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  • 1
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The effects of elevated pCO2 on net ecosystem CO2 exchange were investigated in managed Lolium perenne (perennial ryegrass) and Trifolium repens (white clover) monocultures that had been exposed continuously to elevated pCO2 (60 Pa) for nine growing seasons using Free Air CO2 Enrichment (FACE) technology. Two levels of nitrogen (N) fertilization were applied. Midday net ecosystem CO2 exchange (mNEE) and night-time ecosystem respiration (NER) were measured in three growing seasons using an open-flow chamber system. The annual net ecosystem carbon (C) input resulting from the net CO2 fluxes was estimated for one growing season. In both monocultures and at both levels of N supply, elevated pCO2 stimulated mNEE by up to 32%, the exact amount depending on intercepted PAR. The response of mNEE to elevated pCO2 was larger than that of harvestable biomass. Elevated pCO2 increased NER by up to 39% in both species at both levels of N supply. NER, which was affected by mNEE of the preceding day, was higher in T. repens than in L. perenne. High N increased NER compared to low N supply. According to treatment, the annual net ecosystem C input ranged between 210 and 631 g C m−2 year−1 and was not significantly affected by the level of pCO2. Low N supply led to a higher net C input than high N supply. We demonstrated that at the ecosystem level, there was a long-term stimulation in the net C assimilation during daytime by elevated pCO2. However, because NER was also stimulated, net ecosystem C input was not significantly increased at elevated pCO2. The annual net ecosystem C input was primarily affected by the amount of N supplied.
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  • 2
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Gas exchange measurements were carried out on ash and oak trees in a forest plantation during three whole growing seasons characterized by different water availability (2001, 2002 and 2003). A quantitative limitation analysis was applied to estimate the effects of drought and leaf ontogeny on stomatal (SL) and non-stomatal limitations (NSL) to light-saturated net photosynthesis (Amax), relative to the seasonal maximum rates obtained under conditions of optimal soil water content. Furthermore, based on combined gas exchange and chlorophyll fluorescence measurements, NSL was partitioned into a diffusive (due to a decrease in mesophyll conductance, MCL) and a biochemical component (due to a decrease in carboxylation capacity, BL). During the wettest year (2002), the seasonal pattern of both Amax and stomatal conductance (gsw) was characterized in both species by a rapid increase during spring and a slight decline over the summer. However, with a moderate (year 2001) or a severe (year 2003) water stress, the summer decline of Amax and gsw was more pronounced and increased with drought intensity (30–40% in 2001, 60–75% in 2003). The limitation analysis showed that during the spring and the autumn periods SL, MCL and BL were of similar magnitude. By contrast, from the summer data it emerged that all the limitations increased with drought intensity, but their relative contribution changed. At mild to moderate water stress (corresponding to values of gsw 〉 100 mmol H2O m−2 s−1) about two-thirds of the decline in Amax was attributable to SL. However, with increasing drought intensity, NSL increased more than SL and nearly equalled it when the stress was very severe (i.e. with gsw 〈 60 mmol H2O m−2 s−1). Within NSL, MCL represented the main component, except at the most severe water stress levels when it was equalled by BL. It is concluded that diffusional limitations (i.e. SL + MCL) largely affect net assimilation during most of the year, whereas biochemical limitations are quantitatively important only during leaf development and senescence or with severe droughts.
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  • 3
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The pattern of mRNA accumulation of genes coding for the putative potassium transporters HvHAK1A, HvHAK1B, HvHAK2, HvHAK3 and HvAKT1 along seminal roots was studied in K+ starved barley (Hordeum vulgare) plants. Accumulation of these transcripts was lower in young, relative to older root zones, indicating the existence of a coordinated spatial pattern of gene regulation. A study of rubidium (Rb+) uptake kinetics showed that for all root zones transport can be dissected into a linear and a saturable component. Paralleling the pattern of mRNA accumulation the Vmax of the saturable term was lowest in the youngest root zone. No differences in the Rb+ Km or in the linear term were observed among root zones. K+ channel blockers Ba2+, Al3+, and tetraethylammonium exerted no effect on Rb+ uptake from diluted Rb+ solutions, while it was inhibited by Cs+, NH4+, methylamine, and K+ in all root zones. These results show that high-affinity Rb+ transport over the entire axis is mediated by transporters displaying HAK1-like properties. The observation of a differential effect of Na+ on Rb+ uptake along roots is compatible with a change in the proportion and/or the activity of those transport entities following a longitudinal gradient.
