ORIGINAL ARTICLE Decomposition and Fungi of Needle Litter from Slow- and Fast-growing Norway Spruce (Picea abies) Clones Tiina Korkama-Rajala & Michael M. Müller & Taina Pennanen Received: 29 June 2007 / Accepted: 24 September 2007 / Published online: 18 October 2007 # Springer Science + Business Media, LLC 2007 Abstract The fungal species involved in the decomposi- tion of needle litter and their response to intraspecific genetic variation of trees are poorly known. First, we compared the needle decomposition and fungal decomposers underneath eight different Norway spruce clones in situ. This experi- ment revealed 60-70% loss of needle mass in two years. Although spruce clones differed considerably in growth (twofold height difference) and their needles differed in chemical composition, no significant difference was found for loss of needle mass under the spruce clones. Further- more, the spruce clones did not affect the community struc- ture of the fungal decomposers. Fungi inhabiting needle litter were identified by extracting ribosomal RNA (rRNA) and sequencing complementary DNA (cDNA) of internal trascribed spacer 1 (ITS1) region. The most frequent iden- tifications were Lophodermium, Pezizales, Mycena, and Marasmius, suggesting that endophytic fungi were involved in the decomposition process. Second, we evaluated the potential of endophytes to decompose needle material in a microcosm experiment in which all other fungi than endo- phytes were excluded. Within 2 years, the endophytes had decomposed 35-45% of the needle mass. Sequences of Mollisia, Lophodermium, Lachnum, and Phialocephala were most frequently found in rRNA and rDNA extracted from the needles at the end of the microcosm experiment. The dominant needle endophyte in fresh, green needles was Lophodermium piceae, and this species was also found frequently in the needle material after 2 years of decay both in the field and laboratory experiments. Moreover, the relative abundance of Lophodermium-derived denaturing gradient gel electrophoresis (DGGE) bands correlated posi- tively with the decomposition in the microcosm experiment. Hence, our results suggest a significant role of endophytic fungi, and particularly L. piceae, in the process of needle decomposition in boreal forests. Introduction In boreal forests, fungi are particularly important litter de- composers because of their acidity tolerance and enzyme activities [12, 20]. Endophytic fungi commonly inhabit co- niferous needles without showing any external signs of their presence or causing any symptoms of disease [53]. The ecological role of endophytes is not clear, but as they are often found in the litter layer [24, 26, 32], they may par- ticipate in nutrient re-translocation and primary decomposi- tion [25, 33]. It is well known that temperature, moisture, various site properties, and the quality of litter collectively influence the community structure of microbial decomposers and their activity (e.g., [4, 37, 52]). Providing that endo- phytic fungi play a significant role in needle decomposition, factors controlling endophytic colonization may also affect decomposition rate. In general, endophyte colonization is influenced by host species, host genotype, microclimatic conditions, and age of the needle [10, 11, 18, 42, 48]. Loss of mass determined by the litter bag technique is widely used to estimate decomposition rate in the field (e.g., [6, 8, 13, 45]). Although this technique has proven useful in demonstrating variation in decomposition, it cannot discern the relative importance of the various microbial species in needle litter decomposition. DNA sequencing has enabled the detection and identification of microbes in litter layer but it does not permit the discrimination of active and functionally Microb Ecol (2008) 56:76–89 DOI 10.1007/s00248-007-9326-y T. Korkama-Rajala (*) : M. M. Müller : T. Pennanen Vantaa Research Unit, Finnish Forest Research Institute (Metla), P.O. Box, 18, 01301 Vantaa, Finland e-mail: tiina.rajala@metla.fi