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1.
Carbon isotopes and water use efficiency: sense and sensitivity   总被引:1,自引:0,他引:1  
Seibt U  Rajabi A  Griffiths H  Berry JA 《Oecologia》2008,155(3):441-454
We revisit the relationship between plant water use efficiency and carbon isotope signatures (δ13C) of plant material. Based on the definitions of intrinsic, instantaneous and integrated water use efficiency, we discuss the implications for interpreting δ13C data from leaf to landscape levels, and across diurnal to decadal timescales. Previous studies have often applied a simplified, linear relationship between δ13C, ratios of intercellular to ambient CO2 mole fraction (C i/C a), and water use efficiency. In contrast, photosynthetic 13C discrimination (Δ) is sensitive to the ratio of the chloroplast to ambient CO2 mole fraction, C c/C a (rather than C i/C a) and, consequently, to mesophyll conductance. Because mesophyll conductance may differ between species and over time, it is not possible to determine C c/C a from the same gas exchange measurements as C i/C a. On the other hand, water use efficiency at the leaf level depends on evaporative demand, which does not directly affect Δ. Water use efficiency and Δ can thus vary independently, making it difficult to obtain trends in water use efficiency from δ13C data. As an alternative approach, we offer a model available at to explore how water use efficiency and 13C discrimination are related across leaf and canopy scales. The model provides a tool to investigate whether trends in Δ indicate changes in leaf functional traits and/or environmental conditions during leaf growth, and how they are associated with trends in plant water use efficiency. The model can be used, for example, to examine whether trends in δ13C signatures obtained from tree rings imply changes in tree water use efficiency in response to atmospheric CO2 increase. This is crucial for predicting how plants may respond to future climate change. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

2.
The seasonal trends in water use efficiency of sun and shade leaves of mature oak (Quercus robur) and sycamore (Acer pseudoplatanus) trees were assessed in the upper canopy of an English woodland. Intrinsic water use efficiency (net CO2 assimilation rate/leaf conductance, A/g) was measured by gas exchange and inferred from C isotope discrimination (δ13C) methods. Shade leaves had consistently lower δ13C than sun leaves (by 1–2‰), the difference being larger in sycamore. Buds had distinct sun and shade isotopic signatures before bud break and received an influx of 13C-rich C before becoming net autotrophs. After leaf full expansion, δ13C declined by 1–2‰ gradually through the season, emphasising the importance of imported carbon in the interpretation of leaf δ13C values in perennial species. There was no significant difference between the two species in the value of intrinsic water use efficiency for either sun or shade leaves. For sun leaves, season-long A/g calculated from δ13C (72–78 μmol CO2 [mol H2O]−1) was 10–16% higher than that obtained from gas exchange and in situ estimates of leaf boundary layer conductance. For shade leaves, the gas exchange–derived values were low, only 10–18% of the δ13C-derived values. This is ascribed to difficulties in obtaining a comprehensive sample of gas exchange measurements in the rapidly changing light environment.  相似文献   

3.
Sullivan PF  Welker JM 《Oecologia》2007,151(3):372-386
Leaf carbon isotope discrimination (Δ13C) varies with the balance between net photosynthesis (A) and stomatal conductance (g s ). Inferences that can be made with Δ13C are limited, as changes could reflect variation in A and/or g s . Investigators have suggested that leaf δ18O enrichment above source water (Δ18O) may enable differentiation between sources of variation in Δ13C, as leaf Δ18O varies with transpiration rate (E), which is closely correlated with g s when leaves experience similar leaf to air vapor pressure differences. We examined leaf gas exchange of Salix arctica at eight sites with similar air temperatures and relative humidities but divergent soil temperatures and soil water contents near Pituffik, Greenland (76°N, 38°W). We found negative correlations at the site level between g s and Δ18O in bulk leaf tissue (r 2 = 0.62, slope = −17.9‰/mol H2O m−2 s−1, P = 0.02) and leaf α-cellulose (r 2 = 0.83, slope = −11.5‰ mol H2O m−2 s−1, P < 0.01), consistent with the notion that leaf water enrichment declines with increasing E. We also found negative correlations at the site-level between intrinsic water-use efficiency (iWUE) and Δ13C in bulk leaf tissue (r 2 = 0.65, slope = −0.08‰/μmol CO2 /mol H2O, P = 0.02) and leaf α-cellulose (r 2 = 0.50, slope = −0.05 ‰/[μmol CO2 /mol H2O], P = 0.05). When increasing Δ13C was driven by increasing g s alone, we found negative slopes between Δ13C and Δ18O for bulk leaf tissue (−0.664) and leaf α-cellulose (−1.135). When both g s and A max increased, we found steeper negative slopes between Δ13C and Δ18O for bulk leaf tissue (−2.307) and leaf α-cellulose (−1.296). Our results suggest that the dual isotope approach is capable of revealing the qualitative contributions of g s and A max to Δ13C at the site level. In our study, bulk leaf tissue was a better medium than leaf α-cellulose for application of the dual isotope approach.  相似文献   

