Carbon Isotope Discrimination Values Research Articles

Spiderδ: an empirical method to extrapolate grapevine (<em>Vitis vinifera</em> L.) water status at the whole denomination scale using δ<sup>13</sup>C as ancillary data

<p style="text-align: justify;"><strong>Aims</strong>: The aim of this study is to test a method to extrapolate vine water status (estimated by the water potential; <strong>Ψ</strong>) over a whole appellation (protected geographical indication). The spatial extrapolation is based on an empirical approach that combines a reference site (baseline measurements) and carbon isotope discrimination (δ<sup>13</sup>C) values as ancillary data (AD).</p><p style="text-align: justify;"><strong>Methods and results</strong>: Experiments were conducted on the whole Tavel appellation (Gard, France). The study focused on the dominant variety: Grenache. <strong>Ψ</strong> was measured as predawn leaf water potential and was monitored over three consecutive years, 2008, 2009 and 2010, on 10, 24 and 24 sites, respectively. δ<sup>13</sup>C measurements were made at harvest in 2010 on the 24 sites. The spatial model (SPIDERδ) was calibrated using Ydata from 2009 and 2010 and δ<sup>13</sup>C data from 2010. The quality of prediction was tested on the 2008 data, considered as an independent data set. The results show that SPIDERδ was relevant in estimating <strong>Ψ</strong> at the whole appellation scale. The extrapolation model significantly improves the prediction (R² = 0.88) compared to a conventional method based on <strong>Ψ</strong> averages across the appellation (R² = 0.66).</p><p style="text-align: justify;"><strong>Conclusion</strong>: Based on a single measurement taken at time «t» on a reference site, SPIDERδ makes it possible to estimate <strong>Ψ</strong> on all sites where a δ<sup>13</sup>C value is available. The use of AD like δ<sup>13</sup>C makes it possible to consider the spatial extrapolation of <strong>Ψ</strong> with higher spatial resolution than when only direct measurements are used to calibrate the model.</p><p style="text-align: justify;"><strong>Significance and impact of the study</strong>: This work demonstrates the value of using an AD like δ<sup>13</sup>C to assess <strong>Ψ</strong> at a scale larger than the single field. This significant result opens the door to the practical use of spatial extrapolation models with higher spatial resolution.</p>

Higher peroxidase activity, leaf nutrient contents and carbon isotope composition changes in Arabidopsis thaliana are related to rutin stress

Rutin, a plant secondary metabolite that is used in cosmetics and food additive and has known medicinal properties, protects plants from UV-B radiation and diseases. Rutin has been suggested to have potential in weed management, but its mode of action at physiological level is unknown. Here, we report the biochemical, physiological and oxidative response of Arabidopsis thaliana to rutin at micromolar concentrations. It was found that fresh weight; leaf mineral contents (nitrogen, sodium, potassium, copper and aluminum) were decreased following 1 week exposure to rutin. Arabidopsis roots generate significant amounts of reactive oxygen species after rutin treatment, consequently increasing membrane lipid peroxidation, decreasing leaf Ca(2+), Mg(2+), Zn(2+), Fe(2+) contents and losing root viability. Carbon isotope composition in A. thaliana leaves was less negative after rutin application than the control. Carbon isotope discrimination values were decreased following rutin treatment, with the highest reduction compared to the control at 750μM rutin. Rutin also inhibited the ratio of CO2 from leaf to air (ci/ca) at all concentrations. Total protein contents in A. thaliana leaves were decreased following rutin treatment. It was concluded carbon isotope discrimination coincided with protein degradation, increase lipid peroxidation and a decrease in ci/ca values may be the primary action site of rutin. The present results suggest that rutin possesses allelopathic potential and could be used as a candidate to develop environment friendly natural herbicide.

