Nutrient-Poor Breeding Substrates of Ambrosia Beetles Are Enriched With Biologically Important Elements.

Fungus-farming within galleries in the xylem of trees has evolved independently in at least twelve lineages of weevils (Curculionidae: Scolytinae, Platypodinae) and one lineage of ship-timber beetles (Lymexylidae). Jointly these are termed ambrosia beetles because they actively cultivate nutritional "ambrosia fungi" as their main source of food. The beetles are obligately dependent on their ambrosia fungi as they provide them a broad range of essential nutrients ensuring their survival in an extremely nutrient-poor environment. While xylem is rich in carbon (C) and hydrogen (H), various elements essential for fungal and beetle growth, such as nitrogen (N), phosphorus (P), sulfur (S), potassium (K), calcium (Ca), magnesium (Mg), and manganese (Mn) are extremely low in concentration. Currently it remains untested how both ambrosia beetles and their fungi meet their nutritional requirements in this habitat. Here, we aimed to determine for the first time if galleries of ambrosia beetles are generally enriched with elements that are rare in uncolonized xylem tissue and whether these nutrients are translocated to the galleries from the xylem by the fungal associates. To do so, we examined natural galleries of three ambrosia beetle species from three independently evolved farming lineages, Xyleborinus saxesenii (Scolytinae: Xyleborini), Trypodendron lineatum (Scolytinae: Xyloterini) and Elateroides dermestoides (Lymexylidae), that cultivate unrelated ambrosia fungi in the ascomycete orders Ophiostomatales, Microascales, and Saccharomycetales, respectively. Several elements, in particular Ca, N, P, K, Mg, Mn, and S, were present in high concentrations within the beetles' galleries but available in only very low concentrations in the surrounding xylem. The concentration of elements was generally highest with X. saxesenii, followed by T. lineatum and E. dermestoides, which positively correlates with the degree of sociality and productivity of brood per gallery. We propose that the ambrosia fungal mutualists are translocating essential elements through their hyphae from the xylem to fruiting structures they form on gallery walls. Moreover, the extremely strong enrichment observed suggests recycling of these elements from the feces of the insects, where bacteria and yeasts might play a role.

Elemental composition, heat capacity from 2 to 300 K and derived thermodynamic functions of 5 microorganism species.

Detailed elemental analysis and low-temperature calorimetric measurement results are reported for the first time for Gram-positive bacteria, Gram-negative bacteria and mold fungi. Microorganism unit carbon formulas (empirical formulas) were calculated. Standard molar heat capacity and entropy were found to be C°p,m = 38.200 J/C-mol K and S°m = 31.234 J/C-mol K for Escherichia coli, C°p,m = 54.188 J/C-mol K and S°m = 47.141 J/C-mol K for Gluconobacter oxydans, C°p,m = 31.475 J/C-mol K and S°m = 33.222 J/C-mol K for Pseudomonas fluorescens, C°p,m = 38.118 J/C-mol K and S°m = 37.042 J/C-mol K for Streptococcus thermophilus, and C°p,m = 35.470 J/C-mol K and S°m = 34.393 J/C-mol K for Penicillium chrysogenum. Microorganism heat capacities below 10 K were best described by an expanded Debye-T³ law. Based on the collected data, empirical formulas and entropies per C-mole of the analyzed organisms were determined. The measured heat capacities were compared to predictions of Kopp's rule and Hurst-Harrison equation, both of which were found to be able to give reasonably accurate predictions. The determined entropies were compared to predictions of Battley and Roels models. The Battley model was found to be more accurate. The measured microorganism entropies lay between the values of their principal macromolecular constituents: DNA, and globular and fibrillar proteins. This indicates that self-assembly of the macromolecular components into cellular structures does not lead to decrease in thermal entropy.

Uniform climate sensitivity in tree-ring stable isotopes across species and sites in a mid-latitude temperate forest.

