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Carbon Gain (carbon + gain)
Kinds of Carbon Gain Selected AbstractsSpring 2007 warmth and frost: phenology, damage and refoliation in a temperate deciduous forestFUNCTIONAL ECOLOGY, Issue 6 2009Carol K. Augspurger Summary 1.,Climate change is predicted to bring earlier bud break and perhaps a greater risk of frost damage to developing leaves and flowers. Given the rarity and unpredictability of major frost events and limited community-level phenological observations, comparisons among deciduous forest species experiencing frost damage and refoliation are rare. 2.,This study used phenological observations ongoing at the time of a hard freeze to compare leaf and flower development, frost damage and leaf refoliation of 20 deciduous woody species in Trelease Woods, Champaign Co., IL, USA. Freezing temperatures from 5 to 9 April 2007 followed 22 days after very warm temperatures began in March. 3.,Bud break was the earliest in 17 years. Frost caused damage to leaf buds, developing shoots and/or expanding leaves of canopy trees of six species and saplings of two species. Undamaged species were inactive, or in bud break or shoot expansion. Among damaged species, 11,100% of individuals exhibited some frost damage. Mean damage level per individual ranged from 20% to 100% among species. 4.,Refoliation from dormant buds led to mean final canopy fullness that ranged from 46% to 99% among damaged species, but time of full leaf expansion was extended by 16,34 days for refoliating species. 5.,Frost damaged flowers, but not flower buds or developing fruit, of five of eight species that flowered during the frost period. 6.,The extent of frost damage in 2007 was unusual; damage was greater than any of the other 4 years with frost damage from 1993 to 2009 because record-breaking March temperatures in 2007 caused more species to be at later vulnerable stages with the advent of subfreezing temperatures in April. 7.,Differences among individuals and species in frost damage and ability to refoliate caused strong selection on individuals and differences in carbon gain that could, in the long-term, affect species' abundances. The frost also reduced fruit/seed abundance for insects and mammals. [source] Stem hydraulics mediates leaf water status, carbon gain, nutrient use efficiencies and plant growth rates across dipterocarp speciesFUNCTIONAL ECOLOGY, Issue 4 2009Jiao-Lin Zhang Summary 1Stem vascular system strongly influences structure and functioning of leaves, life-history, and distribution of plants. Xylem structure and hydraulic conductivity of branches, leaf functional traits, and growth rates in 17 dipterocarp species in a mature plantation stand were examined to explore the functional relationships between these traits. 2Maximum hydraulic conductivity on the bases of both sapwood and leaf area (kL) were positively correlated with midday leaf water potential in the rainy season, stomatal conductance, area-based maximum photosynthetic rate, photosynthetic N (PNUE) and P use efficiencies (PPUE), and mean height and diameter growth rates. Moreover, kL was positively correlated with mesophyll thickness and mass-based maximum photosynthetic rate. These results revealed the mechanistic linkage between stem hydraulics and leaf photosynthesis through nutrient use efficiency and mesophyll development of leaves. 3A detrended correspondence analysis (DCA) using 37 traits showed that the traits related to stem hydraulics and leaf carbon gain were loaded on the first axis whereas traits related to light harvesting were loaded on the second axis, indicating that light harvesting is a distinct ecological axis for tropical canopy plants. The DCA also revealed a trade-off between photosynthetic water use efficiency and hydraulic conductivity along with PNUE and PPUE. 4The congeneric species were scattered fairly close together on the DCA diagram, indicating that the linkages between stem hydraulics, leaf functional traits, and plant growth rates are phylogenetically conserved. 5These results suggest that stem hydraulics mediates leaf water status, carbon gain, nutrient use efficiencies, and growth rates across the dipterocarp species. The wide variation in functional traits and growth rates among these dipterocarp species along with the trade-offs mentioned above provide a possible explanation for their co-existence in tropical forest communities. [source] Freezing induced leaf movements and their potential implications to early spring carbon gain: Rhododendron maximum as exemplarFUNCTIONAL ECOLOGY, Issue 3 2009Raymond B. Russell Summary 1Thermonastic leaf movements (TLM) are induced by freezing and are correlated with freezing tolerance, and our goal was to determine the significance of TLM to photosynthesis during the winter and early spring. 2We performed field experiments in which we prevented TLM of Rhododendron maximum leaves and determined the consequences of that prevention to photoinhibition (measured by chlorophyll fluorescence) from fall to spring, photosynthesis (measured by gas exchange) in the winter, and recovery of photosynthesis in the spring. 3TLM significantly reduced photoinhibition in the winter for leaves on branches in the outer canopy of R. maximum plants, but not for leaves on inner canopy branches. 4During warm periods in the winter, TLM were associated with significantly lower photoinhibition, but TLM did not have a significant effect on photosynthesis during these times. 5In early spring, leaves with TLM recovered from photoinhibition more quickly than for leaves prevented from TLM. 6Photosynthesis in the early spring was higher at any stomatal conductance for leaves with TLM than for leaves prevented from TLM for outer canopy leaves only. 7Our results demonstrate that TLM during the winter prevent excessive photoinhibition and promote rapid recovery of photosynthesis in the early spring. [source] Relative importance of microhabitat, plant form and photosynthetic physiology to carbon gain in two alpine herbsFUNCTIONAL ECOLOGY, Issue 2 2001M. J. Germino Abstract 1.,The effects of microhabitat and plant form on sunlight interception, leaf temperatures, frost occurrence and photosynthesis were evaluated for Caltha leptosepala DC and Erythronium grandiflorum Pursh. Both plants are perennials that commonly emerge from alpine snowbanks where the combination of cool temperatures and strong sunlight is among the most extreme for vascular plants. 2., Caltha leptosepala occurred in microsites where colder air accumulates, and has larger, less inclined and more densely clustered leaves compared to E. grandiflorum (which has two steeply inclined leaves). 