Leaf Carbon Isotope Composition Research Articles

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.

The physiological response of ‘Hass’ avocado to salinity as influenced by rootstock

With increasing demands on both potable and agricultural water supplies, drought, and extreme temperatures worldwide, agricultural production is challenged with reduced water availability and lower water quality. Salinity, which is associated with low water quality is a critical issue for California avocado growers and, coupled with avocado root rot, threatens the long-term sustainability of the industry since avocados (Persea americana Mill.) are known to be extremely salt sensitive. Salt tolerance of the ‘Hass’ variety, the most commonly grown scion in California, is influenced by rootstock. We investigated ‘Hass’ scions grafted onto three different avocado rootstocks under control (irrigation using water with EC = 0.65 dS/m) and salinity (irrigation using water with EC = 1.5 dS/m) conditions. Results indicated that, compared to control conditions, the irrigation of avocado trees using water with EC = 1.5 dS/m increased canopy damage by 44%, reduced survival by half of the trees tested, and caused yield losses of more than 63%. Avocado leaves visibly damaged by the salinity treatment (named as partially burned or PB leaves) experienced photoinhibition, and reduction of photosynthetic rate and water-use efficiency, suggesting that the poor performance in carbon assimilation contributed to reductions in yield and increases in mortality. The salinity treatment did not cause water stress and the poor performance of treated trees was attributable to chloride accumulation previously reported. Leaf carbon isotopic composition was affected in trees under salinity treatment by increasing the values of δ13C however, this affect was nor correlated with water-use efficiency. Overall, ‘R0.05’, ‘PP40’ and ‘Dusa’ performed similarly and, considering the conditions of the experiment and the intrinsic susceptibility of avocado trees to salinity, were superior to all other rootstocks tested. Future screenings for salinity tolerant rootstocks are required to improve yield when poor quality soil or water is used. Overall, our results showed a coordination between the physiological performance, health and productivity of the ‘Hass’ scion and how these parameters were negatively affected by salinity.

Evaluating Leaf Wax and Bulk Leaf Carbon Isotope Surrogates for Water Use Efficiency and Grain Yield in Winter Wheat

Bulk leaf carbon isotopic composition (δ13Cbulk) has been widely used to investigate leaf level water use efficiency (WUEl) in efforts to boost grain yield relative to crop water use. Although widely used for isotopic analyses, the bulk leaf represents a complex mixture of compounds. Single‐compound isotopic analyses carry diagnostic advantages over bulk analyses in a range of applications and may also serve as surrogates for WUEl and grain yield in crops. This study tests whether compound‐specific carbon and hydrogen isotopes of leaf wax n‐alkanes (δ13Calk and δDalk) and n‐alcohols (δ13Calc) could be used as surrogates for WUEl and grain yield using conventional δ13Cbulk as a reference. Ten winter wheat (Triticum aestivum L.) cultivars were planted under two irrigation treatments (full and deficit irrigation) at Uvalde (wet location) and Amarillo (dry location), TX, during two growing seasons. There were significant relationships between δ13Calk or δDalk and δ13Cbulk, indicating they can all serve as surrogates for WUEl in most cases. Compared with δ13Cbulk, we found stronger relationships between δ13Calk at Uvalde or δDalk under deficit irrigation at Amarillo and grain yield. The δ13Calk also had higher broad‐sense heritability than δ13Cbulk, indicating larger cultivar effects in δ13Calk than in δ13Cbulk. In contrast, the δ13Calc was not consistently related with δ13Cbulk or grain yield. Our study introduces the idea that δ13Calk and δDalk may supplement conventional δ13Cbulk with potential to assist in the breeding process when selecting for high‐WUE and high‐yielding cultivars.

