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The carbon and oxygen isotopic composition of tree-ring cellulose was examined in ponderosa pine (Pinus ponderosa Dougl.) trees in the western USA to study seasonal patterns of precipitation inputs. Two sites (California and Oregon) had minimal summer rainfall inputs, whereas a third site (Arizona) received as much as 70% of its annual precipitation during the summer months (North American monsoon). For the Arizona site, both the δ18O and δ13C values of latewood cellulose increased as the fraction of annual precipitation occurring in the summer (July through September) increased. There were no trends in latewood cellulose δ18O with the absolute amount of summer rain at any site. The δ13C composition of latewood cellulose declined with increasing total water year precipitation for all sites. Years with below-average total precipitation tended to have a higher proportion of their annual water inputs during the summer months. Relative humidity was negatively correlated with latewood cellulose δ13C at all sites. Trees at the Arizona site produced latewood cellulose that was significantly more enriched in 18O compared with trees at the Oregon or California site, implying a greater reliance on an 18O-enriched water source. Thus, tree-ring records of cellulose δ18O and δ13C may provide useful proxy information about seasonal precipitation inputs and the variability and intensity of the North American monsoon. [ABSTRACT FROM AUTHOR]

The aim of this work was to study carbon and nitrogen metabolism during suspension culture of protocorm-like bodies (PLBs) from Dendrobium huoshanense. No significant lag phase of PLB growth was found, and a maximum biomass of 288.6 g l-1 was obtained at day 30 of culture. Sucrose concentration was halved as PLB growth proceeded, while no change in glucose and fructose levels in the medium was found in the first 3 days, followed by a gradual increase until day 9 of culture. Conversely, sucrose in PLBs accumulated dramatically in the first 6 days of culture, followed by a rapid decrease. At the same time, glucose and fructose content of PLBs increased, then declined after 9 days of culture. Soluble acidic invertase (soluble acidic IT) and alkaline invertase (alkaline IT) were activated after inoculation, and reached the highest value on day 6 and day 18, respectively whereas cell wall-bound invertase (cell wall-bound IT) seemed to be repressed throughout culture. The maximum value of sucrose synthase (SuSy) activity was observed on day 18, while sucrose phosphate synthase (SPS) stayed low and constant from inoculation to the end of culture. Ammonium concentration in the medium decreased rapidly, and was hardly detectable after 12 days, when the rapid utilization of nitrate began. Conversely, ammonium in PLBs showed a sharp increase in the first 3 days of culture, followed a rapid decrease until day 12, corresponding to nitrate depletion. Peaks in glutamine synthase (GS) and glutamate synthase (GOGAT) activity were observed on day 12 and 15, respectively. Nitrate reductase (NR) was repressed in the early culture stage, and activated from day 9 to 15 of culture. These results suggest that soluble acidic IT, alkaline IT, SuSy, GS, GOGAT and NR control carbon and nitrogen metabolism at different PLB growth stages. [ABSTRACT FROM AUTHOR]

In different-aged sand-fixing zones and shifting sand dunes, the seasonal variations of foliar carbon isotope discrimination (Δ), potassium (K) concentration and ash content were investigated in three dominated deserted plants ( Artemisia ordosica, Hedysarum scoparium and Caragana korshinskii) during growth season in Shapotou, which is in the southeast margin of the Tengger Desert. The correlations of foliar Δ with foliar K concentration and ash content were examined to evaluate the foliar K and ash content as surrogates of Δ in those deserted plants. Results showed that there were significant effects of plant species, micro-habitation and growth season on foliar Δ, K concentration and ash content. Foliar Δ of C. korshinskii was significantly lower than those of A. ordosica and H. scoparium, and K concentrations in A. ordosica were 2.14 and 2.36 times those of C. korshinskii and H. scoparium. At the same time, micro-habitation and the conditions in growth seasons had significant effects on foliar Δ, K concentration and ash content. Ash content and K concentration were positively correlated to Δ in A. ordosica and H. scoparium, while there was significantly negative relationship between foliar K concentration and Δ in C. korshinskii. Thus, those findings suggest that foliar ash content and K concentration can serve as surrogates of carbon isotope discrimination (Δ) in A. ordosica and H. scoparium, while they do not in C. korshinskii. This result implied that the correlations of foliar Δ with ash content and K concentration were various due to the physiological features of plant species, and species differences should be fully considered when evaluating the surrogates of carbon isotope discrimination in plants. [ABSTRACT FROM AUTHOR]

Abstract: The excess of carbon leads to changes in the production of plant defensive secondary chemicals, which in turn may modify the plant responses to herbivores and pathogens. Age and/or developmental stage as well as environmental conditions influence race-specific accumulation of phytoalexins in soybean. Thus, we hypothesized that elevated CO2 atmospheres could lead to distinct phytoalexin production in soybean cultivars differing in their resistance to fungal attack. Two cultivars of soybean (Glycine max, IAC-14 and IAC-18) differing in the resistance to the causal agent of the stem canker disease were subjected to 320 and 720μmolmol−1 of CO2 in open top chambers. Plants were kept under both CO2 atmospheres from germination up to 9 days (VC stage), when CO2 assimilation rates, chlorophyll a fluorescence, leaf and cotyledon area, dry mass and root: shoot ratio were measured. Phytoalexin content were evaluated in detached cotyledon diffusates of both cultivars elicited with β-glucan elicitor from mycelial walls of Phythophytora sojae. Exposure to elevated CO2 stimulated photosynthesis, leaf and cotyledon areas and the enhancement of glyceollin production by the elicitor in the resistant cultivar (IAC-18). No changes were observed in growth parameters (biomass and area of photosynthetic tissues) and phytoalexin response in susceptible cultivar (IAC-14), despite the stimulation of photosynthetic assimilation in cotyledons under high CO2. These findings corroborate the assumption that exposure to enriched CO2 atmospheres can change inducible defensive responses in soybean against pathogens. These changes occurred in individual metabolites and were dependent on the cultivar resistance patterns. [Copyright &y& Elsevier]

An anaerobic incubation experiment was conducted to investigate methane (CH4) production potential in soil samples collected from a paddy field after exposure to free-air CO2 enrichment (FACE). The FACE experiment with two CO2 levels, ambient and ambient + 200 p.p.m.v CO2 during the rice growing season, was conducted at Shizukuishi, Iwate Prefecture, Japan. The soil was a wet Andosol. Soil samples were taken from the surface (0–1 cm) and the sub-surface (1–10 cm) soil layers 2 months after rice harvest. Sub-samples of the fresh soils were put into glass bottles and submerged under N2 gas headspace during the incubation. The results showed that, prior to incubation, the contents of total C and dissolved organic C (DOC) were significantly greater in FACE soil than ambient soil. During the incubation, CH4 production potential was approximately 2–4-fold higher in FACE soil than ambient soil and approximately 500–1,000-fold greater in surface soil than sub-surface soil. In general, the FACE soil contained more DOC than ambient soil, particularly in the surface soil layer. These findings suggest that FACE treatment exerted long-term positive effects on CH4 production and increased organic C content in this paddy soil, particularly in the surface soil layer. [ABSTRACT FROM AUTHOR]

