Leaf Carbon Isotope Discrimination Research Articles

Bias in estimated online leaf carbon isotope discrimination due to woody tissues

Branch or shoot chamber measurements integrate over both foliar and woody tissue carbon dioxide (CO2) fluxes and their associated influences on the carbon isotopic composition of atmospheric/headspace CO2. Here, we quantified the bias introduced by woody tissue carbon isotope fluxes on apparent leaf 13C discrimination (Δ13Capparent) estimates, using laser spectroscopy under controlled conditions. CO2 efflux from woody tissues of defoliated beech saplings in the dark was strongly related to temperature (R2 = 0.78), which served as the basis to model light-dependent woody tissue photosynthesis (R2 = 0.72). We then quantified the contributions of leaf and woody tissues to leaf Δ13Capparent of foliated beech saplings in the light. Unbiased foliar Δ13C was 1.1 to 4.9 ‰ lower than leaf Δ13Capparent, depending on photosynthetic rates of woody tissues. Therefore, we strongly recommend accounting for isotope-related bias due to woody tissues when estimating leaf Δ13Capparent based on branch or shoot chamber measurements.

A preliminary study of water use strategy of desert plants in Dunhuang, China

Water is a restrictive factor for plant growth and ecosystem stability in arid and semiarid areas. The dynamics of water availability in soils and water use by plants are consequently critical to ecosystem functions, e.g. maintaining a high resistance to the changing climate. Plant water use strategies, including water-use efficiency (WUE) and the main water source that a plant species utilizes, play an important role in the evaluation of stability and sustainability of a plantation. The water use strategies of desert plants (Tamarix chinensis, Alhagi sparsifolia, Elaeagnus angustifolia, Sophora alopecuroides, Bassia dasyphylla and Nitraria sphaerocarpa) in three different habitats (saline land, sandy land and Gobi) in Dunhuang (located in the typical arid area of northwestern China) were studied. The stable isotope of oxygen was used to determine the main water source and leaf carbon isotope discrimination was used to estimate the long-term WUE of plant species in the summer of 2010. The results suggest that: 1) the studied desert plants took up soil water below the depth of 80 cm; 2) T. chinensis in the three habitats used deeper soil water and T. chinensis in the Gobi site had higher WUE than those in the saline land and the sandy land. The results indicated that desert plants in Dunhuang depended on stable water source and maintained high WUE to survive in water limited environments.

Genetic control of water use efficiency and leaf carbon isotope discrimination in sunflower (Helianthus annuus L.) subjected to two drought scenarios.

High water use efficiency (WUE) can be achieved by coordination of biomass accumulation and water consumption. WUE is physiologically and genetically linked to carbon isotope discrimination (CID) in leaves of plants. A population of 148 recombinant inbred lines (RILs) of sunflower derived from a cross between XRQ and PSC8 lines was studied to identify quantitative trait loci (QTL) controlling WUE and CID, and to compare QTL associated with these traits in different drought scenarios. We conducted greenhouse experiments in 2011 and 2012 by using 100 balances which provided a daily measurement of water transpired, and we determined WUE, CID, biomass and cumulative water transpired by plants. Wide phenotypic variability, significant genotypic effects, and significant negative correlations between WUE and CID were observed in both experiments. A total of nine QTL controlling WUE and eight controlling CID were identified across the two experiments. A QTL for phenotypic response controlling WUE and CID was also significantly identified. The QTL for WUE were specific to the drought scenarios, whereas the QTL for CID were independent of the drought scenarios and could be found in all the experiments. Our results showed that the stable genomic regions controlling CID were located on the linkage groups 06 and 13 (LG06 and LG13). Three QTL for CID were co-localized with the QTL for WUE, biomass and cumulative water transpired. We found that CID and WUE are highly correlated and have common genetic control. Interestingly, the genetic control of these traits showed an interaction with the environment (between the two drought scenarios and control conditions). Our results open a way for breeding higher WUE by using CID and marker-assisted approaches and therefore help to maintain the stability of sunflower crop production.

