How clonal are clones? A quest for loss of heterozygosity during asexual reproduction in Daphnia magna

Due to the lack of recombination, asexual organisms are predicted to accumulate mutations and show high levels of within‐individual allelic divergence (heterozygosity); however, empirical evidence for this prediction is largely missing. Instead, evidence of genome homogenization during asexual reproduction is accumulating. Ameiotic crossover recombination is a mechanism that could lead to long genomic stretches of loss of heterozygosity (LOH) and unmasking of mutations that have little or no effect in heterozygous state. Therefore, LOH might be an important force for inducing variation among asexual offspring and may contribute to the limited longevity of asexual lineages. To investigate the genetic consequences of asexuality, here we used high‐throughput sequencing of Daphnia magna for assessing the rate of LOH over a single generation of asexual reproduction. Comparing parthenogenetic daughters with their mothers at several thousand genetic markers generated by restriction site‐associated DNA (RAD) sequencing resulted in high LOH rate estimation that largely overlapped with our estimates for the error rate. To distinguish these two, we Sanger re‐sequenced the top 17 candidate RAD‐loci for LOH, and all of them proved to be false positives. Hence, even though we cannot exclude the possibility that short stretches of LOH occur in genomic regions not covered by our markers, we conclude that LOH does not occur frequently during asexual reproduction in D. magna and ameiotic crossovers are very rare or absent. This finding suggests that clonal lineages of D. magna will remain genetically homogeneous at least over time periods typically relevant for experimental work.     

Are rodents a source of biotic resistance to tree invasion in Pampean grasslands? Tree seed consumption under different conditions

Biotic resistance has been invoked as a major barrier to woody species invasion, although the role of resident generalist consumers and their interaction with seed availability in a local community has received little attention. We assessed tree seed consumption by rodents under two different scenarios: (i) We documented in field spatio‐temporal patterns of seed predation by native rodents on two exotic tree species, Gleditsia triacanthos or ‘honey locust’ and Robinia pseudoacacia or ‘white locust’ (family Leguminosae), in five grassland habitats of the Inland Pampa, Argentina. (ii) We conducted laboratory feeding trials to evaluate tree seed consumption in the presence (cafeteria‐style feeding trials) and in the absence (non‐choice feeding trials) of alternative food supplies. Seed predation was generally higher for Robinia than for Gleditsia seeds, both in field and laboratory conditions. For both tree species, seed predation varied between habitats and seasons and was higher in the native tussock grassland than in the remaining studied communities, whereas the crop field showed the lowest levels of consumption along with the absence of captured rodents. Seed consumption of Gleditsia and Robinia among the four grassland communities (which did not differ in rodent abundance) was negatively associated with the availability of alternative food. Laboratory feeding trials showed a higher consumption of Gleditsia seeds in the non‐choice than in the cafeteria‐style feeding trials, while the consumption of Robinia seeds did not differ in the absence or presence of alternative seeds. These patterns indicate that the contribution of resident granivores to invasion resistance might depend on colonizer species identity, recipient community type and season of the year. We suggest that rodent preferences for different invader seeds will interact with the availability of alternative food in the local habitat in influencing the amount of predator‐mediated biotic resistance to invasion.     

Is the proportion of clonal species higher at higher latitudes in Australia?

We provide a large‐scale quantification of the relationship between latitude and the proportion of species with clonal reproduction. Parasite pressure is thought to be higher at low latitudes, while abiotic stress is thought to be higher at high latitudes. We therefore predicted that there would be a higher proportion of clonal species at high latitudes than at low latitudes. We collected data of 4386 native seed plant species from 446 genera and 99 families present in ABRSFlora of Australia. Species' occurrence records were taken from the Atlas of Living Australia, including 817 450 species‐site combinations spanning 34.5° of latitude. Logistic regression showed that the proportion of clonal species significantly increased with latitude, rising from 3.3% clonal species at 9.25°S to 26.7% clonal species at 43.75°S. The overall average proportion of clonal species in Australian seed plants was 9.4%. This study adds to our growing understanding of dramatic latitudinal gradients in the way plants grow and reproduce. It also reveals that Australian vegetation contains a relatively low proportion of clonally reproducing species.     

