Leaf Carbon Isotope Composition Research Articles

Proteomic and physiological signatures of altitude adaptation in a Myrsine coriacea population under common garden conditions

Plants exhibit phenotypic plasticity in response to environmental variations, which can lead to stable genetic and physiological adaptations if exposure to specific conditions is prolonged. Myrsine coriacea demonstrates this through its ability to thrive in diverse environments. The objective of the article is to investigate potential differences in protein accumulation and physiological responses of M. coriacea by cultivating plants from seeds collected from four populations at different altitudes in a common garden experiment. Additionally, we aim to evaluate whether these differences exhibit genetic fixation. Through integrated physiological and proteomic analyses, we identified 170 differentially accumulated proteins and observed significant physiological differences among the populations. The high-altitude population (POP1) exhibited a unique proteomic profile with significant down-regulation of proteins involved in carbon fixation and energy metabolism, suggesting a potential reduction in photosynthetic efficiency. Physiological analyses showed lower leaf nitrogen content, net CO2 assimilation rate, specific leaf area, and relative growth rate in stem height for POP1, alongside higher leaf carbon isotopic composition (δ13C) and leaf carbon (C) content. These findings provide insight into the complex interplay between proteomic and physiological adaptations in M. coriacea and underscore the importance of local adaptations. SignificanceWe investigate the adaptive responses of M. coriacea, a shrub with a broad phenotypic range, by cultivating plants from seeds collected at four different altitudes in a common garden experiment. These findings provide insight into the complex interplay between proteomic and physiological adaptations in M. coriacea and underscore the importance of local adaptations in the face of climate change. This study contributes to advancing our understanding of the influence of altitude-specific selection pressures on the molecular biology and physiology of plants in natural populations. Our findings provide valuable insights that enhance our ability to predict and comprehend how plants respond to climate change.

Woody species with higher hydraulic efficiency or lower photosynthetic capacity discriminate more against 13C at the global scale

Leaf carbon isotope composition (δ13C) provides an integrative record on the carbon and water balance of plants over long periods. Photosynthetic ability and hydraulic traits which are highly associated with stomatal behavior could affect leaf δ13C. Association between photosynthetic ability and leaf δ13C has been examined, however, how hydraulic traits influence leaf δ13C has not been fully understood. To fill this gap, we investigated the variations in leaf δ13C among 2591 woody species (547 shrub and 2044 tree species), and analyzed the link of leaf δ13C with leaf photosynthetic and xylem hydraulic traits. Our result showed that leaf δ13C was positively correlated to leaf photosynthetic ability and capacity. For hydraulic traits, leaf δ13C was negatively related to hydraulic conductivity (Ks), xylem pressure inducing 50 % loss of hydraulic conductivity (P50) and vessel diameter (Vdia). Associations of leaf δ13C with xylem hydraulic traits indicate woody species with stronger hydraulic safety discriminated less against 13C, while woody species with higher hydraulic efficiency had more negative leaf δ13C. Shrub species, which showed a lower Vdia and P50, had a significant less negative leaf δ13C than tree species. Furthermore, woody species inhabiting in dry regions discriminated less against 13C than those growing in humid regions. Moreover, leaf δ13C displayed a low phylogenetic signal based on Blomberg's K statistic. Overall, woody species with a higher leaf photosynthetic ability or stronger hydraulic safety system discriminated less against 13C and adopt the provident water use strategy.

Ecophysiological traits change little along a successional gradient in a tropical dry deciduous woodland from Margarita Island, Venezuela