Recent studies have shown that the tussock grass Stipa tenacissima L. facilitates the establishment of late-successional shrubs, in what constitutes the first documented case of facilitation of woody plants by grasses. With the aim of increasing our knowledge of this interaction, in the present study we investigated the effects of S. tenacissima on the foliar δ13C, δ15N, nitrogen concentration, and carbon : nitrogen ratio of introduced seedlings of Pistacia lentiscus L., Quercus coccifera L., and Medicago arborea L. in a semi-arid Mediterranean steppe. Six months after planting, the values of δ13C ranged between −26.9‰ and −29.6‰, whereas those of δ15N ranged between −1.9‰ and 2.7‰. The foliar C : N ratio ranged between 10.7 and 53.5, and the nitrogen concentration ranged between 1.0% and 4.4%. We found no significant effect of the microsite provided by S. tenacissima on these variables in any of the species evaluated. The values of δ13C were negatively correlated with predawn water potentials in M. arborea and were positively correlated with relative growth rate in Q. coccifera. The values of δ15N were positively correlated with the biomass allocation to roots in the latter species. The present results suggest that the modification of environmental conditions in the are surrounding S. tenacissima was not strong enough to modify the foliar isotopic and nitrogen concentration of shrubs during the early stages after planting. (Managing editor: Ya-Qin Han) [ABSTRACT FROM AUTHOR]

Carbon and nitrogen balance in Acorus calamus, a wetland species colonising littoral zones with a high trophic status, was studied under experimental conditions using water or sand culture with a defined composition of the nutrient solution. Influence of graded level of N (1.86, 7.5 and 18.6 mM) and/or forms of N (NH versus NO ) on the content of non-structural carbohydrates, free amino acids, total C, and total N was studied in Acorus rhizomes and roots to find possible connection with a reduced growth of Acorus plants under high N and NH–N nutrition described in our previous study [Vojtíšková et al., 2004. Hydrobiologia 518: 9–22]. High N availability and pure NH–N nutrition affected the C/N balance of rhizome and root systems of Acorus in a similar way. NH–N was the only form of N elevated under the high N treatment. The major proportion of the total non-structural carbohydrates (TNC) was starch (91–93% and 51–64% in rhizomes and roots, respectively). The content of starch was significantly and and negatively affected by high N availability ( P = 0.001), as well as by NH–N nutrition ( P=0.001). Amounts of simple soluble carbohydrates (sucrose, glucose, and fructose) were negligible in comparison to starch in rhizomes and branched roots (up to 5% of TNC), while roots without developed lateral roots (unbranched) contained up to 33% of TNC in the form of simple soluble sugars. Moreover, high hexoses/sucrose ratio, low starch/soluble sugars ratio, high content of N, and low C/N ratio support the notion that unbranched roots are metabolically active young roots with tissue differentiation in progress. A high content of free amino acids, typically with dominance of N-rich amino acids (Arg-46%, Gln-8%, Asn-7%), was found simultaneously with a low carbohydrate content under high N supply, which indicates that NH received is effectively incorporated into the organic form by this species. Since the decrease in carbohydrate content was not accompanied by luxurious growth, other possible carbon consuming processes were discussed in relation to NH nutrition. More dramatic changes in total N than C were found under high N availability resulting a shift in C/N ratio in favour of N. Although the shift towards N metabolism was obvious, no serious carbohydrate depletion occurred, which could explain the reduced growth of Acorus plants under high N and sole NH–N nutrition described previously. [ABSTRACT FROM AUTHOR]

The atmospheric concentration of CO2 is predicted to reach double current levels by 2075. Detritus from aboveground and belowground plant parts constitutes the primary source of C for soil organic matter (SOM), and accumulation of SOM in forests may provide a significant mechanism to mitigate increasing atmospheric CO2 concentrations. In a poplar (three species) plantation exposed to ambient (380 ppm) and elevated (580 ppm) atmospheric CO2 concentrations using a Free Air Carbon Dioxide Enrichment (FACE) system, the relative importance of leaf litter decomposition, fine root and fungal turnover for C incorporation into SOM was investigated. A technique using cores of soil in which a C4 crop has been grown (δ13C −18.1‰) inserted into the plantation and detritus from C3 trees (δ13C −27 to −30‰) was used to distinguish between old (native soil) and new (tree derived) soil C. In-growth cores using a fine mesh (39 μm) to prevent in-growth of roots, but allow in-growth of fungal hyphae were used to assess contribution of fine roots and the mycorrhizal external mycelium to soil C during a period of three growing seasons (1999–2001). Across all species and treatments, the mycorrhizal external mycelium was the dominant pathway (62%) through which carbon entered the SOM pool, exceeding the input via leaf litter and fine root turnover. The input via the mycorrhizal external mycelium was not influenced by elevated CO2, but elevated atmospheric CO2 enhanced soil C inputs via fine root turnover. The turnover of the mycorrhizal external mycelium may be a fundamental mechanism for the transfer of root-derived C to SOM. [ABSTRACT FROM AUTHOR]

Summary: Plant growth and development is dependent on coordinated assimilate production, distribution and allocation. Application of biochemical and molecular techniques substantially contributed to a better understanding of these processes, although the underlying regulatory mechanisms are still not fully elucidated and attempts to improve crop yield by modulating carbon partitioning were only partially successful. Plant pathogens also interfere with source–sink interaction. To this end they have evolved a wide range of sophisticated strategies to allow their systemic spread, suppression of plant defence and induction of sink function to support nutrient acquisition for their growth. Studying compatible interactions of plants and pathogens like viruses, bacteria and fungi can be exploited to investigate different levels of source–sink regulation. The identification of microbial factors and their host targets involved in regulation of plant primary metabolism may allow developing novel strategies to increase crop yield. Here we will discuss recent studies on plant–microbe interactions aimed at elucidating mechanisms of compatibility. [Copyright &y& Elsevier]

Wetlands are an important natural source of methane to theatmosphere. The amounts of methane emitted from inundated ecosystems in the United States can vary greatly from area to area. Seasonal temperature, water table dynamics, and carbon content of soils are principal controlling factors. To calculate the effect of wetlands (and their potential conversion to other land uses) on global greenhouse gas emissions, information on area covered by various wetland types is needed, along with verified projections of spatial variation in net methane emissions. Both of these variables are poorly known, and estimates are largely unavailable at the country level. Nationwide satellite datasets for the coterminous United States (excluding Alaska) have been combined with ecosystem model predictions of monthly net carbon exchange with the atmosphere to produce the first detailed mapping of methane fluxes from natural wetlands on a monthly and annual basis. The Carnegie¿Ames¿Stanford Approach (CASA) model¿s predicted mean emission flux of methane from wetlands of the continental United States totaled 5.5 Tg CH4 per year. Ranked in terms of total annual flux, the 10 states with the highest predicted emissions (not considering Alaska) are all located in the Great Lakes region and the southern coastal regions of the country. [ABSTRACT FROM AUTHOR]

• Here, we analysed the transition from heterotrophic to autotrophic growth of the epigeal species sunflower ( Helianthus annuus), and how transition is affected by CO2. • Growth analysis and steady-state 13CO2/12CO2 and 15NO3−/14NO3− labelling were used to quantify reserve- and current assimilation-derived carbon (C) and nitrogen (N) allocation to shoots and roots in the presence of 200 and 1000 µmol CO2 mol−1 air. • Growth was not influenced by CO2 until cotyledons unfolded. Then, C accumulation at elevated CO2 increased to a rate 2–2.5 times higher than in subambient CO2 due to increased unit leaf rate (+ 120%) and leaf expansion (+ 60%). CO2 had no effect on mobilization and allocation of reserve-derived C and N, even during the transition period. Export of autotrophic C from cotyledons began immediately following the onset of photosynthetic activity, serving roots and shoots near-simultaneously. Allocation of autotrophic C to shoots was increased at subambient CO2. • The synchrony in transition from heterotrophic to autotrophic supply for different sinks in sunflower contrasts with the sequential transition reported for species with hypogeal germination. [ABSTRACT FROM AUTHOR]

