Wood properties of Populus and Betula in long‐term exposure to elevated CO2 and O3

We studied the interactive effects of elevated concentrations of CO₂ and O₃ on radial growth and wood properties of four trembling aspen (Populus tremuloides Michx.) clones and paper birch (Betula papyrifera Marsh.) saplings. The material for the study was collected from the Aspen FACE (free‐air CO₂ enrichment) experiment in Rhinelander (WI, USA). Trees had been exposed to four treatments [control, elevated CO₂ (560 ppm), elevated O₃ (1.5 times ambient) and combined CO₂ + O₃] during growing seasons 1998–2008. Most treatment responses were observed in the early phase of experiment. Our results show that the CO₂‐ and O₃‐exposed aspen trees displayed a differential balance between efficiency and safety of water transport. Under elevated CO₂, radial growth was enhanced and the trees had fewer but hydraulically more efficient larger diameter vessels. In contrast, elevated O₃ decreased radial growth and the diameters of vessels and fibres. Clone‐specific decrease in wood density and cell wall thickness was observed under elevated CO₂. In birch, the treatments had no major impacts on wood anatomy or wood density. Our study indicates that short‐term impact studies conducted with young seedlings may not give a realistic view of long‐term ecosystem responses.     

Stem wood properties of mature Norway spruce after 3 years of continuous exposure to elevated [CO2] and temperature

The objective of the study was to investigate the interactive effects of elevated atmospheric carbon dioxide concentration, [CO₂], and temperature on the wood properties of mature field-grown Norway spruce ( Picea abies (L.) Karst.) trees. Material for the study was obtained from an experiment in Flakaliden, northern Sweden, where trees were grown for 3 years in whole-tree chambers at ambient (365 μmol mol⁻¹) or elevated [CO₂] (700 μmol mol⁻¹) and ambient or elevated air temperature (ambient +5.6 °C in winter and ambient +2.8 °C in summer). Elevated temperature affected both wood chemical composition and structure, but had no effect on stem radial growth. Elevated temperature decreased the concentrations of acetone-soluble extractives and soluble sugars, while mean and earlywood (EW) cell wall thickness and wood density were increased. Elevated [CO₂] had no effect on stem wood chemistry or radial growth. In wood structure, elevated [CO₂] decreased EW cell wall thickness and increased tracheid radial diameter in latewood (LW). Some significant interactions between elevated [CO₂] and temperature were found in the anatomical and physical properties of stem wood (e.g. microfibril angle, and LW cell wall thickness and density). Our results show that the wood material properties of mature Norway spruce were altered under exposure to elevated [CO₂] and temperature, although stem radial growth was not affected by the treatments.     

Stomatal density, anatomy and nutrient concentrations of Scots pine needles are affected by elevated CO2 and temperature

Stomatal density, anatomy and nutrient concentrations of Scots pine (Pinus sylvestris L.) needles were studied during 3 years of growth at elevated CO₂ (693 ± 30 µmol mol⁻¹), at elevated temperature (ambient +2·8–6·2 °C depending on the time of the year) and in a combination of elevated CO₂ and temperature in closed-top chambers. The treatments were started in August 1996. At elevated temperature, the needles that were grown in the first year (i.e. the 1997 cohort) were thinner, had thinner mesophyll in the abaxial side, thinner vascular cylinder and lower stomatal density than those grown at ambient temperature. The proportion of mesophyll area occupied by vascular cylinder or intercellular spaces were not changed. Lower stomatal density apparently did not lead to decreased use of water, as these needles had higher concentrations of less mobile nutrients (Ca, Mg, B, Zn and Mn), which could indicate increased total transpiration. In the 1997 and 1998 cohorts, elevation of temperature decreased concentrations of N, P, K, S and Cu. In the 1999 cohort, contradictory, higher concentrations of N and S at elevated temperature may be related to increased nutrient mineralization in the soil. Elevation of CO₂ did not affect stomatal density, needle thickness, thickness of epidermis or hypodermis, vascular cylinder or intercellular spaces. Concentrations of N, P, S and Cu decreased at elevated CO₂. Reductions were transient and most distinct in the 1997 cohort. The effects of CO₂ and temperature were in some cases interactive, which meant that in the combined treatment stomatal density decreased less than at elevated temperature, and concentrations of nutrients decreased less than expected on the basis of separate treatments, whereas the thickness of the epidermis and hypodermis decreased more than in the separate treatments. In conclusion, alterations in the anatomy and stomatal density of Scots pine needles were more distinct at elevated temperature than at elevated CO₂. Both elevated CO₂ and temperature-induced changes in nutrient concentrations that partly corresponded to the biochemical and photosynthetic alterations in the same cohorts ( Luomala et al. Plant, Cell and Environment 26, 645–660, 2003 ) Reductions in nutrient concentrations and alterations in the anatomy were transient and more evident in the needle cohort that was grown in the first treatment year.     