Tropical dry forests (TDFs) are the most threatened terrestrial ecosystems and studying how functional traits of plant species change as secondary succession advances is important for understanding how and how fast can TDFs recover from disturbance. In this work we asked the question: how do functional traits change during secondary succession in a tropical dry woodland? We studied functional traits, especially ecophysiological traits, such as gas exchange, plant-water relations, leaf carbon isotope composition (δ13C), specific leaf area (SLA) and nitrogen concentration, in shrubs and trees in three successional stages (6 and 20 years after abandonment, and the dry deciduous woodland, 6 years, 20 years, and DW, respectively) along a successional gradient in a TDF in both wet and dry seasons to understand how TDFs recover after disturbance by opencast sand mining. During the wet season, similar mass-based photosynthetic rates (Amass), water potential, relative water content, instantaneous and intrinsic water-use efficiency (WUE and IWUE) and SLA were found in the 6 years and DW stages. During seasonal drought, similar reductions in these variables were observed for all three successional stages. However, δ13C of the 6 years species was higher than in 20 years and DW species, indicating a higher long-term integrated WUE in the former due to a strong reduction in stomatal conductance (gs) in the dry season. Species from the DW seem to couple metabolic changes to their characteristically low gs, such that nitrogen concentration per unit mass explained 86% of the variation in Amass. Given the functional similarity among species from the different successional stages, native species from the DW stage could have good physiological performance in the 6 and 20 years sites, and therefore could be used to restore these degraded areas.

Leaf Carbon and Water Isotopes Correlate with Leaf Hydraulic Traits in Three Solanum Species (S. peruvianum, S. lycopersicum and S. chilense)

Leaf hydraulic conductance (KLeaf) is a measure of the efficiency of water transport through the leaf, which determines physiological parameters such as stomatal conductance, photosynthesis and transpiration rates. One key anatomical structure that supports KLeaf is leaf venation, which could be subject to evolutionary pressure in dry environments. In this context, it is useful to assess these traits in species from arid climates such as S. peruvianum and S. chilense, in order to determine their hydraulic strategy and potential aptitude for the improvement of domestic tomato (S. lycopersicum). In this work, we measured KLeaf, vein density, together with leaf water isotope composition (δ18O, δ2H) and leaf carbon isotope composition (δ13C), from which we derived proxies for outside-vein hydraulic resistance (Rox) and intrinsic water use efficiency (WUEi), respectively. The two wild species showed contrasting hydraulic strategies, with S. chilense performing as a water-spender, whereas S. peruvianum showed a water-saving strategy. Interestingly, S. lycopersicum was rather conservative, and showed the highest WUEi. The low water transport capacity of S. peruvianum was not explained by vein density traits, but was related with the effective pathlength L, an isotope-derived proxy for Rox. The low WUEi of S. peruvianum suggest strong photosynthetic limitations. Our results show a wide diversity in water-use strategies in the genus, encouraging a detailed characterization of wild relatives. From a methodological point of view, we provide evidence supporting the use of water isotopes to assess changes in mesophyll hydraulic conductance, not attributable to vein density.

Atmospheric factors outweigh species traits and soil properties in explaining spatiotemporal variation in water-use efficiency of tropical and subtropical forest species

• Plant iWUE presented a non-linear increase in the last century in Sothern China. • The annual rate of change of iWUE in Southern China showed an S-curve pattern. • Multiple atmospheric factors jointly affected iWUE in subtropical and tropical forests. Intrinsic water-use efficiency (iWUE) is a key physiological trait; however, the spatiotemporal variation in iWUE and which factors affect iWUE in the tropics and subtropics are poorly known. We determined the temporal (1920-2010) and spatial patterns of iWUE using leaf carbon-isotopic composition (δ 13 C) of 1,811 herbarium specimens and associated these patterns with environmental factors across biomes in southern China. We found that iWUE increased by 15.7 μmol mol −1 in the entire studied area from 1920 to 2010. The iWUE declined from west to east in southern China, with higher values concentrated in the southwest. Rising CO 2 concentrations ([CO 2 ]), N deposition, increases in mean annual temperature (MAT) and vapor pressure deficit (VPD), and changes in temperature seasonality (TS) contributed to the spatiotemporal changes in iWUE. Our results confirm that, in addition to a continuous increase in iWUE has, the rate of change of iWUE decreased in southern China in the later years. Multiple atmospheric factors jointly determine the changes in both iWUE and the rate of change of iWUE in the studied regions.

Apple rootstocks affect functional leaf traits with consequential effects on carbon isotope composition and vegetative vigour.

