Decomposition of residues and loss of the δ-endotoxin from transgenic (Bt) corn (Zea mays L.) in soil

Abstract

. 2005. Decomposition of residues and loss of the δ-endotoxin from transgenic (Bt) corn (Zea mays L.) in soil. Can. J. Soil Sci. 85: 19-26. Corn and other crops genetically modified to express the insecticidal δ-endotoxin from Bacillus thuringiensis (Bt) are grown widely across north America. Studies have shown that the δ-endotoxin can be stabilised on soil colloids where its activity is retained, but reports of direct ecological effects of the δ-endotoxin on soil processes are limited. We have determined the concentrations of the δ-endotoxin in organic residues from Bt-corn plants at increasing stages of ageing and decay, and the subsequent decomposition in soil of these residues and the δ-endotoxin in them. The δ-endotoxin concentrations declined from 6.8 µg g -1 in the fresh plant material, to 0.82 µg g -1 in the post-harvest residues collected in the fall, and to 0.026 µg g -1 in the residues collected from soil surface the following spring. The concentration of δ-endotoxin in buried residues collected in the spring was not significantly different from zero. When incubated in soil in the laboratory over 84 d, the δ-endotoxin decomposed more rapidly than bulk plant C by factors of 1.85 for the fresh plant materials and 3.21 for the post-harvest residues. Within 14 d of incubation, the δ-endotoxin concentration in the residues collected at the soil surface was below the limit of detection. We contrasted the laboratory decomposition data with data from a field experiment to estimate the period that the δ-endotoxin in corn residues may survive in the field. Based on estimates derived from this comparison, we predict that following an October harvest in eastern Ontario the δ-endotoxin would fall below the detection threshold during November for post-harvest residues. Since stabilisation of the δ-endotoxin on soil colloids depends on it surviving (i.e., not being decomposed) for long enough to be released from the plant residue matrix and come into proximity with colloid surfaces, the rapid decay of the δ-endotoxin suggests that only a small fraction of the δ-endotoxin from post-harvest residues persists long enough to become stabilised in the field. Des études ont montré que la δ-endotoxine se stabilise sur les colloïdes du sol et garde son activité, mais on sait peu de choses au sujet de son incidence écologique sur les processus du sol. Les auteurs ont établi la concentration de δ-endotoxine dans les résidus organiques de plants de maïs Bt à différents stades de vieillissement et de pourrissement ainsi que la décomposition subséquente de ces résidus et de la δ-endotoxine dans le sol. La concentration de δ-endotoxine passe de 6,8 µg par gramme dans les tissus végétaux frais à 0,82 µg par gramme dans les résidus post-messianiques recueillis à l'automne puis à 0,026 µg par gramme dans ceux prélevés à la surface du sol le printemps suivant. La concentration de δ-endotoxine dans les résidus enfouis, prélevés au printemps, ne diffère pas significativement de zéro. Incubée pendant 84 jours dans le sol en laboratoire, ...

Effects of water management practices on residue decomposition and degradation of Cry1Ac protein from crop-wild Bt rice hybrids and parental lines during winter fallow season

“…Similar findings were previously reported by Hopkins and Gregorich (2003) who observed a close relationship between the degradation of water-soluble components and the Bt protein in a 43-day incubation. Moreover, the dynamic of the Cry1Ac protein degradation was significantly correlated with the dynamic of total C as reported by Hopkins and Gregorich (2005), and was weakly correlated with the total N in the rice residue under both conditions, similar to our previous study (Xiao et al, 2014). These results suggest that the Bt protein degraded with the decomposition of the chemical nutrients in the crop residue, and the presence of the Bt protein does not affect the mass decomposition of the crop residue.…”

In-field rates of decomposition and microbial communities colonizing residues vary by depth of residue placement and plant part, but not by crop genotype for residues from two Cry1Ab Bt corn hybrids and their non-transgenic isolines

“…Given the ecological implications of transgenic plant materials decomposing more slowly in soil, and the controversial nature of research in this field, a number of decomposition studies conducted under field conditions have been undertaken in order to elucidate such discrepancies. None of these studies has found significant differences in either lignin content (Jung and Sheaffer, 2004;Griffiths et al, 2007;Tarkalson et al, 2008) or decomposition rates of Cry1Ab Bt residues as compared to non-Bt residues (Lachnicht et al, 2004;Hopkins and Gregorich, 2005;Cortet et al, 2006;Griffiths et al, 2007). Differential rates of decomposition of different plant parts, on the other hand is commonly observed and is expected considering that corn leaves contain more nitrogen (N) than corn stalks (Jung and Sheaffer, 2004;Tarkalson et al, 2008).…”

Request from the European Commission related to the safeguard clause invoked by Austria on maize lines MON863 according to Article 23 of Directive 2001/18/EC

“…Subsequently, there would be further degradation of proteins in the manure due to microbial processes. Even though it has been observed that Cry proteins can bind to certain soil particles (e.g., humic acids, clays) resulting in protection from degradation, a number of studies revealed that there is no accumulation of Cry proteins from GM crops in soil (Herman et al, 2001(Herman et al, , 2002Head et al, 2002;Baumgarte and Tebbe, 2005;Hopkins and Gregorich, 2005;Ahmad et al, 2005;Dubelman et al, 2005;Icoz and Stotzky, 2007;Krogh and Griffiths, 2007;Lawhorn et al, 2009).…”