Photosynthetic responses of Eucalyptus nitens (Deane and Maiden) Maiden to green pruning

 Three-year-old Eucalyptus nitens (Deane and Maiden) Maiden trees and 1-year-old ramets of a single clone of E. nitens were pruned to remove 0, 50% or 70% of the green crown length. This was equivalent to removal of 0, 55% or 88% of foliage area of trees, and 0, 77% or 94% of foliage area of ramets. CO₂ assimilation (A) and stomatal conductance (g_s) were measured at constant illumination in five height zones and three foliage-age classes of trees over a 16-month period following pruning. Foliar nitrogen (N) and phosphorus (P) concentrations were determined for each measurement time during the first 12 months of the experiment. In ramets A and g_s were measured in four height zones and two foliage-age classes over a six-week period, and N and P concentrations were measured only once, at the end of the experiment. Rates of A increased by up to 175% following pruning. This response occurred throughout the canopy irrespective of position in the crown or foliage age. The magnitude of the response was generally greater in ramets than in trees, and increased with increasing severity of pruning. The initiation of the response was later, and the duration of the response was longer, in trees than ramets. In the lower crown of trees there was evidence of delayed senescence following pruning. Photosynthetic enhancement was not related to changes in foliar N concentrations. The ratio of A/N increased in many zones following pruning, especially after more severe defoliation. There was no evidence that changes in P concentrations were responsible for the result. The increases in A may have been related to changes in g_s, as maximum values of g_s were greater, and the ratio of A/g_s was generally lower, in pruned than unpruned plants. Received: 31 December 1996 / Accepted: 19 August 1997     

Effect of nitrogen application on growth and photosynthetic nitrogen use efficiency in two ecotypes of wild strawberry, Fragaria chiloensis

The relationships between increasing nitrogen fertilization and growth, maximum CO₂ assimilation and the initial slope of the CO₂ response curve were studied in 2 ecotypes of wild strawberry, Fragaria chiloensis (L.) Duchn. Nitrogen accumulation of CA11, an ecotype from a low-nutrient dune site, was greater at all nitrogen concentrations than that of RCP37, an ecotype from a higher-nutrient strand site. Maximum CO₂ assimilation, total Rubisco activity, dry weight, and initiation of leaves and crowns were higher in CAI1 than RCP37 as nitrogen treatment was increased from 0 to 200 mg ^l-1, whereas these parameters were lower in CAl1 when fertilized at 300 mg T¹, but not in RCP37. The mean leaf area of CA11 was greater than RCP37 when grown with no supplemental nitrogen, but mean leaf area of the 2 lines was similar under nitrogen fertilization. Maximum CO₂ assimilation and carboxylation efficiency increased with increasing leaf nitrogen in both clones. At equivalent concentrations of leaf nitrogen, RCP37 had higher CO₂ assimilation and carboxylation efficiency than CA11 and the difference between the 2 clones increased as ieaf nitrogen increased. Thus, RCP37 had a higher photosynthetic nitrogen use efficiency than CA11. However, at a given applied nitrogen level, CA11 allocated more nitrogen to a unit of leaf area so that photosynthetic rates were higher than RCP37, except at the highest application of 300 mg ^l-1. The high nitrogen accumulation capacity and resource allocation to fruiting structures (crowns) in CA11 leads us to suggest that this clone may possess genes that could increase fruit yield in cultivated strawberry.     

The influence of drought on the relationship between leaf and conducting sapwood area in Eucalyptus globulus and Eucalyptus nitens

 Development of the relationship between leaf area (A _l ) and sapwood area (A _s ) was investigated in two important hardwoods, Eucalyptus globulus (Labill) and E. nitens (Deane and Maiden) Maiden, growing in an experimental plantation established in a low rainfall zone (approx. 515 mm year^–1) of Tasmania. The experiment compared irrigated controls and a rainfed treatment which was subjected to cyclical summer droughts from age 1 to 6 years old. Leaf area and sapwood area were determined by destructive sampling at ages 2, 3 and 6 years old. There was no effect of stand age on A _l :A _s when sapwood area was measured at crown break. At age 3 years old A _l :A _s was significantly greater in the rainfed than the irrigated trees. It was concluded that this difference was due to earlier canopy closure in the irrigated trees. When the plantation was 6 years old A _l :A _s was significantly greater in the irrigated than the rainfed treatment. An analysis based on an equation which links A _l :A _s with transpiration and volumetric flow rate (Whitehead et al. 1984) was used to infer a positive correlation between stem hydraulic conductivity (k _h ) and water availability. Independent of water availability E. globulus maintained a higher A _l :A _s than E. nitens at all ages. Received: 20 March 1997 / Accepted: 30 December 1997     

