<Emphasis Type="Italic">δ</Emphasis><Superscript>13</Superscript>C values and crassulacean acid metabolism in <Emphasis Type="Italic">Clusia</Emphasis> species from Panama

The genus Clusia is notable in that it contains arborescent crassulacean acid metabolism (CAM) plants. As part of a study of CAM in Clusia, titratable acidities were measured in 25 species and ¹³C values were measured for 38 species from Panamá, including seven undescribed species, and 11 species from Colombia, Costa Rica and Honduras. CAM was detected in 12 species. Clusia flava, C. rosea and C. uvitana exhibited ¹³C values or diurnal fluctuations in acidity indicative of strong CAM. In C. croatii, C. cylindrica, C. fructiangusta, C. lineata, C. odorata, C. pratensis, C. quadrangula, C. valerioi and C. sp. D diurnal fluctuations in acidity were consistent with weak CAM but the ¹³C values were C₃-like. All of the species that exhibited strong or weak CAM were in the C. flava or C. minor species groups. CAM was not detected in any member of the C. multiflora species group. Strong CAM species were not collected at altitudes above 680 m a.s.l. On the basis of ¹³C values, the expression of CAM was similar in terrestrial, hemi-epiphytic and epiphytic species and did not differ between individuals of the same species that exhibited different life-forms. This study indicates that phylogenetic affiliation may be a predictor of an ability to exhibit CAM in Clusia species from the Panamanian region, and that weak CAM is probably a common photosynthetic option in many Clusia species. ¹³C value is not a particularly good indicator of a potential of Clusia species growing in the field to exhibit CAM because it appears that the contribution in most species of CAM to carbon gain is generally rather small when integrated over the life-time of leaves.     

Induction by drought of crassulacean acid metabolism in the terrestrial bromeliad, <Emphasis Type="Italic">Puya floccosa</Emphasis>

In the terrestrial bromeliad, Puya floccosa, a value of carbon isotopic composition (δ¹³C) of −22‰ has been previously reported, suggesting the operation of weak and/or intermediate (C₃-CAM) crassulacean acid metabolism (CAM). In order to characterize the operation of CAM in P. floccosa and its possible induction by drought, plants were grown in Caracas and subjected to four independent drought cycles. Additionally, since plants of this species grow in Venezuela in a large range of elevations, leaf samples were collected at elevations ranging from 725 to 2,100 m a.s.l. in the Venezuelan Andes and the Coastal Range, in order to evaluate the effect of elevation on CAM performance. Even though nocturnal acid accumulation occurred in both watered and droughted plants, mean ΔH⁺ was higher in droughted than watered plants [ΔH⁺ = 60.17.5 and 22.9 ± 5.2 μmol g⁻¹(FM), respectively]. The majority of plants from all the natural populations sampled had low values of δ¹³C not differing significantly from those of C₃ plants collected as standards and δ¹³C did not change with elevation. We conclude that P. floccosa is capable of a weak CAM activity, with a large variability among populations and drought experiments probably due to local and temporal differences in microclimatic variables and drought stress; elevation bears no influence on values of δ¹³C in this species.     

Environmental regulation of carbon isotope composition and crassulacean acid metabolism in three plant communities along a water availability gradient

Expression of crassulacean acid metabolism (CAM) is characterized by extreme variability within and between taxa and its sensitivity to environmental variation. In this study, we determined seasonal fluctuations in CAM photosynthesis with measurements of nocturnal tissue acidification and carbon isotopic composition (δ¹³C) of bulk tissue and extracted sugars in three plant communities along a precipitation gradient (500, 700, and 1,000 mm year⁻¹) on the Yucatan Peninsula. We also related the degree of CAM to light habitat and relative abundance of species in the three sites. For all species, the greatest tissue acid accumulation occurred during the rainy season. In the 500 mm site, tissue acidification was greater for the species growing at 30% of daily total photon flux density (PFD) than species growing at 80% PFD. Whereas in the two wetter sites, the species growing at 80% total PFD had greater tissue acidification. All species had values of bulk tissue δ¹³C less negative than −20‰, indicating strong CAM activity. The bulk tissue δ¹³C values in plants from the 500 mm site were 2‰ less negative than in plants from the wetter sites, and the only species growing in the three communities, Acanthocereus tetragonus (Cactaceae), showed a significant negative relationship between both bulk tissue and sugar δ¹³C values and annual rainfall, consistent with greater CO₂ assimilation through the CAM pathway with decreasing water availability. Overall, variation in the use of CAM photosynthesis was related to water and light availability and CAM appeared to be more ecologically important in the tropical dry forests than in the coastal dune.     