Composite trees combine optimal traits from both the rootstock and the scion. Dwarfing rootstocks are commonly used to reduce shoot vigour and improve fruit quality and productivity. Although growth habits of different rootstocks have been clearly described, the underlying physiological traits affecting scion vigour are not well understood. Plant water status and stem water potential are strongly influenced by water supply and demand through the soil–plant–atmosphere continuum. In the scion, stomata regulate water loss and are essential to prevent hydraulic failure. Stomatal conductance influences leaf carbon isotope composition. Combined, the effects of reduced stomatal conductance and, consequently, carbon fixation may affect tree growth. These differences could also correspond to differences in scion vigour controlled by rootstock genotype. Here, vegetative growth, gas exchange, stem water potential and leaf δ13C were compared to determine how rootstocks affect scion water relations and whether these differences correspond to shoot vigour. There was a range in vigour among rootstocks by almost 2-fold. Net leaf carbon assimilation rates were lower in rootstocks with lower vigour. Rootstock vigour was closely associated with leaf gas exchange and stem water potential in the scion and was reflected in leaf δ13C signatures. Dwarfing was strongly affected by changes to plant water status induced by rootstock genotype and these changes are distinguishable when measuring leaf and stem δ13C composition. These observations indicate that scion water relations and leaf carbon isotope discrimination were affected by rootstock genotype. These results have implications for better understanding dwarfing mechanisms in apple rootstocks and the relationship with water-use traits.

Moderate Grazing Increases Water Use Efficiency for Environmental Health in Alpine Meadows of the Tibetan Plateau

Water use efficiency is an important indicator of drought tolerance in plants. The response of the water use efficiency to different grazing intensities and adaptive mechanisms in alpine meadows remains unclear. To understand the changes in water use in alpine meadow ecosystems under different grazing gradients, grazing systems have to be optimized, and severely receding grasslands should be effectively restored. This study analyzed the response of water use efficiency of plant dominant species, coexisting species, and functional group-level plants to grazing intensity using the δ13C index in an alpine meadow. We found that grazing increased the leaf carbon isotope composition in plants (δ13C) of Gramineae by 3.37% and grazing at a moderate level significantly increased it by 4.84% (P < 0.05). In addition, an increase in δ13C was observed in the functional groups of Cyperaceae (3.45%), Leguminosae (0.81%), and Forb (1.40%). However, some dominant species and coexisting species showed the highest δ13C values under moderate grazing. These results indicate that moderate grazing may significantly improve the water use efficiency of species in alpine meadows. The path analysis showed that water use efficiency was negatively correlated with evapotranspiration (P < 0.05), soil water content, soil organic carbon, and soil bulk density. Nevertheless, there was a positive correlation between water use efficiency and the available nitrogen. This study concluded that moderate grazing could improve the efficiency of grassland water use to a certain extent. Additionally, soil evapotranspiration was the main driving factor affecting the water use efficiency of alpine meadows.

High-throughput phenotyping of a large tomato collection under water deficit: Combining UAVs’ remote sensing with conventional leaf-level physiologic and agronomic measurements

Field high-throughput phenotyping (HTPP) studies are highly needed to study water use efficiency (WUE), stress tolerance capacities, yield and quality in tomato to improve crop breeding strategies and adapt them to the climatic change scenario. In this study, UAV remote sensing is tested by comparison with leaf-level physiologic and agronomic measurements in a collection including 91 tomato genotypes. These genotypes include long shelf-life (LSL) and non-LSL (CON) Mediterranean landraces, cultivated under well-watered (WW, covering 100% crop evapotranspiration demands) and water deficit (WD, irrigation stopped one month after plantlet transplantation to field) conditions. Aerial remote sensing (including multispectral imaging), leaf gas-exchange, leaf carbon isotope composition (δ13C), fruit production and quality measurements, including total soluble solids and acidity, were performed. Differences between CON and LSL genotypes were observed in leaf-level physiologic and remote sensing measurements under both WW and WD conditions, while for agronomic measurements differences were only found for quality traits under WW conditions. Significant relationships were detected between remote sensing and leaf-level physiologic and agronomic measurements when considering all genotypes and treatments. However, different regressions were described for CON and LSL genotypes, mainly due their different physiologic behavior and response to WD. For instance, for the same NDVI value LSL genotypes showed near 30% lower AN and half gs than CON, and therefore higher intrinsic water use efficiency (WUEi). Also, tomato fruit quality was approached through remote sensing measurements, being correlated with multispectral indices. In conclusion, this study shows how remote sensing can help to optimize tomato physiologic and agronomic phenotyping processes. However, it also points out that the inclusion of genotypes with a different water use efficiency behavior and response to WD lead to a large scattering in the relationships between remote sensing and physiologic and agronomic traits and prevents to obtention of reliable models.

