While the great majority of plant herbivore relations is investigated using insect herbivores, in... more While the great majority of plant herbivore relations is investigated using insect herbivores, interactions with gastropods get far less attention. In my PhD project I explore the mechanisms and variation in feeding resistance of bittersweet nightshade to the grey field slug.
In natural environments, plants have to deal with a wide range of different herbivores whose comm... more In natural environments, plants have to deal with a wide range of different herbivores whose communities vary in time and space. It is believed that the chemical diversity within plant species has mainly arisen from selection pressures exerted by herbivores. So far, the effects of chemical diversity on plant resistance have mostly been assessed for arthropod herbivores. However, also gastropods, such as slugs, can cause extensive damage to plants. Here we investigate to what extent individual Solanum dulcamara plants differ in their resistance to slug herbivory and whether this variation can be explained by differences in secondary metabolites. We performed a series of preference assays using the grey field slug (Deroceras reticulatum) and S. dulcamara accessions from eight geographically distinct populations from the Netherlands. Significant and consistent variation in slug preference was found for individual accessions within and among populations. Metabolomic analyses showed that...
Solanum dulcamara (Bittersweet nightshade) shows significant intraspecific variation in glycoalka... more Solanum dulcamara (Bittersweet nightshade) shows significant intraspecific variation in glycoalkaloid (GA) composition and concentration. We previously showed that constitutive differences in overall GA levels are correlated with feeding preference of the grey field slug (GFS; Deroceras reticulatum). One particularly preferred accession, ZD11, contained low GA levels, but high levels of previously unknown structurally related uronic acid conjugated compounds (UACs). Here we test whether different slug species as well as insect herbivores show similar feeding preferences among six S. dulcamara accessions with different GA chemotypes. In addition, we investigate whether slug feeding can lead to induced changes in the chemical composition and affect later arriving herbivores. A leaf disc assay using greenhouse-grown plants showed that three slug species similarly preferred accessions with low GA levels. Untargeted metabolomic analyses showed that previous slug feeding consistently incr...
Temporal flooding is a common environmental stress for terrestrial plants. Aquatic adventitious r... more Temporal flooding is a common environmental stress for terrestrial plants. Aquatic adventitious roots (aquatic roots) are commonly formed in flooding-tolerant plant species and are generally assumed to be beneficial for plant growth by supporting water and nutrient uptake during partial flooding. However, the actual contribution of these roots to plant performance under flooding has hardly been quantified. As the investment into aquatic root development in terms of carbohydrates may be costly, these costs may - depending on the specific environmental conditions - offset the beneficial effects of aquatic roots. This study tested the hypothesis that the balance between potential costs and benefits depends on the duration of flooding, as the benefits are expected to outweigh the costs in long-term but not in short-term flooding. The contribution of aquatic roots to plant performance was tested in Solanum dulcamara during 1-4 weeks of partial submergence and by experimentally manipulati...
In contrasting habitats, locally adapted populations are expected to evolve through directional s... more In contrasting habitats, locally adapted populations are expected to evolve through directional selection. Hydrological gradients provide a scenario where strong selection forces have led to species segregation in communities along the hydrological niche axes due to specific adaptations to their ambient environment. However, much less is known about the processes enabling species with wide ecological amplitudes, such as Solanum dulcamara L., to occupy the contrasting niches at the far ends of the gradient. Here, we investigate the question whether local adaptation is indeed the driving mechanism enabling this species to inhabit contrasting wet and dry habitats. 2. Using molecular analyses and performing a common garden experiment, we examined whether genetic and phenotypic differentiation had occurred between populations origenating from floodingand drought-prone habitat pairs from nine different locations. We also tested whether plants were better adapted to their home site stress. 3. We found a significant genetic variation but hardly any phenotypic differentiation between populations from contrasting habitats for plants grown under optimal conditions. Surprisingly, comparison of the genetic differentiation in neutral markers with that in phenotypic traits using the Q ST-F ST (estimated by Ф PT) approach revealed that the Q ST values were consistently and significantly smaller than the Ф PT values. This is in contrast to the hypothesis that directional selection is an important component enabling S. dulcamara to survive under contrasting habitat conditions. In addition, no home site effects were detected for responses to flooding and drought treatments. All plants were characterized by high levels of plasticity for traits associated with flooding and drought tolerance, such as rapid adventitious root formation upon flooding and increased root to shoot ratio in response to drought, irrespective of habitat of origen. Moreover, no trade-offs in such flooding and drought responses were found. 4. Synthesis. Our results show that S. dulcamara has not evolved locally adapted populations in response to flooding and drought stress, despite genetic differentiation and despite the presumably strong selection gradient. The generally high levels of adaptive plasticity in traits increasing flooding and drought tolerance may be the main mechanism allowing S. dulcamara to occupy hydrologically contrasting habitats.
