Correlation of Activity and Amount of Ribulose 1,5-bisphosphate Carboxylase with Chloroplast Stroma Crystals in Water-Stressed Willow Leaves

Changes in the activity and amount of ribulose 1,5-bisphosphate(RuBP)carboxylase (E.C. 4.1.1.39 [EC] ) were studied in well-watered plantsof Salix ‘aquatica gigantea’ and in similar plantsduring three different water stress treatments and after rewatering.The chloroplast ultrastructure of these plants was examinedby electron microscopy. The amounts of crystallized proteinin the chloroplast stroma were assessed according to the areaof crystal structure seen in the thin sections. RuBP carboxylase activity decreased with decreasing leaf waterpotentials but recovered upon rewatering, except when leaveshad been exposed to severe water stress. The percentage of totalchloroplast area made up of crystal inclusions decreased withdecreasing leaf water potentials. After rewatering, the crystalseither disappeared or the amount decreased markedly. Both RuBPcarboxylase activity and the area of crystal inclusions increasedinitially with increased extractable RuBP carboxylase proteinbut decreased with further increases above 6700–7000 µgRuBP carboxylase protein mg^–1 chlorophyll. In well-wateredand water-stressed plants the activity of RuBP carboxylase,based on amount of chlorophyll, increased with an increasingamount of crystal inclusions in the chloroplast stroma. In rewateredplants no such correlation was observed, and the low percentageof crystal inclusions in the chloroplast area was independentof RuBP carboxylase activity. Key words: Chloroplast stroma crystals, ribulose 1,5-bisphosphate carboxylase, Salix, water stress     

HCO−3 uptake through the roots and its effect on the productivity of willow cuttings

Abstract Young willow plants (Salix‘aquatica gigantea’) were grown in hydroponic culture media, and ¹⁴C–labelled sodium bicarbonate was fed to the roots. Uptake of ¹⁴C-label in the leaves and shoots was assayed after two different feeding periods (6 h, 48 h). Even during the shortest feeding period, ¹⁴C-label had been transferred to the leaves and shoots. Compared with the longer feeding period, after the 6 h feeding period more label was in the form of acid-labile products, whereas after the 48 h feeding period most of the label was in acid-stable products. A second experiment was designed to test whether carbon uptake by roots affects the growth of young willow plants. Uniform rooted cuttings were grown in hydroponic cultures at five different levels of bicarbonate: 0, 0.015, 0.147 0.737, and 1.473 mol m^?3 NaHCO₃. After a 4-week growing period we determined the biomass of leaves, shoots, roots and cuttings. Production of total dry matter (shoots, leaves and roots) increased with increasing bicarbonate concentration. Saturation of dry matter production was reached at 0.737 mol m^?3 NaHCO₃, but a higher concentration of NaHCO₃ (1.470 mol m^?3) caused a slight decrease in the dry matter production. At 0.737 mol m^?3 NaHCO₃ the total dry weight increased by 31.1%, which suggests that uptake of dissolved carbon dioxide through the roots might affect carbon budgeting in young willow plants.     

Photosynthetic Rate in Willow Leaves during Water Stress and Changes in the Chloroplast Ultrastructure, with Special Reference to Crystal Inclusions

The response of CO² uptake and transpiration of individual leavesto intercellular CO² concentration was studied in well-wateredplants of Salix ‘aquatica gigantea’ and in similarplants in three different water stress treatments. Chloroplaststructure was examined by electron microscopy. With decreasingwater potentials, the net CO² uptake decreased at all measuredconcentrations of intercellular CO², which was due mainly toincreased resistance of the mesophyll to CO² diffusion. Twodays after rewatering, in plants suffering from moderate andsevere stress, the CO² uptake had increased at all concentrationsof intercellular CO², but not to the rate of the well-wateredplants. Stomatal resistance had returned to almost the samevalue as for well-watered controls, but factors causing increasedmesophyll resistance reverted more slowly. With electron microscopy,the leaves exposed to water stress showed small changes in thelamellar structure of the chloroplasts. In well-watered plants,the plastoglobuli were small and strongly osmiophilic, but withincreasing water stress they became large and less osmiophilic.Large crystal inclusions were observed in the chloroplast stromain well-watered controls. These crystals were similar to crystalsof ribulose 1,5-bisphosphate carboxylase that have been foundin chloroplasts. With increasing water stress the number ofcrystals decreased; in severely stessed plants, the crystalswere absent. Key words: Photosynthetic rate, Chloroplast ultrastructure, Crystal inclusions.     

