Shade induced changes in biomechanical petiole properties in the stoloniferous herb <Emphasis Type="Italic">Trifolium repens</Emphasis>

Increased cell number and cell length both contribute to shade induced elongation of petioles which enables stoloniferous plants to place their leaf lamina higher up in the canopy. Although petiole elongation is assumed to be beneficial, it may also imply costs in terms of decreased biomechanical stability. We test the hypothesis that shade induced elongation changes the biomechanical properties of petioles and that the underlying mechanisms, cell division and cell elongation, differentially affect biomechanical properties. This was done by subjecting 14 genotypes differing in the relative contribution of cell size and cell number to shade induced elongation responses to high light conditions and to simulated canopy shade. Developmental traits (cell size and cell number), morphological traits characterizing the petioles, as well as biomechanical characteristics were measured. Our results show that, comparable to stems of non-clonal plants, the rigidity of a petiole’s tissue (the Young’s modulus) increases, leading to increased flexural stiffness of petioles subjected to shading. Increased flexural stiffness proved to be associated with increased performance under shaded conditions. Our results also indicate that cell number affected the material properties and the flexural stiffness of petioles. However, the degree and pattern of the effects differed between light environments. Shade induced increase in cell number translated into shade induced increase of Young’s modulus and flexural stiffness. Genotypes producing relatively larger cells under shaded conditions experienced a decrease in tissue rigidity. In concert our results indicate that the pattern of selection on flexural stiffness, and thereby also on shade induced changes of cell number and cell size differs among light environments. An erratum to this article can be found at     

Phytochrome control of the growth and development of Rumex obtusifolius under simulated canopy light environments*

Abstract Studies on the growth and development of Rumex obtusifolius seedlings under simulated shade conditions show that both light quantity and quality contribute to the observed responses. In the shade situation the plants have lower dry matter, lower leaf area and lower net assimilation rates. Petiole elongation occurs under shade conditions only after transfer of the plants from non-shade environments. The effects of light quality are related to phytochrome photoequilibria set up by the increased relative photon flux in the far-red found under vegetation canopies.     

The Response of Petioles of Glechoma hederacea to a Dynamic Light Climate

Abstract: In herbaceous vegetation patterns of light distribution may change over time. Prostrate plants growing in such a dynamic light environment may benefit from petioles that respond plastically to changing light conditions. In an experiment, the response of petioles of Glechoma hederacea to changing light conditions was analyzed. Treatments included continuous shade, continuous high light, a shift from shade to high light and from high light to shade when the plants had formed 10 ramets. In all four treatments, even petioles that had apparently ceased growing, were still able to elongate slightly but the extent of elongation decreased with the age of the petiole. In the oldest petioles relative extension rates were higher in shade than in high light. In plants that were exposed to full daylight in the second half of the experiment, even newly formed petioles were longer than those in plants that grew in full daylight continuously though they had elongated over a shorter period. In plants that were shaded in the second half of the experiment, only the youngest 4 to 5 petioles reached lengths similar to that in continuous shade. This mechanism may enable plants to keep young (productive) leaves in the upper layers of the canopy while other less productive leaves remain at lower levels of the vegetation.     

The role of leaf lobation in elongation responses to shade in the rosette-forming forb Serratula tinctoria (Asteraceae)

BACKGROUND AND AIMS: Lobed leaves are considered selectively advantageous in conditions of high irradiance. However, most studies have involved woody species, with only a few considering the role of leaf lobation in herbaceous rosette species. In this study, it is hypothesized that, in addition to its adaptive value in high light, leaf lobation may add to the function of petioles as vertical spacers in herbaceous species in conditions of strong competition for light. METHODS: To test this hypothesis, leaf development was examined under seasonally changing natural light conditions and a field experiment was conducted in which light climate was manipulated in a wooded meadow population of Serratula tinctoria. KEY RESULTS: No changes in leaf lobation were observed in response to experimental shading or different natural light conditions. However, in tall herbaceous vegetation, plants with highly lobed leaves achieved significantly greater vertical elongation than plants with less-lobed leaves. In contrast to herbaceous shade, tree shade had no effect on leaf elongation, suggesting differential responsiveness to competition from neighbouring herbs versus overhead shade. In shading treatments, imposed shade could only be responded to by the elongation of leaves that were produced late in development. CONCLUSIONS: The results show that extensive leaf lobation can enable greater leaf elongation in response to shade from surrounding herbaceous vegetation. The different morphological responses displayed by Serratula tinctoria to different types of shade demonstrate the importance of critically assessing experimental designs when investigating phenotypic plasticity in response to shade.     

