Effects Of Biochar With Different Silicon Content On Amelioration Of Soil Acidification And Greenhouse Gas Emissions In Camellia Oleifera Plantantions

Camellia oleifera Abel.,belonging to the Camellia L.of Theaceae,is an important woody oil tree species in China,widely planted in the red soil area of southern China.Tea oil pressed by Camellia oleifera is a kind of high-quality edible oil,which is of great significance to ensure the safety of edible oil in China.Camellia oleifera Abel.is an acid-loving plant,and the suitable soil p H is 5.5-6.5.Due to intensive fertilization management,regional climate characteristics,and its own physiological characteristics and other factors,the soil of Camellia oleifera plantantions is continuously acidified,the process of desilication and aluminum enrichment is intense,and the fertility of soil is decreased,which not only affect the normal growth of Camellia oleifera Abel.,but also potentially promote nitrous oxide（N₂O）and other greenhouse gas emissions.Silicon fertilizer plays an important role in increasing soil p H and improving soil fertility.Biochar can effectively alleviate soil acidification and greenhouse gas emissions,but the effects and mechanism of biochar with different silicon content on amelioration of soil acidification and greenhouse gas emissions reduction in Camellia oleifera forests with nitrogen application are not clear.The red soil is strongly weathered,desiliconized and aluminized,while the enrichment of aluminum ions leads to further acidification of the soil.It has not been studied whether silicon-rich biochar interacts with soil aluminum to affect amelioration of soil acidification and greenhouse gas emissions reduction.In this study,the acidified soil of Camellia oleifera plantantions was taken as the research object,and biochar was prepared by pyrolysis of the plant residues of silicon-rich（rice straw,moso bamboo leaves）and non-silicon-rich（Camellia oleifera fruit shell、Camellia oleifera leaves）at 600℃for soil amelioration and greenhouse gas emissions reduction.The research mainly includes two parts:the effects of different silicon content biochar on amelioration of soil acidification and greenhouse gas emissions with nitrogen application;the effects of silicon input and aluminum interaction on soil acidification improvement and greenhouse gas emissions.This study also analyzed and measured the abundance of soil N₂O microbial functional genes,and explored the microbiological mechanism of the effects of different silicon content biochar on soil N₂O emissions of Camellia oleifera.The results suggest:（1）The biochar prepared from rice straw and bamboo leaves was rich in silicon content,and the total silicon content was 30426.2mg kg^-1 and 25770.0mg kg^-1,respectively.The content of silicon of biochar prepared from Camellia oleifera fruit shell and Camellia oleifera leaves was 1891.4mg kg^-1,1566.5mg kg^-1,respectively.The addition of silicon-rich biochar significantly increased available silicon content in nitrogen application soil.Compared with the control,moso bamboo leaves and rice straw biochar treatments increased available silicon content by 63.18%and 70.03%,respectively.Non-silicon-rich biochar significantly reduced the available silicon content in nitrogen application soil.The interaction of aluminum and amendments had a significant effect on soil available silicon.The input of exogenous aluminum significantly reduced the soil available silicon content of Camellia oleifera fruit shell biochar treatment.（2）In terms of amelioration of soil acidification effects,both silicon-rich biochar and non-silicon-rich biochar and silicon fertilizer significantly increased soil p H,and the amelioration effects of biochar was better than that of silicon fertilizer.The input of biochar significantly reduced soil exchangeable acid and exchangeable aluminum content,and moso bamboo leaves biochar,rice straw biochar and Camellia oleifera leaves biochar have similar effects,which are better than Camellia oleifera fruit shell biochar.Silicon fertilizer treatment significantly increased exchangeable acid content in nitrogen application soil and exchangeable aluminum content in soil.The interaction of aluminum and amendments had significant effects on exchangeable acid,exchangeable aluminum and exchangeable H⁺in soil.Exogenous aluminum addition significantly increased soil exchangeable acid and exchangeable H⁺content,but had no significant effects on the exchangeable acid content of moso bamboo leaves,rice straw biochar and silicon fertilizer treatment.（3）Biochar addition significantly reduced N₂O emissions in nitrogen application soil,among which Camellia oleifera leaves had the best emission reduction effect.Under no nitrogen application,biochar addition significantly increased soil CO₂ emissions.Under nitrogen application,silicon fertilizer treatment reduced soil CO₂ emissions.Aluminum treatment significantly increased soil N₂O emissions and CO₂ emissions.（4）Microbial functional gene analysis showed that the abundance of amo A（AOA）gene was significantly higher than that of amo A（AOB）gene,and biochar treatment significantly reduced the copy number of AOA gene in soil.In addition,biochar treatment significantly increased the abundance of nir K and nos Z genes in nitrogen application soil.The ratios of nir S/nir K、nir K/nos Z、nir（K+S）/nos Z were significantly increased by moso bamboo leaves,Camellia oleifera fruit shell,Camellia oleifera leaves biochar and silicon fertilizer treatments.（5）Structural equation modeling results indicated that silicon input directly reduced soil N₂O emissions and indirectly reduced N₂O emissions by affecting soil exchangeable acid and p H.Aluminum indirectly regulated other soil factors by influencing soil p H,and then affected soil N₂O emissions.In addition,the input of silicon and aluminum reduced the rate of soil CO₂ emission,which mainly affected soil CO₂ emission indirectly.In conclusion,silicon input has an important effect on soil N₂O emissions and emissions reduction.In acidified soil of Camellia oleifera plantantions with serious desilication and aluminum enrichment,the application of silica-rich biochar for acid ameliorating can significantly increased soil available silicon content and decreased exchangeable aluminum content,which amended soil acidification and achieved N₂O emissions reduction.In intensive production activities,silicon-rich biochar can be considered to replace silicon fertilizer,which will benefit the sustainable development of agricultural and forestry production in subtropical acid soil region and the mitigation of global climate change.