冰冻对珊瑚树(Viburnum odoratissimum)叶片光合效率的影响

光合作用的冰冻伤害研究大多利用离体叶片、原生质体,甚至叶绿体类囊体进行人工冰冻预处理,关于室外自然温度下出现的植物光合作用冰冻伤害,特别是冰冻影响光合量子效率的研究报告还很少。虽然光合碳同化受抑是最早可以测到的冰冻伤害征状,但其机理迄今不清楚(Krause等1982,Krause和Klosson1983)。     

Interactive effect of CO2 enrichment and temperature on the photosynthesis of field-grown hinoki cypress (Chamaecyparis obtusa) branches

Two branches of a field-grown Chamaecy-paris obtusa tree were enclosed in chambers of an open gas exchange system for continuous CO₂ exchange measurements. One branch was subjected to ambient air (CO₂, 370 μmol mol^–1) and the other was subjected to CO₂-enriched air (800 μmol mol^–1). The CO₂ exchange rate of the branches, air temperature and photosynthetic photon flux density were recorded every 4 min by a computer during the two experimental periods of July 1994 to June 1995 (experiment 1) and April 1996 to August 1997 (experiment 2). The response of CO₂ gas exchange rate to light changed with the seasonal temperature. The highest saturated rate of net photosynthesis on a leaf area basis was observed in May and October in both CO₂ treatments when the mean daytime temperature was about 18–19°C. This temperature was almost equal to the yearly mean daytime temperature. Above and below this temperature, the saturated net photosynthesis rate decreased. The net photosynthesis rate was usually higher in the elevated CO₂ treatment. The ratio of monthly net photosynthesis rate in elevated CO₂ to that in ambient CO₂ was linearly related to the monthly mean daytime temperature. This ratio increased by 3.3% for each 1°C increase in the monthly mean daytime temperature; the highest ratio of 1.8 occurred in August. When the ratio was 1.0, the temperature was about 5–6°C, which was close to the mean daytime temperature of the coldest month. Elevated CO₂ increased per unit area net photosynthesis by 38.5% and 43.7% in experiments 1 and 2, respectively. Received: 29 March 1999 / Accepted: 22 October 1999     

Control of carbon partitioning and photosynthesis by the triose phosphate/phosphate translocator in transgenic tobacco plants (Nicotiana tabacum L.). I. Comparative physiological analysis of tobacco plants with antisense repression and overexpression of the triose phosphate/phosphate translocator

 The physiological properties of transgenic tobacco plants (Nicotiana tabacum L.) with decreased or increased transport capacities of the chloroplast triose phosphate/phosphate translocator (TPT) were compared in order to investigate the extent to which the TPT controls metabolic fluxes in wild-type tobacco. For this purpose, tobacco lines with an antisense repression of the endogenous TPT (αTPT) and tobacco lines overexpressing the TPT gene isolated from the C₄ plant Flaveria trinervia (FtTPT) were used. The F. trinervia TPT expressed in yeast cells exhibited transport characteristics identical to the TPT from C₃ plants. Neither antisense TPT plants nor FtTPT overexpressors showed a phenotype when grown in a greenhouse in air. Contents of starch and soluble sugars in upper source leaves were similar in TPT underexpressors and FtTPT overexpressors compared to the wild type at the end of the photoperiod. The FtTPT overexpressors incorporated more ¹⁴CO₂ in sucrose than the wild type, indicating that the TPT limits sucrose biosynthesis in the wild type. There were only small effects on labelling of amino acids and organic acids. The mobilisation of starch was enhanced in αTPT lines but decreased in FtTPT overexpressors compared to the wild type. Enzymes involved in starch mobilisation or utilisation, such as α-amylase or hexokinase were increased in αTPT plants and, in the case of amylases, decreased in FtTPT overexpressors. Moreover, α-amylase activity exhibited a pronounced diurnal variation in αTPT lines with a maximum activity after 8 h in the light. These changes in starch hydrolytic activities were confirmed by activity staining of native gels. Activities of glucan phosphorylases were unaffected by either a decrease or an increase in TPT activity. There were also effects of TPT activities on steady-state levels of phosphorylated intermediates as well as total amino acids and malate. In air, there was no or little effect of altered TPT transport activity on either rates of photosynthetic electron transport and/or CO₂ assimilation. However, in elevated CO₂ (1500 μl · l⁻¹) and low O₂ (2%) the rate of CO₂ assimilation was decreased in the αTPT lines and was slightly higher in FtTPT lines. This shows that the TPT limits maximum rates of photosynthesis in the wild type. Received: 26 March 1999 / Accepted: 21 August 1999     