3.,These differences in microsite and plant form led to leaf temperatures below 0 °C on 70% of nights during the summer growth season in C. leptosepala, compared to only 38% in E. grandiflorum. Leaves of C. leptosepala warmed more slowly on mornings following frosts compared to E. grandiflorum, due to less aerodynamic coupling between leaf and air temperature, and also a 45% smaller ratio of sunlit to total leaf area due to mutual shading among leaves. 4.,As a result, night frost did not affect subsequent CO2 assimilation (A) in E. grandiflorum, while frostless nights and warmer mornings led to 35% greater A in C. leptosepala in the early morning. 5.,There were no appreciable differences in the temperature and light response of photosynthesis between the two species. The apparent quantum yield of A declined only ,8% in both species following frost and exposure to strong sunlight, indicating little adjustment of photosynthetic physiology. 6.,Greater daily carbon gain probably occurs for E. grandiflorum because of its plant form and microclimate, rather than differences in photosynthetic physiology. [source] Last-century changes of alpine grassland water-use efficiency: a reconstruction through carbon isotope analysis of a time-series of Capra ibex hornsGLOBAL CHANGE BIOLOGY, Issue 4 2010INÊS C. R. BARBOSA Abstract The ecophysiological response of an alpine grassland to recent climate change and increasing atmospheric CO2 concentration was investigated with a new strategy to go back in time: using a time-series of Capra ibex horns as archives of the alpine grasslands' carbon isotope discrimination (13,). From the collection of the Natural History Museum of Bern, horns of 24 males from the population of the Augstmatthorn,Brienzer Rothorn mountains, Switzerland, were sampled covering the period from 1938 to 2006. Samples were taken from the beginning of each year-ring of the horns, representing the beginning of the horn growth period, the spring. The horns' carbon 13C content (,13C) declined together with that of atmospheric CO2 over the 69-year period, but 13, increased slightly (+0.4,), though significantly (P<0.05), over the observation period. Estimated intercellular CO2 concentration increased (+56 ,mol mol,1) less than the atmospheric CO2 concentration (+81 ,mol mol,1), so that intrinsic water-use efficiency increased by 17.8% during the 69-year period. However, the atmospheric evaporative demand at the site increased by approximately 0.1 kPa between 1955 and 2006, thus counteracting the improvement of intrinsic water-use efficiency. As a result, instantaneous water-use efficiency did not change. The observed changes in intrinsic water-use efficiency were in the same range as those of trees (as reported by others), indicating that leaf-level control of water-use efficiency of grassland and forests followed the same principles. This is the first reconstruction of the water-use efficiency response of a natural grassland ecosystem to last century CO2 and climatic changes. The results indicate that the alpine grassland community has responded to climate change by improving the physiological control of carbon gain to water loss, following the increases in atmospheric CO2 and evaporative demand. But, effective leaf-level water-use efficiency has remained unchanged. [source] Evaluating the impacts of climate and elevated carbon dioxide on tropical rainforests of the western Amazon basin using ecosystem models and satellite dataGLOBAL CHANGE BIOLOGY, Issue 1 2010HIROFUMI HASHIMOTO Abstract Forest inventories from the intact rainforests of the Amazon indicate increasing rates of carbon gain over the past three decades. However, such estimates have been questioned because of the poor spatial representation of the sampling plots and the incomplete understanding of purported mechanisms behind the increases in biomass. Ecosystem models, when used in conjunction with satellite data, are useful in examining the carbon budgets in regions where the observations of carbon flows are sparse. The purpose of this study is to explain observed trends in normalized difference vegetation index (NDVI) using climate observations and ecosystem models of varying complexity in the western Amazon basin for the period of 1984,2002. We first investigated trends in NDVI and found a positive trend during the study period, but the positive trend in NDVI was observed only in the months from August to December. Then, trends in various climate parameters were calculated, and of the climate variables considered, only shortwave radiation was found to have a corresponding significant positive trend. To compare the impact of each climate component, as well as increasing carbon dioxide (CO2) concentrations, on evergreen forests in the Amazon, we ran three ecosystem models (CASA, Biome-BGC, and LPJ), and calculated monthly net primary production by changing a climate component selected from the available climate datasets. As expected, CO2 fertilization effects showed positive trends throughout the year and cannot explain the positive trend in NDVI, which was observed only for the months of August to December. Through these simulations, we demonstrated that the positive trend in shortwave radiation can explain the positive trend in NDVI observed for the period from August to December. We conclude that the positive trend in shortwave radiation is the most likely driver of the increasing trend in NDVI and the corresponding observed increases in forest biomass. [source] Physiological responses of two contrasting desert plant species to precipitation variability are differentially regulated by soil moisture and nitrogen dynamicsGLOBAL CHANGE BIOLOGY, Issue 5 2009LISA D. PATRICK Abstract Alterations in global and regional precipitation patterns are expected to affect plant and ecosystem productivity, especially in water-limited ecosystems. This study examined the effects of natural and supplemental (25% increase) seasonal precipitation on a sotol grassland ecosystem in Big Bend National Park in the Chihuahuan Desert. Physiological responses , leaf photosynthesis at saturating light (Asat), stomatal conductance (gs), and leaf nitrogen [N] , of two species differing in their life form and physiological strategies (Dasylirion leiophyllum, a C3 shrub; Bouteloua curtipendula, a C4 grass) were measured over 3 years (2004,2006) that differed greatly in their annual and seasonal precipitation patterns (2004: wet, 2005: average, 2006: dry). Precipitation inputs are likely to affect leaf-level physiology through the direct effects of altered soil water and soil nitrogen. Thus, the effects of precipitation, watering treatment, soil moisture, and nitrogen were quantified via multivariate hierarchical Bayesian models that explicitly linked the leaf and soil responses. The two species differed in their physiological responses to precipitation and were