Test of soil extractants for their suitability in predicting Ca/Sr ratios in leaves and stems of sugar maple seedlings

Differential uptake and translocation of Ca and Sr in organisms have been reported, calling into question the use of Sr to track Ca cycling in the environment. We investigated the relationship between Ca/Sr ratios in soil extracts of various strengths (H₂O, NH₄Cl, and NH₄EDTA) and seedlings of sugar maple (Acer saccharum Marsh.) grown from natural regeneration on 37 sites. Our objectives were to determine if Ca/Sr ratios in soil extracts are correlated with those in sugar maple tissues, and what soil extractant best duplicate plant tissue Ca/Sr ratios. Leaves had higher Ca/Sr ratios than stems and the extractants did not produce equal Ca/Sr ratios: H₂O had the lowest Ca/Sr, and NH₄EDTA the highest. The relationships between soil extract Ca/Sr ratios and leaf and stem Ca/Sr ratios were significant and linear, but the slopes differed among extractants. The lowest slope (0.45) was observed for the water extract/leaves and the highest (2.15) for the NH₄EDTA extract/stem with discrimination factors ranging from 0.22 with NH₄EDTA to 1.59 for water. Leaf extracts were more strongly correlated with soil Ca/Sr than stem extracts (R ² of 0.57–0.7 vs. R ² of 0.45–0.6, respectively). These findings support the use of Ca/Sr ratios in plants to track their source of soil Ca, but they highlight the need to calibrate the relationships for the plant tissue and soil extractant used.     

The relative uptake of Ca and Sr into tree foliage using a whole-watershed calcium addition

The use of strontium isotopes and ratios of alkaline earth elements (i.e., ⁸⁷Sr/⁸⁶Sr and Ca/Sr) to trace Ca sources to plants has become common in ecosystem studies. Here we examine the relative uptake of Ca and Sr in trees and subsequent accumulation in foliage. Using a whole-watershed Ca addition experiment at the Hubbard Brook Experimental Forest in N.H., we measured the uptake of Ca relative to Sr in foliage and roots of sugar maple (Acer saccharum), yellow birch (Betula alleghaniensis), American beech (Fagus grandifolia), and red spruce (Picea rubens). Vegetation was analyzed for Ca and Sr concentrations and the ⁸⁷Sr/⁸⁶Sr ratio. A comparison of the Ca/Sr ratio in the vegetation and the Ca/Sr ratio of the applied mineral allows for the calculation of a discrimination factor, which defines whether Ca and Sr are incorporated and allocated in the same ratio as that which is available. A discrimination factor greater than unity indicates preferential uptake of Ca over Sr; a factor less than unity reflects preferential uptake of Sr over Ca. We demonstrate that sugar maple (SM) and yellow birch (YB) have similar and small discrimination factors (1.14 ± 0.12,1σ and 1.16 ± 0.09,1σ) in foliage formation and discrimination factors of less than 1 in root formation (0.55–0.70). Uptake into beech suggests a larger discrimination factor (1.9 ± 1.2) in foliage but a similar root discrimination factor to SM and YB (0.66 ± 0.06,1σ). Incorporation into spruce foliage occurs at a much slower rate than in these other tree species and precludes evaluation of Ca and Sr discrimination in spruce foliage at this time. Understanding the degree to which Ca is fractionated from Sr in different species allows for refinement in the use of ⁸⁷Sr/⁸⁶Sr and Ca/Sr ratios to trace Ca sources to foliage. Methods from this study can be applied to natural environments in which various soil cation pools have different ⁸⁷Sr/⁸⁶Sr and Ca/Sr ratios. The results reported herein have implications for re-evaluating Ca sources and fluxes in forest ecosystems.     