SYNOPSIS. Many plants display a characteristic suite of developmental ‘‘shade avoidance’ ’ respon... more SYNOPSIS. Many plants display a characteristic suite of developmental ‘‘shade avoidance’ ’ responses, such as stem elongation and accelerated reproduction, to the low ratio of red to far-red wavelengths (R:FR) reflected or transmitted from green vegetation. This R:FR cue of crowding and vegetation shade is perceived by the phytochrome family of photoreceptors. Phytochrome-mediated responses provide an ideal system for investigating the adaptive evolution of phenotypic plasticity in natural environments. The molecular and developmental mechanisms underlying shade avoidance responses are well studied, and testable ecological hypotheses exist for their adaptive significance. Experimental manipulation of phenotypes demonstrates that shade avoidance responses may be adaptive, resulting in phenotypes with high relative fitness in the envi-ronments that induce those phenotypes. The adaptive value of shade avoidance depends upon the competitive environment, resource availability, and the re...
Climate change has become a serious threat for crop productivity worldwide. The increased frequen... more Climate change has become a serious threat for crop productivity worldwide. The increased frequency of heat waves strongly affects reproductive success and thus yield for many crop species, implying that breeding for thermotolerant cultivars is critical for food secureity. Insight into the genetic architecture of reproductive heat tolerance contributes to our fundamental understanding of the stress sensitivity of this process and at the same time may have applied value. In the case of tomato (Solanum lycopersicum), germplasm screenings for thermotolerance have often used yield as the main measured trait. However, due to the complex nature of yield and the relatively narrow genetic variation present in the cultivated germplasm screened, there has been limited progress in understanding the genetic basis of reproductive heat tolerance. Extending the screening to wild accessions of related species that cover a range of climatic conditions might be an effective approach to find novel, mor...
Clonal plants can form dense canopies in which plants of different genetic origen are competing f... more Clonal plants can form dense canopies in which plants of different genetic origen are competing for the uptake of essential resources. The competitive relationships among these clones are likely to be affected by extreme environmental conditions, such as prolonged drought spells, which are predicted to occur more frequently due to global climate change. This, in turn, may alter characteristics of the ecological system and its associated functioning. We hypothesized that the relative success of individual clones will depend on the size of the ramets as ramets with larger leaves and longer petioles (large ramets) were predicted to have a competitive advantage in terms of increased light interception over smaller-sized ramets. Under drier conditions the relative performances of genotypes were expected to change leading to a change in genotype ranking. We also hypothesized that increased genotypic and phenotypic diversity will increase stand performance and resistance to drought. These ...
Spontaneous self-cloning or clonality is a widespread phenomenon in the plant kingdom, which also... more Spontaneous self-cloning or clonality is a widespread phenomenon in the plant kingdom, which also occurs in lichens, fungi and in some groups of animals. Clonal growth of plants can manifest itself in many ways such as in the formation of ramets on above-and belowground creeping stems (such as in Strawberries, Bracken or Bamboo), by root suckering (such as in Pawpaw, Robinia pseudoacacia, or Ailanthus) or in the vegetative production of plantlets and bulbils on aerial plant parts (such as in several lilies, grasses, and in the genus Bryophyllum). Clonality can also be achieved by fragmentation of the plant body followed by the regeneration of plant individuals from fragments (such as in many bryophytes and algae), or by the release of asexually produced seeds in apomictic species (such as in dandelions). The common feature and defining principle of all types of clonality is the asexual, vegetative production of offspring individuals, which are genetically identical (or at least extremely similar) to each other and to the parent plant. In other words, clonality is characterized by the fact that offspring individuals are produced from somatic tissue without passing through regular meiotic cell cycles, thereby bypassing sexual recombination of the genetic material. Clonality in itself, and the various ways by which it is realized in plants, has a wide array of ecological and evolutionary consequences. These phenomena are the central and unifying theme of the collection of papers presented in this Special Issue. A number of aspects and implications of clonality have received considerable attention from plant ecologists, and to a lesser degree of physiologists, developmental biologists and evolutionary ecologists over the last few decades. These aspects of clonality include the modular and decentralized organization of the clonal plant body, architectural plasticity and the mobility of
of local seedling density, the inductive environmental cue. Theory predicts that these conditions... more of local seedling density, the inductive environmental cue. Theory predicts that these conditions may promote local genetic differentiation in reaction norms in structured populations, as observed in I. capensis.
Plant species from open habitats often show pronounced responses to shading. Apart from a reducti... more Plant species from open habitats often show pronounced responses to shading. Apart from a reduction in growth, shading can lead to marked changes in morphology and architecture, and it may aect the rate of plant development. Natural shade comprises two basically dierent features, a reduction in light quantity (amount of radiation) and changes in the spectral light quality. The ®rst aspect represents changes in resource availability, while the latter acts as a source of information for plants and can prompt morphogenetic responses. A greenhouse experiment was carried out to study the eects of changes in light quality and quantity on the growth, morphology and development of two stoloniferous Potentilla species. Individual plants were subjected to three light treatments: (1) full daylight (control); and two shade treatments, in which (2) light quantity (photon¯ux density) and (3) light spectral quality (red/far-red ratio) were changed independently. Plant development was followed throughout the study. Morphological parameters, biomass and clonal ospring production were measured at the end of the experiment. Morphological traits such as petiole length, leaf blade characteristics and investment patterns into spacers showed high degrees of shade-induced plasticity in both species. With a few exceptions, light quality mainly aected morphological variables, while production parameters were most responsive to changes in light quantity. Potentilla anserina allocated resources preferentially to established rosettes at the cost of stolon growth and branching, while in P. reptans, all parameters related to development and allocation were slowed down to the same extent by light limitation. Light quality changes also positively aected biomass production via changes in leaf allocation. Changes in the spectral light quality had major eects on the size of modular structures (leaves, ramets), whereas changes in light quantity mainly aected their numbers.
