Does morphological and anatomical plasticity during the vegetative stage make wheat more tolerant of water deficit stress than rice?
Kadam, N.N. ; Yin, X. ; Bindraban, P.S. ; Struik, P.C. ; Jagadish, K.S.V. - \ 2015
Plant Physiology 167 (2015)4. - ISSN 0032-0889 - p. 1389 - 1401.
carbon-isotope discrimination - oryza-sativa l. - hydraulic conductance - drought stress - root length - grain-yield - leaf-area - genotypic variation - spikelet fertility - use efficiency
Water scarcity and the increasing severity of water deficit stress are major challenges to sustaining irrigated rice (Oryza sativa) production. Despite the technologies developed to reduce the water requirement, rice growth is seriously constrained under water deficit stress compared with other dryland cereals such as wheat (Triticum aestivum). We exposed rice cultivars with contrasting responses to water deficit stress and wheat cultivars well adapted to water-limited conditions to the same moisture stress during vegetative growth to unravel the whole-plant (shoot and root morphology) and organ/tissue (root anatomy) responses. Wheat cultivars followed a water-conserving strategy by reducing specific leaf area and developing thicker roots and moderate tillering. In contrast, rice ‘IR64’ and ‘Apo’ adopted a rapid water acquisition strategy through thinner roots under water deficit stress. Root diameter, stele and xylem diameter, and xylem number were more responsive and varied with different positions along the nodal root under water deficit stress in wheat, whereas they were relatively conserved in rice cultivars. Increased metaxylem diameter and lower metaxylem number near the root tips and exactly the opposite phenomena at the root-shoot junction facilitated the efficient use of available soil moisture in wheat. Tolerant rice ‘Nagina 22’ had an advantage in root morphological and anatomical attributes over cultivars IR64 and Apo but lacked plasticity, unlike wheat cultivars exposed to water deficit stress. The key traits determining the adaptation of wheat to dryland conditions have been summarized and discussed.
Methods for measuring arctic and alpine shrub growth: A review
Myers-Smith, I.H. ; Hallinger, M. ; Blok, D. ; Sass-Klaassen, U.G.W. ; Rayback, S.A. - \ 2015
Earth-Science Reviews 140 (2015). - ISSN 0012-8252 - p. 1 - 13.
carbon-isotope discrimination - winter climate-change - tree line dynamics - cassiope-tetragona - dwarf-shrub - environmental-change - salix-arctica - empetrum-hermaphroditum - retrospective analysis - summer temperature
Shrubs have increased in abundance and dominance in arctic and alpine regions in recent decades. This often dramatic change, likely due to climate warming, has the potential to alter both the structure and function of tundra ecosystems. The analysis of shrub growth is improving our understanding of tundra vegetation dynamics and environmental changes. However, dendrochronological methods developed for trees, need to be adapted for the morphology and growth eccentricity of shrubs. Here, we review current and developing methods to measure radial and axial growth, estimate age, and assess growth dynamics in relation to environmental variables. Recent advances in sampling methods, analysis and applications have improved our ability to investigate growth and recruitment dynamics of shrubs. However, to extrapolate findings to the biome scale, future dendroecological work will require improved approaches that better address variation in growth within parts of the plant, among individuals within populations and between species.
Terrestrial cycling of (CO2)-C-13 by photosynthesis, respiration, and biomass burning in SiBCASA
Velde, I.R. van der; Miller, J.B. ; Schaefer, K. ; Werf, G.R. van der; Krol, M.C. ; Peters, W. - \ 2014
Biogeosciences 11 (2014). - ISSN 1726-4170 - p. 6553 - 6571.
carbon-isotope discrimination - surface parameterization sib2 - ecosystem respiration - interannual variability - biophysical parameters - stomatal conductance - co2 assimilation - atmospheric gcms - global fields - dioxide
We present an enhanced version of the SiBCASA terrestrial biosphere model that is extended with (a) biomass burning emissions from the SiBCASA carbon pools using remotely sensed burned area from the Global Fire Emissions Database (GFED), (b) an isotopic discrimination scheme that calculates 13C signatures of photosynthesis and autotrophic respiration, and (c) a separate set of 13C pools to carry isotope ratios into heterotrophic respiration. We quantify in this study the terrestrial exchange of CO2 and 13CO2 as a function of environmental changes in humidity and biomass burning. The implementation of biomass burning yields similar fluxes as CASA-GFED both in magnitude and spatial patterns. The implementation of isotope exchange gives a global mean discrimination value of 15.2‰, ranges between 4 and 20‰ depending on the photosynthetic pathway in the plant, and compares favorably (annually and seasonally) with other published values. Similarly, the isotopic disequilibrium is similar to other studies that include a small effect of biomass burning as it shortens the turnover of carbon. In comparison to measurements, a newly modified starch/sugar storage pool propagates the isotopic discrimination anomalies to respiration much better. In addition, the amplitude of the drought response by SiBCASA is lower than suggested by the measured isotope ratios. We show that a slight increase in the stomatal closure for large vapor pressure deficit would amplify the respired isotope ratio variability. Our study highlights the importance of isotope ratio observations of 13C to assess and improve biochemical models like SiBCASA, especially with regard to the allocation and turnover of carbon and the responses to drought.