Partial Substitution of K by Na Alleviates Drought Stress and Increases Water Use Efficiency in Eucalyptus Species Seedlings.

Eucalyptus, the most widely planted tree genus worldwide, is frequently cultivated in soils with low water and nutrient availability. Sodium (Na) can substitute some physiological functions of potassium (K), directly influencing plants’ water status. However, the extent to which K can be replaced by Na in drought conditions remains poorly understood. A greenhouse experiment was conducted with three Eucalyptus genotypes under two water conditions (well-watered and water-stressed) and five combination rates of K and Na, representing substitutions of 0/100, 25/75, 50/50, 75/25, and 100/0 (percentage of Na/percentage of K), to investigate growth and photosynthesis-related parameters. This study focused on the positive effects of Na supply since, depending on the levels applied, the Na supply may induce plants to salinity stress (>100 mM of NaCl). Plants supplied with low to intermediate K replacement by Na reduced the critical level of K without showing symptoms of K deficiency and provided higher total dry matter (TDM) than those Eucalyptus seedlings supplied only with K in both water conditions. Those plants supplied with low to intermediate K replacement by Na had improved CO2 assimilation (A), stomatal density (Std), K use efficiency (UEK), and water use efficiency (WUE), in addition to reduced leaf water potential (Ψw) and maintenance of leaf turgidity, with the stomata partially closed, indicated by the higher values of leaf carbon isotope composition (δ13C‰). Meanwhile, combination rates higher than 50% of K replacement by Na led to K-deficient plants, characterized by the lower values of TDM, δ13C‰, WUE, and leaf K concentration and higher leaf Na concentration. There was positive evidence of partial replacement of K by Na in Eucalyptus seedlings; meanwhile, the ideal percentage of substitution increased according to the drought tolerance of the species (Eucalyptus saligna < Eucalyptus urophylla < Eucalyptus camaldulensis).

Foliar heavy metals and stable isotope (δ13C, δ15N) profiles as reliable urban pollution biomonitoring tools

Anthropogenic heavy metal pollution is an important health issue in urban areas, and therefore rapid and inexpensive monitoring in time and space is desirable. This study aimed (i) to assess the suitability of Tilia cordata leaves as a valuable heavy metal bioindicator, including seasonal changes in concentrations and (ii) to evaluate the use of leaf carbon and nitrogen isotope composition (δ13C and δ15N) as novel indicators of urban heavy metal pollution. Leaves were collected from three different pollution intensity locations (Bilbao, Vitoria, and Muskiz) in the Basque Country (northern Spain). Analysis of leaf heavy metals related to traffic emissions and δ13C and δ15N determinations were carried out during July-October 2018. Leaf samples from Bilbao, the most populated and traffic-intense location, showed the highest concentration of heavy metals (mainly from polluted air). Additionally, the two urban areas, Bilbao and Vitoria, showed stronger correlation between these heavy metals, indicating a traffic-related source of emissions. The source of contamination (soil or air) in relation to elements and optimal sampling time is discussed herein. On the other hand, Pearson correlation analysis revealed significant trends between leaf δ13C and δ15N and the studied heavy metals, especially Pb, Cr and Cd, supporting the hypothesis of δ13C and δ15N as tools to distinguish locations according to their heavy metal pollution levels. To our knowledge, this is the first time that δ13C and δ15N have been used as monitoring tools in heavy metal pollution and consequently more research is still needed to calibrate this tool through extensive vegetation screening.