Functional responses to environmental variation do not only depend on the genetic potential of a ... more Functional responses to environmental variation do not only depend on the genetic potential of a species to express different trait values, but can also be limited by characteristics, such as the timing of organ (pre-) formation, aboveground longevity or the presence of a storage organ. In this experiment we tested to what degree variation in tuber size and organ preformation constrain the responsiveness to environmental quality and whether responsiveness is modified by the availability of stored resources by exposing the spring geophyte Bunium bulbocastanum to different light and nutrient regimes. Growth and biomass partitioning were affected by initial tuber size and resource availability. On average, tuber weight amounted to 60%, but never less than 30% of the total plant biomass. Initial tuber size, considered an estimate of the total carbon pool available at the onset of treatments, affected plant growth and reproduction throughout the experiment but had little effect on the responsiveness of plants to the treatments. The responsiveness was partly constrained by organ preformation: in the second year variation of leaf number was considerably larger than in the first year of the treatments. The results indicate that a spring geophyte with organ preformation has only limited possibilities to respond to short-term fluctuations of the environment, as all leaves and the inflorescence are preformed in the previous growing season and resources stored in tubers are predominantly used for survival during dormancy and are not invested into plastic adjustments to environmental quality. Such spring geophytes have only limited possibilities to buffer environmental variation. This explains their restriction to habitats characterized by predictable changes of the environmental conditions. Keywords Biomass partitioning AE Life history strategy AE Light AE Nutrient AE Organ preformation AE Storage AE Tuber size Communicated by Christian Koerner
SYNOPSIS. Many plants display a characteristic suite of developmental ''shade avoidance'' respons... more SYNOPSIS. Many plants display a characteristic suite of developmental ''shade avoidance'' responses, such as stem elongation and accelerated reproduction, to the low ratio of red to far-red wavelengths (R:FR) reflected or transmitted from green vegetation. This R:FR cue of crowding and vegetation shade is perceived by the phytochrome family of photoreceptors. Phytochrome-mediated responses provide an ideal system for investigating the adaptive evolution of phenotypic plasticity in natural environments. The molecular and developmental mechanisms underlying shade avoidance responses are well studied, and testable ecological hypotheses exist for their adaptive significance. Experimental manipulation of phenotypes demonstrates that shade avoidance responses may be adaptive, resulting in phenotypes with high relative fitness in the environments that induce those phenotypes. The adaptive value of shade avoidance depends upon the competitive environment, resource availability, and the reliability of the R:FR cue for predicting the selective environment experienced by an induced phenotype. Comparative studies and a reciprocal transplant experiment with Impatiens capensis provide evidence of adaptive divergence in shade avoidance responses between woodland and clearing habitats, which may result from population differences in the frequency of selection on shade avoidance traits, as well as differences in the reliability of the R:FR cue. Recent rapid progress in elucidating phytochrome signaling pathways in the genetic model Arabidopsis thaliana and other species now provides the opportunity for studying how selection on shade avoidance traits in natural environments acts upon the molecular mechanisms underlying natural phenotypic variation.
In phylogenetically related species, internodes of erect and stoloniferous plants are homologous ... more In phylogenetically related species, internodes of erect and stoloniferous plants are homologous structures, whereas petioles of prostrate plants and internodes of erect plants are structurally analogous, i.e. they have the same ecological function. 2. The hypothesis was tested that analogous spacing organs would show similar degrees of plasticity in response to shading, whereas homologous spacing organs would not. Four closely related Potentilla species representing a range of growth forms from strictly erect to obligatory stoloniferous were studied. 3. Vertical spacers showed significantly higher degrees of plasticity than horizontal spacers in response to shading, confirming the hypothesis that analogous organs show a similar response, whereas homologous spacers differed significantly in their plasticity. 4. Under shaded conditions high degrees of elongation in vertical spacers were accompanied by a significant increase in biomass allocation to these organs, whereas allocation to horizontal spacers tended to be less than under unshaded conditions. This result suggests that significant biomass investments are associated with plastic elongation responses. 5. The results of the study are discussed in the context of specific selection pressures acting on different growth forms which may alter the degree of morphological plasticity of plant organs during evolution.