The impact of elevated CO2 on growth and photosynthesis in Agrostis canina L. ssp. monteluccii adapted to contrasting atmospheric CO2 concentrations

 The aim of this study was to characterise growth and photosynthetic capacity in plants adapted to long-term contrasting atmospheric CO₂ concentrations (C _a). Seeds of Agrostis canina L. ssp. monteluccii were collected from a natural CO₂ transect in central-western Italy and plants grown in controlled environment chambers at both ambient and elevated CO₂ (350 and 700 μmol mol⁻¹) in nutrient-rich soil. Seasonal mean C _a at the source of the plant material ranged from 610 to 451 μmol CO₂ mol⁻¹, derived from C₄ leaf stable carbon isotope discrimination (δ¹³C). Under chamber conditions, CO₂ enrichment stimulated the growth of all populations. However, plants originating from elevated C _a exhibited higher initial relative growth rates (RGRs) irrespective of chamber CO₂ concentrations and a positive relationship was found between RGR and C _a at the seed source. Seed weight was positively correlated with C _a, but differences in seed weight were found to explain no more than 34% of the variation in RGRs at elevated CO₂. Longer-term experiments (over 98 days) on two populations originating from the extremes of the transect (451 and 610 μmol CO₂ mol⁻¹) indicated that differences in growth between populations were maintained when plants were grown at both 350 and 700 μmol CO₂ mol⁻¹. Analysis of leaf material revealed an increase in the cell wall fraction (CWF) in plants grown at elevated CO₂, with plants originating from high C _a exhibiting constitutively lower levels but a variable response in terms of the degree of lignification. In vivo gas exchange measurements revealed no significant differences in light and CO₂ saturated rates of photosynthesis and carboxylation efficiency between populations or with CO₂ treatment. Moreover, SDS-PAGE/ LISA quantification of leaf ribulose bisphosphate carboxylase/oxygenase (Rubisco) showed no difference in Rubisco content between populations or CO₂ treatments. These findings suggest that long-term adaptation to growth at elevated CO₂ may be associated with a potential for increased growth, but this does not appear to be linked with differences in the intrinsic capacity for photosynthesis. Received: 16 August 1996 / Accepted: 19 October 1996     

Adventitious shoot regeneration in cultures of Humulus lupulus L. (hop) cvs. Brewers Gold and Nugget

 A very efficient protocol for plant regeneration from two commercial Humulus lupulus L. (hop) cultivars, Brewers Gold and Nugget has been established, and the morphogenetic potential of explants cultured on Adams modified medium supplemented with several concentrations of cytokinins and auxins studied. Zeatin at 4.56 μm produced direct caulogenesis and caulogenic calli in both cultivars. Subculture of these calli on Adams modified medium supplemented with benzylaminopurine (4.4 μm) and indolebutyric acid (0.49 μm) promoted shoot regeneration which gradually increased up to the third subculture. Regeneration rates of 60 and 29% were achieved for Nugget and Brewers Gold, respectively. By selection of callus lines, it has been possible to maintain caulogenic potential for 14 months. Regenerated plants were successfully transferred to field conditions. Received: 10 March 1997 / Revision received: 12 November 1997 / Accepted: 22 November 1998     

Symbiotic properties of Lotus pedunculitis root nodules induced by Rhizobium loti and Bradyrhizobium sp. (Lotus)