The δ13C changes in four plant species of the Loess Plateau over the last 70 years

The relative abundance of carbon isotope (δ¹³C) was measured in four C₃ species (Sophora viccifolia, Quercus liaotungensis, Ostryopsis davidiana and Zizyphus jujuba var. spinosa) of the Loess Plateau in China from the 1930’s to 2002. The results showed that the δ¹³C values in the four species varied from −25.05‰ to −29.75‰ with their a average at −27.04‰. A decrease in the δ¹³C value with time was found in all the four species, which indicating that the water use efficiencies (WUEs) of all the measured species declined during 70 years. However, the decrease in δ¹³C value differed among the four species with its significant decreases measured in two of the species, Sophora viciifolia and Quercus liaotungensis, its relatively significant decrease found in Ostryopsis davidiana, and its slight decrease appearing in Zizyphus jujuba var. spinosa. in the δ¹³C values in the four species decreased by 14.65 ‰, 14.46‰, 11.99‰ and 2.44‰, respectively. The different species were shown to have different sensitivities to climatic change, and Zizyphus jujuba var. spinosa was found to be the most drought-tolerant species of the four, which had a high WUE.     

Foliar δ<Superscript>13</Superscript>C values of nine dominant species in the Loess Plateau of China

The foliar stable carbon isotope compositions (δ¹³C) of nine dominant species in seven sites, Yangling, Yongshou, Tongchuan, Fuxian, Ansai, Mizhi, and Shenmu, standing from the south to the north in the Loess Plateau of China were studied. The results showed that foliar δ¹³C values ranged from −22.61 to −30.73 ‰ with an average of −27.23 ‰ in 141 C₃ plant samples collected from the Loess Plateau. Foliar δ¹³C values varied significantly (p<0.001) among the nine C₃ species, which were Pinus tabulaeformis Carr., Robinia pseudoacacia L., Zizyphus jujuba Mill. var. spinosus Hu., Rubus parvifolius L., Hippophae rhamnoides L., Caragana korshinskii Kom., Lespedeza davurica (Laxm.) Schindl., Artemisia sacrorum Ledeb. var. incana Mattf., and Agropyron cristatum Gaertn. Comparatively, R. pseudoacacia, H. rhamnoides, and C. korshinskii had much higher δ¹³C values than the other six species, while A. sacrorum had the lowest δ¹³C value. There was no significant difference in foliar δ¹³C value among five species, P. tabulaeformis, Z. jujuba, R. parvifolius, L. davurica, and A. cristatum. Considering the life forms categorized from nine C₃ species, trees and shrubs had significantly higher δ¹³C values than herbs (p<0.001). The deciduous tree R. pseudoacacia had much higher δ¹³C value than the evergreen tree P. tabulaeformis (p<0.01). Among the four shrubs, foliar δ¹³C values in H. rhamnoides and C. korshinskii were markedly higher (p<0.01) than those in Z. jujuba and R. parvifolius. Among the three herbs, L. davurica and A. cristatum had significantly higher δ¹³C values than A. sacrorum (p<0.01). Leguminous species such as R. pseudoacacia, C. korshinskii, and L. davurica as well as a non-leguminous species with nitrogen-fixation capacity, H. rhamnoides, had higher δ¹³C values than other non-leguminous species with same life-form. The mean δ¹³C value increased by about 7 % from Yangling in the south to Shenmu in the north as climatic drought increased, and foliar δ¹³C values differed much (p<0.001) among the seven sites. For nine species in the Loess Plateau, foliar δ¹³C values were significantly and negatively (p<0.001) correlated with the mean annual precipitation, moreover, an increase of 100 mm in annual precipitation would result in a decrease of 1.2 ‰ in δ¹³C value.     

