基于根际与凋落物际评价转Bt水稻对土壤线虫群落的影响

转基因作物在商业化推广前,有必要评价其对非靶标土壤生物的生态影响。根系和凋落物与土壤的界面是代表植物直接影响土壤的两个典型活性微域,即根际和凋落物际。基于室内盆栽实验构建水稻根际和凋落物际,比较了这两个高活性微域中转Bt水稻克螟稻(KMD)与亲本水稻秀水11(XSD)对土壤可利用资源、微生物学性质和线虫群落的影响。结果表明:转Bt水稻对土壤性质的影响依赖于水稻生育期和微域的变化。与XSD相比,KMD在苗期和拔节期显著提高了凋落物际土壤可溶性有机氮含量(P0.05);在苗期显著降低了凋落物际土壤铵态氮含量,但在成熟期显著提高了凋落物际与交互微域土壤的铵态氮含量(P0.05)。与亲本水稻相比,转Bt水稻分别在苗期和成熟期显著提高了凋落物际土壤微生物生物量碳和活性,而在拔节期和成熟期显著降低了根际土壤微生物生物量氮含量(P0.05)。微域间的交互作用显著影响土壤微生物生物量、可溶性有机碳和氮、线虫总数和各食性线虫的数量(P0.05)。转Bt水稻总体上降低了土壤线虫总数,尤其在苗期和拔节期的凋落物际土壤中达到显著水平。重复测量方差分析表明转Bt水稻显著影响土壤食细菌(P0.01)和食真菌(P0.05)线虫数量,及线虫群落的通道指数和富集指数。水稻收获后KMD秸秆的Bt蛋白含量显著高于亲本,全部KMD处理的土壤样品中Bt蛋白含量无显著变化,因而转Bt水稻对土壤生物学性质的影响可能并非来源于Bt蛋白的作用,而更可能来自于水稻生长性状和凋落物性质的差异。

Influences of rhizosphere and detritusphere of Bt rice on soil nematode communities

It is important to evaluate the ecological risks of transgenic Bt rice on soil non-target organisms before it is widely released in the market. Rhizosphere and detritusphere formed by plant roots and organic residues that contact soil directly, and represent two distinct microsites that are highly affected by plants. Pot experiments were established to investigate the effects of rice, a variety genetically modified to express the Bt protein, KMD, and its parental line, XSD, on soil chemical, microbial properties and nematode assemblages of the two microsites. Results indicated that effects of transgenic Bt rice on soil properties varied with plant growth stage and microsite type. Compared with XSD, KMD increased the concentrations of soil dissolved organic nitrogen in detritusphere (D) at seedling and elongation stages, whereas the concentrations of ammonium in the detritusphere were decreased significantly by KMD at seedling stage (P<0.05). At maturing stage, KMD increased the concentrations of ammonium in the detritusphere and overlapped microsite (DR, i.e. the area that affected by both rhizosphere and detritusphere) significantly (P<0.05). With regard to soil microbial biomass, KMD significantly increased the concentrations of soil microbial biomass carbon (MBC) in detritusphere at seedling and maturing stages (P<0.05), whereas significantly decreased microbial biomass nitrogen (MBN) in rhizosphere at elongation and maturing stages (P<0.05). Integrated effects of the two microsites had a significant effect on concentrations of microbial biomass carbon and nitrogen as well as dissolved organic matter, total nematode numbers and nematode numbers of different feeding groups (P<0.05). Generally, KMD decreased the total nematode numbers, especially there were significantly fewer nematodes in the detritusphere of KMD than XSD at seedling and elongation stages (P<0.05). Repeated-measure ANOVA indicated that transgenic Bt rice KMD had significant effects on numbers of bacterial feeders (P<0.01) and fungal feeders (P<0.05), nematode channel ratio (NCR) and enrichment index (EI). In addition, the genetically modified KMD significantly decreased (P<0.05) the proportions of bacterial feeders and fungal feeders in detritusphere at seedling and elongation stages, and such trends were consistent to the responses of ammonium concentrations of the same microsite and growth stage. In light of soil Bt protein concentrations under KMD treatments after maturing stage, Bt rice showed no significant effect, though the content of Bt protein in straw of KMD was significantly higher than that of XSD, indicating that significant differences of effects of KMD from XSD might not result from Bt protein itself, but from the difference of other traits such as rice growth and residue chemical composition. Together, we found that microsite studies combining the rhizosphere and detritusphere would facilitate to demonstrate the responses of soil microbial properties and nematode assemblages to explore the ecological impacts and mechanisms of growing genetically modified rice.