Is fire a selective force of seed size in pine species?

Fire is selectively shaping most of the traits of plants growing in fire-prone environments. However, seed size and other features related to seed production have not been studied in the light of the evolutionary role of fire. Our research tests the hypothesis that larger seeds have a higher chance of surviving wildfires and produce more vigorous seedlings with a lower death rate. To test this hypothesis the germination and early seedling growth of five Spanish pine species were studied. Weight, length and width of all seeds were measured. The biomass (fresh and dry weight) and length (root and total) of subsequent seedlings were also measured after 30 d from emergence. Seeds were submitted to elevated temperatures for periods in which the chance of survival was 50 % (calculated by means of a logistic model for each pine species). The differences observed among species suggests that fire may be adaptively shaping seed size in pines with larger seeds (Pinus canariensis and P. pinaster), because larger seeds are more likely to survive after heat shocks. Furthermore, in P. canariensis, seedlings after heat treatment are even larger than those submitted to control. In P. halepensis, despite being well adapted to fire, our results indicated no relationships between fire and seed characteristics. Finally, although heat treatment has a general adverse effect on seedling growth in the case of the two subalpine pines, we have detected a positive relationship between seed size and seedling growth but only in the largest seeds. This might also suggest the relevance of fire as a selective force for these pines which is outperformed by the relevance of dispersal and emergence time as adaptive traits in the post-fire scenario.     

Pollination and seed set of an obligatory outcrossing plant in an urban–peri-urban gradient

Urban land use strongly affects pollinators and plant pollination due to fragmentation and isolation of natural plant populations. On the other hand, urban land use can potentially be beneficial to pollinators through the presence of urban gardens and parks which are usually designed to ensure abundant flowering. However, little is known about the effects of urban land use on bees and the pollination services they provide. In an urban–peri-urban gradient around Leuven, Belgium we studied flower visitation rates to, and seed set of Trifolium repens (white clover) in public lawns. T. repens is an obligatory outcrossing plant and is therefore sensitive to reductions in pollinator services. We related our results to both local and regional variables using Boosted Regression Trees. The two variables that best explained the variability in visitation rates and seed set were the amount of green areas (gardens, parks, grasslands) in the surroundings and the abundance of T. repens in the lawns. Surprisingly, an increasing amount of green areas in the surroundings had a negative effect on both flower visitation rates to, and seed set of T. repens. Flower visitation rates by bumblebees responded positively to urban land use resulting in higher visitation rates and increased seed set in the more urban sites. This may point either to increased abundance of bumblebees in more urban sites or to a concentration effect of bumblebees in our urban study sites due to a lack of alternative forage resources. Responses will likely differ for other bee and plant species, but this shows that at least for T. repens, pollination is not compromised by urban land use.     

Is acid-induced extension in seed plants only protein-mediated?

Cell wall extensibility controls the rate of plant cell growth. It is determined by intrinsic mechanical properties of wall polymers and by wall proteins modifying these polymers and their interactions. Heat-inactivation of endogenous cell wall proteins inhibited acid-induced extension of onion epidermis peels transverse to the net cellulose alignment in the cell wall but not parallel to it. In the former case the acid-induced extension could be controlled by expansins and in the latter case by pectins restricting shear between microfibrils. Heat-inactivated cell walls stretched transversely to the net cellulose orientation extended faster at pH 5.7 and slower at pH 4.5 compared to native walls. Expansins seem to be inactive at pH 5.7, so that faster extension may result from heat-induced viscous flow of pectins and conformational changes in the cuticle of the epidermis. This stimulation of wall extension is not seen at pH 4.5 as it is outweighed by the inhibitory effect of expansin heat-inactivation. Thus, cell wall extension in higher plants might be controlled by a complex interplay between protein-dependent and protein-independent mechanisms, the result of which depends on pH and preferential orientation of main wall polymers.     