Effects of drought regimes on growth and physiological traits of a typical shrub species in subtropical China

Drought represents the most important limiting factor controlling performance of subtropical plants, leading to reduced growth and die-offs. However, the mechanisms underlying growth and physiological responses of subtropical woody plants to different types of drought are poorly understood. Here, potted seedlings of a typical evergreen shrub species Ardisia lindleyana D. Dietr. in subtropical China, were exposed to three water regimes: well watered (WW), fast drought (FD) and slow drought (SD) until death. Leaf gas exchange and water potential were measured over the experimental period. Dry mass production and allocation, leaf nitrogen and carbon isotopic composition, and non-structural carbohydrates (NSC) were measured at mortality. Results showed that growth, leaf water potential and photosynthesis were significantly reduced in both drought regimes. FD induced significant increase of root soluble sugars, but promoted significant depletion of leaf and root starch, finally displaying depletion of root NSC. By contrast, SD led to significant depletion of stem and root starch, whereas the accumulation of soluble sugars in stem and root was significantly higher than that of WW, thereby resulting in no significant change of NSC. Neither FD nor SD has affected leaf carbon isotopic composition or nitrogen concentration at mortality. Our results demonstrate the divergent effects of two different drought treatments on carbon and water economy of A. lindleyana, which may have implications for understanding the mortality mechanism of understory plants in subtropical forests in China.

Mesophyll CO2 conductance and leakiness are not responsive to short‐ and long‐term soil water limitations in the C4 plant Sorghum bicolor

Breeding economically important C4 crops for enhanced whole-plant water-use efficiency (WUEplant ) is needed for sustainable agriculture. WUEplant is a complex trait and an efficient phenotyping method that reports on components of WUEplant , such as intrinsic water-use efficiency (WUEi , the rate of leaf CO2 assimilation relative to water loss via stomatal conductance), is needed. In C4 plants, theoretical models suggest that leaf carbon isotope composition (δ13 C), when the efficiency of the CO2 -concentrating mechanism (leakiness, ϕ) remains constant, can be used to screen for WUEi . The limited information about how ϕ responds to water limitations confines the application of δ13 C for WUEi screening of C4 crops. The current research aimed to test the response of ϕ to short- or long-term moderate water limitations, and the relationship of δ13 C with WUEi and WUEplant , by addressing potential mesophyll CO2 conductance (gm ) and biochemical limitations in the C4 plant Sorghum bicolor. We demonstrate that gm and ϕ are not responsive to short- or long-term water limitations. Additionally, δ13 C was not correlated with gas-exchange estimates of WUEi under short- and long-term water limitations, but showed a significant negative relationship with WUEplant . The observed association between the δ13 C and WUEplant suggests an intrinsic link of δ13 C with WUEi in this C4 plant, and can potentially be used as a screening tool for WUEplant in sorghum.

Shifts in carbon and nitrogen stable isotope composition and epicuticular lipids in leaves reflect early water-stress in vineyards

Changes in leaf carbon and nitrogen isotope composition (δ13C and δ15N values) and the accumulation of epicuticular lipids have been associated with plant responses to water stress. We investigated their potential use as indicators of early plant water deficit in two grapevine (Vitis vinifera L.) cultivars, Chasselas and Pinot noir, that were field-grown under well-watered and water-deficient conditions. We tested the hypothesis that the bulk δ13C and δ15N values and the concentrations of epicuticular fatty acids may change in leaves of similar age with the soil water availability. For this purpose, leaves were sampled at the same position in the canopy at different times (phenological stages) during the 2014 growing season. Bulk dry matter of young leaves from flowering to veraison had higher δ13C values, higher total nitrogen content, and lower δ15N values than old leaves. In both cultivars, δ15N values were strongly correlated with plant water deficiency, demonstrating their integration of the plant water stress response. δ13C values recorded the water deficiency only in those plants that had not received foliar organic fertilization. The soil water deficiency triggered the accumulation of C>26 fatty acids in the cuticular waxes. The compound-specific isotope analysis (CSIA) of fatty acids from old leaves showed an increase in δ13C among the C16-C22 chains, including stress signaling linoleic and linolenic acids. Our results provide evidence for leaf 13C-enrichment, 15N-depletion, and enhanced FA-chain elongation and epicuticular accumulation in the grapevine response to water stress. The leaf δ13C and δ15N values, and the concentration of epicuticular fatty acids can be used as reliable and sensitive indicators of plant water deficit even when the level of water stress is low to moderate. They could also be used, particularly the more cost-efficient δ13C and δ15N measurements, for periodic biogeochemical mapping of the plant water availability at the vineyard and regional scale.

