Shade-induced changes in the branching pattern of a stoloniferous herb: functional response or allometric effect (original) (raw)
Related papers
Annals of Botany, 2007
Aims Because plants protect each other from wind, stand density affects both the light climate and the amount of mechanical stress experienced by plants. But the potential interactive effects of mechanical stress and canopy shading on plant growth have rarely been investigated and never in stoloniferous plants which, due to their creeping growth form, can be expected to respond differently to these factors than erect plants. † Methods Plants of ten genotypes of the stoloniferous species Potentilla reptans were subjected to two levels of mechanical stress (0 or 40 daily flexures) and two levels of spectral shading (15 % of daylight with a red : far red ratio of 0.3 vs. 50 % daylight and a red : far red ratio of 1.2). † Key Results Mechanically stressed plants produced more leaves with shorter more flexible petioles, more roots, and more but less massive stolons. Responses to spectral shading were mostly in the opposite direction to thigmomorphogenesis, including the production of thinner, taller petioles made of more rigid tissue. The degree of thigmomorphogenesis was either independent of light climate or stimulated by spectral shading. At the genotypic level there were no clear correlations between responses to shade and mechanical stress. † Conclusions These results suggest that in stoloniferous plants mechanical stress results in clones with a more compact, shorter shoot structure and more roots. This response does not appear to be suppressed by canopy shading, which suggests that wind shielding (reduced mechanical stress) by neighbours in dense vegetation serves as a cue that induces shade avoidance responses such as increased petiole elongation.
Oecologia, 1997
Previous studies have shown that internodes and petioles of closely related erect and stoloniferous species show marked dierences in their response to shading. Vertical structures show strong elongation responses while horizontal structures show signi®cantly smaller elongation responses. This paper reports an experiment designed to test whether internodes and petioles on orthotropic (vertically oriented) and plagiotropic (horizontally oriented) shoots produced by the same plant, also show such dierential responses. The study species, Glechoma hirsuta, produces plagiotropic shoots in its vegetative stage and orthotropic shoots during its generative stage. Shoots of G. hirsuta were grown either in full daylight or under simulated canopy shade. Internode and petiole elongation, biomass investment patterns and other growth-related parameters were measured on plants in each light treatment. In orthotropic shoots the length of internodes responded more strongly to shading than the length of petioles, while the opposite was true for plagiotropic shoots, con®rming the hypothesis that vertical spacers have higher degrees of shade-induced plasticity than horizontally oriented spacers. Growth and development of horizontally oriented shoots was reduced by shading, whereas that of vertically oriented shoots was unaected by light treatment. The results are discussed in terms of the dierences in function of vertically and horizontally oriented spacers, and the probable bene®ts of plasticity in enhancing essential activities including photosynthesis, habitat exploration and seed dispersal.
PLoS ONE, 2012
Background and aims: In contrast to seeds, high sensitivity of vegetative fragments to unfavourable environments may limit the expansion of clonal invasive plants. However, clonal integration promotes the establishment of propagules in less suitable habitats and may facilitate the expansion of clonal invaders into intact native communities. Here, we examine the influence of clonal integration on the morphology and growth of ramets in two invasive plants, Alternanthera philoxeroides and Phyla canescens, under varying light conditions. Methods: In a greenhouse experiment, branches, connected ramets and severed ramets of the same mother plant were exposed under full sun and 85% shade and their morphological and growth responses were assessed.
PLoS ONE, 2012
Correlations between developmentally plastic traits may constrain the joint evolution of traits. In plants, both seedling deetiolation and shade avoidance elongation responses to crowding and foliage shade are mediated by partially overlapping developmental pathways, suggesting the possibility of pleiotropic constraints. To test for such constraints, we exposed inbred lines of Impatiens capensis to factorial combinations of leaf litter (which affects de-etiolation) and simulated foliage shade (which affects phytochrome-mediated shade avoidance). Increased elongation of hypocotyls caused by leaf litter phenotypically enhanced subsequent elongation of the first internode in response to low red:far red (R:FR). Trait expression was correlated across litter and shade conditions, suggesting that phenotypic effects of early plasticity on later plasticity may affect variation in elongation traits available to selection in different light environments. Citation: von Wettberg EJB, Stinchcombe JR, Schmitt J (2012) Early Developmental Responses to Seedling Environment Modulate Later Plasticity to Light Spectral Quality. PLoS ONE 7(3): e34121.