• The influence of external nitrogen (N) on carbon (C) allocation and processes related to phosphorus (P) metabolism were studied in monoxenic arbuscular mycorrhiza (AM) cultures of Daucus carota. • Fungal hyphae of Glomus intraradices proliferated from colonized roots growing on solid medium into C-free liquid minimal medium with two different N and P levels. Furthermore, we exposed the colonized roots to high or low N availability and then studied the mycelial development. Roots were provided with 13C-glucose in order to follow the C allocation. The mycelium was analysed for phosphatase activity and transcription levels of two nutrient regulated genes. • High N availability to the monoxenic AM root reduced the C allocation to the AM fungus while N availability to the mycelium was important for the upregulation of the fungal inorganic phosphorus (Pi)-transporter GiPT. • We found that N availability can regulate nutritional processes in arbuscular mycorrhiza. We conclude that negative impacts of N on AM abundance are caused by reduced C allocation from the plant. Upregulation of the fungal Pi-transporter GiPT indicated that increased N availability might induce P limitation in the mycelium. [ABSTRACT FROM AUTHOR]

• The use of the 13C : 12C isotopic ratio (δ13C) of leaf-respired CO2 to trace carbon fluxes in plants and ecosystems is limited by little information on temporal variations in δ13C of leaf dark-respired CO2 (δ13Cr) under field conditions. • Here, we explored variability in δ13Cr and its relationship to key respiratory substrates from collections of leaf dark-respired CO2, carbohydrate extractions and gas exchange measurements over 24-h periods in two Quercus canopies. • Throughout both canopies, δ13Cr became progressively 13C-enriched during the photoperiod, by up to 7, then 13C-depleted at night relative to the photoperiod. This cycle could not be reconciled with δ13C of soluble sugars (δ13Css), starch (δ13Cst), lipids (δ13Cl), cellulose (δ13Cc) or with calculated photosynthetic discrimination (Δ). However, photoperiod progressive enrichment in δ13Cr was correlated with cumulative carbon assimilation ( r2 = 0.91). • We concluded that there is considerable short-term variation in δ13Cr in forest canopies, that it is consistent with current hypotheses for 13C fractionation during leaf respiration, that leaf carbohydrates cannot be used as surrogates for δ13Cr, and that diel changes in leaf carbohydrate status could be used to predict changes in δ13Cr empirically. New Phytologist (2005) doi: 10.1111/j.1469-8137.2005.01475.x © New Phytologist (2005) [ABSTRACT FROM AUTHOR]

Catechol 2,3-dioxygenase (C2,3O) from Pseudomonas stutzeri OX1, which is able to grow on various aromatic substrates as the sole source of carbon and energy, has been expressed in Escherichia coli, purified, characterized, and found to be very similar to other dioxygenases from Pseudomonas species. Interestingly, the activity of the protein shows a rather unusual pH dependence when assayed on catechol. A model of the catalytic mechanism was developed that is able to reproduce the catalytic behavior of the protein as a function of the pH. The model includes multiple equilibria and four productive intermediates with different ionization states of the enzyme-substrate complex. The fitting of the theoretical curve to the experimental data suggests that a tyrosine and two histidine residues are involved in catalysis. Mutants (H246N)-, (H246A)-, (H199N)- and (Y255F)-C2,3O were produced to investigate the role of highly conserved His-199, His-246, and Tyr-255. The strongly reduced activity of the mutants suggests a primary catalytic role for each of these residues. Moreover, mutants at positions 199 and 246 display pH profiles different from that of the wild-type protein, thus indicating that residues His-246 and His-199 play a role in determining the unusual pH dependence of the enzyme. In addition, electron-withdrawing groups on catechol, which increase the acidity of the phenolic hydroxyl group, are able to counterbalance the effect of the mutation H246N in reducing catalytic activity but cause a further reduction of the activity of (H199N)-C2,3O. This finding suggests that His-246 is involved in the initial catechol deprotonation, whereas His-199 promotes the reaction between oxygen and the aromatic ring. [ABSTRACT FROM AUTHOR]

We calculated carbon budgets for a chronosequence of harvested jack pine ( Pinus banksiana Lamb.) stands (0-, 5-, 10-, and∼29-year-old) and a∼79-year-old stand that originated after wildfire. We measured total ecosystem C content (TEC), above-, and belowground net primary productivity (NPP) for each stand. All values are reported in order for the 0-, 5-, 10-, 29-, and 79-year-old stands, respectively, for May 1999 through April 2000. Total annual NPP (NPPT) for the stands (Mg C ha−1 yr−1±1 SD) was 0.9±0.3, 1.3±0.1, 2.7±0.6, 3.5±0.3, and 1.7±0.4. We correlated periodic soil surface CO2 fluxes ( RS) with soil temperature to model annual RS for the stands (Mg C ha−1 yr−1±1 SD) as 4.4±0.1, 2.4±0.0, 3.3±0.1, 5.7±0.3, and 3.2±0.2. We estimated net ecosystem productivity (NEP) as NPPT minus RH (where RH was calculated using a Monte Carlo approach as coarse woody debris respiration plus 30–70% of total annual RS). Excluding C losses during wood processing, NEP (Mg C ha−1 yr−1±1 SD) for the stands was estimated to be −1.9±0.7, −0.4±0.6, 0.4±0.9, 0.4±1.0, and −0.2±0.7 (negative values indicate net sources to the atmosphere.) We also calculated NEP values from the changes in TEC among stands. Only the 0-year-old stand showed significantly different NEP between the two methods, suggesting a possible mismatch for the chronosequence. The spatial and methodological uncertainties allow us to say little for certain except that the stand becomes a source of C to the atmosphere following logging. [ABSTRACT FROM AUTHOR]

Woody encroachment and thickening have occurred throughout the western United States and have been proposed as important processes in the US carbon (C) budget despite large uncertainty in the magnitude of these effects. In this study we investigated ponderosa pine encroachment near Boulder, Colorado. We reconstructed a time series of forest structure to estimate changes in C storage by the trees. Advantages of this technique include the ability to estimate changes in C stocks over time with a single series of measurements (i.e., no historical measurements), and the ability to calculate accumulation rate changes through time. Substantial variation occurred in the C amounts and accumulation rates among the three plots resulting from differences in slope, aspect, and soil conditions. Accumulation rates increased exponentially as trees increased in size and additional trees established within the plots, and were highly variable among plots (0.09–0.7 Mg C·ha–1·year–1 during 1980–2001). These rates were less than those used in studies of the US carbon budget, and only by assuming no mortality for the densest stand could we generate a projected rate in 2050 that was similar. Thus, time since the initiation of encroachment and rate of encroachment are variables that should be considered for accurately computing the continental C budget. [ABSTRACT FROM AUTHOR]

Coupling growth of Lolium perenne L. in sterile solution culture with steady-state 13CO2 labelling allowed quantification of the contribution of C, assimilated either before or after a specific time point, both to plant compartments and root exudates. Plants were grown for 27 days in atmospheres containing CO2 with δ13C signatures of either −13.5 or −36.1‰. Air supplies to plants were then reciprocally switched to the opposing signature (day 0), plants were destructively harvested and root exudates collected over the next 8 days. Following the switch, C assimilated after day 0 and transported to the roots initially only appeared in root tips, later appearing in both tip and non-tip material. The δ13C signature of the root exudate changed exponentially with time. Assimilation pre- and post-day 0 contributed equally to exudate C at 4.5 days. Beyond day 8, assimilation pre-day 0 still contributed 41.7% of exudate C. Over all 8 days, a linear relationship existed between the δ13C signatures of root tips and exudate, suggesting that all newly assimilated C in the exudate was from root tips. Results imply pulse-labelling approaches to study root exudates are discriminative in the sources of exudates labelled and in the sites from which exudation occurs. [ABSTRACT FROM AUTHOR]