The Use of a Tomato Landrace as Rootstock Improves the Response of Commercial Tomato under Water Deficit Conditions

Grafting onto drought tolerant rootstocks has been proposed as a useful strategy to overcome future water scarcity periods. The ‘de Ramellet’ tomato is a drought tolerant landrace selected under semiarid Mediterranean summer conditions under rain-fed or low irrigation. In this manuscript, the responses of a commercial hybrid ‘de Ramellet’ genotype grafted onto a traditional ‘de Ramellet’ (RL) and a commercial Maxifort (Mx) tomato rootstocks under commercial greenhouse conditions are studied. Non-grafted (NON) and self-grafted (SELF) plants were used as controls. Two water regimes were established: well-watered (WW, covering plant water demands) and water deficit (WD, reducing 50% irrigation as compared to WW). The results confirm an improvement in agronomic performance of Mx as compared to NON, but also show a similar improving effect of RL. Grafting enhanced plant growth regardless of the rootstock under WW conditions. Similarly, water-use efficiency (assessed as leaf carbon isotope composition) increased in grafted plants under WD treatment as compared to NON. Despite the lack of significant differences, RL tended to promote higher fruit production and fruit number than Mx, irrespective of the water treatment, whereas RL was the single graft combination with higher fruit production than NON under WD. In conclusion, the results uncover the potential of drought-adapted landraces to be used as rootstocks in order to increase plant growth and fruit production under both well-watered and water deficit cultivation conditions.

Post-fire effects on development of leaves and secondary vascular tissues in Quercus pubescens.

An increased frequency of fire events on the Slovenian Karst is in line with future climate change scenarios for drought-prone environments worldwide. It is therefore of the utmost importance to better understand tree-fire-climate interactions for predicting the impact of changing environment on tree functioning. To this purpose, we studied the post-fire effects on leaf development, leaf carbon isotope composition (δ13C), radial growth patterns and the xylem and phloem anatomy in undamaged (H-trees) and fire-damaged trees (F-trees) of Quercus pubescens Willd. with good resprouting ability in spring 2017, the growing season after a rangeland fire in August 2016. We found that the fully developed canopy of F-trees reached only half of the leaf area index values measured in H-trees. Throughout the season, F-trees were characterized by higher water potential and stomatal conductivity and achieved higher photosynthetic rates compared to unburnt H-trees. The foliage of F-trees had more negative δ13C values than those of H-trees. This reflects that F-trees less frequently meet stomatal limitations due to reduced transpirational area and more favourable leaf-to-root ratio. In addition, the growth of leaves in F-trees relied more on the recent photosynthates than on reserves due to the fire disturbed starch accumulation in the previous season. Cambial production stopped 3weeks later in F-trees, resulting in 60 and 22% wider xylem and phloem increments, respectively. A novel approach by including phloem anatomy in the analyses revealed that fire caused changes in conduit dimensions in the early phloem but not in the earlywood. However, premature formation of the tyloses in the earlywood vessels of the youngest two xylem increments in F-trees implies that xylem hydraulic integrity was also affected by heat. Analyses of secondary tissues showed that although xylem and phloem tissues are interlinked changes in their transport systems due to heat damage are not necessarily coordinated.

A genetic link between leaf carbon isotope composition and whole-plant water use efficiency in the C4 grass Setaria.

