Bulk Leaf Research Articles

Allele frequency analysis of Chinese chestnut (Castanea mollissima) populations using fluorescent simple sequence repeats (SSR) analysis

The aim of this study was to establish a method for allele frequency detection in bulk samples. The abundance of polymerase chain reaction (PCR) products in bulk leaf samples was detected using fluorescent labeled Simple sequence repeat (SSR) primers and an Applied biosystems (AB) automatic DNA analyzer. Compared with the conventional SSR technique based on polyacrylamide gel electrophoresis (PAGE) and silver staining, fluorescent SSR was much more sensitive. A total of 78 alleles, an average of 4.6 alleles per locus, were detected among 17 chestnut populations with the primer CmTCR10 (NED) and a total of 41 alleles, an average of 2.4 alleles per locus, were detected with the primer CmTCR24 (6-FAM). Multiplexing the PCR reaction by combining the primer pairs of CmTCR10 and CmTCR24, using different fluorescent dyes for different primers, showed that the alleles could be discriminated and the sizes of the amplified segments were similar. Furthermore, the exact sizes of the amplified fragments and the abundance of the PCR products were determined by fluorescent SSR. After data analysis with GeneScan software and allele calling and output with Genotyper software, allele frequencies were calculated for equal pooled samples in each population using the FREQS-R module in the R statistical computing language. The results indicate that it is feasible to determine allele frequencies in bulked samples based on the detection of SSR-PCR products. The advantages and additional applications of this method are also discussed. The abundance of the PCR products can be used to determine the allele frequencies in bulk samples of chestnut populations.

Genotype differences in 13C discrimination between atmosphere and leaf matter match differences in transpiration efficiency at leaf and whole‐plant levels in hybrid Populus deltoides ×nigra

(13) C discrimination between atmosphere and bulk leaf matter (Δ(13) C(lb) ) is frequently used as a proxy for transpiration efficiency (TE). Nevertheless, its relevance is challenged due to: (1) potential deviations from the theoretical discrimination model, and (2) complex time integration and upscaling from leaf to whole plant. Six hybrid genotypes of Populus deltoides×nigra genotypes were grown in climate chambers and tested for whole-plant TE (i.e. accumulated biomass/water transpired). Net CO(2) assimilation rates (A) and stomatal conductance (g(s) ) were recorded in parallel to: (1) (13) C in leaf bulk material (δ(13) C(lb) ) and in soluble sugars (δ(13) C(ss) ) and (2) (18) O in leaf water and bulk leaf material. Genotypic means of δ(13) C(lb) and δ(13) C(ss) were tightly correlated. Discrimination between atmosphere and soluble sugars was correlated with daily intrinsic TE at leaf level (daily mean A/g(s) ), and with whole-plant TE. Finally, g(s) was positively correlated to (18) O enrichment of bulk matter or water of leaves at individual level, but not at genotype level. We conclude that Δ(13) C(lb) captures efficiently the genetic variability of whole-plant TE in poplar. Nevertheless, scaling from leaf level to whole-plant TE requires to take into account water losses and respiration independent of photosynthesis, which remain poorly documented.

Osmotic and elastic adjustments in cold desert shrubs differing in rooting depth: coping with drought and subzero temperatures

Physiological adjustments to enhance tolerance or avoidance of summer drought and winter freezing were studied in shallow- to deep-rooted Patagonian cold desert shrubs. We measured leaf water potential (Ψ(L)), osmotic potential, tissue elasticity, stem hydraulic characteristics, and stomatal conductance (g (S)) across species throughout the year, and assessed tissue damage by subzero temperatures during winter. Species behavior was highly dependent on rooting depth. Substantial osmotic adjustment (up to 1.2MPa) was observed in deep-rooted species exhibiting relatively small seasonal variations in Ψ(L) and with access to a more stable water source, but having a large difference between predawn and midday Ψ(L). On the other hand, shallow-rooted species exposed to large seasonal changes in Ψ(L) showed limited osmotic adjustment and incomplete stomatal closure, resulting in turgor loss during periods of drought. The bulk leaf tissue elastic modulus (ε) was lower in species with relatively shallow roots. Daily variation in g (S) was larger in shallow-rooted species (more than 50% of its maximum) and was negatively associated with the difference between Ψ(L) at the turgor loss point and minimum Ψ(L) (safety margin for turgor maintenance). All species increased ε by about 10MPa during winter. Species with rigid tissue walls exhibited low leaf tissue damage at -20°C. Our results suggest that osmotic adjustment was the main water relationship adaptation to cope with drought during summer and spring, particularly in deep-rooted plants, and that adjustments in cell wall rigidity during the winter helped to enhance freezing tolerance.

