Effects Of Different Land-use Types And Soil Parent Materials On Silicon And Aluminum Forms In The Subtropical Forest Soils

The change of land use type is one of the most intensive business activities that may causesignificant change of common composition and structure, microbiological compositions，and soil quality.Since150years, natural forest coverage in the subtropics of China has decreased year after year, theother man-made forest such as moso bamboo（phyllostachy pubescens）and Chinese fir stand haveincreased. After the subtropical natural forest is converted to man-made forest, community structure isturned from multilayer to monolayer, monophyletic species, which resulting in the changes in water andtemperature condition, soil physical and chemical properties, and carbon and nutrient biogeochemicalcycle. Silicon is a beneficial element, which has improved effects on the growth and development ofplants. In recent years, deterioration of the acid rain and application of acidic fertilizers in large amountsin agriculture have resulted in the acceleration of aluminum release in soils and the deterioration ofecological environment. However, silicon plays an important role in the remission of aluminum toxicity,and thus it is attracting more and more attention. So the research on the fractions of silicon andaluminum is an extremely important.In this study,5different forest stands （broad-leaved forest, Chinese chestnut forest, Masson pineforest, Lei bamboo forest, and Moso bamboo forest） and5Moso bamboo forests grown in the derivedfrom5different parent materials （granodiorites, granite, basalt, tuff, and sand shale） were selected inZhejiang to sample of soil layers of0～20and20～40cm.The objective of this study was conducted to determine the distribution of silicon and aluminum inthe soils derived from the same parent material grown different forest types and in the soils derivedfrom different parent materials grown Moso bamboo forest and provides scientific reference for theprevention of silicon and aluminum toxicity. The research results are as follows:（1）The SiO2contents in the soils derived from the same parent materials grown5forest specieshad no significant difference and the content range from618.30g kg^-1707.80g kg^-1. The contents ofSiO2in the soil derived from different parent materials grown Moso bamboo forest had significantdifference. SiO2content in the soil derived from basalt was the lowest (285.98g kg^-1), whereas SiO2content in the soil derived from tuff was the highest (878.50g kg^-1).（2） The percentages of different forms of Si accounted for extractable Si in the soils growndifferent forest species, amorphous Si was the highest （70.53%⁹4.12%with an average of85.03%）,followed by Fe/Mn-oxide Si （2.87%¹2.54%with an average of7.18%） an organic Si （1.58%¹0.84%with an average of5.00%）, available Si was the lowest （0.62%⁷.52%with an average of2.79%）.Thepercentages of different forms of Si accounted for extractable Si in the soils derived from differentparent materials, amorphous Si was the highest （77.31%⁹4.16%with an average of88.92%）, followedby Fe/Mn-oxide Si （3.60%¹1.43%with an average of6.15%） and organic Si （1.54%⁷.58%with anaverage of3.36%）, available Si was the lowest （0.70%³.67%with an average of1.57%）. The contentof available Si in the soil derived from shale was significantly higher than in the soils derived from other parent materials.（3） In the soils grown5forest species, amorphous Si contents in phyllostachys pubescens andphyllostachys praecox were much greater than in Masson pine, Chinese chestnut, and broad-leavedforests. Available Si account accounts for a little part of amorphous Si and depends on amorphous Sicontent. The content of amorphous Si in the soil with large amounts of organic mulch underphyllostachys praecox forest was significant higher than in the soils under the other4kinds of forests. Alarge amount of available Si in the soil is absorbed by phyllostachys praecox, which resulting in thedecrease in the content of available Si in the soil.（4）The average concent of total Al in the soils under different forests was185.30g·kg^-1, in which thecontent of total Al in the soils under phyllostachys pubescens forest was the highest(257.70g kg^-1)，whereas the content of total Al in the soils under broad leaved forest was the lowest (134.30g kg^-1).The average content of total Al in the soils derived from different parent materials under Moso bambooforest was185.3g·kg^-1In the soils under Moso bamboo forest, the content of total Al in the soils thatderived from granodiorite was the highest(332.40g kg^-1)，whereas the content of total Al in the soilsderived from shale was the lowest(128.10g kg^-1).（5）The amorphousAl was main extractableAl in the soil under different forests（41.66%⁶0.37%with an average of53.83%）. The percentage of amorphous Al to extractable Al in the soil underphyllostachys pubescens forest was the highest（60.37%）, where as the percentage of amorphous Al toextractable Al in the soil under Masson pine forests was the lowest （41.66%）. The amorphous Al wasmain extractable Al in the soil under different forest（s41.66%⁶0.37%with an average of53.83%）.Theamorphous Al was also the main fractions of extractable Al in the soils derived from different parentmaterials under Moso bamboo forest （55.94%⁶5.26%with an average of60.12%）.Organically boundAl was an important part of active Al. The percentages of organically bound Al/active Al in the soilsunder different forests ranged from12.88%to16.94%with an average of14.40%).（6） The content of amorphous Si in soils with a large amount of organic mulching materials underphyllostachys praecox was significantly higher than under other forest species. Application of organicmulching materials could significantly increase the percentages of organically bound Al to active Al inthe soils. The percentage of organically bound Al to active Al in the soil with organic mulchingmaterials under phyllostachys praecox forest was20.65%. The increase in organically bound Al contentin the soils could reduce the Al toxicity to plants. Therefore, addition of organic mulching materials notonly can solve the problem of Si deficiency in the soils, but also can mitigate the damage of soilaluminum toxicity.