Vance, C. P., Reibach, P. H. and Pankhurst, C. E. 1987. Symbiotic properties of Lotus pedunculatus root nodules induced by Rhizobium loti and Bradyrhizobium sp. ( Lotus ).
Symbiotic properties of root nodules were evaluated in glasshouse-grown Lotus pedunculatus Cav. cv. Maku inoculated with either a fast-growing Rhizobium loti strain NZP2037 or a slow-growing Bradyrhizobium sp. ( Lotus ) strain CC814s. Although the nodule mass of plants inoculated with NZP2037 was twice that of plants inoculated with CC814s, the yield of NZP2037 shoots and roots was 50% that of CC814s shoots and roots. Nodules induced by Bradyrhizobium fixed substantially more N than nodules induced by R. loti. Glucose requirements [mol glucose (mol N₂ fixed)^-1] of nodules induced by CC814s and NZP2037 were 7.1 and 16.6, respectively. Nodule enzymes of carbon and nitrogen assimilation reflected the disparity of the two sym-bioses. Xylem sap of the symbiosis with the higher yield contained a higher concentration of asparagine [9.86 μmol (ml xylem sap)'] than did the lower yielding symbiosis [5.80 umol (ml xylem sap)']. Nodule CO₂ fixation was directly linked to nodule N assimilation in both symbioses. The results indicate that the difference between the two symbioses extend to nodule N and C assimilation and whole plant N transport. The data support a role for host plant modulation of bacterial efficiency and assimilation of fixed N.     

The effects of elevated CO2 atmospheres on the nutritional quality of Eucalyptus foliage and its interaction with soil nutrient and light availability

 Seedlings of Eucalyptus tereticornis (Smith) were grown under two levels of availability each of CO₂ (352 and 793 μmol mol⁻¹), soil nutrients (1/24 and 1/4 Hoagland’s solution) and light (full and 30% sunlight). Low soil nutrient availability or high light increased the C:N ratio of leaves, leading to lower leaf nitrogen concentrations, higher leaf specific weights and higher levels of both total phenolics and condensed tannins. These results were consistent with other studies of the effect of environmental resource availability on foliage composition. Similar results were observed when the C:N ratio of leaves was increased under elevated CO₂. The changes in leaf chemistry induced by the treatments affected the performance of 4th-instar larvae of Chrysophtharta flaveola (Chapuis) fed on the leaves. Increased C:N ratios of leaves reduced digestive efficiencies and pupal body sizes and increased mortality. Below a threshold nitrogen concentration of approximately 1% dry mass, severe reductions in the performance of larvae were recorded. Such changes may have significant consequences for herbivores of Eucalyptus, particularly in view of projected increases in atmospheric CO₂. Received: 8 January 1996 / Accepted: 26 June 1996     

Escape of volcanic gas into shallow groundwater systems at Unzen Volcano (Japan): evidence from chemical and stable carbon isotope compositions of dissolved inorganic carbon

 Chemical and stable carbon isotopic analyses of dissolved inorganic carbon (DIC) were carried out for groundwater samples collected from cold springs and shallow wells in the Unzen volcanic region in 1999 and 2000. All of the data sets plotted on the carbon isotope ratio (δ¹³C) vs 1/DIC diagram can be explained by mixing of volcanic CO₂ with DIC equilibrated with soil CO₂. Groundwater DIC showing a high mixing ratio of volcanic CO₂ appears to have a tendency to distribute along two major faults near the activity center of the 1990–1995 eruption. This suggests that these faults are escape routes of volcanic CO₂ diffused into the volcanic edifice. The total flux of the volcanic DIC discharged from the cold springs is shown to be one to two orders of magnitude lower than the roughly estimated flux of volcanic CO₂ discharged from the summit during the eruptive period. Received: November 10, 2001 / Accepted: June 6, 2002 Acknowledgments The Unzen Scientific Drilling Project, Ministry of Education, Culture, Sports, Science and Technology (Japan), provided funding. We acknowledge G. Lyon and W. Gooley for stable carbon isotope measurement, K. Amita for DIC analysis, and students of Kyoto University and Okayama University of Science for assistance in field work. Correspondence to:S. Ohsawa     

Interactions of culture vessels, media volume, culture density, and carbon dioxide levels on lettuce and spearmint shoot growth in vitro

