A world revision of Strobilomyia gen.n.: the anthomyiid seed pests of conifers (Diptera: Anthomyiidae)

Abstract. The world species of anthomyiid cone and seed pests are revised. A new genus, Strobilomyia gen.n., is erected for the eighteen species, including seven new to science, presently recognized. Author's views on homologies in the male and female terminalia of Anthomyiidae and other Diptera Cyclorrhapha are amplified as background for the terminology employed. The monophyly and systematic position of Strobilomyia are discussed with reassessions of related genera: Lasiomma Stein, Chirosia Rondani, Egle Robineau-Desvoidy and Acklandia Hennig. Zoogeographic aspects, especially vicariance across the Beringia, are analysed from a partial hypothesis of phylogenetic relationships among the species of Strobilomyia in conjunction with paleo-environmental data. New generic synonyms are: Macrophorbia Malloch, Crinurina Karl, Si-nohylemya Hsue (all =Lasiomma); Acrostilpna Ringdahl, Shakshainia Suwa, Meliniella Suwa (all =Chirosia). The species recognized in Strobilomyia (with geographic range and host trees in parentheses) are: anthracina (Czerny) (Palearctic, Picea); neanthracina sp.n. (Nearctic, Picea and ITsuga); appalachensis sp.n. (E. Nearctic); melania (Ackland) (Europe, Larix); sibirica sp.n. (N.E. Europe, Siberia, Larix); viaria (Huckett) (E. Palearctic, Nearctic, Larix); infrequens (Ackland) (Palearctic, Larix); luteoforceps (Fan & Fang) (E. Palearctic, Larix); baicalensis (Elberg) (E. Palearctic, Larix); laricicola (Karl) (Palearctic, Larix); laricis sp.n. (Nearctic, Larix); macalpinei sp.n. (W. Canada, Larix); carbonaria (Ringdahl) (C. Europe, E. Nearctic, Abies); svenssoni sp.n. (N. Europe, Mongolia); suwai sp.n. (Japan); todocola (Suwa) (Japan, Abies); abietis (Huckett) (Nearctic, Abies); and oriens (Suwa) (E. Palearctic, Abies).     

Benthic resources are the key to Daphnia middendorffiana survival in a high arctic pond

1. Shallow arctic lakes and ponds have simple and short food webs, but large uncertainties remain about benthic–pelagic links in these systems. We tested whether organic matter of benthic origin supports zooplankton biomass in a pond in NE Greenland, using stable isotope analysis of carbon and nitrogen in the pond itself and in a ¹³C‐enrichment enclosure experiment. In the latter, we manipulated the carbon isotope signature of benthic algae to enhance its isotopic discrimination from other potential food sources for zooplankton. 2. The cladoceran Daphnia middendorffiana responded to the ¹³C‐enrichment of benthic mats with progressively increasing δ¹³C values, suggesting benthic feeding. Stable isotope analysis also pointed towards a negligible contribution of terrestrial carbon to the diet of D. middendorffiana. This agreed with the apparent dominance of autochthonous dissolved organic matter in the pond revealed by analysis of coloured dissolved organic matter. 3. Daily net production by phytoplankton in the pond (18 mg C m^?2 day^?1) could satisfy only up to half of the calculated minimum energy requirements of D. middendorffiana (35 mg C m^?2 day^?1), whereas benthic primary production alone (145 mg C m^?2 day^?1) was more than sufficient. 4. Our findings highlight benthic primary production as a major dietary source for D. middendorffiana in this system and suggest that benthic organic matter may play a key role in sustaining pelagic secondary production in such nutrient‐limited high arctic ponds.     

Significance of cold-season respiration and photosynthesis in a subarctic heath ecosystem in Northern Sweden

While substantial cold-season respiration has been documented in most arctic and alpine ecosystems in recent years, the significance of cold-season photosynthesis in these biomes is still believed to be small. In a mesic, subartic heath during both the cold and warm season, we measured in situ ecosystem respiration and photosynthesis with a chamber technique at ambient conditions and at artificially increased frequency of freeze–thaw (FT) cycles during fall and spring. We fitted the measured ecosystem exchange rates to respiration and photosynthesis models with R²-values ranging from 0.81 to 0.85. As expected, estimated cold-season (October, November, April and May) respiration was significant and accounted for at least 22% of the annual respiratory CO₂ flux. More surprisingly, estimated photosynthesis during this period accounted for up to 19% of the annual gross CO₂ uptake, suggesting that cold-season photosynthesis partly balanced the cold-season respiratory carbon losses and can be significant for the annual cycle of carbon. Still, during the full year the ecosystem was a significant net source of 120 ± 12 g C m⁻² to the atmosphere. Neither respiration nor photosynthetic rates were much affected by the extra FT cycles, although the mean rate of net ecosystem loss decreased slightly, but significantly, in May. The results suggest only a small response of net carbon fluxes to increased frequency of FT cycles in this ecosystem.     