4.
Associations between δ13C values and leaf gas exchanges and tree-ring or needle growth, used in ecophysiological compositions, can be complex depending on the relative timing of CO2 uptake and subsequent redistribution and allocation of carbon to needle and stem components. For palaeoenvironmental and dendroecological studies it is often interpreted in terms of a simple model of δ13C fractionation in C3 plants. However, in spite of potential complicating factors, few studies have actually examined these relationships in mature trees over inter- and intra-annual time-scales. Here, we present results from a 4 years study that investigated the links between variations in leaf gas-exchange properties, growth, and dated δ13C values along the needles and across tree rings of Aleppo pine trees growing in a semi-arid region under natural conditions or with supplemental summer irrigation. Sub-sections of tissue across annual rings and along needles, for which time of formation was resolved from growth rate analyses, showed rapid growth and δ13C responses to changing environmental conditions. Seasonal cycles of growth and δ13C (up to ~4‰) significantly correlated (P<0.01) with photosynthetically active radiation, vapour pressure deficit, air temperature, and soil water content. The irrigation significantly increased leaf net assimilation, stomatal conductance and needle and tree-ring growth rate, and markedly decreased needle and tree-ring δ13C values and its sensitivity to environmental parameters. The δ13C estimates derived from gas-exchange parameters, and weighted by assimilation, compared closely with seasonal and inter-annual δ13C values of needle- and tree-ring tissue. Higher stomatal conductances of the irrigated trees (0.22 vs. 0.08 mol m−2 s−1 on average) corresponded with ~2.0‰ lower average δ13C values, both measured and derived. Derived and measured δ13C values also indicated that needle growth, which occurs throughout the stressful summer was supported by carbon from concurrent, low rate assimilation. For Aleppo pine under semi-arid and irrigated conditions, the δ13C of tree-ring and needle material proved, in general, to be a reasonable indicator of integrated leaf gas-exchange properties.  相似文献   

5.
S. K. Rice 《Oecologia》2000,123(1):1-8
Field samples of bryophytes are highly variable in carbon isotope discrimination values (Δ, a measure of 13CO2 uptake relative to 12CO2), but it is unknown what affects Δ under field conditions, or how variation in Δ relates to bryophyte performance. This study employed field and greenhouse common garden studies to evaluate the influence of microsite, seasonal, and genetic variation on Δ in peatmosses. Three species of Sphagnum that occupy hollow (S. recurvum), carpet (S. palustre), and hummock (S. tenerum) habitats were sampled for relative growth rates (RGR), C:N ratio, and Δ throughout a growing season. Values of Δ ranged from 19.0 to 27.1‰. This variation was unrelated to species (P=0.61). However, Δ varied seasonally (P<0.001), with lower discrimination in the spring (mean 22.5‰), followed by summer (23.8‰) and winter (24.7‰). There was also significant microsite variation (P=0.015) which disappeared when plants were grown in a common garden. In both spring and summer, microsite variation in Δ was inversely related to RGR (P<0.001), but unrelated to C:N ratios (P>0.08). These results suggest that environmental, not genetic, variation at microsites affects Δ in non-vascular plants. However, environmental control of Δ is unlike that in vascular plants where water limitation lowers chloroplastic demand and increases resistance to carbon uptake. In non-vascular plants, water limitation lowers chloroplastic demand and decreases resistance to carbon uptake. These processes have additive effects and generate high spatial and seasonal variability in Δ. Received: 29 April 1999 / Accepted: 8 November 1999  相似文献   