Use of foliar Ca/Sr discrimination and <Superscript>87</Superscript>Sr/<Superscript>86</Superscript>Sr ratios to determine soil Ca sources to sugar maple foliage in a northern hardwood forest

Calcium/strontium and ⁸⁷Sr/⁸⁶Sr ratios in foliage can be used to determine the relative importance of different soil sources of Ca to vegetation, if the discrimination of Ca/Sr by the plant between nutrient sources and foliage is known. We compared these tracers in the foliage of sugar maple (Acer saccharum) to the exchange fraction and acid leaches of soil horizons at six study sites in the White Mountains of New Hampshire, USA. In a previous study, sugar maple was shown to discriminate for Ca compared to Sr in foliage formation by a factor of 1.14 ± 0.12. After accounting for the predicted 14% shift in Ca/Sr, foliar Ca/Sr and ⁸⁷Sr/⁸⁶Sr ratios closely match the values in the Oie horizon at each study site across a 3.6-fold variation in foliar Ca/Sr ratios. Newly weathered cations, for which the Ca/Sr and ⁸⁷Sr/⁸⁶Sr ratios are estimated from acid leaches of soils, can be ruled out as a major Ca source to current foliage. Within sites, the ⁸⁷Sr/⁸⁶Sr ratio of the soil exchange pool in the Oa horizon and in the 0–10 cm and 10–20 cm increments of the mineral soil are similar to the Oie horizon and sugar maple foliar values, suggesting a common source of Sr in all of the actively cycling pools, but providing no help in distinguishing among them as sources to foliage. The Ca/Sr ratio in the soil exchange pool, however, decreases significantly with depth, and based on this variation, the exchange pool below the forest floor can be excluded as a major Ca source to the current sugar maple foliage. This study confirms that internal recycling of Ca between litter, organic soil horizons and vegetation dominate annual uptake of Ca in northern hardwood ecosystems. Refinement of our understanding of Ca and Sr uptake and allocation in trees allows improvement in the use of Ca/Sr and ⁸⁷Sr/⁸⁶Sr ratios to trace Ca sources to plants.     

Effects of elevated ozone on CO2 uptake and leaf structure in sugar maple under two light environments

The interactive effects of ozone and light on leaf structure, carbon dioxide uptake and short-term carbon allocation of sugar maple ( Acer saccharum Marsh.) seedlings were examined using gas exchange measurements and ¹⁴C-macroautoradiographic techniques. Two-year-old sugar maple seedlings were fumigated from budbreak for 5 months with ambient or 3 × ambient ozone in open-top chambers, receiving either 35% (high light) or 15% (low light) of full sunlight. Ozone accelerated leaf senescence, and reduced net photosynthesis, ¹⁴CO₂ uptake and stomatal conductance, with the effects being most pronounced under low light. The proportion of intercellular space increased in leaves of seedlings grown under elevated ozone and low light, possibly enhancing the susceptibility of mesophyll cells to ozone by increasing the cumulative dose per mesophyll cell. Indeed, damage to spongy mesophyll cells in the elevated ozone × low light treatment was especially frequent. ¹⁴C macroautoradioraphy revealed heterogeneous uptake of ¹⁴CO₂ in well defined areole regions, suggesting patchy stomatal behaviour in all treatments. However, in seedlings grown under elevated ozone and low light, the highest ¹⁴CO₂ uptake occurred along larger veins, while interveinal regions exhibited little or no uptake. Although visible symptoms of ozone injury were not apparent in these seedlings, the cellular damage, reduced photosynthetic rates and reduced whole-leaf chlorophyll levels corroborate the visual scaling of whole-plant senescence, suggesting that the ozone × low light treatment accelerated senescence or senescence-like injury in sugar maple.     

Determination of the freshwater mark in otoliths of Japanese eel elvers using microstructure and Sr/Ca ratios

The microstructure, in particular checks within the otolith edge, of Anguilla japonica glass-eels and elvers and changes in otolith Sr/Ca ratios were examined to ascertain the environmental history of the eels, especially with regard to the time when glass-eels entered the river, and as a benchmark for count daily increments. The percentage of glass eels and elvers with checks and the mean number of checks within the otoliths of glass-eels caught at four localities, Tosa Bay off Tosa City, the mouth of the Gokase River, the mouth of the Saigo River and the dam of the Tsuri River were 0% (0), 15.0% (0.2), 51.6% (1.0) and 100.0% (4.2), respectively. The Sr/Ca ratios and Sr content peaked in the region where checks were formed and the values decreased rapidly towards the edge of the checks; on the other hand, these decreased gradually in the otolith when checks were not formed. These checks were estimated to be formed by stress when the glass-eels were affected by ambient fresh water within the river. The innermost check was called the freshwater mark in the present study and this mark may be useful as a benchmark in studying the growth history of the eel before and after entering freshwater.     