Is farther seed dispersal better? Spatial patterns of offspring mortality in three rainforest tree species with different dispersal abilities

The paradigm that tropical trees with farther seed dispersal experience lower offspring mortality is currently based on within-species studies documenting higher survival of offspring located farther from conspecific adults and/or closer to light gaps. We determined whether the paradigm also holds among species by comparing spatial patterns of offspring mortality among three sympatric Neotropical rainforest tree species with the same seed dispersers but with different dispersal abilities. First, we assessed spatially non-random mortality for each species by measuring spatial shifts of the population recruitment curve (PRC) with respect to conspecific adults and light gaps across three early life stages: dispersed seeds, young seedlings and old seedlings. Then, we determined whether PRC shifts were greater for the species with short dispersal distances than for the species with greater dispersal distances. We found that the PRC shifted away from conspecific adults consistently across life stages, but we found no consistent PRC shifts towards gaps, suggesting that mortality was related more to the proximity of conspecifics than to absence of light gaps. PRC shifts away from adults were greatest in the species with the lowest dispersal ability, supporting the paradigm. Differential PRC shifts caused the spatial distribution of offspring to become almost independent with respect to adult trees and gaps in all three species, despite large differences in seed dispersal distance among these species. Our results provide direct empirical support for the paradigm that among tropical trees, species with farther seed dispersal are less impacted by spatially non-random mortality than are similar species with shorter dispersal distances. Thus, greater dispersal effectiveness merits extra investments of trees in seed dispersal ability, even at the cost of fecundity.     

Does perianth colour affect the seed germination of two desert shrubs under different storage periods and conditions?

Haloxylon salicornicum and Salsola vermiculata (Amaranthaceae) are two perennial shrubs producing fruits with differently coloured perianths (yellow vs pink) on separate individuals. To test the impact of different storage periods (four, eight and twelve months) and temperature conditions (freezing, room temperature and natural field temperatures) on the seed germination of the two seed categories, germination tests were carried out on both species. For both species, collected from wild plants in the Arabian desert (Qatar), seed germination was tested under two photoperiods (light 12/12; dark 24 hours) at 20/30°C for winged (intact) and de‐winged seeds. For each species, all the considered factors (perianth colour, wing presence, photoperiod, storage period and storage conditions) had significant effects on seed germination (p < 0.001), while the interactions among factors varied in their level of significance depending on the species. In both species, yellow seeds germinated considerably better than the pink ones, the presence of wings slowed the germination, and both storage period and temperature conditions highly influenced their germination ability. Our results indicate that seeds from different perianth colours have different germination strategies to delay their germination and distribute the species through time by escaping germination time by imposing some kind of after‐ripening or seed dormancy. The variation in storage time and storage conditions might help in extending their germination period, where one set of seeds germinate immediately, and the other set of seeds becomes dormant and thus contributes to the formation of a soil seed bank for the long‐term recruitment of seedlings. This study highlights an ecological advantageous strategy for these two species growing in the unpredictable desert habitat.     

Is there an optimal number of helpers in Alpine marmot family groups?

The consequence of helping behavior on breeders fitness is stillcontroversial. We used multivariate analyses to investigatefor the effects of male and female subordinates on breeders'components of fitness in the Alpine marmot, Marmota marmota.We found that male and female subordinates, respectively, increasedand decreased juvenile survival during winter. Thus, we giveevidence that male subordinates should be considered as helpers,and that helpers provided breeders with immediate reproductivesuccess gains, whereas subordinates females were costly. Helpershad no positive effects on female body condition, on persistence(future survival) of dominants, and on future reproduction (occurrenceand size of a litter). Helpers thus did not provide breederswith delayed fitness benefits, and therfore, the load-lighteninghypothesis was not supported. On the contrary, helpers had delayedfitness cost for dominant males and, consequently, for dominantfemales. Immediate benefits counterbalanced by delayed costssuggested an optimal number of helpers in the family group bothfrom male and female perspectives. An optimality model wellpredicted the observed mean number of helpers in Alpine marmotfamily groups. Optimal numbers of helpers were slightly differentfor males and females, suggesting a potential conflict of interestbetween dominants. We finally discuss the possible mechanismsof helping that may explain the observed pattern in the Alpinemarmot.     