Plasticity in stomatal size and density of potato leaves under different irrigation and phosphorus regimes

The morphological features of stomata including their size and density could be modulated by environmental cues; however, the underlying mechanisms remain largely elusive. Here, the effect of different irrigation and phosphorus (P) regimes on stomatal size (SS) and stomatal density (SD) of potato leaves was investigated. The plants were grown in split-root pots under two P fertilization rates (viz., 0 and 100mgkg−1 soil, denoted as P0 and P1, respectively) and subjected to full (FI), deficit (DI), and partial root-zone drying (PRD) irrigation regimes. Results showed that SS and SD were unresponsive to P but significantly affected by the irrigation treatment. FI plants had the largest SS, followed by DI, and PRD the smallest; and the reverse was the case for SD. Compared to FI and DI, PRD plants had significantly lower values of specific leaf area (SLA) and leaf carbon isotope discrimination (Δ13C) under P0. Midday leaf water potential (Ψleaf) and stomatal conductance (gs) was similar for DI and PRD, which was significantly lower than that of FI. Leaf contents of C, N, K, Ca and Mg were higher in PRD than in DI plants, particularly under P0. When analyzed across the three irrigation regimes, it was found that the P1 plants had significantly higher leaf contents of P and Mg, but significantly lower leaf K content compared to the P0 plants. Linear correlation analyses revealed that SS was positively correlated with Ψleaf and Δ13C; whereas SD was negatively correlated with Ψleaf, Δ13C and SLA, and positively correlated with leaf C, N and Ca contents. And gs was positively correlated with SS but negatively correlated with SD. Collectively, under low P level, the smaller and denser stomata in PRD plants may bring about a more efficient stomatal control over gas exchange, hereby potentially enhance water-use efficiency as exemplified by the lowered leaf Δ13C under fluctuating soil moisture conditions.

Study of genetic variation among soybean [Glycine Max(L.) Merrill] accessions in CID values

A set of 91 diverse soybean accessions were analysed for 10 morphological traits with special reference to water use efficiency using carbon isotope discrimination (CID) technique. The coefficient of variation for CID values was found to be 3.36%. There is negative correlation between Δ13C values (CID values) and WUE. The genotypes which registered lower values of Δ13C are more water efficient than the genotypes with higher Δ13C values. The range of Δ13C values observed in this experiment are slightly lower than that reported in sugar beet (Δ13C 17.66‰ to 22.96‰), (Rajabi et al., 2009). Genotype UPSL309 has highest CID value (22.91‰) indicating low WUE and genotype DS9813 has lowest CID value (19.95 ‰) with high WUE. In present study randomly classified genotypes as high WUE (CID less than 20.5 ‰), medium WUE (CID between 20.6 to 22.4 ‰) and low WUE (CID above 22.5 ‰). There were 7 genotypes which were found to show high WUE, and 13 exhibited low WUE whereas, rests of the 71 genotypes were medium in WUE.

Declining moisture availability on the Antarctic Peninsula during the Late Eocene

Paleobotanical data have indicated that the Antarctic landscape shifted from a beech (Nothofagus)-dominated forest to a more sparsely vegetated taiga-like woodland and tundra during the Late Eocene, coincident with progressive cooling and glacial growth. Reduced moisture availability may have contributed to this vegetation change, but there is limited evidence for assessing the Late Eocene hydrologic regime. We evaluated the relationship between Nothofagus δ13C and moisture availability by determining δ13C of modern Nothofagus pollen, sporopollenin, and leaves and comparing these results to precipitation data. To assess plant moisture availability and vegetation composition just prior to the Eocene–Oligocene boundary, we measured δ13C of fossil Nothofagus sporopollenin (Nothofagidites) from the SHALDRIL 3C cores (which date to ~35.9My) and evaluated these results in the context of temporal variation in pollen assemblages from the same sediments. Values of carbon isotope discrimination (∆) for modern Nothofagus sporopollenin range between 18.1 and 22.4‰. These values are positively correlated with precipitation amount, as well as pollen and leaf ∆, which suggests that fossil sporopollenin ∆ records the level of plant moisture availability. ∆ values obtained from Nothofagidites sporopollenin from the SHALDRIL 3C sediments range between 17.9 and 20.2‰ and generally decline through time. These results suggest a decrease in plant moisture availability on the Antarctic Peninsula during the Late Eocene, perhaps as a result of declining precipitation and/or soil moisture. Therefore, moisture stress experienced by Nothofagus likely contributed to the shift to a more sparsely vegetated Late Eocene landscape. Our results show that carbon isotopic analysis of pollen from C3 plants may aid understanding how variations in moisture availability contribute to shifts in plant community composition in the paleorecord.

Benzoxazolin-2(3H)-one (BOA) induced changes in leaf water relations, photosynthesis and carbon isotope discrimination in Lactuca sativa.