 The influence of culture chamber capacity, medium volume and culture density on the growth yields of lettuce (Lactuca sativa L.) and spearmint (Mentha spicata L.) shoots were determined in an environment containing either 350 or 10,000 μmol mol^–1 CO₂ after 8 weeks of incubation. High positive correlations occurred between the culture vessel capacity and spearmint fresh weight, leaf number, root number, and shoot number. Similarly, high positive correlations occurred between culture vessel capacity and lettuce fresh weight, leaf number, and root number. Higher fresh weights, leaf numbers, and root numbers were obtained from lettuce and spearmint shoots when cultured in 1-quart Mason jars containing 100- or 150-ml aliquots of medium compared to jars containing 25- or 50-ml aliquots of medium within an environment containing either 350 or 10,000 μmol mol^–1 CO₂. High culture density decreased growth yields, and this phenomenon could only be slightly off-set by the employment of an elevated CO₂ environment or larger culture vessels. Received: 22 December 1998 / Revision received: 2 July 1999 / Accepted: 12 July 1999     

Specific leaf area and leaf nitrogen concentration in annual and perennial grass species growing in Mediterranean old-fields

 We evaluated the hypothesis that photosynthetic traits differ between leaves produced at the beginning (May) and the end (November–December) of the rainy season in the canopy of a seasonally dry forest in Panama. Leaves produced at the end of the wet season were predicted to have higher photosynthetic capacities and higher water-use efficiencies than leaves produced during the early rainy season. Such seasonal phenotypic differentiation may be adaptive, since leaves produced immediately preceding the dry season are likely to experience greater light availability during their lifetime due to reduced cloud cover during the dry season. We used a construction crane for access to the upper canopy and sampled 1- to 2-month-old leaves marked in monthly censuses for six common tree species with various ecological habits and leaf phenologies. Photosynthetic capacity was quantified as light- and CO₂-saturated oxygen evolution rates with a leaf-disk oxygen electrode in the laboratory (O_2max) and as light-saturated CO₂ assimilation rates of intact leaves under ambient CO₂ (A_max). In four species, pre-dry season leaves had significantly higher leaf mass per unit area. In these four species, O_2max and A_max per unit area and maximum stomatal conductances were significantly greater in pre-dry season leaves than in early wet season leaves. In two species, A_max for a given stomatal conductance was greater in pre-dry season leaves than in early wet season leaves, suggesting a higher photosynthetic water-use efficiency in the former. Photosynthetic capacity per unit mass was not significantly different between seasons of leaf production in any species. In both early wet season and pre-dry season leaves, mean photosynthetic capacity per unit mass was positively correlated with nitrogen content per unit mass both within and among species. Seasonal phenotypic differentiation observed in canopy tree species is achieved through changes in leaf mass per unit area and increased maximum stomatal conductance rather than by changes in nitrogen allocation patterns. Received: 7 March 1996 / Accepted: 1 August 1996     

Deformability of Fe(II)CO and Fe(III)CN groups in heme protein models: nonlocal density functional theory calculations

 High-quality nonlocal density functional calculations have been carried out on the deformability of Fe(II)CO and Fe(III)CN units in model compounds of heme proteins. The results confirm our previous finding with a local functional that the Fe(II)CO unit is significantly deformable with respect to tilting and bending. This deformability stems in large part from a large, negative interaction constant between the FeC tilt and FeCO bend coordinates. The Fe(III)CN unit is also significantly deformable, but in this case the deformability results from a very small Fe(III)CN bend force constant and the ability of the cyano nitrogen to act as a hydrogen bond acceptor. The prediction that the energetic penalty associated with deforming the Fe(II)CO unit is relatively modest indicates that such deformations are unlikely to be the dominant contributor to myoglobin's discrimation against CO in favor of O₂. Received, accepted: 16 June 1997     

Somatic embryogenesis and plant regeneration in chrysanthemum (Dendranthema grandiflorum (Ramat.) Kitamura)