There is growing interest in the addition of carbon (C) as sucrose or sawdust to the soil as a tool to reduce plant-available nitrogen (N) and alter competitive interactions among species. The hypothesis that C addition changes N availability and thereby changes competitive dynamics between natives and exotics was tested in a California grassland that had experienced N enrichment. Sawdust (1.2 kg/m) was added to plots containing various combinations of three native perennial bunchgrasses, exotic perennial grasses, and exotic annual grasses. Sawdust addition resulted in higher microbial biomass N, lower rates of net N mineralization and net nitrification, and higher concentrations of extractable soil ammonium in the soil. In the first year sawdust addition decreased the degree to which exotic annuals competitively suppressed the seedlings of Nassella pulchra and, to a lesser extent, Festuca rubra, both native grasses. However there was no evidence of reduced growth of exotic grasses in sawdust-amended plots. Sawdust addition did not influence interactions between the natives and exotic perennial grasses. In the second year, however, sawdust addition did not affect the interactions between the natives and either group of exotic grasses. In fact, the native perennial grasses that survived the first year of competition with annual grasses significantly reduced the aboveground productivity of annual grasses even without sawdust addition. These results suggest that the addition of sawdust as a tool in the restoration of native species in our system provided no significant benefit to natives over a 2-year period. [ABSTRACT FROM AUTHOR]

The rate of photosynthetic carbon fixation (P) in the diatom Thalassiosira weissflogii cultivated in the presence of exogenous glucose in the medium (0–10.56 μg C/l) at different levels of illumination—25, 50, and 100 μE/(m2 s)—was studied as a function of nitrate nitrogen supply. In the diatoms limited in nitrogen and assimilating exogenous glucose, P was found to decrease or increase depending on the light intensity, glucose concentration, and the duration of exposure. In the diatoms assimilating both nitrate nitrogen and glucose, compared to those supplied with nitrates alone, P was higher at the medium and high light intensities and lower at the low light intensity. The interrelation of the processes of carbon and nitrogen metabolism in mixotrophic algae and the ecological role of glucose uptake by phytoplankton are discussed. [ABSTRACT FROM AUTHOR]

ABSTRACT This study investigated the possibility that abscisic acid (ABA) and cytokinins may mediate the effect of water deficit that enhances plant senescence and remobilization of pre-stored carbon reserves. Two high lodging-resistant wheat (Triticum aestivum L.) cultivars were field grown and treated with either a normal or high amount of nitrogen at heading. Well-watered (WW) and water-stressed (WS) treatments were imposed from 9 d post-anthesis until maturity. Chlorophyll (Chl) and photosynthetic rate (Pr) of the flag leaves declined faster in WS plants than in WW plants, indicating that the water deficit enhanced senescence. Water stress facilitated the reduction of non-structural carbohydrate in the stems and promoted the re-allocation of prefixed [sup 14] C from the stems to grains, shortened the grain filling period and increased the grain filling rate. Water stress substantially increased ABA but reduced zeatin (Z) + zeatin riboside (ZR) concentrations in the stems and leaves. ABA correlated significantly and negatively, whereas Z + ZR correlated positively, with Pr and Chl of the flag leaves. ABA but not Z + ZR, was positively and significantly correlated with remobilization of pre-stored carbon and grain filling rate. Exogenous ABA reduced Chl in the flag leaves, enhanced the remobilization, and increased grain filling rate. Spraying with kinetin had the opposite effect. The results suggest that both ABA and cytokinins are involved in controlling plant senescence, and an enhanced carbon remobilization and accelerated grain filling rate are attributed to an elevated ABA level in wheat plants when subjected to water stress. [ABSTRACT FROM AUTHOR]

The sexes of dioecious species may differ in a range of vegetative and reproductive traits as well as in physiological traits. In Siparuna grandifiora, a Neotropical dioecious shrub, we examined differences in leaf-level photosynthesis of different classes of leaf age and, using simulation models, explored whether differences in leaf-level carbon gain led to sex differences in whole-plant daily carbon gain. Male plants had higher photosynthetic capacity at the leaf level. As leaves of both sexes aged their photosynthetic capacity and specific leaf area declined as expected. Simulations of daily carbon gain using the architecturally explicit model Y-Plant and a non-architectural model incorporating a wide range of realistic light environments revealed that the difference in leaf-level photosynthetic capacity did not translate into greater crown-level carbon gain for males. Rather, differences in patterns of allocation to leaf area allow females to achieve higher crown-level carbon gain. The results demonstrate that sex differences at the leaf level do not necessarily predict patterns at the whole-plant level. [ABSTRACT FROM AUTHOR]

Examines the suitability of carbon isotope analysis in plants for the assessment of environmental changes. Impact of carbon isotope analysis on crops and natural systems; Relationship between different environmental parameters and carbon isotope composition in both herbaceous plants and trees; Composition of the carbon isotope.

One-year-old peach trees (Prunus persica (L.) Batsch) were severely pruned in July by removing 60% of the shoots. Tree responses were analyzed in terms of architecture and nutritional status. Tree growth was recorded from July to September by nondestructive (leaf production, thickening and branching of the remaining secondary axes) and destructive measurements (biomass partitioning and concentrations of total nitrogen (N) and nonstructural carbohydrates (NC) in specific tissues). The dry weights of pruned trees were lower than those of control trees at the end of the growing season (i.e., 2.5 months after pruning), whereas shoot:root ratios were restored to the initial values. Tree response occurred in two stages. During the first 24 days following pruning, the growth components of the remaining secondary axes were similar to the control, and new secondary axes were produced. During the next 17 days, increases in both diameter and branching of secondary axes contributed to the maintenance of pruned tree growth rate (similar to that of control trees) and restoration of initial shoot:root ratios. No significant effect of pruning was observed on NC concentrations, whereas N concentrations increased in several organs of the pruned trees during the first growth period. The transient increase in internal N availability contributed to the initiation of new axes and the restoration of a more functional biomass partitioning between shoots and roots. [ABSTRACT FROM PUBLISHER]

Abstract Models of photosynthesis, respiration, and export predict that foliar labile carbon (C) should increase with elevated CO2 but decrease with elevated temperature. Sugars, starch, and protein can be compared between treatments, but these compounds make up only a fraction of the total labile pool. Moreover, it is difficult to assess the turnover of labile carbon between years for evergreen foliage. Here, we combined changes in foliar Carea (C concentration on an areal basis) as needles aged with changes in foliar isotopic composition (δ13 C) caused by inputs of 13 C-depleted CO2 to estimate labile and structural C in needles of different ages in a four-year, closed-chamber mesocosm experiment in which Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings were exposed to elevated temperature (ambient + 3.5 °C) and CO2 (ambient + 179 ppm). Declines in δ 13 C of needle cohorts as they aged indicated incorporation of newly fixed labile or structural carbon. The δ 13 C calculations showed that new C was 41 ± 2% and 28 ± 3% of total needle carbon in second- and third-year needles, respectively, with higher proportions of new C in elevated than ambient CO2 chambers (e.g. 42 ± 2% vs. 37 ± 6%, respectively, for second-year needles). Relative to ambient CO2 , elevated CO2 increased labile C in both first- and second-year needles. Relative to ambient temperature, elevated temperature diminished labile C in second-year needles but not in first-year needles, perhaps because of differences in sink strength between the two needle age classes. We hypothesize that plant-soil feedbacks on nitrogen supply contributed to higher photosynthetic rates under elevated temperatures that partly compensated for higher turnover rates of labile C. Strong positive correlations between labile C and sugar concentrations... [ABSTRACT FROM AUTHOR]