The ideal percentage of K substitution by Na in Eucalyptus seedlings: Evidences from leaf carbon isotopic composition, leaf gas exchanges and plant growth

Potassium (K) is the most required macronutrient by Eucalyptus, while sodium (Na) can partially substitute some physiological functions of K and have a positive response on plant growth in K-depleted tropical soils. However, the right percentage of K substitution by Na is not yet known for Eucalyptus seedlings, since a few experiments have only compared treatments receiving K or Na. This study evaluated five levels of Na supply (0, 0.45, 0.90, 1.35 and 1.80 mM) as substitution for K in Eucalyptus seedlings grown in nutrient solution. Plants growth, biomass, K-nutritional status, leaf gas exchange, leaf carbon isotopic composition (δ13C ‰), leaf water potential (Ψw), leaf area (LA), stomatal density (SD) and water use efficiency (WUE) were measured. The highest total biomass yield was achieved by the Na estimated rate of 0.25 mM, corresponding to a leaf K: Na ratio of 3.41, and having the lowest δ13C values. Conversely, the highest Na rate (1.8 mM) induced K deficiency symptoms, lower growth, reduced total dry matter yield, leaf gas exchange, LA, SD and a higher δ13C, which presented a trend to an inverse correlation with CO2 assimilation rate (A), WUE and shoot dry matter. Collectively, our results conclude that substitution of 25% of K by Na (0.45 mM of Na) provided significant gains in nutritional status and positive plant physiological responses by increasing WUE, stomatal diffusion, and by augmenting CO2 uptake efficiency. This nutritional management can therefore be an alternative option to optimize yields and resource use efficiencies in Eucalyptus cultivation.

Evaluation of leaf carbon isotopes and functional traits in avocado reveals water-use efficient cultivars

Plant water-use efficiency (WUE) describes the ratio of carbon gain to water loss during photosynthesis. It has been shown that WUE varies among crop genotypes, and crops with high WUE can increase agricultural production in the face of finite water supply. We used measures of leaf carbon isotopic composition to compare WUE among 24 cultivars of Persea americana Mill (avocado) to determine genotypic variability in WUE, identify potentially efficient cultivars, and to better understand how breeding for yield and fruit quality has affected WUE. To validate carbon isotope measurements, we also measured leaf photosynthetic gas exchange of water and carbon, and leaf and stem functional traits of cultivars with the highest and lowest carbon isotope composition to quantify actual WUE ranges during photosynthesis. Our results indicate large variation in WUE among cultivars and coordination among functional traits that structure trade-offs in water loss and carbon gain. Identifying cultivars of subtropical tree crops that are efficient in terms of water use is critical for maintaining a high level of food production under limited water supply. Plant functional traits, including carbon isotopes, appear to be an effective tool for identifying species or genotypes with particular carbon and water economies in managed ecosystems.

Leaf carbon and oxygen isotopes are coordinated with the leaf economics spectrum in Mediterranean rangeland species

Abstract The leaf economics spectrum (LES) describes covariation in traits relevant to carbon and nutrient economics across plant species, but much less is known about the relationship between the LES and leaf water economy. We propose an approach combining the measurement of two leaf traits related to water‐use economy, leaf carbon (δ13C) and oxygen (δ18O) isotopic composition, and the measurement of leaf morphological and nutrient traits to investigate the link between leaf carbon and nutrient economics and water use. We tested the relationships between leaf traits linked to carbon and nutrient use within the LES and water‐use traits using leaf δ18O as a proxy of stomatal conductance (gs) and δ13C as a proxy of intrinsic water‐use efficiency (WUEi) across 15 Mediterranean rangeland species grown in an irrigated common garden and in a natural rangeland in Southern France. The target species spanned a wide range of variation in leaf morphological and nutrient trait values and a wide range of leaf δ18O and δ13C values. Principal component analysis revealed multiple associations among leaf morphology, nutrients and isotopic composition, with the first axis alone explaining 56.0% of the total variation across species. Leaf δ18O and δ13C covaried with leaf morphology and leaf nutrient concentrations along a single resource‐use axis. Species with high leaf δ18O and δ13C (low gs and high WUEi) exhibited a resource‐conservative strategy (high leaf dry matter content, low leaf N, P and K), whereas species with low leaf δ18O and δ13C (high gs and low WUEi) showed a more resource‐acquisitive strategy (high specific leaf area and leaf N, P and K). These leaf trait syndromes and resource‐use strategies were strongly conserved across sites with contrasting environmental conditions, indicating that foliar δ18O and δ13C can be included as an integral part of the LES for this set of rangeland species. Overall, the data suggest a tight coupling and coordination between water, carbon and nutrient‐use strategies across herbaceous plant species. A dual δ18O and δ13C isotope approach combined with LES trait measurements is a promising tool to more comprehensively assess the diversity of resource‐use strategies among coexisting plant species. A plain language summary is available for this article.

