Acidification Characteristics And Microbial Community Diversities Of Brown Soils In Jiaodong Peninsula,China

Soil acidification is a global problem affecting human health and environmental quantity.The decrease of soil pH values will destroy the soil structure,accelerate the loss of nutrient elements,accumulate toxic substances,and reduces crop yield.In addition,soil acidification also changes the soil microbial structure,and destroys soil ecosystem.Acidified soil mainly distributed in the southern China,which is mainly caused by rainfall leaching and other natural causes.Recently,soil acidification becomes more and more serious because of anthropogenic activities in the Jiaodong Peninsula,northern China.Therefore,it is necessary to analyze the characteristics of soil acidification in Jiaodong Peninsula,clarify the characteristics of soil acidification,analyze the response of microbial communities to soil pH.In this study,soil samples with various acidification gradients were collected to study the characteristics of soil acidification in the Jiaodong Peninsula.Besides,cultivated land and orchard soils were selected to analyze soil acidification characteristics under different land use patterns.High-throughput sequencing technology was implemented to exhibit the characteristics of soil microbial community under different acidification degrees.The influence of soil environmental factors on the distribution of microbial community was also clarified.The main results are as follows:(1)The acidification characteristics of soil profile samples(0-20 cm,20-40 cm,40-60 cm)with different acidification degrees(pH<4.5?pH 4.5-5.5?pH 5.5-6.5?pH>6.5)in Jiaodong Peninsula were analyzed.The results showed that the exchangeable acidity content was significantly correlated(R²=0.6392,P<0.001;R²=0.2349,P<0.001)with pH value in 0-20 cm and 20-40 cm soil layers,respectively.In the range of pH<4.5,the contents of exchangeable acidity in 0-20 cm and 20-40 cm soil layers were 2.55 cmol·kg^-1 and 2.06 cmol·kg^-1,respectively.In the range of pH>6.5,the content of exchangeable acidity in 0-20 cm and 20-40 cm soil layers was 0.42 cmol·kg^-1 and 0.52 cmol·kg^-1,respectively.The results showed that the ration of exchangeable hydrogen and exchangeable aluminium was significantly correlated(R²=0.1346,P<0.01;R²=0.0921,P<0.01)with pH value in 0-20 cm and 20-40 cm soil layers,respectively.In the range of pH<4.5,the ration of exchangeable hydrogen and exchangeable aluminium in 0-20 cm and 20-40 cm soil layers were 0.21 and 0.30,respectively.In the range of pH 5.5-6.5,the ration of exchangeable hydrogen and exchangeable aluminium in 0-20 cm and 20-40 cm soil layers were 0.99 and 0.76.According to the regression analysis of soil pH value to the ration of exchangeable hydrogen and exchangeable aluminium,we found that the contribution of exchangeable aluminium to exchangeable acidity is increased with the increasing of acidification degree.(2)Soil samples(0-20 cm,20-40 cm,40-60 cm)with various acidification degrees(pH<4.5,pH 4.5-5.5,pH 5.5-6.5)of cultivated land and orchard were selected to analyze the effects of different land use patterns on characteristics of soil acidification.In the acidified soil of Jiaodong Peninsula,the surface soil(0-20 cm)of cultivated land is more acidified than orchard soil,while that in the 20-40 cm and 40-60 cm soil layers follows the opposite trend.In the range of pH<4.5,the content of exchangeable acidity in surface soil(0-20 cm)of cultivated land(3.29 cmol·kg^-1)was 1.43 times higher than in orchard soil(2.30 cmol·kg^-1),however,the content of exchangeable acidity in 20-40 cm soil layer of orchard soil(2.45cmol·kg^-1)was 1.38 times higher than in cultivated land(1.77 cmol·kg^-1),and the content of exchangeable acidity in 40-60 cm soil layer of orchard soil(1.63 cmol·kg^-1)was 2.12 times higher than in cultivated land(0.77 cmol·kg^-1).(3)The taxonomic composition of bacteria and fungi in soil with different acidification degrees was studied showed that Actinobacteria,Proteobacteria,Acidobacteria and Chloroflexi were the main bacterial phyla,they account for more than 80%of the bacterial community.While Ascomycota and Basidiomycota were the main fungal phyla in the acidified brown soils,they account for more than 90%of the fungal community.The principal component analysis revealed that soil acidification has a significant impact on soil microbial community.The stronger the degree of soil acidification,the greater the impact on microbial(bacteria and fungi)community.(4)The canonical correlation analysis of bacteria and fungi in soil with different acidification degrees(pH 4-5?pH 5-6?pH 6-7)showed that soil factors,such as soil pH value(P<0.001),soil organic matter(P<0.001),total nitrogen(P<0.001),available phosphorus(P<0.001),available potassium(P<0.001),exchangeable acidity(P<0.001),exchangeable hydrogen(P<0.001),and exchangeable magnesium(P<0.001)shaped the distributions of bacterial communitie;Edaphic factors,including soil pH value(P<0.001),exchangeable hydrogen(P<0.01),exchangeable aluminium(P<0.01)and exchangeable magnesium(P<0.01)were found to structure the compositions of fungal communities.