Jana Martínková

Intermediate growth forms as a model for the study of plant clonality functioning: an example with root sprouters

Abstract.In this contribution we want to show that growth forms intermediate between non-clonal and clonal plants can be used to ask questions about the functional ecology of clonality. We discuss this idea on plants sprouting adventitiously from roots and accomplishing clonal growth via root spacers. Based on extensive literature dealing with growth forms of root sprouting plants, we characterise forms functionally intermediate between clonal root-sprouters and non-clonal plants. We delimit them according to their potential ability to form adventitious shoots and horizontal roots. By reviewing experimental work with root sprouters, we identify the most important triggering factors and developmental constraints influencing these intermediate forms plant age, life-history mode and life-history stage. Using this information we ask questions about the importance of root sprouting in (1) conditions of unpredictable disturbance, where root-sprouting ability may be viewed as a tool for vegetative regeneration, and in (2) temporarily and spatially heterogeneous environment, where foraging by roots may serve as a way of exploiting patchy resources.

Phenological pattern of grassland species: relation to the ecological and morphological traits

Summary We have described changes in abundance of phenological phases of individual plant populations during one vegetative season in an oligotrophic dry meadow. We found that, the capability to record species presence or to estimate species cover is probably dependent on species phenological stage. Many grassland species start their reproductive cycle before mowing, but not all species are able to finish their reproductive cycle before that event. Some species and many individuals (mostly graminoids) never finish their reproductive cycle. We found that the largest changes in phenological phase composition occur immediately before the mowing time. Furthermore, we attempt to find the predictors of phenological peaks position among species’ traits. We compare positions of phenological peaks between graminoids and forbs and between dominant and non-dominant species. Graminoids were found to start their reproductive cycle earlier than forbs. Phenological transition from flowering to fruiting seems to be slower for graminoids than for forbs. Transition of forbs species is slower during the spring then in the summer. On the mentioned gradient of time (from spring to the autumn) is the transition of forbs still faster. Dominant species concentrate their reproductive cycle in the middle of the vegetative season, non-dominant species “exploit” the edges of vegetative season. Positions of phenological peaks are significantly different between graminoids and forbs.

Life-history variation in the short-lived herb Rorippa palustris : effect of germination date and injury timing

Life-history variation in annuals is known to be caused by size requirements for photoinduction of flowering, but the importance of germination date and injury was overlooked so far even though they may play an important role in disturbed habitats. To test the effect of germination date and timing of injury on life-history variation of an annual plant, we performed a 2-year pot experiment with the root-sprouting herb Rorippa palustris. Plants belonging to six different cohorts, and sown at monthly intervals from April to September, were injured (all stem parts removed) in three ontogenetic stages: vegetative rosettes, flowering plants and fruiting plants. Plants from the April, and partly from the May, cohort behaved as summer annuals: they started to bolt at the same time, resprouted and overwintered poorly. Plants from the June cohort flowered in the first season as well, but they entered the bolting stage a month later than the preceding cohorts, produced the least fruits, but overwintered successfully and flowered again the second year (polycarpic perennials). Cohorts germinating after the summer solstice did not flower during the first year and, with the exception of the September cohort, overwintered successfully and flowered the second year (winter annuals). After injury, the pattern of life-histories was the same as in control plants, although generative reproduction was interrupted by injury in the first year of the experiment. About one quarter of␣plants injured in the vegetative stage regenerated after injury irrespective of cohort, however, regeneration was enhanced in larger plants. Regeneration of plants in the flowering and fruiting stages depended on date of injury in relation to day length, being the most successful after the summer solstice. Life-history variation, together with the ability to resprout after severe injury in the pioneer wetland herb Rorippa palustris is caused by its ability to germinate throughout the season. Even the second tested factor, the effect of injury, is modified by germination time. The experiment points to a complex nature of factors affecting life-history variation as well as resprouting after severe injury in short lived plants.

RESPROUTING AFTER DISTURBANCE: AN EXPERIMENTAL STUDY WITH SHORT-LIVED MONOCARPIC HERBS

We experimentally demonstrated the ability of three short-lived monocarpic species to vegetatively regenerate (resprout) from roots after severe disturbance. We assessed the relationship between resprouting ability and (1) timing of injury with respect to life-cycle stage (reproductive vs. vegetative plant), life-history mode (annual vs. winter annual) and phenological stage (flowering vs. fruiting plant), (2) nutrient availability, and (3) disturbance severity (removal of all axillary buds Yes/No).In a chamber experiment with the annual or potentially winter annualRorippa palustris, all injured plants resprouted in all nutrient levels and day-length regimes (day-length regimes simulated conditions of an annual and a winter annual cohort). The number of adventitious buds on roots was positively affected only by injury. The extent of regeneration and amount of regenerated biomass were higher at high nutrient level and long-day regime.In a field experiment with the biennials,Oenothera biennis andOenothera issleri, both species responded to injuries by resprouting from axillary buds when at least only one axillary bud was still present. However, they were also able to resprout from adventitious buds on roots. Reproductive plants resprouted more frequently at the flowering stage than at the fruiting stage. Resprouting of vegetative plants (rosettes) was equal throughout the year and more frequent than in the reproductive plants.

Biological flora of Central Europe: Rorippa palustris (L.) Besse

Summary Rorippa palustris is an autogamous short-lived polycarpic herb capable of sprouting from roots. It prefers open wet habitats, such as pond and river shores or emergent pond bottoms. Recently it has expanded into disturbed fertile wetlands. This article reviews the taxonomic status and morphology, the distribution, ecology, life cycle, population biology and genetics of this species.