The effects are reported here of Benzoxazolin-2(3H)-one (BOA), an allelopathic compound, on plant water relations, growth, components of chlorophyll fluorescence, and carbon isotope discrimination in lettuce (Lactuca sativa L.). Lettuce seedlings were grown in 1:1 Hoagland solution in perlite culture medium in environmentally controlled glasshouse. After 30 days, BOA was applied at concentration of 0.1, 0.5, 1.0 and 1.5 mM and distilled water (control). BOA, in the range (0.1-1.5 mM), decreased the shoot length, root length, leaf and root fresh weight. Within this concentration range, BOA significantly reduced relative water content while leaf osmotic potential remained unaltered. Stress response of lettuce was evaluated on the basis of six days of treatment with 1.5 mM BOA by analyzing several chlorophyll fluorescence parameters determined under dark-adapted and steady state conditions. There was no change in initial fluorescence (F₀) in response to BOA treatment while maximum chlorophyll fluorescence (F(m)) was significantly reduced. BOA treatment significantly reduced variable fluorescence (F(v)) on first, second, third, fourth, fifth and sixth day. Quantum efficiency of open PSII reaction centers (F(v)/F(m)) in the dark-adapted state was significantly reduced in response to BOA treatment. Quantum yield of photosystem II (ΦPSII) electron transport was significantly reduced because of decrease in the efficiency of excitation energy trapping of PSII reaction centers. Maximum fluorescence in light-adapted leaves (F'(m)) was significantly decreased but there was no change in initial fluorescence in light-adapted state (F'₀) in response to 1.5 mM BOA treatment. BOA application significantly reduced photochemical fluorescence quenching (qP) indicating that the balance between excitation rate and electron transfer rate has changed leading to a more reduced state of PSII reaction centers. Non photochemical quenching (NPQ) was also significantly reduced by BOA treatment on third, fourth and fifth day. BOA had dominant effect on C isotope ratios (δ¹³C) that was significantly less negative (-26.93) at 1.0 mM concentration as compared to control (-27.61). Carbon isotope discrimination (Δ¹³C) values were significantly less (19.45) as compared to control (20.17) at 1.0 mM. BOA also affect ratio of intercellular to air CO₂ concentration (ci/ca) that was significantly less (0.66) as compared to control (0.69) when treated with 1.0 mM BOA. Protein content of lettuce leaf tissue decreased under BOA treatment at 1.5 mM concentration as compared to control.

Morphological and physiological acclimation of Quercus coccifera L. seedlings to water availability and growing medium

One of the main constraints of reforestation in the Mediterranean region is low summer water availability during the first years after out planting. Plant water availability depends on the precipitation regime, but also on the physical properties of the soil. Higher survival rates result when seedlings are soil acclimated. Our main goal was to describe the morpho-physiological responses of 6-, 10- and 18-month-old Quercus coccifera seedlings growing in a natural soil (terra rossa) or a standard nursery growing medium, and to assess in the nursery if seedlings growing in natural soil were more resistant to deficit irrigation. The high growth rate achieved after 10–18 months by terra rossa-grown seedlings in contrast with those grown in the nursery substrate suggests that the former were acclimated to the soil. Higher photosynthetic rate (A), transpiration (E) and stomatal conductance (gs) were observed in terra rossa seedlings, mainly during the first months. The higher carbon availability may account for the higher root nitrogen concentration in terra rossa-grown seedlings, which could favor their later field growth. Low-watered seedlings showed a certain degree of hardening, since after 18 months, they showed higher A, E, gs and lower photoinhibition than well-watered seedlings, likely attributable to the sharp leaf-to-root biomass ratio reduction. Carbon isotope discrimination (Δ) values were similar to those of well-watered plants and indicated a non-stomatal component as the main factor controlling photosynthesis in these leaves. Eighteen-month-old low irrigated seedlings had the highest mortality. Overall, results suggest that nursery terra rossa-acclimated Q. coccifera seedlings with improved physiological status and hydraulic soil-root continuity would have a higher survival rate in the field.

Conductance mesophyllienne pour le CO2 et caractéristiques morphologiques des feuilles sous stress hydrique pendant la repousse de Quercus ilex L.