Integrating Stand and Soil Properties to Understand Foliar Nutrient Dynamics during Forest Succession Following Slash-and-Burn Agriculture in the Bolivian Amazon
Broadbent, E.N. ; Zambrano, A.M.A. ; Asner, G.P. ; Soriano, M. ; Field, C.B. ; Souza, H.R. de; Pena Claros, M. ; Adams, R.I. ; Dirzo, R. ; Giles, L. - \ 2014
PLoS ONE 9 (2014)2. - ISSN 1932-6203 - 23 p.
carbon-isotope discrimination - tropical rain-forests - n-15 natural-abundance - northeastern costa-rica - below-ground carbon - land-use change - n-p ratios - secondary forest - organic-matter - brazilian amazon
Secondary forests cover large areas of the tropics and play an important role in the global carbon cycle. During secondary forest succession, simultaneous changes occur among stand structural attributes, soil properties, and species composition. Most studies classify tree species into categories based on their regeneration requirements. We use a high-resolution secondary forest chronosequence to assign trees to a continuous gradient in species successional status assigned according to their distribution across the chronosequence. Species successional status, not stand age or differences in stand structure or soil properties, was found to be the best predictor of leaf trait variation. Foliar d13C had a significant positive relationship with species successional status, indicating changes in foliar physiology related to growth and competitive strategy, but was not correlated with stand age, whereas soil d13C dynamics were largely constrained by plant species composition. Foliar d15N had a significant negative correlation with both stand age and species successional status, – most likely resulting from a large initial biomass-burning enrichment in soil 15N and 13C and not closure of the nitrogen cycle. Foliar %C was neither correlated with stand age nor species successional status but was found to display significant phylogenetic signal. Results from this study are relevant to understanding the dynamics of tree species growth and competition during forest succession and highlight possibilities of, and potentially confounding signals affecting, the utility of leaf traits to understand community and species dynamics during secondary forest succession.
Increased water-use efficiency does not lead to enhanced tree growth under xeric and mesic conditions
Lévesque, M. ; Siegwolf, R. ; Saurer, M. ; Eilmann, B. ; Rigling, A. - \ 2014
New Phytologist 203 (2014)1. - ISSN 0028-646X - p. 94 - 109.
carbon-isotope discrimination - scots pine - atmospheric co2 - climate-change - conceptual-model - stomatal conductance - c-13/c-12 variations - forest ecosystems - drought response - oxygen isotopes
Higher atmospheric CO2 concentrations (ca ) can under certain conditions increase tree growth by enhancing photosynthesis, resulting in an increase of intrinsic water-use efficiency (i WUE) in trees. However, the magnitude of these effects and their interactions with changing climatic conditions are still poorly understood under xeric and mesic conditions. We combined radial growth analysis with intra- and interannual d(13) C and d(18) O measurements to investigate growth and physiological responses of Larix decidua, Picea abies, Pinus sylvestris, Pinus nigra and Pseudotsuga menziesii in relation to rising ca and changing climate at a xeric site in the dry inner Alps and at a mesic site in the Swiss lowlands. i WUE increased significantly over the last 50 yr by 8-29% and varied depending on species, site water availability, and seasons. Regardless of species and increased i WUE, radial growth has significantly declined under xeric conditions, whereas growth has not increased as expected under mesic conditions. Overall, drought-induced stomatal closure has reduced transpiration at the cost of reduced carbon uptake and growth. Our results indicate that, even under mesic conditions, the temperature-induced drought stress has overridden the potential CO2 'fertilization' on tree growth, hence challenging today's predictions of improved forest productivity of temperate forests
Understanding causes of tree growth response to gap formation: D13C-values in tree rings reveal a predominant effect of light
Sleen, J.P. van der; Soliz-Gamboa, C.C. ; Helle, G. ; Pons, T.L. ; Anten, N.P.R. ; Zuidema, P.A. - \ 2014
Trees-Structure and Function 28 (2014)2. - ISSN 0931-1890 - p. 439 - 448.