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.

Leaf Carbon Isotope Discrimination as an Accurate Indicator of Water‐Use Efficiency in Sunflower Genotypes Subjected to Five Stable Soil Water Contents

AbstractLeaf carbon isotope discrimination (CID) has been suggested as an indirect tool for breeding for water‐use efficiency (WUE) in various crops. This work focused on assessing phenotypic correlations between WUE and leaf CID and analysing genotypic variability in four sunflower genotypes grown in a greenhouse in pots with five different stable levels of soil water content (SWC). We measured WUE at whole plant and leaf (intrinsic) level. At whole plant level, WUE was derived from the ratio of total dry aerial biomass (BM) to cumulative water transpired (CWT). At leaf level, intrinsic WUE was calculated as the ratio of light‐saturated CO2 assimilation to stomatal conductance (A/gs) in younger expanded leaves. Significant differences among the four genotypes and the five SWCs were observed for whole plant and leaf WUE and CID. Strong negative correlations were observed between whole plant WUE and CID as well as between intrinsic WUE and CID with decreasing water availability. No relationships appeared between BM production and WUE or CID. Our results can help agronomists and breeders to evaluate sunflower lines with high WUE for adaptation to drought conditions and for reducing water consumption and crop water needs. Leaf CID appears to be a pertinent and valuable trait to select sunflower genotypes with high WUE.

Variability and plasticity of productivity, water-use efficiency, and nitrogen exportation rate in Salix short rotation coppice

Short rotation coppice (SRC) willow plantations may play an important role in the future for biomass production purposes. However, the high planting density schemes combined with the frequent harvests occurring in such plantations could rapidly deplete soil resources. The use of genotypes able to produce greater amounts of biomass by using the least water and nutrients may help mitigating this risk. This study aimed at assessing among six willow genotypes (1) the variability of traits related to productivity (e.g. aboveground dry biomass or stem height), leaf and wood nitrogen (N) contents, N exportation rate and water-use efficiency (WUE) as estimated through bulk leaf carbon isotope discrimination (Δ13C), (2) the relationships among traits, and (3) the plasticity of these traits and of the relationships among them across different sites. The six genotypes were grown under SRC at three sites in northern France differing primarily in pedoclimatic characteristics for two years. A significant genotypic variability was found for all traits, except for the N exportation rate. The pedoclimatic context impacted the values of all traits, and the genotypic ranking for traits related to productivity and for Δ13C. Δ13C was negatively correlated with total shoot dry biomass and/or height irrespective of the site, meaning that the most productive genotypes were also the most efficient to use water. In conclusion, no antagonism was detected between biomass production and WUE. The most productive and most water-use efficient genotypes were the ones responsible for the highest nitrogen removal from the plantation during harvest.

Leaf carbon isotope ratio and water use efficiency of urban roadside trees in summer in Kyoto city

AbstractThe effect of summer climate on leaf carbon isotope composition (δ13C) of the major roadside tree species Prunus × yedoensis (P. yedoensis) was investigated in Kyoto city, Japan, to explore the implications for alterations in urban environments. Temperature and the vapor pressure deficit were higher at sites of higher traffic volumes, possibly affected by a heat island effect. The leaf δ13C of P. yedoensis trees was affected strongly by leaf carbon isotope discrimination (Δ), with much less effect of δ13C on atmospheric CO2. Leaf Δ values in the summer were smaller at sites of higher traffic volumes with high atmospheric temperatures, suggesting a higher long‐term water use efficiency (WUE) at these sites. Gas exchange measurements of P. yedoensis leaves indeed suggested a higher intrinsic WUE at sites of higher traffic volumes with high atmospheric temperatures. These results suggest that leaf Δ is related to the response of WUE to summer climates, and that leaf δ13C in urban areas is a useful tracer for understanding the influences of urban environments on plant photosynthetic processes.