Variation in the δ<Superscript>13</Superscript>C of Two Mangrove Plants is Correlated with Stomatal Response to Salinity

To better understand the relationship between salinity and the carbon stable isotope composition (expressed as δ¹³C) of mangrove plants and to test whether the patterns of variation in δ¹³C of mangrove plants differ from those of nonhalophytes as response to salinity, the effect of salinity on leaf δ¹³C in two dominant mangrove species, Aegiceras corniculatum and Kandelia candel, was studied. Furthermore, to determine whether the variation in δ¹³C of mangrove species is adjusted by stomatal conductance, K. candel was selected as an example, and leaf gas-exchange characteristics of the seedlings were measured. It was observed that both mangrove species had a lower leaf δ¹³C under their optimum salinity (1.50% for Ae. corniculatum and 2.00% for K. candel). This variation in δ¹³C of mangrove plants was attributable largely to stomatal adjustment as for nonhalophytes in which a strong correlation between δ¹³C and relevant photosynthetic properties is observed. This result suggests that the different response pattern in δ¹³C was a consequence of the variation in stomata in relation to the different tolerance to salinity. The optimum salinity inferred by leaf δ¹³C provides a feasible method for comparing salt tolerance between mangrove plants belonging to different species, which is useful for mangrove restoration.     

Crassulacean acid metabolism in tropical dicotyledonous trees of the genusClusia

Summary The performance of crassulacean acid metabolism (CAM) by dicotyledonous trees of the genusClusia sampled at three sites in the state of Falcon in northern Venezuela is characterized.Clusia leaves have a somewhat succulent appearance. Unlike leaves of many other CAM plants, which are uniformly built up of very large isodiametric cells, there are distinct layers of palisade and spongy mesophyll, with individual cells being smaller. There is no specialized water storage tissue. ¹³C values indicate thatC. multiflora in the elfin-cloud forest on top of Cerro Santa Ana, at 800 m altitude, performs C₃ photosynthesis (¹³ –27.1). However,C. rosea in the tall cloud forest on Cerro Santa Ana (600m altitude), andC. rosea andC. alata in the dry forest on Serrania San Luis (900 m altitude) perform CAM (¹³C –14.1 to –19.2). InC. alta andC. rosea there were large day-night changes in the levels of malic and citric acids ranging from 63 to 240 mmol 1^–1 for malid acid and from 35 to 112 mmol 1^–1 for citric acid. The sum of the changes in malate and citrate levels accounts for the changes of titratable protons measured. With a day-night change of titratable protons of 768 mmol 1^–1 in one of the analyses,C. rosea showed the highest value yet encountered in a CAM plant. Oscillations of free sugars (fructose, glucose, sucrose) and of starch were also analysed in the CAM performingClusia species. Carbon skeletons of the precursors involved in nocturnal malate and citrate synthesis largely derive from free sugars and not from polyglucan. Unlike some other CAM plants, there is no clear and quantitative correlation between day-night changes of organic acid levels and cell sap osmolality.Dedicated to Professor Dr. Otto L. Lange on the occasion of his 60th birthday.     

Controlling for anthropogenically induced atmospheric variation in stable carbon isotope studies

Increased use of stable isotope analysis to examine food-web dynamics, migration, transfer of nutrients, and behavior will likely result in expansion of stable isotope studies investigating human-induced global changes. Recent elevation of atmospheric CO₂ concentration, related primarily to fossil fuel combustion, has reduced atmospheric CO₂ δ¹³C (¹³C/¹²C), and this change in isotopic baseline has, in turn, reduced plant and animal tissue δ¹³C of terrestrial and aquatic organisms. Such depletion in CO₂ δ¹³C and its effects on tissue δ¹³C may introduce bias into δ¹³C investigations, and if this variation is not controlled, may confound interpretation of results obtained from tissue samples collected over a temporal span. To control for this source of variation, we used a high-precision record of atmospheric CO₂ δ¹³C from ice cores and direct atmospheric measurements to model modern change in CO₂ δ¹³C. From this model, we estimated a correction factor that controls for atmospheric change; this correction reduces bias associated with changes in atmospheric isotopic baseline and facilitates comparison of tissue δ¹³C collected over multiple years. To exemplify the importance of accounting for atmospheric CO₂ δ¹³C depletion, we applied the correction to a dataset of collagen δ¹³C obtained from mountain lion (Puma concolor) bone samples collected in California between 1893 and 1995. Before correction, in three of four ecoregions collagen δ¹³C decreased significantly concurrent with depletion of atmospheric CO₂ δ¹³C (n ≥ 32, P ≤ 0.01). Application of the correction to collagen δ¹³C data removed trends from regions demonstrating significant declines, and measurement error associated with the correction did not add substantial variation to adjusted estimates. Controlling for long-term atmospheric variation and correcting tissue samples for changes in isotopic baseline facilitate analysis of samples that span a large temporal range.     

