Investigation of organic anions in tree root exudates and rhizosphere microbial communities using in situ and destructive sampling techniques

Abstract

Purpose - Understanding of the role of low molecular weight organic anions (OAs) in structuring rhizosphere microbial communities in situ is limited due to challenges associated with sampling. Improved techniques are needed for such studies. Methods - This study used in situ and destructive sampling techniques and compared two exudate extraction methods [anion exchange membrane (AEM) capturing and water extraction] from rhizosphere and non-rhizosphere samples of genetically modified (GM) and control Pinus radiata D. Don trees grown in large-scale rhizotrons for ~10 months. Metabolically active soil microbial communities were analysed using rRNA-DGGE. Results - Recovery of eight out of 12 anions was influenced by extraction methods, and in situ sampling using AEM was shown to be the most efficient method. Only minor differences were detected in OAs in root exudates collected from the GM and control trees. Significant differences in α-Proteobacterial and Pseudomonas communities were associated with the two tree lines in the topsoil at both sampling events. Additional differences in β-Proteobacterial and fungal communities between tree lines were detected in the rhizosphere using destructive sampling. Conclusion - This study demonstrated that in situ sampling was superior to destructive sampling for the efficient collection of root exudates and analysis of associated rhizosphere microbial communities.