6.
Leaf carbon isotope ratios (δ13C) and photosynthetic gas exchange were measured on plants growing in hanging garden communities in southern Utah, USA. Hanging gardens are unusual, mesic cliff communities occurring where water seeps from the sandstone bedrock in an otherwise extremely arid region; there is very limited overlap in species distributions inside and outside these gardens. Solar exposure in hanging gardens varied with orientation and one of the gardens (Ribbon Garden) was shaded throughout the day. The leaf δ13C values of plants in hanging gardens were significantly more negative than for plants from either nearby ephemeral wash or riparian communities. In Ribbon Garden, the observed δ13C values were as low as −34.8‰, placing them among the most negative values reported for any terrestrial plant species growing in a natural environment. Hanging garden plants were exposed to normal atmospheric CO2 with an average δ13C value of −7.9‰ and so the low leaf δ13C values could not be attributed to exposure to a CO2 source with low 13C content. There was a seasonal change toward more negative leaf δ13C values at the end of the growing season. The observed leaf δ13C values were consistent with photosynthetic gas exchange measurements that indicated unusually high leaf intercellular CO2 concentrations associated with the relatively low light levels in hanging gardens. Thus, extremely negative leaf δ13C values would be expected if significant amounts of the seasonal carbon gain occur at light levels low enough to be near the light compensation point. Maximum observed photosynthetic rates varied with light levels at each of the gardens, with maximum rates averaging 20.3, 14.6, and 3.1 μmol m−2 s−1 at Double Garden, Lost Garden, and Ribbon Garden, respectively. Leaf nitrogen contents averaged 18.5 mg g−1 in species from the more shaded hanging gardens (Lost and Ribbon). When expressed on a leaf area basis, nitrogen contents averaged 117 mmol N m−2 at Lost Garden and 65 mmol N m−2 at Ribbon Garden (shadiest of the two gardens). Leaf nitrogen isotope ratios averaged −2.3‰ (range of −0.7 to −6.1‰), suggesting that most of the nitrogen was derived from a biological fixation source which is most likely the Nostoc growing on the sandstone walls at the seep. These values contrast with leaf nitrogen isotope ratios of 5–9‰ which have been previously reported for arid zone plants in nearby ecosystems. Received: 19 January 1997 / Accepted: 19 April 1997  相似文献   

7.
A. Ares  J. H. Fownes 《Oecologia》1999,121(4):458-466
We studied changes in stand structure, productivity, canopy development, growth efficiency, and intrinsic water use efficiency (WUE=photosynthesis/stomatal conductance) of the native tree koa (Acacia koa) across a gradient of decreasing rainfall (2600–700 mm) with increasing elevation (700–2000 m) on the island of Hawaii. The stands were located on organic soils on either smooth (pahoehoe) or rough (aa) lava flows. In the greenhouse, we also examined growth and WUE responses to different water regimes of koa seedlings grown from seeds collected in the study area. We tested the hypotheses that (1) stand basal area, aboveground net primary productivity (ANPP), leaf area index (LAI), and growth per unit leaf area decreased with decreasing rainfall, (2) WUE increased with decreasing rainfall or water supply, and (3) WUE responses were caused by stomatal limitation rather than by nutrient limitations to photosynthesis. The carbon isotope composition of phyllode tissues (δ13C) was examined as an integrated measure of WUE. Basal area and LAI of koa stands on both pahoehoe and aa lava flows, and ANPP on aa lava flows decreased with elevation. Basal area, LAI, and ANPP of koa in mixed stands with the exotic tropical ash (Fraxinus udhei) were lower compared to single-species koa stands at similar elevations. Along the gradient, phyllode δ13C (and therefore WUE) increased with elevation from –30.2 to –26.8‰. Koa in mixed stands exhibited higher (less negative) δ13C than in single-species stands suggesting that koa and tropical ash competed for water. In the greenhouse, we observed the same trend observed in the field, as phyllode δ13C increased from –27.7 to –24‰ as water supply decreased. Instantaneous gas exchange measurements in the greenhouse showed an inverse correlation of both maximum (morning) photosynthesis (A) and conductance (g) with δ13C values and, also, a good agreement between instantaneous (A/g) and integrated measures of WUE. Phyllode δ13C was not correlated with foliar concentrations of N or other nutrients in either the field or the greenhouse, indicating that differences in δ13C were caused by stomatal limitation rather than by nutrient-related changes in photosynthetic capacity. This study provided evidence that long-term structural and growth adjustments as well as changes in WUE are important mechanisms of koa response to water limitation.  相似文献   