Differences in morpho-physiological leaf traits reflect the response of growth to drought in a seeder but not in a resprouter Mediterranean species.

Understanding the mechanisms underlying the response of different plant functional types to current and projected changes in rainfall is particularly important in drought-prone areas like the Mediterranean. Here, we report the responses of two species with contrasting leaf characteristics and post-fire regeneration strategies (Cistus ladanifer L., malacophyllous, seeder; Erica arborea L., sclerophyllous, resprouter) to a manipulative field experiment that simulated a severe drought (45% reduction of historical average rainfall). We measured monthly changes in relative growth rate (RGR), specific leaf area (SLA), bulk leaf carbon isotope composition (δ13C), predawn water potential (Ψpd), photosynthetic gas exchange, bulk modulus of elasticity and osmotic potential at maximum turgor (π). Temporal (monthly) changes in RGR of C. ladanifer were correlated with all measured leaf traits (except π) and followed Ψpd variation. However, the temporal pattern of RGR in E. arborea was largely unrelated to water availability. SLA monthly variation reflected RGR variation reasonably well in C. ladanifer, but not in E. arborea, in which shoot growth and δ13C increased at the time of maximum water stress in late summer. The relationship between water availability, and RGR and carbon assimilation in C. ladanifer, and the lack of any relationship in E. arborea suggest that the former has an enhanced capacity to harness unpredictable rainfall pulses compared with the latter. These contrasting responses to water availability indicate that the projected changes in rainfall with global warming could alter the competitive ability of these two species, and contribute to changes in plant dominance in Mediterranean shrublands.

Responses of woody species to spatial and temporal ground water changes in coastal sand dune systems

Abstract. In spite of the relative importance of groundwater in costal dune systems, studies concerning the responses of vegetation to ground water (GW) availability variations, particularly in Mediterranean regions, are scarce. Thus, the main purpose of this study is to compare the responses of co-occurring species possessing different functional traits, to changes in GW levels (i.e. the lowering of GW levels) in a sand dune ecosystem. For that, five sites were established within a 1 km2 area in a meso-mediterranean sand dune ecosystem dominated by a Pinus pinaster forest. Due to natural topographic variability and anthropogenic GW exploitation, substantial variability in depth to GW between sites was found. Under these conditions it was possible to identify the degree of usage and dependence on GW of different plant species (two deep-rooted trees, a drought adapted shrub, a phreatophyte and a non-native woody invader) and how GW dependence varied seasonally and between the heterogeneous sites. Results indicated that the plant species had differential responses to changes in GW depth according to specific functional traits (i.e. rooting depth, leaf morphology, and water use strategy). Species comparison revealed that variability in pre-dawn water potential (Ψpre) and bulk leaf δ13C was related to site differences in GW use in the deep-rooted (Pinus pinaster, Myrica faya) and phreatophyte (Salix repens) species. However, such variation was more evident during spring than during summer drought. The exotic invader, Acacia longifolia, which does not possess a very deep root system, presented the largest seasonal variability in Ψpre and bulk leaf δ13C. In contrast, the response of Corema album, an endemic understory drought-adapted shrub, seemed to be independent of water availability across seasons and sites. Thus, the susceptibility to lowering of GW due to anthropogenic exploitation, in plant species from sand dunes, is variable, being particularly relevant for deep rooted species and phreatophytes, which seem to depend heavily on access to GW.

