Biogeochemical Cycle Of Silicon In Typical Karst Area

Silicon is the second largest constituent element in the Earth's crust.At present,the research of silicon cycle has become the key and foundation for the study of land-sea interaction,carbon cycle and global environmental change.Study on silicon cycle in the karst area is an important part for ecological restoration,and it is conducive to a more comprehensive understanding of the biogeochemical cycle of silicon in terrestrial ecosystems.In this paper,the plant,soil,water and sediments in the Wujiang River Basin were used as research objects to investigate the distribution of silicon in plants,soil,water and sediments,and the effects of topography?slope position?on the variation of total silicon content and silicon forms in the soils and plant silicon content.The main findings of this paper were:?1?The content of silicon in the aboveground part of ferns and cogongrass in Chenqi small watershed showed a trend of decreasing first and then increasing with the increase of available silicon content in the soil.When the content of available silicon in the soil is less than 0.09%,the content of silicon in the aerial part of the ferns and cogongrass decreased with the increase of soil available silicon content,indicating that the silicon absorption of the two plants has a small effect on the soil available silicon.When the soil available silicon is greater than 0.09%,the content of silicon in the aboveground part of the two plants increases with the increase of soil available silicon content,indicating that the silicon absorption of the two plants has a larger effect on the soil available silicon.?2?In the water-fluctuating area of the Wujiang River Basin,the silicon content of the plant aerial part is lower than that under flooded conditons.?3?The content of available silicon,organically bound silicon,iron-manganese oxide bound silicon and amorphous silicon in the soil increased from the top slope position to the lower slop positon.This indicates that changes of local topographical have a potential impact on soil silicon morphological.?4?In this study,the average content of total silicon in the surface sediments of the reservoir varies from 15.92%to 25.22%.The average content of biogenic silicon in the surface sediments of the reservoir varies from 0.74%to 2.92%.The average content of biogenic silicon in the surface sediments of different reservoirs is opposite to that of total silicon.When the total silicon content in the surface sediments of the reservoir is low,the content of biogenic silicon is relatively high.This indicates that the generation and accumulation of biogenic silicon in the reservoir may be mainly affected by the change of dissolved silicon content in the reservoir water,rather than the change of silicon content in the sediments.?5?The sizes of soil available silicon pool,plant silicon pool and soil biogenic silicon pool in Chenqi small watershed are 253.62 kg ha^-1,139.75 kg ha^-1 and 1537.97kg ha^-1,respectively.For steady-state ecosystems,the flux of silicon from plants to the soil is approximately 72.59 kg ha^-1 yr^-1,and the flux of litter input to the BSi pool is greater than 5.44 kg ha^-1 yr^-1.The flux of the soil available silicon reservoir is less than67.15 kg ha^-1 yr^-1.