The effects of high-tannin leaf litter from transgenic poplars on microbial communities in microcosm soils

Richard S Winder,C Peter Constabel,Josyanne Lamarche,Richard C Hamelin

doi:10.3389/fmicb.2013.00290

Abstract

The impacts of leaf litter from genetically modified hybrid poplar accumulating high levels of condensed tannins (proanthocyanidins) were examined in soil microcosms consisting of moss growing on sieved soil. Moss preferentially proliferated in microcosms with lower tannin content; DGGE (denaturing gradient gel electrophoresis) detected increased fungal diversity in microcosms with low-tannin litter. The proportion of cloned rDNA sequences from Actinobacteria decreased with litter addition while Bacteroidetes, Chloroflexi, Cyanobacteria, and α-Proteobacteria significantly increased. β-Proteobacteria were proportionally more numerous at high-tannin levels. Tannins had no significant impact on overall diversity of bacterial communities analyzed with various estimators. There was an increased proportion of N-fixing bacteria corresponding to the addition of litter with low-tannin levels. The addition of litter increased the proportion of Ascomycota/Basidiomycota. Dothideomycetes, Pucciniomycetes, and Tremellomycetes also increased and Agaricomycetes decreased. Agaricomycetes and Sordariomycetes were significantly more abundant in controls, whereas Pucciniomycetes increased in soil with litter from transformed trees (P = 0.051). Richness estimators and diversity indices revealed no significant difference in the composition of fungal communities; PCoA (principal coordinate analyses) partitioned the fungal communities into three groups: (i) those with higher amounts of added tannin from both transformed and untransformed treatments, (ii) those corresponding to soils without litter, and (iii) those corresponding to microcosms with litter added from trees transformed only with a β-glucuronidase control vector. While the litter from transformed poplars had significant effects on soil microbe communities, the observed impacts reflected known impacts on soil processes associated with tannins, and were similar to changes that would be expected from natural variation in tannin levels.

Highlights

With increasing global demand for wood products, interest has grown in methods that could potentially provide trees with promising new and desirable traits for the forest products industry
MACROSCOPIC OBSERVATIONS At the end of the 60-d incubation, it became clear that moss preferentially proliferated in microcosms with lower tannin content (GV, parental wild-type line (PT), and litter-free controls), versus scant growth in microcosms with higher tannin content (HP)
Chloroplast sequences detected in the GUS vector (GV) (KC663735, KC663739), PT (KC663842, KC663928), and higher expression of proanthocyanidins (HP) (KC664033) soil samples corresponded to the moss taxa

Summary

Introduction

With increasing global demand for wood products, interest has grown in methods that could potentially provide trees with promising new and desirable traits for the forest products industry. Concerns about potential risks associated with out-planting genetically modified trees on the landscape have led to regulatory restrictions (bans) on their use in Canada (Hay et al, 2002; van Frankenhuyzen and Beardmore, 2004). Other concerns include the possibility of gene escape (Hay et al, 2002) and the potential for “genetic pollution” of natural populations. These issues are pertinent to the biodiversity of native forest ecosystems, which is considered more valuable than the biodiversity of agro-ecosystems because trees are a long-lived component (Gartland et al, 2003; Halpin et al, 2007). It is important to pay particular attention to the potential “side-effects” that transgenic trees such as poplar might have on their immediate environment, including the soil environment and its key nutrient cycling microbial communities

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