Biochemical and transcriptomic analysis of maize diversity to elucidate drivers of leaf carbon isotope composition.

Carbon isotope discrimination is used to study CO2 diffusion, substrate availability for photosynthesis, and leaf biochemistry, but the intraspecific drivers of leaf carbon isotope composition (δ13C) in C4 species are not well understood. In this study, the role of photosynthetic enzymes and post-photosynthetic fractionation on δ13C (‰) was explored across diverse maize inbred lines. A significant 1.3‰ difference in δ13C was observed between lines but δ13C did not correlate with in vitro leaf carbonic anhydrase (CA), phosphoenolpyruvate carboxylase (PEPC), or ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity. RNA-sequencing was used to identify potential differences in post-photosynthetic metabolism that would influence δ13C; however, no correlations were identified that would indicate significant differences in post-photosynthetic fractionation between lines. Variation in δ13C has been observed between C4 subtypes, but differential expression of NADP-ME and PEP-CK pathways within these lines did not correlate with δ13C. However, co-expression network analysis provided novel evidence for isoforms of C4 enzymes and putative transporters. Together, these data indicate that diversity in maize δ13C cannot be fully explained by variation in CA, PEPC, or Rubisco activity or gene expression. The findings further emphasise the need for future work exploring the influence of stomatal sensitivity and mesophyll conductance on δ13C in maize.

Cell anatomy and leaf δ13C as proxies for shading and canopy structure in a Miocene forest from Ethiopia

Plant fossils are most commonly preserved as isolated organs, making it difficult to determine plant life habit or ecosystem structure from fossils. In particular, paleoecologists have struggled to reconstruct forest canopy structure, a character that fundamentally influences hydrology, nutrient cycling, and plant and animal life. Analyses utilizing cellular morphology and leaf carbon isotope composition have been proposed to reconstruct light regime, itself a proxy for canopy structure, and we apply these proxies to exquisitely preserved leaf fossils from the early Miocene Mush Valley site in central Ethiopia. Epidermal cell wall undulation (undulation index, UI) and carbon isotope values (δ13C) were measured for 21 fossil leaves of a legume morphospecies, “Legume 1”. Five leaves of a second legume morphospecies were also analyzed using the same procedures. Carbon isotope ratios and total organic carbon content were measured for 85 additional fossil leaves belonging to at least nine morphospecies. A large range of both leaf δ13C and UI values were obtained for Legume 1, indicating that different leaves were exposed to different amounts of light, as would be expected in a closed-canopy forest. However, Legume 1 leaf UI values do not correlate with leaf δ13C values, implying that one or both of these variables is driven by factors other than light exposure. Additional modern calibrations are needed to determine the key environmental variables for each measure, as well as the influence of forest openings on preserved signatures.

Canopy gradients in leaf functional traits for species that differ in growth strategies and shade tolerance