Dominant roles but distinct effects of groundwater depth on regulating leaf and fine-root N,P and N:P ratios of plant communities

地下水位对植物群落叶片与细根氮磷化学计量特征的调控作用不同但影响显著 地下水作为干旱区水资源可利用性的决定因素,在调节植被分布和生态系统过程中具有至关重要的作用。尽管近年来在环境胁迫与群落水平性状的关系方面取得了较大的研究进展,但对于干旱区地下水变化所引起的水分胁迫如何影响植物群落水平化学计量比仍知之甚少。本研究的目的是评估植物群落地上地下部分化学计量比对地下水变化的不同响应。我们通过对典型干旱内陆河流域的110个样方进行调查,测定叶片和细根的氮磷含量,利用生物量加权法计算其化学计量比,并试图探究沿地下水位梯度,群落水平的化学计量比的变化模式及其关键驱动因素。研究结果表明,在群落水平上,地下水、植被类型以及物种组成是影响叶片与细根氮、磷与氮磷比的主要因素,其中地下水位起着主导性作用。地下水的作用主要表现为间接作用,其主要通过调控植被类型和物种组成来影响群落水平的氮磷化学计量比。植被类型和物种组成均对群落水平的氮磷化学计量比具有显著的直接作用。此外,在群落水平上,地下水对叶片与细根氮磷化学计量比的作用不同。地下水通过影响植被类型进而降低叶片氮、磷含量,以及增加叶片氮磷比与细根氮含量。地下水通过影响物种组成进而增加细根磷含量,降低细根氮磷比。综上所述,地下水而不是气候有效的调控了群落水平的氮磷化学计量比。此外,植物群落地上地下部分氮磷化学计量比对地下水位变化具有不同的响应。     

Evaluation of the mobility and discrimination of Ca, Sr and Ba in forest ecosystems: consequence on the use of alkaline-earth element ratios as tracers of Ca

A comprehensive understanding of Ca cycling in an ecosystem is desirable because of the role of this element in tree mineral nutrition and its status as a major base cation on the soil exchange complex. The determination of the origin of Ca in forests is particularly indicated in regard of important changes linked to acid inputs and intensive logging. Natural strontium isotopes are increasingly used as tracers of Ca in forest ecosystems for qualitative and quantitative assessments. Nevertheless this method is limited to relatively simple systems with two sources of nutrients. Some recent studies coupled Sr/Ca or Sr/Ba ratios to Sr isotopic measurements in order to solve more complex systems. Such method has however associated with it some uncertainties: this approach assumed that Ca, Sr and Ba behave similarly throughout the ecosystem and does not take into account the Ca biopurification processes occurring in some tree’s organs which can alter element ratio. The present work focuses on two deciduous species covering large areas in Europe: European beech (Fagus sylvatica L.) and pedunculate oak (Quercus robur L.). In order to test the similarity of behaviour between Ca, Sr and Ba, their concentrations were measured extensively in the major compartments of two forest ecosystems. In parallel, the discrimination process inside tree organs was studied in 23 stands for beech and 10 stands for oak. We found that Sr and Ca behave similarly in all soil and tree compartments. By contrast, Ba and Ca appear to have contrasting behaviours, especially in streams, soil solution and soil exchange complex (no correlations between element concentrations). Sr/Ba and Ba/Ca ratios must therefore be used with care as tracer of Ca. The Ca biopurification is absent in roots and slight in bole wood but is large in bark, twigs and leaves. The discrimination factors (DF) between wood and leaves are characteristic of the two species studied and do not change significantly as a function of the soil Ca status (acidic or calcareous soils). Therefore, strontium–calcium DF can be used as a correction factor of the Sr/Ca ratio of leaves when this ratio is used in connection with Sr isotopic ratios. This correction allows to solve systems of tree nutrition with more than two sources of Ca.     

