Progress 09/15/01 to 09/14/04
Outputs
A field trial with replicate plots of transgenic corn (MON863) resistant to the corn rootworm (CRW) and a non-transgenic isoline with and without the insecticide tefluthrin applied was established in 2001 and replanted to the same treatments in the 2002 and 2003 growing seasons by J. Losey and L. Allee. Our goal was to conduct a comparative assessment of the effects of transgenic corn and insecticide on the soil microbial community. There are clear environmental and health disadvantages to using insecticide, but the literature suggests that farmers will use it in the absence of transgenic Bt corn. Two composite soil samples consisting of 10 sub-samples across a transect of each plot were collected before planting (pre-plant), at anthesis, and at harvest to assess the effect of treatments on abundance, activity, and community composition of soil bacteria, fungi, and protozoa in bulk and rhizosphere soil. Statistical analyses were conducted using the General Linear Model
and Tukeys Test at P = 0.05. The abundance of protozoa (amoebae, flagellates, and ciliates) was determined by the most probable number (MPN) method, while bacterial and fungal plate counts provided estimates of the abundance of culturable members of these groups. There was no effect of treatment (Bt corn or insecticide) on the abundance of protozoa or culturable bacteria and fungi. Microbial biomass measured by fumigation-extraction and determination of ninhydrin-reactive N also indicated that neither treatment had an adverse effect; in fact, harvest levels of microbial biomass in Bt and insecticide plots were higher than in control plots in 2001 and 2003. Biomass at anthesis decreased compared to that at pre-plant and harvest in each year. Year to year variation in microbial biomass for any given sampling time across the crop cycle was also significant. Soil microbial activity was assessed by measuring nitrogen mineralization potential, short-term nitrification potential, and soil
respiration. Once again, a significant effect of crop phenological stage was observed for all three measures of activity, but no adverse effect of the Bt or insecticide treatments was observed for any of these measures. Nitrogen mineralization and nitrification potentials differed with year for the pre-plant and harvest sample points. Eubacterial community structure was evaluated by terminal-restriction fragment length polymorphism (T-RFLP) analysis. For all three years, there was no observable effect of treatment on bacterial community structure. However, clear variations in community structure were associated with crop phenological stage and year, indicating that the method was robust and sensitive enough to pick up variations when they existed. T-RFLP analysis of the fungal community structure again showed no effects of either treatment compared to the control, but undeniable differences associated with phenology and year were observed. Our results clearly showed that the effect of
sampling time during and between growing seasons was significant for all measured variables and far outweighed the impact of CRW Bt corn or tefluthrin on the soil microbial community.
Impacts
Our research indicates that neither corn rootworm (CRW)-resistant Bt corn (MON863) nor tefluthrin, a pesticide commonly used to control CRW, adversely affected key microbial processes or community structure of protozoa, bacteria or fungi under field conditions. Thus, processes such as organic matter decomposition and nutrient cycling that are largely microbially-mediated are unlikely to be negatively influenced by the use of CRW Bt corn or tefluthrin sprays in cropping systems any more than they would be by changes in environmental variables such as rainfall and temperature or crop variables such as stage of crop development. These results provide information on previously overlooked, but key components of agroecosystems, and should enhance the ability of regulatory agencies to make recommendations for the deployment and longer-term monitoring of transgenic Bt crop varieties.
Publications
- Thies, J.E and M. Devare. 2005. Transgenic crops: an impending ecological disaster or blessing for the poor? Journal of Sustainable Development: accepted.
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Progress 09/16/02 to 09/15/03
Outputs
We are examining the effects on the soil microbial community of growing transgenic corn resistant to the corn rootworm (CRW) or applying the insecticide tefluthrin. Three treatments: MON863 transgenic Bt corn and the non-transgenic isoline with and without tefluthrin applied at planting were established in field plots in Freeville, NY in 2001. The site was replanted to the same treatments in 2002 and 2003. Two composite soil samples from each of at least 3 replicate plots have been collected before planting (pre-plant), at anthesis and at harvest to assess the effect of treatments on the abundance, activity, and diversity of soil bacteria, fungi, and protozoa. The abundance of protozoa (amoebae, flagellates, and ciliates) is being determined by the most probable number (MPN) method. The abundance of culturable bacteria and fungi is being estimated by plate counts. Neither MPN results nor plate counts indicate any treatment effect on the abundance of protozoa or
culturable bacteria and fungi, respectively, at any sample point thus far. Further, microbial biomass measurements by fumigation-extraction and determination of ninhydrin-reactive N also indicate that there is no effect of treatment. Microbial biomass does differ significantly, however, with phenological stage of the plants (time of sampling within season) as well as between years (P=0.05). Soil microbial activity is being assessed by measuring soil respiration, N mineralization potential, and short-term nitrification potential. No significant effect of treatment on any of these measures of activity has been detected for any sample point thus far; however, effects of phenological stage and year have once again been observed on N mineralization and nitrification potential. The data for soil respiration is still in review. Eubacterial community structure is being evaluated by terminal restriction fragment length polymorphism (T-RFLP) analysis. Data from 2001 and 2002 has been analyzed
thus far and show the same pattern as the microbial activity analyses: there is no observable effect of treatment on bacterial community structure, which does vary significantly with phenological stage and year. Denaturing gradient gel electrophoresis (DGGE) is being used to assess fungal community structure. DGGE analyses of anthesis samples in 2001 and 2002 and pre-plant samples in 2002 once again indicated no effect of treatment, while showing a significant effect of sample timing within and across years. Our results thus far show that the effects of sampling time during the growing season and between growing seasons on soil microbial abundance, activity and diversity are significant and far outweigh the generally non-significant effects of CRW Bt corn and the insecticide tefluthrin on the soil microbial community. Ongoing research plans include: continuation of abundance and activity measurements on pre-plant and anthesis samples in 2004; completion of T-RFLP for bacterial and
fungal community analyses; and refinement of a real-time PCR technique to assess CRW corn and insecticide effects on populations of ammonia-oxidizing and nitrogen-fixing bacteria in the field plots.