The controversy over traits conferring shade-tolerance in trees: ontogenetic changes revisited
Journal of Ecology, 2006
1 Successional replacement of intolerant species by shade tolerators along gapunderstorey gradients is commonly associated with increasingly higher low-light carbon acquisition capacities of more tolerant species. This doctrine has recently been challenged because of evidence demonstrating larger leaf dry mass per unit area ( M A ), lower photosynthetic capacities and inferior whole plant relative growth rates (RGR) in both high and low irradiance in seedlings of shade-tolerators. However, as the individuals of shade-tolerant species often need to endure canopy shade for many years before gap formation, testing of the carbon gain hypothesis of shade tolerance requires examination of species carbon gain potentials during the entire plant ontogeny. 2 Light vs. M A relationships throughout ontogeny demonstrate that saplings and canopy individuals of shade tolerators do have lower M A than intolerant species, and moderately higher photosynthetic capacities in low light, resulting in greater whole plant carbon gain capacities at lower light. The apparent discrepancy between results from studies on seedlings vs. saplings/trees is due to M A increasing at a faster rate in shade intolerators during ontogeny. A strong positive linkage between seed size and species shade tolerance further implies that shade tolerators have larger initial size, absolute growth rate and survivorship in low light despite their lower RGR. 3 The evidence reviewed collectively suggests that the carbon balance concept of species' successional position is valid for both seedlings and saplings, and that the apparent discrepancies in species rankings on the basis of structural and physiological characteristics are driven by variations in initial size and rate of ontogeny. Analyses of species shade tolerance potentials should therefore consider how any suite of adaptive traits varies with ontogeny.
International Journal of Forestry Research
This study compared the effects of shading in individual branch orders 2 and 3 on the needle survival, growth, and reproduction of five categories of short shoots of the proximal part of wild Atlas cedar (Cedrus atlantica (Endl.) G. Manetti ex Carrière). The sun exposure did not affect the number of short shoots in the two branch orders, whereas light compared to shade only stimulates the unbranched short shoot elongation of the branch order 3. The impact of shade exposure compared to sun on the loss of needles depends on the order of branching; it is weak to order 2 and increases to higher order. This effect in the branch order 3 is achieved by a significant decrease of the fallen leaf number in the unbranched short shoot SSnr and the short shoot SS/T worn by Twigs while in the branch order 2 only short shoot SS (nr + r) loses significantly few needles. In terms of short shoot extension and needle loss, the SS/T of the branch order 3 behaves in the same way as the SS (nr + r) of th...
Effects of cell number and cell size on petiole length variation in a stoloniferous herb
American Journal of Botany, 2008
In stoloniferous species, the length of petioles is of pivotal importance because it determines the position of leaf blades within the canopy. From a mechanistic perspective, two developmental processes, cell division and cell elongation, are responsible for the length of a given petiole. This study aimed at quantifying the relative contributions of cell division and cell elongation to genotypic and plastic variation in petiole length of the stoloniferous herb Trifolium repens. Thirty-four genotypes of T. repens were grown under high light conditions and simulated canopy shade. Cells were counted and their lengths measured on epidermal prints from fully grown petioles of leaves that had been initiated in the experimental light conditions. Cell number was the main trait explaining petiole length differences among genotypes grown under high light, while both cell number and length changed in response to shading. Our study revealed a strong negative correlation between shade-induced changes in cell number and cell length: genotypes that responded to shading by increasing cell numbers hardly changed in cell length, and vice versa. Our results suggest that genotypic and phenotypic variation in petiole length results from a complex interplay between the developmental processes of cell elongation and cell division.
Acta Oecologica-international Journal of Ecology, 2003
Clonal fragments of the stoloniferous herb Glechoma longituba were subjected to a complementary patchiness of light and soil nutrients including two spatially homogeneous treatments (SR-SR and IP-IP) and two spatially heterogeneous treatments (IP-SR and SR-IP). SR and IP indicate patches (shaded, rich) with low light intensity (shaded, S), high nutrient availability (rich, R) and patches (illuminated, poor) with high light intensity (illuminated, I) and low nutrient availability (poor, P), respectively. Plasticity of the species in root-shoot ratio, fitness-related traits (biomass, number of ramets and dry weight per ramet) and clonal morphological traits (length and specific length of stolon internodes, area and specific area of laminae, length and specific length of petioles) were experimentally examined. The aim is to understand adaptation of G. longituba to the environment with reciprocal patches of light and soil nutrients by plasticities both in root-shoot ratio and in (clonal) morphology. Our experiment revealed performance of the clonal fragments growing from patches with high light intensity and low soil nutrient availability into the adjacent opposite patches was increased in terms of the fitness-related characters. R/S ratio and clonal morphology were plastic. Meanwhile, the capture of light resource from the light-rich patches was enhanced while the capture of soil nutrients from either the nutrient-rich or the nutrient-poor patches was not. Analysis of cost and benefit disclosed positive effects of clonal integration on biomass production of ramets in the patches with low light intensity and high soil nutrient availability. These results suggest an existence of reciprocal translocation of assimilates and nutrients between the interconnected ramets. The reinforced performance of the clonal fragments seems to be related with specialization of clonal morphology in the species.