differentially controlled by soil water vs. soil nitrogen. In the relatively deeply rooted C3 shrub, D. leiophyllum, Asat was highest in moist periods and was primarily regulated by deep (16,30 cm) soil water. In the shallow-rooted C4 grass, B. curtipendula, Asat was only coupled to leaf [N], both of which increased in dry periods when soil [N] was highest. Supplemental watering during the wet year generally decreased Asat and leaf [N] in D. leiophyllum, perhaps due to nutrient limitation, and physiological responses in this species were influenced by the cumulative effects of 5 years of supplemental watering. Both species are common in this ecosystem and responded strongly, yet differently, to soil moisture and nitrogen, suggesting that changes in the timing and magnitude of precipitation may have consequences for plant carbon gain, with the potential to alter community composition. [source] Changes in grassland ecosystem function due to extreme rainfall events: implications for responses to climate changeGLOBAL CHANGE BIOLOGY, Issue 7 2008PHILIP A. FAY Abstract Climate change is causing measurable changes in rainfall patterns, and will likely cause increases in extreme rainfall events, with uncertain implications for key processes in ecosystem function and carbon cycling. We examined how variation in rainfall total quantity (Q), the interval between rainfall events (I), and individual event size (SE) affected soil water content (SWC) and three aspects of ecosystem function: leaf photosynthetic carbon gain (), aboveground net primary productivity (ANPP), and soil respiration (). We utilized rainout shelter-covered mesocosms (2.6 m3) containing assemblages of tallgrass prairie grasses and forbs. These were hand watered with 16 I×Q treatment combinations, using event sizes from 4 to 53 mm. Increasing Q by 250% (400,1000 mm yr,1) increased mean soil moisture and all three processes as expected, but only by 20,55% (P,0.004), suggesting diminishing returns in ecosystem function as Q increased. Increasing I (from 3 to 15 days between rainfall inputs) caused both positive () and negative () changes in ecosystem processes (20,70%, P,0.01), within and across levels of Q, indicating that I strongly influenced the effects of Q, and shifted the system towards increased net carbon uptake. Variation in SE at shorter I produced greater response in soil moisture and ecosystem processes than did variation in SE at longer I, suggesting greater stability in ecosystem function at longer I and a priming effect at shorter I. Significant differences in ANPP and between treatments differing in I and Q but sharing the same SE showed that the prevailing pattern of rainfall influenced the responses to a given event size. Grassland ecosystem responses to extreme rainfall patterns expected with climate change are, therefore, likely to be variable, depending on how I, Q, and SE combine, but will likely result in changes in ecosystem carbon cycling. [source] Long-term carbon exchange in a sparse, seasonally dry tussock grasslandGLOBAL CHANGE BIOLOGY, Issue 10 2004John E. Hunt Abstract Rainfall and its seasonal distribution can alter carbon dioxide (CO2) exchange and the sustainability of grassland ecosystems. Using eddy covariance, CO2 exchange between the atmosphere and a sparse grassland was measured for 2 years at Twizel, New Zealand. The years had contrasting distributions of rain and falls (446 mm followed by 933 mm; long-term mean=646 mm). The vegetation was sparse with total above-ground biomass of only 1410 g m,2. During the dry year, leaf area index peaked in spring (November) at 0.7, but it was <0.2 by early summer. The maximum daily net CO2 uptake rate was only 1.5 g C m,2 day,1, and it occurred before mid-summer in both years. On an annual basis, for the dry year, 9 g C m,2 was lost to the atmosphere. During the wet year, 41 g C m,2 was sequestered from the atmosphere. The net exchange rates were determined mostly by the timing and intensity of spring rainfall. The components of ecosystem respiration were measured using chambers. Combining scaled-up measurements with the eddy CO2 effluxes, it was estimated that 85% of ecosystem respiration emanated from the soil surface. Under well-watered conditions, 26% of the soil surface CO2 efflux came from soil microbial activity. Rates of soil microbial CO2 production and net mineral-N production were low and indicative of substrate limitation. Soil respiration declined by a factor of four as the soil water content declined from field capacity (0.21 m3 m,3) to the driest value obtained (0.04 m3 m,3). Rainfall after periods of drought resulted in large, but short-lived, respiration pulses that were curvilinearly related to the increase in root-zone water content. Coupled with the low leaf area and high root : shoot ratio, this sparse grassland had a limited capacity to sequester and store carbon. Assuming a proportionality between carbon gain and rainfall during the summer, rainfall distribution statistics suggest that the ecosystem is sustainable in the long term. [source] Abiotic constraints on the establishment of Quercus seedlings in grasslandGLOBAL CHANGE BIOLOGY, Issue 2 2003Brett T. Danner Abstract High evaporative demand and periodic drought characterize the growing season in midwestern grasslands relative to deciduous forests of the eastern US, and predicted climatic changes suggest that these climatic extremes may be exacerbated. Despite this less than optimal environment for tree seedling establishment, deciduous trees have expanded into adjacent tallgrass prairie within the last century leading to a dramatic land cover change. In order to determine the role of light and temperature on seedling establishment, we assessed carbon and water relations and aboveground growth of first-year Quercus macrocarpa seedlings exposed to one of three conditions: (1) intact tallgrass prairie communities (control), (2) aboveground herbaceous biomass removed (grass removal), and (3) shade plus biomass removal to reduce light (PFD) to levels typical of the grassland-forest ecotone (shade). In the 2000 growing season, precipitation was 35% below the long-term average, which had a significant negative effect on oak seedling carbon gain at midseason (photosynthesis declined to 10% of maximum rates). However, net photosynthesis and stomatal conductance in the shade treatment was ca. 2.5 and 1.5 times greater, respectively, than in control treatment seedlings during this drought. During this period, leaf and air temperatures in control seedlings were similar whereas leaf temperatures in the shade treatment remained below air temperature. A late-season recovery period, coincident with decreased air temperatures, resulted in increased net photosynthesis for all seedlings. Increased