8.
Density functional theory calculations of isolated Watson–Crick A:U and A:T base pairs predict that adenine 13C2 trans-hydrogen bond deuterium isotope shifts due to isotopic substitution at the pyrimidine H3, 2hΔ13C2, are sensitive to the hydrogen-bond distance between the N1 of adenine and the N3 of uracil or thymine, which supports the notion that 2hΔ13C2 is sensitive to hydrogen-bond strength. Calculated 2hΔ13C2 values at a given N1–N3 distance are the same for isolated A:U and A:T base pairs. Replacing uridine residues in RNA with 5-methyl uridine and substituting deoxythymidines in DNA with deoxyuridines do not statistically shift empirical 2hΔ13C2 values. Thus, we show experimentally and computationally that the C7 methyl group of thymine has no measurable affect on 2hΔ13C2 values. Furthermore, 2hΔ13C2 values of modified and unmodified RNA are more negative than those of modified and unmodified DNA, which supports our hypothesis that RNA hydrogen bonds are stronger than those of DNA. It is also shown here that 2hΔ13C2 is context dependent and that this dependence is similar for RNA and DNA. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.  相似文献   

9.
Tropical small mountainous rivers deliver a poorly quantified, but potentially significant, amount of carbon to the world’s oceans. However, few historical records of land–ocean carbon transfer exist for any region on Earth. Corals have the potential to provide such records, because they draw on dissolved inorganic carbon (DIC) for calcification. In temperate systems, the stable- (δ13C) and radiocarbon (Δ14C) isotopes of coastal DIC are influenced by the δ13C and Δ14C of the DIC transported from adjacent rivers. A similar pattern should exist in tropical coastal DIC and hence coral skeletons. Here, δ13C and Δ14C measurements were made in a 56-year-old Montastraea faveolata coral growing ~1 km from the mouth of the Rio Fajardo in eastern Puerto Rico. Additionally, the δ13C and Δ14C values of the DIC of the Rio Fajardo and its adjacent coastal waters were measured during two wet and dry seasons. Three major findings were observed: (1) synchronous depletions of both δ13C and Δ14C in the coral skeleton are annually coherent with the timing of peak river discharge, (2) riverine DIC was always more depleted in δ13C and Δ14C than seawater DIC, and (3) the correlation of δ13C and Δ14C was the same in both coral skeleton and the DIC of the river and coastal waters. These results indicate that coral skeletal δ13C and Δ14C are recording the delivery of riverine DIC to the coastal ocean. Thus, coral records could be used to develop proxies of historical land–ocean carbon flux for many tropical regions. Such information could be invaluable for understanding the role of tropical land–ocean carbon flux in the context of land-use change and global climate change.  相似文献   

10.
The interspecific variability of sunlit leaf carbon isotope composition (δ13C), an indicator of leaf intrinsic water-use efficiency (WUE, CO2 assimilation rate/leaf conductance for water vapour), was investigated in canopy trees of three lowland rainforest stands in French Guiana, differing in floristic composition and in soil drainage characteristics, but subjected to similar climatic conditions. We sampled leaves with a rifle from 406 trees in total, representing 102 species. Eighteen species were common to the three stands. Mean species δ13C varied over a 6.0‰ range within each stand, corresponding to WUE varying over about a threefold range. Species occurring in at least two stands displayed remarkably stable δ13C values, suggesting a close genetic control of species δ13C. Marked differences in species δ13C values were found with respect to: (1) the leaf phenology pattern (average δ13C=–29.7‰ and –31.0‰ in deciduous-leaved and evergreen-leaved species, respectively), and (2) different types of shade tolerance defined by features reflecting the plasticity of growth dynamics with respect to contrasting light conditions. Heliophilic species exhibited more negative δ13C values (average δ13C=–30.5‰) (i.e. lower WUE) than hemitolerant species (–29.3‰). However, tolerant species (–31.4‰) displayed even more negative δ13C values than heliophilic ones. We could not provide a straightforward ecophysiological interpretation of this result. The negative relationship found between species δ13C and midday leaf water potential (Ψwm) suggests that low δ13C is associated with high whole tree leaf specific hydraulic conductance. Canopy carbon isotope discrimination (Δ A ) calculated from the basal area-weighed integral of the species δ13C values was similar in the three stands (average Δ A =23.1‰), despite differences in stand species composition and soil drainage type, reflecting the similar proportions of the three different shade-tolerance types among stands. Received: 30 November 1999 / Accepted: 23 March 2000  相似文献   

