Transpiration Stream Research Articles

Phosphorylation of PSII proteins in maize thylakoids in the presence of Pb ions

Lead is potentially toxic to all organisms including plants. Many physiological studies suggest that plants have developed various mechanisms to contend with heavy metals, however the molecular mechanisms remain unclear. We studied maize plants in which lead was introduced into detached leaves through the transpiration stream. The photochemical efficiency of PSII, measured as an Fv/Fm ratio, in the maize leaves treated with Pb was only 10% lower than in control leaves. The PSII activity was not affected by Pb ions in mesophyll thylakoids, whereas in bundle sheath it was reduced. Protein phosphorylation in mesophyll and bundle sheath thylakoids was analyzed using mass spectrometry and protein blotting before and after lead treatment. Both methods clearly demonstrated increase in phosphorylation of the PSII proteins upon treatment with Pb2+, however, the extent of D1, D2 and CP43 phosphorylation in the mesophyll chloroplasts was clearly higher than in bundle sheath cells. We found that in the presence of Pb ions there was no detectable dephosphorylation of the strongly phosphorylated D1 and PsbH proteins of PSII complex in darkness or under far red light. These results suggest that Pb2+ stimulates phosphorylation of PSII core proteins, which can affect stability of the PSII complexes and the rate of D1 protein degradation. Increased phosphorylation of the PSII core proteins induced by Pb ions may be a crucial protection mechanism stabilizing optimal composition of the PSII complexes under metal stress conditions. Our results show that acclimation to Pb ions was achieved in both types of maize chloroplasts in the same way. However, these processes are obviously more complex because of different metabolic status in mesophyll and bundle sheath chloroplasts.

Endophytic actinomycetes from Pinus thunbergii and their antifungal activity against Cylindrocladium sp.

The inside of Pinus thunbergii could be a reliable screening source for a useful agent in controlling plant disease. Isolation of endophytic actinomycetes from P. thunbergii and their potential as biocontrol agents against the plant pathogen Cylindrocladium sp. were investigated. Two endophytic actinomycetes, Streptomyces sp. and Microbispora sp., were isolated from surface-sterilised root tissues of P. thunbergii seedlings. The recovery test of these two endophytic actinomycetes from pine seedling showed that Streptomyces sp. was isolated from only roots, but Microbispora sp. was isolated from both roots and leaves. Thus, Microbispora sp. is able to move to leaves from roots. Moreover, we evaluated the potential of both strains as biocontrol agents against Cylindrocladium sp. Two weeks after inoculation of Cylindrocladium sp. alone, pine seedlings showed a 50% mortality rate. Co-inoculation of Cylindrocladium sp. and Microbispora sp. did not affect seedling mortality rate. However, inoculation with both Cylindrocladium sp. and Streptomyces sp. reduced seedling mortality to 12%. Streptomyces sp. could be a useful agent in controlling pine disease caused by Cylindrocladium sp. Thus, it seems that Streptomyces sp. may induce a local host defence reaction and Microbispora sp. systemically spreads to aerial parts through the transpiration stream.

Integrated Dynamic Modeling of Contaminant Fate and Transport within a Soil–Plant System

Contaminants found in the soil and in the atmosphere frequently find their way into plants. Because plants are at the bottom of the food chain, analysis of this pathway contributes to health risk assessment studies. On the other hand, plants that exist at a contaminated site have a potential effect on contaminant transformation and migration within the soil or the atmosphere. In this study, a modeling framework was developed to integrate the plant pathway into soil contaminant transport models. A soil–plant system model was developed by coupling soil moisture distribution, contaminant transport, plant life cycle, and plant pathway models. The outcome unifies single‐medium continuous models with multimedia compartmental models in a flexible framework. The framework recognizes that plants are dynamic biologic systems that regulate their life cycle in interaction with existing conditions in the ambient environment, which significantly influence the dynamics of the overall complex system. The model developed was applied to a hypothetical contamination scenario where the effect of plants on contaminant migration within the system was investigated. Also, the outcome of the plant pathway as it responds to water flow and contaminant transport dynamics was analyzed. A mass balance analysis found that the processes of volatilization and root water uptake are very critical in determining the contaminant fate within the system. A sensitivity analysis showed that the contaminant concentration within the plant is significantly affected by the variation in the values of the retardation factor, transpiration stream concentration factor, and contaminant half‐life within the plant. The outcome of these applications reflects the effect of multiple levels of complexity associated with plant growth and root water uptake representations within the soil.

