Microbial Communities Poplar Plantation 399 © 2007 ecomed publishers (Verlagsgruppe Hüthig Jehle Rehm GmbH), D-86899 Landsberg and Tokyo • Mumbai • Seoul • Melbourne • Paris J Soils Sediments 7 (6) 399 – 405 (2007) Microbial Communities Structural and Functional Diversity of Soil Microbes is Affected by Elevated [CO 2 ] and N Addition in a Poplar Plantation* Alessandra Lagomarsino 1** , Brigitte A. Knapp 3 , M.Cristina Moscatelli 1 , Paolo De Angelis 2 , Stefano Grego 1 and Heribert Insam 3 1 Dip. di Agrobiologia e Agrochimica, Università della Tuscia, Viterbo, Italy 2 Dip. di Scienze dell'Ambiente Forestale e delle sue Risorse, Università della Tuscia, Viterbo, Italy 3 Institut für Mikrobiologie, Leopold-Franzens-Universität Innsbruck, Austria ** Corresponding author (lagomarsino@unitus.it) ent poplar species were the main factors of variation. The FACE treatment, on average, resulted in lower C utilization rates in un-fertilized soils and higher in fertilized soils. Discussion. Fungal biomass and fungal composition depend on different factors: from previous studies we know that the greater quantity and the higher C/N ratio of organic inputs under el- evated [CO 2 ] influenced positively the fungal biomass both in fertilized and in un-fertilized soil, whereas nitrogen availability resulted to be the main determinant of fungal community com- position in this work. Whole active microbial community was directly influenced by the soil nutrient availability and the pop- lar species. Under elevated CO 2 the competition for N with plants strongly affected the microbial communities, which were not able to benefit from added rhizospheric substrates. Under N- sufficient conditions, the increase of microbial activity due to [CO 2 ] enrichment was related to a more active microbial com- munity, favoured by the current availability of C and N. Conclusions. Different factors influenced the microbial com- munity at different levels: poplar species and root exudates af- fected the functional properties of the microbial community, while the fungal specific composition (as seen with DGGE) re- mained unaffected. On the other hand, factors such as N and C availability had a strong impact on the community functional- ity and composition. Fungal community structure reflected the availability of N in soils and the effect of elevated [CO 2 ] on community structure and function was evident only in N-suffi- cient soils. The simultaneous availability of C and N was there- fore the main driving force for microbial structure and function in this plantation. Recommendations and Perspectives. Using the soil instead of soil extracts for CLPP determination provides a direct measure- ment of substrate catabolism by microbial communities and re- flects activity rather than growth because more immediate re- sponses to substrates are measured. Further applications of this approach could include selective inhibition of different micro- bial functional groups to investigate specific CLPPs. To com- bine the structural analysis and the catabolic responses of spe- cific microbial communities (i.e. fungi or bacteria) could provide new outlooks on the role of microbes on SOM decomposition. Keywords: CLPP; community level physiological profiling; el- evated [CO 2 ]; microbial communities; MicroResp-CLPP; N fer- tilization; PCR-denaturing gradient gel electrophoresis; PCR- DGGE; poplars; soil microbes * ESS-Submission Editor: Dr. Kirk Semple (k.semple@lancaster.ac.uk) DOI: http://dx.doi.org/10.1065/jss2007.04.223 Please cite this paper as: Lagomarsino A, Knapp BA, Mos- catelli MC, De Angelis P, Grego S, Insam H (2007): Structural and Functional Diversity of Soil Microbes is Affected by Elevated [CO 2 ] and N Addition in a Poplar Plantation. J Soils Sediments 7 (6) 399–405 Abstract Background, Aims, and Scope. The genetic structure and the functionality of soil microbes are both important when study- ing the role of soil in the C cycle in elevated CO 2 scenarios. The aim of this work was to investigate the genetic composition of the fungal community by means of PCR-DGGE and the func- tional diversity of soil micro-organisms in general with MicroResp-based community level physiological profiling (CLPP) in a poplar plantation (POPFACE) grown under elevated [CO 2 ] with and without nitrogen fertilization. Materials and Methods. The POPFACE experimental planta- tion and FACE facility are located in central Italy, Tuscania (VT). Clones of Populus alba, Populus nigra and Populus x eur- americana were grown, from 1999 to 2004, in six 314 m 2 plots treated either with atmospheric (control) or enriched (550 μmol mol –1 ) CO 2 with FACE (Free Air CO 2 Enrichment) technology in each growing season. Each plot is divided into six triangular sectors, with two sectors per poplar genotype: three species x two nitrogen levels. After removal of the litter layer one soil core per genotype (10 cm wide, 20 cm depth) was taken inside each of the three sectors in each plot, for a total of 36 soil cores (3 replicates x 2 [CO 2 ] x 2 fertilization x 3 species) in October 2004 and in July 2005. DNA was extracted with a bead beating procedure. 18S rDNA gene fragments were amplified with PCR using fungal primers (FR1 GC and FF390). Analysis of CLPP was performed using the MicroResp method. Carbon substrates were selected depending on their ecological relevance to soil and their solubility in water. In particular rhizospheric C sources (carboxylic acids and carbohydrates) were chosen considering the importance of root inputs for microbial metabolism. Results. The fertilization treatment differentiated the fungal community composition regardless of elevated [CO 2 ] or the poplar species; moreover the number of fungal species was lower in fertilized soil. The effect of elevated [CO 2 ] on the fungal com- munity composition was evident only as interaction with the fertilization treatment as, in N-sufficient soils, the elevated [CO 2 ] selected a different microbial community. For CLPP, the differ-