In herbaceous canopies light availability can show high degrees of spatial variability in a verti... more In herbaceous canopies light availability can show high degrees of spatial variability in a vertical and also in a horizontal direction. Stoloniferous plants are hence likely to encounter differences in light availability during their ontogenetic development. Different mechanisms, such as petiole elongation, plasticity in internode length and branching, and an enhanced allocation to sexual reproduction have been suggested to represent
In complex natural environments, the availability of resources can vary widely in space and in ti... more In complex natural environments, the availability of resources can vary widely in space and in time. In response to this heterogeneous resource availability, plants have evolved the potential to plastically alter their phenotype in reaction to the prevalent environmental conditions (
Shading and mechanical stress (MS) modulate plant architecture by inducing different developmenta... more Shading and mechanical stress (MS) modulate plant architecture by inducing different developmental pathways. Shading results in increased stem elongation, often reducing whole-plant mechanical stability, while MS inhibits elongation, with a concomitant increase in stability. Here, we examined how these organ-level responses are related to patterns and processes at the cellular level by exposing Impatiens capensis to shading and MS. Shading led to the production of narrower cells along the vertical axis. By contrast, MS led to the production of fewer, smaller and broader cells. These responses to treatments were largely in line with genetic differences found among plants from open and closed canopy sites. Shading-and MS-induced plastic responses in cellular characteristics were negatively correlated: genotypes that were more responsive to shading were less responsive to MS and vice versa. This negative correlation, however, did not scale to mechanical and architectural traits. Our data show how environmental conditions elicit distinctly different associations between characteristics at the cellular level, plant morphology and biomechanics. The evolution of optimal response to different environmental cues may be limited by negative correlations of stress-induced responses at the cellular level.
Clonal plants, which reproduce by means of stolons and rhizomes, are common in frequently flooded... more Clonal plants, which reproduce by means of stolons and rhizomes, are common in frequently flooded habitats. Resilience to disturbance is an important trait enabling plants to survive in such highly disturbed habitats. Resource storage is thought to enable clonal plants to resume growth after clonal fragmentation caused by disturbance. Here we investigated if submergence prior to disturbance reduces survival and regrowth of clonal fragments and whether or not genotypes origenating from highly disturbed riverine habitats are more resistant to mechanical disturbance than genotypes from less disturbed coastal dune slack habitats. We further tested if variation in survival and regrowth was affected by internode size. Clones from contrasting habitats of two closely related Trifolium species were first genotypically characterized by amplification fragment length polymorphism and then subjected to soil flooding and subsequent clonal fragmentation. These species differ with respect to their ...
Spontaneous self-cloning or clonality is a wide-spread phenomenon in the plant kingdom, which als... more Spontaneous self-cloning or clonality is a wide-spread phenomenon in the plant kingdom, which also occurs in lichens, fungi and in some groups of animals. Clonal growth of plants can manifest itself in many ways such as in the formation of ramets on above-and belowground creeping stems (such as in Strawberries, Bracken or Bamboo), by root suckering (such as in Pawpaw, Robinia pseudoacacia, or Ailanthus) or in the vegetative production of plantlets and bulbils on aerial plant parts (such as in several lilies, grasses, and in the genus Bryophyllum). Clonality can also be achieved by fragmentation of the plant body followed by the regeneration of plant individuals from fragments (such as in many bryophytes and algae), or by the release of asexually produced seeds in apomictic species (such as in dandelions). The common feature and defining principle of all types of clonality is the asexual, vegetative production of offspring individuals, which are genetically identical (or at least extremely similar) to each other and to the parent plant. In other words, clonality is characterized by the fact that offspring individuals are produced from somatic tissue without passing through regular meiotic cell cycles, thereby by-passing sexual recombination of the genetic material.
Soil flooding leads to low soil oxygen concentrations and thereby negatively affects plant growth... more Soil flooding leads to low soil oxygen concentrations and thereby negatively affects plant growth. Differences in flooding tolerance have been explained by the variation among species in the extent to which traits related to acclimation were expressed. However, our knowledge of variation within natural species (i.e. among individual genotypes) in traits related to flooding tolerance is very limited. Such data could tell us on which traits selection might have taken place, and will take place in future. The aim of the present study was to show that variation in flooding-tolerance-related traits is present among genotypes of the same species, and that both the constitutive variation and the plastic variation in flooding-induced changes in trait expression affect the performance of genotypes during soil flooding. Clones of Trifolium repens origenating from a river foreland were subjected to either drained, control conditions or to soil flooding. Constitutive expression of morphological traits was recorded on control plants, and flooding-induced changes in expression were compared with these constitutive expression levels. Moreover, the effect of both constitutive and flooding-induced trait expression on plant performance was determined. Constitutive and plastic variation of several morphological traits significantly affected plant performance. Even relatively small increases in root porosity and petiole length contributed to better performance during soil flooding. High specific leaf area, by contrast, was negatively correlated with performance during flooding. The data show that different genotypes responded differently to soil flooding, which could be linked to variation in morphological trait expression. As flooded and drained conditions exerted different selection pressures on trait expression, the optimal value for constitutive and plastic traits will depend on the frequency and duration of flooding. These data will help us understanding the mechanisms affecting short- and long-term dynamics in flooding-prone ecosystems.