A sum of its individual parts? Relative contributions of different eggshell regions to intraclutch variation in birds

The rejection of eggs of brood parasites in several species of hosts is based on cues only at the blunt pole (BP) and not at the sharp pole (SP) of the foreign and own eggshell. We investigated whether intraclutch variation is confined to a specific egg pole in species where the extent of intraclutch variation in the overall egg appearance is known to positively covary with either egg rejection rate or the probability of being parasitized. For the two poles separately, we analysed intraclutch variation of eggshell brightness and blue chroma. We quantified intraclutch variation as the standard deviations of these colour metrics, instead of their coefficients of variation which would represent a statistically flawed approach. Pooling measurements of brightness across the whole egg surface led to statistically non‐significant results and masked positive correlations of BP brightness with egg rejection or parasitism risk, respectively. In contrast, patterns of blue chroma were important across the whole egg. Thus, the traditional whole egg ‘averaging’ approach may mask biologically important effects of intraclutch variation when the variation and potential signalling functions of egg appearance are confined to a specific egg part (brightness). However, analyses based on only BP and SP eggshell region specific data may also lack the power to detect effects of phenotypic traits that do not vary between egg poles (blue chroma). We advocate the use of a combination of region‐specific and whole‐eggshell based colour metrics and manipulations in cognitive, perceptual, and ecological studies of foreign egg rejection.     

Is optimism optimal? Functional causes of apparent behavioural biases

We review the use of the terms ‘optimism’ and ‘pessimism’ to characterize particular types of behaviour in non-human animals. Animals can certainly behave as though they are optimistic or pessimistic with respect to specific motivations, as documented by an extensive range of examples in the literature. However, in surveying such examples we find that these terms are often poorly defined and are liable to lead to confusion. Furthermore, when considering behaviour within the framework of optimal decision theory using appropriate currencies, it is often misleading to describe animals as optimistic or pessimistic. There are two common misunderstandings. First, some apparent cases of biased behaviour result from misidentifying the currencies and pay-offs the animals should be maximising. Second, actions that do not maximise short-term pay-offs have sometimes been described as optimistic or pessimistic when in fact they are optimal in the long term; we show how such situations can be understood from the perspective of bandit models. Rather than describing suboptimal, unrealistic behaviour, the terms optimism and pessimism are better restricted to informal usage. Our review highlights the importance of choosing the relevant currency when attempting to predict the action of natural selection.     

Is tree diversity different in the Southern Hemisphere?

Questions: Is tree diversity higher in the southern hemisphere? Are latitudinal asymmetries in diversity sensitive to sampling effects? Location: 198 forested locales worldwide. Methods: I re‐analysed the Gentry database, which I augmented with an additional survey from New Zealand. Data were used to test whether latitudinal declines in tree diversity differ between the northern and southern hemispheres. Data were also used to test whether hemispheric asymmetries in diversity are sensitive to sampling effects, or geographic variation in tree densities. Results: Area‐based measurements of species diversity are higher in the southern hemisphere. However, southern forests house denser plant populations. After controlling for geographic variation in tree densities, diversity patterns reverse, indicating tree diversity is higher in the northern hemisphere. Conclusions: Latitudinal changes in tree diversity differ between hemispheres. However, the nature of hemispherical asymmetries in species diversity hinges on how diversity is defined, illustrating how different definitions of diversity can yield strikingly different solutions to common ecological problems.     

Is cell polarity under mechanical control in plants?