 Somatic embryogenesis was observed in ray-floret explants of Dendranthema grandiflorum (Ramat.) Kitamura cv. Aboukyu on Murashige and Skoog medium containing high concentrations of 3-indoleacetic acid (IAA) and kinetin. 1-Naphthaleneacetic acid also induced somatic embryogenesis but indole-3-butyric acid or 2,4-dichlorophenoxy acetic acid did not. Other cytokinins, such as 6-benzylaminopurine (BAP) and thidiazuron, were also not effective. No embryos were seen at lower IAA concentrations with kinetin and various concentrations of BAP, although higher BAP concentrations yielded many adventitious shoots. In contrast, no somatic embryogenesis was observed from leaves using any combination of plant growth regulators. Histologically, primordia showed a typical embryo shape with a well-developed vascular bundle between the shoot and the root primordia. Embryos had both stomata cells and a root system with polarity. Plants were efficiently regenerated from ray floret-derived embryos subcultured in the appropriate medium. Received: 30 April 1999 / Revision received: 7 October 1999 / Accepted: 27 January 2000     

Fruiting of putative ectomycorrhizal fungi under blue gum (Eucalyptus globulus) plantations of different ages in Western Australia

 The species richness of putative ectomycorrhizal (EM) fungi fruiting in blue gum (Eucalyptus globulus Labill.) plantations in Western Australia was investigated in relation to plantation age. Eleven plantations, 1–8 years old, were selected for study and two native Eucalyptus forest sites in the same region were chosen for comparison. Sporocarps of 44 species of putative EM fungi were collected from the 13 sites. Of these, 30 species were found in blue gum plantations. The number of fungal species was highly positively correlated with plantation age and inversely correlated with soil pH. Young plantations (1–5 years) had 2–9 fungal species and were overwhelmingly dominated by species of Laccaria and Scleroderma. In older plantations (6–8 years), the relative abundance of sporocarps of each species within the fungal community decreased, accompanied by an increase in the number of fungal species (12–17 per site). A brief survey of the two native eucalypt forests in this region revealed a much higher number of fungal species than that observed in plantations. In plantations, species of Descolea, Laccaria, Pisolithus and Scleroderma typically fruited in young plantations. Species of epigeous fungi of the genera Boletus, Cortinarius, Hydnum, Inocybe, Lactarius, Paxillus, Russula and hypogeous fungi, including species of Descomyces, Hysterangium and Mesophellia, were found only in older plantations, or in native forests. Some of the fungi that fruit in young plantations are now being evaluated for use in commercial spore inoculation programs to increase the species diversity of EM fungi in exotic eucalypt plantations. Accepted: 8 October 1998     

Mapping of two genes for resistance to clubroot (Plasmodiophora brassicae) in a population of doubled haploid lines of Brassica oleracea by means of RFLP and AFLP markers

A genetic map covering 615 cM in 12 linkage groups was assembled based on 92 RFLP and AFLP markers segregating in a population of 107 doubled haploid lines (DH lines) of Brassica oleracea. The DH-line population was obtained through microspore culture from the of two homozygous parents: DH-line Bi derived from the cabbage landrace Bindsachsener, and DH-line Gr from broccoli cv ‘Greenia’. Sixty-five percent of the loci, and in some cases complete linkage groups, displayed distorted segregation ratios, a frequency much higher than that observed in populations of the same species. DH-line Bi was resistant to clubroot, which is caused by a Dutch field isolate of Plasmodiophora brassicae. Resistance in the DH-line population was determined in two ways: by assigning symptom grades to each plant, and by measuring the fresh weights of the healthy and affected parts of the root system of each plant. Using a multiple QTL mapping approach to analyze the fresh weight data, we found two loci for clubroot resistance; these were designated pb-3 and pb-4. The additive effects of these loci were responsible for 68% of the difference between the parents and for 60% of the genetic variance among DH-line means. Also, indications for the presence of two additional, minor QTLs were found. Analysis of symptom grades revealed the two QTLs pb-3 and pb-4, as well as one of the two minor QTLs indicated by analysis of the fresh weight data. Received: 29 April 1996 / Accepted: 10 May 1996     

Changes in leaf photosynthesis of transgenic rice with silenced <Emphasis Type="Italic">OsBP-73</Emphasis> gene

In comparison with its wild type (WT), the transgenic (TG) rice with silenced OsBP-73 gene had significantly lower plant height, grain number per panicle, and leaf net photosynthetic rate (P _N). Also, the TG rice showed significantly lower chlorophyll (Chl), ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO), RuBPCO activase, and RuBP contents, photosystem 2 (PS2) photochemical efficiency (F_v/F_m and ΔF/F_m′), apparent quantum yield of carbon assimilation (Φ_c), carboxylation efficiency (CE), photosynthetic electron transport and photophosphorylation rates as well as sucrose phosphate synthase activity, but higher intercellular CO₂ concentration, sucrose, fructose, and glycerate 3-phosphate contents, and non-photochemical quenching of Chl fluorescence (NPQ). Thus the decreased P _N in the TG rice leaves is related to both RuBP carboxylation and RuBP regeneration limitations, and the latter is a predominant limitation to photosynthesis.     

