Effects of different fertilization practices on anammox activity,abundance,and community compositions in a paddy soil

The return of crop residue and green manure into agricultural soil is known to be important agricultural management strategies,yet how they affect the anammox process remains poorly characterized.A field experiment containing four treatments:chemical fertilizer(F),F plus rice straw(FS),FS plus green manure(FSM),FSM with integrated management(FSMM),was performed to examine the effects of incorporation of rice straw and green manure residues on anammox.The results showed that the anammox activities in FS and FSM treatments(0.65 and 0.80 nmol N g^(–1)soil h^(–1),respectively)were significantly lower than those in F and FSMM treatments(1.60 and 1.28 nmol N g^(–1)soil h^(–1),respectively).Anammox contributed 4.07%-4.95%of total N loss in soil incorporated with residues,lower than soil treated with chemical fertilizer only(9.13%),the remaining being due to denitrification.However,the abundance of the hzsB gene(the hydrazine synthaseβ-subunit gene)in FS and FSM treatments(1.13106 and 1.18106 copies g^(–1)soil)were significantly higher than soil using chemical fertilizer only(7.49105 copies g^(–1)soil)while showed no significant difference with FSMM treatment(8.81105 copies g^(–1)soil).Illumina sequencing indicated that Brocadia was the dominant anammox genus,following by Scalindua and Kuenenia.Anammox bacterial diversity was altered after 4-year incorporation of rice straw and green manure,as shown byα-diversity indices.We concluded that rice straw and green manure incorporated with mineral fertilizer reduce N removal from paddy soil in terms of anammox in spite of stimulating anammox bacterial growth.