photosynthetic rates and water relations in shaded seedlings compared to seedlings in full sun suggest that, at least in dry years, high light and temperature may negatively impact oak seedling performance. However, high survival rates for all seedlings indicate that Q. macrocarpa seedlings are capable of tolerating both present-day and future climatic extremes. Unless historic fire regimes are restored, forest expansion and land cover change are likely to continue. [source] Biomass and leaf-level gas exchange characteristics of three African savanna C4 grass species under optimum growth conditionsAFRICAN JOURNAL OF ECOLOGY, Issue 4 2009K. B. Mantlana Abstract C4 savanna grass species, Digitaria eriantha, Eragrostis lehmanniana and Panicum repens, were grown under optimum growth conditions with the aim of characterizing their above- and below-ground biomass allocation and the response of their gas exchange to changes in light intensity, CO2 concentration and leaf-to-air vapour pressure deficit gradient (Dl). Digitaria eriantha showed the largest above- and below-ground biomass, high efficiency in carbon gain under light-limiting conditions, high water use efficiency (WUE) and strong stomatal sensitivity to Dl (P = 0.002; r2 = 0.5). Panicum repens had a high aboveground biomass and attained high light saturated photosynthetic rates (Asat, 47 ,mol m,2 s,1), stomatal conductance, (gsat, 0.25 mol m,2 s,1) at relatively high WUE. Eragrostis lehmanniana had almost half the biomass of other species, and had similar Asat and gsat but were attained at lower WUE than the other species. This species also showed the weakest stomatal response to Dl (P = 0.19, r2 = 0. 1). The potential ecological significance of the contrasting patterns of biomass allocation and variations in gas exchange parameters among the species are discussed. Résumé On a fait pousser des espèces herbeuses de savane de type C4, Digitaria eriantha, Eragrostis lehmanniana et Panicum repens, dans des conditions optimales dans le but de caractériser l'allocation de leur biomasse aérienne et racinaire et la réponse de leur échange gazeux à des changements d'intensité de la lumière, de concentrations de CO2, et à un gradient déficitaire (Dl) de pression de vapeur feuille-air. D. eriantha montrait la plus grande biomasse aérienne et racinaire, une grande efficience de l'assimilation de carbone dans des conditions de luminosité limitée, une grande efficience d'utilisation de l'eau (WUE) et une forte sensibilité des stomates à Dl (P = 0,002; r2 = 0,5). P. repens avait une grande biomasse aérienne et atteignait des taux photosynthétiques élevés en lumière saturée (Asat, 47 ,mol m,2 s,1), et une conductance stomatique (gsat 0.25 mol m,2 s,1) à une WUE relativement élevée. E. lehmanniana avait une biomasse qui était presque la moitié de celle des autres espèces et avait un Asat et un gsat similaires mais qui étaient atteints à une WUE plus basse que les autres espèces. Cette espèce montrait aussi la plus faible réponse stomatique àDl (P = 0,19, r2 = 0,1). L'on discute de la signification écologique potentielle de ces schémas contrastés d'allocations de biomasse et des variations des paramètres des échanges gazeux entre les espèces. [source] Diversity of algal endosymbionts (zooxanthellae) in octocorals: the roles of geography and host relationshipsMOLECULAR ECOLOGY, Issue 8 2005M. J. H. VAN OPPEN Abstract The presence, genetic identity and diversity of algal endosymbionts (Symbiodinium) in 114 species from 69 genera (20 families) of octocorals from the Great Barrier Reef (GBR), the far eastern Pacific (EP) and the Caribbean was examined, and patterns of the octocoral,algal symbiosis were compared with patterns in the host phylogeny. Genetic analyses of the zooxanthellae were based on ribosomal DNA internal transcribed spacer 1 (ITS1) region. In the GBR samples, Symbiodinium clades A and G were encountered with A and G being rare. Clade B zooxanthellae have been previously reported from a GBR octocoral, but are also rare in octocorals from this region. Symbiodinium G has so far only been found in Foraminifera, but is rare in these organisms. In the Caribbean samples, only Symbiodinium clades B and C are present. Hence, Symbiodinium diversity at the level of phylogenetic clades is lower in octocorals from the Caribbean compared to those from the GBR. However, an unprecedented level of ITS1 diversity was observed within individual colonies of some Caribbean gorgonians, implying either that these simultaneously harbour multiple strains of clade B zooxanthellae, or that ITS1 heterogeneity exists within the genomes of some zooxanthellae. Intracladal diversity based on ITS should therefore be interpreted with caution, especially in cases where no independent evidence exists to support distinctiveness, such as ecological distribution or physiological characteristics. All samples from EP are azooxanthellate. Three unrelated GBR taxa that are described in the literature as azooxanthellate (Junceella fragilis, Euplexaura nuttingi and Stereonephthya sp. 1) contain clade G zooxanthellae, and their symbiotic association with zooxanthellae was confirmed by histology. These corals are pale in colour, whereas related azooxanthellate species are brightly coloured. The evolutionary loss or gain of zooxanthellae may have altered the light sensitivity of the host tissues, requiring the animals to adopt or reduce pigmentation. Finally, we superimposed patterns of the octocoral,algal symbiosis onto a molecular phylogeny of the host. The data show that many losses/gains of endosymbiosis have occurred during the evolution of octocorals. The ancestral state (azooxanthellate or zooxanthellate) in octocorals remains unclear, but the data suggest that on an evolutionary timescale octocorals can switch more easily between mixotrophy and heterotrophy compared to scleractinian corals, which coincides with a low reliance on photosynthetic carbon gain in the former group of organisms. [source] Direct and Indirect Climate Change Effects on Photosynthesis and TranspirationPLANT BIOLOGY, Issue 3 2004M. U. F. Kirschbaum Abstract: Climate change affects plants in many different ways. Increasing CO2 concentration can increase photosynthetic rates. This is especially pronounced for C3 plants, at high temperatures and under water-limited conditions. Increasing temperature also affects photosynthesis, but plants have a considerable ability to adapt to their growth conditions and can function even at extremely high temperatures, provided adequate water is available. Temperature optima differ between species and growth conditions, and are higher in elevated atmospheric CO2. With increasing temperature, vapour pressure deficits of the air may increase, with a concomitant increase in the