Field decomposition of Bt-506 maize leaves and its effect on collembola in the black soil region of Northeast China

The litters from Bt maize are always plowed into the soil after harvest. To clarify whether the decomposition rate of Bt litters and the nontarget soil fauna in the litters are influenced by Bt protein or the other organic matter, the leaf pieces of Bt-506, its near isoline Zheng 58 and a local type Zhengdan 958 were put into litterbags and buried into the field in Northeast China. Then, the Bt protein content of Bt-506 litters, the nonstructural carbohydrate and total nitrogen contents, and decomposition rates of all leaf litters and the collembolan communities in these litters were investigated after a period of buried time. There was 43.5 ng/g Bt protein remained in Bt-506 litters at the end of the experiment, when the Bt-506 litters had been kept in field for decomposition for 7 months. Except for Bt protein, none of the other investigated indexes were significantly different between Bt-506 and Zheng 58 at any sampling time. However, when compared with Zhengdan 958, the leaf litters of Bt-506 and Zheng 58 contained less nonstructural carbohydrate but more total nitrogen, and had lower decomposition rate, lower collembolan abundance and Shannon-Wiener index at some sampling times. Correlation analysis showed that the leaf litter decomposition rate and the collembolan abundance in litters were significantly correlated with the nonstructural carbohydrate content and the total nitrogen content of maize litters on May 20 (after buried in field for 6 months), and neither collembolan abundance nor leaf litter decomposition rate was correlated with maize type at any sampling time. In sum, Bt protein did not affect the decomposition rate of leaf litters and the collembolan community in litters; the differences of leaf litter decomposition rate and the collembolan community in litters between Bt-506, Zheng 58 and Zhengdan 958 were probably resulted from the different contents of nonstructural carbohydrate and total nitrogen in the leaf litters.