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  • 4
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Five cadmium-sensitive insertional mutants, all affected at the CDS1 (‘cadmium-sensitive 1’) locus, have been previously isolated in the unicellular green alga Chlamydomonas reinhardtii. We here describe the cloning of the Cds1 gene (8314 bp with 26 introns) and the corresponding cDNA. The Cds1 gene, strongly induced by cadmium, encodes a putative protein (CrCds1) of 1062 amino acid residues that belongs to the ATM/HMT subfamily of half-size ABC transporters. This subfamily includes both vacuolar HMT-type proteins transporting phytochelatin-cadmium complexes from the cytoplasm to the vacuole and mitochondrial ATM-type proteins involved in the maturation of cytosolic Fe/S proteins. Unlike the Δsphmt1 cadmium-sensitive mutant of Schizosaccharomyces pombe that lacks a vacuolar HMT-type transporter, the cds1 mutant accumulates a high amount of phytochelatin–cadmium complexes. By epitope tagging, the CrCds1 protein was localized in the mitochondria. Even though mitochondria of cds1 do not accumulate important amounts of ‘free’ iron, the mutant cells are hypersensitive to high iron concentrations. Our data show for the first time that a mitochondrial ATM-like transporter plays a major role in tolerance to cadmium.
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  • 5
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Variation in tolerance to nutrient limitations may contribute to the differential success of sugar maple (Acer saccharum Marsh.) and red maple (Acer rubrum L.) on acid soils. The objectives of this study were to examine these relationships as influenced by light environment and test whether sensitivity to nutrient stress is mediated by oxidative stress. First-year sugar maple and red seedlings were grown on forest soil cores contrasting in nutrient availability under high or low light intensity. Foliar nutrition, photosynthesis, growth and antioxidant enzyme activity were assessed. Photosynthesis and growth of sugar maple were significantly lower on nutrient-poor soils and were correlated with leaf nutrient status with Ca and P having the strongest influence. For red maple, only chlorophyll content showed sensitivity to the nutrient-poor soils. High light exacerbated the negative effects of nutrient imbalances on photosynthesis and growth in sugar maple. Antioxidant enzyme activity in sugar maple was highest in seedlings growing on nutrient-poor soils and was inversely correlated with photosynthesis, Ca, P, and Mg concentrations. These results suggest that: (1) sugar maple is more sensitive to nutrient stresses associated with low pH soils than red maple; (2) high light increases sugar maple sensitivity to nutrient stress; (3) the negative effects of nutrient imbalances on sugar maple may be mediated by oxidative stress.
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  • 6
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Isoprene is a biogenic hydrocarbon that has significant effects on tropospheric chemistry. It is emitted by a number of plant species, including kudzu, a leguminous vine that grows profusely in the south-eastern United States. This study investigated development of the capacity for isoprene emission in kudzu. Previous studies examined isoprene emission during leaf development, but a molecular explanation for the observed developmental delay in emission was lacking. This study found that kudzu leaves grown at a high temperature could emit isoprene at least a week before they were fully expanded and 1 d after becoming photosynthetically competent. When grown at low temperature, however, leaves did not emit isoprene until 1 week after they became fully expanded and 2 weeks after the onset of photosynthetic competence. Levels of mRNA and protein for isoprene synthase, which catalyses the final step in isoprene biosynthesis, were investigated; it was found that transcription and translation of this gene began at the same developmental stage as onset of emission in both growth conditions. Therefore, plant growth conditions, not leaf developmental stage, have primary control over expression of isoprene synthase and onset of kudzu isoprene emission. This finding may be useful in modelling early season isoprene emission rates.
