| This study selected the dominant tree species and common herbs species from Saihanba and nearby area forest vegetation in temperate zone of China, and selected samples of mature leaves, leaf litters and soils from Qingshan moso bamboo(Phyllostachys pubescens) stands in subtropical zone of China. Then used lithium metaborate fusion-dilute nitric acid dissolution, sequential chemical extraction, microwave digestion, Walkley-Black method, potassium dichromate oxidation heating method, and ultraviolet spectrophotometric method to checked and analyzed silicon(Si) distribution of different plants, Si fraction of different slope position, and variation of phytolith and phytolith-occluded-carbon(Phyt OC) content within different plants. The purposes of this study are to offer scientific references for Si nutrition cycle of forest ecosystem and long-term biogeochemical carbon(C) sequestration of phytolith.According to the Angiosperm Phylogeny Group III classification, the results showed that the variation of Si content within 108 plant species of Saihanba and nearby area forest was related to the plant phylogenetic position. For angiosperms, the commelinoid monocot orders accumulated substantially more Si than the other monocot orders and the asteroid dicot orders accumulated more Si than the other dicot orders. Ecologically, herbaceous species had the highest Si content(0.47 ± 0.26% d. wt.) followed by tree(0.33 ± 0.13% d. wt.) and shrub species(0.24 ± 0.09% d. wt.). The Phyt OC production rate in the forests of north China was about 0.48 ± 0.20 × 106 t CO2 year-1, approximately 44% of which was contributed from the understory vegetation comprising of herbaceous and shrubs species.The Saihanba Mechanized Forest Farm is mainly composed of six forest types. The Phyt OC production flux of Quercus mongolica forest, Mongolian pine forest, Betula-Picea meveri mixed forest, Larix principis-rupprechtii forest, Betula forest, and Picea meyeri forest were estimated to be 4.28 kg CO2 ha–1 year–1, 1.12 kg CO2 ha–1 year–1, 2.02 kg CO2 ha–1 year–1, 1.69 kg CO2 ha–1 year–1, 1.73 kg CO2 ha–1 year–1, and 3.93 kg CO2 ha–1 year–1, respectively. In conclusion, the Phyt OC production flux of Saihanba Mechanized Forest Farm was estimated to be 1.86 kg CO2 ha–1 year–1, the contribution of trees and herbs were 54% and 46%, respectively. Therefore, the Saihanba Mechanized Forest Farm would sequester 141.44 t CO2 with the Phyt OC fraction.The variation of Si fraction contents and availability between different slope positions showed that the soil total Si(Si O2) content of moso bamboo stands varied from 487.80 g kg–1 to 580.72 g kg–1, but the non-amorphous Si only contributed 2.56% ~ 3.88%. Among different Si fractions of non-amorphous Si, Acid Na-acetate-Si contributed 1.94% ~ 4.33%, H2O2-Si contributed 2.43% ~ 3.47%, NH2 OH HCl-Si contributed 5.90% ~ 8.38% and Na OH-Si contributed 85.29% ~ 89.02%. For upper layer soils, the contents of Acid Na-acetate-Si increased from upper slope to lower slope. Conversely, the contents of Na OH-Si decreased from upper slope to lower slope. The contents of H2O2-Si and NH2 OH HCl-Si have no obvious regularity from upper slope to lower slope.The variation of phytolith content and Phyt OC content within mature leaves and leaf litters of moso bamboo between different slope positions showed that the phytoliths content and Phyt OC content in mature leaves were all lower than which in leaf litter. There was a significant influence of slope position on variation of soil p H, available-Si, and production of phytolith and Phyt OC in moso bamboo ecosystems. The Phyt OC production flux of moso bamboo stand was ranged from 6.50 kg ha–1 year–1 to 20.47 kg ha–1 year–1 and increased with slope position as: lower slope < middle slope < upper slope.Phylogenetic classification, ecological context, and different slope position effected both the Si distribution and Phyt OC sequestration potential. Our results indicate that during the further process of afforestation/reforestation, the Phyt OC sequestration potential of the forests may be further enhanced by planting plants accumulated more phytolith content, selecting middle to upper slope position of hills and low height mountains, preserving the understory vegetation, and maximizing the aboveground net primary productivity(ANPP) of all layers. |
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