water-use efficiency - carbon-isotope discrimination - tropical rain-forest - nutrient availability - microbial biomass - wood delta-c-13 - canopy gaps - size - photoinhibition - dynamics
Carbon isotope ratios in growth rings of a tropical tree species show that treefall gaps stimulate diameter growth mainly through changes in the availability of light and not water. The formation of treefall gaps in closed canopy forests usually entails considerable increases in light and nutrient availability for remaining trees, as well as altered plant water availability, and is considered to play a key role in tree demography. The effects of gaps on tree growth are highly variable and while usually stimulatory they may also include growth reductions. In most studies, the causes of changes in tree growth rates after gap formation remain unknown. We used changes in carbon isotope 13C discrimination (D13C) in annual growth rings to understand growth responses after gap formation of Peltogyne cf. heterophylla, in a moist forest of Northern Bolivia. We compared growth and D13C of the 7 years before and after gap formation. Forty-two trees of different sizes were studied, half of which grew close (\10 m) to single treefall gaps (gap trees), the other halfmore than 40 m away from gaps (controls). We found variable responses among gap trees in growth and D13C. Increased growth was mainly associated with decreased D13C, suggesting that the growth response was driven by increased light availability, possibly in combination with improved nutrient availability. Most trees showing zero or negative growth change after gap formation had increased D13C, suggesting that increased water stress did not play a role, but rather that light conditions had not changed much or nutrient availability was insufficient to support increased growth. Combining growth rates withD13Cproved to be a valuable tool to identify the causes of temporal variation in tree growth.
Biosphere model simulations of interannual variability in terrestrial 13C/12C exchange.
Velde, I.R. van der; Miller, J.B. ; Schaefer, K. ; Masarie, K.A. ; Denning, S. ; White, J.W.C. ; Krol, M.C. ; Peters, W. ; Tans, P.P. - \ 2013
Global Biogeochemical Cycles 27 (2013)3. - ISSN 0886-6236 - p. 637 - 649.
carbon-isotope discrimination - ocean co2 sink - stomatal conductance - c-13 discrimination - atmospheric co2 - cycle - climate - fires - photosynthesis - assimilation
Previous studies suggest that a large part of the variability in the atmospheric ratio of (CO2)-C-13/(12)CO(2)originates from carbon exchange with the terrestrial biosphere rather than with the oceans. Since this variability is used to quantitatively partition the total carbon sink, we here investigate the contribution of interannual variability (IAV) in biospheric exchange to the observed atmospheric C-13 variations. We use the Simple Biosphere - Carnegie-Ames-Stanford Approach biogeochemical model, including a detailed isotopic fractionation scheme, separate C-12 and C-13 biogeochemical pools, and satellite-observed fire disturbances. This model of (CO2)-C-12 and (CO2)-C-13 thus also produces return fluxes of (13)CO(2)from its differently aged pools, contributing to the so-called disequilibrium flux. Our simulated terrestrial C-13 budget closely resembles previously published model results for plant discrimination and disequilibrium fluxes and similarly suggests that variations in C-3 discrimination and year-to-year variations in C(3)and C-4 productivity are the main drivers of their IAV. But the year-to-year variability in the isotopic disequilibrium flux is much lower (1 sigma=1.5PgCyr(-1)) than required (12.5PgCyr(-1)) to match atmospheric observations, under the common assumption of low variability in net ocean CO2 fluxes. This contrasts with earlier published results. It is currently unclear how to increase IAV in these drivers suggesting that SiBCASA still misses processes that enhance variability in plant discrimination and relative C-3/C(4)productivity. Alternatively, C-13 budget terms other than terrestrial disequilibrium fluxes, including possibly the atmospheric growth rate, must have significantly different IAV in order to close the atmospheric C-13 budget on a year-to-year basis.
Genetic dissection of drought tolerance and recovery potential by quantitative trait locus mapping of a diploid potato population
Anithakumari, A.M. ; Nataraja, K.N. ; Visser, R.G.F. ; Linden, C.G. van der - \ 2012
Molecular Breeding 30 (2012)3. - ISSN 1380-3743 - p. 1413 - 1429.
carbon-isotope discrimination - water-use efficiency - chlorophyll fluorescence - solanum-tuberosum - transpiration efficiency - soil-water - arabidopsis-thaliana - arid conditions - winter-wheat - leaf growth
Potato is the third most important staple food crop in terms of consumption, yet it is relatively susceptible to yield loss because of drought. As a first step towards improving drought tolerance in this crop, we set out to identify the genetic basis for drought tolerance in a diploid potato mapping population. Experiments were carried out under greenhouse conditions in two successive years by recording four physiological, seven growth and three yield parameters under stress and recovery treatments. Genotypes showed significant variation for drought and recovery responses. The traits measured had low to moderately high heritabilities (ranging from 22 to 74 %). A total of 47 quantitative trait loci (QTL) were identified, of which 28 were drought-specific, 17 under recovery treatment and two under well-watered conditions. The majority of these growth and yield QTL co-localized with a QTL for maturity on chromosome 5. Four QTL for d13C, three for chlorophyll content and one for chlorophyll fluorescence (Fv/Fm) were found to co-localize with yield and other growth trait QTL identified on other chromosomes. Several multi-year and multi-treatment QTL were detected and QTL 9 environment interaction was found for d13C. To our knowledge, this is the first comprehensive QTL study on water deficit and recovery potential in potato.
