Leaf Carbon Isotope Ratios Research Articles

Leaf anatomy and subgeneric affiliations of C3 and C4 species of Suaeda (Chenopodiaceae) in North America

The halophytic genus Suaeda (Chenopodiaceae) includes species with the C3 and C4 photosynthetic pathways. North American species of this genus were investigated to determine whether C3 and C4 leaf anatomy are consistent within the two sections of Suaeda, Chenopodina and Limbogermen, present on this continent. All species from section Chenopodina were found to possess C3 anatomy, whereas all species from section Limbogermen were found to be C4 species. Characteristics of leaf anatomy and chloroplast ultrastructure are similar to those reported from C3 and C4 species, respectively, from the Eastern Hemisphere. All species from section Limbogermen have the suaedoid type of leaf anatomy, characterized by differentiation of the mesophyll into palisade parenchyma and a chlorenchymatous sheath surrounding central water-storage tissue, as well as leaf carbon isotope ratios (_13C) of above -20. All species from section Chenopodina have austrobassioid leaf anatomy without a chlorenchymatous sheath and _13C values of below -20. According to our literature review, the photosynthetic pathway has now been reported for about half (44) of the Suaeda species worldwide. The C3 and C4 photosynthetic syndromes are with few exceptions distributed along sectional or subsectional lines. These findings throw new light on the infrageneric taxonomy of this genus.

Unusually low carbon isotope ratios in plants from hanging gardens in southern Utah.

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.

Leaf carbon isotope ratios in three landscape species growing in an arid environment

The effect of leaching fraction (LF = drainage volume/irrigation volume) and tree planting size on the carbon isotope ratio measured in leaves of live oak (Quercus virginiana), desert willow (Chilopsis linearis) and tall fescue (Festuca arundinacea; LF only) were investigated in an arid climate. Irrigations were applied to maintain LFs of +0·25, 0·00 or −0·25 (theoretical). Live oak and desert willow were planted as 3·8, 18·9 or 56·8 l nursery container plants in lysimeters where hydrologic balances were maintained weekly. Leaf carbon isotope ratios varied by species across the three LFs (live oak>desert willow>tall fescue). In live oak, leaf carbon isotope ratios increased as LF decreased but did not change with planting size. In desert willow the ratios increased with decreasing LF and with increasing planting size. In tall fescue the leaf carbon isotope ratio decreased as the LF increased. Leaf carbon isotope ratios also varied with stomatal conductance, leaf xylem water potentials and water-use efficiency (WUE). In live oak, both average midday stomatal conductance and leaf xylem water potential decreased with increasing leaf carbon isotope ratio. Average stomatal conductance for live oak was negatively correlated with average leaf WUE. Average leaf WUE in live oak and tall fescue were correlated with average leaf carbon isotope ratios. However, in tall fescue leaf WUE increased as the leaf carbon isotope ratio became more negative. In live oak the ratio became more positive as leaf WUE increased. This study has demonstrated that leaf carbon isotope ratios can be used as a way of screening plant response for low water-use landscapes, but only after careful correlations for each species have been established between growth form and growing conditions.

Leaf carbon isotope ratios from a tropical dry forest in Venezuela

Summary Leaf carbon isotope ratios were measured on dominant deciduous-leaved and evergreen-leaved species in a seasonally dry tropical forest in Venezuela. Carbon isotope ratios were higher and the intercellular to ambient CO 2 concentrations were lower in the deciduous-leaved species. Associated with this are predicted lower water-use efficiencies in evergreen-leaved than in deciduous-leaved species. Predawn water potentials were more positive in evergreen-leaved species, leading to a negative correlation between leaf carbon isotope ratio values and predawn water potential among the different species.

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.

Morphological and physiological responses of Scaevola sericea (Goodeniaceae) seedlings to salt spray and substrate salinity

The effects of substrate salinity and salt spray upon seedlings of Scaevola sericea were examined in this study. Three levels of substrate salinity: 0.0 ppt, 3.0 ppt, and 10.0 ppt were examined in conjunction with three levels of salt spray: zero, medium (200 mg m‐2mdd‐1), and high (1200–1500 mg‐m‐2mdd‐1). Leaf surface area, root to shoot ratio, as well as leaf, stem, and root mass decreased significantly (P 0.05) with increasing substrate salinity. Biomass accumulation was very low at 10.0 ppt substrate salinity, suggesting that higher levels of substrate salinity cannot be tolerated by the seedlings. Salt spray had a substantial effect on several of these variables, however its effects were less pronounced than those of substrate salinity. Cell sap osmolarity, leaf thickness, and leaf specific mass increased significantly (P 0.05) with both increasing substrate salinity and salt spray levels. Leaf carbon isotope ratios (δl3C) became more positive with increasing salinity, indicating an enhancement of the intrinsic water use efficiency of the seedlings at higher salinities. Scaevola sericea is one of the dominant plants found at the leading edge of strand communities in the Hawaiian archipelago and throughout much of the tropical Pacific. Since substrate salinity and salt spray increase with proximity to the ocean, the two factors may act together to limit the seaward expansion of S. sericea in coastal habitats.