Estimating the contribution of leaf litter decomposition to soil CO2 efflux in a beech forest using 13C-depleted litter

The contribution of leaf litter decomposition to total soil CO₂ efflux (F_L/F) was evaluated in a beech (Fagus sylvatica L.) forest in eastern France. The Keeling‐plot approach was applied to estimate the isotopic composition of respired soil CO₂ from soil covered with either control (?30.32‰) or ¹³C‐depleted leaf litter (?49.96‰). The δ¹³C of respired soil CO₂ ranged from ?25.50‰ to ?22.60‰ and from ?24.95‰ to ?20.77‰, respectively, with depleted or control litter above the soil. The F_L/F ratio was calculated by a single isotope linear mixing model based on mass conservation equations. It showed seasonal variations, increasing from 2.8% in early spring to about 11.4% in mid summer, and decreasing to 4.2% just after leaf fall. Between December 2001 and December 2002, cumulated F and F_L reached 0.98 and 0.08 kg_C m^?2, respectively. On an annual basis, decomposition of fresh leaf litter accounted for 8% of soil respiration and 80% of total C loss from fresh leaf litter. The other fraction of carbon loss during leaf litter decomposition that is assumed to have entered the soil organic matter pool (i.e. 20%) represents only 0.02 kg_C m^?2.     

Mitochondrial calcium signalling and cell death: Approaches for assessing the role of mitochondrial Ca uptake in apoptosis

Local Ca²⁺ transfer between adjoining domains of the sarcoendoplasmic reticulum (ER/SR) and mitochondria allows ER/SR Ca²⁺ release to activate mitochondrial Ca²⁺ uptake and to evoke a matrix [Ca²⁺] ([Ca²⁺]_m) rise. [Ca²⁺]_m exerts control on several steps of energy metabolism to synchronize ATP generation with cell function. However, calcium signal propagation to the mitochondria may also ignite a cell death program through opening of the permeability transition pore (PTP). This occurs when the Ca²⁺ release from the ER/SR is enhanced or is coincident with sensitization of the PTP. Recent studies have shown that several pro-apoptotic factors, including members of the Bcl-2 family proteins and reactive oxygen species (ROS) regulate the Ca²⁺ sensitivity of both the Ca²⁺ release channels in the ER and the PTP in the mitochondria. To test the relevance of the mitochondrial Ca²⁺ accumulation in various apoptotic paradigms, methods are available for buffering of [Ca²⁺], for dissipation of the driving force of the mitochondrial Ca²⁺ uptake and for inhibition of the mitochondrial Ca²⁺ transport mechanisms. However, in intact cells, the efficacy and the specificity of these approaches have to be established. Here we discuss mechanisms that recruit the mitochondrial calcium signal to a pro-apoptotic cascade and the approaches available for assessment of the relevance of the mitochondrial Ca²⁺ handling in apoptosis. We also present a systematic evaluation of the effect of ruthenium red and Ru360, two inhibitors of mitochondrial Ca²⁺ uptake on cytosolic [Ca²⁺] and [Ca²⁺]_m in intact cultured cells.     

Migratory patterns and contribution of stocking to the population of European eel in Lithuanian waters as indicated by otolith Sr:Ca ratios

Otolith Sr:Ca ratios were examined to evaluate the contribution of the stocked eel Anguilla anguilla elvers, which have been stocked in Lithuanian waters and mixed with naturally recruited eels for several decades, to the native eel population. Stocked eels were identified by the freshwater signature (Sr:Ca ratios <2·24 × 10⁻³) on the otolith after the glass eel stage. Naturally recruited eels, that had migrated through the North and Baltic Seas, were characterized by an extended seawater and brackish-water signature (Sr:Ca ratios >3·23 × 10⁻³) after the glass eel stage. Of 108 eels analysed, 21 eels had otolith Sr:Ca ratio profiles consistent with stocking while 87 showed patterns of natural recruitment. The ages of naturally recruited eels arriving in Lithuanian fresh waters varied from 1 to 10 years, with a mean ±  s.d . age of 5·2 ± 2·1 years. Eels from the inland Lake Baluošai were all freshwater residents of stocked origin. Stocked eels, however, accounted for only 20% of the eels from the Curonian Lagoon and 2% of eels sampled in Baltic coastal waters. This finding does not support the hypothesis that the eel fishery in the Curonian Lagoon depends mostly on stocking.     