Physiological basis of genetic variation in leaf photosynthesis among rice (Oryza sativa L.) introgression lines under drought and well-watered conditions
Gu, J. ; Yin, X. ; Stomph, T.J. ; Wang, H. ; Struik, P.C. - \ 2012
Journal of Experimental Botany 63 (2012)14. - ISSN 0022-0957 - p. 5137 - 5153.
carbon-isotope discrimination - chlorophyll fluorescence measurements - combined gas-exchange - mesophyll conductance - use efficiency - co2 diffusion - internal conductance - c-3 plants - ribulose-1,5-bisphosphate carboxylase - transpiration efficiency
To understand the physiological basis of genetic variation and resulting quantitative trait loci (QTLs) for photosynthesis in a rice (Oryza sativa L.) introgression line population, 13 lines were studied under drought and well-watered conditions, at flowering and grain filling. Simultaneous gas exchange and chlorophyll fluorescence measurements were conducted at various levels of incident irradiance and ambient CO2 to estimate parameters of a model that dissects photosynthesis into stomatal conductance (g s), mesophyll conductance (g m), electron transport capacity (J max), and Rubisco carboxylation capacity (V cmax). Significant genetic variation in these parameters was found, although drought and leaf age accounted for larger proportions of the total variation. Genetic variation in light-saturated photosynthesis and transpiration efficiency (TE) were mainly associated with variation in g s and g m. One previously mapped major QTL of photosynthesis was associated with variation in g s and g m, but also in J max and V cmax at flowering. Thus, g s and g m, which were demonstrated in the literature to be responsible for environmental variation in photosynthesis, were found also to be associated with genetic variation in photosynthesis. Furthermore, relationships between these parameters and leaf nitrogen or dry matter per unit area, which were previously found across environmental treatments, were shown to be valid for variation across genotypes. Finally, the extent to which photosynthesis rate and TE can be improved was evaluated. Virtual ideotypes were estimated to have 17.0% higher photosynthesis and 25.1% higher TE compared with the best genotype investigated. This analysis using introgression lines highlights possibilities of improving both photosynthesis and TE within the same genetic background
Determinants of barley grain yield in a wide range of Mediterranean environments
Francia, E. ; Tondelli, A. ; Rizza, F. ; Badeck, F.W. ; Li Destri Nicosia, O. ; Akar, T. ; Grando, S. ; Al-Yassin, A. ; Benkelkacim, A. ; Thomas, W.T.B. ; Eeuwijk, F.A. van; Romagosa, I. ; Stanca, A.M. ; Pechionni, N. - \ 2011
Field Crops Research 120 (2011)1. - ISSN 0378-4290 - p. 169 - 178.
carbon-isotope discrimination - drought tolerance - stress tolerance - number - genes - wheat - improvement - adaptation - temperature - photoperiod
Barley grain yield in rainfed Mediterranean regions can be largely influenced by terminal drought events. In this study the ecophysiological performance of the ‘Nure’ (winter) × ‘Tremois’ (spring) barley mapping population (118 Doubled Haploids, DHs) was evaluated in a multi-environment trial of eighteen site–year combinations across the Mediterranean Basin during two consecutive harvest years (2004 and 2005). Mean grain yield of sites ranged from 0.07 to 5.43 t ha-1, clearly dependent upon both the total water input (rainfall plus irrigation) and the water stress index (WSI) accumulated during the growing season. All DHs were characterized for possessing molecular marker alleles tagging four genes that regulate barley cycle, i.e. Vrn-H1, Vrn-H2, Ppd-H2 and Eam6. Grain yield differences were initially interpreted in terms of mean differences between genotypes (G), environments (E), and for each combination of genotype and environment (GE) through a “full interaction” ANOVA model. Variance components estimates clearly showed the greater importance of GE over G, although both were much lower than E. Alternative linear and bilinear models of increasing complexity were used to describe GE. A linear model fitting allelic variation at the four genes explained genotype main effect and genotype × environment interaction much better than growth habit itself. Adaptation was primarily driven by the allelic constitution at three out of the four segregating major genes, i.e. Vrn-H1, Ppd-H2 and Eam6. In fact, the three genes together explained 47.2% of G and 26.3% of GE sum of squares. Grain yield performance was more determined by the number of grains per unit area than by the grain weight (phenotypic correlation across all genotypic values: r = 0.948 and 0.559, respectively). The inter-relationships among a series of characters defining grain yield and its components were also explored as a function of the length of the different barley developmental phases, i.e. vegetative, reproductive, and grain filling stages. In most environments, the best performing (adapted) genotypes were those with faster development until early occurrence of anthesis. This confirmed the crucial role of the period defining the number of grains per unit area in grain yield determination under Mediterranean environments
Using a biochemical C4 photosynthesis model and combined gas exchange and chlorophyll fluorescence measurements to estimate bundle-sheath conductance of maize leaves differing in age and nitrogen content
Yin, X. ; Sun, Z. ; Struik, P.C. ; Putten, P.E.L. van der; Ieperen, W. van; Harbinson, J. - \ 2011
Plant, Cell & Environment 34 (2011)12. - ISSN 0140-7791 - p. 2183 - 2199.
