Arbuscular mycorrhizal (AM) fungi play an important role in plant nutrient absorption and stress resistance. AM fungal spore-associated bacteria are essential for mycorrhizal colonization, but their responses to environmental changes remain largely unknown. We collected surface soil samples from a Chinese fir plantation in both summer and winter to investigate the responses of AM fungal morphological traits and spore-associated bacterial communities to simulated nitrogen deposition (40 kg N·hm-2·a-1 addition) and drought (-50% precipitation exclusion). Our results showed that nitrogen addition and precipitation exclusion significantly affected AM fungal spore density and extraradical hyphal length, respectively. AM fungal intraradical colonization rate, extraradical hyphal length and spore density were significantly differed between the two seasons. Compared to control (no nitrogen addition and no precipitation exclusion treatment), both nitrogen addition and precipitation exclusion significantly reduced spore density in winter, while precipitation exclusion alone and the combined nitrogen addition and precipitation exclusion significantly increased extraradical hyphal length in summer. The dominant spore-associated bacterial phyla were Proteobacteria, Acidobacteria, Actinobacteria, Chloroflexi, and Planctomycetes. Nitrogen addition and precipitation exclusion did not affect the diversity of spore-associated bacteria. However, the combined nitrogen addition and precipitation exclusion treatment altered the composition of the bacterial community, with significant variations between the two seasons. The spore-associated bacterial diversity was significantly higher and community variability (or turnover) was lower during summer than winter. Soil total nitrogen, nitrate nitrogen and dissolved organic carbon were important factors influencing the bacterial community composition. In all, the effects of nitrogen addition and precipitation exclusion on the morphological traits of AM fungi are seasonally dependent. The combination of nitrogen addition and precipitation exclusion has a significant impact on AM fungal spore-associated bacterial community structure.
丛枝菌根(AM)真菌对促进宿主植物的养分吸收和提高抗逆能力具有重要作用。土壤中AM真菌孢子相关细菌能够促进菌根定殖,但其对环境变化的响应知之甚少。本研究以杉木人工林表层土壤为对象,在分析AM真菌形态学指标的基础上,重点探究孢子相关细菌群落结构对模拟氮沉降(40 kg N·hm-2·a-1)和干旱(-50%穿透雨)的响应及季节差异。结果表明: 氮添加、隔离降雨分别显著影响AM真菌的孢子密度与根外菌丝长度;季节显著影响AM真菌根系侵染率、根外菌丝长度及孢子密度。与对照(不进行氮添加和不隔离降雨处理)相比,氮添加、隔离降雨在冬季均显著降低了孢子密度;单独隔离降雨、氮添加和隔离降雨同时处理在夏季均显著增加了根外菌丝长度。AM真菌孢子中相对多度占优势的细菌包括变形菌门、酸杆菌门、放线菌门、绿弯菌门、浮霉菌门等。氮添加和隔离降雨单独处理对孢子相关细菌多样性无显著影响;氮添加和隔离降雨同时处理显著改变了细菌群落组成,两个季节间差异显著,且夏季细菌的丰富度显著高于冬季,群落变异度小于冬季。土壤总氮、硝态氮和可溶性有机碳含量显著影响孢子相关细菌群落组成。综上,氮添加、隔离降雨对AM真菌形态特征的影响具有季节依赖性,氮添加和隔离降雨同时处理对孢子相关细菌群落结构有明显影响。.
Keywords: arbuscular mycorrhizal fungi; community structure; diversity; drought; simulated nitrogen deposition; spore-associated bacteria.