Diurnal changes in chlorophyll fluorescence and light utilization in Colocasia esculenta leaves grown in marshy waterlogged area

Diurnal cycle of chlorophyll fluorescence parameters was done in Colocasia esculenta L. (swamp taro) grown in marshy land under sun or under shade. The sun leaves maintained higher electron transport rate (ETR) and steady state to initial fluorescence ratio (F_s/F₀) than shade leaves. In spite of lower ETR, higher photochemical quenching (PQ), and effective quantum yield of photosystem 2 (Φ_PS2) was evident in shade plants compared to plants exposed to higher irradiance. ETR increased linearly with increase in irradiance more under low irradiance (r ² = 0.84) compared to higher irradiance (r ² = 0.62). The maximum quantum yield of PS 2 (F_v/F_m) did not differ much in sun and shade leaves with the exception of midday when excess of light energy absorbed by plants under sun was thermally dissipated. Hence swamp taro plants adopted different strategies to utilize radiation under different irradiances. At higher irradiance, there was faster decline in proportion of open PS 2 centers (PQ) and excess light energy was dissipated through non-photochemical quenching (NPQ). Under shade, absorbed energy was effectively utilized resulting in higher Φ_PS2.     

Theories on adaptations to high light intensity in the aquatic moss Fontinalis

Abstract

Fontinalis antipyretica, collected from a cold stream in bright sunlight, served as a model for adaptations of Fontinalis to sun and shade. Sun leaves produced red pigments and had less chlorophyll, greater specific leaf weight, and less specific leaf area than shade leaves. The chlorophyll a/b ratio was not significantly different under high and low light conditions. Except for the relatively constant a/b ratio, Fontinalis behaved like higher plants in its sun/shade differences.     

Effects of light quality and quantity on growth of the clonal plant Eichhornia crassipes

Summary Plant canopy shade reduces photosynthetic photon flux density (PPFD) and ratio of red to far-red light (z). Both effects can cause plants to increase potential for light acquisition through vertical growth and leaf area expansion. Clonal plants such as Eichhornia crassipes might alternatively increase light interception via horizontal growth of stolons or rhizomes and placement of new ramets in less shaded microsites. Effect of simulated canopy shade and component effects of PPFD and z were tested by filtering or adding light uniformly, to a whole group of connected ramets, or locally, to individual ramets within a group. In uniform treatments, low PPFD reduced total growth but low z did not. Low PPFD and low z independently reduced stolon and ramet production and caused etiolation of petioles; effect of low PPFD plus low z on ramet production was greater than that of either factor alone. Lateral clonal growth thus did not seem to be a response to uniform shading; instead, uniformly low PPFD or low z increased partitioning to established ramets. Low z changed partitioning without changing total growth. In local treatments, reduction of growth of individual ramets due to low PPFD and inhibition of new ramet production attributable to spectral composition of light were mitigated when connected ramets were unshaded; plants may respond differently to patchy than to uniform shade.     

Variation in petiole and internode length affects plant performance in <Emphasis Type="Italic">Trifolium repens</Emphasis> under opposing selection regimes

