| Forest ecosystem is considered to be the most important carbon sink of terrestrial ecosystem. Phytolith-occluded organic carbon(Phyt OC) in forest ecological system is a kind of long-term(decades to millennia) mechanism for sequestrating soil organic carbon and has a vital significance to the global carbon sequestration. China’ subtropical forest zone cover a total area of 2.5×108 hm2 and has various types of vegetation. It has the largest area of global forest zone and plays a unique and important role in global forest carbon sink. In this study, several forest types in subtropical forest zone of China were selected to estimate Phyt OC stocks in the forest litter layers and the flux of phytolith carbon sequestion of tree species. The main results of this study are as follow:1. A litter experiment including Moso bamboo(Phyllostachys edulis) stand, Chinese fir(Cunninghamia lanceolata) stand, broad leaved stand and mixed coniferous and broad-leaved stand in in subtropical forest zone of China was coducted to study the Phyt OC stocks of litter layers.The results show that(1) there were significant variations in the litters’ phytolith contents between different forest types. The phytolith contents in the litters under different forest stands were in the following order : Moso bamboo stand(146.27 g·kg-1) > broad leaved stand(21.52 g·kg-1) > mixed coniferous and broad-leaved stand(15.56 g·kg-1) > Chinese fir stand(7.12 g·kg-1);(2) the Phyt OC contents in the litters also had significant variations between different forest types. The Phyt OC contents in the litters under different forest stands were in the following order : Moso bamboo stand(4.04 g·kg-1) > broad leaved stand(1.30 g·kg-1) > mixed coniferous and broad-leaved stand(1.09 g·kg-1) > Chinese fir stand(0.86 g·kg-1);(3) there were strong linear relationships between Si contents and phytolith contents in the litter under different forest types(R2=0.8278, P < 0.01), phytolith contents and Phyt OC contents in the litters under 4 stands(R2=0.8668, P < 0.01) as well as occluded carbon contents in phytolith and Phyt OC contents in the litters under 4 stand types(R2=0.5369, P < 0.01);(4) the Phyt OC stocks in the litter layers under Moso bamboo stand, Chinese fir stand, broad leaved stand, and mixed coniferous, and broad-leaved stand were 14.66, 2.87, 6.22, 4.84 kg·hm-2, respectively;(5)The area of Moso bamboo stand, Chinese fir stand, broad leaved stand, and mixed coniferous and broad-leaved stand in subtropical China is 3.87× 106, 1.13× 107, 2.49×107, and 1.55× 106 hm2, respectively. Assuming the area of these four forest types, the total Phyt OC stocks of Moso bamboo stand, Chinese fir stand, broad leaved stand, and mixed coniferous and broad-leaved stand were 5.68× 104, 3.24× 104, 1.55× 105, and 7.50×103 t, equivalent about 2.08× 105, 1.19× 105, 5.68× 105, and 2.75× 104 t CO2. In the litters of these four forest types, Moso bamboo stand had the highest Phyt OC contents and Phyt OC stocks, thus Moso bamboo had stronger Phyt OC sequestration potentials.2. A leaf experiment of seven major tree species including Moso bamboo stand, Coniferous stand, and broad leaved stand in subtropical forest zone of China was conducted to study the phytoliths carbon bio-sequestration rates of seven major tree species.The results show that(1) the phytolith contents in the leaves of different tree species were in the following order: Phyllostachys pubescens(117.79 g·kg-1) > Cyclobalanopsis glaua(26.92 g·kg-1) > Liquidambar formosana(9.79 g·kg-1) > Schima superba(4.36 g·kg-1) > Cunninghamia lanceolata(3.16 g·kg-1) > Pinus massoniana(2.92 g·kg-1) > Castanopsis sclerophylla(1.90 g·kg-1);(2) The Phyt OC contents in the leaves of different tree species were in the following order: Phyllostachys pubescens(3.31 g·kg-1) > Liquidambar formosana(1.12 g·kg-1) > Cyclobalanopsis glaua(0.88 g·kg-1) > Schima superba(0.49 g·kg-1) > Pinus massoniana(0.40 g·kg-1) > Cunninghamia lanceolata(0.30 g·kg-1) > Castanopsis sclerophylla(0.19 g·kg-1);(3) there were strong linear relationships between Si contents and phytolith contents in the leaf under different tree species(R2=0.9897,P < 0.01), phytolith contents and Phyt OC contents in the leaf(R2=0.8816,P < 0.01), occluded carbon contents in phytolith and Phyt OC contents in the leaf(R2=0.3544,P < 0.01);(4) Phyllostachys pubescens had the highest phytoliths carbon bio-sequestration rate(0.0506 t-e-CO2·hm-2·a-1), bio-sequestration via phytolith carbon from leaf-litter under 3.87× 106 hm2 of Phyllostachys pubescens stands in subtropical China is estimated to be about 1.96× 105 t CO2; the phytoliths carbon bio-sequestration rates of Cunninghamia lanceolata and Pinus massoniana were 0.0056 and 0.0108 t-e-CO2·hm-2·a-1, respectively; bio-sequestration via phytolith carbon from leaf-litter under 1.13× 107 and 1.20×107 hm2 of Cunninghamia lanceolata and Pinus massoniana stands is estimated to be about about 6.33× 104 and 1.30× 105 t CO2, respectively; the phytoliths carbon bio-sequestration rates of broad-leaved forests ranged from 0.0005 to 0.0193 t-e-CO2·hm-2, bio-sequestration via phytolith carbon from leaf-litter under 2.49× 107 hm2 of broad-leaved forests in subtropical China is estimated to be about(1.25~ 48.15)× 104 t CO2. |
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