bluuebunny/crossref_metadata_2025_split huggingface dataset:
A computer‐controlled system for studying ammonia exchange, photosynthesis and transpiration of plant canopies growing under controlled environmental conditions
Authors: HUSTED S. , SCHJOERRING J. K. 
Published: April 2006

ABSTRACTA fully automatic growth chamber system was built in order to study NH3, exchange and NH3, compensation points of plant canopies growing under controlled environmental conditions in which atmospheric NH3, concentrations corresponded to those naturally occurring over terrestrial ecosystems. The system included plant cuvettes with separate root and shoot compartments constructed of coated polycarbonate. This material did not change the spectral composition of photosynthetically active light and had a low adsorption of NH3, and water vapour. Atmospheric NH3, concentrations in the inlet of the cuvettes were controlled by mass‐flow controllers. Inlet and outlet NH3, concentrations were measured on‐line with a modified chemiluminescent NH3, monitor. At airflow rates per unit leaf area of about 3 dm3 m−2 s−1, the system allowed accurate determinations of NH3, exchange rates down to about 0.1 nmol NH3, m−2 s−1. The NH3, compensation points at anthesis for barley cultivars Laevigatum and Golf were 4.2±2.8 and 4.6±2.9nmol mol−1 of NH3, in air (SE, n=4), respectively. NH3, absorption in both cultivars increased linearly with atmospheric NH3, concentration in the range 0–30 nmol mol−1 of NH3, in air. NH3, absorption was much higher in the light than in the dark, indicating a strong stomatal and/or metabolic control of NH3, exchange. Photosynthesis and transpiration were not affected by exposure to NH3, concentrations in the range 0–30nmol mol−1 for 7d.
Scaling the seas
Authors: RAVEN J. A. 
Published: April 2006

ABSTRACTPrimary producers in aquatic environments cover a range of living biomasses from 10−13 to 104 g dw. Benthic plants at the high end of this range contribute 5 Gt C year,1 to global primary productivity. Plankton at the lower end (up to 10−4 g dw) contributes about 30 Gt C year−1. While many problems of interpretation remain, in general terms the size of the organisms which dominate particular habitats can be related to the physics of water movement and its interaction with the availability of light and nutrients, the generation time of the organism, and the attentions of grazers. A second scaling problem is that of methods of studying the global energy flow and nutrient cycling roles of aquatic primary producers. Problems with scaling up from small‐scale and mesoscale to regional or global scale, and the prospects of more direct estimates of large‐scale productivity, are discussed.
Towards a better experimental basis for upscaling plant responses to elevated CO2 and climate warming
Authors: KÖRNER Ch. 
Published: April 2006

ABSTRACTFew of the most common assumptions used in models of responses of plants and ecosystems to elevated CO2 and climate warming have been tested under realistic life con‐ditions. It is shown that some unexpected discrepancies between predictions and experimental findings exist, suggesting that a better empirical basis is required for predictions. The following ten suggestions may improve our potential to scale up from experimental scales to the real world.(1) Experiments should be timed to account for non‐linearity in system responsiveness, asynchrony of responses and developmental differences. (2) By altering mineral nutrient supply, a wide range of CO2 responses can be ‘produced’, thus requiring realistic soil conditions. (3) Distinctions should be made between ‘doubling CO2 sup‐ply’ and biologically effective degrees of CO2 enrichment. (4) Because of the non‐linearity of plant responses to CO2, studies of at least three instead of two CO2 concentrations are necessary to describe future trends adequately. (5) Edge effects, in particular unscreened side light, may lead to allometric anomalies, strongly constraining up‐scaling to stand‐scale CO2 responses. (6) Variables such as growth, yield, net primary production and C turnover are often confused with carbon pools, carbon sequestration or net ecosystem production. (7) Mono‐ and interspecific interactions between individuals may lead to completely unpredictable CO2 responses. (8) Experiments with seedlings benefit from the absence of prehistory effects but are likely to be irrelevant for the responses of larger trees which, on the other hand, may be constrained by carry‐over effects. Tree ring research indicates immediate sensitivity of large trees to environmental changes, supporting their usefulness in short‐term CO2‐enrichment experiments. (9) In predicting temperature responses, acclimation deserves more attention. (10) The significance of developmental responses is largely under‐represented in experimental research, although these responses may overrule many of the other effects of atmospheric change. Results of more realistic experiments which account for these problems will provide a better basis for modelling the future of the biosphere.
Scaling gross ecosystem production at Harvard Forest with remote sensing: a comparison of estimates from a constrained quantum‐use efficiency model and eddy correlation
Authors: WARING R.H. , LAW B.E. , GOULDEN M.L. , BASSOW S.L. , McCREIGHT R.W. , WOFSY S.C. , BAZZAZ F.A. 
Published: April 2006