We studied the effects of genotypic and plastic variation in vertical and horizontal spacer lengths on plant performance in a stoloniferous herb subjected to opposing selection regimes. We hypothesized that longer vertical structures are beneficial if plants are subjected to competition, but they should negatively affect plant performance if plants are exposed to aboveground disturbance. To test these hypotheses we subjected 34 genotypes of Trifolium repens to competition and disturbance treatments. Competition was imposed by a grass canopy consisting of Lolium perenne, and disturbance was simulated by regularly clipping the target plants and all the surrounding vegetation at 1 cm above soil level. Conform to our hypothesis, genotypes with longer vertical structures (petioles) produced fewer ramets than genotypes with shorter petioles in the disturbance treatment. However, genotypes with longer petioles did not perform better under competition than genotypes with shorter petioles. Genotypes with highly plastic vertical structures tended to produce more shoot mass under competition, and they produced fewer ramets if subjected to disturbance. Unexpectedly, horizontal structures (stolon internodes) expanded in response to competition which, furthermore, was associated with enhanced plant performance. However, producing longer internodes is inherently associated with costs in terms of increased resource allocation to the longer structures, but not to benefits in terms of increased resource capture. Positive correlations among the length and plasticity of vertical and horizontal structures may explain the apparent positive effect of producing longer internodes on plant performance. Our data thus support the notion that trait correlations may weaken selective forces acting on a focal trait in a specific environment if opposing selection pressures act on genetically correlated traits.     

Biomass Allocation of Erythronium americanum Populations in Different Irradiance Levels

The forest herb Erythronium americanum was collected from threeNew Jersey habitats and grown in 100%, 43%, or 23% glasshouselight to determine if biomass allocation responses to irradiancediffered between populations. Shaded plants had longer petioles,produced fewer runners, and had greater specific leaf areasthan unshaded plants; these responses did not differ significantlyamong populations. All populations produced smaller bulbs whengrown in shade. Over all light treatments, mean leaf area ofplants from a stable, established site was greater than thatof plants from others. In 100 % light, these plants had thegreater bulb growth. The simple architecture of Erythroniummay constrain morphological responses to the light environment. Erythronium americanum(Ker.), forest herb, biomass allocation, light intensity     

Temperature‐dependent shade avoidance involves the receptor‐like kinase ERECTA

Plants detect the presence of neighbouring vegetation by monitoring changes in the ratio of red (R) to far‐red (FR) wavelengths (R:FR) in ambient light. Reductions in R:FR are perceived by the phytochrome family of plant photoreceptors and initiate a suite of developmental responses termed the shade avoidance syndrome. These include increased elongation growth of stems and petioles, enabling plants to overtop competing vegetation. The majority of shade avoidance experiments are performed at standard laboratory growing temperatures (>20°C). In these conditions, elongation responses to low R:FR are often accompanied by reductions in leaf development and accumulation of plant biomass. Here we investigated shade avoidance responses at a cooler temperature (16°C). In these conditions, Arabidopsis thaliana displays considerable low R:FR‐mediated increases in leaf area, with reduced low R:FR‐mediated petiole elongation and leaf hyponasty responses. In Landsberg erecta, these strikingly different shade avoidance phenotypes are accompanied by increased leaf thickness, increased biomass and an altered metabolite profile. At 16°C, low R:FR treatment results in the accumulation of soluble sugars and metabolites associated with cold acclimation. Analyses of natural genetic variation in shade avoidance responses at 16°C have revealed a regulatory role for the receptor‐like kinase ERECTA.     

Differential response to shading in orthotropic and plagiotropic shoots of the clonal herb Glechoma hirsuta

Previous studies have shown that internodes and petioles of closely related erect and stoloniferous species show marked differences in their response to shading. Vertical structures show strong elongation responses while horizontal structures show significantly 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 differential 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, confirming 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 unaffected by light treatment. The results are discussed in terms of the differences in function of vertically and horizontally oriented spacers, and the probable benefits of plasticity in enhancing essential activities including photosynthesis, habitat exploration and seed dispersal. Received: 23 December 1996 / Accepted: 19 July 1997     

Dynamic stomatal behavior and its role in carbon gain during lightflecks of a gap phase and an understory Piper species acclimated to high and low light

