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2. Growth form of Potentilla reptans. Clockwise, starting from top left: Rosette of Genotype H in pot without stolons in November 2005; Rosette of Genotype B grown in the homogeneous shade (see Chapter 2) with newly formed ramets on two stolons; and the washed roots of a Genotype I plant as harvested in November 2005, showing the fine roots and the start of the tap root.
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The ability to adjust the phenotype (e.g. plasticity) is thought to be beneficial for the performance of a plant, because it prevents overinvestment in support structures when plant density is low, and allows a plant to position its leaves high in the canopy when density is high. However, as the plastic responses differ within species, exclusion of...
Citations
... The ten genotypes were previously used in a long-term competition experiment, where all nine remaining genotypes after 5 years reached similar heights (Vermeulen et al., 2008b). Yet several experiments have shown that they differ in their responses to shade signals (Liu et al., 2007; Vermeulen, 2008). We expected (1) that when grown in monogenotypic stands, genotypes would differ in their plastic response to density; (2) consequently, these differences in response should lead to differences between the genotypes in the increase in height and in investment in height growth (i.e.the petioles); (3) with the two positively correlated. ...
... These genotypes have been used in a range of experiments, including a longterm competition experiment (Stuefer et al., 2009). Several shading experiments showed marked differences among these genotypes in their plasticity in height investment (Vermeulen, 2008). On 13 June 2006, 160 trays were prepared with nine pots each. ...
... The results confirm this idea: the covariance analysis revealed that for most traits a significant genotype  density interaction had occurred. Consequently, the genotypes showed large differences in vegetation height at high density and the differences in vegetation height at high density were consistent with the maximum petiole lengths in single pot shading experiments where the same genotypes were used (Liu et al., 2007; Vermeulen, 2008). So while results from a 5-year competition experiment between the same ten genotypes showed that they converge to a similar height when competing (Vermeulen et al., 2008b), differences do occur when genotypes determine their own canopy structure and light climate. ...
Background and Aims Game theoretical models predict that plants growing in dense stands invest so much biomass in height growth that it trades-off with investment in other organs such as the leaves, leading to decreased plant production. Using the stoloniferous plant Potentilla reptans, we tested the hypothesis that genotypes investing more in the petioles in response to increased density show a greater decrease in total plant mass. We also tested whether a greater increase in mother ramet investment would lead to a greater decrease in investment in vegetative propagation.Methods
To uncouple costs and benefits of investments in petioles, ten genotypes that were known to differ in their response to shading signals were grown in monogenotypic stands at two different densities.Key ResultsGenotypes differed in their increase in petiole investment in response to an increase in density, but not in their decrease in total plant mass or root mass. Total lamina area per plant did not differ significantly between the densities, nor did the mass invested in the laminae per unit of total plant mass. Genotypes differed considerably in the change in vegetation height and petiole investment, but this was not significantly negatively correlated with the change in total plant mass. The genotypes did differ in the change of mass investment in the mother ramet: a greater increase in investment in the mother ramet was correlated to a greater decrease in vegetative propagation.Conclusions
While a greater increase in height investment did not lead to a greater decrease in biomass production, it did lead to a decrease in vegetative propagation. This ability to change allocation towards the mother ramets may imply that competition within a stand of stoloniferous plants does not necessarily result in lower total biomass production due to increased height investment.
... Size–number trade-offs (Stuefer, Van Hulzen & During 2002) with respect to vegetative offspring production can be expected to result in environment-dependent differences in genotype performance. In dense canopies, selection for competitive ability and local persistence should lead to a dominance of genotypes with high growth rates, large offspring individuals, and the ability to exert strong asymmetric competition by producing large leaves (Vermeulen 2008 ). On the contrary , genotypes producing many small offspring should decrease in frequency under strong competition. ...
... S A M P L I N G P R O C E D U R E S Five years after starting the experiment, we determined the frequency of the 10 genotypes by taking 100 leaf samples from each of the populations . At the time of sampling, all populations were very dense (LAI around 4–6; Vermeulen 2008) and consisted of multiple leaf layers. Random positions on a horizontal grid (grid cell size: 2 · 2 cm) were generated and the closest leaf to each position was sampled. ...
1. An increasing body of evidence suggests that within-species diversity plays an important role for community and ecosystem functioning, alters complex trophic interactions and affects patterns of species diversity and coexistence. Nonetheless, we lack a good understanding of how genotypic trait variation translates into shifts in the relative abundance of genotypes within populations.
2. In this study, we show that genotypic selection strongly alters dominance relationships among genotypes over a period of 5 years. This resulted in remarkably consistent changes in the proportional representation of genotypes, and in a concomitant decline of diversity and evenness in our experimental populations.
3. High growth rates and the production of large offspring were positively associated with genotypic performance. Vegetative abundances of genotypes translated monotonically into flowering frequencies.
4. Synthesis. We conclude that genotypic selection markedly affects patterns of diversity and consistently alters genotypic abundance and mean trait distributions in plant populations over a relatively short period of time.
... The leaf area index (m 2 m − 2 ground surface) quickly reached high values and remained high from then on. Throughout the season, leaf turnover was high, with an average leaf lifespan of around four to six weeks (Vermeulen 2008). In 1996 10 ramets of P. reptans were taken from 10 different locations, from a broad array of natural and semi-natural habitats from parking lots to river flood plains, and propagated on potting compost in the botanical gardens of Utrecht University. ...
... The reason why a genotype with rather shade-tolerant physiological traits may have become dominant in this vegetation may be due to the high leaf area that develops during the growth season. After winter, new leaves emerge from the tap roots and these are placed in high light conditions (Vermeulen 2008). Once the leaf lamina reaches high light conditions its height growth stops. ...