Abstract Natural peatlands accumulate carbon (C) and nitrogen (N). They affect the global climate by binding carbon dioxide (CO2 ) and releasing methane (CH4 ) to the atmosphere; in contrast fluxes of nitrous oxide (N2 O) in natural peatlands are insignificant. Changes in drainage associated with forestry alter these greenhouse gas (GHG) fluxes and thus the radiative forcing (RF) of peatlands. In this paper, changes in peat and tree stand C stores, GHG fluxes and the consequent RF of Finnish undisturbed and forestry-drained peatlands are estimated for 1900–2100. The C store in peat is estimated at 5.5 Pg in 1950. The rate of C sequestration into peat has increased from 2.2 Tg a--1 in 1900, when all peatlands were undrained, to 3.6 Tg a--1 at present, when c . 60% of peatlands have been drained for forestry. The C store in tree stands has increased from 60 to 170 Tg during the 20th century. Methane emissions have decreased from an estimated 1.0–0.5 Tg CH4 --C a--1 , while those of N2 O have increased from 0.0003 to 0.005 Tg N2 O--N a--1 . The altered exchange rates of GHG gases since 1900 have decreased the RF of peatlands in Finland by about 3 mW m--2 from the predrainage situation. This result contradicts the common hypothesis that drainage results in increased C emissions and therefore increased RF of peatlands. The negative radiative forcing due to drainage is caused by increases in CO2 sequestration in peat (--0.5 mW m--2 ), tree stands and wood products (--0.8 mW m--2 ), decreases in CH4 emissions from peat to the atmosphere (--1.6 mW m--2 ), and only a small increase in N2 O emissions (+0.1 mW m--2 ). Although the calculations presented include many uncertainties, the above results are considered qualitatively reliable and may be expected to be... [ABSTRACT FROM AUTHOR]

Abstract Data from 57 permanent monitoring sites are used to document the growth in woody vegetation and estimate the carbon sink in 27 M ha of eucalypt woodlands (savannas), contained within c. 60 M ha of grazed woodlands in Queensland (northeast Australia). The study sites are shown to be representative of the environment and structure of the eucalypt woodlands in the defined study area. Mean basal area increment for all live woody plants in 30 long-term sites, with an average initial basal area of 11.86 ± 1.38 (SE) m2 ha-1 , was 1.06 m2 ha-1 over a mean 14 years timeframe. The majority of the measurement period, commencing between 1982 and 1988, was characterized by below-average rainfall. The increase in live tree basal area was due primarily to growth of existing trees (3.12 m2 ha-1 ) rather than establishment of new plants (0.25 m2 ha-1 ) and was partly offset by death (2.31 m2 ha-1 ). A simple but robust relationship between stand basal area and stand biomass of all woody species was developed for the eucalypt dominant woodlands. Analysis of above-ground carbon stocks in live and standing dead woody plants gave a mean net above-ground annual carbon increment for all 57 sites of 0.53 t C ha-1 y-1 , similar to values estimated elsewhere in world savannas. Published root : shoot ratios were used to infer C flux in woody root systems on these sites. This results in an estimated sink in above- and below-ground biomass of 18 Mt C y-1 over the eucalypt woodlands studied, and potentially up to 35 Mt C y-1 if extended to all grazed woodlands in Queensland. It is suggested that introduction of livestock grazing and altered fire regimes have triggered the change in tree-grass dominance in these woodlands. Thus, change in carbon stocks in the grazed woodlands of Queensland is identified as an important... [ABSTRACT FROM AUTHOR]

Leaf ash content and potassium (K) concentration were evaluated as surrogates of carbon isotope discrimination (Δ) of the dominant species in an upland grassland in a 3-year experiment. Previous results reported positive correlations between Δ and ash content or mineral concentrations, attributing this relationship to the passive accumulation, through the transpiration stream, of minerals in the vegetative plant parts. We found only a weak positive correlation between Δ and ash content or K concentration in 1997 (r=0.79, P < 0.05 and r=0.77, P < 0.05, respectively). No significant correlation was found between the traits in 1998 and 1999. When four of the seven most abundant species (Poa pratensis , Lolium perenne , Festuca valida and Taraxacum officinale ) were grown under different treatments (mixed sward, monoculture, and nitrogen and P additions in mixed sward), a curvilinear relationship between Δ and ash content or K concentration was evident. Thus, our findings suggest that leaf ash content and K concentration cannot serve as surrogates of carbon isotope discrimination (Δ). Small genotype × environment interactions were reported for the three traits measured; the interactions were smallest for ash content. A positive correlation between leaf ash content and soil water content (at 5 and 15 cm depth) was found for four species (P. pratensis , L. perenne , F. valida and Achillea millefolium ) and for the community as a whole. No significant correlation was found between leaf K concentration and soil water content. [ABSTRACT FROM AUTHOR]

Presents carbon isotopic records in paleosols over the Pliocene in northern China. Magnetic susceptibility curves; Effects of carbon isotopes on vegetation; Decline in atmospheric carbon dioxide concentration.

Summary • The potential amelioration of Al (Al) toxicity by elevated dissolved inorganic carbon (DIC = CO2 + HCO3-) in the root medium was investigated in both NH4+- and NO3--fed Lycopersicon esculentum (tomato) plants. • Hydroponically grown L. esculentum seedlings were intermittently supplied with 50 µM AlCl3 and the nutrient solutions aerated with either 360 or 5000 ppm CO2. Relative growth rate (RGR), nitrogen uptake, root respiration and root incorporation of DI14C and subsequent partitioning were measured. • Al reduced the RGR of plants grown with 360 ppm root-zone CO2. At elevated root-zone CO2, Al had no significant effect on the RGR of NO3--fed plants whereas the RGR of the NH4+-fed plants was increased by 21%. Al decreased the respiratory quotient (Rq) by 15% at 360 ppm CO2, but had no influence at 2000 ppm CO2. Exudation of organic 14C, especially of [14C]-organic acids derived from root incorporation of DI14C, was increased by Al. • It is concluded that elevated DIC partially ameliorated Al toxicity by providing anaplerotic carbon for organic acid synthesis. [ABSTRACT FROM AUTHOR]

Examines the role of the demand for carbon assimilates in regulating photosynthetic carbon assimilation in response to phosphate deficiency in tobacco. Method of maintenance or withdrawal of phosphate supply; Rates of sucrose export from leaves; Conclusion that low sink strength imposes the primary limitation on photosynthesis in phosphate-deficient plants.

