Carbon-nitrogen relations of ectomycorrhizal mycelium across a natural nitrogen supply gradient in boreal forest.

The supply of carbon (C) from tree photosynthesis to ectomycorrhizal (ECM) fungi is known to decrease with increasing plant nitrogen (N) supply, but how this affects fungal nutrition and growth remains to be clarified. We placed mesh-bags with quartz sand, with or without an organic N (15 N-, 13 C-labeled) source, in the soil along a natural N supply gradient in boreal forest, to measure growth and use of N and C by ECM extramatrical mycelia. Mycelial C : N declined with increasing N supply. Addition of N increased mycelial growth at the low-N end of the gradient. We found an inverse relationship between uptake of added N and C; the use of added N was high when ambient N was low, whereas use of added C was high when C from photosynthesis was low. We propose that growth of ECM fungi is N-limited when soil N is scarce and tree belowground C allocation to ECM fungi is high, but is C-limited when N supply is high and tree belowground C allocation is low. This suggests that ECM fungi have a major role in soil N retention in nutrient-poor, but less so in nutrient-rich boreal forests.

Translocation of an arctic seashore plant reveals signs of maladaptation to altered climatic conditions.

Ongoing anthropogenic climate change alters the local climatic conditions to which species may be adapted. Information on species' climatic requirements and their intraspecific variation is necessary for predicting the effects of climate change on biodiversity. We used a climatic gradient to test whether populations of two allopatric varieties of an arctic seashore herb (Primula nutans ssp. finmarchica) show adaptation to their local climates and how a future warmer climate may affect them. Our experimental set-up combined a reciprocal translocation within the distribution range of the species with an experiment testing the performance of the sampled populations in warmer climatic conditions south of their range. We monitored survival, size, and flowering over four growing seasons as measures of performance and, thus, proxies of fitness. We found that both varieties performed better in experimental gardens towards the north. Interestingly, highest up in the north, the southern variety outperformed the northern one. Supported by weather data, this suggests that the climatic optima of both varieties have moved at least partly outside their current range. Further warming would make the current environments of both varieties even less suitable. We conclude that Primula nutans ssp. finmarchica is already suffering from adaptational lag due to climate change, and that further warming may increase this maladaptation, especially for the northern variety. The study also highlights that it is not sufficient to run only reciprocal translocation experiments. Climate change is already shifting the optimum conditions for many species and adaptation needs also to be tested outside the current range of the focal taxon in order to include both historic conditions and future conditions.

Dramatic changes in ectomycorrhizal community composition, root tip abundance and mycelial production along a stand-scale nitrogen deposition gradient.

• Nitrogen (N) availability is known to influence ectomycorrhizal fungal components, such as fungal community composition, biomass of root tips and production of mycelia, but effects have never been demonstrated within the same forest. • We measured concurrently the abundance of ectomycorrhizal root tips and the production of external mycelia, and explored the changes in the ectomycorrhizal community composition, across a stand-scale N deposition gradient (from 27 to 43 kg N ha⁻¹ yr⁻¹) at the edge of a spruce forest. The N status was affected along the gradient as shown by a range of N availability indices. • Ectomycorrhizal root tip abundance and mycelial production decreased five and 10-fold, respectively, with increasing N deposition. In addition, the ectomycorrhizal fungal community changed and the species richness decreased. The changes were correlated with the measured indices of N status, in particular N deposition and N leaching. • The relationship between the altered ectomycorrhizal community, root tip abundance and mycelial production is discussed in the context of the N parameters. We suggest that increased N deposition to forests will cause large changes in ectomycorrhizal fungal community structure and functioning, which, in turn, may result in reduced N uptake by roots and fungi, and increased losses of N by leaching.

Growth of ectomycorrhizal mycelia and composition of soil microbial communities in oak forest soils along a nitrogen deposition gradient.

Deciduous forests may respond differently from coniferous forests to the anthropogenic deposition of nitrogen (N). Since fungi, especially ectomycorrhizal (EM) fungi, are known to be negatively affected by N deposition, the effects of N deposition on the soil microbial community, total fungal biomass and mycelial growth of EM fungi were studied in oak-dominated deciduous forests along a nitrogen deposition gradient in southern Sweden. In-growth mesh bags were used to estimate the production of mycelia by EM fungi in 19 oak stands in the N deposition gradient, and the results were compared with nitrate leaching data obtained previously. Soil samples from 154 oak forest sites were analysed regarding the content of phospholipid fatty acids (PLFAs). Thirty PLFAs associated with microbes were analysed and the PLFA 18:2omega6,9 was used as an indicator to estimate the total fungal biomass. Higher N deposition (20 kg N ha(-1)y(-1) compared with 10 kg N ha(-1)y(-1)) tended to reduce EM mycelial growth. The total soil fungal biomass was not affected by N deposition or soil pH, while the PLFA 16:1omega5, a biomarker for arbuscular mycorrhizal (AM) fungi, was negatively affected by N deposition, but also positively correlated to soil pH. Other PLFAs positively affected by soil pH were, e.g., i14:0, a15:0, 16:1omega9, a17:0 and 18:1omega7, while some were negatively affected by pH, such as i15:0, 16:1omega7t, 10Me17:0 and cy19:0. In addition, N deposition had an effect on the PLFAs 16:1omega7c and 16:1omega9 (negatively) and cy19:0 (positively). The production of EM mycelia is probably more sensitive to N deposition than total fungal biomass according to the fungal biomarker PLFA 18:2omega6,9. Low amounts of EM mycelia covaried with increased nitrate leaching, suggesting that EM mycelia possibly play an important role in forest soil N retention at increased N input.