Effects of elevated O3, alone and in combination with elevated CO2, on tree leaf chemistry and insect herbivore performance: a meta-analysis

We reviewed the effects of elevated ozone (O₃), alone and in combination with elevated carbon dioxide (CO₂) on primary and secondary metabolites of trees and performance of insect herbivores by means of meta‐analysis. Our database consisted of 63 studies conducted on 22 species of trees and published between 1990 and 2005. Ozone alone had no overall effect on concentrations of carbohydrates or nutrients, whereas in combination with CO₂, elevated O₃ reduced nutrient concentrations and increased carbohydrate concentrations. In contrast to primary metabolites, concentrations of phenolics and terpenes were significantly increased by 16% and 8%, respectively, in response to elevated O₃. Effects of ozone in combination with elevated CO₂ were weaker than those of ozone alone on phenolics, but stronger than those of ozone alone on terpenes. The magnitude of secondary metabolite responses depended on the type of ozone exposure facility and increased in the following order: indoor growth chamber 3 than gymnosperms, as shifts in concentrations of carbohydrate and phenolics were observed in the former, but not in the latter. Elevated O₃ had positive effects on some indices of insect performance: pupal mass increased and larval development time shortened, but these effects were counteracted by elevated CO₂. Therefore, despite the observed increase in secondary metabolites, elevated O₃ tends to increase tree foliage quality for herbivores, but elevated CO₂ may alleviate these effects. Our meta‐analysis clearly demonstrated that effects of elevated O₃ alone on leaf chemistry and some indices of insect performance differed from those of O₃+CO₂, and therefore, it is important to study effects of several factors of global climate change simultaneously.     

Meteorological drivers of the dynamics of autotrophic picoplankton

1. The tiny non‐motile autotrophic picoplankton (APP; size range 0.2–2 μm) occur in all types of aquatic habitats and are comprised of prokaryotic as well as eukaryotic taxa. In the Boreal Zone, the majority of lakes have high concentrations of coloured humic substances that can adversely affect lake light climate and cause steep summertime stratification resulting in epilimnetic nutrient depletion. APP are more effective in nutrient and light acquisition than larger phytoplankton and thus should be competitive in humic lakes. 2. Most lacustrine APP studies have been based on short sampling periods, and thus, interannual variation and its drivers are still unclear. We studied APP in the small, boreal, humic Lake Valkea‐Kotinen during five open‐water periods in 2002–06 to determine interannual variation and the importance of meteorological drivers for APP dynamics. 3. Total APP showed a bimodal annual pattern, but the timing and vertical location of the two maxima varied during the study. In general, APP thrived in warm water and the most important abiotic factor controlling APP was stability of the water column (N_s). On average, 82% of APP were found in the epilimnion or metalimnion during summertime stratification. 4. There was niche separation of APP and larger phytoplankton in the lake because, with only one exception, APP maxima occurred separately from the maxima of larger phytoplankton. 5. Two groups, solitary eukaryotic APP and colonial picocyanobacteria (Merismopedia warmingiana), responded differently to the abiotic factors. Solitary APP preferred high water colour and low pH, both of which occurred after heavy rain, whereas colonial APP did not fare well when water colour was high. Our findings suggest that when future climate change‐related processes increase incoming allocthonous organic matter load from the catchment, solitary eukaryotic APP will be favoured.     

The fragmented Atlantic rain forest of Brazil: size, shape and distribution of forest fragments

The geographical characteristics of a total of 1839 forest fragments surrounded by sugar cane fields were studied in the Brazilian Atlantic rain forest region of the northeastern state of Pernambuco. The size and shape of the fragments as well as inter-fragment distances and the effects of varying edge width were examined using a geographical information system. The analyses show that the fragments are relatively small and close to each other. Approximately 48% of the rain forest fragments are <10 hectares, while only about 7% are >100 hectares. Forest fragments are close to each other, as fragments located 50m or less apart formed groups that included ca. 50% of the total forest area. At 350m inter-fragment distance, 98% of the rain forest area was included in groups of fragments. Due to the small size and irregular shape of the fragments, the total area of edge zone exceeds that of the interior habitat when the edge width is ca. 60m. At an edge width of 300m ca. 94% of the total fragment area is edge zone. For conservation purposes, ways of establishing networks of forest fragments connected by corridors and stepping stone fragments are demonstrated using GIS. Simulations using these techniques show that reforestation of sugar cane fields between the forest fragments would considerably increase the area of interior forest habitat and connectivity between fragments.     