Planting density affects growth and water-use efficiency depending on site in Populus deltoides × P. nigra

Poplar coppice plantations for biomass production can be conducted under either short rotation coppice (SRC) or short rotation forestry (SRF) systems, depending on planting density and rotation length. It is likely that differences in planting density affect tree physiology through competition for resource acquisition, including light, water and nutrients. In this paper, we hypothesized that the effects of planting density on growth and water-use efficiency (assessed through bulk leaf carbon isotope discrimination, Δ13C) in poplar depend on site characteristics in terms of soil fertility and water availability. To test this hypothesis, 56 Populus deltoides×P. nigra genotypes were planted under both SRC and SRF and replicated at two sites differing for pedoclimatic conditions. At the most favorable site for growth, trees grown at the higher density (SRC) displayed higher stem height, lower stem circumference, higher specific leaf area, higher mass-based leaf nitrogen contents and higher Δ13C, indicating that increased tree density mainly accentuated competition for light. Under less favorable conditions, trees grown under SRC still displayed lower stem circumference, higher specific leaf area and higher mass-based leaf nitrogen contents. However, stem height remained unaffected by increasing planting density while Δ13C was lower, likely because of increased competition for water availability. Genotypic rankings across planting densities were overall conserved while they were significantly modified across sites, suggesting that rankings for genotypic performances were much less affected by planting density than by site. Realized growth measured after 2years (height and circumference) was weakly correlated with Δ13C, but a negative relationship between Δ13C and growing season leaf increment rate was observed in most cases. The absence of trade-off between growth and water-use efficiency combined with the large genotypic variations observed for these traits confirms the potential for selecting genotypes with high water-use efficiency without counter-selecting on biomass production in P. deltoides×P. nigra.

Different Water Use Strategies of Juvenile and Adult Caragana intermedia Plantations in the Gonghe Basin, Tibet Plateau

BackgroundIn a semi-arid ecosystem, water is one of the most important factors that affect vegetation dynamics, such as shrub plantation. A water use strategy, including the main water source that a plant species utilizes and water use efficiency (WUE), plays an important role in plant survival and growth. The water use strategy of a shrub is one of the key factors in the evaluation of stability and sustainability of a plantation.Methodology/Principal Findings Caragana intermedia is a dominant shrub of sand-binding plantations on sand dunes in the Gonghe Basin in northeastern Tibet Plateau. Understanding the water use strategy of a shrub plantation can be used to evaluate its sustainability and long-term stability. We hypothesized that C. intermedia uses mainly deep soil water and its WUE increases with plantation age. Stable isotopes of hydrogen and oxygen were used to determine the main water source and leaf carbon isotope discrimination was used to estimate long-term WUE. The root system was investigated to determine the depth of the main distribution. The results showed that a 5-year-old C. intermedia plantation used soil water mainly at a depth of 0–30 cm, which was coincident with the distribution of its fine roots. However, 9- or 25-year-old C. intermedia plantations used mainly 0–50 cm soil depth water and the fine root system was distributed primarily at soil depths of 0–50 cm and 0–60 cm, respectively. These sources of soil water are recharged directly by rainfall. Moreover, the long-term WUE of adult plantations was greater than that of juvenile plantations.ConclusionsThe C. intermedia plantation can change its water use strategy over time as an adaptation to a semi-arid environment, including increasing the depth of soil water used for root growth, and increasing long-term WUE.

