Search

Clonal herbs form belowground organs where they store reserves and bear regenerative buds. Based on these characteristics, clonal herbs may deal with disturbances better than non-clonal herbs, and clonality is seen as an adaptive strategy in disturbed habitats. The advantage of being clonal is likely to be enhanced in stressful conditions where larger belowground storage is beneficial. We conducted a greenhouse experiment to examine the ability of young plants to deal with biomass removal when exposed to light or nutrient stress or its combination. Using congeneric pairs of species, we evaluated the ability of clonal versus non-clonal groups to cope with biomass removal in terms of mortality, biomass productivity, specific leaf area and root-to-shoot ratio. We found that clonal and non-clonal herbs produce the same amount of biomass when injured and that nutrient and light stress does not alter biomass production. Both groups responded similarly to the biomass removal by increasing the specific leaf area and root-to-shoot ratio. Very young clonal herbs had higher mortality than non-clonal herbs of the same age. This fact suggests a higher survival probability in the non-clonal group, presumably originating from a greater population dependence on generative reproduction. We conclude that belowground organs in young plants, and thus bud banks and belowground storage, are not yet formed enough to give clonal herbs an advantage over non-clonal ones, and the advantage of clonality might manifest later in life when belowground organs are fully developed.

Aims Woody plants represent the ancestral growth form in angiosperms with herbs evolving repeatedly from them. While there are a number of hypotheses about drivers of the evolution of the herbaceous habit, the ability to avoid frost damage in winter by discarding their aboveground biomass has often been invoked as the main force in their evolution. We propose instead that any unpredictable disturbance might have been much more important than the seasonal frost, as herbs easily survive repeated disturbance. Methods We tested this hypothesis by comparing herbs and woody plants in their ability to deal with three types of simulated disturbances, more predictable winter freezing, less predictable spring freezing and herbivory. Comparison was made in an experimental common garden setup with 20 species differing in woodiness. We evaluated the effects of these disturbances on mortality and regrowth of plants. Important Findings Herbs did not have an advantage over woody plants in survival when exposed to winter freezing. In less predictable conditions of spring freezing herbs survived the treatment better than woody plants and this advantage was even larger in case of the simulated herbivory treatment. The advantage of herbs over woody plants in less predictable conditions suggests that herbaceous growth form might be an adaptation to unpredictable disturbance, which herbs are able to tolerate thanks to their ability to survive loss of aboveground biomass. Consequently, factors such as mammal herbivory or fire might have been the most likely factors in the transition from woody species to herbs.

Background and Aims Although the plant economic spectrum seeks to explain resource allocation strategies, carbohydrate storage is often omitted. Belowground storage organs are the centre of herb perennation, yet little is known about the role of their turnover, anatomy and carbohydrate storage in relation to the aboveground economic spectrum. Methods We collected aboveground traits associated with the economic spectrum, storage organ turnover traits, storage organ inner structure traits and storage carbohydrate concentrations for ~80 temperate meadow species. Key Results The suites of belowground traits were largely independent of one another, but there was significant correlation of the aboveground traits with both inner structure and storage carbohydrates. Anatomical traits diverged according to leaf nitrogen concentration on the one hand and vessel area and dry matter content on the other; carbohydrates separated along gradients of leaf nitrogen concentration and plant height. Conclusions Contrary to our expectations, aboveground traits and not storage organ turnover were correlated with anatomy and storage carbohydrates. Belowground traits associated with the aboveground economic spectrum also did not fall clearly within the fast–slow economic continuum, thus indicating the presence of a more complicated economic space. Our study implies that the generally overlooked role of storage within the plant economic spectrum represents an important dimension of plant strategy.

In angiosperms, herbs evolved from ancestral woody growth form. A number of hypotheses on what was the driver of their evolution have been proposed, but none of them has received clear support so far. We are putting forward a new hypothesis that an important advantage of the herbaceous growth form lies in its greater capacity for plastic response to neighbour shading. Since most herbs form aboveground structures only for 1 year, they can respond to light heterogeneity more plastically than woody plants with long-living structures which need to pursue long-term goals such as stability and upward growth. To test the hypothesis, we carried out an experiment comparing plastic response to directional green shading of 21 species of young herbaceous and woody plants. We measured change of their tilt and length and compared it between herbs and woody plants using phylogenetic techniques. Both herbs and woody plants in our experiment responded to directed green shading by growing away from the shading plastic film. Overall response of herbs was, in agreement with the hypothesis, slightly stronger than response of woody plants, although there was high interspecific variation. The data indicate that herbs indeed have greater plasticity of stem growth in response to neighbour shading than woody plants, although the overall difference is not very strong. This capacity for plastic response might have played a role as one of the drivers of the evolution of the herbaceous growth form.