Cavitation induced by a surfactant leads to a transient release of water stress and subsequent ‘run away’ embolism in Scots pine (Pinus sylvestris) seedlings

Cavitation decreases the hydraulic conductance of the xylem and has, therefore, detrimental effects on plant water balance. However, cavitation is also hypothesized to relieve water stress temporarily by releasing water from embolizing conduits to the transpiration stream. Stomatal closure in response to decreasing water potentials in order to avoid excessive cavitation has been well documented in numerous previous studies. However, it has remained unclear whether the stomata sense cavitation events themselves or whether they act in response to a decrease in leaf water potential to a level at which cavitation is initiated. The effects of massive cavitation on leaf water potential, transpiration, and stomatal behaviour were studied by feeding a surfactant into the transpiration stream of Scots pine (Pinus sylvestris) seedlings. The stomatal response to cavitation in connection with the capacitive effect was also studied. A major transient increase in leaf water potential was found due to cavitation in the seedlings. As cavitation was induced by lowering the surface tension, the two mechanisms could be uncoupled, as the usual relation between xylem water potential and the onset of cavitation did not hold. Our results indicate that the seedlings responded more to leaf water potential and less to cavitation itself, as stomatal closure was insufficient to prevent the seedlings from being driven to ‘run-away’ cavitation in a manner of hours.

Phytoscreening for Chlorinated Solvents Using Rapid in Vitro SPME Sampling: Application to Urban Plume in Verl, Germany

Rapid detection and delineation of contaminants in urban settings is critically important in protecting human health. Cores from trees growing above a plume of contaminated groundwater in Verl, Germany, were collected in 1 day, with subsequent analysis and plume mapping completed over several days. Solid-phase microextraction (SPME) analysis was applied to detect tetrachloroethene (PCE) and trichloroethene (TCE) to below nanogram/liter levels in the transpiration stream of the trees. The tree core concentrations showed a clear areal correlation to the distribution of PCE and TCE in the groundwater. Concentrations in tree cores were lower than the underlying groundwater, as anticipated; however, the tree core water retained the PCE:TCE signature of the underlying groundwater in the urban, populated area. The PCE:TCE ratio can indicate areas of differing degradation activity. Therefore, the phytoscreening analysis was capable not only of mapping the spatial distribution of groundwater contamination but also of delineating zones of potentially differing contaminant sources and degradation. The simplicity of tree coring and the ability to collect a large number of samples in a day with minimal disruption or property damage in the urban setting demonstrates that phytoscreening can be a powerful tool for gaining reconnaissance-level information on groundwater contaminated by chlorinated solvents. The use of SPME decreases the detection level considerably and increases the sensitivity of phytoscreening as an assessment, monitoring, and phytoforensic tool. With rapid, inexpensive, and noninvasive methods of detecting and delineating contaminants underlying homes, as in this case, human health can be better protected through screening of broader areas and with far faster response times.

Barriers to predicting changes in global terrestrial methane fluxes: analyses using CLM4Me, a methane biogeochemistry model integrated in CESM