Fifteen years of climate change manipulations alter soil microbial communities in a subarctic heath ecosystem

Soil microbial biomass in arctic heaths has been shown to be largely unaffected by treatments simulating climate change with temperature, nutrient and light manipulations. Here, we demonstrate that more than 10 years is needed for development of significant responses, and that changes in microbial biomass are accompanied with strong alterations in microbial community composition. In contrast to slight or nonsignificant responses after 5, 6 and 10 treatment years, 15 years of inorganic NPK fertilizer addition to a subarctic heath had strong effects on the microbial community and, as observed for the first time, warming and shading also led to significant responses, often in opposite direction to the fertilization responses. The effects were clearer in the top 5 cm soil than at the 5–10 cm depth. Fertilization increased microbial biomass C and more than doubled microbial biomass P compared to the non-fertilized plots. However, it only increased microbial biomass N at the 5–10 cm depth. Fertilization increased fungal biomass and the relative abundance of phospholipid fatty acid (PLFA) markers of gram-positive bacteria. Warming and shading decreased the relative abundance of fungal PLFAs, and shading also altered the composition of the bacterial community. The long time lag in responses may be associated with indirect effects of the gradual changes in the plant biomass and community composition. The contrasting responses to warming and fertilization treatments show that results from fertilizer addition may not be similar to the effects of increased nutrient mineralization and availability following climatic warming.     

Reduced N cycling in response to elevated CO2, warming,and drought in a Danish heathland: Synthesizing results of the CLIMAITE project after two years of treatments

Field‐scale experiments simulating realistic future climate scenarios are important tools for investigating the effects of current and future climate changes on ecosystem functioning and biogeochemical cycling. We exposed a seminatural Danish heathland ecosystem to elevated atmospheric carbon dioxide (CO₂), warming, and extended summer drought in all combinations. Here, we report on the short‐term responses of the nitrogen (N) cycle after 2 years of treatments. Elevated CO₂ significantly affected aboveground stoichiometry by increasing the carbon to nitrogen (C/N) ratios in the leaves of both co‐dominant species (Calluna vulgaris and Deschampsia flexuosa), as well as the C/N ratios of Calluna flowers and by reducing the N concentration of Deschampsia litter. Belowground, elevated CO₂ had only minor effects, whereas warming increased N turnover, as indicated by increased rates of microbial NH₄⁺ consumption, gross mineralization, potential nitrification, denitrification and N₂O emissions. Drought reduced belowground gross N mineralization and decreased fauna N mass and fauna N mineralization. Leaching was unaffected by treatments but was significantly higher across all treatments in the second year than in the much drier first year indicating that ecosystem N loss is highly sensitive to changes and variability in amount and timing of precipitation. Interactions between treatments were common and although some synergistic effects were observed, antagonism dominated the interactive responses in treatment combinations, i.e. responses were smaller in combinations than in single treatments. Nonetheless, increased C/N ratios of photosynthetic tissue in response to elevated CO₂, as well as drought‐induced decreases in litter N production and fauna N mineralization prevailed in the full treatment combination. Overall, the simulated future climate scenario therefore lead to reduced N turnover, which could act to reduce the potential growth response of plants to elevated atmospheric CO₂ concentration.     

Long‐term warming and litter addition affects nitrogen fixation in a subarctic heath

Nitrogen (N) availability is the main constraint on primary production in most Arctic ecosystems, with microbial fixation of atmospheric N as the primary source of N input. However, there are only few reports on N fixation rates in relation to climate change in the Arctic. In order to investigate the effects of anticipated global climate change on N fixation rates in a subarctic moist heath, a field experiment was carried out in Northern Sweden. Warming was induced by plastic tents, and in order to simulate the effects of future increased tree cover, birch litter was added each fall for 9 years before the measurements. We analyzed N fixation rates on both whole‐ecosystem level and specifically on two moss species: Sphagnum warnstorfii and Hylocomium splendens. The whole‐ecosystem N fixation of the warmed plots almost tripled compared with the control plots. However, in the Sphagnum and Hylocomium mosses we observed either no change or occasionally even a decrease in N fixation after warming. Both measured on whole‐ecosystem level and on the two moss species separately, litter addition increased N fixation rates. The results suggest that warming will lead to a general increased ecosystem N input, but also that the N fixation associated to some moss species is likely to decrease. Hence, this study shows that the scale of measurements is crucial when investigating on ecosystem responses to manipulations.     

Responses of fungal root colonization,plant cover and leaf nutrients to long‐term exposure to elevated atmospheric CO2 and warming in a subarctic birch forest understory

Responses of the mycorrhizal fungal community in terrestrial ecosystems to global change factors are not well understood. However, virtually all land plants form symbiotic associations with mycorrhizal fungi, with approximately 20% of the plants' net primary production transported down to the fungal symbionts. In this study, we investigated how ericoid mycorrhiza (ErM), fine endophytes (FE) and dark septate endophytes (DSE) in roots responded to elevated atmospheric CO₂ concentrations and warming in the dwarf shrub understory of a birch forest in the subarctic region of northern Sweden. To place the belowground results into an ecosystem context we also investigated how plant cover and nutrient concentrations in leaves responded to elevated atmospheric CO₂ concentrations and warming. The ErM colonization in ericaceous dwarf shrubs increased under elevated atmospheric CO₂ concentrations, but did not respond to warming following 6 years of treatment. This suggests that the higher ErM colonization under elevated CO₂ might be due to increased transport of carbon belowground to acquire limiting resources such as N, which was diluted in leaves of ericaceous plants under enhanced CO₂. The elevated CO₂ did not affect total plant cover but the plant cover was increased under warming, which might be due to increased N availability in soil. FE colonization in grass roots decreased under enhanced CO₂ and under warming, which might be due to increased root growth, to which the FE fungi could not keep up, resulting in proportionally lower colonization. However, no responses in aboveground cover of Deschampsia flexuosa were seen. DSE hyphal colonization in grass roots significantly increased under warmer conditions, but did not respond to elevated CO₂. This complex set of responses by mycorrhizal and other root‐associated fungi to global change factors of all the fungal types studied could have broad implications for plant community structure and biogeochemistry of subarctic ecosystems.