Multiple Regenerative Strategies of Short-Lived Species: An Effect on Geographical Distribution, Preference of Human-Made Habitats and Invasive Status

It is expected that plant species with multiple regenerative strategies have a wider ecological amplitude and geographical distribution. However there is still an anxious question why species with multiple regenerative strategies are not more frequent. In the presented work we asked whether short-lived plants with a potential bud bank i) have a wider geographical distribution, ii) occur more frequently in human-made habitats and iii) more frequently possess invasive status in comparison with the short-lived species without this additional regenerative strategy. Results show that short-lived plants with a potential bud bank are i) more widely geographically distributed, ii) under-represented in natural habitats and weakly over-represented in habitats disturbed by human activities and iii) contrary to expectation, less numerous among neophytes than species without a potential bud bank. This suggests that short-lived root-sprouters are more habitat-specialized when compared with such plants without adventitious bud-bank formation, but are more widely geographically distributed. A higher frequency of multiple regeneration strategies seems to be restricted by costs of having this ability in habitats or situations without a disturbance regime.

Root sprouting in Knautia arvensis (Dipsacaceae): effects of polyploidy, soil origin and nutrient availability

Plants able to resprout from roots have a potential bud bank that gets initiated after injury to overcome meristem limitation after loss of all stem parts and to facilitate regeneration. Knautia arvensis is reportedly able to sprout from its roots on arable land, but information is missing regarding such ability in serpentine populations or how it might differ between diploids and tetraploids. We hypothesized that (1) ‘ruderal’ non-serpentine populations better tolerate severe disturbance than relic, serpentine ones; (2) tetraploid populations resprout more readily than diploids due to enhanced growth of higher ploidy levels; and (3) plants of different ploidy levels from serpentine soils are, for evolutionary reasons, more similar in their response to disturbances than plants from non-serpentine soils. To test these hypotheses, we conducted a pot experiment. Its results do not support our hypothesis that the ability to sprout from roots is a factor driving the spread of new weedy taxa into central Europe or the hypothesis that it is related to polyploidization in the genus Knautia. Both tetraploids and plants from non-serpentine populations regenerated less vigorously than diploids and plants from serpentine populations. However, the genetically closer populations of serpentine origin were more similar in their response to experimental manipulations than their genetically distinct non-serpentine counterparts. The success of non-serpentine taxa in disturbed habitats of central Europe might be related to traits other than the ability to resprout.

On Plant Modularity Traits: Functions and Challenges

On-spot persistence, space occupancy, and recovery after damage are key plant functions largely understudied. Traits relevant to these functions are difficult to assess because of their relationships to plant modularity. We suggest that developing collection protocols for these traits is feasible and could facilitate their inclusion in global syntheses.

To resprout or not to resprout? Modeling population dynamics of a root-sprouting monocarpic plant under various disturbance regimes

Monocarpic plants are favored in conditions of high mortality of reproductive individuals, whereas situations with low juvenile survival give an advantage to polycarpic perennials. However, certain plant species combine both strategies, showing high plasticity and life-history variation in recurrently disturbed habitats. Life-history variation caused by resprouting from roots after injury has been reported in many weedy and invasive species, but the long-term effects of resprouting on population dynamics are not known. In this study, we asked how different disturbance scenarios affect long-term fitness of plants with varied capacities for root-sprouting. We used projection matrix analysis to simulate growth of populations of the annual herb Rorippa palustris having factorial combinations of root-sprouting intensities, disturbance timings (intra-annual), and frequencies (inter-annual). The contributions of these factors to population growth variation were enumerated using variance decomposition. Population growth was affected by all examined parameters. Disturbance frequency negatively affected population growth rate, but its effect was modulated by disturbance timing. Summer disturbance decreased population growth rate dramatically, whereas winter disturbance had no effect. Resprouting from roots was important for plant overwintering. In pre-reproductive plants, disturbance frequency and root-sprouting intensity strongly interacted in the spring, such that the negative effect of frequent disturbance was overcome by resprouting. Our results imply that, in this species, conditions of unpredictable, severe disturbance, would select for high phenotypic plasticity in life histories, whereas only regular spring disturbance would favor resprouting.

Position of tillers in a clone determines their ontogeny: :example of the clonal grass Phalaris arundinacea

For practical reasons, all ramets of a clonal plant are considered to be independent individuals in demographical studies, but there are reports that ramet ontogeny is affected by their position in a clone. This means that ramets growing from buds located in certain parts of the rhizome system differ in size and probability of flowering from ramets emerging from buds at various positions. We studied the growth characteristics and ontogeny of tillers (ramets) of a rhizomatous grass in relation to their position in a clone and examined whether it is affected by the disturbance regime. We assessed the position of tillers in a clone, the developmental stage of their apical meristem and growth characteristics in mown and unmown stands of the rhizomatous grass Phalaris arundinacea at two sites, one representing optimal (lowland) and the other suboptimal (highland) environmental conditions. We found that tiller characteristics and the probability of a tiller to start flowering are related to the tiller position in a clone. Tiller differences were preserved even in suboptimal environmental conditions but disappeared after mowing, which equalized size and ontogeny. Our results imply that ramets of clonal plants are not independent demographical units, thus their position in a clone should be taken into account.