Phosphorus Fertilization and Fungal Inoculations Affected the Physiology, Phosphorus Uptake and Growth of Spring Wheat Under Rainfed Conditions on the Canadian Prairies

AbstractSome fungal species have been shown to improve plant growth under drought conditions and to increase plant phosphorus (P) uptake from the soil. How moisture limitation, P availability and fungal inoculation interact to affect plant physiology and growth is, however, poorly understood. Here, we studied the combined effects of fungal (arbuscular mycorrhizal fungi (AMF) or Penicillium spp.) inoculations and phosphorus (P) fertilization (0, 45 and 90 kg ha−1) on the net rate of photosynthesis, water‐use efficiency, P uptake and growth of spring wheat (Triticum aestivum var. Superb) under field conditions at two locations (Castor and Vegreville) in Alberta, Canada. Both fungal inoculation and P application increased the rate of photosynthesis. Under the same P level, AMF inoculation had a greater positive effect on the rate of photosynthesis than Penicillium inoculation. The AMF inoculation increased the instantaneous water‐use efficiency (WUEi) of plants at Castor, but not at Vegreville. Leaf carbon isotope discrimination (CID, Δ13C) increased with the rate of P application but was not affected by fungal inoculations. Phosphorus concentrations of stem and seed increased with both fungal inoculation and P application irrespective of location, with AMF inoculation showing the largest effects. The interaction between P addition and fungal inoculation was significant for stem P concentration in Vegreville. Both fungal inoculation and P application increased the leaf area index (LAI), biomass production and grain yield at both locations. Under the same P level, AMF inoculation had a greater positive effect on LAI, biomass production and grain yields than Penicillium inoculation. Morphological characters such as spike length and kernels/spike were also improved by fungal inoculation and P application at both locations. We conclude that the studied sites were deficient in P availability, and both fungal inoculation and P application improved P uptake and crop productivity, while the effect of fungal inoculation on water‐use efficiency was site specific.

Green Revolution Trees: Semidwarfism Transgenes Modify Gibberellins, Promote Root Growth, Enhance Morphological Diversity, and Reduce Competitiveness in Hybrid Poplar

Semidwarfism has been used extensively in row crops and horticulture to promote yield, reduce lodging, and improve harvest index, and it might have similar benefits for trees for short-rotation forestry or energy plantations, reclamation, phytoremediation, or other applications. We studied the effects of the dominant semidwarfism transgenes GA Insensitive (GAI) and Repressor of GAI-Like, which affect gibberellin (GA) action, and the GA catabolic gene, GA 2-oxidase, in nursery beds and in 2-year-old high-density stands of hybrid poplar (Populus tremula × Populus alba). Twenty-nine traits were analyzed, including measures of growth, morphology, and physiology. Endogenous GA levels were modified in most transgenic events; GA(20) and GA(8), in particular, had strong inverse associations with tree height. Nearly all measured traits varied significantly among genotypes, and several traits interacted with planting density, including aboveground biomass, root-shoot ratio, root fraction, branch angle, and crown depth. Semidwarfism promoted biomass allocation to roots over shoots and substantially increased rooting efficiency with most genes tested. The increased root proportion and increased leaf chlorophyll levels were associated with changes in leaf carbon isotope discrimination, indicating altered water use efficiency. Semidwarf trees had dramatically reduced growth when in direct competition with wild-type trees, supporting the hypothesis that semidwarfism genes could be effective tools to mitigate the spread of exotic, hybrid, and transgenic plants in wild and feral populations.

Evaluation of Grain Yield and Three Physiological Traits in 30 Spring Wheat Genotypes across Three Irrigation Regimes

ABSTRACTAccurate field evaluation of yield‐related physiological traits is critical for selecting high yield and drought resistance in wheat (Triticum aestivum L.). To characterize grain yield and three physiological traits for 30 spring wheat genotypes, field experiments with three irrigation regimes were conducted in 2009 and 2010 field seasons. Our study suggests that Feekes 11.2 is the optimal stage to evaluate flag leaf senescence (FLS) and canopy temperature (CT) when making selections for high grain yield and drought resistance among wheat genotypes. Flag leaf carbon isotope discrimination (CID) was positively correlated with grain yield, whereas FLS and CT were negatively correlated with grain yield. The three traits together explained 92% of the total phenotypic variation of grain yield. Selected genotypes were classified into four groups based on yield performance across irrigation regimes. High‐yield genotypes IDO599, ‘Alturas’, and IDO702 produced high grain yield across different water conditions; drought‐resistant genotypes ‘Agawam’, ‘McNeal’, and ‘Alpowa’ produced higher grain yield under the nonirrigated regime. High yield of those genotypes was contributed by good performance of physiological traits such as late FLS, great CID, or low CT or combinations of these traits. Preliminary results indicate that using physiological traits to estimate yield performance can be effective, and selecting suitable genotypes for different water environments may be crucial for improving yield productivity.