Influence of plant internal nitrogen (N) stocks on carbon (C) and N uptake and allocation in 3-year-old beech (Fagus sylvatica L.) was studied in two 15N- and 13C-labeling experiments. In the first experiment, trees were grown in sand and received either no N nutrition (–N treatment) or 4 mM unlabeled N (+N treatment) for 1 year. The –N- and +N-pretreated trees were then supplied with 4 mM 15N and grown in a 13CO2 atmosphere for 24 weeks. In the second experiment, trees were pretreated with 4 mM 15N for 1 year and then supplied with unlabeled N for 24 weeks and the remobilization of stored 15N was monitored.On the whole-plant level, uptake of new C was significantly reduced in –N-pretreated trees; however, partitioning of new C was not altered, although there was a trend toward increased belowground respiration. The amount of N taken up was not influenced by N nutrition in the previous year. In +N-pretreated trees, partitioning of new N was dominated by the fine roots (59.7% at Week 12), whereas in –N-pretreated trees, partitioning of new N favored stem, coarse roots and fine roots (24, 21 and 31.9%, respectively, at Week 12), indicating the formation of N stores. The contribution of previous-year N to leaf N was about 15%. The N remobilized for leaf formation had been stored in stem and coarse roots. We conclude that, within a growing season, the growth of beech is strongly determined by the availability of tree internal N stores, whereas the current N supply is of less importance. [ABSTRACT FROM AUTHOR]

To gain insight into the limitations imposed by a typical Mediterranean-climate summer drought on the uptake of carbon and ozone in the ponderosa pine (Pinus ponderosa Dougl. ex Laws.) ecosystem, we compared diurnal trends in leaf physiology of young trees in a watered and a control plot located in the Sierra Nevada Mountains, CA, USA (Blodgett Forest, 38°53′ N, 120°37′ W, 1315 m elevation). Predawn water potential of trees in the watered plot remained above –0.3 MPa throughout the growing season, whereas it dropped in the control plot from –0.24 to –0.52 MPa between late May and mid-August. Photosynthesis and stomatal conductance of trees in the watered plot were relatively insensitive to atmospheric vapor pressure deficit (VPD), whereas gas exchange of trees in the control plot varied with changes in soil water, VPD and temperature. Although the 1998 growing season was abnormally wet, we saw a pronounced drought effect at the control site. Over the 2 months following the onset of watering, carbon and ozone uptake were measured on three days at widely spaced intervals. Carbon uptake per unit leaf area by 1-year-old foliage of trees in the control plot was 39, 35 and 30 % less, respectively, than in the watered plot, and estimated ozone deposition per unit leaf area (ozone concentration times stomatal conductance) was 36, 46 and 41 % less. [ABSTRACT FROM PUBLISHER]

Drought stress plays an important role in determining both the structure and function of forest ecosystems, because of the close association between the carbon (C) and hydrological cycles. We used a detailed model of the soil–plant–atmosphere continuum to investigate the links between carbon uptake and the hydrological cycle in a mature, open stand of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) at the Metolius river in eastern Oregon over a 2-year period (1996–1997). The model was parameterized from local measurements of vegetation structure, soil properties and meteorology, and tested against independent measurements of ecosystem latent energy (LE) and carbon fluxes and soil water content. Although the 2 years had very different precipitation regimes, annual uptake of C and total transpiration were similar in both years, according to both direct observation and simulations. There were important differences in ratios of evaporation to transpiration, and in the patterns of water abstraction from the soil profile, depending on the frequency of summer storms. Simulations showed that, during periods of maximum water limitation in late summer, plants maintained a remarkably constant evapotranspirative flux because of deep rooting, whereas changes in rates of C accumulation were determined by interactions between atmospheric vapor pressure deficit and stomatal conductance. Sensitivity analyses with the model suggest a highly conservative allocation strategy in the vegetation, focused belowground on accessing a soil volume large enough to buffer summer droughts, and optimized to account for interannual variability in precipitation. The model suggests that increased allocation to leaf area would greatly increase productivity, but with the associated risk of greater soil water depletion and drought stress in some years. By constructing sparse canopies and deep rooting systems, these stands balance reduced productivity in the short term with risk avoidance over the long term. [ABSTRACT FROM PUBLISHER]

Mycorrhizal symbiosis involves reciprocal transfer of carbon and nutrients between shoots on the one hand and roots colonized by symbiotic fungi on the other. Mycorrhizas may improve the mineral nutrient acquisition rates, but simultaneously increase the belowground demand for carbon. Mycorrhizal plants will have a selective advantage over non-mycorrhizal ones if they are more cost-efficient in terms of carbon cost per unit of acquired mineral nutrient. However, we demonstrate here in a simple model system that this is not a necessary condition. Mycorrhizas may evolve even when they are less cost-efficient, provided that photosynthesis and/or growth are strongly nutrient-limited. This result implies a unique hypothesis for the evolution of mycorrhizal associations which may be inherently cost-inefficient as compared to plant roots. Such symbioses may have evolved when the superior nutrient acquisition rate of fungi combines with the relatively high photosynthetic nutrient use efficiency of the host plant. Consequently, provided that mycorrhizas are really cost-inefficient, the selective advantage of mycorrhizal plants will disappear when an increase in the nutrient acquisition rate is not associated with a sufficiently high nutrient use efficiency of photosynthesis, as at high soil nutrient levels or due to a loss of leaf area, shading or low temperatures. [ABSTRACT FROM AUTHOR]

The objectives of this study were to investigate Piliostigma reticulatum (shrub) and Cordyla pinnata (tree) residues for chemical composition, and C, N, and P mineralizationin Senegalese soils. Soil samples (Sols ferrugineux tropicaux) were collected from a native agroforestry system beneath and outside a C. pinnata canopy. Soils were incubated for 11 weeks with P. reticulatum (leaves), C. pinnata (stem, leaves or stem + leaves), peanut (Arachis hypogea), or pearl millet (Pennisetum glaucum) residues. Nitrogen and P mineralization for the soil-plant mixtures was determined by periodic leaching with a 0.01 M CaCl[sub 2] solution. An additional separate incubation was conducted to investigate C mineralization. The results showed that only peanut residues caused net N mineralization, while N immobilization occurred in the remaining treatments in both the soils derived from beneath or outside the canopy. This indicates that, at least in the short-term, these agroforestry residues would not likely be a source of N for crops. Net P mineralization varied among plant residues and soils sites but P. reticulatum amended soils increased soluble PO in both soils. This suggested that it could be useful for improving P avail4 ability. Peanut residues had the highest CO evolution in both soils suggesting a 2 probable relationship between C and N mineralization. [ABSTRACT FROM AUTHOR]

When carrot suspension cells were cultured on medium containing no carbon source (starvation), the levels of phosphatidylserine (PS) increased transiently 3–4 d after the initiation of starvation while levels of most other phospholipid (PL) species decreased. We previously reported that fatty acids of these PLs served as an alternative carbon source during starvation. The present study showed that cells possess two different biosynthetic pathways involving phosphatidylcholine (PC)/phosphatidylethanolamine (PE) exchange enzymes and PS synthase to synthesize PS. These activities peaked similarly 4 d after the initiation of starvation and coincided with the peak of PS level. The synthesis of serine was also significantly activated during starvation. The activity of phosphoserine aminotransferase (PSAT) which is involved in serine synthesis increased with a time course similar to that of the increase in the PS level. These observations suggest that the increase in PS level plays an important role in membranes which are degraded during starvation. [ABSTRACT FROM PUBLISHER]

Growth during pre-emergence of three sugarbeet genotypes, all tolerant to the root disease rhizomania but with poor emergence features, was studied. Dry mass, carbon and nitrogen content, and N isotope composition were measured for the seeds and each seedling part. These results were compared with those obtained for Vega, a genotype with no emergence problems. The depletion of seed reserves and carbon use were similar for all genotypes. Tolerant genotypes had altered nitrogen absorption: the net nitrogen balance (total N in the seedling/N initial mass in the seed) was 20% lower in these genotypes at the end of the experiments. Differences in the natural abundance of15N in seeds and nutrient solutions were used to determine the proportion of N originating from seed reserves or from absorption by the organs. N absorbed from the nutrient solution was found mainly in the hypocotyl and radicle, with less in the cotyledons of all genotypes. Tolerant genotypes had less absorbed N in all parts than non-tolerant genotypes. Hypocotyl and radicle elongation was the same in all genotypes, but the emergence forces in rhizomania-tolerant genotypes were smaller. These results suggest that breeding to introduce tolerance to rhizomania has also led to a lowered mineral absorption capacity. Copyright 2000 Annals of Botany Company [ABSTRACT FROM AUTHOR]

Examines various hypothesis regarding the changes in 13C of emitted CO[sub2] that follow the addition C[sub4]-sucrose to the soil of a C[sub3]-ecosystem. Calculation of total soil respiration; Estimation of 13C with the help of three on sieved mor-layer material; Difference between carbon dioxide evolved from microbial mineralization of added sucrose and carbon dioxide evolved from endogenous carbon sources.