ABSTRACTTwo independent methods of estimating gross ecosystem production (GEP) were compared over a period of 2 years at monthly integrals for a mixed forest of conifers and deciduous hardwoods at Harvard Forest in central Massachusetts. Continuous eddy flux measurements of net ecosystem exchange (NEE) provided one estimate of GEP by taking day to night temperature differences into account to estimate autotrophic and heterotrophic respiration. GEP was also estimated with a quantum efficiency model based on measurements of maximum quantum efficiency (Qmax), seasonal variation in canopy phenology and chlorophyll content, incident PAR, and the constraints of freezing temperatures and vapour pressure deficits on stomatal conductance. Quantum efficiency model estimates of GEP and those derived from eddy flux measurements compared well at monthly integrals over two consecutive years (R2= 0–98).Remotely sensed data were acquired seasonally with an ultralight aircraft to provide a means of scaling the leaf area and leaf pigmentation changes that affected the light absorption of photosynthetically active radiation to larger areas. A linear correlation between chlorophyll concentrations in the upper canopy leaves of four hardwood species and their quantum efficiencies (R2= 0–99) suggested that seasonal changes in quantum efficiency for the entire canopy can be quantified with remotely sensed indices of chlorophyll. Analysis of video data collected from the ultralight aircraft indicated that the fraction of conifer cover varied from < 7% near the instrument tower to about 25% for a larger sized area. At 25% conifer cover, the quantum efficiency model predicted an increase in the estimate of annual GEP of < 5% because unfavourable environmental conditions limited conifer photosynthesis in much of the non‐growing season when hardwoods lacked leaves.
Carbon balance in the tundra, boreal forest and humid tropical forest during climate change: scaling up from leaf physiology and soil carbon dynamics
Authors: WANG Y. P. , POLGLASE P. J. 
Published: April 2006

ABSTRACTCarbon exchange by the terrestrial biosphere is thought to have changed since pre‐industrial times in response to increasing concentrations of atmospheric CO2 and variations (anomalies) in inter‐annual air temperatures. However, the magnitude of this response, particularly that of various ecosystem types (biomes), is uncertain. Terrestrial carbon models can be used to estimate the direction and size of the terrestrial responses expected, providing that these models have a reasonable theoretical base. We formulated a general model of ecosystem carbon fluxes by linking a process‐based canopy photosynthesis model to the Rothamsted soil carbon model for biomes that are not significantly affected by water limitation. The difference between net primary production (NPP) and heterotrophic soil respiration (Rh) represents net ecosystem production (NEP). The model includes (i) multiple compartments for carbon storage in vegetation and soil organic matter, (ii) the effects of seasonal changes in environmental parameters on annual NEP, and (iii) the effects of inter‐annual temperature variations on annual NEP. Past, present and projected changes in atmospheric CO2 concentration and surface air temperature (at different latitudes) were analysed for their effects on annual NEP in tundra, boreal forest and humid tropical forest biomes. In all three biomes, annual NEP was predicted to increase with CO2 concentration but to decrease with warming. As CO2 concentrations and temperatures rise, the positive carbon gains through increased NPP are often outweighed by losses through increased Rh, particularly at high latitudes where global warming has been (and is expected to be) most severe. We calculated that, several times during the past 140 years, both the tundra and boreal forest biomes have switched between being carbon sources (annual NEP negative) and being carbon sinks (annual NEP positive). Most recently, significant warming at high latitudes during 1988 and 1990 caused the tundra and boreal forests to be net carbon sources. Humid tropical forests generally have been a carbon sink since 1960. These modelled responses of the various biomes are in agreement with other estimates from either field measurements or geochemical models. Under projected CO2 and temperature increases, the tundra and boreal forests will emit increasingly more carbon to the atmosphere while the humid tropical forest will continue to store carbon. Our analyses also indicate that the relative increase in the seasonal amplitude of the accumulated NEP within a year is about 0–14% year−1 for boreal forests and 0–23% year−1 in the tundra between 1960 and 1990.
‘Photoinhibition’ of Heliconia under natural tropical conditions: the importance of leaf orientation for light interception and leaf temperature
Authors: HE J. , CHEE C. W. , GOH C. J. 
Published: April 2006