Plant cells experience a tremendous amount of mechanical stress caused by turgor pressure. Because cells are glued to their neighbors by the middle lamella, supracellular patterns of physical forces are emerging during growth, usually leading to tension in the epidermis. Cortical microtubules have been shown to reorient in response to these mechanical stresses, and to resist them, indirectly via their impact on the anisotropic structure of the cell wall. In a recent study, we show that the polar localization of the auxin efflux carrier PIN1 can also be under the control of physical forces, thus linking cell growth rate and anisotropy by a common mechanical signal. Because of the known impact of auxin on the stiffness of the cell wall, this suggests that the mechanical properties of the extracellular matrix play a crucial signaling role in morphogenesis, notably controlling the polarity of the cell, as observed in animal systems.Key words: development, growth, auxin, microtubule, PIN1, stiffness, cell wall, biophysics, meristemThe current development of high throughput analyses of gene regulatory networks is feeding a very complex view of growth control and shape changes. To go beyond the accumulation of data, the identification of universal and parsimonious mechanisms explaining the robustness of morphogenesis becomes a central issue in today''s developmental biology.^1–3 Among them, the coupling between molecular and mechanical signals has the strong advantage of providing a simple way to coordinate cell behavior synchronously and over long distances. The role of such signals has been investigated in different systems and the contribution of mechanical forces to animal development is now widely accepted, as the expression of key genes (e.g., TWIST⁴) and key cellular events (e.g., mitotic spindle orientation⁵) have been shown to depend on the mechanical environment of the tissue. Several mechanosensors have also been identified.⁶In an earlier study, we showed that the orientation of the cortical microtubular cytoskeleton in plant shoot meristems depends on the principal direction of mechanical stress. Cortical microtubules are known to guide the deposition of the cellulose microfibrils in the cell wall and thus to control the main direction of growth, and consequently, shape. Evidence indicates that the epidermis is under tension, and therefore the shape of the tissue can influence the pattern of mechanical stress. In this framework, multicellular shape is transposed into a map of stress directions in the epidermis that can act as a supracellular instructional signal. By applying mechanical constraints on a meristem with GFP-marked microtubules, we were able to close the feedback loop: microtubule orientation became parallel to the externally applied stress, supporting a view in which mechanical stress controls cell behavior.⁷In a more recent study we showed that in addition to the cortical microtubules, the polar localization of the auxin efflux carrier PIN1 can also be controlled by its mechanical environment. In particular, we observed that, when viewed from the top, PIN1 is usually concentrated on the membrane that is parallel to the microtubule orientation. Furthermore, a single cell ablation, which induces both a circumferential pattern of stress around the wound and a circumferential orientation of microtubules, also induced a relocalization of PIN1 away from the wound on the circumferential membrane, consistent with the hypothesis that PIN1 would be preferentially recruited on the membrane undergoing the most tensile stress.⁸ Mechanistically, it is unclear how this could be achieved, but the PIN1 vesicle recycling machinery is likely to play a major role, since it is now well established that membrane tension inhibits endocytosis and favors exocytosis.⁹ In such a scenario, PIN1 would be trapped in a membrane as long as the tension of the membrane is higher than that of its neighbours.To further test the response of PIN1 to mechanical forces, we used a pharmacological approach. Figure 1 highlights the correlation between the predicted opposable impacts of isoxaben and oryzalin on stress and the response of PIN1. In the presence of isoxaben, a well known inhibitor of cellulose synthesis, the thickness of the cell wall is supposed to decrease. Knowing that mechanical stress is here defined as a force divided by the area of a section of the wall, stress is expected to increase after isoxaben treatment. When we treated PIN1-GFP meristems with isoxaben, we observed a “hyper” localization of PIN1, with in most cases a preferential localization of PIN1 along the supracellular stress patterns, and within the cell, a concentration of the signal at cell corners, predicted sites of stress maxima. In contrast, in the presence of oryzalin, which by depolymerising the microtubules leads to isotropic growth and thus isotropic stresses, PIN1 localization became more homogeneous.Open in a separate windowFigure 1Impact of isoxaben and oryzalin on the localization of PIN1 in meristematic cells. The PIN1-GFP signal (in black) is very heterogenous in the control meristematic cells, consistent with the preferential localization of PIN1 to one side of the cells. Sometimes the signal is even restricted to one cell corner. After microtubule depolymerization with oryzalin, cell growth becomes more isotropic, and while PIN1 localization remains heterogenous, the signal becomes more widespread on each plasma membranes and thus tends to homogeneity. In contrast, after isoxaben treatment (which inhibits cellulose synthesis and thus is predicted to increase stress levels), the PIN1-GFP protein concentrates at the corners of the cells.⁸It seems therefore plausible that mechanical stress acts as a common instructional signal for both microtubule-dependent cell anisotropy and PIN1/auxin-dependent growth rate. Mathematical modeling further supported this proposal. Several successful models for the generation of organ patterns in the meristem assume an ability of individual cells to sense auxin concentration in their neighbours.^10–16 However to date no mechanism had been proposed to explain how one cell could measure the concentration of auxin in its vicinity. One of the main implications of our study is that, if PIN1 can respond to the mechanical status of the wall, then it also integrates auxin concentration of the neighboring cells, indirectly, as auxin loosens the cell wall, allowing cell expansion. Using such a hypothesis, computer simulations were able to reproduce the stereotyped pattern of organogenesis in the shoot further confirming the plausibility of the model.It must be noted however that our work does not exclude other hypotheses. In particular, it has recently been proposed that the ROP2 and ROP6 proteins, well known effectors of cell polarity, could respond differently to ABP1-dependent auxin signaling, thus providing a model in which cell-cell communication via ROP could “measure” local differences in auxin between neighbors.¹⁷ These different scenarios could actually be reconciled some day, especially knowing that Rho proteins in animals have been involved in the responses to mechanical forces.¹⁸ Last, the control of PIN1 polar localization by its mechanical environment could actually reveal a more universal response of cells to the stiffness and tension of the extracellular matrix. Similarly, animal motile (and polar) cells can sense the rigidity of their substrate^19–21 and respond by reinforcing the cytoskeleton at the cell cortex.^22–25     