11.
Increasing leaf photosynthesis offers a possible way to improve yield potential in rice (Oryza sativa L.). Carbon isotope discrimination (Δ13C) has potential as an indirect selection criterion. In this study, we searched for quantitative trait loci (QTLs) controlling Δ13C, and assessed their association with leaf photosynthesis. Substitution mapping by using chromosome segment substitution lines (CSSLs), that carry segments from the indica cultivar Kasalath in the genetic background of the japonica cultivar Koshihikari, identified genomic regions affecting Δ13C on chromosomes (Chr.) 2, 3, 6, 7, and 12. One of the CSSLs, SL208, in which most regions on Chr. 3 were substituted with Kasalath segments, showed higher leaf stomatal conductance for CO2 (g s) and Δ13C than Koshihikari during the vegetative stage although leaf photosynthetic rate did not differ between them. These results suggest an association between Δ13C and g s. To test this association, we performed a QTL analysis for Δ13C at vegetative and heading stages in an F2 population derived from a cross between SL208 and Koshihikari. The results confirmed a QTL controlling Δ13C on the long arm of Chr. 3. By using a near-isogenic line specific to Hd6, we ruled out the possibility that variation in Δ13C was generated through the pleiotropic effect of heading date.  相似文献   

12.
In this study, sun leaf carbon isotope composition (δ13C) of two co-occurring woody Mediterranean species (Quercus pubescens Willd., a deciduous oak, and Q. ilex L., an evergreen one) was investigated on four sites with different water availability. The total range of δ13C values was 4.4 and 3.1‰ for Q. pubescens and Q. ilex respectively. The intra-site variability was about 3‰. Total mean per species was equal. There were significant differences among sites, but at each site means of δ13C were not significantly different between species. A simple physiological model predicts no difference in intrinsic water-use efficiency (WUEi) between evergreen and deciduous oaks. The relationship between site means of δ13C and water parameters suggests that there is a leaf functional adjustment with respect to available water resource. No correlation was found between δ13C and the contents of any mass-based biochemical constituent. Nevertheless there was a significant correlation between δ13C and leaf mass per area of Q. ilex. For both species, there is also a positive correlation between leaf δ13C and individual crown area, i.e. a structural characteristic at tree level. Causal relations between δ13C and plant-environment interactions are discussed. Received: 25 October 1996 / Accepted: 19 January 1997  相似文献   

13.
We report on community structural, ecophysiological, phenological, and morphological measurements made on woody plant species in the high elevation pre-altiplano zone on the western slopes of the Andean Cordillera of northern Chile. Notwithstanding extreme conditions of low rainfall, high atmospheric vapour demand and diurnal temperature fluctuation, a diversity of habitats (associated with drainage and slope aspect), appreciable local plant species richness (28 woody perennial plant species in a small area), and an array of adaptive morphological ecophysiological and phenological traits are present among woody species in these shrublands. Family diversity was low with four families accounted for 82% of the species. A range of gas exchange and watering use efficiency strategies was present ranging from highly efficient CAM species with a carbon isotope discrimination (Δ) of 3.7–7.5‰ through C3 species with varying stomatal and gas exchange characteristics with a Δ of 14.4 to 19.8‰. Drought-deciduous small-leaved amphistomatic species from arid slopes generally had high stomatal conductance and high carbon assimilation rates during the rainy season. These drought deciduous species were largely leafless and, with one exception had low water potentials, during the dry season. Wash and less xeric site species commonly had broader evergreen to semi-evergreen leaves, higher dry season water potentials, and relatively consistent and moderate rates of gas exchange throughout the year. For all species, intrinsic water use efficiency (as estimated from the inverse of c i :c a ratio) correlated positively with mean leaf width (broader leaves had a lower higher intrinsic WUE) and dry season water potential. The charismatic high altitude tree, Polylepis rugulosa (Roaceae), had a population structure that suggests highly episodic establishment of seedlings, likely in sequences of wet years. Little of the area of these significant shrublands is currently protected. It would be desirable to add areas of pre-altiplano shrublands to adjacent national parks to ensure the persistence of these important communities. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