Impacts
Our research indicates that neither corn rootworm-resistant Bt corn nor tefluthrin used to control this pest are likely to adversely affect microbial communities under field conditions. Thus, processes such as nutrient cycling and plant pest and disease suppression which are largely microbially-mediated are unlikely to be affected. These results provide information on the effects of a widely disseminated technology on microbial ecology-a previously overlooked, but key component of agroecosystems-and will enhance the ability of regulatory agencies as well as private industry and farmers to make recommendations and decisions for optimal management of corn cropping systems.
Publications
- Devare, M.H., C.M. Jones, and J.E. Thies. 2004. Effect of Cry3Bb transgenic corn and tefluthrin on the soil microbial community: biomass, activity and diversity. Journal of Environmental Quality, In press (May/June).
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Progress 01/01/02 to 12/31/02
Outputs
We are quantifying the impacts of transgenic (Bt) corn and insecticide use on the soil microbial food web. A field trial with corn root worm (CRW) resistant corn, established in 2001 in Freeville, NY, was continued through the 2002 cropping season. Field plots were sown with one of the following: CRW corn producing the Cry3Bb toxin (Bt), a non-transgenic isoline (NoBt), or the NoBt isoline with the tefluthrin insecticide Force 3G (AstraZeneca Corp., Wayne, PA) applied at planting (I). Seed was obtained from Monsanto Corp. (St. Louis, MO). All Bt seed and half of the noBt seed supplied had been treated with Gaucho (G) insecticide, containing imidacloprid. Consequently, the trial consisted of 5 treatments: NoBtG, IG, BtG, NoBt and I. Soil samples were taken from all plots planted with Gaucho treated seed prior to planting, at anthesis and at harvest for soil microbial activity, abundance and diversity measurements. Root and soil samples were taken from all plots to
assess plant parasitic and non-parasitic nematodes at 4 times during the cropping cycle. Soil respiration, nitrogen (N) mineralization potential, short-term nitrification rate, and microbial biomass C were measured. There was no treatment effect on any measure of activity in 2001. Microbial biomass C and short-term nitrification rate did not differ with treatment in 2002. However, at anthesis and harvest N mineralization potential was significantly higher (p = 0.05) in soil planted to BtG corn compared to plots planted with NoBtG or IG. Respiration in soil from IG plots was depressed at anthesis (p = 0.05) as compared to other treatments. Our results indicate no adverse effect of CRW corn on soil microbial activity. Soil bacterial and fungal population structure under the various treatments is currently underway. Total soil DNA was extracted and amplified using either eubacterial or eukaryal primers. Bacterial community structure has been evaluated for the anthesis samples from both
years by terminal restriction fragment length polymorphism (T-RFLP) analysis. The results show a similar bacterial community structure in all soils regardless of treatment. Results for bacterial diversity at other sample points will be available shortly. Eukaryotic diversity and community structure is currently being evaluated by denaturing gradient gel electrophoresis (DGGE) analysis. Nematodes in roots were extracted using a modified Baermann method and counted. Nematodes in soil samples were extracted by a modified sugar floatation method and counted. Counts were transformed with log (x + 1) and analyzed by one-way ANOVA. Preliminary results from 2002: mean counts of lesion nematodes per root system in non-Bt Gaucho treatments (NoBtG, IG) were highly significantly greater than all non-Gaucho and Bt treatments (NoBt, I, BtG) (p greater than 0.001). Counts did not differ within these two treatment groups. For soil extracts, there were no significant differences among treatments for
the numbers of lesion nematodes extracted for the first 3 sampling dates. At the last sampling, there were no significant differences among treatments for numbers of non-plant parasitic nematodes (p = 0.039).