Short-term changes in carbon-isotope discrimination in the C3-CAM intermediate Clusia minor L. growing in Trinidad.

On-line instantaneous carbon isotope discrimination was measured in conjunction with net uptake of CO2 in leaves of exposed and shaded plants of the C3-CAM intermediate Clusia minor growing under natural conditions in Trinidad. At the end of the rainy season (late January-early February, 1992) C3 photosynthesis predominated although exposed leaves recaptured a small proportion of respiratory CO2 at night for the synthesis of malic acid. Citric acid was the major organic acid accumulated by exposed leaves at this time with a citric: malic acid ratio of 11:1. Values of instantaneous discrimination (Δ) in exposed leaves during the wet season rose from 17.1‰ shortly after dawn to 22.7‰ around mid-day just before stomata closed, suggesting that most CO2 was fixed by Rubisco at this time. During the late afternoon, instantaneous Δ declined from 22.2‰ to 17‰, probably reflecting the limited contribution from PEPc activity and an increase in diffusional resistance to CO2 in exposed leaves. Shaded leaves showed no CAM activity and CO2 uptake proceeded throughout the day in the wet season. The decrease in instantaneous Δ from 27‰ in the morning to 19.2‰ in the late afternoon was therefore entirely due to diffusional limitation. Leaves sampled in the dry season (mid-March, 1992) had by now induced full CAM activity with both malic and citric acids accumulated overnight and stomata closed for 4-5 h over the middle of the day. Values of instantaneous Δ measured over the first 3 h after dawn (6.4-9.1‰) indicated that C4 carboxylation dominated CO2 uptake for most of the morning when rates of photosynthesis were maximal, implying that under natural conditions, the down regulation of PEPc in phase II occurs much more slowly than laboratory-based studies have suggested. The contribution from C3 carboxylation to CO2 uptake during phase II was most marked in leaves which accumulated lower quantities of organic acids overnight. In exposed leaves, measurements of instantaneous Δ during the late afternoon illustrated the transition from C3 to C4 carboxylation with stomata remaining open during the transition from dusk into the dark period. Uptake of CO2 by shaded leaves during the late afternoon however appeared to be predominantly limited by decreased stomatal conductance. The short-term measurements of instantaneous Δ were subsequently integrated over 24 h in order to predict the leaf carbon isotope ratios (δp) and to compare this with the δp measured for leaf organic material. Whilst there was close agreement between predicted and measured δp for plants sampled in the wet season, during the dry season the predicted carbon isotope ratios were 5-9‰ higher than the measured isotope ratios. During the annual cycle of leaf growth most carbon was fixed via the C3 pathway although CAM clearly plays an important role in maintaining photochemical integrity in the dry season.

Influence of Nitrogen, Water and Competition on Carbon Isotope Ratios (δ13C) in a CAM Plant (Crassula argentea)

Abstract Leaf carbon isotope ratios (δ13C), an indicator of long-term intercellular carbon dioxide concentration, and also stem and root carbon isotope ratios were measured on the obligate CAM species Crassula argentea cultivated in pure and mixed cultures with the succulent C3 Peperomia obtusifolia in open-air conditions under two different levels of nitrogen and water supply. As expected, a diminished water supply and a relatively dry and hot summer climate cause a shift of δ13C values to a less strong 13C discrimination (less negative δ13C values). A diminished nitrogen supply causes a shift of the δ13C values in direction of a higher 13C discrimination (more negative δ13C values), particularly in the leaves. Competition causes also an increased 13C discrimination, especially valid for shoot axes. The shift of 13C/12C isotope ratios in case of nitrogen deficiency is discussed to be a result of a decreased PEPCase activity in the night.