In temperate deciduous forests, vertical gradients in leaf mass per area (LMA) and area-based leaf nitrogen (Narea) are strongly controlled by gradients in light availability. While there is evidence that hydrostatic constraints on leaf development may diminish LMA and Narea responses to light, inherent differences among tree species may also influence leaf developmental and morphological response to light. We investigated vertical gradients in LMA, Narea and leaf carbon isotope composition (δ13C) for three temperate deciduous species (Carpinus caroliniana Walter, Fagus grandifolia Ehrh., Liriodendron tulipifera L.) that differed in growth strategy (e.g., indeterminate and determinate growth), shade tolerance and leaf area to sapwood ratio (Al:As). Leaves were sampled across a broad range of light conditions within three vertical layers of tree crowns to maximize variation in light availability at each height and to minimize collinearity between light and height. All species displayed similar responses to light with respect to Narea and δ13C, but not for LMA. Light was more important for gradients in LMA for the shade-tolerant (C. caroliniana) and -intolerant (L. tulipifera) species with indeterminate growth, and height (e.g., hydrostatic gradients) and light were equally important for the shade-tolerant (F. grandifolia) species with determinate growth. Fagus grandifolia had a higher morphological plasticity in response to light, which may offer a competitive advantage in occupying a broader range of light conditions throughout the canopy. Differences in responses to light and height for the taller tree species, L. tulipifera and F. grandifolia, may be attributed to differences in growth strategy or Al:As, which may alter morphological and functional responses to light availability. While height was important in F. grandifolia, height was no more robust in predicting LMA than light in any of the species, confirming the strong role of light availability in determining LMA for temperate deciduous species.

Determination of leaf carbon isotope discrimination in C4 plants under variable N and water supply

Understanding the mechanisms underlying variations in carbon isotope discrimination (Δ) in C4 plants is critical for predicting the C3/C4 ratio in C3/C4 mixed grassland. The value of Δ is determined by bundle sheath leakiness (Ф) and the ratio of intercellular to ambient CO2 concentration (Ci/Ca). Leaf nitrogen concentration (Nleaf) is considered a driver of Δ in C4 plants. However, little is known about how Nleaf affects Ф and Ci/Ca, and subsequently Δ. Here leaf carbon isotope composition, Nleaf, Ф, and leaf gas exchange were measured in Cleistogenes squarrosa, a dominant C4 species in the Inner Mongolia grassland. Δ remained relatively stable under variable N and water supply. Higher N supply and lower water supply increased Nleaf, stimulated photosynthesis and further decreased Ci/Ca. High N supply increased Ф, which responded weakly to water supply. Nleaf exerted similar effects on Ci/Ca and on Ф in the field and pot experiments. Pooling all the data, Nleaf explained 73% of the variation in Ci/Ca. Overall, both Ф and Ci/Ca determined Δ; however, the contribution of Ф was stronger. Nleaf influenced Δ primarily though Ci/Ca, rather than Ф. Ф should be considered in estimating Δ of C4 endmember.

Post-fire environments are favourable for plant functioning of seeder and resprouter Mediterranean shrubs, even under drought.

Understanding how drought affects seeder and resprouter plants during post-fire regeneration is important for the anticipation of Mediterranean vegetation vulnerability in a context of increasing drought and fire caused by climate change. A Mediterranean shrubland was subjected to various drought treatments (including 45% rainfall reduction, 7months droughtyr-1 ), before and after experimental burning, by means of a rainout-shelter system with an irrigation facility. Predawn shoot water potential (Ψpd ), relative growth rate (RGR), specific leaf area (SLA) and bulk leaf carbon isotopic composition (δ13 C) were monitored in the main woody species during the first 3yr after fire. Cistus ladanifer seedlings showed higher Ψpd , RGR and SLA, and lower δ13 C, than unburned plants during the first two post-fire years. Seedlings under drought maintained relatively high Ψpd , but suffered a decrease in Ψpd and RGR, and an increase in δ13 C, relative to control treatments. Erica arborea, E.scoparia and Phillyrea angustifolia resprouts had higher Ψpd and RGR than unburned plants during the first post-fire year. Resprouters were largely unaffected by drought. Overall, despite marked differences between the two functional groups, post-fire environments were favourable for plant functioning of both seeder and resprouter shrubs, even under the most severe drought conditions implemented.