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 Herbage Intake and Sward Structure of Grazed Temperate Grasses

Temperate grasses differ in sward structure, which may influence herbage intake of grazing cattle. We compared herbage intake of meadow fescue [Schedonorus pratensis (Huds.) P. Beauv.], orchardgrass (Dactylis glomerata L.), quackgrass [Elymus repens (L.) Gould], and reed canarygrass (Phalaris arundinacea L.) grazed by dairy heifers, and determined its relationship with sward structure. Grasses were grazed at vegetative stage for 24 h over 5‐d periods in the spring, summer, and fall of 2 yr. Forage dry matter (DM) allowance was a minimum of two times expected daily intake (11 kg animal−1 d−1). Sward characteristics were measured before grazing (height, mass, vertical distribution of leaf and stem bulk density and nutritive value). Herbage DM intake was estimated daily (pregraze minus postgraze herbage mass). Despite species differences in pregraze sward height (range of 29–49 cm across seasons), herbage mass (range of 1480–2540 kg DM ha−1), and neutral detergent fiber (NDF) digestibility (range of 713–843 g kg−1 NDF), no differences in leaf bulk density and herbage intake were found among grasses during four of six grazing seasons. Herbage intake differences during two seasons were related to either sward leaf bulk density (r = 0.79) or stem bulk density (r = −0.84), and the associated changes in leaf and stem mass of the canopy layers grazed by cattle, indicating that these sward characteristics were the primary determinants of grazed herbage intake in vegetative meadow fescue, orchardgrass, quackgrass, and reed canarygrass.

Diferimento de pastos de Brachiaria decumbens adubados com nitrogênio no início e no final do período das águas

O objetivo com este trabalho foi avaliar a massa de matéria seca forragem e de seus componentes morfológicos, a altura e o índice de tombamento do pasto, a densidade volumétrica e o valor nutritivo da forragem em pastos de Brachiaria decumbens diferidos por 95 dias sob quatro estratégias de adubação nitrogenada. Foram estudadas quatro estratégias de aplicação de nitrogênio no início e no final do período chuvoso, respectivamente (0-0, 100-0, 50-50, 0-100 kg de N.ha-1), avaliados em três estratos verticais a cada 20 cm, num delineamento experimental de blocos casualizados em esquema de parcelas subdivididas com quatro repetições. Os pastos adubados com 100 kg de N no final do período chuvoso apresentaram maiores massas de matéria seca de forragem total, lâmina de folha e de colmo verde, bem como altura, altura estendida e densidade volumétrica da forragem total, lâmina de folha e de colmo verde em todos os estratos estudados. Os índices de tombamento foram maiores para os pastos adubados no final do período chuvoso (0-100 e 50-50). Os percentuais de fibra em detergente neutro foram menores no estrato A (acima de 40 cm do solo) e os teores proteína bruta (PB) maiores em todos os estratos para os tratamentos 0-100 e 50-50. Embora a adubação com 100 kg de N no final do período chuvoso permita aumentar a massa de forragem total e de lâminas de folhas e melhorar a qualidade desta forragem, a maior densidade de colmos nos estratos superiores e o elevado índice de tombamento podem caracterizar dificuldades na seleção da forragem e redução no consumo e desempenho animal.

Effect of leaf litter degradation and seasonality on D/H isotope ratios of n-alkane biomarkers

