abundance and Phyt OC distribution and explored the potential for Phyt OC sequestration in the above-ground portions of Masson pine stands in subtropical China,investigated spatial distribution of Phyt OC in soil.It provides a scientific basis for the accurate estimation of the phytolith carbon sink in the subtropical Masson pine stands ecosystem in China.The primary results of this study were summarized as follows:1.There are significant differences in phytolith and Phyt OC contents in above-ground organs of Masson pine:phytolith contents decreased in the order of leaf(1.829 g·kg^-1)>branch(0.771 g·kg^-1)>trunk(0.452 g·kg^-1),whereas Phyt OC contents decreased in the order of leaf(0.357 g·kg^-1)>branch(0.172 g·kg^-1)>trunk(0.104 g·kg^-1).Both phytolith and Phyt OC contents in leaves and branches were greatly affected by stand ages（P<0.05）,while no differences were observed for organic carbon in phytoliths in the above-ground organs（P>0.05）.Phytolith cotents in the leaves of Masson pine stands with stand age were in the order:55a(2.358 g·kg^-1)>63a(1.923g·kg^-1)>36a(1.719g·kg^-1)>24a(1.655g·kg^-1)>15a(1.489g·kg^-1).The phytolith contents of in the leaves of Masson pine stands were negatively correlated with contents of available silicon（R²=0.27,P<0.05）and p H（R²=0.45,P<0.05）in the 0-10 cm soil depth.2.Phyt OC storage in the branches and trunks accounted for 20.7%and 69.2%of the total storage in the above-ground of Masson pine stands,respectively.The Phyt OC storage in above-ground biomass was affected by stand ages and decreased in the order of 55a(15.97 kg·hm^-2)>63a(15.54 kg·hm^-2)>36a(10.63 kg·hm^-2)>15a(10.46 kg·hm^-2)>24a(10.13 kg·hm^-2).The annual Phyt OC sequestration rate in the above-ground part of Masson pine stands was affected by stand ages and decreased in the order of 15a(10.94 kg-e-CO₂·hm^-2·a^-1)>24a(9.97kg-e-CO₂·hm^-2·a^-1)>36a(7.20 kg-e-CO₂·hm^-2·a^-1)>55a(5.10 kg-e-CO₂·hm^-2·a^-1)>63a(4.76kg-e-CO₂·hm^-2·a^-1).Taking the area of 1.20×10⁷ hm² of Masson pine stands in subtropical China and the mean Phyt OC production flux of 7.58 kg-e-CO₂·hm^-2·a^-1,it was estimated approximately 9.10×10⁴ t CO₂·a^-1being sequestered in Masson pine phytoliths.3.The contents of phytolith and Phyt OC in the soils under Masson Pine stands with different ages varied from 6.01 to 15.98 g·kg^-1 and from 0.062 to 0.219 g·kg^-1,respectively;The contents of Phytolith and Phyt OC in the surface soils（0-10cm）did not increase with the stand ages and decreased with soil depth;The ratio of Phyt OC to TOC in the soils under Masson Pine stands with different stand ages ranged from 0.73 to 1.51%;Significant positive correlations were observed between Phyt OC contents and phytolith contents or total OC contents in the soils（P<0.01）.