Tree-ring stable isotopes, providing insight into drought-induced eco-physiological mechanisms, are frequently used to reconstruct past changes in growing season temperature and precipitation. Their climatic response is, however, still not fully understood, particularly for data originating from non-extreme, mid-latitude environments with differing ecological conditions. Here, we assess the response of δ(13)C, δ(18)O and tree-ring width (TRW) from a temperate mountain forest in the Austrian pre-Alps to climate and specific drought events. Variations in stem growth and isotopic composition of Norway spruce, common beech and European larch from dry, medium and moist sites are compared with records of sunshine, temperature, moisture, precipitation and cloud cover. Results indicate uniform year-to-year variations in δ(13)C and δ(18)O across sites and species, but distinct differences in TRW according to habitat and species. While the climate sensitivity of TRW is overall weak, the δ(13)C and δ(18)O chronologies contain significant signals with a maximum sensitivity to cloud cover changes (r = -0.72 for δ(18)O). The coherent inter-annual isotopic variations are accompanied by substantial differences in the isotopic signatures with offsets up to ∼3‰ for δ(13)C, indicating species-specific physiological strategies and varying water-use efficiencies. During severe summer drought, beech and larch benefit from access to deeper and moist soils, allowing them to keep their stomata open. This strategy is accompanied by an increased water loss through transpiration, but simultaneously enables enhanced photosynthesis. Our findings indicate the potential of tree-ring stable isotopes from temperate forests to reconstruct changes in cloud cover, and to improve knowledge on basic physiological mechanisms of tree species growing in different habitats to cope with soil moisture deficits.

Nutrient status: a missing factor in phenological and pollen research?

Phenology ranks among the best ecosystem processes for fingerprinting climate change since temperature explains a high percentage of the interannual or spatial variation in phenological onset dates. However, roles of other environmental variables, such as foliar nutrient concentrations, are far from adequately understood. This observational study examined the effects of air temperature and 11 nutrients on spring phenology of Betula pendula Roth (birch) along an urban-rural gradient in Munich, Germany, during the years 2010/2011. Moreover, the influence of temperature, nutrients, and air pollutants (NO2 and O3) on the amounts of pollen and catkin biomass in 2010 was evaluated. In addition to the influence of higher temperatures advancing phenological onset dates, higher foliar concentrations of potassium, boron, zinc, and calcium were statistically significantly linked to earlier onset dates. Since flushing of leaves is a turgor-driven process and all the influential nutrients are involved in cell extension, membrane function, and stability, there might be a reasonable physiological interpretation of the observed association. The amounts of pollen were negatively correlated with temperature, atmospheric NO2, and foliar iron concentration, suggesting that these variables restrict pollen production. The results of this study suggested an influence of nutritional status on both phenology and pollen production. The interaction of urbanization and climate change should be considered in the assessment of the impact of global warming on ecosystems and human health.

Effects of twice-ambient carbon dioxide and nitrogen amendment on biomass, nutrient contents and carbon costs of Norway spruce seedlings as influenced by mycorrhization with Piloderma croceum and Tomentellopsis submollis.