Summary Steady-state and dynamic stomatal and assimilation responses to light transients were characterized in sun- and shade-acclimated plants of Piper auritum, a pioneer tree, and Piper aequale a shade-tolerant shrub from a tropical forest at Los Tuxtlas, Veracruz, México. Despite essentially identical steady-state responses of stomatal conductance to PFD of P. aequale and P. auritum shade plants, the dynamic responses to lightflecks were markedly different and depended on the growth regime. For both species from both growth environments, the increase in stomatal conductance occurring in response to a lightfleck continued long after the lightfleck itself so that the maximum stomatal conductance was not reached until 20–40 min after the lightfleck. Closing then occurred until stomatal conductance returned to near its original value before the lightfleck. Plants that were grown under light regimes similar to those of their natural habitat (high light for P. auritum and shade for P. aequale) had large maximum excursions of stomatal conductance and slower closing than opening responses. Plants grown under the opposite conditions had smaller excursions of stomatal conductance, especially in P. auritum, and more symmetrical opening and closing. The large and hysteretic response of stomatal conductance of P. aequale shade plants to a lightfleck was shown to improve carbon gain during subsequent lightflecks by 30–200%, depending on lightfleck duration. In contrast the very small stomatal response to lightflecks in P. auritum shade plants, resulted in no significant improvement in use of subsequent lightflecks.     

Photosynthetic acclimation of the liana Stigmaphyllon lindenianum to light changes in a tropical dry forest canopy

Tropical plant canopies show abrupt changes in light conditions across small differences in spatial and temporal scales. Given the canopy light heterogeneity, plants in this stratum should express a high degree of plasticity, both in space (allocation to plant modules as a function of opportunity for resource access) and time (photosynthetic adjustment to temporal changes in the local environment). Using a construction crane for canopy access, we studied light acclimation of the liana Stigmaphyllon lindenianum to sun and shade environments in a tropical dry forest in Panama during the wet season. Measured branches were randomly distributed in one of four light sequences: high- to low-light branches started the experiment under sun and were transferred to shade during the second part of the experiment; low- to high-light branches (LH) were exposed to the opposite sequence of light treatments; and high-light and low-light controls , which were exposed only to sun and shade environments, respectively, throughout the experiment. Shade branches were set inside enclosures wrapped in 63% greenhouse shade cloth. After 2 months, we transferred experimental branches to opposite light conditions by relocating the enclosures. Leaf mortality was considerably higher under shade, both before and after the transfer. LH branches reversed the pattern of mortality by increasing new leaf production after the transfer. Rates of photosynthesis at light saturation, light compensation points, and dark respiration rates of transferred branches matched those of controls for the new light treatment, indicating rapid photochemical acclimation. The post-expansion acclimation of sun and shade foliage occurred with little modification of leaf structure. High photosynthetic plasticity was reflected in an almost immediate ability to respond to significant changes in light. This response did not depend on the initial light environment, but was determined by exposure to new light conditions. Stigmaphyllon responded rapidly to light changes through the functional adjustment of already expanded foliage and an increase in leaf production in places with high opportunity for carbon gain. Received: 24 April 1998 / Accepted: 11 May 1999     

藤本植物Potentilla reptans叶对风和遮阴的响应

生长在一个密集植物群中的植株由于相互遮蔽而不可能对风的影响做出反应,因为这样的环境条件(有限的光资源)对由风导致的矮小表型植株的生长是不利的。为弄清在密集植物群体中生长的植株对风的响应,利用藤本植物Potentilla reptans的10种基因型做实验材料,在温室条件下(光照强度为日光照的50%,红光/远红光=1.2)模拟冠层遮阴(相当于15%的日光照,红光/远红光=0.3),研究了藤本植物叶对风的响应。结果表明,Potentilla reptans的10种基因型植株在冠层遮阴下(低的红光/远红光)都表现出典型的避阴生长响应:较少的叶(叶生物量少),长而细但硬度系数高(higher Young's modulus)的叶柄;而受风影响的植株,无论遮阴或不遮阴,其植株的叶相对较多,叶柄短、粗且柔韧性强(lower Young's modulus),说明Potentilla reptans叶对风的响应并未因遮阴而被压抑,其可塑性变化不过是对复杂生境做出的一种生长权衡:尽可能增强抗风能力(矮壮)和获取最大光能(足够高而避免被遮光),即保证在存活下去的前提下获取最大的生长效率。     

Xylem development and hydraulic conductance in sun and shade shoots of grapevine (Vitis vinifera L.): evidence that low light uncouples water transport capacity from leaf area