Water sources and water‐use efficiency of desert plants in different habitats in Dunhuang, NW China

AbstractTo understand habitat associated differences in desert plant water‐use patterns, water stable oxygen isotope composition was used to determine water source and leaf carbon isotope composition (δ13C) was used to estimate long‐term water‐use efficiency in three typical habitats (saline land, sandy land and Gobi) in Dunhuang. The primary findings are: (1) in the three habitats, plant species used mainly deep soil water (>120 cm), except for Kalidium foliatum in the saline land, which relied primarily on 0–40 cm soil water; (2) in the saline land and Gobi habitat, Alhagi sparsifolia had the most negative foliar δ13C; in the sandy land, Elaeagnus angustifolia leaf was enriched in 13C than the other three species in 2011, but no species differences in foliar δ13C was observed among the four species in 2012; (3) common species (Tamarix ramosissima and A. sparsifolia) may alter their water sources to cope with habitat differences associated changes in soil water availability with deeper water sources were used in the Gobi habitat with lower soil water content (SWC) compared to in the saline land and sandy land; (4) we detected significant habitat differences in foliar δ13C in A. sparsifolia which may have resulted from differences in SWC and soil electrical conductivity. However, no habitat differences in foliar δ13C were observed in T. ramosissima, which may attribute to the strong genetic control in T. ramosissima or the ability to access stable deep soil water. Overall, the results suggest that extremely arid climate, root distribution and soil properties worked together to determine plant water uptake in Dunhuang area.

Impact of genetic variation and long-term limited water availability on the ecophysiology of young Sitka spruce (Picea sitchensis (Bong.) Carr.).

Future limited water availability may reduce the potential of tree improvement to increase timber yields. We investigated ecophysiological variation between full-sibling families of Sitka spruce (Picea sitchensis (Bong.) Carr.) growing under contrasting water availability conditions: control (optimal) water availability and limited water availability. One-year-old seedlings of nine improved families plus an unimproved seed lot were grown in pots in a greenhouse and the two water availability treatments imposed via drip irrigation. Whole-plant water use varied between families. Stomatal conductance and the light-saturated quantum yield of photosystem II at times differed between families, but not consistently. Certain families showed considerably greater increases in electron transport rate with increasing photosynthetically active radiation. Limited water availability resulted in reduced branch water potential, leaf stomatal conductance and transpiration per unit leaf area, and increased whole-plant water-use efficiency, in all genetic material. The responses of plant water use and leaf carbon isotope composition to water limitation, were, however, initially influenced by variation in vigour between families-with conservative growth in some material slowing the decline in substrate moisture content. As the duration of water deficit extended, these variables showed a more uniform response across families. Between-family variation in physiological mechanisms of drought tolerance was not detected. Thus, for Sitka spruce, assessing juvenile material may not allow selection to prevent reductions in productivity associated with long-term sub-optimal growing conditions, but screening for conservative growth (within families as well as between families) may be beneficial where survival of relatively short-term water limitation is the primary concern.

Variation in biochemical characteristics, water status, stomata features, leaf carbon isotope composition and its relationship to water use efficiency in pistachio (Pistacia vera L.) cultivars under drought stress condition

Pistachio (P. vera L., Anacardiaceae) is cultivated in regions where soil water deficits and salinity conditions are higher than usual. Despite adult pistachio trees having been documented as being drought tolerant; there is only a limited understanding of the physiological mechanisms pistachio cultivars use to survive drought. We therefore, carried out a greenhouse experiment to evaluate the effects of three osmotic drought stress treatments including; control conditions (−0.1MPa), moderate (−0.75MPa) and severe drought (−1.5MPa) stress, using PEG 6000 for 14days with a subsequent two weeks recovery period. Carbohydrate contents, relative water content, water use efficiency, stomatal characteristics, and nitrogen and carbon isotope composition were evaluated in three Iranian pistachio cultivars, i.e. Akbari, Kaleghochi and Ohadi.Results revealed that the drought stress treatments induced osmotic adjustment by carbohydrate accumulation. Both drought stress treatments increased soluble carbohydrate and starch contents of the leaves. Relative water content was only affected by drought stress in Kaleghochi. Stomatal density and morphology varied with pistachio cultivars but was hardly affected by the stress treatments.Drought stress significantly increased the overall mean of water use efficiency (intrinsic and instantaneous WUE). There were no significant differences between the leaf carbon isotope compositions of all pistachio cultivars under stress. This indicates that this relation may not be used to determine pistachio cultivars with appropriate WUE via leaf carbon isotope composition within the time frame of the experiment. Leaf nitrogen isotope composition decreased under drought stress regardless off the cultivar.

