Effects Of Long-term Fertilization And Management On PhoD Harboring Microbial Community And Alkaline Phosphatase On Loess Soil

Alkaline phosphatase（ALP）secreted by bacteria those encoded with phoD gene participates in the mineralization of soil organic phosphorus and plays an important role in the phosphorus cycle.Understanding the effects of long-term fertilization and management on the abundance,diversity and community composition of phoD bacteria in soil,as well as the relationship between ALP activity and phoD bacteria abundance,diversity and community composition,ALP and Po forms,which help to better understand the effects of fertilization and management on soil phosphorus transformation,and provide new insights for formulating reasonable fertilization regime and land management and improving the effectiveness of phosphorus in Loess soil.Taking the soil with different fertilization and management for a long time as the research object,the following treatments were selected:no fertilization（CK）,synthetic nitrogen and potassium（NK）,synthetic nitrogen,phosphorus and potassium（NPK）,NPK and crop stalk return（SNPK）,and NPK plus organic manure（MNPK）,bare fallow and farmland set-aside.Mi Seq sequencing was used to analyze the abundance,diversity and community composition of phoD bacteria,ALP activity,organic phosphorus forms and their relationships,and the following main results were obtained:（1）Fertilization increased the abundance and diversity of phoD gene harboring microbial over CK.Those receiving NPK and NPK treatments integrated with organic supplements significantly improved the relative abundance of Proteobacteria but decreased Gemmatimonadetes at the phylum level,while all fertilized treatments appreciably increased the relative abundance of Lysobacter but decreased that of Gemmatirosa and Afipia at the genus level.SNPK and MNPK treatments noticeably increased the relative abundance of Methylobacter but reduced Pseudomonas and Streptomyces relative to those receiving synthetic fertilizer treatments.Long-term fertilization markedly raised ALP activity,which was significantly and positively correlated with the relative abundance of the phylum Proteobacteria as represented by the genera Methylobacterium and Lysobacter.ALP was closely associated with moderately labile Po,followed by enzyme P,recalcitrant Po,and labile Po.The changes in phoD bacteria and ALP were mainly driven by soil organic carbon,Olsen P and p H.（2）Balanced application of fertilizer significantly increased the proportion of great macro-aggregates（>2 mm）and decreased the proportion of macro-aggregates（0.25-2 mm）,and combined application of chemical fertilizer and organic fertilizer also significantly decreased the proportion of silt clay fractions（<0.053 mm）,thus significantly increasing the average weight diameter of aggregates.Balanced application of chemical fertilizer significantly improved the abundance,diversity and ALP activity of phoD bacteria in aggregates with different particle sizes.In great macro-aggregates（>2 mm）,the relative abundance of Actinobacteria increased significantly with the application of fertilizers,while the relative abundance of Planctomycetes decreased significantly.In clay and silt fractions（<0.053 mm）,fertilization（combined application of chemical fertilizer and chemical fertilizer and organic fertilizer）significantly increased the relative abundance of Actinobacteria and significantly decreased the relative abundance of Proteobacteria.The relationship between phoD bacteria in macroaggregates（0.25-2 mm）and microaggregates（0.053-0.25 mm）is more complicated than that in macroaggregates（>2 mm）and silty clay fractions（<0.053 mm）.The main factors affecting phoD bacteria in aggregates with different particle sizes are the contents of organic carbon,total nitrogen and total phosphorus in aggregates.（3）The research results of maize growing season show that,balanced application of chemical fertilizer and organic fertilizer significantly increased the contents of total,available,microbial biomass carbon,nitrogen and phosphorus,and increased the enzyme activities related to carbon,nitrogen and phosphorus cycle.The increase of available nitrogen（MBN,NO₃^-/NH₄⁺-N）and available phosphorus（MBP,Olsen P）in soil significantly reduced soil microbial nitrogen limitation and phosphorus limitation,especially the application of organic fertilizer relieved soil microbial phosphorus limitation;The reduction of microbial nitrogen and phosphorus limitation significantly improved the soil microbial carbon utilization efficiency.（4）Long-term balanced application of fertilizer significantly improved the ALP activity,and the rhizosphere activity was higher than that in bulk soil.Olsen P in rhizosphere soil mainly comes from ML-OP and Al-P while in bulk soil mainly comes from L-OP and Ca₂-P.（5）Compared with CK,long-term farmland set-aside significantly improved ALP activity and the abundance,diversity of phoD.Fallow and set-aside significantly reduced the relative abundance of Afipi and Rhizobium,fallow treatment was lower than set-aside.Fallow treatment increased the relative abundance of Xanthomonas and Streptomyces,while set-aside treatment decreased the relative abundance of Xanthomonas.At the phylum level,Proteobacteria was positively correlated with ALP,while Actinobacteria was negatively correlated with ALP.At the genus level,there was a significant positive correlation between Pleomorphomonas and ALP,and a significant negative correlation between Xanthomonas and ALP.SOC is the key factor affecting ALP activity and phoD bacteria in set-aside soil.（6）Compared with CK,the species and numbers of the enriched phoD bacteria increased significantly in set-aside treatment,while decreased significantly in fallow.Set-aside also significantly improved the abundance,diversity of phoD bacteria and ALP activity in aggregates with different particle sizes.Set-aside significantly increased the relative abundance of Proteobacteria in each particle size but decreased the relative abundance of Planctomycetes and Actinobacteria in each particle size.The key factor affecting ALP activity and phoD bacteria in aggregates is SOC.In a word,long-term balanced application of chemical fertilizers,especially N,P,K fertilizers combined with organic fertilizers,which can significantly improve the soil nutrient level,reduce microbial nutrient limitation,improve the abundance and diversity of phoD bacteria,and thus improve the availability of soil phosphorus.Long-term farmland set-aside improves soil nutrient content,available phosphorus level and the abundance,diversity of phoD bacteria,which is beneficial to restore and improve soil environment damaged by farming and improve soil phosphorus availability.