Abstract. Terrestrial net CH4 surface fluxes often represent the difference between much larger gross production and consumption fluxes and depend on multiple physical, biological, and chemical mechanisms that are poorly understood and represented in regional- and global-scale biogeochemical models. To characterize uncertainties, study feedbacks between CH4 fluxes and climate, and to guide future model development and experimentation, we developed and tested a new CH4 biogeochemistry model (CLM4Me) integrated in the land component (Community Land Model; CLM4) of the Community Earth System Model (CESM1). CLM4Me includes representations of CH4 production, oxidation, aerenchyma transport, ebullition, aqueous and gaseous diffusion, and fractional inundation. As with most global models, CLM4 lacks important features for predicting current and future CH4 fluxes, including: vertical representation of soil organic matter, accurate subgrid scale hydrology, realistic representation of inundated system vegetation, anaerobic decomposition, thermokarst dynamics, and aqueous chemistry. We compared the seasonality and magnitude of predicted CH4 emissions to observations from 18 sites and three global atmospheric inversions. Simulated net CH4 emissions using our baseline parameter set were 270, 160, 50, and 70 Tg CH4 yr−1 globally, in the tropics, in the temperate zone, and north of 45° N, respectively; these values are within the range of previous estimates. We then used the model to characterize the sensitivity of regional and global CH4 emission estimates to uncertainties in model parameterizations. Of the parameters we tested, the temperature sensitivity of CH4 production, oxidation parameters, and aerenchyma properties had the largest impacts on net CH4 emissions, up to a factor of 4 and 10 at the regional and gridcell scales, respectively. In spite of these uncertainties, we were able to demonstrate that emissions from dissolved CH4 in the transpiration stream are small (<1 Tg CH4 yr−1) and that uncertainty in CH4 emissions from anoxic microsite production is significant. In a 21st century scenario, we found that predicted declines in high-latitude inundation may limit increases in high-latitude CH4 emissions. Due to the high level of remaining uncertainty, we outline observations and experiments that would facilitate improvement of regional and global CH4 biogeochemical models.

Inoculation of growing media with the rhizobacterium Variovorax paradoxus 5C-2 reduces unwanted stress responses in hardy ornamental species

Inoculation of growing media with plant growth promoting rhizobacteria (PGPR) has a number of potential benefits for the production of ornamental plants. Certain rhizobacteria synthesise the enzyme ACC deaminase, which cleaves ACC, the precursor of the plant hormone ethylene. Bacterial metabolism is now known to lead to a reduction in [ACC] in the plant transpiration stream and bacteria are hypothesised to act on ACC exuded from roots. This in turn reduces the ethylene generated in plants growing in growing media inoculated with these bacteria. Here we tested if applications of the ACC deaminase containing rhizobacteria Variovorax paradoxus 5C– 2could be of benefit to ornamental growers by reducing ethylene generation in stressed plants. Ethylene is produced at levels that are inhibitory to growth and development under a number of abiotic stresses. The propagation and production of hardy ornamentals is deleteriously affected by abiotic stresses that involve ethylene signalling, including drought and physical wounding. Inoculation of growing media with V. paradoxus 5C-2 lowered ethylene emission from mature leaves of Cytisus × praecox experiencing drought stress. In addition, bacterial inoculation of the growing media resulted in significantly reduced abscission of the mature leaves under drought treatment. Beneficial effects of inoculation where also found in the wounding response of Fargesia murielae following divisional propagation and late season senescence in Aquilegia × hybrida in response to drought stress. Together these results demonstrate that V. paradoxus 5C– 2has real potential for use on ornamental nurseries in situations where plant stresses are unavoidable.

Imparipinnate neuropteroid foliage (Medullosales) from the middle Westphalian of the West and Central Bohemia Coal Basin, Czech Republic

The Bolsovian-age Radnice Member of the West and Central Bohemian Coal Basin in the Czech Republic has yielded eight species of imparipinnate neuropteroid fronds, four of which are endemic to the basin. They mostly belong to the fossil-genera Laveineopteris, Macroneuropteris and a previously unrecognised genus named here Havlenaea; unlike the contemporary macrofloras of the lowland paralic basins, Neuropteris sensu stricto is absent from the Radnice Member. Havlenaea represents a group of neuropteroid species with distinctive stomata that are only found in intramontane basins. Laveineopteris loshii is identified here for the first time from an intramontane basin, but only from peat substrate vegetation; in the clastic substrate habitats, the genus is mainly represented by Laveineopteris tenuifolia. A palaeobiogeographcial analysis confirms the distinctiveness of the mid-Westphalian medullosaleans of Western and Central Bohemia, which probably reflects the relatively high elevation of the basin. Many of the species show features that superficially suggest adaptations to xeric conditions, but in fact are probably adaptations to facilitate water run-off from the foliage, and thus to improve the transpiration stream in a high-humidity tropical environment. There are also numerous holes in the cuticles probably representing hydathode pores, which are another adaptation to growth in high-humidity tropical conditions.