Differences in morphology, carbon isotope ratios, and photosynthesis between scrub and fringe mangroves in Florida, USA

All three mangrove species in Florida (USA), Rhizophora mangle L., Laguncularia racemosa Gaert. and Avicennia germinans (L.) L., are found frequently in scrub mangrove forests, in which individuals rarely exceed 1.5 m in height. In the present study, the differences in morphological characteristics, leaf carbon isotope ratios and photosynthetic gas exchange between individuals in scrub and fringe mangrove forests in south Florida were investigated quantitatively. Plants in the scrub forests had much lower canopy height, more main stems per tree and smaller leaves, relative to those in the fringe forests. There was a significant correlation between tree height and leaf δ 13C value, with higher δ 13C values (1–4% more positive) for plants in the scrub mangrove forests. Correspondingly, scrub mangroves showed significantly lower intercellular carbon dioxide (CO 2) concentration and higher intrinsic water use efficiency over long-term carbon assimilation, relative to fringe mangroves. Photosynthetic gas exchange measurements on R. mangle individuals showed a 15.5% lower CO 2 assimilation rate, 6.1% lower intercellular CO 2 concentration and 11.6% higher intrinsic water use efficiency in scrub mangroves, consistent with those estimated from leaf carbon isotope ratios. A higher slope for the linear correlation between CO 2 assimilation rate and stomatal conductance was observed for the individuals in the scrub mangrove forest, which is in agreement with other measurements indicating higher water use efficiency in scrub mangroves. Possible environmental factors responsible for these morphological and physiological differences between scrub and fringe mangroves are discussed.

Influence of sunflecks on the δ 13 C of Adenocaulon bicolor plants occurring in contrasting forest understory microsites.

Leaf characteristics and carbon isotope ratios (δ13C) of Adenocaulon bicolor were examined in the understory of a redwood forest along a gradient of microsites that differed in the amount of direct (sunfleck) photon flux density. Comparisons were made between plants that had been shaded from sunflecks with shadow bands but still received diffuse light, and adjacent plants that received both sunflecks and diffuse light. The δ13C of the shaded plants were 1.2‰ lower than predicted from the intercellular CO2 pressure (pi), probably because of recycling of respired CO2 in the understory. Plants receiving sunflecks had higher δ13C values because assimilation during sunflecks occurred at a lower pi than assimilation in diffuse light. The amount that their δ13C was higher was positively correlated with predicted direct photon flux density received by a plant. Leaf weight per unit area increased with increasing PFD. Although plants receiving sunflecks had greater leaf weights per unit area and photosynthetic capacities than those under shadow bands, there was no apparent acclimation of photosynthetic capacity to the differences in PFD among the microsites.

Correlations between carbon isotope ratio and microhabitat in desert plants.

Water is usually considered to be the key limiting factor for growth of desert plants, yet there is little information available of the water-use efficiency of species within a desert community. Leaf carbon isotope ratios, an indicator of long-term intercellular carbon dioxide concentrations and thus of water-use efficiency in C3 plants, were measured on species occurring within a Sonoran Desert community, consisting of wash, transition and slope microhabitats. Along a soil moisture gradient from the relatively wetter wash to the relatively drier slope, leaf carbon isotope ratios increased in all species, indicating that water-use efficiency increased as soil water availability decreased. Leaf carbon isotope ratios of long-lived perennials were substantially more positive than in short-lived perennials, even though plants were growing adjacent to each other. Leaf carbon isotope ratio and leaf duration (evergreen versus deciduous) were not correlated with each other. The results are discussed in terms of how the efficiency of water use may affect community structure and composition.

Leaf carbon isotope ratios of plants from a subtropical monsoon forest.

Carbon isotope ratios were used to survey the distribution of photosynthetic pathways among taxa, the relationship between photosynthetic pathway and habitat light levels, and the relationship between intercellular CO2 levels of C3 plants and habitat light levels within a subtropical monsoon forest in southern China. Of 128 species, most (94) possessed the C3 photosynthetic pathway; 33 species possessed the C4 pathway and all of these were restricted to high light locations. There was one epiphytic CAM species. The C3 species were classified as occurring in open, intermediate, and closed canopy sites. Among C3 species, carbon isotope ratios tended to become more negative with decreasing light availability in the habitat.

Leaf carbon isotope and mineral composition in subtropical plants along an irradiance cline.

Leaf carbon isotope ratios and leaf mineral composition (Ca, K, Mg, Mn, N, and P) were measured on the dominant species along an irradiance cline in a subtropical monsoon forest of southern China. This irradiance cline resulted from disturbance caused by fuel-harvesting. Leaf carbon isotope ratios increased from undisturbed to disturbed sites for all species, indicating that leaf intercellular CO2 concentrations decreased and leaf water use efficiencies increased along this cline. Nitrogen and magnesium levels were lower in leaves of species on the disturbed sites, but there were no clear patterns for calcium, potassium, phosphorus or manganese.