A popular conceptual model asserts that shade tolerance is characterized by morphological and physiological traits that enhance the net rate of carbon capture in low light. We tested this model by quantitatively reviewing growth, leaf lifespan. CO2 exchange and morphological data from 76 studies on woody seedlings grown under conditions of low light. Data were placed into three tolerance categories (intolerant, intermediate, tolerant), tow light categories (less than 4% and 4-12%) and two leaf phenology categories (broad-leaved evergreen and winter diciduous). For both evergreen and deciduous groups, intolerant species had traits conferring greater growth potential than tolerant species in both light categories. These traits included greater leaf mass ratio, leaf area ratio, specific leaf area and mass-based photosynthetic rates above light together with higher respiration rates for intolerant species limited to expression of their growth potential differences. Deciduous and evergreen intolerant species were similar in many respects. However, both intermediate and tolerant deciduous species had markedly lower leaf mass ratios and higher root mass ratios than intermediate and tolerant evergreen species. In addition, deciduous species and intolerant evergreen must cope with as much as stifled higher leaf turnover rates than tolerant evergreen species. Thus, rather than maximizing growth rates in low light, tolerant evergreen species minimize biomass losses by minimizing whole-plant respiration rates but they accomplish low biomass turnover though low leaf mass ration and not low leaf turnover rates. Furthermore, unlike most tropical evergreens, tolerant deciduous species can gain large fractions of their total growing season carbon during short periods when the overstay is leafless and then allocate this carbon to storage (as reflected by high root mass ratios) rather than new leaves. In conclusion, we found no support for the low-hight-enhanced carbon capture model of shade tolerance as viewed strictly from the perspective of physiological growth capacity. This can be explained by the disadvantage to net growth and survival o maintaining a high growth potential at low light, because high growth potential results in greater rates of whole-plant respiration, tissue turnover, herbivory and mechanical damage and in decreased storage. Thus, shade tolerance can be characterized by traits that maximize survival and net growth, where net growth includes losses to all agents. [ABSTRACT FROM AUTHOR]

1. We present data on the gas exchange of 32 Beech–Spruce model ecosystems including understorey species, which were planted on acidic or calcareous soil in 16 (half-split) open-top chambers in 1994 and were continuously exposed to the combinations of two CO2 concentrations and two wet nitrogen deposition rates for 3 years. 2. Instantaneous mid-season net ecosystem carbon-exchange rates (NEC) were determined during the day (11.00–16.00 h, NECd) and at night (22.00–02.00 h, NECn) with a mobile chamber in July 1996 and August 1997 for both soil types and, in addition, in August and September 1996 on acidic soil only. 3. Elevated CO2 increased NECd at all sampling dates on both soil types and under both N deposition rates. Increased nitrogen deposition stimulated NECd on acidic soil but not on calcareous soil, irrespective of the CO2 level. NECn was increased in elevated CO2 on both soil types (but more on the calcareous soil), but did not respond to increased nitrogen deposition in both years. The daytime instantaneous ecosystem evapotranspiration (ETd) was not significantly affected by the CO2 and nitrogen treatments at any sampling date. Year to year differences in NECn and ETd were small, but a doubling in NECd occurred throughout the observation period. 4. Elevated CO2 caused a small but significant increase in stem dry mass on calcareous soil only and increased nitrogen deposition stimulated stem biomass production on acidic soil only. Leaf area index was not affected by CO2, but was increased under high nitrogen deposition. 5. Our results suggest that nitrogen deposition and soil type are major co-determinants of the carbon balance of forests in a future CO2-rich world. [ABSTRACT FROM AUTHOR]

A mathematical model of carbon accumulation by growing fruit is presented. The model implicitly incorporates the concepts of sink activity and sink size but avoids the need to stipulate sink strength. In addition to sink activity and size, carbon accumulation depends on characteristics such as photosynthesis and respiration of the fruit itself as well as carbon supply via the peduncle attachment. Simulations with prescribed limitations of carbon supply show similar results to field observations. The proposed model coupled with a carbon distribution/supply model could simulate the growth of individual fruit within a heterogeneous canopy.Copyright 1999 Annals of Botany Company [ABSTRACT FROM AUTHOR]

To determine how plants control leaf phenology to maximize annual carbon gain, I examined ontogenetic changes in leaf phenology of Japanese elm, Ulmus davidiana var. japonica Nakai plants of different ages growing in contrasting light environments. Leaf emergence occurred earlier in 1- and 2-year-old seedlings than in current-year seedlings. Although leaf emergence was not affected by light conditions at the sites, it was influenced by plant height. The delay in leaf emergence increased with increasing plant height. These traits indicate that seedlings that received the least light during the summer intercepted light for a long period during the spring; however, the advantage of earlier leaf emergence decreased with increasing plant height. At each site, 1-year-old seedlings had a longer duration of leaf emergence than adults, because of a longer period of favorable light conditions even in the forest understory. Duration of leaf emergence, leaf duration and leaf longevity were usually longer in sun than in shade for both seedlings and adults; however, flexibility in the response to light was greater in seedlings than in adults. The plastic response in leaf phenology during the juvenile stages may contribute to the optimization of light acquisition in habitats with differing light conditions, thereby enhancing seedling survival. [ABSTRACT FROM PUBLISHER]

Continuous wetness of leaves in the light causes a reduction in the carbon exchange rate (CER) in Phaseolus vulgaris L. [Ishibashi and Terashima (1995) Plant Cell Environ. 18: 431]. In this study, we investigated the initial cause of photoinhibition upon application of water, designated rain treatment, and we found a large decrease in the rate of electron transport through the whole chain from water to methyl viologen via PSII and PSI. In spite of the decrease in the rate of electron transport, there was no decrease in the activity of either PSI or PSII when these activities were measured separately. The intactness of PSI was also confirmed by the absence of any change in the pho-tooxidizable amount of P-700, the reaction centre of PSI, and the intactness of PSII was confirmed by measurements of Chi fluorescence. The results suggest that the inhibition by the rain treatment, which occurs at the site between PSI and PSII, might be a novel type of photoinhibition, unlike the conventional types of photoinhibition that involve PSI and PSII. [ABSTRACT FROM AUTHOR]