Using leaf δ13C and photosynthetic parameters to understand acclimation to irradiance and leaf age effects during tropical forest regeneration

Regenerating forests are important for the maintenance of tropical biodiversity. Forest management in fragments of Atlantic forest in Brazil includes removal of exotic eucalyptus trees that were once part of plantations, in order to reestablish native flora. However, it is unclear how native tree saplings regenerating under former plantations respond to abrupt changes in environmental conditions associated with exotic tree removal. We used leaf carbon isotope composition (δ13C) and photosynthetic parameters to evaluate physiological responses of native tree saplings to canopy opening. We analyzed young and mature leaves of the three most representative species of regenerating trees (Byrsonima sericea, Siparuna guianensis, Xylopia sericea) in one secondary forest fragment and three managed areas that form an irradiance gradient (9, 85, 230 and 550μmolm−2s−1) in Brazilian Atlantic forest. Eucalyptus removal increased photosynthetic CO2 assimilation and stomatal conductance in mature leaves of all species, but there was no change in intercellular CO2 concentration. In young leaves, two species showed increasing A and one species showed increasing gs in response to canopy opening. Leaf δ13C did not vary significantly among species, but site and age affected δ13C, as leaves from shaded sites showed lower δ13C values (around −33‰) than leaves from lighter sites (around −30‰), and young leaves showed higher δ13C values (around −30‰) than mature leaves (around −32‰). Mature leaves showed greater photosynthesis and stomatal conductance than young leaves. The sensitivity of young leaf δ13C to irradiance increases suggests that δ13C in these organs is controlled not only through carbon imported to new leaves during growth, but also through direct responses of stomatal control and carboxylation as these young leaves develop their photosynthetic competency. Young and mature leaves showed decreased total chlorophyll/carotenoids with increasing irradiance, indicating acclimation capacity from early developmental phases. Young leaves in high irradiance sites showed susceptibility to irradiance stress (Fv/Fm around 0.7), but values for mature leaves did not show high irradiance stress (Fv/Fm around 0.8). In conclusion, forest management affected leaf δ13C of the main regenerating understory species, with site effects being more important than species-specific features for photosynthetic performance. The data also indicate that these species are resilient to forest management that includes exotic eucalyptus canopy tree removal. In this context, carbon stable isotopes can be considered as recorders of ecological change and can be used to study the effects of management on forest regeneration and photosynthetic competency.

Taxonomic and ecological relevance of the chlorophyll a fluorescence signature of tree species in mixed European forests.

The variability of chlorophyll a fluorescence (ChlF) parameters of forest tree species was investigated in 209 stands belonging to six European forests, from Mediterranean to boreal regions. The modifying role of environmental factors, forest structure and tree diversity (species richness and composition) on ChlF signature was analysed. At the European level, conifers showed higher potential performance than broadleaf species. Forests in central Europe performed better than those in Mediterranean and boreal regions. At the site level, homogeneous clusters of tree species were identified by means of a principal component analysis (PCA) of ChlF parameters. The discrimination of the clusters of species was influenced by their taxonomic position and ecological characteristics. The species richness influenced the tree ChlF properties in different ways depending on tree species and site. Tree species and site also affected the relationships between ChlF parameters and other plant functional traits (specific leaf area, leaf nitrogen content, light-saturated photosynthesis, wood density, leaf carbon isotope composition). The assessment of the photosynthetic properties of tree species, by means of ChlF parameters, in relation to their functional traits, is a relevant issue for studies in forest ecology. The connections of data from field surveys with remotely assessed parameters must be carefully explored.