... In tropical secondary forests, the longer leaf life span of long-lived pioneer species has been found to result in a higher light capture over the leaf life span than in short-lived pioneer species, enabling these species to replace the latter in the long run (Selaya et al. 2008). Although we have no data on the differences in leaf turnover between the genotypes within this competition experiment, the average leaf life span is approximately 1.5 months (Vermeulen 2008), indicating it plays an important role in the development of the canopy. If a low-light requirement (i.e. a low I*) is associated with a longer leaf life span, then this may allow the dominant genotype I to have higher life time carbon gains than genotypes with high-light adapted and hence shorter-lived leaves. ...
Different views exist as to what traits will lead to dominance when plants compete for light. One view is that taller plants with better relative positions in the canopy will exclude shorter plants because they intercept almost all light and thus can achieve a higher carbon gain. Alternatively, resource competition models predict that plants that are capable of positive net photosynthesis at the lowest light level will win. In a 5‐year‐old dense competition experiment with 10 genotypes of the clonal plant Potentilla reptans , both these views were tested to see if either of them could explain the dominance of one of the genotypes, or the possible coexistence of several others.
Using a combination of measured morphological and physiological traits, a canopy model was constructed to calculate whole‐shoot daily photosynthetic rates of the genotypes in the different layers of the canopy in relation to the invested mass.
Results show that the dominant genotype exhibited characteristics of relative shade tolerance: low rates of light‐saturated photosynthesis and respiration. This resulted in a calculated daily carbon gain at the bottom of the canopy, where other genotypes could not achieve that. However, the dominant genotype did not have the highest photosynthetic rates throughout the whole canopy. Some genotypes that persisted in the stand in coexistence with the dominant one achieved greater daily carbon gain at the top of the canopy.
Synthesis . The dominant genotype had characteristics similar to those predicted by resource competition models such as the ability to have positive growth at lower light levels. The persistence of several other genotypes, in contrast, may be explained by traits that allowed them to achieve higher carbon gains at the top of the canopy. This suggests that the light gradient formed by the plants themselves creates enough heterogeneity for strategies for dealing with different light requirements to coexist, even within a single species.
... The genotypes were propagated in the botanical gardens of Utrecht University. In shading experiments these genotypes differed in several traits, such as SLA, LMR and petiole length (Liu et al., 2007; Vermeulen, 2008). ...
... The reason why no asymmetric competition for light was found, while genotypes differed in the relative number of leaves at the top of the canopy, may be due to the dynamics of the system. Surveys in 2005 showed that leaf turnover is very high in this canopy (six to eight leaves were formed and shed between early April and the end of June; Vermeulen, 2008). Genotypes of Potentilla reptans place their leaves at or near the top of a light gradient (Vermeulen et al., 2008). ...
While within-species competition for light is generally found to be asymmetric - larger plants absorbing more than proportional amounts of light - between-species competition tends to be more symmetric. Here, the light capture was analysed in a 5-year-old competition experiment that started with ten genotypes of the clonal plant Potentilla reptans. The following hypotheses were tested: (a) if different genotypes would do better in different layers of the canopy, thereby promoting coexistence, and (b) if leaves and genotypes with higher total mass captured more than proportional amounts of light, possibly explaining the observed dominance of the abundant genotypes.
In eight plots, 100 leaves were harvested at various depths in the canopy and their genotype determined to test for differences in leaf biomass allocation, leaf characteristics and the resulting light capture, calculated through a canopy model using the actual vertical light and leaf area profiles. Light capture was related to biomass to determine whether light competition between genotypes was asymmetric.
All genotypes could reach the top of the canopy. The genotypes differed in morphology, but did not differ significantly in light capture per unit mass (Phi(mass)) for leaves with the laminae placed at the same light levels. Light capture did increase disproportionately with leaf mass for all genotypes. However, the more abundant genotypes did not capture disproportionately more light relative to their mass than less-abundant genotypes.
Vertical niche differentiation in light acquisition does not appear to be a factor that could promote coexistence between these genotypes. Contrary to what is generally assumed, light competition among genetic individuals of the same species was size-symmetric, even if taller individual leaves did capture disproportionately more light. The observed shifts in genotype frequency cannot therefore be explained by asymmetric competition for light.
Game theoretical models predict that plant competition for light leads to reduced productivity of vegetation stands through selection for traits that maximize carbon gains of individuals. Using empirical results from a 5-year competition experiment with 10 genotypes of the clonal plant Potentilla reptans, we tested this prediction by analyzing the effects of the existing leaf area values on the carbon gain of the different genotypes and the consequent whole canopy carbon gain. We focused on specific leaf area (SLA) due to its role in the trade-off between light capture area and photosynthetic capacity per unit area. By combining a canopy model based on measured leaf area and light profiles with a game theoretical approach, we analyzed how changes in the SLA affected genotypic and whole-stand carbon gain. This showed that all genotypes contributed to reduced stand productivity. The dominant genotype maximized its share of total carbon gain, resulting in lower than maximal absolute gain. Other genotypes did not maximize their share. Hypothetical mutants of the dominant genotype were not able to achieve a higher carbon gain. Conversely, in other genotypes, some mutations did result in increased carbon gain. Hence, genotypic differences in the ability to maximize performance may determine genotype frequency. It shows how genotypic selection may result in lower carbon gains of the whole vegetation, and of the individual genotypes it consists of, through similar mechanisms as those that lead to the tragedy of the commons.