Spatial patterns of foliar stable carbon isotope compositions of C<Subscript>3</Subscript> plant species in the Loess Plateau of China

The spatial pattern of foliar stable carbon isotope compositions (δ¹³C) of dominant species and their relationships with environmental factors in seven sites, Yangling, Yongshou, Tongchuan, Fuxian, Ansai, Mizhi and Shenmu, standing from south to north in the Loess Plateau of China, was studied. The results showed that in the 121 C₃ plant samples collected from the Loess Plateau, the foliar δ¹³C value ranged from −22.66‰ to −30.70‰, averaging −27.04‰. The foliar δ¹³C value varied significantly (P<0.01) among the seven sites, and the average δ¹³C value increased by about 1.69‰ from Yangling in the south to Shenmu in the north as climatic drought increased. There was a significant difference in foliar δ¹³C value among three life-forms categorized from all the plant samples in the Loess Plateau (P<0.001). The trees (−26.74‰) and shrubs (−26.68‰) had similar mean δ¹³C values, both significantly (P<0.05) higher than the mean δ¹³C value of herbages (−27.69‰). It was shown that the trees and shrubs had higher WUEs and employed more conservative water-use patterns to survive drier habitats in the Loess Plateau. Of all the C₃ species in the Loess Plateau, the foliar δ¹³C values were significantly and negatively correlated with the mean annual rainfall (P<0.001) and mean annual temperature (P<0.05), while being significantly and positively correlated with the latitude (P<0.001) and the annual solar radiation (P<0.01). In general, the foliar δ¹³C values increased as the latitude and solar radiation increased and the rainfall and temperature decreased. The annual rainfall as the main influencing factor could explain 13.3% of the spatial variations in foliar δ¹³C value. A 100 mm increment in annual rainfall would result in a decrease by 0.88‰ in foliar δ¹³C values.     

Does Bienertia cycloptera with the single-cell system of C(4) photosynthesis exhibit a seasonal pattern of delta (13)C values in nature similar to co-existing C (4) Chenopodiaceae having the dual-cell (Kranz) system?

Family Chenopodiaceae is an intriguing lineage, having the largest number of C₄ species among dicots, including a number of anatomical variants of Kranz anatomy and three single-cell C₄ functioning species. In some previous studies, during the culture of Bienertia cycloptera Bunge ex Boiss., carbon isotope values (δ¹³C values) of leaves deviated from C₄ to C₃−C₄ intermediate type, raising questions as to its mode of photosynthesis during growth in natural environments. This species usually co-occurs with several Kranz type C₄ annuals. The development of B. cycloptera morphologically and δ¹³C values derived from plant samples (cotyledons, leaves, bracts, shoots) were analyzed over a complete growing season in a salt flat in north central Iran, along with eight Kranz type C₄ species and one C₃ species. For a number of species, plants were greenhouse-grown from seeds collected from the site, in order to examine leaf anatomy and C₄ biochemical subtype. Among the nine C₄ species, the cotyledons of B. cycloptera, and of the Suaeda spp. have the same respective forms of C₄ anatomy occurring in leaves, while cotyledons of members of tribe Caroxyloneae lack Kranz anatomy, which is reflected in the δ¹³C values found in plants grown in the natural habitat. The nine C₄ species had average seasonal δ¹³C values of −13.9‰ (with a range between species from −11.3 to −15.9‰). The measurements of δ¹³C values over a complete growing season show that B. cycloptera performs C₄ photosynthesis during its life cycle in nature, similar to Kranz type species, with a seasonal average δ¹³C value of −15.2‰. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Leaf δ13C in Pinus resinosa trees and understory plants: variation associated with light and CO2 gradients

