环渤海湾苹果产区老果园与连作果园土壤线虫群落特征

应用类群多样性、类群丰富度、个体密度和功能类群指数等群落参数,于2009年5-10月分3次对环渤海湾苹果栽植区老果园不同位置和连作果园取样研究了土壤线虫群落特征。结果表明:苹果连作对果园土壤生物环境具有明显的恶化作用,连作果园土壤环境条件恶劣;对功能类群指数的统计表明,苹果连作明显改变了果园土壤中植物寄生性线虫r-选择和k-选择的比例,与自由生活线虫比较,连作对植物寄生线虫影响更明显;连作提高了果园的土壤线虫PPI/MI,说明连作对果园土壤健康的扰动最大;土壤不同食性线虫数量统计结果显示,环渤海湾苹果栽植区植食性线虫数量未达线虫伤害阈值,线虫不是引起环渤海湾地区苹果连作障碍的主要原因。

Characterization of nematode communities in the soil of long-standing versus replanted apple orchards surrounding Bohai Gulf

Apple replant disease (ARD) is a common problem affecting the reuse of lands just removed from apple production. ARD problem is caused by soil-borne organisms, which stunts the growth of apple trees, suppresses the yield and quality of apple fruits, and enhances susceptibility to diseases and pests. Apple replanting impacts the pH value, nutrition level, enzymatic activity, concentration of toxic substances (e.g. phenolic compounds), and microorganism community (e.g. pathogenic fungi) in the soil, deteriorating physical and chemical properties of soil. Healthy soil is essential for producing healthy foods and protecting human health. Soil nematodes (Phylum nematoda) are important components in the soil ecosystem, play significant roles during the processes of soil formation and maturation, and are major parts in the soil food chain. Soil nematodes are sensitive to physical and chemical changes in the soil, and are often used as the biological indicator measuring soil quality. In this study, soil nematodes were analyzed on apple orchards surrounding Bohai Gulf from May to October in 2009. The structure and dynamic change of nematode communities were assessed by using generic diversity, generic richness, nematode density, and a functional group index. In comparison, the generic diversity, generic richness and uniformity of soil nematodes in the replanted apple orchards were significantly lower than those in the long-standing apple orchards. Data of generic diversity also suggested that apple replanting impacts the biological properties of the soil, leading to a less favorable soil environment for apple growth. The maturity index (MI) of free-living nematodes was similar between long-standing and replanted apple orchards, but the maturity index of plant parasitic nematodes, or the plant parasite index (PPI), was significantly higher in the replanted apple orchards than those in the long-standing apple orchards. According to the functional group index, apple replanting significantly changed the ratio of r- and k- selection of plant parasitic nematodes. When compared with free-living nematodes, plant parasitic nematodes were more adaptable to replanted apple orchards, increasing the PPI/MI ratio. Analysis of nematodes with different feeding habits revealed that the overall numbers (36.8 nematodes per 100g dry soil) of herbivorous nematodes in replanted orchards around Bohai Gulf was greatly below the density threshold (114 nematodes per 100g dry soil) that can damage apple trees. Therefore, it appears that nematodes are not the major causal agent for apple replant disease in the Bohai Gulf area. However, it is still possible that soil nematodes might boost the ARD problem in some replanted apple orchards.