连续施用不同氮量对半干旱地区马铃薯根际真菌群落结构的影响

Effects of continuous application of different nitrogen rates on fungal community structure in potato rhizosphere in semi-arid area of Gansu Province

针对马铃薯生产中因氮肥过量施用导致的土壤微生物群落结构失衡和多样性下降等问题,在始于2013年的不同氮肥用量(N0:不施氮,对照;N75:施氮量75 kg·hm^-2;N150:施氮量150 kg·hm^-2;N225:施氮量225 kg·hm^-2;N300:施氮量300 kg·hm^-2;N375:施氮量375 kg·hm^-2)田间定位试验中,于2017年马铃薯成熟期采集根际土壤,应用Illumina PE250测序等分子生物学手段,研究连续5 a施用不同氮量对半干旱地区马铃薯根际真菌群落结构的影响。结果表明:不同施氮量对马铃薯根际真菌群落物种组成造成了显著影响,子囊菌门、Mucoromycota和担子菌门是3个优势门类真菌(相对丰度>1.0%),以子囊菌门的相对丰度最大,占总序列的75.48%~83.95%,其优势属是Plectosphaerella(29.92%)和镰刀菌属(13.54%);马铃薯干腐病和枯萎病的病原菌——镰刀菌属的相对丰度随施氮量增加呈增大的趋势。马铃薯根际真菌Alpha多样性随施氮量的增加而降低。连续5 a超量施氮导致了0~20 cm表层土壤中NO3^--N含量显著增加,N375处理的NO3^--N含量是N0处理的3.76倍。连续5 a超量施氮也显著降低了根际pH值和速效磷含量,N375处理比N0处理pH值和速效磷含量分别降低了0.17个单位和32.10%。RDA及相关性分析结果表明,土壤硝态氮含量是影响马铃薯根际真菌群落结构变化的主要因素(F=1.571,P=0.043*)。连续大量施用氮肥显著降低了马铃薯块茎产量,连续施氮5 a后,由于土壤剖面中NO3^--N的积累,最高产量施肥量由2013—2014年的N225减低为N75,其它施氮处理较N75分别减产了3.46%、22.81%、26.05%和25.32%。长期过量施用氮肥使马铃薯根际硝态氮大量累积,导致pH值降低,进而使根际真菌多样性降低;同时过量氮肥施用会使根际中土壤真菌病原菌相对丰度增加,不利于土壤的健康和马铃薯的高产。

In view of the imbalance of soil microbial community structure and the decline of diversity caused by excessive application of nitrogen(N)fertilizer in potato production,a positioned field experiment of different N application rates(N0:no N application,control,N75:75 kg·hm^-2,N150:150 kg·hm^-2,N225:225 kg·hm^-2,N300:300 kg·hm^-2,and N375:375 kg·hm^-2)was conducted in 2013.Rhizosphere soil was collected during potato ripening period for 7 years.Molecular biological sequencing methods,Illumina PE250,was used to study the effects of different N levels on the rhizosphere fungi community structure of potato in semi-arid areas for 5 consecutive years.The species composition of the potato rhizosphere fungi community was significantly affected by different N application rates.Ascomycota,Mucoromycota,and Basidiomycota were the three dominant fungi(relative abundance>1.0%).The relative abundance of Ascomycota was the largest,accounting for 75.48%~83.95%of the total sequence.The dominant species were Plectosphaerella(29.92%)and Fusarium(13.54%).The relative abundance of Fusarium,the pathogens of potato dry rot,and Fusarium wilt,increased with the increase in N application.Alpha diversity of potato rhizosphere fungi decreased with the increase in N application.Over-application of N for 5 years resulted in a significant increase of NO3^--N content in 0~20 cm topsoil.The NO3^--N content in N375 treatment was 3.76 times higher than that in N0 treatment.Over-application of N for 5 years also significantly reduced the pH value and available phosphorus content in rhizosphere.N375 treatment decreased 0.17 units and 32.10%,respectively,compared with N0 treatment.RDA and correlation analysis showed that soil nitrate N content was the main factor affecting the changes in fungal community structure in potato rhizosphere(F=1.571,P=0.043*).Continuous large-scale application of N fertilizer significantly reduced potato tuber yield:after 5 years of continuous N application,due to the accumulation of NO3^--N in soil profile,the maximum yield fertilization decreased from N225 in 2013-2014 to N75,and other N treatments reduced the yield by 3.46%,22.81%,26.05%and 25.32%,respectively,compared with N75.Long-term excessive N application resulted in a large accumulation of nitrate N in potato rhizosphere,which led to a decrease in pH,thus reducing the diversity of rhizosphere fungi.At the same time,excessive nitrogen application increased the relative abundance of soil fungal pathogens in the rhizosphere,which was not conducive to soil health and improving potato yield.