Morphotype community structure of ectomycorrhizas on Douglas fir (Pseudotsuga menziesii Mirb. Franco) seedlings grown under elevated atmospheric CO2 and temperature

Mycorrhizas alter the acquisition of carbon and nutrients, thereby affecting numerous plant and ecosystem processes. It is important, therefore, to determine how mycorrhizal populations will change under possible future climate conditions. Individual and interactive effects of elevated atmospheric CO₂ concentration and atmospheric temperature were assessed in a 2×2 factorial design [ambient and elevated (200 ppm above ambient) CO₂ concentrations, and ambient and elevated (4°C above ambient) temperatures]. In June 1993, 2-year-old Douglas fir (Pseudotsuga menziesii Mirb. Franco) seedlings were planted in 12 environment-tracking chambers (n=3) containing reconstructed, low-nitrogen, native forest soil. Climate treatments were imposed shortly thereafter, and the seedlings grew until June 1997. Soil cores were taken twice per year during the exposure period. We present findings on changes in the community structure of ectomycorrhizal (ECM) root tips, categorized into morphotypes using gross morphological traits. A diverse and stable community of morphotypes (a total of 40) was encountered; no more than 30 of which were seen at any sampling time. In the first sample, there were only 15 morphotypes found in the 12 chambers. Morphotype numbers increased during the first half of the experiment, remaining fairly constant thereafter. Near the end of the exposure, elevated-temperature treatments maintained more morphotypes than ambient treatments. However, overall, absolute measures (number of ECM tips) were affected primarily by CO₂ treatment, whereas proportional measures (e.g., Simpson’s index) were affected primarily by temperature. While some morphotypes were negatively affected seasonally by higher temperatures (putative Rhizopogon group), others (Cenococcum) seemed to thrive. Underlying the dominant patterns of change in diversity, driven by the Rhizopogon group, subdominant populations responded slightly differently. Community diversity through time tended to increase at a greater rate for all subdominant populations compared with the rate when dominant populations were included. Received: 16 August 1999 / Accepted: 2 March 2000     

Photosynthetic light acclimation in fully developed leaves of the juvenile and adult life phases of Hedera helix

The aim of this study was to investigate the extent to which fully developed leaves of Hedera helix L. are capable of acclimating to new light conditions and how this ability is determined by the life phase of the plant. To this end juvenile and adult plants were transferred from a low (L) to a moderately high (H) light regime and vice versa and changes of photosynthetic gas exchange, RuBP carboxylase (EC 4.1.1.39) activity and specific anatomy were monitored in leaves that were fully developed prior to the transfer.
Immediately after transfer from L to H there was a decrease in the rate of net photosynthesis (F_n). This photoinhibition was particularly pronounced in leaves of the adult life phase. F_n recovered after 10 to 20 days at H, and 40 to 65 days after transfer the rate exceeded that of control plants by about 20% in leaves of the adult life phase and by about 50% in leaves of the juvenile life phase. If H plants were transferred to L, F_n had declined only slightly after 30 to 40 days and regained its initial level within a few days, when the plants were returned to the original high light regime.
The increased rates of F_n per unit leaf area in leaves transferred from L to H were associated with higher light levels necessary to saturate F_n, higher carboxylation efficiencies, higher contents of soluble protein and higher activities of RuBP carboxylase, whereas the quantum yield did not change. Although fully differentiated before transfer, the leaves had formed a further cell layer in the palisade parenchyma. Related to leaf volume there was no increase in F_n.
Our results indicate that in the adult life phase of ivy phenotypie light acclimation occurs mainly during leaf development, whereas in juvenile plants fully expanded leaves still possess a rather wide modulativc acclimation plasticity.