渭北塬区不同龄苹果园土壤微生物空间分布特征

以渭北塬区塬面5、10、15和20龄苹果园为对象,距树干1.0、1.5、2.0 m处用土钻法分层采集0—30 cm土样,稀释平板法测定土壤微生物数量,平行测定土壤有机碳、总氮和总磷,分析不同龄果园土壤微生物的空间分布状况及其与土壤碳、氮、磷的关系。结果表明:土壤真菌数量随树龄增大而增加,龄间差异显著(P0.05);与对照农田相比,各龄果园放线菌数量及5龄和20龄果园细菌数量偏低,10龄和15龄果园细菌数量偏高;各龄果园土壤真菌、细菌和放线菌数量均随深度增加而减小。就相同深度土层而言,真菌数量随果园年限增大而增加,细菌则以10龄和15龄果园较多,同深度土层的放线菌龄间差异随深度增加而减小。在沿树干向外的径向水平方向上,真菌数量随果园年限的增加相应增多;10龄和15龄果园土壤细菌和放线菌高于5龄果园和20龄果园。5龄果园土壤总氮有沿树干向外、沿表层向下逐步降低的趋势,果园从5龄经10龄到15龄,其"高氮点"则逐步向外、向下移动。塬区果园土壤C∶N比偏低。

Spatial distribution of soil microorganisms in apple orchards of different ages on the Weibei rainfed tableland of the Loess Plateau, China

Soil microorganisms are vital for orchard ecosystems, as they determine and promote the material cycle and energy flow. The Weibei Loess Plateau is one of the main regions producing high-quality apples since the 1980s. The planting structure of apple orchards has following characteristics: simple and long-term fertilizer, high quality management, and "double high" (high investment and high harvest) production, which results in different soil fertility and quality in orchards of different ages, leading to different habitat conditions for microorganisms. Consequently, different aged orchards have different soil microbial species composition, quality, and spatial distributions. Yet, differences in soil microorganism parameters affect apple yield and quality, because of their involvement in maintaining and improving the feedback effect on soil properties and fertility in orchards. To maintain sustainable development, prevent soil quality degradation, and reform orchard degradation, it is essential to understand the long-term dynamics and trends of microorganisms in orchards. This work investigated the spatial distribution of soil microorganisms in different apple orchards of different ages (5, 10, 15, and 20 years old) on the Weibei rainfed tableland of the Loess Plateau. Soil samples were first collected from the 0-30cm soil layer at root radial distances of 1.0, 1.5, and 2.0 m away from the main tree trunk using a soil coring method. Soil total nitrogen (TN), soil total phosphorus (TP), and soil organic carbon (SOC) were then determined using the Flowsys III and Liqui TOC II analyzer. Relationships between soil microorganisms and soil nutrients (i.e., TN, TP, and SOC) were also analyzed. The results showed that the soil fungal population increased with increasing apple orchard age. There were significant differences in soil fungal population among orchard ages, at the P=0.05 level. The soil actinomycete population in orchards of all ages and soil bacterial population in 5-year and 20-year old apple orchards was lower than that in agricultural fields (control check). In comparison, the soil bacterial population in 10-year and 15-year old apple orchards was higher than that in the agricultural field. Fungal, actinomycete and bacterial populations decreased with increasing soil depth. At the same soil depth, the soil fungal population increased with increasing orchards age, with the soil bacterial population in 10-year and 15-year old apple orchards being higher than that in 5-year and 20-year old orchards. Soil actinomycete populations declined with the increasing in soil depth in all ages of apple orchards. In the radial horizontal direction, the soil fungal population in all apple orchards increased with age, while the soil bacterial population during the full fruit bearing period (10 and 15-years old) was higher than that in 5-year and 20-year old orchards, with soil actinomycetes exhibiting the same trend. The TP in 5-year old apple orchards declined outward from the apple trunk and downward from the topsoil. The "High spot of TN" moved outward from the apple trunk and downward from the topsoil for 5-year to 15-year old apple orchards. The soil C : N ratio was low in apple orchards on the Weibei rainfed tableland of the Loess Plateau.