Genetic selection for whole-plant water use efficiency (yield per transpiration; WUEplant ) in any crop-breeding programme requires high-throughput phenotyping of component traits of WUEplant such as intrinsic water use efficiency (WUEi ; CO2 assimilation rate per stomatal conductance). Measuring WUEi by gas exchange measurements is laborious and time consuming and may not reflect an integrated WUEi over the life of the leaf. Alternatively, leaf carbon stable isotope composition (δ13 Cleaf ) has been suggested as a potential time-integrated proxy for WUEi that may provide a tool to screen for WUEplant . However, a genetic link between δ13 Cleaf and WUEplant in a C4 species has not been well established. Therefore, to determine if there is a genetic relationship in a C4 plant between δ13 Cleaf and WUEplant under well watered and water-limited growth conditions, a high-throughput phenotyping facility was used to measure WUEplant in a recombinant inbred line (RIL) population created between the C4 grasses Setaria viridis and S. italica. Three quantitative trait loci (QTL) for δ13 Cleaf were found and co-localized with transpiration, biomass accumulation, and WUEplant . Additionally, WUEplant for each of the δ13 Cleaf QTL allele classes was negatively correlated with δ13 Cleaf , as would be predicted when WUEi influences WUEplant . These results demonstrate that δ13 Cleaf is genetically linked to WUEplant , likely to be through their relationship with WUEi , and can be used as a high-throughput proxy to screen for WUEplant in these C4 species.

Exploring molecular evolution of Rubisco in C3 and CAM Orchidaceae and Bromeliaceae

BackgroundThe CO2-concentrating mechanism associated to Crassulacean acid metabolism (CAM) alters the catalytic context for Rubisco by increasing CO2 availability and provides an advantage in particular ecological conditions. We hypothesized about the existence of molecular changes linked to these particular adaptations in CAM Rubisco. We investigated molecular evolution of the Rubisco large (L-) subunit in 78 orchids and 144 bromeliads with C3 and CAM photosynthetic pathways. The sequence analyses were complemented with measurements of Rubisco kinetics in some species with contrasting photosynthetic mechanism and differing in the L-subunit sequence.ResultsWe identified potential positively selected sites and residues with signatures of co-adaptation. The implementation of a decision tree model related Rubisco specific variable sites to the leaf carbon isotopic composition of the species. Differences in the Rubisco catalytic traits found among C3 orchids and between strong CAM and C3 bromeliads suggested Rubisco had evolved in response to differing CO2 concentration.ConclusionsThe results revealed that the variability in the Rubisco L-subunit sequence in orchids and bromeliads is composed of coevolving sites under potential positive adaptive signal. The sequence variability was related to δ13C in orchids and bromeliads, however it could not be linked to the variability found in the kinetic properties of the studied species.

Effects of Soil Microbes on Functional Traits of Loblolly Pine (Pinus taeda) Seedling Families From Contrasting Climates.

Examining factors that influence seedling establishment is essential for predicting the impacts of climate change on tree species’ distributions. Seedlings originating from contrasting climates differentially express functional traits related to water and nutrient uptake and drought resistance that reflect their climate of origin and influence their responses to drought. Soil microbes may improve seedling establishment because they can enhance water and nutrient uptake and drought resistance. However, the relative influence of soil microbes on the expression of these functional traits between seedling families or populations from contrasting climates is unknown. To determine if soil microbes may differentially alter functional traits to enhance water and nutrient uptake and drought resistance between dry and wet families, seeds of loblolly pine families from the driest and wettest ends of its geographic range (dry, wet) were planted in sterilized sand (controls) or in sterilized sand inoculated with a soil microbial community (inoculated). Functional traits related to seedling establishment (germination), water and nutrient uptake and C allocation (root:shoot biomass ratio, root exudate concentration, leaf C:N, leaf N isotope composition (δ15N)), and drought resistance (turgor loss point, leaf carbon isotope composition (δ13C)) were measured. Then, plants were exposed to a drought treatment and possible shifts in photosynthetic performance were monitored using chlorophyll fluorescence. Inoculated plants exhibited significantly greater germination than controls regardless of family. The inoculation treatment significantly increased root:shoot biomass ratio in the wet family but not in the dry family, suggesting soil microbes alter functional traits that improve water and nutrient uptake more so in a family originating from a wetter climate than in a family originating from a drier climate. Microbial effects on photosynthetic performance during drought also differed between families, as photosynthetic performance of the dry inoculated group declined fastest. Regardless of treatment, the dry family exhibited a greater root:shoot biomass ratio, root exudate concentration, and leaf δ15N than the wet family. This indicates that the dry family allocated more resources belowground than the wet and the two family may have used different sources of plant available N, which may be related to their contrasting climates of origin and influence their drought resistance. Examination of variation in impacts of soil microbes on seedling physiology improves efforts to enhance seedling establishment and beneficial plant-microbe interactions under climate change.