carbon-isotope discrimination - co2 concentrating mechanism - flaveria-bidentis leads - zea-mays l. - c-4 photosynthesis - photosystem-ii - co2-concentrating mechanism - mesophyll conductance - electron-transport - quantum yield
Bundle-sheath conductance (gbs) affects CO2 leakiness, and, therefore, the efficiency of the CO2-concentrating mechanism (CCM) in C4 photosynthesis. Whether and how gbs varies with leaf age and nitrogen status is virtually unknown. We used a C4-photosynthesis model to estimate gbs, based on combined measurements of gas exchange and chlorophyll fluorescence on fully expanded leaves of three different ages of maize (Zea mays L.) plants grown under two contrasting nitrogen levels. Nitrogen was replenished weekly to maintain leaf nitrogen content (LNC) at a similar level across the three leaf ages. The estimated gbs values on leaf-area basis ranged from 1.4 to 10.3 mmol m-2 s-1 and were affected more by LNC than by leaf age, although gbs tended to decrease as leaves became older. When converted to resistance (rbs = 1/gbs), rbs decreased monotonically with LNC. The correlation was presumably associated with nitrogen effects on leaf anatomy such as on wall thickness of bundle-sheath cells. Despite higher gbs, meaning less efficient CCM, the calculated loss due to photorespiration was still low for high-nitrogen leaves. Under the condition of ambient CO2 and saturating irradiance, photorespiratory loss accounted for 3–5% of fixed carbon for the high-nitrogen, versus 1–2% for the low-nitrogen, leaves.
The water-water cycle in leaves is not a major alternative electron sink for dissipation of excess excitation energy when CO2 assimilation is restricted
Driever, S.M. ; Baker, N.R. - \ 2011
Plant, Cell & Environment 34 (2011)5. - ISSN 0140-7791 - p. 837 - 846.
carbon-isotope discrimination - bundle-sheath leakiness - photosynthetic oxygen-exchange - chlorophyll fluorescence - oxidative stress - mehler reaction - c-4 grasses - light - plants - o-2
Electron flux from water via photosystem II (PSII) and PSI to oxygen (water–water cycle) may provide a mechanism for dissipation of excess excitation energy in leaves when CO2 assimilation is restricted. Mass spectrometry was used to measure O2 uptake and evolution together with CO2 uptake in leaves of French bean and maize at CO2 concentrations saturating for photosynthesis and the CO2 compensation point. In French bean at high CO2 and low O2 concentrations no significant water–water cycle activity was observed. At the CO2 compensation point and 3% O2 a low rate of water–water cycle activity was observed, which accounted for 30% of the linear electron flux from water. In maize leaves negligible water–water cycle activity was detected at the compensation point. During induction of photosynthesis in maize linear electron flux was considerably greater than CO2 assimilation, but no significant water–water cycle activity was detected. Miscanthus × giganteus grown at chilling temperature also exhibited rates of linear electron transport considerably in excess of CO2 assimilation; however, no significant water–water cycle activity was detected. Clearly the water–water cycle can operate in leaves under some conditions, but it does not act as a major sink for excess excitation energy when CO2 assimilation is restricted.
Are hybrid species more fit than ancestral parent species in the current hybrid species habitats?
Donovan, L.A. ; Rosenthal, D.R. ; Sanchez-Velenosi, M. ; Rieseberg, L.H. ; Ludwig, F. - \ 2010
Journal of Evolutionary Biology 23 (2010)4. - ISSN 1010-061X - p. 805 - 816.