transpiration rate from plant canopies. However, if stomata close in response to increasing CO2 concentration, or if there is a reduction in the diurnal temperature range, then transpiration rates may even decrease. Soil organic matter decomposition rates are likely to be stimulated by higher temperatures, so that nutrients can be more readily mineralised and made available to plants. This is likely to increase photosynthetic carbon gain in nutrient-limited systems. All the factors listed above interact strongly so that, for different combinations of increases in temperature and CO2 concentration, and for systems in different climatic regions and primarily affected by water or nutrient limitations, photosynthesis must be expected to respond differently to the same climatic changes. [source] A Novel System for Spectral Analysis of Solar Radiation within a Mixed Beech-Spruce StandPLANT BIOLOGY, Issue 2 2002H. Reitmayer Abstract: A multi-sensor system is described, based on a 1024 channel diode array spectrometer, to measure spectral radiant flux density in the range of 380 nm to 850 nm, with a resolution of 0.8 nm in minimal 16 milliseconds integration time per sensor (noon, clear sky conditions). 264 space-integrating 4, sensors deployed in the canopies and 2 m above stand floor are sequentially connected to the spectrometer by means of 30-m long fibre optics. During low-level conditions (dawn, overcast sky) the system automatically lengthens the integration time of the spectrometer. About 3 sec per sensor, i.e., 13 min for the total of 264 sensors (worst case) are needed to collect spectral energy data, store them on hard disk and move the channel multiplexer to the next fibre optic position. The detection limit of quartz fibre sensors is 0.2 W/m2; precision and absolute error of radiant flux density are smaller than 3 % and 10 %, respectively. The system, operating since 1999, is derived from a 20-sensor pilot system developed for PAR measurements (PMMA fibre sensor, 400nm to 700 nm). Data achieved with the system serve to determine vertical profiles of wavelength dependent radiation extinction, with special respect to R/FR ratios and to develop a model of spectral radiation distribution in a mature forest stand, prerequisites for the computation of carbon gain of the stand and the evaluation of stand growth models. [source] Effects of chronic elevated ozone concentration on antioxidant capacity, photosynthesis and seed yield of 10 soybean cultivarsPLANT CELL & ENVIRONMENT, Issue 9 2010AMY M. BETZELBERGER ABSTRACT Crops losses to tropospheric ozone (O3) in the United States are estimated to cost $1,3 billion annually. This challenge is expected to increase as O3 concentrations ([O3]) rise over the next half century. This study tested the hypothesis that there is cultivar variation in the antioxidant, photosynthetic and yield response of soybean to growth at elevated [O3]. Ten cultivars of soybean were grown at elevated [O3] from germination through maturity at the Soybean Free Air Concentration Enrichment facility in 2007 and six were grown in 2008. Photosynthetic gas exchange, leaf area index, chlorophyll content, fluorescence and antioxidant capacity were monitored during the growing seasons in order to determine if changes in these parameters could be used to predict the sensitivity of seed yield to elevated [O3]. Doubling background [O3] decreased soybean yields by 17%, but the variation in response among cultivars and years ranged from 8 to 37%. Chlorophyll content and photosynthetic parameters were positively correlated with seed yield, while antioxidant capacity was negatively correlated with photosynthesis and seed yield, suggesting a trade-off between antioxidant metabolism and carbon gain. Exposure response curves indicate that there has not been a significant improvement in soybean tolerance to [O3] in the past 30 years. [source] Nitrogen and carbon source,sink relationships in trees at the Himalayan treelines compared with lower elevationsPLANT CELL & ENVIRONMENT, Issue 10 2008MAI-HE LI ABSTRACT No single hypothesis or theory has been widely accepted for explaining the functional mechanism of global alpine/arctic treeline formation. The present study tested whether the alpine treeline is determined by (1) the needle nitrogen content associated with photosynthesis (carbon gain); (2) a sufficient source,sink ratio of carbon; or (3) a sufficient C,N ratio. Nitrogen does not limit the growth and development of trees studied at the Himalayan treelines. Levels of non-structural carbohydrates (NSC) in trees were species-specific and site-dependent; therefore, the treeline cases studied did not show consistent evidence of source/carbon limitation or sink/growth limitation in treeline trees. However, results of the combined three treelines showed that the treeline trees may suffer from a winter carbon shortage. The source capacity and the sink capacity of a tree influence its tissue NSC concentrations and the carbon balance; therefore, we suggest that the persistence and development of treeline trees in a harsh alpine environment may require a minimum level of the total NSC concentration, a sufficiently high sugar:starch ratio, and a balanced carbon source,sink relationship. [source] Dynamic photo-inhibition and carbon gain in a C4 and a C3 grass native to high latitudesPLANT CELL & ENVIRONMENT, Issue 11 2004D. S. KUBIEN ABSTRACT C4 plants are rare in the cool climates characteristic of high latitudes and altitudes, perhaps because of an enhanced susceptibility to photo-inhibition at low temperatures relative to C3 species. In the present study we tested the hypothesis that low-temperature photo-inhibition is more detrimental to carbon gain in the C4 grass Muhlenbergia glomerata than the C3 species Calamogrostis Canadensis. These grasses occur together in boreal fens in northern Canada. Plants were grown under cool (14/10 °C day/night) and warm (26/22 °C) temperatures before measurement of the light responses of photosynthesis and chlorophyll fluorescence at different temperatures. Cool growth temperatures led to reduced rates of photosynthesis in M. glomerata at all measurement temperatures, but had a smaller effect on the C3 species. In both species the amount of xanthophyll cycle pigments increased when plants were grown at 14/10 °C, and in M. glomerata the xanthophyll epoxidation state was greatly reduced. The detrimental effect of low growth temperature on photosynthesis in M. glomerata was almost completely reversed by a 24-h exposure to the warm-temperature regime. These data indicate that reversible dynamic photo-inhibition is a strategy by which C4 species may tolerate cool climates and overcome the Rubisco limitation that is prevalent at low temperatures in C4 plants. [source] Low