Quercus ilex L., the dominant species in Mediterranean forests and one with a great capacity for resprouting after disturbances, is threatened by the expected increase in fire frequency and drought associated with climate change. • The aim of this study was to determine the contribution of photosynthesis limitants, especially mes- ophyll conductance (gmes) during this species' resprouting and under summer drought. • Resprouts showed 5.3-fold increased gmes and 3.8-fold increased stomatal conductance (gs )a t mid- day with respect to leaves of undisturbed individuals. With increased drought, structural changes (decreased density and increased thickness) in resprouts contributed to the observed higher photosyn- thesis and increased gmes .H owever,gmes only partially depended on leaf structure, and was also under physiological control. Resprouts also showed lower non-stomatal limitations (around 50% higher car- boxylation velocity (Vc,max) and capacity for ribulose-1,5-bisphosphate regeneration (Jmax)). A sig- nificant contribution of gmes to leaf carbon isotope discrimination values was observed. • gmes exhibits a dominant role in photosynthesis limitation in Q. ilex and is regulated by factors other than morphology. During resprouting after disturbances, greater capacity to withstand drought, as evidenced by higher gmes, gs and lower non-stomatal limitants, enables increased photosynthesis and rapid growth.

Carbon isotope discrimination function analysis and drought tolerance of stylo species grown under rain-fed environment

Limited germplasm and narrow genetic base in the past has hinders wider applicability of Stylosanthes in India. However, build up in Stylosanthes germplasm in recent years provided an opportunity to evaluate and use them under different agro-ecological situations preferably targeting drought tolerance. Rate reducing resistance (RRR) allo-tetraploid lines of S. scabra and diploid S. seabrana, a newly introduced species, observed well suited in hard and cracking soils under complete rainfed condition. Genotypes of S. scabra were more tolerant to drought over lines of other species as evidenced by high leaf thickness, more proline accumulation, contents of malondialdehyde (MDA), sugars, starch and chlorophyll and low carbon isotope discrimination (CID) values. Both in control and stress conditions, a positive relationship (r = 0.465 and 0.328) was observed between specific leaf area (SLA) and CID. Earlier reports have emphasized measurement of CID as an indirect way of measuring the transpiration efficiency (TE) in Stylosanthes (Thumma et al. Aust J Agr Res 49:1039–1045, 1998). The negative relationship observed between TE and CID suggested low CID bearing lines would have high TE, useful traits to select lines growing better in dry environments. Thus, selected lines having low CID provided better scope for the introduction of this important range legume for semi- arid regions of India.

Evaluation of genus Cenchrus based on malondialdehyde, proline content, specific leaf area and carbon isotope discrimination for drought tolerance and divergence of species at DNA level

Cenchrus (family Poaceae) is an important component of major grass covers of the world. Largely it is apomictic and both annual and perennial species exist in nature. Variations in contents of malondialdehyde, proline, specific leaf area and carbon isotope discrimination for drought tolerance were estimated among eight prominent species of Cenchrus. Simultaneously, genetic variations were also estimated by employing 187 RAPD primers. Of these, 23 primers did not react, 2 performed poorly and 7 produced many non-scorable bands and one primer yielded a single monomorphic band. Rest of the 154 primers generated one or more unambiguously scorable fragments. Twelve hundred and four of the 1,296 putative loci were polymorphic (93%) between at least one pair-wise comparisons among eight species. Dice coefficient and neighbor-joining algorithm analyses showed clustering patterns that fit with the known habitat of the species except perennial, C. myosuroides which formed a node between two annuals species. When these species were subjected to water stress tolerance test, a correlation (r = 0.612) between specific leaf area (SLA) and carbon isotope discrimination (CID) and difference in levels of drought tolerance based parameters among eight species were observed. Of the eight species investigated two annuals viz., C. biflorus and C. echinatus showed highest level of genetic similarity which was also evident from the similar levels of SLA, MDA, proline contents and carbon isotope discrimination values observed in these two species.