Morphology, water relations, and xylem anatomy of high-light (sun)- and low-light (shade)-grown Vitis vinifera L. shoots were studied to determine the effects of shading on the hydraulic conductance of the pathway for water flow from the roots to the leaves. Shade shoots developed leaf area ratios (leaf area: plant dry weight) that were nearly threefold greater than sun shoots. Water-potential gradients (·m^–1) in the shoot xylem accounted for most of the ·m^–1 between soil and shoot apex at low and high transpiration rates in both sun and shade shoots, but the gradients were two- to fourfold greater in shade-grown plants. Low light reduced xylem conduit number in petioles, but had an additional slight effect on conduit diameter in internodes. The hydraulic conductance per unit length (Kh) and the specific hydraulic conductivity (k_s, i.e. Kh per xylem cross-sectional area) of internodes, leaf petioles, and leaf laminae at different developmental stages leaf plastochron index was calculated from measurements of water potential and water flow in intact plants, from flow through excised organs, and from vessel and tracheid lumen diameters according to Hagen-Poiseuille's equation. For all methods and conductance parameters, the propensity to transport water to sink leaves was severalfold greater in internodes than in petioles. The Kh and k_s increased logarithmically until growth ceased, independent of treatment and measurement method, and increased further in pressurized-flow experiments and Hagen-Poiseuille predictions. However, the increase was less in shade internodes than in sun internodes. Mature internodes of shade-grown plants had a two- to fourfold reduced Kh and significantly lower k_s than sun internodes. Except very early in development, leaf lamina conductance and k_s from shade-grown plants was also reduced. The strong reduction in Kh with only a slight reduction in leaf area (17% of sun shoots) in the shade shoots indicated a decoupling of water-transport capacity from the transpirational surface supplied by that capacity. This decoupling resulted in strongly reduced leaf specific conductivities and Huber values for both internodes and petioles, which may increase the likelihood of cavitation under conditions of high evaporative demand or soil drought.Abbreviations A_c total cross-sectional area (internodes, petioles, leaf laminae) - A_x xylem cross-sectional area - HV Huber value - Kh hydraulic conductance per unit length - k_s specific hydraulic conductivity - LPI leaf plastochron index - LSC leaf specific conductivity - water potential - water-potential gradient - q volume flow of water per unit time Hans R. Schultz was supported in part by the Deutsche Forschungsgemeinschaft (grant Ki-114/8-1). We wish to thank Dr. Thomas Geier, Institut für Biologie, Forschungsanstalt D-6222 Geisenheim, Germany for his advice on sample preparation and microscopy, and two anonomous reviewers for their helpful comments.     

Phenotypic plasticity and morphological adaptation of Halimeda opuntia (Bryopsidales,Chlorophyta) to light intensity

Plasticity gives plants the ability to adapt their morphology and growth to various environments. Environmental factors can lead to changes in the growth forms of algae. Halimeda opuntia was used as a model organism to determine the effects of highly irradiated and shade conditions in the field and its responses to low light conditions in the laboratory, which are known to be some of the main factors driving its morphological plasticity. To investigate the morphological and anatomical characteristics of the species, a total of 61 characteristics and 54 samples from Thailand, Japan and Indonesia were examined. In addition, we also tested the response under different light conditions in the laboratory. A phylogenetic tree was constructed using the tufA marker to confirm the species identification. We found that the thallus forms, branching patterns and segment shapes and sizes responded to the different light conditions. A brittle thallus network was found under shade conditions with low light intensity, while a compact thallus form was found under highly irradiated conditions. The H. opuntia segment shape was reniform under highly irradiated conditions, but its segments were adapted to be deeply trilobed in the lower thallus and tripartite shape in the upper thallus under shade conditions. The segment size also adapted; the segments in shaded areas were longer than those in sunny areas, which might have helped them increase their thallus height to ensure exposure to the high light habitat. This morphological variation and plasticity expanded our understanding of the range of H. opuntia plasticity present in the field and could help explain why this species is common and successfully colonizes various habitats worldwide.     