Limited transfer of nitrogen between wood decomposing and ectomycorrhizal mycelia when studied in the field.

Transfer of (15)N between interacting mycelia of a wood-decomposing fungus (Hypholoma fasciculare) and an ectomycorrhizal fungus (Tomentellopsis submollis) was studied in a mature beech (Fagus sylvatica) forest. The amount of (15)N transferred from the wood decomposer to the ectomycorrhizal fungus was compared to the amount of (15)N released from the wood-decomposing mycelia into the soil solution as (15)N-NH(4). The study was performed in peat-filled plastic containers placed in forest soil in the field. The wood-decomposing mycelium was growing from an inoculated wood piece and the ectomycorrhizal mycelium from an introduced root from a mature tree. The containers were harvested after 41 weeks when physical contact between the two foraging mycelia was established. At harvest, (15)N content was analyzed in the peat (total N and (15)NH(4) (+)) and in the mycorrhizal roots. A limited amount of (15)N was transferred to the ectomycorrhizal fungus and this transfer could be explained by (15)NH(4) (+) released from the wood-decomposing fungus without involving any antagonistic interactions between the two mycelia. Using our approach, it was possible to study nutritional interactions between basidiomycete mycelia under field conditions and this and earlier studies suggest that the outcomes of such interactions are highly species-specific and depend on environmental conditions such as resource availability.

Growth and biomass of mycorrhizal mycelia in coniferous forests along short natural nutrient gradients.

Total fungal biomass, the biomass of ectomycorrhizal and ericoid mycorrhizal (EM + ErM), and arbuscular mycorrhizal (AM) fungi, as well as the production of EM and AM fungi, were estimated in coniferous forest soils along four natural nutrient gradients. Plant community changes, forest productivity, soil pH and N availability increase over relatively short distances (< 100 m) along the gradients. The amounts of the phospholipid fatty acid (PLFA) 18 : 2omega6,9 were used to estimate total fungi (not including AM), and the PLFA 16 : 1omega5 to estimate AM fungi in soil samples. The decrease in the PLFA 18 : 2omega6,9 during incubation of soils was used to estimate EM + ErM biomass. Production of AM and EM mycorrhiza was estimated using ingrowth mesh bags. Total fungal biomass was highest in soils with the lowest nutrient availability and tree productivity. Biomass of ErM + EM was also highest in these soils. We found tendencies that EM mycelial production was lowest in the soils with the highest nutrient availability and tree productivity. Production of AM fungi was highest in nutrient-rich soils with high pH. Our results suggest that mycorrhizal communities change from being ErM-, to EM- and finally to AM-dominated along these gradients. The observed changes in mycorrhizal type in the short nutrient gradients follow similar patterns to those suggested for altitudinal or latitudinal gradients over longer distances.

Estimation of the biomass and seasonal growth of external mycelium of ectomycorrhizal fungi in the field.

• In-growth mesh bags were used to quantify the production of external mycelium of ectomycorrhizal (EM) fungi in the field. • Colonization of the mesh bags was followed by visual estimation of the amount of mycelium, and by measuring fungal biomarkers (the phospholipid fatty acid (PLFA) 18 : 2ω6,9 and ergosterol). Mesh bags were placed inside and outside plots that were root isolated in order to estimate the amount of saprotrophic mycelium in relation to EM mycelium. The majority of mycelium in the mesh bags were EM, and this was confirmed by analysis of the δ13 C value in mycelia. • Fungal colonization of mesh bags peaked during autumn. The total amount of EM mycelium produced in the mesh bags during a year was calculated to be between 125 and 200 kg ha-1 . The total amount of EM mycelium (including EM mantles) in the humus was estimated to be 700-900 kg ha-1 . • The biomass of EM mycelium in the soil was in the same range as the biomass of fine roots and peaks of mycelial growth coincided with periods of maximum growth of fine-roots.