Shift in birch leaf metabolome and carbon allocation during long-term open-field ozone exposure

Current and future ozone concentrations have the potential to reduce plant growth and increase carbon demand for defence and repair processes, which may result in reduced carbon sink strength of forest trees in long‐term. Still, there is limited understanding regarding the alterations in plant metabolism and variation in ozone tolerance among tree species and genotypes. Therefore, this paper aims to study changes in birch leaf metabolome due to long‐term realistic ozone stress and to relate these shifts in the metabolism with growth responses. Two European white birch (Betula pendula Roth) genotypes showing different ozone sensitivity were growing under 1.4–1.7 × ambient ozone in open‐field conditions in Central Finland. After seven growing seasons, the trees were analysed for changes in leaf metabolite profiling, based on 339 low molecular weight compounds (including phenolics, polar and lipophilic compounds, and pigments) and related whole‐tree growth responses. Genotype caused most of the variance of metabolite concentrations, while ozone concentration was the second principal component explaining the metabolome profiling. The main ozone caused changes included increases in quercetin‐phenolic compounds and compounds related to leaf cuticular wax layer, whereas several compounds related to carbohydrate metabolism and function of chloroplast membranes and pigments (such as chlorophyll‐related phytol derivatives) were decreasing. Some candidate compounds such as surface wax‐related squalene, 1‐dotriacontanol, and dotriacontane, providing growth‐related tolerance against ozone were demonstrated. This study indicated that current growth‐based ozone risk assessment methods are inadequate, because they ignore ecophysiological impacts due to alterations in leaf chemistry.     

Do elevated atmospheric CO2 and O3 affect food quality and performance of folivorous insects on silver birch?

The individual and combined effects of elevated CO₂ and O₃ on the foliar chemistry of silver birch (Betula pendula Roth) and on the performance of five potential birch‐defoliating insect herbivore species (two geometrid moths, one lymantrid moth and two weevils) were examined. Elevated CO₂ decreased the water concentration in both short‐ and long‐shoot leaves, but the effect of CO₂ on the concentration of nitrogen and individual phenolic compounds was mediated by O₃ treatment, tree genotype and leaf type. Elevated O₃ increased the total carbon concentration only in short‐shoot leaves. Bioassays showed that elevated CO₂ increased the food consumption rate of juvenile Epirrita autumnata and Rheumaptera hastata larvae fed with short‐ and long‐shoot leaves in spring and mid‐summer, respectively, but had no effect on the growth of larvae. The contribution of leaf quality variables to the observed CO₂ effects indicate that insect compensatory consumption may be related to leaf age. Elevated CO₂ increased the food preference of only two tested species: Phyllobius argentatus (CO₂ alone) and R. hastata (CO₂ combined with O₃). The observed stimulus was dependent on tree genotype and the measured leaf quality variables explained only a portion of the stimulus. Elevated O₃ decreased the growth of flush‐feeding young E. autumnata larvae, irrespective of CO₂ concentration, apparently via reductions in general food quality. Therefore, the increasing tropospheric O₃ concentration could pose a health risk for juvenile early‐season birch folivores in future. In conclusion, the effects of elevated O₃ were found to be detrimental to the performance of early‐season insect herbivores in birch whereas elevated CO₂ had only minor effects on insect performance despite changes in food quality related foliar chemistry.     

Effects of elevated carbon dioxide and ozone on aphid oviposition preference and birch bud exudate phenolics

The effect of atmospheric change on birch aphid ( Euceraphis betulae Koch) oviposition preference was examined and plant characteristics that are possibly responsible for the observed effects were investigated. It was hypothesized that the increasing concentrations of CO₂ and O₃ affect singly or in combination the oviposition of birch aphids via changes in host plant characteristics. Two genotypes of field-growing silver birch ( Betula pendula Roth) trees (clones 4 and 80), which were exposed to doubled ambient concentration of CO₂ and O₃, singly and in combination, in a 3-year open-top chamber experiment, were used in an aphid oviposition preference test. It was found that elevated CO₂, irrespective of ozone concentration, increased the number of aphid eggs laid on clone 4, but not in clone 80. Several flavonoid aglycones were identified from the exudate coating of birch buds. Although elevated CO₂ and O₃ affected these phenolic compounds in clone 4, the effects did not correlate with the observed changes in aphid oviposition. It is suggested that neither bud length, which was not affected by the treatments, nor surface exudate phenolics mediate birch aphid oviposition preference.