Photosynthetic acclimation to light in juveniles of two cloud forest tree species

The photosynthetic response of juveniles of Decussocarpus rospigliosii, an emergent primary forest species and shade tolerant in its juvenile stages and Alchornea triplinervia, a gap-colonizing species of tropical cloud forest in Venezuela was studied. Daily courses of microenvironmental variables and gas exchange under contrasting light conditions (gap and understory) were carried out in their natural environment and transplanted to different light regimes (shade and sun) in the field. The photosynthetic response and some anatomical characteristics of plants from different treatments were analyzed in the laboratory. Photosynthetic rates were low for both species, and were negative during some diurnal periods, related to the low photosynthetically active radiation levels obtained at both gap (6% of total radiation) and understory (2%). A. triplinervia shows higher rates (1.5–3.0 molm^{-2 -1}) than D. rospigliosii (0.7–1.1 molm^-2s^-1). Both species showed increased photosynthetic rates when grown in gaps. A. triplinervia did not adjust its maximum photosynthetic rates to the prevailing light conditions. In contrast, D. rospigliosii responded to increased light levels. Both species showed low light compensation points when grown under total shade. There was a partial stomatal closure generally during midday in D. rospigliosii. A. triplinervia presented lower leaf conductances, transpiration rates and lesser stomatal control. Some leaf anatomical characteristics, in both species, were affected by variations in the light regime (i.e. increased leaf thickness, leaf specific weight and stomatal density). These results suggest that both species have the ability to respond to variations in their natural light environments, therefore maintaining a favorable carbon balance during the day.     

Light energy partitioning in photosystems I and II during development of Nothofagus nitida growing under different light environments in the Chilean evergreen temperate rain forest

Nothofagus nitida (Phil.) Krasser (Nothofagaceae) regenerates under the shade. Nonetheless, older seedlings are commonly found at full sun. We tested the hypothesis that light capture and photochemical and non-photochemical energy dissipation of both photosystems PSI and PSII adjust with ontogeny and brighter environment. Light energy partitioning in both photosystems was studied in seedlings of different developmental stages (small 9.7 cm, tall 36 cm) under contrasting light environments (8–200 and 1,800–2,043 μmol photons m⁻² s⁻¹) in the Chilean evergreen temperate forest. Higher A _max, dark respiration, and light compensation and saturation points in sun seedlings of both developmental stages were accompanied by higher rates of electron transport. These seedlings also showed a high fraction of open PSII reaction centres and similar non-photochemical quenching at high-light in both photosystems, showing no effect of developmental stage in these parameters. Conversely, light capture, total thermal dissipation after photoinhibition, active down-regulation of antenna efficiency, and state transitions were higher in smaller seedlings than in taller ones. These changes maintain photostasis, preventing photodamage, while favouring a more oxidized quinone pool. There is an independent effect of seedling development and light acclimation on this transition from shade to sun during early ontogeny. This transition reflects short-term responses of the photosynthetic apparatus to light and longer term responses that depend on seedling developmental stage.     

Genes affecting phenotypic plasticity in Arabidopsis: pleiotropic effects and reproductive fitness of photomorphogenic mutants

Many plants exhibit characteristic photomorphogenic shade ’avoidance’ responses to crowding and vegetation shade; this plasticity is often hypothesized to be adaptive. We examined the contribution of specific photomorphogenic loci to plastic shade avoidance responses in the annual crucifer Arabidopsis thaliana by comparing single-gene mutants defective at those loci with wild type plants exhibiting normal photomorphogenesis. The hy1 and hy2 mutants, deficient in all functional phytochromes, were less plastic than the wild type in response to a nearby grass canopy or to a low-red/far-red light ratio characteristic of vegetation shade. These mutants displayed constitutively shade-avoiding phenotypes throughout the life cycle regardless of the treatment: they bolted at an earlier developmental stage and were characterized by reduced branching. In contrast, the hy4 mutant, deficient in blue light reception, exhibited greater plasticity than the wild type in response to vegetation shade after the seedling stage. This mutant produced more leaves before bolting and more basal branches under normal light conditions when compared to the wild type. These results indicate that specific photomorphogenic loci have different and sometimes antagonistic pleiotropic effects on the plastic response to vegetation shade throughout the life cycle of the plant. The fitness of the constitutively shade-avoiding phytochrome-deficient mutants was lower than that of the plastic wild type under normal light, but was not different in the vegetation shade treatments, where all genotypes converged toward similar shade avoidance phenotypes. This outcome supports one key prediction of the adaptive plasticity hypothesis: that inappropriate expression of shade avoidance traits is maladaptive.