Abstract During the last decade, compound-specific hydrogen isotope analysis of plant leaf-wax and sedimentary n -alkyl lipids has become a promising tool for paleohydrological reconstructions. However, with the exception of several previous studies, there is a lack of knowledge regarding possible effects of early diagenesis on the δD values of n -alkanes. We therefore investigated the n -alkane patterns and δD values of long-chain n -alkanes from three different C3 higher plant species ( Acer pseudoplatanus L., Fagus sylvatica L. and Sorbus aucuparia L.) that have been degraded in a field leaf litterbag experiment for 27 months. We found that after an initial increase of long-chain n -alkane masses (up to ∼50%), decomposition took place with mean turnover times of 11.7 months. Intermittently, the masses of mid-chain n -alkanes increased significantly during periods of highest total mass losses. Furthermore, initially high odd-over-even predominances (OEP) declined and long-chain n -alkane ratios like n -C 31 /C 27 and n -C 31 /C 29 started to converge to the value of 1. While bulk leaf litter became systematically D-enriched especially during summer seasons (by ∼8‰ on average over 27 months), the δD values of long-chain n -alkanes reveal no systematic overall shifts, but seasonal variations of up to 25‰ ( Fagus , n -C 27 , average ∼13‰). Although a partly contribution by leaf-wax n -alkanes by throughfall cannot be excluded, these findings suggest that a microbial n- alkane pool sensitive to seasonal variations of soil water δD rapidly builds up. We propose a conceptual model based on an isotope mass balance calculation that accounts for the decomposition of plant-derived n -alkanes and the build-up of microbial n -alkanes. Model results are in good agreement with measured n -alkane δD results. Since microbial ‘contamination’ is not necessarily discernible from n -alkane concentration patterns alone, care may have to be taken not to over-interpret δD values of sedimentary n -alkanes. Furthermore, since leaf-water is generally D-enriched compared to soil and lake waters, soil and water microbial n -alkane pools may help explain why soil and sediment n -alkanes are D-depleted compared to leaves.

Leaf δ18O of remaining trees is affected by thinning intensity in a semiarid pine forest

Silvicultural thinning usually improves the water status of remaining trees in water-limited forests. We evaluated the usefulness of a dual stable isotope approach (δ¹³C, δ¹⁸O) for comparing the physiological performance of remaining trees between forest stands subjected to two different thinning intensities (moderate versus heavy) in a 60-year-old Pinus halepensis Mill. plantation in semiarid southeastern Spain. We measured bulk leaf δ¹³C and δ¹⁸O, foliar elemental concentrations, stem water content, stem water δ¹⁸O (δ¹⁸O(stem water)), tree ring widths and leaf gas exchange rates to assess the influence of forest stand density on tree performance. Remaining trees in low-density stands (heavily thinned) showed lower leaf δ¹⁸O, and higher stomatal conductance (g(s)), photosynthetic rate and radial growth than those in moderate-density stands (moderately thinned). By contrast, leaf δ¹³C, intrinsic water-use efficiency, foliar elemental concentrations and δ¹⁸O(stem water) were unaffected by stand density. Lower foliar δ¹⁸O in heavily thinned stands reflected higher g(s) of remaining trees due to decreased inter-tree competition for water, whereas higher photosynthetic rate was largely attributable to reduced stomatal limitation to CO₂ uptake. The dual isotope approach provided insight into the early (12 months) effects of stand density manipulation on the physiological performance of remaining trees.

Vertical and seasonal variation in the 13C of leaf-respired CO2 in a mixed conifer forest

The C-isotopic composition (δ¹³C) of leaf respiration (δ(LR)) has previously been shown to vary among functional groups, plant organs and times of day. We here investigated vertical and seasonal variation in δ(LR) through deep (~35 m) forest canopies. We measured δ(LR), δ¹³C of leaf bulk organic matter (δ(LB)), specific leaf area, net photosynthesis (A) and dark respiration in shade, middle and sun foliage in four conifer species from May to August. We used Keeling plots to estimate δ(LR); we developed a novel technique for ensuring that the respiratory substrate was not changing over the course of the measurement. Variables δ(LR) and δ(LB) displayed a vertical pattern in Abies grandis, Pseudotsuga menziesii and Thuja plicata, but were independent of canopy position in Larix occidentalis. Vertical gradients in δ(LB) (3.6‰) and δ(LR) (2.8‰) were similar. The respiratory enrichment (δ(LR)-δ(LB)) was smaller in expanding (3‰) than mature (4-8‰) foliage. There was a linear relationship between the respiratory enrichment and A. Our data support the hypothesis that δ(LR) values are related to patterns of C allocation among metabolic pathways. We demonstrated that considerable variation in δ(LR) occurs vertically through the canopy (3‰ gradient) and seasonally (3-7‰). Understanding sources of variation in respiratory signals is fundamental to comprehending C dynamics and for global model applications.