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.     

Metabolism of Inorganic Carbon Taken Up by Roots in Salix Plants

The metabolic products of inorganic carbon taken up throughthe roots from nutrient solution were studied in willow plants.Willow cuttings (Salix cv. Aquatica gigantea) were suppliedwith unlabelled or ¹⁴C-labelled NaHC0₃ for 1, 5, 10, and 24h in light or in darkness. After feeding, the plants were dividedinto six samples (upper and lower leaves and corresponding stems,cuttings and roots), which were frozen in liquid N₂. Freeze-driedground samples were extracted into water-soluble, chloroform-solubleand insoluble fractions. The water-soluble fraction was furtherseparated into basic, acidic, and neutral fractions by ion-exchangechromatography. In the light experiment pronase treatment wasused to separate the insoluble fraction into proteins and insolublecarbohydrates. After I h feeding time, most of the ¹⁴C was fixed into organicacids and amino acids both in light and in darkness in all partsof the plants. In the roots a large part of the ^l4C-carbon wasincorporated into the protein and insoluble fractions alreadyduring short feeding times, and the amounts incorporated increasedwith time. In the leaves, after 1 and 5 h the main labelledcompounds were the organic acids and amino acids, but after10 h about half of the total ¹⁴C was in protein and in the insolublefraction. A further analysis of amino acids and organic acidswith HPLC showed that C-4 acids were labelled initially andthat over time the proportion of different acids changed. These results indicate that the metabolism of carbon in rootsmight take place via ß-carboxylation of PEP. Partof the fixed ¹⁴C is transported from the roots, probably asamino acids and organic acids, to the shoot. In roots the C-4acids are metabolized further into structural compounds (proteinsand insoluble carbohydrates). Key words: DIC, Salix, roots, metabolism, HPLC     

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.     

Photosynthetic parameters of birch (Betula pendula Roth) leaves growing in normal and in CO2- and O3- enriched atmospheres

Two silver birch (Betula pendula Roth) clones K1659 and V5952 were grown in open‐top chambers over 3 years (age 7–9 years). The treatments were increased CO₂ concentration (+CO₂, 72 Pa), increased O₃ concentration (+O₃, 2 × ambient O₃ with seasonal AOT40 up to 28 p.p.m. h) and in combination (+CO₂ + O₃). Thirty‐seven photosynthetic parameters were measured in the laboratory immediately after excising leaves using a computer‐operated routine of gas exchange and optical measurements. In control leaves the photosynthetic parameters were close to the values widely used in a model (Farquhar, von Caemmerer and Berry, Planta 149, 78–90, 1980). The distribution of chlorophyll between photosystem II and photosystem I, intrinsic quantum yield of electron transport, uncoupled turnover rate of Cyt b₆f, Rubisco specificity and K_m (CO₂) were not influenced by treatments. Net photosynthetic rate responded to +CO₂ with a mean increase of 17% in both clones. Dry weight of leaves increased, whereas protein, especially Rubisco content and the related photosynthetic parameters decreased. Averaged over 3 years, eight and 17 mechanistically independent parameters were significantly influenced by the elevated CO₂ in clones K1659 and V5952, respectively. The elevated O₃ caused a significant decrease in the average photosynthetic rate of clone V5952, but not of clone K1659. The treatment caused changes in one parameter of clone K1659 and in 11 parameters of clone V5952. Results of the combined treatment indicated that +O₃ had less effect in the presence of +CO₂ than alone. Interestingly, changes in the same photosynthetic parameters were observed in chamberless grown trees of clone V5952 as under +O₃ treatment in chambers, but this was not observed for clone K1659. These results suggest that during chronic fumigation, at concentrations below the threshold of visible leaf injuries, ozone influenced the photosynthetic parameters as a general stress factor, in a similar manner to weather conditions that were more stressful outside the chambers. According to this hypothesis, the sensitivity of a species or a clone to ozone is expected to depend on the growth conditions: the plant is less sensitive to ozone if the conditions are close to optimal and it is more sensitive to ozone under conditions of stress.