Variations in life‐form composition and foliar carbon isotope discrimination among eight plant communities under different soil moisture conditions in the Xilin River Basin, Inner Mongolia, China

AbstractWater is one of the key limiting factors for the survival and growth of plant species in arid and semi‐arid steppe regions. Different plant functional groups (PFGs) based on life‐forms differ in their strategies to cope with limited water availability. The foliar carbon isotope discrimination (Δ) value provides an integrated measurement of internal plant physiological and external environmental properties affecting photosynthetic gas exchange over the time interval when the carbon was fixed. In this study, we surveyed the composition and Δ values of various life‐forms (shrubs, sub‐shrubs, perennial grasses, perennial forbs and annuals) in eight different plant communities along a soil moisture gradient in the Xilin River Basin, Inner Mongolia, China. Our results showed that: (1) life‐forms occurred variously in eight steppe communities with different soil moisture status; (2) in wetter habitats, forbs were more abundant and accounted for the majority of aboveground biomass, whereas grasses became more important in drier habitats. Shrubs and sub‐shrubs increased with decreasing soil water availability and their relative biomass rapidly increased in degraded steppe and sand dune communities. (3) The numerical order of the mean Δ values of life‐forms is as follows: perennial grasses (15.86‰) < shrubs (16.10‰) < perennial forbs (16.45‰)=annuals (16.41‰) < sub‐shrubs (17.55‰), reflecting their differences in water use efficiencies. The significant differences in the Δ values among these life‐forms suggested that life‐form‐based PFGs not only represent a morphological classification of these plants, but could also represent a functional group integrating different physiological processes such as water use strategies, which may partially explain the differences in PFG composition and competitive ability of co‐existing species along environmental gradients in the Xilin River Basin.

In situ measurements of carbon and nitrogen distribution and composition, photochemical efficiency and stable isotope ratios in Araucaria angustifolia

Araucaria angustifolia (Bertol.) Kuntze is an indigenous conifer restricted to the southern region of South America. In this on-site field study, we provide a detailed description of the nitrogen compounds and sugars allocated to the different plant compartments in tall adult trees, young trees about 2–3 m tall and small seedlings at its northernmost occurrence in the mountains of Itatiaia (20°25′S; 44°50′W; 2,000 m a.s.l.), SE Brazil. We determined C and N contents, soluble sugars, soluble non-protein N-compounds and δ15 N-signatures in leaves, roots, wood of stems, xylem- and phloem- sap. We also measured chlorophyll a fluorescence of photosystem II and carbon isotope discrimination reflecting photosynthetic activity and water-use efficiency. The high C and N concentrations in fine roots suggest that they are important reservoirs of N and C. Most nitrogen taken up from the soil was metabolised in the roots. The only inorganic nitrogen form detectable in the xylem sap was a small amount of ammonium. Glutamine was the dominant transport form of nitrogen in the xylem, while glutamate and the amides glutamine and asparagine were the most abundant soluble N compounds in the phloem. Total soluble non-protein N and sugar concentrations were significantly higher in the phloem of adult trees. In this particular site, A. angustifolia was apparently not exposed to water stress, as indicated by the high values of carbon isotope discrimination. The three developmental stages were clearly separated in terms of photosynthetic performance. Indeed, effective quantum yield of photosystem II increased from seedlings to adult trees under ambient irradiance.

Water-use efficiency and carbon isotope discrimination in two cultivars of upland rice during different developmental stages under three water regimes

A pot experiment was conducted in a glasshouse to clarify and quantify the effect of plant part, water regime, growth period, and cultivar on carbon isotope discrimination (CID), and to analyze the relationship between CID, stomatal behavior and water-use efficiency (WUE). The experiment was comprised of two upland rice (Oryza sativa L.) cultivars and three water regimes (100, 70, and 40% of saturation moisture) in a completely randomized design. Plants were harvested at tillering, flowering, and maturity. No significant cultivar differences in above-ground dry matter-based WUE (WUEA) and total dry matter-based WUE (WUET) were observed. WUEA (and WUET) increased with water stress up to tillering, but decreased with water stress after tillering. Significant cultivar differences in CID in all the analyzed plant parts were observed at all harvest times. Reduction in CID with water stress was greatest at tillering, and the effect was less pronounced at flowering and at maturity. At each harvest, the effect was most pronounced in newly developed plant parts. Root and grain tended to have the lowest CID values, and stem the highest, at all harvest times. A negative relationship was observed between CID measured at tillering and WUEA (and WUET) measured over the period from seedling to tillering, whereas a reverse relationship was obtained between CID measured at flowering and WUEA (and WUET) measured over the period from tillering to flowering, and an unclear relationship between CID measured at maturity and WUEA (and WUET) measured over the period from flowering to maturity. The ratio of the intercellular and atmospheric concentration of CO2 (Ci/Ca) were closely associated with CID throughout the water regimes when one cultivar was considered, however, cultivar differences in CID were not related to variations in Ci/Ca. The results indicate that significant cultivar difference existed in CID in all the analyzed plant parts at all harvest times, while corresponding difference in WUEA (and WUET) between the cultivars was not necessarily consistent. Abbreviations: WUE – water-use efficiency; WUEi – instantaneous WUE (or leaf transpiration efficiency); ADM – above-ground dry matter; TDM – total dry matter; WUEA– ADM-based WUE; WUET– TDM-based WUE} CID – carbon isotope discrimination; NL – the newest leaves; FEL – recently fully expanded leaves; FL – flag leaves; P – photosynthesis rate; g – leaf stomatal conductance to water vapor; Ci– intercellular CO2 concentration; Ca– atmospheric CO2 concentration; T – transpiration rate; gs – total conductance of CO2