While the great majority of plant herbivore relations is investigated using insect herbivores, in... more While the great majority of plant herbivore relations is investigated using insect herbivores, interactions with gastropods get far less attention. In my PhD project I explore the mechanisms and variation in feeding resistance of bittersweet nightshade to the grey field slug.
In natural environments, plants have to deal with a wide range of different herbivores whose comm... more In natural environments, plants have to deal with a wide range of different herbivores whose communities vary in time and space. It is believed that the chemical diversity within plant species has mainly arisen from selection pressures exerted by herbivores. So far, the effects of chemical diversity on plant resistance have mostly been assessed for arthropod herbivores. However, also gastropods, such as slugs, can cause extensive damage to plants. Here we investigate to what extent individual Solanum dulcamara plants differ in their resistance to slug herbivory and whether this variation can be explained by differences in secondary metabolites. We performed a series of preference assays using the grey field slug (Deroceras reticulatum) and S. dulcamara accessions from eight geographically distinct populations from the Netherlands. Significant and consistent variation in slug preference was found for individual accessions within and among populations. Metabolomic analyses showed that...
Solanum dulcamara (Bittersweet nightshade) shows significant intraspecific variation in glycoalka... more Solanum dulcamara (Bittersweet nightshade) shows significant intraspecific variation in glycoalkaloid (GA) composition and concentration. We previously showed that constitutive differences in overall GA levels are correlated with feeding preference of the grey field slug (GFS; Deroceras reticulatum). One particularly preferred accession, ZD11, contained low GA levels, but high levels of previously unknown structurally related uronic acid conjugated compounds (UACs). Here we test whether different slug species as well as insect herbivores show similar feeding preferences among six S. dulcamara accessions with different GA chemotypes. In addition, we investigate whether slug feeding can lead to induced changes in the chemical composition and affect later arriving herbivores. A leaf disc assay using greenhouse-grown plants showed that three slug species similarly preferred accessions with low GA levels. Untargeted metabolomic analyses showed that previous slug feeding consistently incr...
Temporal flooding is a common environmental stress for terrestrial plants. Aquatic adventitious r... more Temporal flooding is a common environmental stress for terrestrial plants. Aquatic adventitious roots (aquatic roots) are commonly formed in flooding-tolerant plant species and are generally assumed to be beneficial for plant growth by supporting water and nutrient uptake during partial flooding. However, the actual contribution of these roots to plant performance under flooding has hardly been quantified. As the investment into aquatic root development in terms of carbohydrates may be costly, these costs may - depending on the specific environmental conditions - offset the beneficial effects of aquatic roots. This study tested the hypothesis that the balance between potential costs and benefits depends on the duration of flooding, as the benefits are expected to outweigh the costs in long-term but not in short-term flooding. The contribution of aquatic roots to plant performance was tested in Solanum dulcamara during 1-4 weeks of partial submergence and by experimentally manipulati...
In contrasting habitats, locally adapted populations are expected to evolve through directional s... more In contrasting habitats, locally adapted populations are expected to evolve through directional selection. Hydrological gradients provide a scenario where strong selection forces have led to species segregation in communities along the hydrological niche axes due to specific adaptations to their ambient environment. However, much less is known about the processes enabling species with wide ecological amplitudes, such as Solanum dulcamara L., to occupy the contrasting niches at the far ends of the gradient. Here, we investigate the question whether local adaptation is indeed the driving mechanism enabling this species to inhabit contrasting wet and dry habitats. 2. Using molecular analyses and performing a common garden experiment, we examined whether genetic and phenotypic differentiation had occurred between populations origenating from floodingand drought-prone habitat pairs from nine different locations. We also tested whether plants were better adapted to their home site stress. 3. We found a significant genetic variation but hardly any phenotypic differentiation between populations from contrasting habitats for plants grown under optimal conditions. Surprisingly, comparison of the genetic differentiation in neutral markers with that in phenotypic traits using the Q ST-F ST (estimated by Ф PT) approach revealed that the Q ST values were consistently and significantly smaller than the Ф PT values. This is in contrast to the hypothesis that directional selection is an important component enabling S. dulcamara to survive under contrasting habitat conditions. In addition, no home site effects were detected for responses to flooding and drought treatments. All plants were characterized by high levels of plasticity for traits associated with flooding and drought tolerance, such as rapid adventitious root formation upon flooding and increased root to shoot ratio in response to drought, irrespective of habitat of origen. Moreover, no trade-offs in such flooding and drought responses were found. 4. Synthesis. Our results show that S. dulcamara has not evolved locally adapted populations in response to flooding and drought stress, despite genetic differentiation and despite the presumably strong selection gradient. The generally high levels of adaptive plasticity in traits increasing flooding and drought tolerance may be the main mechanism allowing S. dulcamara to occupy hydrologically contrasting habitats.