Determining the relationship between tree‐stem respiration and CO2 efflux by δO2/Ar measurements

Respiration in forest tree stems is an important component of the global carbon cycle. This respiration is traditionally estimated by measurements of the CO(2) efflux from the stem. However, recent studies have suggested that movement of CO(2) in the transpiration stream causes large errors in the respiration estimated by the CO(2) efflux. Here we demonstrate a new approach for determining the ratio of respiration to CO(2) efflux, which is based on specially designed chambers, and combined CO(2) and O(2) measurements. The high accuracy O(2) measurement is performed by mass spectrometric measurement of the O(2)/Ar ratio. Testing the method gave repeatable results which point that in some conditions up to 40% of the respired CO(2) can be carried away from the site of respiration.

TRANSLOCATION OF ALKALOIDS IN DATURA SPECIES.

Abstract The ditigloyl esters of the hydroxytropanes, normally found in the roots of Datura spp. occur also in the transpiration stream of D, innoxia and D. cornigera although they do not accumulate in the aerial parts. An alkaloid previously isolated from the leaves or roots of a number of species, and now obtained from the transpiration stream is probably an optical isomer of norhyoscine. Hyoscine is the principal alkaloid of the sap of both the species investigated and noratropine and hyoscyamine are also present.

Drought effects on water relations in beech: The contribution of exchangeable water reservoirs

The exceptional soil drought and heat wave that occurred in Europe in summer 2003 provided a good opportunity to analyze the response of forest ecosystems to extreme climatic conditions. This work aimed at studying the functioning of exchangeable water reservoirs of beech trees under climatic and edaphic constraints, in a 37-year-old beech stand located in north-eastern France. We characterised the impact of drought on seasonal variations in water fluxes at the tree (sap flow measurements) and the forest (eddy covariance measurements) scales and estimated (i) the daily water storage capacity of beech trees as the difference between stand-scaled sap flow and water vapour flux over the stand and (ii) the contribution of exchangeable water in tree reservoirs to the total tree transpiration, under non-limiting soil water (summer 2002) or severe soil drought conditions (summer 2003). In parallel, daily variations in trunk circumference were analyzed to estimate the contribution of elastic tissues as a compartment for water storage to tree transpiration. Stand transpiration was strongly reduced by soil water shortage (up to 80% at the peak of drought in August 2003). From the beginning of August 2003, we observed daytime contraction of stem circumference, with only partial, or even no night recovery, suggesting that trees were less and less able to refill the elastic and strongly depleted reservoirs. Even if those elastic reservoirs were active throughout the season, the corresponding volume of water withdrawn for tree transpiration remained very low (maximum 1% of the daily transpiration). Thus, elastic tissue reservoirs play a minor role in the total water budget of beech trees. The amount of water depleted daily from the whole reservoirs was much higher than the water extracted from elastic tissues. Furthermore, the contribution of total exchangeable water within trees to the transpiration stream increased during the dry period (from a few percent to 67% at the peak of the drought) and was positively correlated with soil water shortage. Our results thus clearly demonstrated the strong sensitivity of beech to both climate and drought and the major role of whole tree water reservoirs to maintain leaf transpiration under severe drought.

Two measures of leaf capacitance: insights into the water transport pathway and hydraulic conductance in leaves.