temperature effects on photosynthesis and growth of grapevinePLANT CELL & ENVIRONMENT, Issue 7 2004L. HENDRICKSON ABSTRACT Growth and photosynthesis of grapevine (Vitis vinifera L.) planted on two sloping cool climate vineyards were measured during the early growth season. At both vineyards, a small difference in mean minimum air temperature (1,3 °C) between two microsites accumulated over time, producing differences in shoot growth rate. The growth rates of the warmer (upper) microsite were 34,63% higher than the cooler (lower) site. Photosynthesis measurements of both east and west canopy sides revealed that the difference in carbon gain between the warmer and cooler microsites was due to low temperatures restricting the photosynthetic contribution of east-facing leaves. East-facing leaves at the warmer microsite experienced less time at suboptimal temperature while being exposed to high irradiance, contributing to an average 10% greater net carbon gain compared to the east-facing leaves at the cooler microsite. This chilling-induced reduction in photosynthesis was not due to net photo-inhibition. Further analysis revealed that CO2 - and light-saturated photosynthesis of grapevines was restricted by stomatal closure from 15 to 25 °C and by a limitation of RuBP regeneration and/or end-product limitation from 5 to 15 °C. Changes in photosynthetic carboxylation efficiency implied that Rubisco activity may also play a regulatory role at all temperatures. This restriction of total photosynthetic carbon gain is proposed to be a major contributor to the temperature dependence of growth rate at both vineyards during the early season growth period. [source] Would transformation of C3 crop plants with foreign Rubisco increase productivity?PLANT CELL & ENVIRONMENT, Issue 2 2004A computational analysis extrapolating from kinetic properties to canopy photosynthesis ABSTRACT Genetic modification of Rubisco to increase the specificity for CO2 relative to O2 (,) would decrease photorespiration and in principle should increase crop productivity. When the kinetic properties of Rubisco from different photosynthetic organisms are compared, it appears that forms with high , have low maximum catalytic rates of carboxylation per active site (kcc). If it is assumed that an inverse relationship between kcc and , exists, as implied from measurements, and that an increased concentration of Rubisco per unit leaf area is not possible, will increasing , result in increased leaf and canopy photosynthesis? A steady-state biochemical model for leaf photosynthesis was coupled to a canopy biophysical microclimate model and used to explore this question. C3 photosynthetic CO2 uptake rate (A) is either limited by the maximum rate of Rubisco activity (Vcmax) or by the rate of regeneration of ribulose-1,5-bisphosphate, in turn determined by the rate of whole chain electron transport (J). Thus, if J is limiting, an increase in , will increase net CO2 uptake because more products of the electron transport chain will be partitioned away from photorespiration into photosynthesis. The effect of an increase in , on Rubisco-limited photosynthesis depends on both kcc and the concentration of CO2 ([CO2]). Assuming a strict inverse relationship between kcc and ,, the simulations showed that a decrease, not an increase, in , increases Rubisco-limited photosynthesis at the current atmospheric [CO2], but the increase is observed only in high light. In crop canopies, significant amounts of both light-limited and light-saturated photosynthesis contribute to total crop carbon gain. For canopies, the present average , found in C3 terrestrial plants is supra-optimal for the present atmospheric [CO2] of 370 µmol mol,1, but would be optimal for a CO2 concentration of around 200 µmol mol,1, a value close to the average of the last 400 000 years. Replacing the average Rubisco of terrestrial C3 plants with one having a lower and optimal , would increase canopy carbon gain by 3%. Because there are significant deviations from the strict inverse relationship between kcc and ,, the canopy model was also used to compare the rates of canopy photosynthesis for several Rubiscos with well-defined kinetic constants. These simulations suggest that very substantial increases (> 25%) in crop carbon gain could result if specific Rubiscos having either a higher , or higher kcc were successfully expressed in C3 plants. [source] Carbon use efficiency depends on growth respiration, maintenance respiration, and relative growth rate.PLANT CELL & ENVIRONMENT, Issue 9 2003A case study with lettuce ABSTRACT Carbon use efficiency (CUE, the ratio between the amount of carbon incorporated into dry matter to the amount of carbon fixed in gross photosynthesis) is an important parameter in estimating growth rate from photosynthesis data or models. It previously has been found to be relatively constant among species and under different environmental conditions. Here it is shown that CUE can be expressed as a function of the relative growth rate (rGR) and the growth (gr) and maintenance respiration coefficients (mr): 1/CUE = 1 + gr + mr/rGR. Net daily carbon gain (Cdg), rGR, and CUE were estimated from whole-plant gas exchange measurements on lettuce (Lactuca sativa L.) ranging from 24 to 66 d old. Carbon use efficiency decreased from 0.6 to 0.2 with increasing dry mass, but there was no correlation between CUE and Cdg. The decrease in CUE with increasing dry mass was correlated with a simultaneous decrease in rGR. From the above equation, gr and mr were estimated to be 0.48 mol mol,1 and 0.039 g glucose g,1 dry matter d,1, respectively. Based on the gr estimate, the theoretical upper limit for CUE of these plants was 0.68. The importance of maintenance respiration in the carbon balance of the plants increased with increasing plant size. Maintenance accounted for 25% of total respiration in small plants and 90% in large plants. [source] Relative enhancement of photosynthesis and growth at elevated CO2 is greater under sunflecks than uniform irradiance in a tropical rain forest tree seedlingPLANT CELL & ENVIRONMENT, Issue 12 2002A. D. B. LEAKEY Abstract The survivorship of dipterocarp seedlings in the deeply shaded understorey of South-east Asian rain forests is limited by their ability to maintain a positive carbon balance. Photosynthesis during sunflecks is an important component of carbon gain. To investigate the effect of elevated CO2 upon photosynthesis and growth under sunflecks, seedlings of Shorealeprosula were grown in controlled environment conditions at ambient or elevated CO2. Equal total daily photon flux density (PFD) (,7·7 mol m,2 d,1) was supplied as either uniform irradiance (,170 µmol m,2 s,1) or shade/fleck sequences (,30 µmol m,2 s,1/,525 µmol m,2 