Replanting potato in double rice system improves straw degradation due to increased fungal community diversity and relative abundance of saprophytic fungi
[Objectives]Straw return to field is an effective way to improve soil fertility and crop yield.The rotation patterns of crops in the replanting systems influence the structure and function of soil fungal communities,thus affect the degree of straw degradation in soil.We studied the straw degradation characteristics under different replanting patterns for achieving efficient straw return technology.[Methods]Soils were collected at flowering stage of early rice in fields of three-maturity replanting patterns[rice-rice-Astragalus sinicus L(RRA),rice-rice-oilseed rape(RRO),rice-rice-potato(RRP)],and two-maturity replanting patterns[rice-rice-no tillage(RRN),and rice-rice-field flooding in water(RRI)],respectively.Each soil had two treatments:straw-addition(0.5 g rice straw mixed with 80 g dry soil)and no addition,then loaded into a sealed bottle and incubated for 120 days under anaerobic condition.CO2 emissions were monitored regularly during the incubation.And soils were sampled for the determination of microbial biomass carbon and nitrogen contents and four straw-degrading enzyme activities.The fungal community structures were analyzed using the amplicon high-throughput sequencing technique.[Results]The soil microbial biomass carbon and nitrogen content,and the β-glucosidase,β-cellobiosidase,β-xylosidase and laccase activities under the three-maturity replanting patterns were significantly higher than those under the two-maturity replanting patterns.And the soil fungal community structures were different between the three and two replanting patterns as well,in particular,the soils under RRP exhibited significantly higher number of fungal ASVs,Chao1,ACE,and Shannon's index,and the relative abundances of stemless fungi of the genera Acaulium,Mortierella,and Oidiodendron,which had the ability to decompose organic substances such as hemicellulose,cellulose,and lignin.Co-occurrence network analyses revealed that soils under RRO and RRP had higher fungal network complexity,and increased number of key fungal species with potential of straw decomposition such as Ascomycota and Chytridiomycota,compared with the soils under RRN.Redundancy and regression analyses revealed that soil total P was an important environmental factor causing the structure differences of soil fungal communities and straw-degrading enzyme activities among the replanting patterns.[Conclusions]Compared with double-rice and winter fallow,replanting winter crop in double rice system is more inductive to increase microbial biomass and straw-degrading enzyme activities,enhance the fungal alpha diversity and the relative abundance of saprophytic fungi.The rice-rice-potato replanting pattern shows the highest potential in stimulating straw degradation and soil fertility enhancement in the experimental region.
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