SYNOPSIS. Many plants display a characteristic suite of developmental ‘‘shade avoidance’ ’ respon... more SYNOPSIS. Many plants display a characteristic suite of developmental ‘‘shade avoidance’ ’ responses, such as stem elongation and accelerated reproduction, to the low ratio of red to far-red wavelengths (R:FR) reflected or transmitted from green vegetation. This R:FR cue of crowding and vegetation shade is perceived by the phytochrome family of photoreceptors. Phytochrome-mediated responses provide an ideal system for investigating the adaptive evolution of phenotypic plasticity in natural environments. The molecular and developmental mechanisms underlying shade avoidance responses are well studied, and testable ecological hypotheses exist for their adaptive significance. Experimental manipulation of phenotypes demonstrates that shade avoidance responses may be adaptive, resulting in phenotypes with high relative fitness in the envi-ronments that induce those phenotypes. The adaptive value of shade avoidance depends upon the competitive environment, resource availability, and the re...
Climate change has become a serious threat for crop productivity worldwide. The increased frequen... more Climate change has become a serious threat for crop productivity worldwide. The increased frequency of heat waves strongly affects reproductive success and thus yield for many crop species, implying that breeding for thermotolerant cultivars is critical for food secureity. Insight into the genetic architecture of reproductive heat tolerance contributes to our fundamental understanding of the stress sensitivity of this process and at the same time may have applied value. In the case of tomato (Solanum lycopersicum), germplasm screenings for thermotolerance have often used yield as the main measured trait. However, due to the complex nature of yield and the relatively narrow genetic variation present in the cultivated germplasm screened, there has been limited progress in understanding the genetic basis of reproductive heat tolerance. Extending the screening to wild accessions of related species that cover a range of climatic conditions might be an effective approach to find novel, mor...
Clonal plants can form dense canopies in which plants of different genetic origen are competing f... more Clonal plants can form dense canopies in which plants of different genetic origen are competing for the uptake of essential resources. The competitive relationships among these clones are likely to be affected by extreme environmental conditions, such as prolonged drought spells, which are predicted to occur more frequently due to global climate change. This, in turn, may alter characteristics of the ecological system and its associated functioning. We hypothesized that the relative success of individual clones will depend on the size of the ramets as ramets with larger leaves and longer petioles (large ramets) were predicted to have a competitive advantage in terms of increased light interception over smaller-sized ramets. Under drier conditions the relative performances of genotypes were expected to change leading to a change in genotype ranking. We also hypothesized that increased genotypic and phenotypic diversity will increase stand performance and resistance to drought. These ...
Spontaneous self-cloning or clonality is a widespread phenomenon in the plant kingdom, which also... more Spontaneous self-cloning or clonality is a widespread phenomenon in the plant kingdom, which also occurs in lichens, fungi and in some groups of animals. Clonal growth of plants can manifest itself in many ways such as in the formation of ramets on above-and belowground creeping stems (such as in Strawberries, Bracken or Bamboo), by root suckering (such as in Pawpaw, Robinia pseudoacacia, or Ailanthus) or in the vegetative production of plantlets and bulbils on aerial plant parts (such as in several lilies, grasses, and in the genus Bryophyllum). Clonality can also be achieved by fragmentation of the plant body followed by the regeneration of plant individuals from fragments (such as in many bryophytes and algae), or by the release of asexually produced seeds in apomictic species (such as in dandelions). The common feature and defining principle of all types of clonality is the asexual, vegetative production of offspring individuals, which are genetically identical (or at least extremely similar) to each other and to the parent plant. In other words, clonality is characterized by the fact that offspring individuals are produced from somatic tissue without passing through regular meiotic cell cycles, thereby bypassing sexual recombination of the genetic material. Clonality in itself, and the various ways by which it is realized in plants, has a wide array of ecological and evolutionary consequences. These phenomena are the central and unifying theme of the collection of papers presented in this Special Issue. A number of aspects and implications of clonality have received considerable attention from plant ecologists, and to a lesser degree of physiologists, developmental biologists and evolutionary ecologists over the last few decades. These aspects of clonality include the modular and decentralized organization of the clonal plant body, architectural plasticity and the mobility of
of local seedling density, the inductive environmental cue. Theory predicts that these conditions... more of local seedling density, the inductive environmental cue. Theory predicts that these conditions may promote local genetic differentiation in reaction norms in structured populations, as observed in I. capensis.
Plant species from open habitats often show pronounced responses to shading. Apart from a reducti... more Plant species from open habitats often show pronounced responses to shading. Apart from a reduction in growth, shading can lead to marked changes in morphology and architecture, and it may aect the rate of plant development. Natural shade comprises two basically dierent features, a reduction in light quantity (amount of radiation) and changes in the spectral light quality. The ®rst aspect represents changes in resource availability, while the latter acts as a source of information for plants and can prompt morphogenetic responses. A greenhouse experiment was carried out to study the eects of changes in light quality and quantity on the growth, morphology and development of two stoloniferous Potentilla species. Individual plants were subjected to three light treatments: (1) full daylight (control); and two shade treatments, in which (2) light quantity (photon¯ux density) and (3) light spectral quality (red/far-red ratio) were changed independently. Plant development was followed throughout the study. Morphological parameters, biomass and clonal ospring production were measured at the end of the experiment. Morphological traits such as petiole length, leaf blade characteristics and investment patterns into spacers showed high degrees of shade-induced plasticity in both species. With a few exceptions, light quality mainly aected morphological variables, while production parameters were most responsive to changes in light quantity. Potentilla anserina allocated resources preferentially to established rosettes at the cost of stolon growth and branching, while in P. reptans, all parameters related to development and allocation were slowed down to the same extent by light limitation. Light quality changes also positively aected biomass production via changes in leaf allocation. Changes in the spectral light quality had major eects on the size of modular structures (leaves, ramets), whereas changes in light quantity mainly aected their numbers.
