长期集约种植对雷竹林土壤氨氧化古菌群落的影响

应用荧光定量PCR以及PCR-DGGE技术研究了雷竹林长期集约种植过程中土壤氨氧化古菌种群数量及群落结构的演变趋势,并利用典范对应分析(CCA)方法研究影响土壤氨氧化古菌群落的主要环境因子。研究结果表明,水稻田改种雷竹后,土壤氨氧化古菌种群数量显著增加,在4 a时达到最高,但在集约种植后快速下降,9 a雷竹林土壤氨氧化古菌数量最低,随后逐渐稳定。雷竹林土壤氨氧化古菌种群主要为不可培养泉古菌,聚类分析结果表明集约种植前后氨氧化古菌群落结构存在明显差异,长期集约经营雷竹林土壤以适应较低pH值的物种为主要优势种群。CCA分析表明,集约种植时间较长的11 a和15 a林地群落结构较为类似,与7 a和9 a样地明显区分。土壤NO-3-N与氨氧化古菌群落变化的相关性最强,说明氨氧化古菌在雷竹林土壤硝化过程中发挥着重要作用。土壤pH值及速效养分对土氨氧化古菌群落也具有较大影响,它们与NO-3-N合计解释了59.7%的样本总变异,表明土壤酸化以及过量养分的积累对氨氧化古菌群落具有重要影响。

Effects of long-term intensive management on soil ammonia oxidizing archaea community under Phyllostachys praecox stands

Phyllostachys praecox is a favorable bamboo species for the production of edible shoots, and has been widely planted in southern China. Intensive management practices such as regular high rate of fertilization and annual heavy winter mulch in the stands established more than 5 years, has been employed by many bamboo growers to improve yields. However, these practices may have adverse effects on the ecosystem. Ammonia-oxidizing archaea (AOA) has been found in various habitats and played a key role in soil nitrification. There is no published information available on the impact of long-term intensive land management practices on the population size and community structure of soil AOA in Phyllostachys praecox stands. In this study, the abundance and composition of soil AOA communities across a long-term chronosequence under intensive managed Phyllostachys praecox stands were investigated using real-time polymerase chain reaction (PCR), denaturing gradient gel electrophoresis (DGGE), cloning and sequencing approaches based on amoA genes. Canonical correspondence analysis (CCA) was also used to determine the environmental variables which are significantly correlated with community structure. Treatments in this study were based on the cultivation history which corresponded to 4, 7, 9, 11 and 15 years after establishment of bamboo stands. Paddy fields with similar topography were used as the control. Each cultivation history had three replications. The archaeal amoA gene copy numbers ranged from 1.79×10⁷ to 3.93×10⁷ per gram of dry soil, and changed greatly in response to the long-term intensive management. The 4-year-old treatment had the highest copy numbers of amoA genes, whereas the lowest copy numbers were recorded in the 9-year-old treatment. Ammonia-oxidizing archaea were more abundant than ammonia-oxidizing bacteria (AOB) in all the corresponding treatments though they were of the same order of magnitude. There was no significant correlation between AOA abundance and soil nitrification potential. The DGGE patterns revealed that the intensive management resulted in an obvious change of the AOA community, significant change was also observed among the treatments with different intensive management history. Phylogenetic analysis of the amoA gene fragments showed that all AOA sequences from different treatments were associated with uncultured Crenarchaeote. The AOA species that adapt to low pH soils dominated in the 7-, 9-, 11- and 15-year-old treatments while species associated with paddy soil and sediment soil clone dominated in the control and 4-year-old treatment, indicating a pronounced difference in the community composition of AOA in response to the long-term intensive management. Canonical correspondence analysis exhibited a significant difference in microbial community structures between the treatments before and after intensive management application. The 11- and 15-year-old treatments were clustered together, and clearly separated from the 7- and 9-year-old treatments along both the first and second ordination axes. Concentrations of soil NO₃^--N, NH₄⁺-N and available phosphorus, and soil pH together explained 62.2% of the total variation of soil AOA community. The first ordination axis explained 33.9% of the variation and the second axis explained 25.8% of the variation. Among the four soil parameters measured, soil NO₃^--N concentration explained most of the variation of AOA community, but the influence was not significant (P<0.05). The results suggest that long-term intensive management had a significant impact on AOA abundance and composition, and the soil acidification and nutrient accumulation should be important factors influencing the shift of AOA community in the intensively managed P. praecox stands.