Carbon isotope discrimination differences within and between contrasting populations of Encelia farinosa raised under common-environment conditions.

Previous studies of the desert shrub Encelia farinosa have shown variation of morpholological and physiological integration that appears to match environmental differences among populations. Such findings led us to ask if there is a genetic basis for such differentiation that may be related to physiological control of intercellular CO(2) concentrations as indicated by carbon isotope discrimination (Delta) values, and if genetic variance for Delta is detectable within populations. Under common environment conditions, Delta values were compared between two populations of E. farinosa from desert regions with contrasting rainfall patterns: Superior, Ariz., a region with high annual rainfall and droughts of short duration, and Oatman, Ariz. a region with lower annual rainfall and longer drought periods. Superior plants had consistently greater mean Delta values than Oatman plants across a broad range of soil water potentials, indicating that there is a genetic basis for Delta variation between these populations. At the intrapopulation level only Oatman plants showed detectable genetic variance of Delta based on: (1) consistent individual-rank values for Delta among soil-drought stages, and (2) evidence of heritable genetic variance for Delta during one drought stage. No genetic variance in Delta was evident for the Superior population. It is hypothesized that the high spatio-temporal heterogeneity of water availability at Oatman may facilitate the maintenance of genetic variance for carbon isotope discrimination within this population. Both the inter- and intra-population level findings suggest that selection associated with rainfall and drought has resulted in genetic divergence of the physiological factors involved in Delta determination for these populations. There appears to be strong differences of water-use and carbon-gain strategies among populations, and broader functional breadth among plants in the habitat of greatest environmental heterogeneity.

Association between Yield and Carbon Isotope Discrimination Value in Different Organs of Durum Wheat Under Drought

AbstractCarbon isotope discrimination (Δ) has been proposed as a selection criterion for transpiration efficiency and grain yield in drought‐prone environments for several C3 species, including cereals. Δ analysis, however, has mainly been concerned with grain or culm tissues and little work has been devoted to other organs. The objective of this study was to describe Δ variation in different organs and to examine the relationships between Δ and grain yield across environments. Six durum wheat genotypes with contrasted grain Δ were cultivated under rainfed conditions during three successive years at Montpellier (South of France). Δ was measured on flag leaf, stalk, awns, chaff and rachis sampled at anthesis and maturity, and on mature grain. Higher genotypic variation and closer correlation with yield were noted for grain Δ compared to other plant parts. The genotype ranking across years was more consistent for grain Δ than for other organs. Consequently, the grain seems the most effective plant part for Δ analysis in durum wheat under Mediterranean conditions. The study of Δ variation in other organs may be useful, however, to evaluate the contribution of those organs to grain filling and final yield according to environmental conditions.

Ecophysiological consequences of contrasting microenvironments on the desiccation tolerant moss Tortula ruralis.