Variations in bulk leaf carbon isotope discrimination, growth and related leaf traits among three Populus nigra L. populations

The ongoing global change could be an additional threat to the establishment and the long-term survival of Populus nigra L., an emblematic European riparian species. With the general aim of gaining insights into the adaptive potential of this species, we (i) quantified variations within and among three French P. nigra populations for key physiological attributes, i.e., water-use efficiency (assessed from bulk leaf carbon isotope discrimination, Δ(13)C), growth performance and related leaf traits, (ii) examined genotype and population by environment interactions, and (iii) explored the relationship between Δ(13)C and growth. Thirty genotypes were sampled in each of three naturally established populations and grown in two different sites, Orléans (ORL) and Guémené-Penfao (GMN). In ORL, two similar plots were established and different watering regimes were applied in order to test for the drought response. Significant variations were observed for all traits within and among populations irrespective of site and watering. Trait variation was larger within than among populations. The effect of drought was neither genotype- nor population-dependent, contrary to the effect of site. The population ranking was maintained in all sites and watering regimes for the two most complex traits: Δ(13)C and growth. Moreover, these two traits were unrelated, which indicates that (i) water-use efficiency and growth are largely uncoupled in this species, and (ii) the environmental factors driving genetic structuration for Δ(13)C and growth act independently. The large variations found within populations combined with the consistent differences among populations suggest a large adaptive potential for P. nigra.

Relationship between carbon isotope discrimination (Δ), yield and water use efficiency of durum wheat in Northern Syria

► Six durum wheat genotypes varying in grain carbon isotope discrimination (CID) were used in a field experiments. ► This study is to relate wheat yields of the different genotypes with CID and other plant traits. ► CID was measured in the grain and the 4th fully expanded leaf together with soil water content . ► Leaf CID was higher compared with grain CID, positive correlations were found between CID and yields of grain and biomass. ► Water use efficiency did not differ between genotypes. CID was correlated to grain ash and protein content. Field experiments were conducted over two seasons (2005–06 and 2006–07) using six durum wheat genotypes varying in grain carbon isotope discrimination ( Δ ) but similar in phenology. Experimental sites at Tel Hadya, Breda, Muslmieh and Yahmoul across rainfall zones in Northern Syria were used. The main objective of this study is to relate the wheat yields of the different genotypes with Δ and other plant traits. Plant growth was monitored throughout the growing season. Δ was measured for every plot in the grain (Δ G ) and the 4th fully expanded leaf (Δ L ). Also, ash and protein contents of grain were analyzed. Soil water content throughout the growing season was measured at some sites to calculate water use. Yield variability between sites was mostly due to rainfall, with variability between cultivars within a site being due to season. Δ L was higher, with no stress evident at this stage, compared with Δ G . Δ L , ranging from 19.97 to 22.76‰, was lower at the drier sites and higher at the wettest site, which changed to the opposites for Δ G ranging from 12.88 to 16.62‰. Positive correlations were found between Δ and yields of grain and biomass. The stronger correlations were at the drier sites, whilst at the wettest site there was no significant relationship. Δ L for the different genotypes was more stable between sites and seasons than Δ G . Water use efficiency did not differ between genotypes, unlike Δ . Δ was also correlated to grain ash and protein content. This suggests to use these cheap and easily obtainable plant traits as surrogate if Δ was unavailable.

Is the ranking of poplar genotypes for leaf carbon isotope discrimination stable across sites and years in two different full-sib families?