Is the behaviour of the leg during oscillation linear?

The linear behaviour of the human leg was studied using a free oscillation method. The lower leg is represented by a simple mass, spring and dashpot model. Forty-five subjects underwent free vibration tests on their right legs. The force amplitude and the time period, for successive oscillations enabled calculation of the stiffness to mass ratio values. It was found that the time period of the second oscillation cycle was significantly lower than that of the first, implying a corresponding increase in stiffness. The experimental data consistently exhibits these non-linear characteristics, indicating that the use of non-linear models could be of benefit for future free oscillation studies.     

Is the potassium channel distribution in glial cells optimal for spatial buffering of potassium?

Glial cells in the nervous system are believed to reduce changes of extracellular potassium concentration ([K+]o), caused by neural activity, by carrying out spatial buffering of potassium. In the case of retinal glial cells (Müller cells), light-evoked increases of [K+]o within the retina are reduced by K ions flowing through the Müller cell to the vitreous fluid of the eye. We have calculated the optimal way to distribute the potassium conductance of the Müller cell to maximize spatial buffering to the vitreous fluid. The best distribution is with half the potassium conductance in the outer part of the cell, where K+ enters, and half the conductance in the vitreal endfoot, where K+ leaves the cell. This calculated distribution is very different from the actual distribution measured by Newman (1984, Nature [Lond.], 309: 155-157), where only 6% of the Müller cell conductance is in the outer cell and 94% is in the endfoot. The experimentally observed distribution gives less than a quarter of the spatial buffering that would be produced by the optimal distribution. The possible advantages of this arrangement are discussed.     

