Research On Noncrystalline Silicon Forms Of Grassland Soils In North China

Grasslands,the most widely distributed terrestrial ecosystem in China,are significantly affected by human production and living activities.The desertification of grasslands will negatively impact the ecological environment and economic growth.As the second most abundant element in earth crust,silicon plays an important role in the growth of plants and the stability of ecosystems.In this study,soil samples were collected from different grassland types,grasslands of different desertification degree and the forests afforested from grasslands.The sequential chemical extraction method and UV-visible spectrophotometry were adopted to determine the acid Na-acetate-Si,H2O2-Si,NH2-OH HCl-Si and NaOH-Si contents of soil samples.The objectives of this study were to explore the effects of grassland types,desertification degrees and afforestation on the distribution and forms of soil noncrystalline silicon,to investigate the mechanisms of soil biogeochemical silicon cycle in grasslands,and to provide scientific references for grassland ecosystem restoration and sustainable utilization of grassland resources.The main results are as follows.For typical steppe,meadow steppe and meadow,the contents of acid Na-acetate-Si,H2O2-Si,NH2-OH HCl-Si and NaOH-Si in the soil profiles varied from 111.09 to 465.51 mg·kg-1,129.21 to 358.85 mg·kg-1,145.50 to 568.02 mg·kg-1 and 1171.73 to 4503.91 mg·kg-1,respectively.Among different soil profiles,the contents of acid Na-acetate-Si,NH2-OH HCl-Si and NaOH-Si in typical steppe were significantly(p < 0.05)higher than those in meadow steppe and meadow.Similarly,the H2O2-Si contents also showed the same trend among typical steppe,meadow steppe and meadow.These results indicate that grassland type has a significant influence on the soil noncrystalline Si distribution and content.For grasslands of different desertification degree,the contents of acid Na-acetate-Si,H2O2-Si,NH2-OH HCl-Si and NaOH-Si in the soil profiles varied from 93.16 to 138.647 mg kg-1,46.23 to 101.96 mg kg-1,53.64 to 110.31 mg kg-1 and 570.47 to 1226.46 mg kg-1,respectively.The acid Na-acetate-Si content of 0-10 cm and 10-30 cm in soil profiles from lightly desertified grasslands were significantly(p < 0.05)higher than that from severely desertified grasslands.Among different soil profiles,the contents of acid H2O2-Si,NH2-OH HCl-Si and NaOH-Si in nondesertified grasslands were significantly(p < 0.05)higher than those in severely desertified grasslands.These results indicate that desertification has a significant impact on the soil noncrystalline silicon distribution.In addition,increasing of desertification degree would promote the transfer of other noncrystalline silicon fractions into the acid Na-acetate-Si.For soil profiles from grasslands and forests afforested from previous grasslands,the contents of acid Na-acetate-Si,H2O2-Si,NH2-OH HCl-Si and NaOH-Si varied from 161.92 to 337.76 mg kg-1,285.01 to 332.88 mg kg-1,213.58 to 334.95 mg kg-1 and 1946.47 to 2763.08 mg kg-1,respectively.The contents of acid Na-acetate-Si,H2O2-Si,NH2-OH HCl-Si and NaOH-Si in the soil profiles afforested from previous grasslands varied from 82.50 to 134.67 mg kg-1,192.85 to 231.50 mg kg-1,204.27 to 213.37 mg kg-1 and 1630.30 to 1226.46 mg kg-1,respectively.The noncrystalline silicon fractions of 0-10 cm soil profile in grassland were significantly(p < 0.05)higher than those in afforestation land.Similarly,the noncrystalline silicon fractions of other soil profiles also showed the same trend.These results indicate that afforestation has a significant(p < 0.05)impact on the content of noncrystalline silicon in grassland soil and it would weaken the process of other noncrystalline silicon fractions transfer into acid Na-acetate-Si.