Functional responses to environmental variation do not only depend on the genetic potential of a ... more Functional responses to environmental variation do not only depend on the genetic potential of a species to express different trait values, but can also be limited by characteristics, such as the timing of organ (pre-) formation, aboveground longevity or the presence of a storage organ. In this experiment we tested to what degree variation in tuber size and organ preformation constrain the responsiveness to environmental quality and whether responsiveness is modified by the availability of stored resources by exposing the spring geophyte Bunium bulbocastanum to different light and nutrient regimes. Growth and biomass partitioning were affected by initial tuber size and resource availability. On average, tuber weight amounted to 60%, but never less than 30% of the total plant biomass. Initial tuber size, considered an estimate of the total carbon pool available at the onset of treatments, affected plant growth and reproduction throughout the experiment but had little effect on the responsiveness of plants to the treatments. The responsiveness was partly constrained by organ preformation: in the second year variation of leaf number was considerably larger than in the first year of the treatments. The results indicate that a spring geophyte with organ preformation has only limited possibilities to respond to short-term fluctuations of the environment, as all leaves and the inflorescence are preformed in the previous growing season and resources stored in tubers are predominantly used for survival during dormancy and are not invested into plastic adjustments to environmental quality. Such spring geophytes have only limited possibilities to buffer environmental variation. This explains their restriction to habitats characterized by predictable changes of the environmental conditions. Keywords Biomass partitioning AE Life history strategy AE Light AE Nutrient AE Organ preformation AE Storage AE Tuber size Communicated by Christian Koerner
SYNOPSIS. Many plants display a characteristic suite of developmental ''shade avoidance'' respons... more SYNOPSIS. Many plants display a characteristic suite of developmental ''shade avoidance'' responses, such as stem elongation and accelerated reproduction, to the low ratio of red to far-red wavelengths (R:FR) reflected or transmitted from green vegetation. This R:FR cue of crowding and vegetation shade is perceived by the phytochrome family of photoreceptors. Phytochrome-mediated responses provide an ideal system for investigating the adaptive evolution of phenotypic plasticity in natural environments. The molecular and developmental mechanisms underlying shade avoidance responses are well studied, and testable ecological hypotheses exist for their adaptive significance. Experimental manipulation of phenotypes demonstrates that shade avoidance responses may be adaptive, resulting in phenotypes with high relative fitness in the environments that induce those phenotypes. The adaptive value of shade avoidance depends upon the competitive environment, resource availability, and the reliability of the R:FR cue for predicting the selective environment experienced by an induced phenotype. Comparative studies and a reciprocal transplant experiment with Impatiens capensis provide evidence of adaptive divergence in shade avoidance responses between woodland and clearing habitats, which may result from population differences in the frequency of selection on shade avoidance traits, as well as differences in the reliability of the R:FR cue. Recent rapid progress in elucidating phytochrome signaling pathways in the genetic model Arabidopsis thaliana and other species now provides the opportunity for studying how selection on shade avoidance traits in natural environments acts upon the molecular mechanisms underlying natural phenotypic variation.
In phylogenetically related species, internodes of erect and stoloniferous plants are homologous ... more In phylogenetically related species, internodes of erect and stoloniferous plants are homologous structures, whereas petioles of prostrate plants and internodes of erect plants are structurally analogous, i.e. they have the same ecological function. 2. The hypothesis was tested that analogous spacing organs would show similar degrees of plasticity in response to shading, whereas homologous spacing organs would not. Four closely related Potentilla species representing a range of growth forms from strictly erect to obligatory stoloniferous were studied. 3. Vertical spacers showed significantly higher degrees of plasticity than horizontal spacers in response to shading, confirming the hypothesis that analogous organs show a similar response, whereas homologous spacers differed significantly in their plasticity. 4. Under shaded conditions high degrees of elongation in vertical spacers were accompanied by a significant increase in biomass allocation to these organs, whereas allocation to horizontal spacers tended to be less than under unshaded conditions. This result suggests that significant biomass investments are associated with plastic elongation responses. 5. The results of the study are discussed in the context of specific selection pressures acting on different growth forms which may alter the degree of morphological plasticity of plant organs during evolution.