Elevated tropospheric CO(2) concentrations may increase plant carbon fixation. In ectomycorrhizal trees, a considerable portion of the synthesized carbohydrates can be used to support the mutualistic fungal root partner which in turn can benefit the tree by increased nutrient supply. In this study, Norway spruce seedlings were inoculated with either Piloderma croceum (medium distance "fringe" exploration type) or Tomentellopsis submollis (medium distance "smooth" exploration type). We studied the impact of either species regarding fungal biomass production, seedling biomass, nutrient status and nutrient use efficiency in rhizotrons under ambient and twice-ambient CO(2) concentrations. A subset was amended with ammonium nitrate to prevent nitrogen imbalances expected under growth promotion by elevated CO(2). The two fungal species exhibited considerably different influences on growth, biomass allocation as well as nutrient uptake of spruce seedlings. P. croceum increased nutrient supply and promoted plant growth more strongly than T. submollis despite considerably higher carbon costs. In contrast, seedlings with T. submollis showed higher nutrient use efficiency, i.e. produced plant biomass per received unit of nutrient, particularly for P, K and Mg, thereby promoting shoot growth and reducing the root/shoot ratio. Under the given low soil nutrient availability, P. croceum proved to be a more favourable fungal partner for seedling development than T. submollis. Additionally, plant internal allocation of nutrients was differently influenced by the two ECM fungal species, particularly evident for P in shoots and for Ca in roots. Despite slightly increased ECM length and biomass production, neither of the two species had increased its capacity of nutrient uptake in proportion to the rise of CO(2). This lead to imbalances in nutritional status with reduced nutrient concentrations, particularly in seedlings with P. croceum. The beneficial effect of P. croceum thus diminished, although the nutrient status of its host plants was still above that of plants with T. submollis. We conclude that the imbalances of nutrient status in response to elevated CO(2) at early stages of plant development are likely to prove particularly severe at nutrient-poor soils as the increased growth of ECM cannot cover the enhanced nutrient demand. Hyphal length and biomass per unit of ectomycorrhizal length as determined for the first time for P. croceum amounted to 6.9 m cm(-1) and 6.0 µg cm(-1), respectively, across all treatments.

Vertical distribution of an ectomycorrhizal community in upper soil horizons of a young Norway spruce (Picea abies [L.] Karst.) stand of the Bavarian Limestone Alps.

The vertical niche differentiation of genera of ectomycorrhiza (ECM) was assessed in a 17-year-old Norway spruce (Picea abies [L.] Karst.) plantation on a mountainous dolomitic site (1,050 m above sea level) of the Bavarian Limestone Alps. We determined ECM anatomotypes, recorded the abundance of corresponding ECM root tips and classified them into groups of ECM exploration types, which refer to the organisation and the extent of their extramatrical mycelia. The abundance of ECM was highest in the organic soil layers, compared to the mineral soil horizon. The ordination of the ECM communities and of the exploration types revealed segregation related to soil horizon properties. While Cenococcum geophilum preferred the organic soil layers, Lactarius spp., Tomentella spp. and Craterellus tubaeformis were generally most abundant in the mineral soil horizons. Cenococcum geophilum was the predominant species, possibly based on enhanced competitiveness under the prevailing site conditions. The short-distance exploration types (e.g. C. geophilum) preferentially colonised the organic soil layer, whereas the contact types (e.g. most of the Tomentella spp., C. tubaeformis) together with medium-distance types (e.g. Amphinema byssoides) were primarily associated with the underlying A-horizons. Therefore, the soil horizons had an important effect on the distribution of ECM and on their community structure. The spatial niche differentiation of ECM genera and exploration types is discussed in regard to specific physico-chemical properties of soil horizon and the assumed ecophysiological strategies of ECM.

Above-ground space sequestration determines competitive success in juvenile beech and spruce trees.

A 2-yr phytotron study was conducted to investigate the intra- and inter-specific competitive behaviour of juvenile beech (Fagus sylvatica) and spruce (Picea abies). Competitiveness was analysed by quantifying the resource budgets that occur along structures and within occupied space of relevance for competitive interaction. Ambient and elevated CO(2) and ozone (O(3)) regimes were applied throughout two growing seasons as stressors for provoking changes in resource budgets, growth and allocation to facilitate the competition analysis. The hypothesis tested was that the ability to sequester space at low structural cost will determine the competitive success. Spruce was a stronger competitor than beech, as displayed by its higher above-ground biomass increments in mixed culture compared with monoculture. A crucial factor in the competitive success of spruce was its ability to enlarge crown volume at low structural costs, supporting the hypothesis. Interspecific competition with spruce resulted in a size-independent readjustment of above-ground allocation in beech (reduced leaf : shoot biomass ratio). The efficient use of resources for above-ground space sequestration proved to be a parameter that quantitatively reflects competitiveness.