麦后复种苜蓿压青还田改善土壤微生物群落结构

Improvement of soil microbial community structure by multiple cropping alfalfa after wheat

黄土高原旱地麦田土壤贫瘠,加上化肥施用不合理,极易导致地力下降;为培肥土壤,麦后引入苜蓿压青还田,探寻合理还田方式.采用二因素裂区设计,主区为播种量(7.5、15和22.5 kg/hm^(2));副区为还田时间(后作小麦播种前30d、20d和10d);以当地农户模式(麦后复种夏玉米秸秆还田)为对照,研究土壤养分、酶活性及土壤微生物群落结构组成和功能变化.结果显示,苜蓿还田相比夏玉米还田显著提高土壤养分和酶活性,苜蓿播种量22.5 kg/hm^(2)、小麦播种前20d还田处理的土壤碱解氮、有机质含量和碱性磷酸酶、脲酶、蔗糖酶活性分别提高5.83、0.64、0.24、0.55和20.84倍,同时提高了细菌群落丰富度和多样性.苜蓿播种量22.5 kg/hm^(2)、小麦播种前30 d和20 d还田处理同时促进有益细菌(酸杆菌门、芽单胞菌门、浮霉菌门等)及真菌子囊菌门和担子菌门的繁殖.PICRUSt结果显示,苜蓿播种量22.5 kg/hm^(2)、小麦播种前30 d还田处理显著增加与碳、氮代谢相关的细菌类群,小麦播种前10 d和20 d还田处理次之.FUNGuild结果显示,苜蓿播种量22.5 kg/hm^(2)、小麦播种前20 d还田处理土壤真菌以腐生型为主,而小麦播种前30 d还田则以病原型为主.综上所述,苜蓿播种量22.5 kg/hm^(2)、后作小麦播种前20 d还田有利于提高土壤养分和酶活性,改善土壤微生物群落结构及多样性,增加有益菌群,促进养分循环,是麦后复种苜蓿较为合理的还田模式.

Soil quality in the wheat-cultivated land is poor in the Loess Plateau area,and the unreasonable application of chemical fertilizer easily leads to a decline in soil fertility.To improve soil fertility,alfalfa was planted after wheat cultivation and returned to the field.This study aims to explore a reasonable way to return alfalfa to the field.The experiment was arranged as two-factor split plot design with sowing rate(7.5 kg/hm^(2),15 kg/hm^(2),and 22.5 kg/hm^(2))as the main-plot,and returning time(30 d,20 d,and 10 d before wheat sowing)as the sub-plot.Maize straw returning was used as the control.Changes in soil nutrients,enzyme activities,and structure and function of the microbial community were studied.The results showed that the soil nutrients and enzyme activities were significantly increased after alfalfa returning compared with those after maize straw returning.The alkalihydrolyzed nitrogen and organic matter content and the alkaline phosphatase,urease,and sucrase activities were increased by 5.83,0.64,0.24,0.55,and 20.84 times,respectively.In addition,the bacterial community richness and diversity were improved in the alfalfa sowing rate of 22.5 kg/hm^(2)with returning of 20 d before wheat sowing.When the alfalfa sowing rate was 22.5 kg/hm^(2)with returning of 30 d and 20 d before wheat sowing,the reproduction of beneficial bacteria such as Acidobacteria,Gemmatimonadetes,and Planctomycetes and beneficial fungi such as Ascomycota and Basidiomycota was enhanced.Results from PICRUSt showed that the bacterial communities related to carbon and nitrogen metabolisms were significantly increased in the alfalfa sowing rate of 22.5 kg/hm^(2)and returning of 30 d before wheat sowing,followed by 10 d and 20 d.FUNGuild showed that with the alfalfa sowing rate of 22.5 kg/hm^(2),saprotroph was the main trophic mode of fungi in returning of 20 d before wheat sowing,whereas pathotroph was the main trophic mode in returning of 30 d before wheat sowing.In conclusion,sowing alfalfa at a rate of 22.5 kg/hm^(2)and returning 20 d before wheat sowing improved soil nutrient content and enzyme activities,soil microbial community structure and diversity,beneficial bacterial community numbers,and nutrient cycling and is a more reasonable way to return alfalfa after wheat cultivation.