Herbaceous climbers (vines) represent a growth strategy in which the stem lacks most of its supporting function. This has led to the hypothesis that herbaceous climbers are structural parasites that invest less into stems than self-supporting plants. So far, the support for this idea has been ambiguous, as woody and herbaceous plants have been discussed jointly and evidence is often based on young plants in pot experiments. We collected in wild fully grown temperate herbaceous climbers and self-supporting herbs to examine the idea. We made a phylogenetically informed comparison of biomass allocation into stems and leaves of 16 climber species and 74 self-supporting herbs. Furthermore, we compared our results with those published for woody climbers to gain insight into different biomass allocation between herbaceous and woody growth forms. We found that herbaceous climbers and self-supporting herbs do not differ in their proportion of stem biomass to leaf biomass. Herbaceous climbers reach much higher in the canopy thanks to their climbing habit and in average more than seven times longer stems, but contrary to the expectation and unlike their woody counterparts, they do not save on investment into the stem. Herbaceous climbers and self-supporting herbs represent a study system which provides insight into biomass scaling with versus without supporting function where both stems as well as leaves are seasonal.

Genome size of alpine plants is not related to their resistance against frost and heat. Genome size is a variable trait in angiosperms, and it was suggested that large genome size represents a constraint in stressful environments. We measured genome size and resistance to frost and heat in 89 species of plants from tropical and temperate alpine habitats. Genome size of the species, ranging from 0.49 pg to 25.8 pg across the entire dataset, was not related to either frost or heat resistance in either group of plants. Genome size does not predict resistance to extreme temperatures in alpine plants and is thus not likely to predict plant responses to climate changes.

Background and AimsPetioles are important plant organs connecting stems with leaf blades and affecting light-harvesting ability of the leaf as well as transport of water, nutrients and biochemical signals. Despite the high diversity in petiole size, shape and anatomy, little information is available regarding their structural adaptations across evolutionary lineages and environmental conditions. To fill this knowledge gap, we investigated the variation of petiole morphology and anatomy of mainly European woody species to better understand the drivers of internal and external constraints in an evolutionary context.MethodsWe studied how petiole anatomical features differed according to whole-plant size, leaf traits, thermal and hydrological conditions, and taxonomic origin in 95 shrubs and trees using phylogenetic distance-based generalized least squares models.Key ResultsTwo major axes of variation were related to leaf area and plant size. Larger and softer leaves are found in taller trees of more productive habitats. Their petioles are longer, with a circular outline and are anatomically characterized by the predominance of sclerenchyma, larger vessels, interfascicular areas with fibres and indistinct phloem rays. In contrast, smaller and tougher leaves are found in shorter trees and shrubs of colder or drier habitats. Their petioles have a terete outline, phloem composed of small cells and radially arranged vessels, fibreless xylem and lamellar collenchyma. Individual anatomical traits were linked to different internal and external drivers. Petiole length and vessel diameter increase with increasing leaf blade area. Collenchyma becomes absent with increasing temperature, and petiole outline becomes polygonal with increasing precipitation.ConclusionsWe conclude that species’ temperature and precipitation optima, plant height, and leaf area and thickness exerted a significant control on petiole anatomical and morphological structures not confounded by phylogenetic inertia. Species with different evolutionary histories but similar thermal and hydrological requirements have converged to similar petiole anatomical structures.

