Abstract
Understanding how soil ecosystem responds to transgenic Bacillus thuringiensis (Bt) rice is necessary for environmental risk assessment. While the influences of short-term cultivation of Bt rice on soil properties have been reported previously, little is known about the long-term effects of Bt rice on soil ecosystems. In this study, soil samples were taken from a long-term rice cultivation site in Fujian Province, China, where transgenic Bt rice (Kefeng-6) and its non-Bt parent breed (Minghui-86) had been continuously cultivated for 8 years. Soil Bt protein concentration and a total of 16 variables were analyzed to assess potential risks of soil health under Bt rice cultivation. The results revealed that soil Bt protein is unlikely to accumulate after Bt rice cultivated in the field, and no consistently significant changes were observed in soil enzymatic activities (catalase, dehydrogenase, acid phosphatase, and urease), microbial biomass (microbial carbon and nitrogen), total organic carbon, decomposition (soil respiration, Q10, and qCO2), soil nitrogen and phosphorus contents. Due to a local tradition that aboveground biomass was removed after harvest, the increased net primary productivity by Bt rice cultivation did not significantly change soil C cycling. Results of this study suggested that on the aspects of soil microbial functioning and C cycling, long-term cultivation of Bt rice is unlikely to result in significant effects on soil health.
Highlights
Transgenic Bacillus thuringiensis (Bt) crops are genetically modified to express certain larvicidal toxins to kill target pests
Soil total organic carbon (TOC) and total nitrogen (TN) pools were insensitive to cultivation of Bt crops[20,21,22]
Short-term cultivation experiments encountered temporal variations in soil environment and crop growth, were not able to reflect the accumulative effects of Bt protein along with the food web in the soil, it is still poorly understood whether long-term cultivation of Bt crops will result in irreversible impacts on soil health
Summary
Transgenic Bacillus thuringiensis (Bt) crops are genetically modified to express certain larvicidal toxins to kill target pests. Under the canopy of Bt rice, soil microbial biomass declined by 7%32; dehydrogenase activity increased by 95% at the initial stage of straw decomposition but decreased by 47% at subsequent stages[33]; soil respiration rate increased by 25%34 All of these studies were based on short-term experiments (1–3 years), mainly due to the lack of long-term experimental platform of transgenic Bt rice cultivation. The objectives of this study were to investigate: (1) whether long-term cultivation of Bt rice causes the accumulation of Bt protein in soil; (2) whether there are irreversibly negative effects of Bt rice cultivation on soil properties mediating soil carbon and nitrogen cycling and maintaining ecosystem health, such as enzymatic activities, microbial biomass, and dynamics of C pool and decomposition
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