High nutrient uptake efficiency and high water use efficiency facilitate the spread of Stellera chamaejasme L. in degraded grasslands

BackgroundStellera chamaejasme L. is a poisonous plant widely distributes in degraded grasslands in China. The mechanism underlying its spread remains unknown. In some degraded grasslands, S. chamaejasme has gradually replaced previous dominant species, such as Leymus chinensis, Stipa krylovii, Artemisia eriopoda on typical steppes. Apart from its unpalatability by livestock, we hypothesized that the survival strategy (nutrient uptake and water use efficiency) of S. chamaejasme in degraded grasslands could be distinct from other coexisting species in the community. Recently, ecological stoichiometry has been suggested as a new approach for studying the demand for natural resources of plants in a changing world, and the leaf carbon isotopic composition (δ13C leaf) as a rapid and effective high throughput phenotyping method for water use efficiency (WUE), both of which can reveal the survival and adaptive strategies of plants. Therefore, in this study we aimed to fill the knowledge gap concerning ecological stoichiometry in the leaf, stem, and root of S. chamaejasme and its surrounding soil on grasslands with different degrees of degradation, and comparing the leaf nutrient content and δ13C of S. chamaejasme with the coexisting species (L. chinensis, S. krylovii, A. eriopoda) in the communities. Toward this goal, we conducted a field survey in which plants and soils were sampled from four different degraded grasslands on typical steppes in China.ResultsOur results showed that there is no significant difference of carbon content (C%) and nitrogen content (N%) in leaves of S. chamaejasme in different degraded grasslands, and all element contents and element ratios in stems did not differ significantly. Meanwhile, ecological stoichiometry of S. chamaejasme is distinct from the coexisting species, with low C%, high N% and phosphorus content (P%) in the leaf, indicating high nutrient uptake efficiency of S. chamaejasme in nutrient-poor environments like degraded grasslands. Additionally, S. chamaejasme showed significant higher WUE than other species.ConclusionsOur results indicated that high nutrient uptake efficiency and high WUE of S. chamaejasme might together contribute to the spread of S. chamaejasme in degraded grasslands.

Contrasting water sources and water-use efficiency in coexisting desert plants in two saline-sodic soils in northwest China.

Soil degradation resulting from various types of salinity is a major environmental problem, especially in arid and semiarid regions. Exploring the water-related physiological traits of halophytes is useful for understanding the mechanisms of salt tolerance. This knowledge could be used to rehabilitate degraded arid lands. To investigate whether different types of salinity influence the water sources and water-use efficiency of desert plants (Karelinia caspia, Tamarix hohenackeri, Nitraria sibirica, Phragmites australis, Alhagi sparsifolia, Suaeda microphylla, Kalidium foliatum) in natural environments, we measured leaf gas exchange, leaf carbon and xylem oxygen isotope composition and soil oxygen isotope composition at neutral saline-sodic site (NSS) and alkaline saline-sodic site (ASS) in northwest China. The studied plants had different xylem water oxygen isotope compositions (δ18 O) and foliar carbon isotope compositions (δ13 C), indicating that desert plants coexist through differentiation in water use patterns. Compared to that at the NSS site, the stem water in K.caspia, A.sparsifolia and S.microphylla was depleted in 18 O at the ASS site, which indicates that plants can switch to obtain water from deeper soil layers when suffering environmental stress from both salinity and alkalinisation. Alhagi sparsifolia had higher δ13 C at the ASS site than at the NSS site, while K.caspia and S.microphylla had lower δ13 C, which may have resulted from interspecific differences in plant alkali and salt tolerance ability. Our results suggest that under severe salinity and alkalinity, plants may exploit deeper soil water to avoid ion toxicity resulting from high concentrations of soluble salts in the superficial soil layer. In managed lands, it is vital to select and cultivate different salt-tolerant or alkali-tolerant plant species in light of local conditions.