Review and parameterisation of bi-directional ammonia exchange between vegetation and the atmosphere

Abstract. Current deposition schemes used in atmospheric chemical transport models do not generally account for bi-directional exchange of ammonia (NH3). Bi-directional exchange schemes, which have so far been applied at the plot scale, can be included in transport models, but need to be parameterised with appropriate values of the ground layer compensation point (χg), stomatal compensation point (χs) and cuticular resistance (Rw). We review existing measurements of χg, χs as well as Rw and compile a comprehensive dataset from which we then propose generalised parameterisations. χs is related to Γs, the non-dimensional ratio of [NH4+]apo and [H+]apo in the apoplast, through the temperature dependence of the combined Henry and dissociation equilibrium. The meta-analysis suggests that the nitrogen (N) input is the main driver of the apoplastic and bulk leaf concentrations of ammonium (NH4 apo

Carbon, nitrogen, and hydrogen isotope ratios in creekside trees in western Kansas

Three species of creekside trees were monitored weekly during the 2007 and 2008 growing seasons. The 2007 growing season was wet early, but became drier as the season progressed. In contrast, the 2008 growing season was dry early, but became wetter as the season progressed. Creekside trees were measured to determine effects of changing water regimes on leaf-level processes. Lonicera tatarica plants were compared to Morus alba and Celtis occidentalis trees. Leaves were monitored for changes in stomatal conductance, transpiration, δ13C, δ15N, δD, leaf temperature, and heat losses via latent, sensible, and radiative pathways. δD of creek water was more similar to ground water than to rain water, but the creek was partially influenced by summer rains. δD of bulk leaf material was significantly higher in individuals of C. occidentalis compared to the other species, consistent with source water coming from shallower soil layers. Despite decreasing water levels, none of these tree species showed signs of water stress. There were no significant differences between species in stomatal conductance or transpiration. Leaf δ13C was significantly lower in individuals of L. tatarica compared to the other species. Differences in δ13C were attributed to a lower carboxylation capacity, consistent with lower leaf nitrogen content in L. tatarica plants. Leaf δ15N was significantly lower in individuals of L. tatarica compared to the other species, consistent with uptake of a different N source. Two of the three sites appeared to be affected by inorganic N from fertilizer run-off. Evidence is presented that these species acquired water and nitrogen from different sources, resulting from differences in root uptake patterns.

Metal hyperaccumulation armors plants against disease.

Metal hyperaccumulation, in which plants store exceptional concentrations of metals in their shoots, is an unusual trait whose evolutionary and ecological significance has prompted extensive debate. Hyperaccumulator plants are usually found on metalliferous soils, and it has been proposed that hyperaccumulation provides a defense against herbivores and pathogens, an idea termed the ‘elemental defense’ hypothesis. We have investigated this hypothesis using the crucifer Thlaspi caerulescens, a hyperaccumulator of zinc, nickel, and cadmium, and the bacterial pathogen Pseudomonas syringae pv. maculicola (Psm). Using leaf inoculation assays, we have shown that hyperaccumulation of any of the three metals inhibits growth of Psm in planta. Metal concentrations in the bulk leaf and in the apoplast, through which the pathogen invades the leaf, were shown to be sufficient to account for the defensive effect by comparison with in vitro dose–response curves. Further, mutants of Psm with increased and decreased zinc tolerance created by transposon insertion had either enhanced or reduced ability, respectively, to grow in high-zinc plants, indicating that the metal affects the pathogen directly. Finally, we have shown that bacteria naturally colonizing T. caerulescens leaves at the site of a former lead–zinc mine have high zinc tolerance compared with bacteria isolated from non-accumulating plants, suggesting local adaptation to high metal. These results demonstrate that the disease resistance observed in metal-exposed T. caerulescens can be attributed to a direct effect of metal hyperaccumulation, which may thus be functionally analogous to the resistance conferred by antimicrobial metabolites in non-accumulating plants.