carbon-isotope discrimination - leaf ecophysiological traits - great-basin desert - helianthus-deserticola - local adaptation - bromus-tectorum - phenotypic selection - mineral-nutrition - wild sunflowers - dune plants
Hybrid speciation is thought to be facilitated by escape of early generation hybrids into new habitats, subsequent environmental selection and adaptation. Here, we ask whether two homoploid hybrid plant species (Helianthus anomalus, H. deserticola) diverged sufficiently from their ancestral parent species (H. annuus, H. petiolaris) during hybrid speciation so that they are more fit than the parent species in hybrid species habitats. Hybrid and parental species were reciprocally transplanted into hybrid and parental habitats. Helianthus anomalus was more fit than parental species in the H. anomalus actively moving desert dune habitat. The abilities to tolerate burial and excavation and to obtain nutrients appear to be important for success in the H. anomalus habitat. In contrast, H. deserticola failed to outperform the parental species in the H. deserticola stabilized desert dune habitat, and several possible explanations are discussed. The home site advantage of H. anomalus is consistent with environmental selection having been a mechanism for adaptive divergence and hybrid speciation and supports the use of H. anomalus as a valuable system for further assessment of environmental selection and adaptive traits
Can the progressive increase of C4 bundle sheath leakiness at low PFD be explained by incomplete suppression of photorespiration?
Kromdijk, J. ; Griffiths, H. ; Schepers, H.E. - \ 2010
Plant, Cell & Environment 33 (2010). - ISSN 0140-7791 - p. 1935 - 1948.
carbon-isotope discrimination - chloroplast atp synthase - short-term changes - water-water cycle - gas-exchange - quantum yield - chlorophyll fluorescence - co2 assimilation - c4 grasses - co2-concentrating mechanism
The ability to concentrate CO2 around Rubisco allows C-4 crops to suppress photorespiration. However, as phosphoenolpyruvate regeneration requires ATP, the energetic efficiency of the C-4 pathway at low photosynthetic flux densities (PFD) becomes a balancing act between primary fixation and concentration of CO2 in mesophyll (M) cells, and CO2 reduction in bundle sheath (BS) cells. At low PFD, retro-diffusion of CO2 from BS cells, relative to the rate of bicarbonate fixation in M cells (termed leakiness phi), is known to increase. This paper investigates whether this increase in phi could be explained by incomplete inhibition of photorespiration. The PFD response of phi was measured at various O-2 partial pressures in young Zea mays plants grown at 250 (LL) and 750 mu mol m-2 s-1 PFD (HL). phi increased at low PFD and was positively correlated with O-2 partial pressure. Low PFD during growth caused BS conductance and interveinal distance to be lower in the LL plants, compared to the HL plants, which correlated with lower phi. Model analysis showed that incomplete inhibition of photorespiration, especially in the HL plants, and an increase in the relative contribution of mitochondrial respiration at low PFD could explain the observed increases in phi.
Towards a reconstruction of Blue Nile baseflow from Ethiopian tree rings
Wils, T. ; Robertson, I. ; Eshetu, Z. ; Koprowski, M. ; Sass-Klaassen, U. ; Touchan, R. ; Loader, N. - \ 2010
Holocene 20 (2010)8. - ISSN 0959-6836 - p. 837 - 848.
carbon-isotope discrimination - water-use efficiency - bomb c-14 data - c-13/c-12 ratios - signal-strength - precipitation reconstruction - climate relationships - northern finland - pinus-sylvestris - atmospheric co2
Most of the water in the River Nile originates from monsoonal rainfall over the Ethiopian Highlands. Despite warnings of future climate change, little is known about the historical variability in this supply, particularly at annual resolution. Development of tree-ring records in this region has been limited by the occurrence of bi- or multimodal rainfall regimes, causing the development of multiple growth rings that cannot be dated with confidence. In this study, we identified annual rings in 30 Juniperus procera trees from northwest Ethiopia by dendrochronology and AMS radiocarbon dating. Carbon isotope ratios(4 series) and ring widths (73 series) were measured. The carbon isotope series did not contain strong trends possibly attributable to increased anthropogenic atmospheric CO2 concentrations or the juvenile effect. Both carbon isotope values and ring widths were strongly correlated with Blue Nile baseflow, and from composite chronology indices (r=0.75, p <0.01), a preliminary reconstruction of Blue Nile baseflow back to AD 1836 was developed. Subsample signal strength remained above 0.85 for most of the reconstruction. Uncertainty bands were relatively narrow and the reliability of the preliminary reconstruction was confirmed by correspondence with reported years of drought and famine. The preliminary reconstruction is characterized by an exceptional decline in baseflow during the late AD 1960s. Flows recovered during the late 1990s. Additional sampling is advised to increase replication, spatial coverage and length of the preliminary reconstruction
Phenotypic selection on leaf ecophysiological traits in Helianthus
Donovan, L.A. ; Ludwig, F. ; Rosenthal, D.R. ; Rieseberg, L.H. ; Dudley, S.A. - \ 2009
New Phytologist 183 (2009)3. - ISSN 0028-646X - p. 868 - 879.