Introduction Because of its vigorous growth, poplar can play an important role for sustainable production of woody biomass to cover renewable energy needs. Hence, the selection of suitable genotypes has to be based on relevant traits, among which intrinsic water use efficiency (Wi, estimated through leaf carbon isotope discrimination, Δ) may be a key trait. Besides a large genetic variation in Δ among the frequently planted poplar hybrids, the use of Δ in deployment or breeding programmes requires insights in the robustness of the genotype ranking for Δ across environments and years.

Photosynthetic physiology of eucalypts along a sub-continental rainfall gradient in northern Australia

Leaf-level photosynthetic parameters of species in the closely related genera Eucalyptus and Corymbia were assessed along a strong rainfall gradient in northern Australia. Both instantaneous gas exchange measurements and leaf carbon isotope discrimination indicated little variation in intercellular CO2 concentrations during photosynthesis (ci) in response to a decrease in mean annual precipitation from ∼1700mm to ∼300mm. Correlation between stomatal conductance and photosynthetic capacity contributed toward the maintenance of relatively constant ci among the sampled leaves, when assessed at ambient CO2 concentration and photon irradiance similar to full sunlight. Leaf mass per area was the most plastic leaf trait along the rainfall gradient, showing a linear increase in response to decreasing mean annual precipitation. The maximum Rubisco carboxylation velocity, Vcmax, expressed on a leaf-area basis, showed a modest increase in response to decreasing rainfall. This modest increase in Vcmax was associated with the strongly expressed increase in leaf mass per area. These results suggest that variation in ecosystem-level gas exchange during the dry season in north-Australian savannas will likely be dominated by changes in leaf area index in response to increasing aridity, rather than by changes in photosynthetic performance per unit leaf area.

The Physiology and Stability of Leaf Carbon Isotope Discrimination as a Measure of Water-Use Efficiency in Barley on the Canadian Prairies

Temporal and seasonal water deficit is one of the major factors limiting crop yield on the Canadian prairie. Selection for low carbon isotope discrimination (Δ 13 C) or high water-use efficiency (WUE) can lead to improved yield in some environments. To understand better the physiology and WUE of barley under drought conditions on the Canadian prairie, 12 barley (Hordeum vulgare L.) genotypes with contrasting levels of leaf Δ 13 C were investigated for performance stability across locations and years in Alberta, Canada. Four of those genotypes ('CDC Cowboy', 'Niobe', '170011' and 'Kasota') were also grown in the greenhouse under well-watered and water-deficit conditions to examine genotypic variations in leaf Δ 13 C, WUE, gas exchange parameters and specific leaf area (SLA). The water-deficit treatment was imposed at the jointing stage for 10 days followed by re-watering to pre-deficit level. Genotypic ranking in leaf Δ 13 C was highly consistent, with '170011', 'CDC Cowboy' and 'W89001002003' being the lowest and 'Kasota' '160049' and 'H93174006' being the highest leaf Δ 13 C. Under field and greenhouse (well-watered) conditions, leaf Δ 13 C was significantly correlated with stomatal conductance (g s ). Water deficit significantly increased WUE, with 'CDC Cowboy' - a low leaf Δ 13 C genotype with significantly higher WUE and lower percentage decline in assimilation rate (A) and g s than the other three genotypes ('Niobe', '170011' and 'Kasota'). We conclude that leaf Δ 13 C is a stable trait in the genotypes evaluated. Low leaf Δ 13 C of 'CDC Cowboy' was achieved by maintaining a high A and a low g s , with comparable biomass and grain yield to genotypes showing a high g s under field conditions; hence, selection for a low leaf Δ 13 C genotype such as 'CDC Cowboy' maybe important for maintaining productivity and yield stability under water-limited conditions on the Canadian prairie.