ABSTRACTThe influence of irradiance on photosynthesis under natural conditions was studied in aseasonal Singapore using three Heliconia taxa: H. rostrata, H. psittacorum × H. spathocircinata cv. Golden Torch and H. psittacorum cv. Tay. When grown under full sunlight, all three heliconias exhibited reduced phatosynthetic capacities and lowered chlorophyll content per leaf area as compared with those grown under intermediate and deep shade. A marked decrease in the chlorophyll fluorescence Fv/Fm ratio and an increase in photochemical quenching (1‐ qp) and non‐photochemical quenching (qN) were observed in upper leaves of plants grown under full sunlight. Increases in qN suggest that ‘photoinhibition’ (decreases in Fv/Fm) in Heliconia grown under natural tropical conditions are probably due to photoprotective energy dissipation processes. The quantum yield, the maximum photosynthetic rate, Fv/Fm and the chlorophyll content of upper leaves were lower than those of lower leaves on the same plants grown under full sunlight. Similarly, lower values were obtained for the tip (sun) portion than for the base (shaded) portion of the leaves. The changes in Fv/Fm and in the levels of (1 –qp) in leaves grown under intermediate and deep shade were negligible in plants during the course of day. However, there was a steep decrease in Fv/Fm and an increase in the levels of (1 –qp), along with an increase in incident light in the sun leaves. The lowest Fv/Fm and the highest level of (1 –qp) indicated minimum PSII efficiency at midday in full sun. These results indicate that, in Heliconia, the top leaves (particularly leaf tips) experienced sustained decreases in PSII efficiency upon exposure to full sunlight. Although all three taxa exhibited sustained decreases in photosynthetic capacity in full sunlight, the sun leaves of ‘Tay’ showed higher photosynthetic capacity than those of the other two taxa. This could be due, at least in part, to the vertical leaf angle and smaller lamina area. When the upright leaves of ‘Tay’ were constrained to a horizontal angle, they exhibited lower PSII efficiency (FvIFm ratio), while horizontal leaves of ‘Rostrata’ and ‘Golden Torch’ inclined lo near‐vertical angles showed increased efficiency. Thus, an increase in leaf angle helps to achieve a reduction in the sustained decrease in PSII efficiency by decreasing the levels of incident sunlight and subsequently the leaf temperature.
Evaluation of the potential to measure photosynthetic rates in C3 plants (Flaveria pringlei and Oryza sativa) by combining chlorophyll fluorescence analysis and a stomatal conductance model
Authors: HE D. , EDWARDS G. E. 
Published: April 2006

ABSTRACTThe response curves of leaf photosynthesis to varying light, temperature and leaf‐to‐air vapour pressure deficit were measured in the C3 plants Flaveria pringlei and Oryza sativa in normal air with a computerized open infrared gas analysis (IRGA) system, and the photochemical efficiency of photosystem II, described as (1–F,/F′m) after Genty. Briantais & Baker (1989, Biochimica et Biophysica Acta 990, 87–92), was simultaneously measured with a modulated fluorometer. A model was written for rates of CO2 fixation as a function of the true rate of O2 evolution measured by fluorescene analysis (Jo2), mesophyll conductance and intercellular CO2 partial pressure. A second model was developed for rates of CO2 fixation as a function of Jo2, mesophyll conductance and stomatal conductance. In the latter case, leaf stomatal conductance was simulated using the stomatal model proposed by Leuning (1995, Plant, Cell and Environment18, 339–355). The rates of CO2 fixation predicted from the models were similar to rates measured by IRGA. The results indicate that there is potential to measure CO2 fixation in C3 plants by combining the non‐invasive measurement of Jo2 by chlorophyll fluorescence analysis with the stomatal conductance model.
Osmotic stress and abscisic acid reduce cytosolic calcium activities in roots of Arabidopsis thaliana*
Authors: CRAMER G. R. , JONES R. L. 
Published: April 2006