Water relations of evergreen and drought-deciduous trees along a seasonally dry tropical forest chronosequence

Seasonally dry tropical forests (SDTF) are characterized by pronounced seasonality in rainfall, and as a result trees in these forests must endure seasonal variation in soil water availability. Furthermore, SDTF on the northern Yucatan Peninsula, Mexico, have a legacy of disturbances, thereby creating a patchy mosaic of different seral stages undergoing secondary succession. We examined the water status of six canopy tree species, representing contrasting leaf phenology (evergreen vs. drought-deciduous) at three seral stages along a fire chronosequence in order to better understand strategies that trees use to overcome seasonal water limitations. The early-seral forest was characterized by high soil water evaporation and low soil moisture, and consequently early-seral trees exhibited lower midday bulk leaf water potentials (ΨL) relative to late-seral trees (−1.01 ± 0.14 and −0.54 ± 0.07 MPa, respectively). Although ΨL did not differ between evergreen and drought-deciduous trees, results from stable isotope analyses indicated different strategies to overcome seasonal water limitations. Differences were especially pronounced in the early-seral stage where evergreen trees had significantly lower xylem water δ18O values relative to drought-deciduous trees (−2.6 ± 0.5 and 0.3 ± 0.6‰, respectively), indicating evergreen species used deeper sources of water. In contrast, drought-deciduous trees showed greater enrichment of foliar 18O (∆18Ol) and 13C, suggesting lower stomatal conductance and greater water-use efficiency. Thus, the rapid development of deep roots appears to be an important strategy enabling evergreen species to overcome seasonal water limitation, whereas, in addition to losing a portion of their leaves, drought-deciduous trees minimize water loss from remaining leaves during the dry season.

Contrasting responses facing peak drought in seedlings of two co-occurring oak species

Summary To evaluate leaf physiological mechanisms involved in plant tolerance to water deficit between sites of varying overstorey density, we investigated leaf water relations of two broadleaved oaks (Quercus petraea (Matt.) Liebl. and Quercus pyrenaica Willd.) planted within a dense Scots pine stand, in a thinned adjacent area and in a nearby gap at a Mediterranean, mid-mountain field site. Leaf water parameters were estimated in established seedlings at the end of June and August over two consecutive years by measuring pressure–volume relationships with the pressure chamber technique. Plant water status was always similar in both species, and it was lower in August than June due to lower soil moisture at the end of summer. Higher light and diurnal water deficits in the gap were associated to more negative osmotic potentials. Impacts of overstorey density on some leaf water parameters depended on the species. While Q. pyrenaica showed active osmotic adjustment across sites, seedlings of Q. petraea were unable to cope with increased water deficit by osmotic adjustment in the unthinned dense area. While Q. pyrenaica showed consistent increases in the maximum bulk modulus of elasticity (emax) from June to August across sites, emax decreased in the unthinned dense area for seedlings of Q. petraea. These results could reflect distinct species strategies to cope with water deficit under the low-light conditions created by a dense overstorey. Higher leaf osmotic adjustment and bulk modulus of elasticity in Q. pyrenaica seedlings at peak summer drought might confer on them a competitive advantage during establishment in dry sub-Mediterranean understories. Opening of moderate canopy gaps in dense Scots pine stands improves some leaf mechanisms involved in drought tolerance in oak seedlings.

Seasonal variations in the isotopic composition of leaf and stem water from an arid region of Southeast Asia

Stable isotopes are powerful research tools in environmental sciences and their use in ecosystem research is increasing. Stable isotope measurements allow the study of evapotranspiration fluxes, soil evaporation and leaf transpiration phenomena. Soil water and leaf water are the sources of the evapotranspiration that transfers large quantities of water from land to the atmosphere; as a result the isotopic composition of water left in the leaves is modified towards enrichment. Evaporation also changes the isotopic composition of water bodies creating a natural isotopic signal. The isotopic identity of soil water affects the oxygen isotopic signature of leaf and stem water. In this paper we present the isotopic data of bulk leaf water, showing the enrichment in isotopic value of oxygen due to evapotranspiration from leaves in conjunction with the isotopic signal of rainwater and other environmental factors such as humidity and temperature. Results suggest that the variation in the values of δ18O of Eucalyptus citriodora, Dalbergia sissoo, Melia azedarach and Pinus roxburghii is due to the seasonal changes in the δ18O of the source water for plants, i. e. rain. It is further observed that leaf water δ18O values are depleted during the months of July, August and September. This occurs due to the following reasons: (a) the sampling areas receive about 50% of the average annual rain during these months, and (b) rainfalls during these months are isotopically depleted compared with winter rains. Citation Butt, S., Ali, M., Fazil, M. & Latif, Z. (2010) Seasonal variations in the isotopic composition of leaf and stem water from an arid region of Southeast Asia. Hydrol. Sci. J. 55(5), 844–848.