Altitude Patterns of Leaf Carbon Isotope Composition in a Subtropical Monsoon Forest

ABSTRACT Leaf carbon isotope composition (δ13C) of both vascular and non-vascular plants were investigated in order to assess their variability along an altitude gradient (414, 620, 850, 1086, 1286 and 1462 m) from a subtropical monsoon forest located at Mt. Tianmu Reserve, eastern China. Leaf δ13C values of all plant species ranged from -34.4 to -26.6‰, with an average of -29.8‰. There is no significant difference in leaf δ13C between vascular plants and mosses, however, trees had significantly higher δ13C values than herbs. For pooled data, leaf δ13C was positively correlated with altitude. Leaf δ13C was significantly and negatively correlated with annual mean temperature and atmospheric pressure, while it was significantly and positively correlated with soil water content. Furthermore, there was no relationship between leaf δ13C and soil nitrogen content or soil phosphorus content. The altitudinal trend in leaf δ13C is the consequence of the interaction between temperature, atmospheric pressure and soi...

How vertical patterns in leaf traits shift seasonally and the implications for modeling canopy photosynthesis in a temperate deciduous forest

Leaf functional traits are used in modeling forest canopy photosynthesis (Ac) due to strong correlations between photosynthetic capacity, leaf mass per area (LMA) and leaf nitrogen per area (Narea). Vertical distributions of these traits may change over time in temperate deciduous forests as a result of acclimation to light, which may result in seasonal changes in Ac To assess both spatial and temporal variations in key traits, we measured vertical profiles of Narea and LMA from leaf expansion through leaf senescence in a sugar maple (Acer saccharum Marshall) forest. To investigate mechanisms behind coordinated changes in leaf morphology and function, we also measured vertical variation in leaf carbon isotope composition (δ(13)C), predawn turgor pressure, leaf water potential and osmotic potential. Finally, we assessed potential biases in Ac estimations by parameterizing models with and without vertical and seasonal Narea variations following leaf expansion. Our data are consistent with the hypothesis that hydrostatic constraints on leaf morphology drive the vertical increase in LMA with height early in the growing season; however, LMA in the upper canopy continued to increase over time during light acclimation, indicating that light is primarily driving gradients in LMA later in the growing season. Models with no seasonal variation in Narea overestimated Ac by up to 11% early in the growing season, while models with no vertical variation in Narea overestimated Ac by up to 60% throughout the season. According to the multilayer model, the upper 25% of leaf area contributed to over 50% of Ac, but when gradients of intercellular CO2, as estimated from δ(13)C, were accounted for, the upper 25% of leaf area contributed to 26% of total Ac Our results suggest that ignoring vertical variation of key traits can lead to considerable overestimation of Ac.

Plant hydraulic responses to long-term dry season nitrogen deposition alter drought tolerance in a Mediterranean-type ecosystem.

Anthropogenic nitrogen (N) deposition represents a significant N input for many terrestrial ecosystems. N deposition can affect plants on scales ranging from photosynthesis to community composition, yet few studies have investigated how changes in N availability affect plant water relations. We tested the effects of N addition on plant water relations, hydraulic traits, functional traits, gas exchange, and leaf chemistry in a semi-arid ecosystem in Southern California using long-term experimental plots fertilized with N for over a decade. The dominant species were Artemisia california and Salvia mellifera at Santa Margarita Ecological Reserve and Adenostoma fasciculatum and Ceanothus greggii at Sky Oaks Field Station. All species, exceptCeanothus, showed increased leaf N concentration, decreased foliar carbon to N ratio, and increased foliar N isotopic composition with fertilization, indicating that added N was taken up by study species, yet each species had a differing physiological response to long-term N addition. Dry season predawn water potentials were less negative with N addition for all species except Adenostoma, but there were no differences in midday water potentials, or wet season water potentials. Artemisiawas particularly responsive, as N addition increased stem hydraulic conductivity, stomatal conductance, and leaf carbon isotopic composition, and decreased wood density. The alteration of water relations and drought resistance parameters with N addition in Artemisia, as well as Adenostoma, Ceanothus, and Salvia, indicate that N deposition can affect the ability of native Southern California shrubs to respond to drought.