carbon-isotope discrimination - water-use efficiency - plant physiological traits - natural-selection - impatiens-capensis - genetic-variation - polygonum-arenastrum - differing selection - variable selection - functional traits
Habitats that differ in soil resource availability are expected to differ for selection on resource-related plant traits. Here, we examined spatial and temporal variation in phenotypic selection on leaf ecophysiological traits for 10 Helianthus populations, including two species of hybrid origin, Helianthus anomalus and Helianthus deserticola, and artificial hybrids of their ancestral parents. Leaf traits assessed were leaf size, succulence, nitrogen (N) concentration and water-use efficiency (WUE). Biomass and leaf traits of artificial hybrids indicate that the actively moving dune habitat of H. anomalus was more growth limiting, with lower N availability but higher relative water availability than the stabilized dune habitat of H. deserticola. Habitats differed for direct selection on leaf N and WUE, but not size or succulence, for the artificial hybrids. However, within the H. anomalus habitat, direct selection on WUE also differed among populations. Across years, direct selection on leaf traits did not differ. Leaf N was the only trait for which direct selection differed between habitats but not within the H. anomalus habitat, suggesting that nutrient limitation is an important selective force driving adaptation of H. anomalus to the active dune habitat
Hydraulic adjustment of Scots pine across Europe
Martínez-Vilalta, J. ; Cochard, H. ; Mencuccini, M. ; Sterck, F.J. ; Herrero, A. ; Korhonen, J.F.J. ; Llorens, P. ; Nikinmaa, E. ; Nolè, A. ; Poyatos, R. ; Ripullone, F. ; Sass-Klaassen, U. ; Zweifel, R. - \ 2009
New Phytologist 184 (2009)2. - ISSN 0028-646X - p. 353 - 364.
carbon-isotope discrimination - quercus-pubescens willd. - xylem cavitation - sapwood area - sylvestris populations - contrasting climates - water deficits - leaf-area - vulnerability - architecture
The variability of branch-level hydraulic properties was assessed across 12 Scots pine populations covering a wide range of environmental conditions, including some of the southernmost populations of the species. The aims were to relate this variability to differences in climate, and to study the potential tradeoffs between traits. Traits measured included wood density, radial growth, xylem anatomy, sapwood- and leaf-specific hydraulic conductivity (KS and KL), vulnerability to embolism, leaf-to-sapwood area ratio (AL : AS), needle carbon isotope discrimination (¿13C) and nitrogen content, and specific leaf area. Between-population variability was high for most of the hydraulic traits studied, but it was directly associated with climate dryness (defined as a combination of atmospheric moisture demand and availability) only for AL : AS, KL and ¿13C. Shoot radial growth and AL : AS declined with stand development, which is consistent with a strategy to avoid exceedingly low water potentials as tree size increases. In addition, we did not find evidence at the intraspecific level of some associations between hydraulic traits that have been commonly reported across species. The adjustment of Scots pine's hydraulic system to local climatic conditions occurred primarily through modifications of AL : AS and direct stomatal control, whereas intraspecific variation in vulnerability to embolism and leaf physiology appears to be limited.
Implications of CO2 pooling on d13C of ecosystem respiration and leaves in Amazonian forest
Araujo, A.C. de; Ometto, J.P.H.B. ; Dolman, A.J. ; Kruijt, B. ; Waterloo, M.J. ; Ehleringer, J.R. - \ 2008
Biogeosciences 5 (2008)3. - ISSN 1726-4170 - p. 779 - 795.
carbon-isotope discrimination - rain-forest - tropical forest - water availability - natural-abundance - deciduous forest - cycle research - use efficiency - boreal forest - french-guiana
The carbon isotope of a leaf (d13Cleaf) is generally more negative in riparian zones than in areas with low soil moisture content or rainfall input. In Central Amazonia, the small-scale topography is composed of plateaus and valleys, with plateaus generally having a lower soil moisture status than the valley edges in the dry season. Yet in the dry season, the nocturnal accumulation of CO2 is higher in the valleys than on the plateaus. Samples of sunlit leaves and atmospheric air were collected along a topographical gradient in the dry season to test whether the d13Cleaf of sunlit leaves and the carbon isotope ratio of ecosystem respired CO2 (d13CReco) may be more negative in the valley than those on the plateau. The d13Cleaf was significantly more negative in the valley than on the plateau. Factors considered to be driving the observed variability in d13Cleaf were: leaf nitrogen concentration, leaf mass per unit area (LMA), soil moisture availability, more negative carbon isotope ratio of atmospheric CO2 (d13Ca) in the valleys during daytime hours, and leaf discrimination (¿leaf). The observed pattern of d13Cleaf might suggest that water-use efficiency (WUE) is higher on the plateaus than in the valleys. However, there was no full supporting evidence for this because it remains unclear how much of the difference in d13Cleaf was driven by physiology or &delta13Ca. The d13CReco was more negative in the valleys than on the plateaus on some nights, whereas in others it was not. It is likely that lateral drainage of CO2 enriched in 13C from upslope areas might have happened when the nights were less stable. Biotic factors such as soil CO2 efflux (Rsoil) and the responses of plants to environmental variables such as vapor pressure deficit (D) may also play a role. The preferential pooling of CO2 in the low-lying areas of this landscape may confound the interpretation of d13Cleaf and d13CReco.