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  • 7
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: To test the involvement of ethylene in mediating ozone-induced cell death and leaf loss in European beech (Fagus sylvatica L.), tree seedlings were exposed to proportionally increased or decreased field ozone levels for up to 6 months. Ozone treatment caused cell death and accelerated leaf loss at higher than ambient levels, but had only minor effects at ambient and no effects at subambient ozone levels. The emission of ethylene, the levels of its precursor, 1-aminocyclopropane-1-carboxylate (ACC), and mRNA levels of specific ACC synthase (FS-ACS2) and ACC oxidase (FS-ACO1) isoforms showed a persistent increase and preceded cell death by approximately 2 weeks. Inhibition of ethylene biosynthesis led to reduced lesion formation whereas application of ACC accelerated ozone-induced cell death and leaf loss. Similar results were obtained when adult beech trees were exposed to 2 × ozone by a whole tree free-air canopy exposure system. The results suggest a role of ethylene in amplifying ozone effects under field conditions in this major European broad-leaved tree species.
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  • 8
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Using a combined method of pulse-labelling trees and analysing detailed distribution of 13C tracer within tree rings, we studied how photo-assimilates incorporated on a given day are then distributed in a tree ring. A branch of a 4-year-old Cryptomeria japonica D.Don tree growing in Tsukuba, Japan was pulse-labelled with non-radioactive 13CO2 on two occasions: 29 May 2001 and 18 September 2001. Two discs were cut from the stem on 4 March 2002, one immediately under and the other 0.5 m below the branch and put through high-resolution δ13C analysis. δ13C peaks were observed in both the earlywood and latewood of the concerned tree ring, corresponding to each pulse-labelling date. The earlywood peaks was broader than the latewood peaks, possibly reflecting seasonal variation of the width of wood developing zone. Half-widths of the peaks were measured and used as indicators for the potential time resolution of tree-ring isotope analysis. The half-widths of the peaks indicated a time resolution no finer than 8.7–28 and 33–42 d in the early and latewood, respectively. Holocellulose extraction yielded only a slight change to the shape of the δ13C peaks. 13C tracer pulse-labelled in May and September reached tangentially different locations in the lower disc, suggesting a seasonal change in the pathway of carbohydrates. Local consumption of spring assimilates and long-distance downward transport of autumn assimilates were also suggested.
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  • 9
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Interspecific variation in the response to transfer from low to high growth irradiance with respect to anatomical and photosynthetic characteristics was studied in mature leaves of three tree species, Betula ermanii Cham., Acer rufinerve Sieb. et Zucc. and Fagus crenata Blume, which occur in different successional stages in temperate deciduous forests. Transfer from low to high irradiance increased the light-saturated rate of photosynthesis per unit leaf area (Pmax) significantly in B. ermanii and A. rufinerve, but not in F. crenata. Leaves of B. ermanii grown at low irradiance were relatively thick and had vacant spaces along the mesophyll cell surfaces which was not occupied by chloroplasts or other organelles. After transfer to high irradiance, chloroplasts enlarged to fill the space along with Pmax without an increase in leaf thickness. Leaves of A. rufinerve were plastic in mesophyll cell surface area and in leaf thickness, both of which increased after the transfer to high irradiance, along with an increase in the amount of chloroplasts and in Pmax. On the other hand, F. crenata had little mesophyll cell surface unoccupied by chloroplasts and leaf anatomy was not changed after the transfer. In all species, Pmax was strongly correlated with chloroplast surface area adjacent to the exposed mesophyll surface across different growth irradiances. An increase in Pmax was observed only when chloroplast volume also increased. We conclude that light acclimation potential is primarily determined by the availability of unoccupied cell surface into which chloroplasts expand, as well as by the plasticity of the mesophyll that allows an increase in its surface area.
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  • 10
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Widespread bleaching (chlorosis) of patches of the dominant desert moss Syntrichia caninervis was observed across the northern Mojave Desert in the winter of 2002–03 following an extended period of drought interrupted by small rain events. These rain events were more frequent during the warmer months just prior to the appearance of chlorosis. We hypothesized that the patches were experiencing physiological stress due to partial hydration/rapid dehydration cycling during the warmer months. Compared to unbleached (green) shoots, chlorotic shoots exhibited significantly reduced photochemical performance, photosynthetic pigments, regenerational potential, sex expression, and lower rates of growth and productivity. However, age-specific analyses revealed older leaves from chlorotic shoots did not show the typical decline in vigour, suggesting that stress may primarily affect younger tissues. It is concluded that this chlorosis phenomenon is indicative of physiological stress presently occurring in the Mojave Desert, and is likely due to exposure to a higher than normal frequency of light rain events (〈 3.5 mm), which serve to partially hydrate moss patches that then rapidly desiccate.
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