Elevated atmospheric CO2 alters root symbiont community structure in forest trees.

• Changes in below-ground ectomycorrhizal (ECM) community structure in response to elevated CO2 and balanced nutrient addition were investigated in a 37-yr-old Picea abies forest. • Trees in whole-tree chambers were exposed to factorial combinations of ambient/elevated CO2 (700 ppm) and fertilization (+/-). ECM fungal community structure was determined in 1997 and 2000 using a combination of morphotyping and molecular analyses. Samples were taken both from chambers and from reference trees receiving the same fertilization treatments but without chambers. • Significant effects on ECM community structure were found in response to elevated CO2 . Neither elevated CO2 nor fertilization altered species richness; however, there was considerable variation among samples, which may have masked treatment effects on individual species. After 3 yr, the effects of elevated CO2 on community composition were of the same magnitude as those seen after 15 yr of fertilization treatment. • Our results show that increasing atmospheric CO2 concentrations affect the community structure of root symbionts colonizing forest trees. The potential effects of altered ECM community structure on allocation and turnover of carbon and nutrients within forest ecosystems are discussed.

Identification of genes for lignin peroxidases and manganese peroxidases in ectomycorrhizal fungi.

• Genes for ligninolytic enzymes, normally associated with white-rot fungi, are shown to be widespread in a broad taxonomic range of ectomycorrhizal (ECM) fungi. • ECM fungi were screened for lignin peroxidase (LiP) and manganese peroxidase (MnP) genes by PCR using primers specific for known isozymes in the white-rot fungus Phanerochaete chrysosporium, with DNA sequencing used to confirm the identity of the amplified fragments. • Genes for LiPs were detected in ECM fungi representing the orders Agaricales, Aphyllophorales, Boletales, Cantharellales, Hymenochaetales, Sclerodermatales, Stereales and Thelephorales. MnP genes were detected in only Cortinarius rotundisporus and three ECM Stereales taxa. • The presence of genes for decomposer activities supports putative evolutionary relationships between ECM and saprotrophic fungi. Expression of the lignolytic genes may facilitate ECM fungal access to nutrients associated with dead plant material in soil and potentially a supplementary carbon supply. Strict functional boundaries between ECM and decomposer fungi may be less clear-cut than previously thought.

Natural 15 N abundance in fruit bodies of ectomycorrhizal fungi from boreal forests.

The 15 N natural abundance and N concentrations of fruit bodies from 70 species (23 genera) of ectomycorrhizal fungi found in boreal forests are presented. Large intraspecific and intrageneric differences were found, e.g. 8.3‰15 N in the species Dermocybe crocea and 12.6‰ in the genus Cortinarius. In addition, significant differences in both δ15 N and %N were found between different parts of fruit bodies, with cap material giving consistently higher values. Proteins and amino acids were enriched by 9.7±0.4‰ (mean ± 1 SE) relative to chitin, irrespective of the part of the fruit body examined. Chitin had δ15 N values similar to that of plant hosts. The higher δ15 N and %N values of the caps than of the stipes probably reflect a higher portion of proteins and amino acids in the caps. The δ15 N of mycorrhizal fungi can be a function of the N species used (organic N, NH4 + , NO3 - ), the depth of soil at which the mycelium occurs, and metabolic fractionations. The metabolic fractionations, e.g. potential transaminations during the flux of N from the soil through the fungus to the plant, make it difficult, at present, to make inferences about sources of N based on δ15 N values alone. No effect of sample drying temperature on δ15 values of fungal material was detected.

Identification of laccase-like genes in ectomycorrhizal basidiomycetes and transcriptional regulation by nitrogen in Piloderma byssinum.

• Ectomycorrhizal (ECM) fungi were screened for laccase-like genes by polymerase chain reaction (PCR) using primers for white rot fungal laccase genes, and expression of the genes was examined by reverse transcriptase polymerase chain reaction (RT-PCR) for Piloderma byssinum in axenic culture under different nutrient conditions. • Laccase-like genes were present in Rhizopogon roseolus along with several Russulales and Atheliaceae taxa, and showed strong nucleotide sequence similarity to laccase genes in white rot fungi. Multiple laccase-like genes were only identified in Piloderma spp. • Laccase-like genes were expressed in Piloderma spp., with transcript levels some six times higher under high nitrogen conditions in P. byssinum than when nitrogen availability was lower. • The potential roles of laccases in nutrient mobilization and/or differentiation of multihyphal ECM fungal structures are discussed.

Intraspecific diversity regulates fungal productivity and respiration.

Individuals and not just species are key components of biodiversity, yet the relationship between intraspecific diversity and ecosystem functioning in microbial systems remains largely untested. This limits our ability to understand and predict the effects of altered genetic diversity in regulating key ecosystem processes and functions. Here, we use a model fungal system to test the hypothesis that intraspecific genotypic richness of Paxillus obscurosporus stimulates biomass and CO(2) efflux, but that this is dependent on nitrogen supply. Using controlled experimental microcosms, we show that populations containing several genotypes (maximum 8) of the fungus had greater productivity and produced significantly more CO(2) than those with fewer genotypes. Moreover, intraspecific diversity had a much stronger effect than a four-fold manipulation of the carbon:nitrogen ratio of the growth medium. The effects of intraspecific diversity were underpinned by strong roles of individuals, but overall intraspecific diversity increased the propensity of populations to over-yield, indicating that both complementarity and selection effects can operate within species. Our data demonstrate the importance of intraspecific diversity over a range of nitrogen concentrations, and the need to consider fine scale phylogenetic information of microbial communities in understanding their contribution to ecosystem processes.

Fungal communities in mycorrhizal roots of conifer seedlings in forest nurseries under different cultivation systems, assessed by morphotyping, direct sequencing and mycelial isolation.

Fungi colonising root tips of Pinus sylvestris and Picea abies grown under four different seedling cultivation systems were assessed by morphotyping, direct sequencing and isolation methods. Roots were morphotyped using two approaches: (1) 10% of the whole root system from 30 seedlings of each species and (2) 20 randomly selected tips per plant from 300 seedlings of each species. The first approach yielded 15 morphotypes, the second yielded 27, including 18 new morphotypes. The overall community consisted of 33 morphotypes. The level of mycorrhizal colonisation of roots determined by each approach was about 50%. The cultivation system had a marked effect on the level of mycorrhizal colonisation. In pine, the highest level of colonisation (48%) was observed in bare-root systems, while in spruce, colonisation was highest in polyethylene rolls (71%). Direct internal transcribed spacer ribosomal DNA sequencing and isolation detected a total of 93 fungal taxa, including 27 mycorrhizal. A total of 71 (76.3%) fungi were identified at least to a genus level. The overlap between the two methods was low. Only 13 (13.9%) of taxa were both sequenced and isolated, 47 (50.5%) were detected exclusively by sequencing and 33 (35.5%) exclusively by isolation. All isolated mycorrhizal fungi were also detected by direct sequencing. Characteristic mycorrhizas were Phialophora finlandia, Amphinema byssoides, Rhizopogon rubescens, Suillus luteus and Thelephora terrestris. There was a moderate similarity in mycorrhizal communities between pine and spruce and among different cultivation systems.