The efficiency and stress tolerance of leaf water transport are key indicators of plant function, but our ability to assess these processes is constrained by gaps in our understanding of the water transport pathway in leaves. A major challenge is to understand how different pools of water in leaves are connected to the transpiration stream and, hence, determine leaf capacitance (Cleaf) to short- and medium-term fluctuations in transpiration. Here, we examine variation across an anatomically and phylogenetically diverse group of woody angiosperms in two measures of Cleaf assumed to represent bulk-leaf capacitance (Cbulk) and the capacitance of leaf tissues that influence dynamic changes in leaf hydration (Cdyn). Among species, Cbulk was significantly correlated with leaf mass per unit area, whereas Cdyn was independently related to leaf lignin content (%) and the saturated mass of leaf water per unit dry weight. Dynamic and steady-state measurements of leaf hydraulic conductance (Kleaf) agreed if Cdyn was used rather than Cbulk, suggesting that the leaf tissue in some species is hydraulically compartmentalised and that only a proportion of total leaf water is hydraulically well connected to the transpiration stream. These results indicate that leaf rehydration kinetics can accurately measure Kleaf with knowledge of the capacitance of the hydraulic pathway.

Absorption and translocation to the aerial part of magnetic carbon-coated nanoparticles through the root of different crop plants

The development of nanodevices for agriculture and plant research will allow several new applications, ranging from treatments with agrochemicals to delivery of nucleic acids for genetic transformation. But a long way for research is still in front of us until such nanodevices could be widely used. Their behaviour inside the plants is not yet well known and the putative toxic effects for both, the plants directly exposed and/or the animals and humans, if the nanodevices reach the food chain, remain uncertain. In this work we show that magnetic carbon-coated nanoparticles forming a biocompatible magnetic fluid (bioferrofluid) can easily penetrate through the root in four different crop plants (pea, sunflower, tomato and wheat). They reach the vascular cylinder, move using the transpiration stream in the xylem vessels and spread through the aerial part of the plants in less than 24 hours. Accumulation of nanoparticles was detected in wheat leaf trichomes, suggesting a way for excretion/detoxification. This kind of studies is of great interest in order to unveil the movement and accumulation of nanoparticles in plant tissues for assessing further applications in the field or laboratory.

Cadmium uptake and sequestration kinetics in individual leaf cell protoplasts of the Cd/Zn hyperaccumulator Thlaspi caerulescens

Hyperaccumulators store accumulated metals in the vacuoles of large leaf epidermal cells (storage cells). For investigating cadmium uptake, we incubated protoplasts obtained from leaves of Thlaspi caerulescens (Ganges ecotype) with a Cd-specific fluorescent dye. A fluorescence kinetic microscope was used for selectively measuring Cd-uptake and photosynthesis in different cell types, so that physical separation of cell types was not necessary. Few minutes after its addition, cadmium accumulated in the cytoplasm before its transport into the vacuole. This demonstrated that vacuolar sequestration is the rate-limiting step in cadmium uptake into protoplasts of all leaf cell types. During accumulation in the cytoplasm, Cd-rich vesicle-like structures were observed. Cd uptake rates into epidermal storage cells were higher than into standard-sized epidermal cells and mesophyll cells. This shows that the preferential heavy metal accumulation in epidermal storage cells, previously observed for several metals in intact leaves of various hyperaccumulator species, is due to differences in active metal transport and not differences in passive mechanisms like transpiration stream transport or cell wall adhesion. Combining this with previous studies, it seems likely that the transport steps over the plasma and tonoplast membranes of leaf epidermal storage cells are driving forces behind the hyperaccumulation phenotype.

Water use characteristics of a bamboo species ( Bambusa blumeana) in the Philippines

We studied water use in a common bamboo species ( Bambusa blumeana J.A. and J.H. Schultes) in the Philippines with the aim to (1) estimate bamboo water use and its dependence on environmental factors, (2) evaluate internal water storage and water dynamics and (3) compare water use characteristics of this bamboo species with those of co-occurring tree species. Two thermal sap flow methods were applied and complemented with a deuterium tracing experiment. Sap flow measured using the stem heat balance method (SHB) was in agreement with simultaneous flow measurements from thermal dissipation probes (TDP) which were used for long term measurements in this study. Maximal sap flux densities measured at the culm base using the TDP method were up to 25.7 g cm −2 h −1, but can be 2–3 times higher at other positions along the culm due to changes in the culm wall cross-section. Maximal water use rates of bamboo culms were on average 12 kg d −1, corresponding to a maximal transpiration rate of 1.4 mm d −1 at the clump level. These values are in line with those of co-occurring tree species, but bamboo tends to limit water use more under reduced soil water availability than most co-occurring tree species. Deuterium added to the transpiration stream at the culm base travelled upwards more slowly than in trees, leading to maximal deuterium levels in the canopy at the 3rd or 6th day after labelling, whereas this was the 1st or 2nd day for trees. This may indicate higher water storage capacities in bamboo relative to its water use rates, although diurnal patterns of sap flux density did not support this interpretation.