Periodic variation in Sr/Ca ratios in statoliths of the Japanese Common Squid Todarodes pacificus Steenstrup, 1880 (Cephalopoda: Ommastrephidae) maintained under constant water temperature

The Japanese Common Squid, Todarodes pacificus Steenstrup, 1880, moves vertically in the water column in time with the natural day-night cycle and this exposes the animal to considerable temperature changes throughout the 24-h period. We considered that this behavior could result in daily fluctuations of the statolith strontium/calcium ratio (Sr/Ca ratio), if this ratio is thermally sensitive, as is found for coral skeletons. To investigate this hypothesis, Japanese Common Squid were reared under constant temperature (15 °C) for 64 days and their statolith Sr/Ca ratios, in the area that had been deposited while in captivity, measured by wavelength dispersive spectrometer. Small repetitive fluctuations were observed in the statolith Sr/Ca ratios of the captive squid (N=5, 2.7-day cycle) but similar fluctuations were also observed in the statoliths of Japanese Common Squid collected from the wild (N=5, 2.4-day cycle). These results imply that the daily vertical movements in the water column are not reflected in the statolith Sr/Ca ratios in the Japanese Common Squid. The observed small repetitive fluctuations are discussed in relation to the periodic feeding activity of the captive squid (1.9-day cycle).     

Ca2+ transport by intact synaptosomes: the voltage-dependent Ca2+ channel and a re-evaluation of the role of sodium/calcium exchange

The verapamil-sensitive Ca2+ channel in the synaptosomal plasma membrane is investigated. Verapamil is without effect on Ca2+ uptake or steady-state content in synaptosomes with a polarized plasma membrane, but completely inhibits the additional Ca2+ uptake following plasma-membrane depolarization by high [K+], by veratridine plus ouabain or by high concentrations of the permeant cation tetraphenylphosphonium. Verapamil-insensitive Ca2+ influx and steady-state content are identical in polarized and depolarized synaptosomes, even though the Na+ electrochemical potential is greatly decreased in the latter, indicating that Na+/Ca2+ exchange is not a significant mechanism for Ca2+ efflux under these conditions. A transient Na+-dependent Ca2+ efflux can only be observed on addition of Na+ to Na+-depleted depolarized synaptosomes. While 0.2 mM verapamil decreases the ate of 86Rb+ efflux and 22Na+ entry during depolarization induced by veratridine plus ouabain, the final steady-state Na+ accumulation is not inhibited. Ca2+ efflux from synaptosomes following mitochondrial depolarization does not occur by a verapamil-sensitive pathway.     

Mitochondrial calcium signalling and cell death: approaches for assessing the role of mitochondrial Ca2+ uptake in apoptosis

Local Ca(2+) transfer between adjoining domains of the sarcoendoplasmic reticulum (ER/SR) and mitochondria allows ER/SR Ca(2+) release to activate mitochondrial Ca(2+) uptake and to evoke a matrix [Ca(2+)] ([Ca(2+)](m)) rise. [Ca(2+)](m) exerts control on several steps of energy metabolism to synchronize ATP generation with cell function. However, calcium signal propagation to the mitochondria may also ignite a cell death program through opening of the permeability transition pore (PTP). This occurs when the Ca(2+) release from the ER/SR is enhanced or is coincident with sensitization of the PTP. Recent studies have shown that several pro-apoptotic factors, including members of the Bcl-2 family proteins and reactive oxygen species (ROS) regulate the Ca(2+) sensitivity of both the Ca(2+) release channels in the ER and the PTP in the mitochondria. To test the relevance of the mitochondrial Ca(2+) accumulation in various apoptotic paradigms, methods are available for buffering of [Ca(2+)], for dissipation of the driving force of the mitochondrial Ca(2+) uptake and for inhibition of the mitochondrial Ca(2+) transport mechanisms. However, in intact cells, the efficacy and the specificity of these approaches have to be established. Here we discuss mechanisms that recruit the mitochondrial calcium signal to a pro-apoptotic cascade and the approaches available for assessment of the relevance of the mitochondrial Ca(2+) handling in apoptosis. We also present a systematic evaluation of the effect of ruthenium red and Ru360, two inhibitors of mitochondrial Ca(2+) uptake on cytosolic [Ca(2+)] and [Ca(2+)](m) in intact cultured cells.     