14.
Metrosideros polymorpha, a dominant tree species in Hawaiian ecosystems, occupies a wide range of habitats. Complementary field and common-garden studies of M. polymorpha populations were conducted across an altitudinal gradient at two different substrate ages to ascertain if the large phenotypic variation of this species is determined by genetic differences or by phenotypic modifications resulting from environmental conditions. Several characteristics, including ecophysiological behavior and anatomical features, were largely induced by the environment. However, other characteristics, particularly leaf morphology, appeared to be mainly determined by genetic background. Common garden plants exhibited higher average rates of net assimilation (5.8 μmol CO2 m−2 s−1) and higher average stomatal conductance (0.18 mol H2O m−2 s−1) than their field counterparts (3.0 μmol CO2 m−2 s−1, and 0.13 mol H2O m−2 s−1 respectively). Foliar δ13C of most common-garden plants was similar among sites of origin with an average value of −26.9‰. In contrast, mean values of foliar δ13C in field plants increased substantially from −29.5‰ at low elevation to −24.8‰ at high elevation. Leaf mass per unit area increased significantly as a function of elevation in both field and common garden plants; however, the range of values was much narrower in common garden plants (211–308 g m−2 for common garden versus 107–407 g m−2 for field plants). Nitrogen content measured on a leaf area basis in common garden plants ranged from 1.4 g m−2 to 2.4 g m−2 and from 0.8 g m−2 to 2.5 g m−2 in field plants. Photosynthetic nitrogen use efficiency (PNUE) decreased 50% with increasing elevation in field plants and only 20% in plants from young substrates in the common garden. This was a result of higher rates of net CO2 assimilation in the common garden plants. Leaf tissue and cell layer thickness, and degree of leaf pubescence increased significantly with elevation in field plants, whereas in common garden plants, variation with elevation of origin was much narrower, or was entirely absent. Morphological characteristics such as leaf size, petiole length, and internode length decreased with increasing elevation in the field and were retained when grown in the common garden, suggesting a potential genetic basis for these traits. The combination of environmentally induced variability in physiological and anatomical characteristics and genetically determined variation in morphological traits allows Hawaiian M. polymorpha to attain and dominate an extremely wide ecological distribution not observed in other tree species. Received: 12 March 1997 / Accepted: 27 August 1997  相似文献   

15.
Studies of selected morphological needle parameters were carried out on young (17–19 year old) Norway spruce trees cultivated inside glass domes at ambient (A, 370 μmol (CO2) mol−1) and elevated (E, 700 μmol (CO2) mol−1) atmospheric CO2 concentrations [CO2] beginning in 1997. Annual analyses performed from 2002 to 2004 revealed higher values for needle length (especially for current needles, up to 18%) and projected needle area (up to 13%) accompanied by lower values for specific needle area (up to 15% lower, as quantified by needle mass to projected area ratio) in the E treatment compared to the A treatment. Statistically significant differences for most of the investigated morphological parameters were found in young needles in the well irradiated sun-adapted crown parts, particularly under water-limiting soil conditions in 2003. This was likely a result of different water relations in E compared to A trees as investigated under temperate water stress (Kuper et al. in Biol Plantarum 50:603–609, 2006). Furthermore, E trees had much higher absorbing root area, which modified and enhanced root:shoot as well as root:conductive stem area proportions. These hydraulic properties and early seasonal stimulation of photosynthesis forced advanced needle development in E trees, particularly under limited soil water conditions. The number of needles per unit shoot length was found to be unaffected by elevated [CO2].  相似文献   