Taller and larger: shifts in Arctic tundra leaf traits after 16 years of experimental warming

AbstractUnderstanding plant trait responses to elevated temperatures in the Arctic is critical in light of recent and continuing climate change, especially because these traits act as key mechanisms in climate‐vegetation feedbacks. Since 1992, we have artificially warmed three plant communities at Alexandra Fiord, Nunavut, Canada (79°N). In each of the communities, we used open‐top chambers (OTCs) to passively warm vegetation by 1–2 °C. In the summer of 2008, we investigated the intraspecific trait responses of five key species to 16 years of continuous warming. We examined eight traits that quantify different aspects of plant performance: leaf size, specific leaf area (SLA), leaf dry matter content (LDMC), plant height, leaf carbon concentration, leaf nitrogen concentration, leaf carbon isotope discrimination (LCID), and leaf δ15N. Long‐term artificial warming affected five traits, including at least one trait in every species studied. The evergreen shrub Cassiope tetragona responded most frequently (increased leaf size and plant height/decreased SLA, leaf carbon concentration, and LCID), followed by the deciduous shrub Salix arctica (increased leaf size and plant height/decreased SLA) and the evergreen shrub Dryas integrifolia (increased leaf size and plant height/decreased LCID), the forb Oxyria digyna (increased leaf size and plant height), and the sedge Eriophorum angustifolium spp. triste (decreased leaf carbon concentration). Warming did not affect δ15N, leaf nitrogen concentration, or LDMC. Overall, growth traits were more sensitive to warming than leaf chemistry traits. Notably, we found that responses to warming were sustained, even after many years of treatment. Our work suggests that tundra plants in the High Arctic will show a multifaceted response to warming, often including taller shoots with larger leaves.

USE OF MOLECULAR MARKERS IN CROP IMPROVEMENT OF PUNICA GRANATUM L. FOR WATER STRESS TOLERANCE

Pomegranate (Punica granatum L.) is an important commercial fruit crop of India. The genetics of pomegranate differs in many aspects from that of seasonal crops due to many biological limitations. Perennial and heterozygous nature of pomegranate precludes the development of inbred lines, near isogenic lines (NIL), recombinant inbred lines (RIL) and back cross progenies. Hence, the novel techniques like molecular markers can be employed for improvement of pomegranate. There are two different types of molecular markers in use and in this study PCR based marker, i.e., Randomly Amplified Polymorphic DNA (RAPD) were used. The DNA finger prints used to correlate the water stress tolerance based on relative water content (RWC). Bulk segregant analysis (BSA) was used in 124 F 2 mapping population which was raised by crossing genetically diverse parents for the water stress tolerance traits viz., crop canopy air temperature difference, specific leaf weight, RWC and carbon isotope discrimination (Δ). The bulks and parents were compared using finger prints and no distinct banding pattern was observed. The results of this investigation could be used as preliminary study in improvement of fruit crops.

Common trade-offs between xylem resistance to cavitation and other physiological traits do not hold among unrelated Populus deltoides ×Populus nigra hybrids

We examined the relationships between xylem resistance to cavitation and 16 structural and functional traits across eight unrelated Populus deltoides x Populus nigra genotypes grown under two contrasting water regimes. The xylem water potential inducing 50% loss of hydraulic conductance (Psi(50)) varied from -1.60 to -2.40 MPa. Drought-acclimated trees displayed a safer xylem, although the extent of the response was largely genotype dependent, with Psi(50) being decreased by as far as 0.60 MPa. At the tissue level, there was no clear relationship between xylem safety and either xylem water transport efficiency or xylem biomechanics; the only structural trait to be strongly associated with Psi(50) was the double vessel wall thickness, genotypes exhibiting a thicker double wall being more resistant. At the leaf level, increased cavitation resistance was associated with decreased stomatal conductance, while no relationship could be identified with traits associated with carbon uptake or bulk leaf carbon isotope discrimination, a surrogate of intrinsic water-use efficiency. At the whole-plant level, increased safety was associated with higher shoot growth potential under well-irrigated regime only. We conclude that common trade-offs between xylem resistance to cavitation and other physiological traits that are observed across species may not necessarily hold true at narrower scales.