 Our objective was to evaluate the relative importance of gradients in light intensity and the isotopic composition of atmospheric CO₂ for variation in leaf carbon isotope ratios within a Pinus resinosa forest. In addition, we measured photosynthetic gas exchange and leaf carbon isotope ratios on four understory species (Dryopteris carthusiana, Epipactus helleborine, Hieracium floribundum, Rhamnus frangula), in order to estimate the consequence of the variation in the understory light microclimate for carbon gain in these plants. During midday, CO₂ concentration was relatively constant at vertical positions ranging from 15 m to 3 m above ground. Only at positions below 3 m was CO₂ concentration significantly elevated above that measured at 15 m. Based on the strong linear relationship between changes in CO₂ concentration and δ¹³C values for air samples collected during a diurnal cycle, we calculated the expected vertical profile for the carbon isotope ratio of atmospheric CO₂ within the forest. These calculations indicated that leaves at 3 m height and above were exposed to CO₂ of approximately the same isotopic composition during daylight periods. There was no significant difference between the daily mean δ¹³C values at 15 m (–7.77‰) and 3 m (–7.89‰), but atmospheric CO₂ was significantly depleted in ¹³C closer to the ground surface, with daily average δ¹³C values of –8.85‰ at 5 cm above ground. The light intensity gradient in the forest was substantial, with average photosynthetically active radiation (PAR) on the forest floor approximately 6% of that received at the top of the canopy. In contrast, there were only minor changes in air temperature, and so it is likely that the leaf-air vapour pressure difference was relatively constant from the top of the canopy to the forest floor. For red pine and elm tree samples, there was a significant correlation between leaf δ¹³C value and the height at which the leaf sample was collected. Leaf tissue sampled near the forest floor, on average, had lower δ¹³C values than samples collected near the top of the canopy. We suggest that the average light intensity gradient through the canopy was the major factor influencing vertical changes in tree leaf δ¹³C values. In addition, there was a wide range of variation (greater than 4‰) among the four understory plant species for average leaf δ¹³C values. Measurements of leaf gas exchange, under natural light conditions and with supplemental light, were used to estimate the influence of the light microclimate on the observed variation in leaf carbon isotope ratios in the understory plants. Our data suggest that one species, Epipactus helleborine, gained a substantial fraction of carbon during sunflecks. Received: 21 March 1996 / Accepted: 13 August 1996     

Effect of light and zooplankton on skeletal δ13C values in the eastern Pacific corals Pavona clavus and Pavona gigantea

 Skeletal δ¹³C levels in symbiotic reef corals are believed to be predominantly influenced by metabolic fractionation. Therefore, environmental variables influencing coral metabolism should also affect skeletal δ¹³C levels. To test this hypothesis, we measured the effects of light (which drives photosynthesis) and relative zooplankton levels (heterotrophy) on skeletal δ¹³C values in the corals Pavona clavus and P. gigantea at two depths (1 m and 7 m). For both species, decreases in light or increases in zooplankton resulted in significant decreases in skeletal δ¹³C levels. A significant decrease in δ¹³C values with depth was observed in Pavona gigantea only. Thus, light and zooplankton directly affect coral skeletal δ¹³C values, supporting the hypothesis that metabolic fractionation significantly contributes to skeletal δ¹³C levels. Simultaneous decreases in both light and zooplankton resulted in decreases in skeletal δ¹³C values, reflecting decreases in light. In Pavona clavus, intra-annual variation in skeletal δ¹³C values over one year correlated with seasonal changes in irradiance. Further study is needed to resolve how skeletal δ¹³C values vary at intermediate levels of irradiance and zooplankton, and in other coral species. Accepted: 14 July 1998     

Functional diversity in an Amazonian rainforest of French Guyana: a dual isotope approach (δ15N and δ13C)

