覆膜对陇东旱地苹果根际土壤化感物质积累与真菌群落特征的影响

Effects of film mulching on allelopathic material accumulation and fungal community characteristics in rhizosphere soil of apple in Longdong dryland

【目的】探究果园地膜覆盖对土壤化感物质及真菌群落的影响。【方法】以红富士苹果为研究对象,采用高效液相色谱技术和Illumina高通量测序技术探究了清耕(CK)、覆膜2年(2Y)、覆膜4年(4Y)和覆膜6年(6Y)对苹果树根际0~20 cm和>20~40 cm土层土壤理化性质、化感物质和真菌群落特征的影响。【结果】苹果根际土壤脲酶活性随着覆膜年限的延长而降低。土壤中主要的化感物质的含量总体上随着覆膜年限的延长呈现出降低的趋势。覆膜措施对苹果根际土壤中真菌群落特征具有显著的影响。土壤真菌群落的多样性随着覆膜年限的延长而增高,其中镰刀菌属丰度显著增加。综合对比,覆膜4年的苹果根际土壤中含水量及有机碳、微生物量碳、全氮含量显著增加,较CK分别增加了5.65%~15.00%、3.72%~8.29%、50.16%~64.31%和14.19%~31.44%。β-1,4-木糖苷酶、β-1,4-葡萄糖苷酶和纤维二糖水解酶的活性显著提高,较CK分别增高了78.71%~84.4%、89.01%~97.43%和83.45%~87.68%。并且在0~20 cm的土层中苹果根系的生长量显著提高。与CK相比,根系生物量、根表面积和根体积分别增加了489.84%、533.87%和542.39%。相关性分析结果表明,土壤脲酶、β-1,4-葡萄糖苷酶和香兰素是影响土壤真菌群落的主要环境因子。【结论】覆盖地膜可通过影响苹果根际土壤酶活性和微生物代谢活性,促进土壤碳循环,效果随覆膜年限而异,以覆膜4 a(年)最佳。同时覆膜年限的延长抑制了土壤中植物化感物质的积累,但覆盖年限过长会对土壤真菌群落结构产生不利的影响,因此在生产中,覆膜4 a为西北旱地苹果园适宜的连续覆膜年限。

【Objective】Long-term film mulching in the Longdong dry plateau area exacerbated the degradation of rhizosphere soil,resulting in a decrease in the content of organic matters in the soil.The community structure and activity of soil microorganisms were closely related to the changes of rhizosphere soil microecological environment,root exudates and soil nutrients.Exploring the effects of different mulching years on the enzyme activity,root exudates and fungal community characteristics of the rhizoosphere soil of apple trees is helpful to lay a theoretical foundation for the improvement and rational implementation of water-saving and water-preserving technology in apple orchards in the dry land of Northwest Loess Plateau.【Methods】This study used 18-year old Nagano Fuji No.2 apple trees as the experimental object.High performance liquid chromatography(HPLC)and Illumina high-flux sequencing technology were used to investigate the effects of clean tillage(Control,CK),film mulching for 2 years(2Y),film mulching for 4 years(4Y)and film mulching for 6 years(6Y)on the root-sphere surface soil(0-20 cm)and subsurface soil(>20-40)in apple orchard.Meanwhile,soil physical properties,carbon and nitrogen accumulation,enzyme activities related to carbon and nitrogen metabolism,root biomass and growth distribution characteristics of different soil layers were monitored.【Results】The results showed that the urease activity of apple rhizosphere soil decreased with the increase of mulching years,while the enzyme activity of soil sucrase existed the opposite trend.Short-term mulching(2Y and 4Y)treatments effectively improved the activities of soil catalase,sucrase,alkaline phosphatase,β-1,4-xylosidase,β-1,4-glucosidase and cellobiohydrolase.Compared with CK,the enzyme activities increased by 19.67%,18.46%,29.39%and 84.4%,89.01%and 83.45%,respectively,which contributed to the increase of soil organic carbon,microbial biomass carbon and total nitrogen,which were significantly increased by 15.00%,8.29%,50.16%and 31.44%,respectively by 4Y treatment relative to CK.Favorable rhizosphere environment was conducive to the growth and development of apple roots.The growth of apple roots under 4Y treatment was better than under the other mulch treatments,and the root biomass,root surface area and root volume in 4Y were 54.62 g,10921.66 cm2 and 220.56 cm3,respectively.In the surface soil,soil ventilation decreased with the increase of mulching years.Compared with CK,2Y,4Y and 6Y treatments had a soil ventilation decreased by 3.23%,24.22%and 18.51%,respectively.Therefore,the root biomass and root surface area of CK,which were 20.63 g and 4956.95 cm2,respectively,were obviously higher than those of the mulching treatments.The contents of main allelochemicals in soil(ferulic acid,benzoic acid,phloroside and vanillin)revealed a decreasing trend with the increase of film mulching years,but p-hydroxybenzoic acid did not appear in CK and 2Y treatment,but increased with mulching years.The contents of p-hydroxybenzoic acid and cinnamic acid in apple rhizosphere soil under 6Y treatment reached the highest level,while coumaric acid reached the highest content at 4Y.Coumaric acid might be the product accumulated under the specific ecological environment of long-term mulch.The dominant fungal groups in the rhizosphere soil of apple with different mulching years were Basidiomycota(5%-19%),Mortierellomycota(5%-22%),Aphelidiomycota(22%-44%)and Aphelidiomycota(1%-7%),with the dominant fungal genera being Mortierella(9%-39%),Solicoccozyma(9%-33%),Petriella(1%-16%)and Fusarium(1%-3%).The characteristics of fungal communities in different soil layers were distinctive.In the surface soil,Chao1 index and Shannon index of the fungal community increased with the increase of mulching years,while in the subsurface soil,Chao1 index of the fungal community decreased with the increase of mulching years,while the Shannon index appeared an opposite trend.With the increase of mulching years,the abundance of Fusarium in rhizosphere soil increased significantly.Compared with CK,the contents of soil water content,organic carbon,microbial biomass carbon and total nitrogen in rhizosphere soil under 4Y treatment were significantly improved by 5.65%-15.00%,3.72%-8.29%,50.16%-64.31%and 14.19%-31.44%,respectively.The enzyme activities ofβ-1,4-xylosidase,β-1,4-glucosidase and cellobiohydrolase were significantly increased by 78.71%-84.4%,89.01%-97.43%and 83.45%-87.68%,respectively,compared with CK.Relative to CK,apple root biomass,root surface area and root volume increased by 489.84%,533.87%and 542.39%,respectively.The activities of soil urease andβ-1,4-glucosidase,and vanillin content in root exudates were the main environmental factors affecting soil fungal community in rhizosphere ecological environment.【Conclusion】In conclusion,mulching measures can improve the enzyme activity and microbial metabolic activity of apple rhizosphere soil to a certain extent,and promote the carbon cycling process in the soil.The increase of mulching years reduces the accumulation of allelochemicals in the soil,but too long mulching may have adverse effects on the soil fungal community structure and promote the accumulation of Fusarium,which is harmful to the healthy development of rhizosphere soil and roots.Therefore,4 years of film mulching is the appropriate continuous mulching years for apple orchards in the northwest dry land.