Tortula ruralis is a homoiochlorophyllous-desiccation-tolerant (HDT) moss that retains all pigments when dehydrated and rapidly recovers physiological function upon rehydration. This moss forms extensive cover in exposed and shaded areas in the sandy semi-arid grasslands of Central Europe. We hypothesized that contrasting drying regimes between these microhabitats would affect plant N status, constraints to gas exchange and growth, as well as result in altered pigment concentrations and ratios, and photochemical light-response dynamics. Furthermore, we believed T. ruralis's HDT habit would limit its ability to acclimate to altered light environment. We found that sun plant T. ruralis had lower plant mass, as well as lower tissue N, C, total photosynthetic pigment concentrations and carbon isotope discrimination (Δ) values compared to shade plant counterparts. Carotenoid/chlorophyll ratios in sun plants were typical of high light-adapted tissue, but chlorophyll a/chlorophyll b ratios were lower, more characteristic of low light-adapted tissue. This unique combination of pigment responses was accompanied by sustained lower levels of optimal quantum efficiency of PSII (F v/F m) in sun plant T. ruralis, even during favorable diurnal conditions, and reduced engagement of energy-dependent thermal dissipation (NPQ). Reciprocal transplants of sun and shade plants showed that T. ruralis is capable of short-term adjustment to altered light level, as evidenced by increases in F v/F m, NPQ, and light-adapted PSII yield (φPSII) in transplanted sun plants, and concurrent decreases in sun-transplanted shade plants. However, the performance of transplanted sun plants remained consistently below that of undisturbed shade plants. These findings show that microenvironmental variation results in different patterns of resource acquisition in this HDT moss, and that growth in the open imparts greater desiccation tolerance, and the development of a greater standing engagement of slowly reversing photoprotective mechanisms. In contrast, prolonged activity and greater resource acquisition in shaded populations may allow T. ruralis to rapidly adjust to changes following disturbance to the plant canopy, fostering the persistence of T. ruralis in these semi-arid grasslands.

Photosynthesis in Salsola Species (Chenopodiaceae) from Southern Africa Relative to their C4 Syndrome Origin and their African‐Asian Arid Zone Migration Pathways

Abstract: Over 60 Salsola species of Chenopodiaceae from South Africa were studied for their photosynthesis type, using δ13C analysis and light microscopy of leaf anatomy. These species cover about 70 % of the total list of Southern African Salsola species and grow naturally in South and Southwest African desert regions. All species are shrubby forms and belong to the single subsection Caroxylon. Only C4 photosynthesis was found in the Salsola species determined with 13C/12C carbon isotope discrimination values that ranged from ‐ 11.04 to ‐ 14.03 % (PDB), plus the presence of a Kranz type assimilation tissue anatomy. The apparent absence of C3 in Salsola in South and Southwest Africa and the known presence of C3 and C3 ‐ C4 intermediate photosynthesis in Caroxylon, Salsola species in Asia strongly indicate that the genus Salsola originated in Asia and later migrated to South Africa.

Crassulacean Acid Metabolism 1975-2000, a Check List

A list of plant species documented over the past 25 years to exhibit Crassulacean Acid Metabolism (CAM) is presented. The list compiles all available information on these species including their growth habits, succulent parts, carbon isotope discrimination values, CAM types, CAM inducers, and CAM modifications.

Variation in carbon isotope discrimination within and among Sphagnum species in a temperate wetland.

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.

Host Associations of the Introduced Annual Root Hemiparasite Parentucellia viscosa in Agricultural and Bushland Settings in Western Australia

Populations of the introduced annual root hemiparasite, Parentucellia viscosa (L.) Caruel (Scrophulariaceae), were examined in habitats where introduced, mixed introduced plus native, or solely native species provided potential hosts. Presence of haustoria on host roots confirmed parasitism of 17 introduced and ten native taxa across the sites investigated. Paired plots, one with all hosts removed early in the season, the other left intact, showed overall increases in shoot dry matter of the parasites over 3 months of growth. Results indicated a substantial growth benefit to the parasite from continued access to introduced and indigenous plant species, although the parasite continued growing to a limited extent after removal of hosts. Carbon isotope discrimination values (δ13C) were consistently more negative for parasites than for associated hosts, and more negative for parasites in plots containing hosts than in plots from which hosts had been removed. Values for δ15N discrimination of shoot dry matter of parasites lay mostly within the range of those of hosts. The δ13C data suggested poorer water use efficiency of parasite than hosts, while corresponding δ15N data indicated particularly effective uptake of N-containing compounds from the N2-fixing host, Lotus angustissimus. Where the parasite had access to only one or a few closely related hosts, the composition of the soluble amino fraction of its leaves generally matched that of foliage of host(s). However, in some instances the parasite accumulated certain amino compounds to a much greater or lesser relative extent than did its partner host(s). Where many hosts were being exploited, compositional features of the soluble amino fraction of the parasite suggested major access to nitrogenous solutes from specific hosts. Data are discussed in relation to previously published observations on haustorial-derived benefits indicated for other species of root hemiparasites.