Improved salinity tolerance of rice through cell type-specific expression of AtHKT1;1.

Previously, cell type-specific expression of AtHKT1;1, a sodium transporter, improved sodium (Na+) exclusion and salinity tolerance in Arabidopsis. In the current work, AtHKT1;1, was expressed specifically in the root cortical and epidermal cells of an Arabidopsis GAL4-GFP enhancer trap line. These transgenic plants were found to have significantly improved Na+ exclusion under conditions of salinity stress. The feasibility of a similar biotechnological approach in crop plants was explored using a GAL4-GFP enhancer trap rice line to drive expression of AtHKT1;1 specifically in the root cortex. Compared with the background GAL4-GFP line, the rice plants expressing AtHKT1;1 had a higher fresh weight under salinity stress, which was related to a lower concentration of Na+ in the shoots. The root-to-shoot transport of 22Na+ was also decreased and was correlated with an upregulation of OsHKT1;5, the native transporter responsible for Na+ retrieval from the transpiration stream. Interestingly, in the transgenic Arabidopsis plants overexpressing AtHKT1;1 in the cortex and epidermis, the native AtHKT1;1 gene responsible for Na+ retrieval from the transpiration stream, was also upregulated. Extra Na+ retrieved from the xylem was stored in the outer root cells and was correlated with a significant increase in expression of the vacuolar pyrophosphatases (in Arabidopsis and rice) the activity of which would be necessary to move the additional stored Na+ into the vacuoles of these cells. This work presents an important step in the development of abiotic stress tolerance in crop plants via targeted changes in mineral transport.

Effect on shoot water relations, and cytokinin and abscisic acid levels of inducing expression of a gene coding for isopentenyltransferase in roots of transgenic tobacco plants

Heat shock (HS) at 40 degrees C was given to the root system of Nicotiana tabacum wild type (WT) and to HSIPT transgenic plants transformed with the bacterial cytokinin biosynthesis gene isopentenyltransferase (ipt) cloned behind the heat shock 70 promoter from Drosophila melanogaster. HS increased cytokinin concentrations in roots and leaves of transgenic plants. The effect was smaller in WT plants and restricted to upper leaves. HS also increased the activity of the cytokinin-degrading enzyme cytokinin oxidase in leaves of transgenic plants. This suggests that increases in cytokinin concentration induced by HS were lessened but not eliminated by increases in cytokinin oxidase. Elevated levels of zeatin riboside (the main transportable form of cytokinin) were also found in the HS-treated roots. It is proposed that increases in leaves were the outcome of increased transport of this hormone from roots in the transpiration stream. In conjunction with increased leaf cytokinin concentration, HS treatment to the roots increased stomatal conductivity and transpiration in both transgenic and WT plants. Subsequently, increased transpiration depressed leaf relative water content. This, in turn, raised leaf abscisic acid (ABA) concentrations, resulting in stomatal closure. It is concluded that the preceding increases in leaf cytokinin concentration, stomatal opening, and faster transpiration resulting from the localized induction of ip gene expression in roots strengthens the concept of cytokinin involvement in root to shoot signalling.