Changes in the nutritional quality of decaying leaf litter in a stream based on fatty acid content

We examined the nutritional quality of decaying leaf litter in a third-order forested stream, using measurements of fatty acid (FA) composition over time. We measured changes in concentrations of total, polyunsaturated, microalgal, and microbial marker FAs in mixed-species leaf packs in spring and autumn and effects of including/excluding macroinvertebrates. Initial concentrations of total FAs in litter were significantly less in spring (5.2 mg/g) than in autumn (6.9 mg/g; F = 6.3; P = 0.03), but total FA concentrations in litter placed in the stream declined significantly over 120 days in both spring (62%; F = 10.9; P < 0.001) and autumn (56%; F = 19.4; P = 0.0001). Quantities of most FAs declined at a greater rate than that of bulk leaf matter. The presence or absence of macroinvertebrates (5 mm vs. 250 μm mesh) had no effect on FA concentration or composition of decomposing litter. Omega-3 polyunsaturated FAs were either nearly absent (20:5ω3) or depleted preferentially over other FAs (18:3ω3). During decomposition the polyunsaturated FA linoleic acid (18:2ω6, common in fungi), declined in concentration more rapidly than other FAs in the spring, but in autumn declined at slower rates, perhaps suggesting greater fungal activity in autumn. Quantities of bacterial (e.g., 16:1ω7) and fungal (e.g., 18:1ω9) FA markers increased over time in autumn (and 16:1ω7 also in spring). Our data provide no evidence for increasing nutritional FA quality of litter during decay and microbial colonization, based on total and polyunsaturated FAs, despite measured increases in bacterial and fungal FA over time. Routine measurements of FA composition of litter could provide insights into the nutrition of allochthonous matter and the importance of fungi and bacteria during decomposition.

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.

Physiological and proteomic characterization of manganese sensitivity and tolerance in rice (Oryza sativa) in comparison with barley (Hordeum vulgare).

Research on manganese (Mn) toxicity and tolerance indicates that Mn toxicity develops apoplastically through increased peroxidase activities mediated by phenolics and Mn, and Mn tolerance could be conferred by sequestration of Mn in inert cell compartments. This comparative study focuses on Mn-sensitive barley (Hordeum vulgare) and Mn-tolerant rice (Oryza sativa) as model organisms to unravel the mechanisms of Mn toxicity and/or tolerance in monocots. Bulk leaf Mn concentrations as well as peroxidase activities and protein concentrations were analysed in apoplastic washing fluid (AWF) in both species. In rice, Mn distribution between leaf compartments and the leaf proteome using 2D isoelectric focusing IEF/SDS-PAGE and 2D Blue native BN/SDS-PAGE was studied. The Mn sensitivity of barley was confirmed since the formation of brown spots on older leaves was induced by low bulk leaf and AWF Mn concentrations and exhibited strongly enhanced H2O2-producing and consuming peroxidase activities. In contrast, by a factor of 50, higher Mn concentrations did not produce Mn toxicity symptoms on older leaves in rice. Peroxidase activities, lower by a factor of about 100 in the rice leaf AWF compared with barley, support the view of a central role for these peroxidases in the apoplastic expression of Mn toxicity. The high Mn tolerance of old rice leaves could be related to a high Mn binding capacity of the cell walls. Proteomic studies suggest that the lower Mn tolerance of young rice leaves could be related to Mn excess-induced displacement of Mg and Fe from essential metabolic functions. The results provide evidence that Mn toxicity in barley involves apoplastic lesions mediated by peroxidases. The high Mn tolerance of old leaves of rice involves a high Mn binding capacity of the cell walls, whereas Mn toxicity in less Mn-tolerant young leaves is related to Mn-induced Mg and Fe deficiencies.