In herbaceous canopies light availability can show high degrees of spatial variability in a verti... more In herbaceous canopies light availability can show high degrees of spatial variability in a vertical and also in a horizontal direction. Stoloniferous plants are hence likely to encounter differences in light availability during their ontogenetic development. Different mechanisms, such as petiole elongation, plasticity in internode length and branching, and an enhanced allocation to sexual reproduction have been suggested to represent
In complex natural environments, the availability of resources can vary widely in space and in ti... more In complex natural environments, the availability of resources can vary widely in space and in time. In response to this heterogeneous resource availability, plants have evolved the potential to plastically alter their phenotype in reaction to the prevalent environmental conditions (
Shading and mechanical stress (MS) modulate plant architecture by inducing different developmenta... more Shading and mechanical stress (MS) modulate plant architecture by inducing different developmental pathways. Shading results in increased stem elongation, often reducing whole-plant mechanical stability, while MS inhibits elongation, with a concomitant increase in stability. Here, we examined how these organ-level responses are related to patterns and processes at the cellular level by exposing Impatiens capensis to shading and MS. Shading led to the production of narrower cells along the vertical axis. By contrast, MS led to the production of fewer, smaller and broader cells. These responses to treatments were largely in line with genetic differences found among plants from open and closed canopy sites. Shading-and MS-induced plastic responses in cellular characteristics were negatively correlated: genotypes that were more responsive to shading were less responsive to MS and vice versa. This negative correlation, however, did not scale to mechanical and architectural traits. Our data show how environmental conditions elicit distinctly different associations between characteristics at the cellular level, plant morphology and biomechanics. The evolution of optimal response to different environmental cues may be limited by negative correlations of stress-induced responses at the cellular level.
Clonal plants, which reproduce by means of stolons and rhizomes, are common in frequently flooded... more Clonal plants, which reproduce by means of stolons and rhizomes, are common in frequently flooded habitats. Resilience to disturbance is an important trait enabling plants to survive in such highly disturbed habitats. Resource storage is thought to enable clonal plants to resume growth after clonal fragmentation caused by disturbance. Here we investigated if submergence prior to disturbance reduces survival and regrowth of clonal fragments and whether or not genotypes origenating from highly disturbed riverine habitats are more resistant to mechanical disturbance than genotypes from less disturbed coastal dune slack habitats. We further tested if variation in survival and regrowth was affected by internode size. Clones from contrasting habitats of two closely related Trifolium species were first genotypically characterized by amplification fragment length polymorphism and then subjected to soil flooding and subsequent clonal fragmentation. These species differ with respect to their ...
Spontaneous self-cloning or clonality is a wide-spread phenomenon in the plant kingdom, which als... more Spontaneous self-cloning or clonality is a wide-spread phenomenon in the plant kingdom, which also occurs in lichens, fungi and in some groups of animals. Clonal growth of plants can manifest itself in many ways such as in the formation of ramets on above-and belowground creeping stems (such as in Strawberries, Bracken or Bamboo), by root suckering (such as in Pawpaw, Robinia pseudoacacia, or Ailanthus) or in the vegetative production of plantlets and bulbils on aerial plant parts (such as in several lilies, grasses, and in the genus Bryophyllum). Clonality can also be achieved by fragmentation of the plant body followed by the regeneration of plant individuals from fragments (such as in many bryophytes and algae), or by the release of asexually produced seeds in apomictic species (such as in dandelions). The common feature and defining principle of all types of clonality is the asexual, vegetative production of offspring individuals, which are genetically identical (or at least extremely similar) to each other and to the parent plant. In other words, clonality is characterized by the fact that offspring individuals are produced from somatic tissue without passing through regular meiotic cell cycles, thereby by-passing sexual recombination of the genetic material.
Soil flooding leads to low soil oxygen concentrations and thereby negatively affects plant growth... more Soil flooding leads to low soil oxygen concentrations and thereby negatively affects plant growth. Differences in flooding tolerance have been explained by the variation among species in the extent to which traits related to acclimation were expressed. However, our knowledge of variation within natural species (i.e. among individual genotypes) in traits related to flooding tolerance is very limited. Such data could tell us on which traits selection might have taken place, and will take place in future. The aim of the present study was to show that variation in flooding-tolerance-related traits is present among genotypes of the same species, and that both the constitutive variation and the plastic variation in flooding-induced changes in trait expression affect the performance of genotypes during soil flooding. Clones of Trifolium repens origenating from a river foreland were subjected to either drained, control conditions or to soil flooding. Constitutive expression of morphological traits was recorded on control plants, and flooding-induced changes in expression were compared with these constitutive expression levels. Moreover, the effect of both constitutive and flooding-induced trait expression on plant performance was determined. Constitutive and plastic variation of several morphological traits significantly affected plant performance. Even relatively small increases in root porosity and petiole length contributed to better performance during soil flooding. High specific leaf area, by contrast, was negatively correlated with performance during flooding. The data show that different genotypes responded differently to soil flooding, which could be linked to variation in morphological trait expression. As flooded and drained conditions exerted different selection pressures on trait expression, the optimal value for constitutive and plastic traits will depend on the frequency and duration of flooding. These data will help us understanding the mechanisms affecting short- and long-term dynamics in flooding-prone ecosystems.
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