ABSTRACTCytosolic Ca2+· ([Ca2+]i, and elongation growth were measured in the roots of Arabidopsis thaliana. Exposure of plant tissues to high NaCl and abscisic acid (ABA) concentrations results in a reduction in the rate of growth, but the mechanism by which growth is inhibited is not understood. Both NaCl and ABA treatments are known to influence [Ca2+]i, and in this study we measured the effects of salinity and ABA on [Ca2+]i in cells from the meristematic region of Arabidopsis roots. The Ca2+‐sensitive dye Fura‐2 and ratiometric techniques were used to measure [Ca2+]i in cells of the root meristem region. Resting [Ca2+]i was found to be between 100 and 200 μmol m−3 in roots of untreated plants. Resting [Ca2+]i changed in response to changes in the [Ca2+] surrounding growing roots. An increase of external [Ca2+] increased [Ca2+]i; conversely, a decrease of external [Ca2+] decreased [Ca2+]i. Exposure of roots to NaCl caused a rapid reduction of [Ca2+]i, a response that was proportional to the external NaCl concentration. Thus, as the NaCl concentration was increased, [Ca2+]i in root meristematic cells decreased. Root elongation was also inhibited in proportion to the external NaCl concentration, with maximal inhibition occurring at 120 mol m−3 NaCl. The [Ca2+]i of root meristem cells also changed in response to ABA, and the magnitude of the effect of ABA was dependent upon ABA concentration. Treatment with 0.2 mmol m−3 ABA caused a momentary increase in [Ca2+]i followed by a decrease after 15 min, but 10 mmol m−3 ABA caused an immediate decline in [Ca2+]i. There was a strong positive correlation between [Ca2+]i and root elongation rates. Experiments with the ABA‐deficient Arabidopsis mutant aba‐3 indicated that the reduction in [Ca2+]i brought about by NaCl was unlikely to be mediated via changes in endogenous ABA. Experiments with solutes such as sorbitol, KCl and NaNO3 indicated that the effects of NaCl could be mimicked by other solutes and was not specific for NaCl.
Sulphate transport in the cyanobacterium Synechococcus R‐2 (Anacystis nidulans, S. leopoliensis) PCC 7942
Authors: RITCHIE R. J. 
Published: April 2006

ABSTRACT Synechococcus R‐2 (PCC 1942) actively accumulates sulphate in the light and dark. Intracellular sulphate was 1.35 ± 0.23 mol m−3 (light) and 0.894 ± 0.152 mol m−3 (dark) under control conditions (BG‐11 media: pHo, 7.5; [SO42−]o, 0.304 mol m−3). The sulphate transporter is different from that found in higher plants: it appears to be an ATP‐driven pump transporting one SO42−/ATP [ΔμSO42−i,o=+ 27.7 ± 0.24 kJ mol−1 (light) and + 24 ± 0.34 kj mol−1 (dark)]. The rate of metabolism of SO42−at pHo, 7.5 was 150 ± 28 pmol m−2 s−1 (n = 185) in the light but only 12.8 ± 3.6 pmol m−2 s−1 (n = 61) in the dark. Light‐driven sulphate uptake is partially inhibited by DCMU and chloramphenicol. Sulphate uptake is not linked to potassium, proton, sodium or chloride transport. The alga has a constitutive over‐capacity for sulphate uptake [light (n= 105): Km= 0.3 ± 0.1 mmol m−3, Vmax, = 1.8 ± 0.6 nmol m−2 s−1; dark (n= 56): Km= 1.4 ± 0.4 mmol m−3, Vmax= 41 ± 22 pmol m−2 s−1]. Sulphite (SO32−) was a competitive inhibitor of sulphate uptake. Selenate (SeO42−) was an uncompetitive inhibitor.
Tree ring responses to elevated CO2 and increased N deposition in Picea abies
Authors: HÄTTENSCHWILER S. , SCHWEINGRUBER F. H. , KÖRNER Ch. 
Published: April 2006