Tropical rain forests account for a significant fraction of global net primary productivity, and are important latent energy (LE) sources, affecting extra-tropical atmospheric circulation. The influence of environmental factors on these fluxes has until recently been poorly understood, largely due to a paucity of data, but in recent years the amount of available data has been increased greatly by use of eddy covariance techniques. In this paper we examine the factors that control daily and seasonal carbon (C) and LE fluxes, by comparing a detailed model of the soil–plant–atmosphere continuum against a unique long-term data-set collected using eddy covariance at an undisturbed rain forest site north of Manaus, Brazil. Our initial application of the model was parametrized with simple measurements of canopy structure, and driven with local meteorological data. It made effective predictions of C and LE exchange during the wet season, but dry season predictions were overestimates in both cases. Sensitivity analyses indicated that the best explanation for this behaviour was a seasonal change in soil and root hydraulic resistances (Rb). An optimization routine was then used to estimate the increase in Rb during the dry season that would be required to explain the reduced dry season fluxes. The local soil, a clay latosol, is typical of much of Amazônia, having very low available water and low hydraulic conductivity. We conclude that an increase in soil–root hydraulic resistance in the dry season introduces a significant seasonal cycle to carbon and water fluxes from this tropical forest. Furthermore, our model structure appears to be an effective tool for regional and temporal scaling of C and LE fluxes, with primary data requirements being regional and temporal information on meteorology, leaf area index (LAI), foliar N, critical leaf water potentials, and plant and soil hydraulic characteristics. [ABSTRACT FROM AUTHOR]

A comparative analysis of daily carbon (C) budgets and aspects of the C physiology of clover (Trifolium repens L.) colonized by vesicular-arbuscular (VA) mycorrhizal fungi was carried out over a 70 d growth period under conditions designed to ensure that shoots of mycorrhizal (M) and non-mycorrhizal (NM) plants were of similar nutrient status. C budgets did not differ on day 24 but by day 42 M plants had a significantly higher rate of photosynthesis than their NM counterparts when expressed on a whole shoot basis or unit dry weight basis. As both sets of plants were of the same size it was concluded that this greater C gain was the result of increased sink strength provided by the mycorrhizal fungus. By day 53 M plants had become larger than their uncolonized counterparts and a sink-induced stimulation in the rate of photosynthesis was no longer apparent. M plants had higher root sucrose, glucose and fructose pools from day 24. Analyses suggested that these sugars were utilized for trehalose and lipid synthesis, for the production of the large extramatrical mycelium and for the support of the respiratory demands of the M root system. Increased C allocation to roots of M plants was associated with a stimulation of the activities of cell wall and cytoplasmic invertases and of sucrose synthase in roots colonized by VA fungi. Such increases in enzyme activity may provide the mechanism enabling increased partitioning of carbohydrate both to the M root system and the fungal symbiont. [ABSTRACT FROM AUTHOR]

Experiments were conducted on well watered 1-year-old Douglas fir [Pseudotsuga menziesii (Mirb.) Franco], western hemlock [Tsuga heterophylla (Raf.) Sarg.] and western redcedar (Thuja plicata Donn) seedlings to determine the effects of temperature on whole-plant photosynthetic and stomatal responses to short-term fluctuations in irradiance (Q). Following a step change in Q, time constants (τ, the period over which 63% of the total change occurs) for stomatal conductance (gs) and assimilation rate (A) decreased linearly with increasing air temperature (Tair). For example, in western redcedar τA decreased from 30±4 min at 5°C to 10±1 min at 25°C. In all cases, τA was within 10-15% of τgs. There was considerable variation in τ among individuals within a given species. Differences between species became more pronounced with decreasing temperature. Multiplicative models that included functions for τ accounted for 99% of the diurnal variability in A and gs for seedlings exposed to varying air temperature, irradiance and vapour pressure deficit. Estimates of daily A were within 2% of those measured. Intermittent cloud cover and understory shading were approximated by exposing seedlings to 3-4 episodes (≥ 1 h) of shade (200 or 500 μmol m-2s-1) or complete darkness during the day. In such cases, daily A was overestimated by up to 4 and 21%, respectively, if a function for τ was excluded from the models. Our results suggest that there is scope for selecting seedling stock for increased carbon assimilation on the basis of reduced time constants. For example, in western redcedar, a 40% reduction in τ could lead to increases in daily carbon gains of almost 5% depending on the frequency and degree of shading. If these daily gains were translated into i... [ABSTRACT FROM AUTHOR]

Photosynthetic capacities of five species of brown algae in red light were found to be strongly limited by the inorganic carbon supply of natural sea water, Under these conditions, pH 8.2 and dissolved inorganic carbon concentration (DIC) of 2.1 mol m-3, a short pulse of blue light was found to increase the subsequent rate of photosynthesis in saturating red light. The degree of blue light stimulation varied between species, ranging from an increase of over 200% of the original rate in Colpomenia peregrina to only 10% in Dictyota dichotoma. Increasing the DIC concentration of sea water by bicarbonate addition resulted in carbon saturation of photosynthesis in all five species. Blue light stimulation was greatly reduced at these higher DIC concentrations. The response in Laminaria digitata was examined in more detail by manipulation of pH and DIC to produce solutions with different concentrations of dissolved CO2. At a CO2 concentration typical of normal sea water (12.4 mmol m-3), blue light treatment increased Photosynthetic rate by approximately 50%. Blue light stimulation was increased to over 150% at CO2 concentrations below that of sea water, whereas at concentrations above that of sea water, the effect was diminished. Therefore, the effect of blue light on photosynthetic capacity appears to involve an increase in the rate of supply of carbon dioxide to the plant. [ABSTRACT FROM AUTHOR]

Ultrastructural and physiological characteristics of the C3-C4 intermediate Neurachne minor S. T. Blake (Poaceae) are compared with those of C3and C4 relatives, and C3-C4 Panicum milioides Nees ex Trin . . N. minor consistently exhibits very low CO2 compensation points (Γ : ≤ 1.0, usually 0.0.6 Pa) yet has C3-like δ13C values. CO2 assimilation rates (A) respond like those of C3 plants to a decrease in O2 partial pressure (2 × 104-1.9 × 103 Pa) at ambient CO2 levels, but this response is progressively attenuated until negligible at very low CO2. By contrast, other species of the Neurachneae are clearly either C4 (two spp.) or C3 (seven spp.). For plants grown and measured at different photon flux densities (PFDs), Γ for N. minor and P. milioides increases from 0.5 to 1.0, and from 1.0 to 2.1 Pa, respectively, as PFD is decreased from 1860 to 460 μmol m-2s-1. In N. minor, the O2response of Γ is either biphasic as in P. milioides, but much diminished and with a higher transition point, or is very C4-like. As in C4 relatives, inner sheath cells contain numerous chloroplasts. Their walls possess a suberized lamella, which may make them more CO2-tight than bundle sheath cells of P. milioides, contributing to the almost C4-like Γ characteristics of N. minor. The biochemical basis of C3-C4 intermediacy is considered. [ABSTRACT FROM AUTHOR]

A comparison of some of the methods used to determined whether aquatic plants have the ability to utilize bicarbonate ions as a source of inorganic carbon for photosynthesis has been applied to the intertidal macroalga Ascophyllum nodosum. These include: observing photosynthesis at a high pH (below the alga's CO2 compensation point), pH compensation point determinations, comparing the photosynthetic characteristics at low pH (5.20) and at high pH (7.95), estimating the maximal rates at which CO2 can diffuse through the unstirred layer and the rate at which CO2 can be produced form bicarbonate dehydration in the unstirred layer. All indicated that Ascophyllum nodosum can use bicarbonate ions for photosynthesis, though some were not always consistent. Calculating the total inorganic carbon concentration form pH measurements and acidification CO2 determinations revealed that the assumption that the alkalinity remains constant during pH drift experiments is not always valid. [ABSTRACT FROM AUTHOR]

Investigates the carbon-nutrient balance of heather, Calluna vulgaris based on the plant's response to treatments of shade and nutrients. Etiolation of shoots; Low shoot density; Increase of total nitrogen; Decrease of carbon-based constituents.