NDLI: Decomposition of Bacillus thuringiensis (Bt) transgenic rice residues (straw and roots) in paddy fields

Content Provider	Springer Nature Link
Author	Wu, Weixiang Lu, Haohao Liu, Wei Devare, Medha Thies, Janice E. Chen, Yingxu
Copyright Year	2009
Abstract	Genetic modification of commercial crops may affect their decomposition and nutrient cycling processes in agricultural ecosystems. Intensive rice cultivation under partially submerged conditions (paddy rice) is an important and widespread cropping system, particularly in the tropics, yet there is little data on the decomposition of Bt rice residue under field conditions. We investigated straw and root decomposition of rice modified to express the Cry1Ab protein of Bacillus thuringiensis (Bt) to kill lepidopteran pests, compared with a parental non-Bt isoline. The objective of this study was to assess the possible impacts of cry gene transformation of rice on residue decomposition under intensive rice cultivation with long period of submergence.The decomposition experiment was set up as a completely randomized design for two types of rice residues, KMD (Bt) and Xiushui 11 (non-Bt parental variety) in triplicate. All together six plots (4 m × 15 m each) were cultivated in two successive years by conventional intensive rice cropping methods. Litterbags were used to evaluate rice residue decomposition. Two grams of Bt and non-Bt rice roots or 5 g of rice straw were sealed in a 10 × 15-cm nylon mesh litterbag. A total of 192 straw and root litterbags each were prepared. Both kinds of litterbags were then placed either at the surface or buried at 10 cm depth along two parallel transects within each plot in the field on 24 December, 2005. Decomposition dynamics were determined by changes in ash-free mass remaining (AFMR), and nutrient content (C and N) of rice straw and root materials contained in mesh litterbags. Cellulose and lignin contents of the original rice residues were determined according to Van Soest’s methods (1963). The AFMR was recorded by calculating ash weight. Total C (TC) and total N (TN) of the samples were analyzed by combustion in an element autoanalyzer and calculated by multiplying %C and %N by the final weights obtained prior to ashing.AFMR, total carbon, and C:N ratios of the rice residues decreased over time. An increase in total nitrogen was observed at the beginning of straw decomposition, from day 17 to 31. There were no substantial differences in straw decomposition between Bt and conventional rice varieties, but Bt roots in buried litterbags displayed significantly lower AFMR, TN, and TC contents at the initial decomposition stage (day 31, 68, and 137 for AFMR and TC and day 68, 137, and 207 for TN) compared to the conventional rice.The significant differences which were detected at the initial decomposition may not result from the expression of the cry1Ab gene. It is more likely that the genetic transformation or the effect of inserting foreign genes may result in differences between Bt and non-Bt rice with respect to chemical composition of rice plant residues. Although there were no statistically significant differences in total lignin or total cellulose content between Bt and non-Bt rice roots, we speculate that significant differences in the decay rate between buried Bt and non-Bt rice roots observed at the early stage of the experiment could result from a variation in the availability of readily metabolizable root components of the transgenic rice roots due to transformation or site effects of the insertion of foreign genes.This is the first report regarding decomposition of Bt rice residue (straw and root) under field conditions. In the traditional rice–rice cropping system, we found no substantial differences of rice straw decomposition between transgenic Bt and conventional near-isogenic variety. However, some statistically significant differences in decompositional properties, such as AFMR, TN, and TC contents between Bt transgenic and non-Bt parental rice roots, were found under buried condition before the end of first rice season. Our results obtained in two consecutive years in the field indicated that Bt transgenic rice root decomposed relatively faster than that of the non-Bt parental rice root under buried condition in the first 200 days.Although genetic modification of plants can offer many benefits, the planting of transgenic crops has raised a number of concerns, including the ecological impact of these plants on decomposition and nutrient cycling processes in agriculture ecosystems. Our results obtained over two consecutive years suggested that the insertion of the cry1Ab gene into the rice genome might result in increasing the rate of rice root decomposition in paddy fields. Attentions need to be paid to the ecological impacts of this phenomenon, especially on nutrient cycling and methane production and flux after its successive incorporated into soil upon harvest. Further studies in the dynamics of the biota associated with root residues is of great significance in assessing its potential effects on microbe-mediated processes and functions in soil.
Starting Page	457
Ending Page	467
Page Count	11
File Format	PDF
ISSN	14390108
Journal	Journal of Soils and Sediments
Volume Number	9
Issue Number	5
e-ISSN	16147480
Language	English
Publisher	Springer-Verlag
Publisher Date	2009-07-02
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Bt transgenic rice Decomposition dynamics Environmental risk Litterbags Rice residues Environmental Physics Environment Soil Science & Conservation
Content Type	Text
Resource Type	Article
Subject	Stratigraphy Earth-Surface Processes

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