在盆栽种植条件下,比较研究了两个转Bt基因棉(Gossypium hirsutum)与对照棉对根际土壤细菌、放线菌、真菌和主要功能类群及多样性的影响差异。结果表明:两个转Bt基因棉根际土壤均可检测到Bt蛋白,且不同转Bt基因棉根系分泌Bt蛋白量以及Bt蛋白在根际土壤中的降解率不同。与各自对照相比,转Bt基因棉对细菌和真菌生长繁殖有促进作用,对放线菌、好气固氮菌和钾细菌数量没有显著影响。苗期和花期转Bt基因棉均可显著提高氨化细菌、显著降低无机溶磷菌数量,花期均可显著提高好气纤维分解菌、显著降低有机溶磷菌数量,‘Bt冀668’苗期也可显著提高好气纤维分解菌数量。转Bt基因棉根际土壤好气纤维分解菌、有机和无机溶磷菌多度发生了变化。尽管功能类群总数转Bt基因棉高于各自对照常规棉,但群落多样性和均匀度都有所下降,优势集中性表现明显,且花期转Bt基因棉多样性参数值以及功能类群数量的变化幅度大于苗期。

Aims Ecological risk assessments have paid increasing attention to the field release of transgenic Bt crops. Some studies have reported that Bt protein could enter the soil ecosystem through root exudates, crop residues, crop decomposition and pollen. Protein from transgenic Bt crops is a potential hazard for soil non-target organisms and biodiversity, and this may affect soil ecological function and soil nutrients. This study aims to evaluate the soil ecological risk of transgenic Bt cotton.
Methods A pot experiment with two types of transgenic Bt cotton, ‘BtXincai1’ and ‘BtJi668’, was conducted to study the effects of transgenic Bt cotton planting on rhizosphere soil microorganisms. The plant was carefully removed from the pot at seedling, budding, flowering, bolling and boll-opening stages. Rhizosphere soil approximately 0-5 mm in diameter was separated from bulk soil by gently shaking the root system. Samples were frozen at -20 ℃ after sieving for subsequent Bt protein analyses, or stored at 4 ℃ for microorganism analyses, which were begun within a day of sampling. Bt protein was analyzed by ELISA BOX. The populations of three main microorganism groups and some functional groups were measured by cultivation.
Important findings The content of Bt protein exuded by different transgenic Bt cottons and the degradation rate of Bt protein in different rhizosphere soils were different. Compared with the controls, transgenic Bt cottons seemed to stimulate the reproduction of rhizosphere soil bacteria and fungi. However, no significant effects on the populations of actinomycete, aerobic nitrogen fixing bacteria and kalium-solubilizing bacteria were observed. Transgenic Bt cottons increased the population of ammonifying bacteria and decreased that of inorganic phosphorus-solubilizing bacteria significantly at seedling and flowering stages, whereas they increased the population of aerobic cellulose-decomposing bacteria and decreased that of organic phosphorus-solubilizing bacteria significantly only at the flowering stage. ‘BtJi668’ also enhanced the population of aerobic cellulose-decomposing bacteria significantly at the seedling stage. The abundance of aerobic cellulose-decomposing bacteria and organic and inorganic phosphorus-solubilizing bacteria in transgenic Bt cottons rhizosphere soils changed. Although the total population of functional groups in transgenic Bt cottons rhizosphere soils was higher than in control cultivars, community diversity (H) and evenness (J) decreased and dominance concentration (C) increased. The change range of diversity indexes and population of functional groups in transgenic Bt cottons rhizosphere soils at the flowering stage was higher than at the seedling stage.