Petioles are important plant organs connecting stems with leaf blades and affecting light-harvesting leaf ability as well as transport of water, nutrient and biochemical signals. Despite petiole’s high diversity in size, shape and anatomical settings, little information is available about their structural adaptations across evolutionary lineages and environmental conditions. To fill our knowledge gap, we investigated the variation of petiole morphology and anatomy in 95 European woody plant species using phylogenetic comparative models. Two major axes of variation were related to leaf area (from large and soft to small and tough leaves), and plant size (from cold-adapted shrubs to warm-adapted tall trees). Larger and softer leaves are found in taller trees of more productive habitats. Their petioles are longer, with a circular outline, thin cuticles without trichomes, and are anatomically characterised by the predominance of sclerenchyma, larger vessels, interfascicular areas with fibers, indistinct phloem rays, and the occurrence of prismatic crystals and druses. In contrast, smaller and tougher leaves are found in shorter trees and shrubs of colder or drier habitats. Their petioles are characterized by teret outline, thick cuticle, simple and non-glandular trichomes, epidermal cells smaller than cortex cells, phloem composed of small cells and radially arranged vessels, fiberless xylem, lamellar collenchyma, acicular crystals and secretory elements. Individual anatomical traits were linked to different internal and external drivers. The petiole length and vessel conduit size increase, while cuticle thickness decreases, with increasing leaf blade area. Epidermis cell walls are thicker in leaves with higher specific leaf area. Collenchyma becomes absent with increasing temperature, epidermis cell size increases with plant height and temperature, and petiole outline becomes polygonal with increasing precipitation. We conclude that species temperature and precipitation optima, plant height, leaf area and thickness exerted a significant control on petiole anatomical and morphological structures not confounded by phylogenetic inertia. Unrelated species with different evolutionary histories but similar thermal and hydrological requirements have converged to similar petiole anatomical structures. Our findings contribute to improving current knowledge about the functional morphoanatomy of the petiole as the key organ that plays a crucial role in the hydraulic pathways in plants.

Clonality is defined as vegetative reproduction via the production of ramets, which are, at least initially, connected by spacers. In general, there are three types of spacers of two origins. Whereas stolons are aboveground spacers, rhizomes are belowground spacers; however, both of stem origin. The third type of spacers are roots in root-sprouting plants. The possibility of foraging in clonal plants has attracted broad interest among ecologists but has been experimentally documented only for stoloniferous clonal plants foraging for light. Foraging for belowground resources has yet to be demonstrated, perhaps because tests of foraging have focused on clonal plants that spread laterally via stolons or rhizomes, i.e. stem organs. Lateral spread based on sprouting roots has not been considered even though, in addition to functioning as conduits between ramets, root spacers are able to sense and take up nutrients. We therefore hypothesized that root-sprouting clonal plants may be able to directly react to environmental heterogeneity and exhibit nutrient foraging. To test this hypothesis, we conducted two experiments with root-sprouters in nutrient-heterogeneous and -homogeneous environments. We found that plants produced more biomass when growing in a heterogeneous environment than in a homogeneous environment and that root biomass was greater in the nutrient-rich patches than in nutrient-poor patches. However, the number of ramets did not differ between patches in the heterogeneous environment. We conclude that plants whose clonality is based on roots, similarly as plants whose clonality is based on stolons or rhizomes, do not exhibit accumulation of ramets in nutrient-rich patches. Foraging at the organ level, i.e. by roots, seems to be more probable in this clonal group. To analyse how clonal plants with different clonal strategies perceive and react to environmental heterogeneity, researchers must account for the high variability in clonal growth forms and in scales of environmental heterogeneity.

Clonal plants have more traits enabling individual persistence (larger belowground storage of buds and assimilates), whereas non-clonal plants have more traits enabling population persistence (a higher reliance on regeneration from seeds). This difference presumably makes those groups respond differently to disturbance. We asked whether this difference is already expressed in the first year of the plant's life. In a pot experiment with 17 congeneric pairs of clonal and non-clonal herbs, we investigated response to a disturbance at the individual level. We were interested whether the leaf C/N ratio (a proxy reflecting active growth and photosynthetic efficiency), the R/S ratio (a proxy for belowground storage) and the amount of compensated biomass differ between clonal and non-clonal herbs. Moreover, we asked whether compensation for the loss of aboveground biomass after disturbance can be predicted by the R/S ratio or explained by the leaf C/N ratio. We found that clonal herbs have higher leaf C/N and R/S ratios than non-clonal herbs. Under disturbance, the leaf C/N and R/S ratios decreased in the clonal herbs and increased in the non-clonal herbs. However, the clonal and non-clonal plants did not differ in biomass compensation ability. Neither the R/S ratio nor the leaf C/N ratio explained the compensation abilities of the herbs. These results show that even though the growth strategies of clonal and non-clonal plants and their reactions to disturbance are different, the groups are similarly capable of compensating for the loss of aboveground biomass. Clonal plants do not have an advantage over non-clonal plants under disturbance during their first year of life.