Improving the accuracy of a solid spherical source radius and depth estimation using the diffusion equation in fluorescence reflectance mode

Background  

Non-invasive planar fluorescence reflectance imaging (FRI) is used for accessing physiological and molecular processes in biological tissue. This method is efficiently used to detect superficial fluorescent inclusions. FRI is based on recording the spatial radiance distribution (SRD) at the surface of a sample. SRD provides information for measuring structural parameters of a fluorescent source (such as radius and depth). The aim of this article is to estimate the depth and radius of the source distribution from SRD, measured at the sample surface. For this reason, a theoretical expression for the SRD at the surface of a turbid sample arising from a spherical light source embedded in the sample, was derived using a steady-state solution of the diffusion equation with an appropriate boundary condition.     

Semi-volatile organic compounds at the leaf/atmosphere interface: numerical simulation of dispersal and foliar uptake

The behaviour of (semi-)volatile organic compounds at the interface between the leaf surface and the atmosphere was investigated by finite-element numerical simulation. Three model systems with increasing complexity and closeness to the real situation were studied. The three-dimensional model systems were translated into appropriate grid structures and diffusive and convective transport in the leaf/atmosphere interface was simulated. Fenpropimorph (cis-4-[3-(4-tert-butylphenyl)-2-methylpropyl]-2,6-dimethylmorpholine) and Kresoxim-methyl ((E)-methyl-2-methoxyimino-2-[2-(o-tolyloxy-methyl)phenyl] acetate) were used as model compounds. The simulation showed that under still and convective conditions the vapours emitted by a point source rapidly form stationary envelopes around the leaves. Vapour concentrations within these unstirred layers depend on the vapour pressure of the compound in question and on its affinity to the lipoid surface layers of the leaf (cuticular waxes, cutin). The rules deduced from the numerical simulation of organic vapour behaviour in the leaf/atmosphere interface are expected to help in assessing how (semi-)volatile plant products (e.g. hormones, pheromones, secondary metabolites) and xenobiotics (e.g. pesticides, pollutants) perform on plant surfaces.     

Migratory life history of European eel Anguilla anguilla from freshwater regions of the River Asi, southern Turkey and their high otolith Sr:Ca ratios

Otolith Sr:Ca ratios from 32 of 34 European eel Anguilla anguilla collected from three freshwater sites in the River Asi, southern Turkey, indicated that they were resident in fresh water without apparent exposure to salt water since the elver stage. The Sr:Ca ratio criterion indicative of residence in fresh water was more than twice that of values from other European countries. Otolith Sr:Ca ratios of A. anguilla from fresh waters can vary among regions, possibly reflecting regional-specific water chemistry. Hence, the use of Sr:Ca ratios determined in one region to interpret results from a different region might lead to misclassification of migratory life-history types.     

Regional variation in otolith Sr:Ca ratios of African longfinned eel Anguilla mossambica and mottled eel Anguilla marmorata: a challenge to the classic tool for reconstructing migratory histories of fishes

Otolith Sr:Ca ratios of the African longfinned eel Anguilla mossambica and giant mottled eel Anguilla marmorata from nine freshwater sites in four rivers of South Africa were analysed to reconstruct their migratory life histories between freshwater and saltwater habitats. For A. mossambica, the Sr:Ca ratios in the otolith edge differed significantly among rivers and had large effect sizes, but did not differ among sites within a river. Otolith Sr:Ca ratios did not differ among rivers for A. marmorata. When rivers were pooled, the edge Sr:Ca ratios of A. mossambica were not significantly different from those of A. marmorata. According to the river-specific critical Sr:Ca ratio distinguishing freshwater from saltwater residence, most A. mossambica and A. marmorata had saltwater habitat experience after settlement in fresh water. This was primarily during their elver stage or early in the yellow eel stage. During the middle and late yellow eel stage, freshwater residency was preferred and only sporadic visits were made to saltwater habitats. The data also suggest that regional variations in otolith Sr:Ca ratios affect the critical Sr:Ca value and are a challenge for the reconstruction of migratory life histories that should be explicitly considered to avoid bias and uncertainty.