Monitoring of aphid flight activities in?seed?potato?crops?in Serbia

Aphid flight activities in seed potato fields have been studied by the yellow water traps. It is a good method for monitoring aphids as vectors of viruses, but this study also showed it is a suitable method for insect-diversity research. During the four-year studies, over 11.500 specimens were collected and a total of 107 different taxa of aphids were identified. The most abundant species were polyphagous species, such as: Acyrthosiphon pisum (Haris), Aphis fabae Scopoli, Aphis gossypii Gloverand Brachycaudus helichrysi (Kaltenbach). The results of the studies show that diversity of aphids in different regions of Serbia is similar regardless of the altitude and the diversity of terrain. At most sites it ranged from 2 to 3. The highest value was recorded in Begeč, locality in northern part of Serbia, in year 2008, and it was 2.92. The maximum values of the Shannon-Weaver diversity index at all sites were recorded in the first weeks of the monitoring of aphid flight activities. Morisita-Horn similarity index shows no significant differences between sites regardless of altitudes. The sites are grouped by year, not by similarity of relief. In spite of these results, the Chi-square analysis showed highly significant difference in vector frequencies among seasons and sites with more pronounced differences for PVY. As a consequence of differences in vector frequencies, the vector pressure index in some regions was different also. The number of vectors and vector pressure index vary depending on the altitude of localities. At localities at altitudes under 1000 m, they were high. The highest index was at Kotraža, locality in central part of Serbia, in 2007, when PVY index exceeded the value of 180, while for PLRV it was 60. At high altitudes on mountain Golija, above 1100 m, the number of aphids was low, as well as the vector pressure index which indicates that these regions are suitable for producing virus-free seed potato.     

Does origin always matter? Evaluating the influence of nonlocal seed provenances for ecological restoration purposes in a widespread and outcrossing plant species

For restoration purposes, nature conservation generally enforces the use of local seed material based on the “local‐is‐best” (LIB) approach. However, in some cases recommendations to refrain from this approach have been made. Here we test if a common widespread species with no obvious signs of local adaptation may be a candidate species for abandoning LIB during restoration. Using 10 microsatellite markers we compared population genetic patterns of the generalist species Daucus carota in indigenous and formerly restored sites (nonlocal seed provenances). Gene diversity overall ranged between H_e = 0.67 and 0.86 and showed no significant differences between the two groups. Hierarchical AMOVA and principal component analysis revealed very high genetic population admixture and negligible differentiation between indigenous and restored sites (F_CT = 0.002). Moreover, differentiation between groups was caused by only one outlier population, where inbreeding effects are presumed. We therefore conclude that the introduction of nonlocal seed provenances in the course of landscape restoration did not jeopardize regional species persistence by contributing to inbreeding or outbreeding depressions, or any measurable adverse population genetic effect. On the basis of these results, we see no obvious objections to the current practice to use the 10‐fold cheaper, nonlocal seed material of D. carota for restoration projects.     

Is the bioavailability index applicable for trace elements in different types of soil?

Abstract

The bioavailability index (BI) is defined as the proportion of reduction in a plant’s accumulation of an element, caused by the removal of the extractable fraction of the element of interest from the soil. The BI and corresponding experimental methods were quantitatively applied to evaluate the bioavailability of trace elements in five Chinese soils. The soil was first extracted with various reagents (DTPA, HCl and NH₂OH.HCI) separately, to remove the extractable elements. The soil, after extraction, was washed with deionised water to eliminate the extractant used in the fractionation analysis. Then the pH of the soil was re-adjusted with CaO. The soil was then fertilised and incubated in a greenhouse for four weeks. Tests showed that after incubation the pH, cation exchange capacity (CEC) and organic matter (OM) of the treated soil were close to their original values. Wheat (Triticum aestivum L.) was planted in both the untreated and treated soil for eight weeks. After harvest the plant concentrations of the elements Cr, Mn, Co, Ni, Zn, Cu, Cd, and Pb were analysed by inductively coupled plasma mass spectrometry (ICPMS). Trace element accumulation by plants grown in the treated soil was reduced significantly compared with that of plants grown in the untreated soil. The results showed that BI values were in the order BI(DTPA)>BI(HCl)>BI(NH₂OH.HCl). This indicated that the DTPA-extractable fraction represented a highly available fraction of the total content. Variations of BI among different trace elements show that Cr, Mn, Zn and Co have a higher BI, in general for the elements tested, whereas, Cu, Cd and Pb have lower values. There are also slight differences in the BI among soils. However, no significant relationship could be found between the BI and the soil characteristics.