Functional aspects of biodiversity were investigated in a lowland tropical rainforest in French Guyana (5°2′N, annual precipitation 2200 mm). We assessed leaf δ¹⁵N as a presumptive indicator of symbiotic N₂ fixation, and leaf and wood cellulose δ¹³C as an indicator of leaf intrinsic water-use efficiency (CO₂ assimilation rate/leaf conductance for water vapour) in dominant trees of 21 species selected for their representativeness in the forest cover, their ecological strategy (pioneers or late successional stage species, shade tolerance) or their potential ability for N₂ fixation. Similar measurements were made in trees of native species growing in a nearby plantation after severe perturbation (clear cutting, mechanical soil disturbance). Bulk soil δ¹⁵N was spatially quite uniform in the forest (range 3–5‰), whereas average leaf δ¹⁵N ranged from −0.3‰ to 3.5‰ in the different species. Three species only, Diplotropis purpurea, Recordoxylon speciosum (Fabaceae), and Sclerolobium melinonii (Caesalpiniaceae), had root bacterial nodules, which was also associated with leaf N concentrations higher than 20 mg g⁻¹. Although nodulated trees displayed significantly lower leaf δ¹⁵N values than non-nodulated trees, leaf δ¹⁵N did not prove a straightforward indicator of symbiotic fixation, since there was a clear overlap of δ¹⁵N values for nodulated and non-nodulated species at the lower end of the δ¹⁵N range. Perturbation did not markedly affect the difference δ¹⁵N_soil−δ¹⁵N_leaf, and thus the isotopic data provide no evidence of an alteration in the different N acquisition patterns. Extremely large interspecific differences in sunlit leaf δ¹³C were observed in the forest (average values from −31.4 to −26.7‰), corresponding to intrinsic water-use efficiencies (ratio CO₂ assimilation rate/leaf conductance for water vapour) varying over a threefold range. Wood cellulose δ¹³C was positively related to total leaf δ¹³C, the former values being 2–3‰ higher than the latter ones. Leaf δ¹³C was not related to leaf δ¹⁵N at either intraspecific or interspecific levels. δ¹³C of sunlit leaves was highest in shade hemitolerant emergent species and was lower in heliophilic, but also in shade-tolerant species. For a given species, leaf δ¹³C did not differ between the pristine forest and the disturbed plantation conditions. Our results are not in accord with the concept of existence of functional types of species characterized by common suites of traits underlying niche differentiation; rather, they support the hypothesis that each trait leads to a separate grouping of species. Received: 18 August 1997 / Accepted: 14 April 1998     

Photosynthetic pathway of dominant plant species in the Qaidam Basin: evidence from foliar stable carbon isotope measurement

Foliar δ¹³C values of Calligogum kozlovi and Haloxylon ammodendron ranged from −13.13 to −15.11 ‰, while those of the rest 11 species were in the range of −22.22 to −27.73 ‰. This indicates that two of 13 dominant plant species in the Qaidam Basin possess a C₄ photosynthetic pathway. Significant differences were observed for the average foliar δ¹³C values between C₃ or C₄ plant communities, between grass and shrub communities, even between the same species derived from different sites. Precipitation accounted for the major part of the differences.     

Stable Isotopic and Trace Elemental Compositions of Otoliths and the Stock Structure of Pacific Cod, Gadus macrocephalus

Synopsis We examined the stock composition and life history of Pacific cod, Gadus macrocephalus, in the northeast Pacific Ocean from sagittal otoliths collected from three marine fishing areas in Washington State, U.S.A. We analyzed both stable isotope ratios (δ¹⁸O and δ¹³C) and trace elemental concentrations (Sr, Mg, Na, Fe, Mn) for these otoliths. The combination of δ¹⁸O and δ¹³C, and correlation of δ¹⁸O vs. 1000Sr/Ca and 1000Mg/Ca showed clear separations between North Puget Sound and coastal cod, suggesting there might be two different spawning stocks in the region. The North Puget Sound cod might represent an ‘Estuary-type’ from the Strait of Georgia, whereas coastal cod might represent an ‘Ocean-type’ from the Pacific west coast. Isotopic variations from five representative otoliths also showed a two-stage life history for Pacific cod, and a critical transition period for cod in migration to the ocean or in age of sexual maturity. These chemical interpretations and conclusions appear in agreement with biological observations of Pacific cod, and are consistent with results of previous studies for other marine fish species in nearby areas.     

