Biomedical subjects

Hans de Kroon

Publications and source records attributed to Hans de Kroon.

6 recordsLinked to original sources

PubMed2006

The interplay between shifts in biomass allocation and costs of reproduction in four grassland perennials under simulated successional change.

When perennial herbs face the risk of being outcompeted in the course of succession, they are hypothesized to either increase their biomass allocation to flowers and seeds or to invest more in vegetative growth. We tested these hypotheses in a 3-year garden experiment with four perennials (Hypochaeris radicata, Cirsium dissectum, Succisa pratensis and Centaurea jacea) by growing them in the midst of a tall tussock-forming grass (Molinia caerulea) that may successionally replace them in their natural habitat. In all species except for the short-lived H. radicata, costs of sexual reproduction were significant over the 3 years, since continuous bud removal enhanced total biomass or rosette number. To mimic succession we added nutrients, which resulted in a tripled grass biomass and higher death rates in the shorter-lived species. The simulated succession resulted also in a number of coupled growth responses in the survivors: enhanced plant size as well as elevated seed production. The latter was partly due to larger plant sizes, but mostly due to higher reproductive allocation, which in turn could be partly explained by lower relative somatic costs and by lower root-shoot ratios in the high-nutrient plots. Our results suggest that perennial plants can increase both their persistence and their colonization ability by simultaneously increasing their vegetative size and reproductive allocation in response to enhanced competition and nutrient influxes. These responses can be very important for the survival of a species in a metapopulation context.

Asteraceae↗

PubMed2006

Shade avoidance in Trifolium repens: costs and benefits of plasticity in petiole length and leaf size.

We tested whether the degree of shade-induced plasticity in petiole length and leaf area is related to the mean trait value expressed under high-light conditions, and to what extent trait values expressed under high-light and shaded conditions affect plant performance. Thirty-four Trifolium repens genotypes were used with a wide range of petiole lengths and leaf areas. Plants were subjected to a high-light environment and two shading regimes: homogeneous shading and a vertical light gradient. Absolute petiole elongation in response to both shading treatments and absolute leaf area expansion in response to homogeneous shading were independent of the trait values expressed in high light. Consequently, relative plasticity was higher for genotypes with lower high-light trait values. Plasticity was associated with enhanced plant performance in a vertical light gradient but not in homogeneously shaded conditions. We also found costs associated with the ability to express plasticity. Our results suggest that selection can act separately on trait values expressed under high-light conditions and on the degree of plasticity.

Adaptation, Physiological↗

PubMed2005

Root foraging theory put to the test.

Roots have a tremendous plasticity that has long fascinated plant scientists. Root proliferation into enriched soil patches is commonly considered as a way for plants to acquire patchily distributed soil resources. In a recent synthetic study involving the responses of over 100 species, Kembel and Cahill concluded that long-standing generalizations explaining variation in root proliferation should be reconsidered.

Hordeum↗

PubMed2005

A modular concept of phenotypic plasticity in plants.

Based on empirical evidence from the literature we propose that, in nature, phenotypic plasticity in plants is usually expressed at a subindividual level. While reaction norms (i.e. the type and the degree of plant responses to environmental variation) are a property of genotypes, they are expressed at the level of modular subunits in most plants. We thus contend that phenotypic plasticity is not a whole-plant response, but a property of individual meristems, leaves, branches and roots, triggered by local environmental conditions. Communication and behavioural integration of interconnected modules can change the local responses in different ways: it may enhance or diminish local plastic effects, thereby increasing or decreasing the differences between integrated modules exposed to different conditions. Modular integration can also induce qualitatively different responses, which are not expressed if all modules experience the same conditions. We propose that the response of a plant to its environment is the sum of all modular responses to their local conditions plus all interaction effects that are due to integration. The local response rules to environmental variation, and the modular interaction rules may be seen as evolving traits targeted by natural selection. Following this notion, whole-plant reaction norms are an integrative by-product of modular plasticity, which has far-reaching methodological, ecological and evolutionary implications.

Adaptation, Physiological↗

PubMed2005

A functional comparison of acclimation to shade and submergence in two terrestrial plant species.

Terrestrial plants experience multiple stresses when they are submerged, caused both by oxygen deficiency due to reduced gas diffusion in water, and by shade due to high turbidity of the floodwater. It has been suggested that responses to submergence are de facto responses to low light intensity. We investigated the extent to which submergence and shade induce similar acclimation responses by comparing two terrestrial Rumex species that differ in their responses to flooding. Our study confirms that there are strong similarities between acclimation responses to shade and submergence. Petiole length, specific leaf area (SLA), chlorophyll parameters and underwater light-compensation points changed at least qualitatively in the same direction. Maximum underwater photosynthesis rate, however, did discriminate between the functionality of the responses, as the acclimation to submergence appeared to be more effective than acclimation to shade at saturating light. We conclude that acclimation to submergence involves more than an increase in SLA to achieve the significant reduction of diffusion resistance for gas exchange between leaves and the water column.

Acclimatization↗

PubMed2004

Canopy studies on ethylene-insensitive tobacco identify ethylene as a novel element in blue light and plant-plant signalling.

Plants growing at high densities express shade avoidance traits as a response to the presence of neighbours. Enhanced shoot elongation is one of the best researched shade avoidance components and increases light capture in dense stands. We show here that also leaf movements, leading to a more vertical leaf orientation (hyponasty), may be crucial in the early phase of competition. The initiation of shade avoidance responses is classically attributed to the action of phytochrome photoreceptors that sense red:far-red (R:FR) ratios in light reflected by neighbours, but also other signals may be involved. It was recently shown that ethylene-insensitive, transgenic (Tetr) tobacco plants, which are insensitive to the gaseous plant hormone ethylene, have reduced shade avoidance responses to neighbours. Here, we report that this is not related to a reduced response to low R:FR ratio, but that Tetr tobacco plants are unresponsive to a reduced photon fluence rate of blue light, which normally suppresses growth inhibition in wild-type (WT) plants. In addition to these light signals, ethylene levels in the canopy atmosphere increased to concentrations that could induce shade avoidance responses in WT plants. Together, these data show that neighbour detection signals other than the R:FR ratio are more important than previously anticipated and argue for a particularly important role for ethylene in determining plant responses to neighbours.

Ethylenes↗