16.
Among grain legumes, faba bean is becoming increasingly popular in European agriculture due to recent economic and environmental interests. Faba bean can be a highly productive crop, but it is sensitive to drought stress and yields can vary considerably from season to season. Understanding the physiological basis of drought tolerance would indicate traits that can be used as indirect selection criteria for the development of cultivars adapted to drought conditions. To assess genotypic variation in physiological traits associated with drought tolerance in faba bean and to determine relationships among these attributes, two pot experiments were established in a growth chamber using genetic materials that had previously been screened for drought response in the field. Nine inbred lines of diverse genetic backgrounds were tested under adequate water supply and limited water conditions. The genotypes showed substantial variation in shoot dry matter, water use, stomatal conductance, leaf temperature, transpiration efficiency, carbon isotope discrimination (Δ13C), relative water content (RWC) and osmotic potential, determined at pre-flowering vegetative stage. Moisture deficits decreased water usage and consequently shoot dry matter production. RWC, osmotic potential, stomatal conductance and Δ13C were lower, whereas leaf temperature and transpiration efficiency were higher in stressed plants, probably due to restricted transpirational cooling induced by stomatal closure. Furthermore, differences in stomatal conductance, leaf temperature, Δ13C and transpiration efficiency characterized genotypes that were physiologically more adapted to water deficit conditions. Correlation analysis also showed relatively strong relationships among these variables under well watered conditions. The drought tolerant genotypes, ILB-938/2 and Melodie showed lower stomatal conductance associated with warmer leaves, whereas higher stomatal conductance and cooler leaves were observed in sensitive lines (332/2/91/015/1 and Aurora/1). The lower value of Δ13C coupled with higher transpiration efficiency in ILB-938/2, relative to sensitive lines (Aurora/1 and Condor/3), is indeed a desirable characteristic for water-limited environments. Finally, the results showed that stomatal conductance, leaf temperature and Δ13C are promising physiological indicators for drought tolerance in faba bean. These variables could be measured in pot-grown plants at adequate water supply and may serve as indirect selection criteria to pre-screen genotypes.  相似文献   

17.
Chlorophyll (Chl) content, dry mass, relative water content (RWC), leaf mass per area (LMA), proline (Pro) content, malondialdehyde (MDA) content, superoxide dismutase (SOD) and peroxidase (POD) activity, P N-PAR response curves and gas exchange were studied to determine the effects of water stress on photosynthetic activity, dry mass partitioning and metabolic changes in four provenances of neem (Azadirachta indica A. Juss). The results indicated that provenance differences existed in the adaptation response to water stress that included changes to growth strategies coupled with ecophysiological and metabolic adjustments. As water stress increased, stomatal conductance (g s), net photosynthetic rate (P N), transpiration rate (E), and leaf RWC decreased while LMA increased in all provenances. Dry mass was reduced in droughted plants and the percentage increased in dry mass allocated to roots, and enzyme activities of SOD and POD were highest in neem originating from Kalyani (KA) provenance and lowest in neem originating from New Dehli (ND) provenance. In contrast, water stress increased MDA content least in KA and most in ND. Furthermore, neem originating from ND also had the greatest decrease in Chl a/b ratio while the ratio was least affected in neem originating from KA. These findings suggest neem originating from KA may have more drought resistance than neem originating from ND. The data from P N-PAR response curves are less clear. While these curves showed that drought stress increased compensation irradiance (I c) and dark respiration (R D) and decreased saturation irradiance (I s) and maximum net photosynthetic rate (P max), the extent of decline in P max was provenance dependent. P max under non-waterlimiting conditions was higher in neem originating from Jodhpur (MA) (about 14 μmol m−2 s−1) than in the other three provenances (all about 10 μmol m−2 s−1), but mild water stress had minimal effect on P max of these three provenances whereas P max of MA provenance declined to 10 μmol m−2 s−1, i.e. a similar value. However, under severe water stress P max of MA and KA provenances had declined to 40% of non-stressed values (about 6 and 4 μmol m−2 s−1, respectively) whereas the decline in P max of neem originating from Kulapachta (KU) and ND provenances was about 50% of nonstressed values (about 5 μmol m−2 s−1). These data suggest the P N responses of KU and ND provenances are most tolerant, and KA and MA least tolerant to increasing water stress, but also suggest MA provenance could be the most desired under both non-water-limiting and water-limiting conditions due to highest P max in all conditions.  相似文献   