ABSTRACTFour‐ to seven‐year‐old spruce trees (Picea abies) were exposed to three CO2 concentrations (280, 420 and 560 cm3 m−3) and three rates of wet N deposition (0, 30 and 90 kg ha−1 year−1) for 3 years in a simulated montane forest climate. Six trees from each of six clones were grown in competition in each of nine 100 × 70 × 36 cm model ecosystems with nutrient‐poor natural forest soil. Stem dises were analysed using X‐ray densitometry. The radial stem increment was not affected by [CO2] but increased with increasing rates of N deposition. Wood density was increased by [CO2], but decreased by N deposition. Wood‐starch concentration increased, and wood nitrogen concentration decreased with increasing [CO2], but neither was affected by N deposition. The lignin concentration in wood was affected by neither [CO2] nor N deposition. Our results suggest that, under natural growth conditions, rising atmospheric [CO2] will not lead to enhanced radial stem growth of spruce, but atmospheric N deposition will, and in some regions is probably already doing so. Elevated [CO2], however, will lead to denser wood unless this effect is compensated by massive atmospheric N deposition. If can be speculated that greater wood density under elevated [CO2] may alter the mechanical properties of wood, and higher ratios of C/N and lignin/N in wood grown at elevated [CO2] may affect nutrient cycles of forest ecosystems.
Phytochrome is required for the occurrence of time‐dependent phototropism in maize coleoptiles
Authors: LIU Y. J. , IINO M. 
Published: April 2006

ABSTRACTTime‐dependent phototropism (TDP), sometimes called second positive curvature, occurs when the duration of phototropic stimulation with blue light (B) exceeds a few minutes. TDP was characterized in maize (Zea mays L.) coleoptiles raised under continuous red light (R). Subsequently, coleoptiles adapted to darkness were used to investigate the effect of R on TDP. It was found that TDP, which is induced in R‐grown coleoptiles, does not occur in dark‐adapted coleoptiles and that dark‐adapted coleoptiles begin to show TDP after treatment with R. The TDP responsiveness became maximal 1–2 h after treatment with a R pulse and decreased during the next few hours. At least 10 min was required after a short pulse of R before the coleoptile began to respond to B for the induction of TDP. The effect of R in establishing the TDP responsiveness was totally suppressed by a pulse of far‐red light given immediately after an inductive pulse of R. It is concluded that the mechanism of TDP requires for its establishment a R signal perceived by phytochrome. The TDP of R‐grown and R‐pretreated coleoptiles showed relationships to stimulation times and fluence rates that are similar to those reported for oat coleoptiles, except that TDP of maize showed a sharp increase in its magnitude within a narrow range of stimulation times as short as 5–10 min.
Effects of turgor potentials of epidermal cells neighbouring guard cells on stomatal opening in detached leaf epidermis and intact leaflets of Vicia faba L. (faba bean)
Authors: KLEIN M. , CHENG G. , CHUNG M. , TALLMAN G. 
Published: April 2006

ABSTRACTLeaflets of Vicia faba L. (faba bean) were used to determine whether the mechanical forces resulting from the turgor potentials (Φp) of the larger epidermal cells neighbouring guard cells play a significant role in regulating stomatal aperture. When Φp, of epidermis and Φp of bulk leaflet tissue were compared at midday, Φp of epidermis were only 15–25% those of bulk leaflet tissue at all but the most negative leaflet water potentials (Φ). When plants were bagged to increase Φ by reducing vapour pressure differences between leaflets and air, Φp of bulk leaflet tissue increased to predawn values, but Φp, of epidermis increased to only = 20% of predawn values and stomata opened to their widest apertures. Stomatal apertures were positively correlated with Φp of bulk leaflet tissue but they were not correlated with Φp of epidermis. Reductions in epidermal Φp, began predawn, before stomata were open, and reached minimum values at midday, when stomata were open. We conclude that, in Vicia faba, (1) reduction of Φp of epidermal cells begins predawn, reducing the counterforce to stomatal opening that would exist if full epidermal turgor were maintained throughout the day, and (2) changes in Φp, of leaf epidermal cells do not play a significant role in regulating stomatal aperture.
Differential proton secretion in the apical elongation zone caused by gravistimulation is induced by a signal from the root cap
Authors: MONSHAUSEN G. B. , ZIESCHANG H. E. , SIEVERS A. 
Published: April 2006

ABSTRACTThe extracellular proton activity along primary roots of Phelcum pratense L. was measured using proton‐selective microelectrodes. Removal of the root cap caused a reduction of the proton influx in the transitional region between the meristem and the apical elongation zone of the vertical root and inhibited the development of pH differences between the physically upper and lower flanks of the gravis‐stimulated root. Disruption of the actin filament system of the root with 5 mmol m−3 cytochalasin D did not result in an altered proton flux and pH pattern compared with untreated vertical control roots, but inhibited the gravity‐induced development of pH differences between the physically upper and lower root flanks as well as gravitropic curvature. These results provide evidence that pH changes following gravistimulation are induced by a signal transmitted from the root cap and that the actin filament system is involved in the gravity perception/transduction mechanism.