Soil Eoclogical Risk Evaluation of Transgenic Bt Rice Through Nematode Community Analysis
|School||Nanjing Agricultural College|
|Keywords||Transgenic Bt rice Soil ecosystem Nematode community Microbial properties|
Transgenic Bt rice had provided an efficient way for reducing rice yield losses by insect pest, especially stem borers, leaffolders and planthoppers in China. The Bt toxic proteins could enter the soil through root and plant residues and lead to accumulation and persistence of Bt toxic proteins in soil. Soil plays a significant role in energy flow and material cycling. Therefore, whether Bt crops could impose potential adverse effects on the soil ecosystem or not, for example, on non-target soil organisms and associated soil processes has raised worldwide concerns. Nematodes are the most abundant and ubiquitous metazoan and occupy key positions in soil food web. The interpretation of nematode community structure can provide a comprehensive summary of soil food web condition. Owing to their irreplaceable functional roles in soil ecosystem, nematodes have increasingly been used as indicators of soil ecological condition.In this study, we compared the effects of three rice varieties (KMD, HH1, BtSY63), transformed to express the Bt protein (Cry1Ab or CrylAb/CrylAc), and their near-isogenic non-Bt controls (XSD, MH63, SY63) on soil chemical properties, microbial properties, and soil nematode community based on a field experiment. We evaluated using multivariate analysis whether nematodes were suitable indicators to assess the impacts of transgenic Bt rice on soil ecology or not.The main results during our two-year’s field investigation were as follows:1) The transgenic Bt rice did not consistently cause the significant changes of soil dissolved organic carbon and nitrogen, and microbial properties. It should be noted that the difference of microbial properties among transgenic Bt rice lines became larger than those among non-Bt lines, implying long-term monitoring will help to display the impacts of transgenic Bt rice on soil ecosystem structure and functioning.2) No negative effects of transgenic Bt rice on soil nematode community was observed in our study. Higher nematode abundance, proportion of fungivores and Shannon-Weaver diversity index (H’) were found under Bt rice (KMD) than its non-Bt control (XSD). Compared to their near-isogenic non-Bt controls (MH63, SY63), there were higher H’ for soil under HH1 and BtSY63 planting. However, the magnititude of such transient effect was markedly less than that caused by seasonal variation.3) In our study, biota and environment analysis (BIO-ENV) indicated that the relations between nematode species and environmental factors of soil were lower not only under species level but also trophic group level. Redundancy analysis (RDA) of the relationship between nematode species and soil environmental factors indicated only the soil dissolved organic carbon (DOC) significantly affected some soil nematode generas (Monte Carlo permutation test, P=0.04).4) Multivariate analysis on the nematode community data revealed that non-metric multidimensional scaling (nMDS), analysis of similarities (ANOSIM), and analysis of similarity percentages (SIMPER) were the efficient analysis methods to identify the nematode indicator to assess the impacts of transgenic Bt rice on soil ecology. Firstly, nMDS was carried out to assess the community structure pattern of nematodes. Secondly, ANOSIM was performed to test differences for nematode communities under transgenic Bt rice and non-Bt rice. Thirdly, SIMPER was used to identify the dominant nematode generas from the groupings formed nMDS analysis. In our study, we found Tylenchorhynchus, Cephalobus, and Chiloplacus were sensitive to response changes between transgenic Bt and non-Bt rice.In summary, no negative effects of transgenic Bt rice on soil resource, microbial properties and soil nematode community were found in our two-year field investigation. However, the interaction of transgenic Bt rice and soil ecosystem was a long-term process and are also environmental and biological context dependent. Thus, the long-term monitoring or mathematical model constructing would be necessary to clarify whether transgenic Bt rice poses ecological risk to soil ecosystem or not.