s,1). Photosynthesis and growth were enhanced by elevated CO2 treatments but lower under flecked irradiance treatments. Acclimation of photosynthetic capacity occurred in response to elevated CO2 but not flecked irradiance. Importantly, the relative enhancement effects of elevated CO2 were greater under sunflecks (growth 60%, carbon gain 89%) compared with uniform irradiance (growth 25%, carbon gain 59%). This was driven by two factors: (1) greater efficiency of dynamic photosynthesis (photosynthetic induction gain and loss, post-irradiance gas exchange); and (2) photosynthetic enhancement being greatest at very low PFD. This allowed improved carbon gain during both clusters of lightflecks (73%) and intervening periods of deep shade (99%). The relatively greater enhancement of growth and photosynthesis at elevated CO2 under sunflecks has important potential consequences for seedling regeneration processes and hence forest structure and composition. [source] Photosynthetic acclimation of plants to growth irradiance: the relative importance of specific leaf area and nitrogen partitioning in maximizing carbon gainPLANT CELL & ENVIRONMENT, Issue 8 2001J. R. Evans Abstract Changes in specific leaf area (SLA, projected leaf area per unit leaf dry mass) and nitrogen partitioning between proteins within leaves occur during the acclimation of plants to their growth irradiance. In this paper, the relative importance of both of these changes in maximizing carbon gain is quantified. Photosynthesis, SLA and nitrogen partitioning within leaves was determined from 10 dicotyledonous C3 species grown in photon irradiances of 200 and 1000 µmol m,2 s,1. Photosynthetic rate per unit leaf area measured under the growth irradiance was, on average, three times higher for high-light-grown plants than for those grown under low light, and two times higher when measured near light saturation. However, light-saturated photosynthetic rate per unit leaf dry mass was unaltered by growth irradiance because low-light plants had double the SLA. Nitrogen concentrations per unit leaf mass were constant between the two light treatments, but plants grown in low light partitioned a larger fraction of leaf nitrogen into light harvesting. Leaf absorptance was curvilinearly related to chlorophyll content and independent of SLA. Daily photosynthesis per unit leaf dry mass under low-light conditions was much more responsive to changes in SLA than to nitrogen partitioning. Under high light, sensitivity to nitrogen partitioning increased, but changes in SLA were still more important. [source] Effects of elevated ozone and low light on diurnal and seasonal carbon gain in sugar maplePLANT CELL & ENVIRONMENT, Issue 7 2001M. A. Topa Abstract The long-term interactive effects of ozone and light on whole-tree carbon balance of sugar maple (Acer saccharum Marsh.) seedlings were examined, with an emphasis on carbon acquisition, foliar partitioning into starch and soluble sugars, and allocation to growth. Sugar maple seedlings were fumigated with ambient, 1·7 × ambient and 3·0 × ambient ozone in open-top chambers for 3 years under low and high light (15 and 35% full sunlight, respectively). Three years of ozone fumigation reduced the total biomass of seedlings in the low- and high-light treatments by 64 and 41%, respectively, but had no effect on whole-plant biomass allocation. Ozone had no effect on net photosynthesis until late in the growing season, with low-light seedlings generally exhibiting more pronounced reductions in photosynthesis. The late-season reduction in photosynthesis was not due to impaired stomatal function, but was associated more with accelerated senescence or senescence-like injury. In contrast, the 3·0 × ambient ozone treatment immediately reduced diurnal starch accumulation in leaves by over 50% and increased partitioning of total non-structural carbohydrates into soluble sugars, suggesting that injury repair processes may be maintaining photosynthesis in late spring and early summer at the expense of storage carbon. The results in the present study indicate that changes in leaf-level photosynthesis may not accurately predict the growth response of sugar maple to ozone in different light environments. The larger reduction in seedling growth under low-light conditions suggests that seedlings in gap or closed-canopy environments are more susceptible to ozone than those in a clearing. Similarly, understanding the effects of tropospheric ozone on net carbon gain of a mature tree will require scaling of leaf-level responses to heterogeneous light environments, where some leaves may be more susceptible than others. [source] Light use efficiency of dry matter gain in five macro-lichens: relative impact of microclimate conditions and species-specific traitsPLANT CELL & ENVIRONMENT, Issue 1 2000K. Palmqvist ABSTRACT Relations between irradiance (I) and lichen growth were investigated for five macro-lichens growing at two sites in Sweden. The lichens represented different mycobiont,photobiont associations, two morphologies (foliose, fruticose) and two life forms (epiphytic, terricolous). The lichens were transplanted at two geographically distant sites in Sweden (1000 km apart) from Sept 1995 to Sept 1996 in their typical microhabitats, where microclimate and growth were followed. Between April/May and Sept 96, the terricolous species had a dry matter gain of 0·2 to 0·4 g (g DW),1 and the epiphytes 0·01 to 0·02 g (g DW),1. When related to area, growth amounted to 30 to 70 g m,2 for the terricolous species and to 1 to 4 g m,2 for the epiphytes. There was a strong correlation between growth and intercepted irradiance when the lichens were wet (Iwet), with 0·2 to 1·1 g lichen dry matter being produced per MJ solar energy. Across the 10 sets of transplants, light use efficiencies of dry matter yield (e) ranged between 0·5 and 2%, using an energy equivalent of 17·5 kJ g,1 of lichen dry matter. The higher productivity of the terricolous species was due to longer periods with thallus water contents sufficient for metabolic activity and because of the higher mean photon flux densities of their microhabitat. A four-fold difference in photosynthetic capacity among the species was also important. It is concluded that lichen dry matter gain was primarily related to net carbon gain during metabolically active periods, which was determined by light duration, photon flux density and photosynthetic capacity. [source] Differences in the structure, growth and survival of Parasenecio yatabei ramets with contrasting water relations on the slope of a stream bankPLANT SPECIES BIOLOGY, Issue 2 2009HAJIME TOMIMATSU Abstract Parasenecio yatabei (Asteraceae), a summer-green perennial herb, is widely distributed on sloping mountain stream banks in cool-temperate