Bundle Sheath Leakiness and Light Limitation during C-4 Leaf and Canopy CO2 Uptake
Kromdijk, J. ; Schepers, H.E. ; Albanito, F. ; Fitton, N. ; Carroll, F. ; Jones, M.B. ; Finnan, J. ; Lanigan, G.J. ; Griffiths, H. - \ 2008
Plant Physiology 148 (2008)4. - ISSN 0032-0889 - p. 2144 - 2155.
carbon-isotope discrimination - miscanthus x giganteus - short-term changes - quantum yield - chlorophyll fluorescence - amaranthus-cruentus - anhydrase activity - flaveria-bidentis - dark respiration - atmospheric co2
Perennial species with the C-4 pathway hold promise for biomass-based energy sources. We have explored the extent that CO2 uptake of such species may be limited by light in a temperate climate. One energetic cost of the C-4 pathway is the leakiness (phi) of bundle sheath tissues, whereby a variable proportion of the CO2, concentrated in bundle sheath cells, retrodiffuses back to the mesophyll. In this study, we scale phi from leaf to canopy level of a Miscanthus crop (Miscanthus x giganteus hybrid) under field conditions and model the likely limitations to CO2 fixation. At the leaf level, measurements of photosynthesis coupled to online carbon isotope discrimination showed that leaves within a 3.3-m canopy (leaf area index = 8.3) show a progressive increase in both carbon isotope discrimination and phi as light decreases. A similar increase was observed at the ecosystem scale when we used eddy covariance net ecosystem CO2 fluxes, together with isotopic profiles, to partition photosynthetic and respiratory isotopic flux densities (isofluxes) and derive canopy carbon isotope discrimination as an integrated proxy for phi at the canopy level. Modeled values of canopy CO2 fixation using leaf-level measurements of phi suggest that around 32% of potential photosynthetic carbon gain is lost due to light limitation, whereas using phi determined independently from isofluxes at the canopy level the reduction in canopy CO2 uptake is estimated at 14%. Based on these results, we identify phi as an important limitation to CO2 uptake of crops with the C-4 pathway.
Contributions of woody and herbaceous vegetation to tropical savanna ecosystem productivity: a quasi-global estimate
Lloyd, J. ; Bird, M.I. ; Vellen, L. ; Miranda, A.C. ; Veenendaal, E.M. ; Djagbletey, G. ; Miranda, H.S. ; Cook, G. ; Fraquhar, G.D. - \ 2008
Tree Physiology 28 (2008)3. - ISSN 0829-318X - p. 451 - 468.
soil organic-matter - carbon-isotope discrimination - precambrian shield region - eastern lowland bolivia - gap ratio c - brazilian cerrado - moisture gradient - grassland soils - south-america - national-park
To estimate the relative contributions of woody and herbaceous vegetation to savanna productivity, we measured the (13)C/(12)C isotopic ratios of leaves from trees, shrubs, grasses and the surface soil carbon pool for 22 savannas in Australia, Brazil and Ghana covering the full savanna spectrum ranging from almost pure grassland to closed woodlands on all three continents. All trees and shrubs sampled were of the C(3) pathway and all grasses of the C(4) pathway with the exception of Echinolaena inflexa (Poir.) Chase, a common C(3) grass of the Brazilian cerrado. By comparing the carbon isotopic compositions of the plant and carbon pools, a simple model relating soil delta(13)C to the relative abundances of trees + shrubs (woody plants) and grasses was developed. The model suggests that the relative proportions of a savanna ecosystem's total foliar projected cover attributable to grasses versus woody plants is a simple and reliable index of the relative contributions of grasses and woody plants to savanna net productivity. Model calibrations against woody tree canopy cover made it possible to estimate the proportion of savanna productivity in the major regions of the world attributable to trees + shrubs and grasses from ground-based observational maps of savanna woodiness. Overall, it was estimated that 59% of the net primary productivity (N(p)) of tropical savannas is attributable to C(4) grasses, but that this proportion varies significantly within and between regions. The C(4) grasses make their greatest relative contribution to savanna N(p) in the Neotropics, whereas in African regions, a greater proportion of savanna N(p) is attributable to woody plants. The relative contribution of C(4) grasses in Australian savannas is intermediate between those in the Neotropics and Africa. These differences can be broadly ascribed to large scale differences in soil fertility and rainfall.