Variation of δ<Superscript>13</Superscript>C of wood and foliage with canopy height differs between evergreen and deciduous species in a temperate forest

We investigated post-photosynthetic fractionation and carbon transfer mechanisms of different plant functional types growing under the same climatic conditions in North-eastern China. The variations in δ¹³C of trunk and branches were compared with leaf δ¹³C at different canopy heights of Pinus koraiensis (evergreen coniferous species), Larix gmelinii (deciduous coniferous species) and Quercus mongolica (deciduous broad-leaved species). Results showed that δ¹³C of leaves increased (became more enriched) with increasing canopy height for both coniferous species (P. koraiensis, L. gmelinii) but not for Q. mongolica (a deciduous broad-leaved species). δ¹³C of both trunk and branches also increased with sampling height for the evergreen conifer P. koraiensis but did not significantly vary for either of the deciduous species (L. gmelinii or Q. mongolica), except a significant increase in branch δ¹³C for L. gmelinii. Similarly, δ¹³C of trunk and branches were strongly correlated with leaf δ¹³C only in the evergreen conifer, P. koraiensis. ¹³C was consistently more enriched in trunk, branches, and roots compared to leaves in all three species. Our findings suggest that, even under the same climatic conditions, different plant functional types may exhibit different carbon transfer mechanisms. This is contrary to the previous hypothesis that different carbon transfer mechanisms operate in forests of different climatic zones, especially in tropical and temperate forests. Particularly, the differences occur predominantly between evergreen and deciduous trees rather than between coniferous and broad-leaved trees. The significant difference in δ¹³C between leaves and wood tissues confirms a previous post-photosynthetic isotope fractionation in temperate forests.     

Nitrogen and carbon isotope responses of Chinese cabbage and chrysanthemum to the application of liquid pig manure

The effects of the liquid pig manure (LM) used in organic farming on the natural abundance of ¹⁵N and ¹³C signatures in plant tissues have not been studied. We hypothesized that application of LM will (1) increase δ¹⁵N of plant tissues due to the high δ¹⁵N of N in LM as compared with soil N or inorganic fertilizer N, and (2) increase δ¹³C of plant tissues as a result of high salt concentration in LM that decreases stomatal conductance of plants. To test these hypotheses, variations in the δ¹⁵N and δ¹³C of Chinese cabbage (Brassica campestris L.) and chrysanthemum (Chrysanthemum morifolium Ramatuelle) with two different LMs (with δ¹⁵N of +15.6 and +18.2‰) applied at two rates (323 and 646 kg N ha^-1 for cabbage and 150 and 300 kg N ha^-1 for chrysanthemum), or urea (δ¹⁵N = -2.7‰) applied at the lower rate above for the respective species, in addition to the control (no N input) were investigated through a 60-day pot experiment. Application of LM significantly increased plant tissue δ¹⁵N (range +9.4 to +14.9‰) over the urea (+3.2 to +3.3‰) or control (+6.8 to 7.7‰) treatments regardless of plant species, strongly reflecting the δ¹⁵N of the N source. Plant tissue δ¹³C were not affected by the treatments for cabbage (range −30.8 to −30.2‰) or chrysanthemum (−27.3 to −26.8‰). However, cabbage dry matter production decreased while its δ¹³C increased with increasing rate of LM application or increasing soil salinity (P < 0.05), suggesting that salinity stress caused by high rate of LM application likely decreased stomatal conductance and limited growth of cabbage. Our study expanded the use of the δ¹⁵N technique in N source (organic vs. synthetic fertilizer) identification and suggested that plant tissue δ¹³C maybe a sensitive indicator of plant response to salinity stress caused by high LM application rates.     

Between-tree variations in leaf δ13C of Quercus pubescens and Quercus ilex among Mediterranean habitats with different water availability

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 (WUE_i) 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     

Characterization of photosynthetic pathway of plant species growing in the eastern Tibetan plateau using stable carbon isotope composition

The photosynthetic pathway of plant species collected at Menyuan, Henan, and Maduo sites, east of Tibetan Plateau, China, during the growing season were studied using stable carbon isotopes in leaves. The 232 samples leaves analyzed belonged to 161 species, 30 families, and 94 genera. The δ¹³C values (from −24.6 to − 29.2 ‰) indicated that all the considered species had a photosynthetic C₃ pathway. The absence of plant species with C₄ photosynthetic pathway might be due to the extremely low air temperature characterizing the Tibetan Plateau. The average δ¹³C value was significantly (p<0.05) different between annuals and perennials at the three considered study sites. Hence the longer-lived species had greater water-use efficiency (WUE) than shorter-lived species, that is, longer-lived species are better adapted to the extreme environmental conditions of the Tibetan Plateau.     

Interspecific variability of δ13C among trees in rainforests of French Guiana: functional groups and canopy integration

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 (Ψ_wm) 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