zone forests of Japan. We investigated the growth pattern, leaf longevity and leaf water relations of vegetatively independent plants (ramets) growing in two contrasting soil water conditions, that is, upper and lower stream banks (U ramets and L ramets, respectively). The objective of the present study was to clarify the physiological and morphological responses of the ramets to soil water conditions. Dry matter allocation to subterranean parts was higher in U ramets than in L ramets. The U ramet leaves survived for approximately 2 months longer than L ramet leaves. The ratio of subterranean part to aerial part dry matter was greater in U ramets than L ramets. Leaf mass per leaf area (LMA) tended to be greater in U ramets than L ramets throughout the growing season. The leaf bulk modulus of elasticity at full hydration was significantly higher in U ramets. Thus, ramet growth patterns and morphological traits varied with changing soil water conditions. The greater longevity of U ramet leaves may play a role in compensating for the reduced annual net carbon gain caused by lower photosynthetic activity. U ramets growing in environments with less water availability achieved high water-use efficiency by a high passive water absorption capacity via a progressed root system and high productivity via longer leaf longevity with higher LMA and elasticity. Therefore, P. yatabei growing along mountain streams could have the ability to colonize the upper bank through higher survivorship based on these traits. [source] Midday depression of photosynthesis and effects of mist spray in citrusANNALS OF APPLIED BIOLOGY, Issue 1 2009M.-J. Hu Abstract Diurnal variations of gas exchange, chlorophyll a fluorescence and some related biochemical characteristics in sun-acclimated mature citrus leaves of mist-sprayed (treatment) and unsprayed (control) trees were compared on sunny days during summer to identify the environmental and physiological factors limiting carbon gain in citrus tree canopies. At midday, net photosynthesis and maximal photochemical efficiency of photosystem II (Fv/Fm) in citrus leaves decreased significantly under control conditions, but the decrease was mitigated by mist spraying. Although the content of malondialdehyde, hydrogen peroxide and activities of antioxidant enzymes increased at midday in both mist-sprayed and control leaves, they were much higher in control leaves than in mist-sprayed leaves. The level of D1 protein decreased significantly in control leaves at midday and then was partly recovered later, while that in treated leaves changed to a much lesser extent because of alleviation of photoinhibition by mist spraying. Both the fast and the slow phases of millisecond-delayed light emissions in treated citrus leaves were higher than those in control leaves, indicating that mist spraying protects the normal operation of the photosynthetic apparatus in leaves. Mist spraying also reduced leaf temperatures and the ratio of air to leaf vapour pressure deficit (ALVPD), leading to increases in stomatal conductance (gs) and alleviation of photoinhibition at midday. It is concluded that the decline of leaf gs under high-ALVPD conditions in summer is an important factor contributing to midday depression of photosynthesis in citrus, and mist spraying is effective in alleviating midday depression of photosynthesis in citrus leaves. [source] Respiratory carbon loss of calcareous grasslands in winter shows no effects of 4 years' CO2 enrichmentFUNCTIONAL ECOLOGY, Issue 2 2002M. Volk Summary 1CO2 exchange measurements in long-term CO2 -enrichment experiments suggest large net carbon gains by ecosystems during the growing season that are not accounted for by above-ground plant biomass. Considerable amounts of C might therefore be allocated below ground. 2Winter ecosystem respiration from temperate grasslands under elevated CO2 may account for the loss of a significant part of the extra C gained during the growing season. To test this hypothesis, dark respiration was assessed throughout the winter of the fourth year of CO2 enrichment in a calcareous grassland. 3Using these data, a model was parameterized to estimate whole-winter respiratory CO2 losses. From November to February, 154 9 g C m,2 were respired under elevated CO2 and 144 5 g C m,2 under ambient [CO2], with no significant difference between the CO2 treatments. 4We conclude that (i) wintertime respiration does not constitute a larger C loss from the ecosystem at elevated CO2; and (ii) the absence of respiratory responses implies no extra growing-season C inputs with month-to-year turnover times at elevated CO2. [source] The impact of co-occurring tree and grassland species on carbon sequestration and potential biofuel productionGCB BIOENERGY, Issue 6 2009RAMESH LAUNGANI Abstract We evaluated how three co-occurring tree and four grassland species influence potentially harvestable biofuel stocks and above- and belowground carbon pools. After 5 years, the tree Pinus strobus had 6.5 times the amount of aboveground harvestable biomass as another tree Quercus ellipsoidalis and 10 times that of the grassland species. P. strobus accrued the largest total plant carbon pool (1375 g C m,2 or 394 g C m,2 yr), while Schizachyrium scoparium accrued the largest total plant carbon pool among the grassland species (421 g C m,2 or 137 g C m,2 yr). Quercus ellipsoidalis accrued 850 g C m,2, Q. macrocarpa 370 g C m,2, Poa pratensis 390 g C m,2, Solidago canadensis 132 g C m,2, and Lespedeza capitata 283 g C m,2. Only P. strobus and Q. ellipsoidalis significantly sequestered carbon during the experiment. Species differed in total ecosystem carbon accumulation from ,21.3 to +169.8 g C m,2 yr compared with the original soil carbon pool. Plant carbon gains with P. strobus were paralleled by a decrease of 16% in soil carbon and a nonsignificant decline of 9% for Q. ellipsoidalis. However, carbon allocation differed among species, with P. strobus allocating most aboveground in a disturbance prone aboveground pool, whereas Q. ellipsoidalis, allocated most carbon in less disturbance sensitive belowground biomass. These differences have strong implications for terrestrial carbon sequestration and potential biofuel production. For P. strobus, aboveground plant carbon harvest for biofuel would result in no net carbon sequestration as declines in soil carbon offset plant carbon gains. Conversely the harvest of Q. ellipsoidalis aboveground biomass would result in net sequestration of carbon belowground due to its high allocation belowground, but would yield lower amounts of aboveground biomass. Our results demonstrate that plant species can differentially impact ecosystem carbon pools and the distribution of carbon above and belowground. [source] | ||||||||||||||||||||||