Background

Bt crops have raised environmental concerns over consequences for sustainability of soil biodiversity and ecosystems services in agricultural land. As Bt crops contain insecticidal proteins potential interactions with non-target organisms are of major concern for the risk assessment. In recent years, numerous field and laboratory studies have been conducted to assess the potential adverse effects of the Bt crops on different non- target organisms including microorganisms living in the soil. Soil microorganisms include primarily bacteria and fungi. They interact with plants and animals and play significant roles in nutrient cycling and energy flow in soils and are actively involved in chemical and biological processes. It is likely that any changes accruing in soil will affect soil microorganisms, and so their abundance/diversity and activities can be used as indicators for many aspects of soil quality, and thus for the assessment of the potential effects Bt crops on the environment.

Methods

The key review question is: Are abundances/diversity/activities of soil microorganisms changed by Bt crops compared with conventional crops? For this purpose relevant literature will be collected systematically through a comprehensive search strategy in a number of general, specialized and personal databases. The search terms will define the locality or type of laboratory/glasshouse study – the field, soil, rhizosphere, the populations - types of soil microorganisms, the exposure - types of Bt proteins, the assessed outcome -abundances/diversity/activity of microorganisms and the crop, will be used for retrieving of relevant studies. We present the criteria against which studies will be included in the review and how they will be assessed. These criteria include appropriate study designs and comparators. This protocol outlines the type of analyses that will be performed to assess bias of the selected studies and if co-variables describing the heterogeneity of the studies introduces biases. The synthesis will be performed as a quantitative synthesis combining the magnitude of potential effects from the individual studies. The synthesis will include assessments of heterogeneity related to the studied abundances/ diversities/activities, types of exposure, methodology, comparators and publication bias.