Contrasting dynamics of water and mineral nutrients in stems shown by stable isotope tracers and cryo‐SIMS

Lateral exchange of water and nutrients between xylem and surrounding tissues helps to de-couple uptake from utilization in all parts of a plant. We studied the dynamics of these exchanges, using stable isotope tracers for water (H(2)(18)O), magnesium ((26)Mg), potassium ((41)K) and calcium ((44)Ca) delivered via a cut stem for various periods to the transpiration stream of bean shoots (Phaseolus vulgaris cv. Fardenlosa Shiny). Tracers were subsequently mapped in stem cross-sections with cryo-secondary ion mass spectrometry. The water tracer equilibrated within minutes across the entire cross-section. In contrast, the nutrient tracers showed a very heterogeneous exchange between xylem vessels and the different stem tissues, even after 4 h. Dynamics of nutrients in the tissues revealed a fast and extensive exchange of nutrients in the xylem parenchyma, with, for example, calcium being completely replaced by tracer in less than 5 min. Dilution of potassium tracer during its 30 s transit in xylem sap through the stem showed that potassium concentration was up-regulated over many hours, to the extent that some of it was probably supplied by phloem recirculation from the shoot.

Mineral nutrition and heterotrophy in the water conservative holoparasite Hydnora Thunb. (Hydnoraceae)

There are large gaps in our understanding of parasite–host nutrient relationships. Our goal was to evaluate transdermal water loss, parasite–host mineral relationships, and heterotrophy in the holoparasitic genus Hydnora. We estimated in situ transdermal water loss in Hydnora and measured nutrient profiles and δ 13C and δ 15N signatures for Hydnora and hosts in southern Africa and Madagascar. For comparison we also measured δ 13C and δ 15N for aerial hemiparasites at the same sites. Transdermal water loss in Hydnora ranged from 0.14 ± 0.02 to 0.38 ± 0.04 mg cm −2 h −1 and was comparable to transpiration rates for water conservative xerophytes. Concentrations of P and K were higher in Hydnora relative to CAM hosts; other mineral concentrations were significantly lower in the parasite or were not different. δ 13C signatures of holoparasites and hemiparasites relative to their hosts reflected host metabolism and differences in commitment to heterotrophic C gain. Holoparasite δ 13C values were significantly enriched (by 0.55‰ ± 0.23) compared to host shoot and depleted compared to host root tissues (by −0.97‰ ± 0.12). Holoparasite δ 13C values were not significantly different compared to the estimated whole host δ 13C value. δ 15N values for holoparasites and hemiparasites were significantly correlated with hosts. The water conservative nature of Hydnora spp. combined with parasite–host mineral nutrition profiles are suggestive of active processes of solute uptake. Stable isotope fractionation in host tissues dictated significant differences between parasite and host (shoot and root) δ 13C signatures. The confirmation of complete heterotrophy and the lack of a confounding transpiration stream may make Hydnora a promising model organism for the examination of parasite solute uptake.

Bioconcentration factor estimates of polycyclic aromatic hydrocarbons in grains of corn plants cultivated in soils treated with sewage sludge

This study presents a model to simulate the organic substance concentrations in corn grains assuming that the substances in soil solution are absorbed via the transpiration stream by plants growing in soils fertilized with sewage sludge (SS). The model was applied and validated using soil and corn grain samples from a long-term field experiment with six successive yearly applications of SS to the soil. The following polycyclic aromatic hydrocarbons (PAHs) were simulated and evaluated in soil and grain samples: acenaphthene, acenaphthylene, anthracene, benz(a)anthracene, benz(a)pyrene, benz(b)fluoranthene, benz(g,h,i)perylene, benz(k)fluoranthene, chrysene, dibenz(a,h)anthracene, fluoranthene, fluorene, indeno(1,2,3-c,d)pyrene, naphthalene, phenanthrene and pyrene. The PAH bioconcentration factors ( BCF) in corn grains ranged from 1.57 to 10.97 L kg − 1 . Polycyclic aromatic hydrocarbons with low soil distribution coefficients and high values of transpiration stream concentration factors ( TSCF) are more likely to be absorbed by corn plants and accumulated in grains. It was possible to estimate and observe that highly lipophilic PAH molecules (heavy PAHs) show lower accumulative potential in corn grains than the less lipophilic ones (light PAHs). Sewage sludges containing significant concentrations of light PAHs with two, three or four benzene rings should be avoided as fertilizers in alimentary field crops.