18.
The photochemical reflectance index (PRI), derived from narrow-band reflectance at 531 and 570 nm, was explored as an indicator of photosynthetic radiation use efficiency for 20 species representing three functional types: annual, deciduous perennial, and evergreen perennial. Across species, top-canopy leaves in full sun at midday exhibited a strong correlation between PRI and ΔF/Fm′, a fluorescence-based index of photosystem II (PSII) photochemical efficiency. PRI was also significantly correlated with both net CO2 uptake and radiation use efficiency measured by gas exchange. When species were examined by functional type, evergreens exhibited significantly reduced midday photosynthetic rates relative to annual and deciduous species. This midday reduction was associated with reduced radiation use efficiency, detectable as reduced net CO2 uptake, PRI, and ΔF/Fm′ values, and increased levels of the photoprotective xanthophyll cycle pigment zeaxanthin. For each functional type, nutrient deficiency led to reductions in both PRI and ΔF/Fm′ relative to fertilized controls. Laboratory experiments exposing leaves to diurnal courses of radiation and simulated midday stomatal closure demonstrated that PRI changed rapidly with both irradiance and leaf physiological state. In these studies, PRI was closely correlated with both ΔF/Fm' and radiation use efficiency determined from gas exchange at all but the lowest light levels. Examination of the difference spectra upon exposure to increasing light levels revealed that the 531 nm Δ reflectance signal was composed of two spectral components. At low irradiance, this signal was dominated by a 545-nm component, which was not closely related to radiation use efficiency. At progressively higher light levels above 100 μmol m−2 s−1, the 531-nm signal was increasingly dominated by a 526-nm component, which was correlated with light use efficiency and with the conversion of the xanthophyll pigment violaxanthin to antheraxanthin and zeaxanthin. Further consideration of the two components composing the 531-nm signal could lead to an index of photosynthetic function applicable over a wide range of illumination. The results of this study support the use of PRI as an interspecific index of photosynthetic radiation use efficiency for leaves and canopies in full sun, but not across wide ranges in illumination from deep shade to full sun. The discovery of a consistent relationship between PRI and photosynthetic radiation use efficiency for top-canopy leaves across species, functional types, and nutrient treatments suggests that relative photosynthetic rates could be derived with the “view from above” provided by remote reflectance measurements if issues of canopy and stand structure can be resolved. Received: 6 January 1997 / Accepted: 14 July 1997  相似文献   

19.
The vertical profile of stable carbon isotope ratios (δ13C) of leaves was analyzed for 13 tree species in a cool-temperate deciduous forest in Japan. The vertical distribution of long-term averaged δ13C in atmospheric CO2a) was estimated from δ13C of dry matter from NADP-malic enzyme type C4 plant (Zea mays L. var. saccharata Sturt.) grown at a tower in the forest for 32␣days, assuming constant Δ value (3.3‰) in Z. mays against height. The δa value obtained from δ13C in Z.␣mays was lowest at the forest floor (−9.30 ± 0.03‰), increased with height, and was almost constant above 10␣m (−7.14 ± 0.14‰). Then leaf Δ values for the tree species were calculated from tree leaf δ13 C andδa. Mean leaf Δ values for the three tall deciduous species (Fraxinus mandshurica, Ulmus davidiana, and Alnus hirsuta) were significantly different among three height levels in the forest: 23.1 ± 0.7‰ at the forest floor (understory), 21.4 ± 0.5‰ in lower canopy, and 20.5 ± 0.3‰ in upper canopy. The true difference in tree leaf Δ among the forest height levels might be even greater, because Δ in Z. mays probably increased with shading by up to ∼‰. The difference in tree leaf Δ among the forest height levels would be mainly due to decreasing intercellular CO2 (C i) with the increase in irradiance. Potential assimilation rate for the three tree species probably increased with height, since leaf nitrogen content on an area basis for these species also increased with height. However, the increase in stomatal conductance for these tree species would fail to meet the increase in potential assimilation rate, which might lead to increasing the degree of stomatal limitation in photosynthesis with height. Received: 30 September 1995 / Accepted: 25 October 1996  相似文献   

20.
The relationship among water use efficiency (WUE), productivity and carbon isotopic composition (δ13C) in white spruce (Picea glauca (Moench) Voss) seedlings was investigated. Sixteen hundred seedlings representing 10 controlled crosses were planted in the field in individual buried sand-filled cylinders. The soil water content in the cylinders was measured using time domain reflectometry over two growing seasons and seedling water use determined by water balance. Two watering treatments were imposed: irrigation and dry land. There was significant (1.6–2.0%c) genetic variation in needle δ13C. Ranking of crosses in terms of δ13C was generally maintained over watering treatments and there was not a significant genetic versus environmental interaction. There was a positive correlation between δ13C and both intrinsic and long-term WUE (more positive δ13C with increased WUE) and between δ13C and productivity, suggesting a correlation due to variation in photosynthetic capacity. Root to shoot ratios did not increase in water-stressed plants, indicating that responses to drought were primarily at the level of gas exchange, rather than through morphological changes. Our results indicate that it should be possible to use δ13C as a surrogate for WUE and to select white spruce genotypes for high WUE without compromising yield.  相似文献   

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