Various types of flat rhizoboxes aid in root visualization and tracking in experiments where the focus is upon root system growth and development. While size of the pot is known to affect experiments, nothing is known about the impact of rhizoboxes—not only their volume, but also their shape might affect root and shoot growth. Therefore, we investigated how rhizoboxes change plant biomass and root:shoot biomass partitioning. We compared biomass and root:shoot ratio of plants growing in the pots with different geometry—usual three-dimensional, cuboid plant pots and flat two-dimensional rhizoboxes about the same volume. We used two different nutritional treatments (deionized water and additional nutrients) for investigating whether the nutrient availability in the substrate changed the impact of rhizoboxes on plant growth. We used 15 species for the generalizability of our results across the phylogenetic tree. Proportional investment of plants into roots was similar in usual pots and in rhizoboxes. This pattern was stable across nutrition treatments and across species. Further, we found no differences in total biomass of plants between pot type within nutrient treatments. With added nutrients, the plants had a higher biomass and lower root:shoot ratio compared to treatments without nutrient addition. Thus, species can be safely compared when grown in the rhizoboxes; rhizoboxes did not affect root system growth comparisons among species and nutrient levels. Also, they did not affect plant growth in terms of total biomass.

Understanding how plants adjust their internal structures to withstand adverse environmental conditions is vital for predicting their responses to ongoing environmental change. Plants have repeatedly evolved small water transporting conduits and large storage parenchyma tissues to cope with anoxia, freezing- or drought‐induced damages. However, how these adaptations evolved in unrelated taxa across hydrological and thermal gradients, remains unclear. Here we show that stem anatomical variations in 212 European aquatic and wetland dicots are driven by thermal and hydrological constraints via control over plant size, growth form, and leaf traits, while phylogenetic constraints have only a weak effect. Phylogenetic comparative analyses controlling for confounding factors showed that both waterlogging (anoxia) and low-temperature promote smaller plants with reduced vessel conduits and limited lignification, but extended parenchyma and hence storage and tissue renewal capacity to secure resilience to biomass loss induced by running water or frost disturbances. Decreasing water depth and anoxia promote larger wetland plants with thick-walled libriform fibers, large vessels with simple perforation plates securing high hydraulic efficiency, and semi-ring porous xylem with wide earlywood vessels in spring and narrow latewood vessels in summer, providing both efficiency and safety in water transport. The aquatic environment promotes plants with a large cortex zone with photosynthetic chlorenchyma and starch-storing parenchyma cells along with extensive air spaces that provide aeration and buoyancy. Low temperatures promote short-stature forbs with smaller vessels, scalariform perforation plate, extended parenchyma, resulting in reduced embolism risk. Although most anatomical variation was explained by differences between aquatic and wet terrestrial growth forms, environmental gradients, plant size, and leaf properties exerted a significant control on plant tissue structures not confounded by phylogenetic inertia. Distinct habitats, spread across broad thermal and hydrological gradients, harbor unrelated species with different evolutionary histories that have converged to similar anatomical and hence morphological structures.

Disturbance is an omnipresent selective factor that shapes plant strategies. While annual species that rely on rapid generative reproduction dominate in habitats frequently affected by severe disturbance, long-lived woody species occupy habitats where the effects of disturbance are weak. These are, however, the extremes in the disturbance gradient. Habitats under intermediate disturbance are occupied by the whole spectrum of plant strategies. In this study, we hypothesized that clonal herbs are better adapted to intermediate disturbance than non-clonal herbs because the characteristics of their bud bank and related belowground carbohydrate storage promote vegetative regeneration. In a greenhouse experiment, we tested the effects of disturbance on the survival and performance of 17 congeneric pairs of clonal and non-clonal herbs cultivated from seed. In addition to a non-disturbed control, we applied five disturbance treatments: biomass removal 2 cm above the soil surface, removal of 70 % of the aboveground biomass, late spring frost, flooding, and belowground injury. Mortality was negligible except the flooding treatment, where it was higher for non-clonal than for clonal plants. Total biomass was reduced more by the disturbance treatments for clonal than for non-clonal plants, suggesting that clonal species suffer more than non-clonal species. On the other hand, clonal plants had significantly greater total belowground biomass and R:S ratios than non-clonal plants, suggesting a strong investment in belowground organs by clonal plants. In response to disturbance, the SLA and SRL values increased in clonal plants but decreased in non-clonal plants, indicating that clonal and non-clonal plants differ in how they cope with disturbance. Although clonality is considered to be an adaptation to disturbance, our results indicate that, during the first year of life, clonal herbs are more sensitive to disturbance than non-clonal herbs, likely due to preferential investment in belowground biomass.