Decomposition of leaf litter from chitinase transgenic silver birch (Betula pendula) and effects on decomposer populations in a field trial

Although the area under cultivation of genetically modified plants (GMPs) has substantially increased during the last decade, the effects of transgenic organisms on ecosystem processes (such as litter decomposition and nutrient cycling) largely remain unknown. In this study, the decomposition of leaf litter from transgenic birch trees (Betula pendula) expressing sugar beet chitinase IV gene was studied in a field experiment. Eight chitinase transgenic lines and a non-transgenic control were included in the study. The decomposition of these litters was investigated by studying: (i) litter mass loss, (ii) fungal (litter ergosterol content) and total microbial biomass (SIR) and their activity (basal respiration), and (iii) the effects of transgenic litter on microbial-feeding soil fauna (number of nematodes and abundance of different functional groups). At the end of the study (8 and 11 months after establishment) mass loss of chitinase transgenic leaf litter did not differ from that of non-transgenic control trees. Similarly, no differences in either the fungal or total microbial biomass between the treatments were recorded. A single transgenic line showing high chitinase IV expression differed significantly from the controls in the mean number of nematodes. The nematode populations in this litter showed distinct temporal dynamics compared to the controls, thus indirectly indicating microbial differences in the litter. The results of this study indicate that conceivable changes, possibly derived from pleiotropic effects due to gene modification, in the litter quality due to gene transformation are either absent or too weak to affect the decomposability of the litter in the soil.