Impacts
Public concern over the use of transgenic crops and insecticides and their effects on human and environmental health is on the rise. At the same time, acreage planted to transgenic maize in the U.S. is continually increasing as farmers seek to widen profit margins. We are quantifying the impacts of transgenic (Bt) maize and insecticide use on microbial abundance, diversity, and biological activities in field soil. Microbial presence and activity are critical for optimizing agricultural production and ensuring the long-term sustainability of agroecosystems in which transgenic crops are grown. Nematodes, which are among the more abundant eumetazoans in soil, integrate soil physical, chemical and biological processes, hence are useful for gauging the potential impact Bt crops might have on soil animals. To date, no risks to the soil microbial community have been identified. Data generated in this project provide information needed to allow public and regulatory bodies to
make better decisions on the release of Cry3Bb transgenic maize.
Publications
- Devare, M, Thies, JE, Jones, CM, Culman, S, and Martinez, CE. 2002. Effects of CRW transgenic corn and tefluthrin on the soil microbial community: activity, diversity and abundance. American Society of Agronomy, Agronomy Abstracts, Indianapolis, IN.
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Progress 09/15/01 to 12/31/01
Outputs
A field trial to assess the effects of growing transgenic (Bt-CRW) corn on the soil microbial foodweb was established in May 2001 in Freeville, NY. Four replicate plots were planted with each of the following 3 treatments: CRW ("Bt-G") corn producing Cry3Bb toxin, a non-transgenic ("NoBt") isoline, or the NoBt isoline with the tefluthrin insecticide Force 3G ("I") applied at planting. All the Bt seed and half of the noBt seed supplied by Monsanto had been treated with Gaucho ("G"), an imidacloprid insecticide. Consequently, the trial was augmented to include 3 replicates of the treatments : "I-G", and "NoBt-G". Two composite soil samples were collected to 25 cm from each of the 18 plots 3 times during the season to give pre-plant, anthesis, and harvest samples for bacterial, fungal, and protozoan analyses. Anthesis and harvest samples were separated into bulk and rhizosphere components. Five soil cores were obtained from each plot 4 times during the growing season for
nematode analyses. Nematodes were extracted using a modified Baermann method (roots) or a modified sugar floatation method (soil). 1). Impact of CRW corn on abundance and diversity of soil microorganisms a). For the anthesis samples, there was no significant treatment effect on the abundance of amoebae, flagellated, or ciliated protozoa, as counted by the Most Probable Number method. Analyses are not yet complete for the harvest sample. b). Epifluorescence microscopy coupled with image analysis was used to enumerate bacteria and fungi in soil suspensions; stored images will be analyzed to obtain bacterial counts and biomass estimates of active and inactive fungal hyphae. c). Preliminary analyses indicate that the mean counts of lesion nematodes/g root were not significantly different among Bt and non-Bt treatments (p = 0.071). Treatment effects on plant parasitic nematodes are still being evaluated. There were no significant differences between treatments on fungivore, bacteriovore or
predator nematodes. d). Evaluation of the diversity of soil bacterial and fungal populations in sampled soils is currently underway. Bacterial diversity and community structure are being evaluated by terminal restriction fragment length polymorphism (T-RFLP) analysis. Fungal diversity and community structure are being evaluated by internal transcribed spacer (ITS) analysis. 2). Impact of CRW corn on microbial activity: Soil respiration, minerizable nitrogen, and short-term nitrification potential were used to assess soil microbial activity. No significant pre-plant treatment differences were observed for soil respiration or mineralizable N. There were no differences in soil respiration among treatments for the anthesis sample. Data from other experiments to assess microbial activity are currently being analyzed. Estimation of microbial biomass by fumigation-extraction and determination of ninhydrin-positive compounds is now nearing completion. 3). A reliable method to evaluate the
persistence of Cry3Bb and tefluthrin in field soil needs to be devised. Fluorescently-labeled monoclonal antibodies will be developed over the coming year and used to aid in the detection of the toxin and insecticide.
Impacts
Public concern over the use of transgenic crops and insecticides and their effects on human and environmental health is on the rise. At the same time, acreage planted to transgenic maize in the U.S. is continually increasing as farmers seek to widen profit margins, and there is growing interest in finding more environmentally-friendly alternatives to insecticides and soil fumigants. We expect to quantify the impacts (positive, negative or neutral) of transgenic corn and insecticide use on microbial abundance, diversity, and biological activities--all of which are critical to optimize agricultural production and the long-term sustainability of the agroecosystem. Data from the activities described is expected to provide reliable scientific information, which will allow public and regulatory bodies to make accurate and justifiable decisions.
Publications
- No publications reported this period
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