Variations among woody plants in stomatal conductance and photosynthesis during and after drought

Acer saccharum, Fraxinus americana, Juglans nigra, Acer rubrum, Cornus amomum, and Ulmus americana seedlings were subjected to a soil drying cycle and then rewatered. At frequent intervals during the drying cycle and following rewatering, determinations were made of equilibrium photosynthesis rates, leaf conductances and leaf water potentials. As the drying cycle progressed, leaf water potentials decreased, stomata closed, and rates of transpiration and photosynthesis were reduced. Stomata of the two Acer species initially were more sensitive to water stress than were those of the other species. At low leaf water potentials, stomata of Juglans and Cornus were more open than those of the other species. Photosynthesis of Acer saccharum, Fraxinus and Juglans was significantly reduced by plant water stress, while photosynthetic water use efficiency of Cornus and Juglans was most unfavourable. Photosynthesis/leaf conductance ratios in water stressed leaves were higher in Fraxinus than in the other species. Immediately after rewatering, only limited stomatal opening occurred in Acer saccharum and Cornus with recovery of stomatal opening most protracted in Fraxinus and Ulmus. There was extended reduction of photosynthesis of all species as a result of the soil drying treatment. This effect was most significant in Acer saccharum and Juglans. Survival of plants on moist and dry sites is discussed in relation to stomatal control of transpiration and metabolic responses to water stress. Research supported by the College of Agricultural and Life Sciences, University of Wisconsin-Madison and the International Shade Tree Conference. The cooperation of the Wisconsin Department of Natural Resources is acknowledged. Research supported by the College of Agricultural and Life Sciences, University of Wisconsin-Madison and the International Shade Tree Conference. The cooperation of the Wisconsin Department of Natural Resources is acknowledged.     

EFFECTS OF TISSUE VOLUME AND LOCATION ON THE MECHANICAL CONSEQUENCES OF DEHYDRATION OF PETIOLES

Data are presented on the mechanical consequences of dehydration for the petioles of two monocots and two dicots differing in leaf morphology (pinnate leaves ofChamaedorea erumpens and simple leaves of Spathiphyllum ‘clevelandii‘; pinnate leaves of Acer negundo and simple leaves of A. saccharum). The flexural stiffness EI of petioles decreased over a broad range of tissue water potential (– 10 < ψ_w <– 50 bars). Within the same range of ψ, the second moment of area I and the elastic modulus E were observed to decrease and increase, respectively. However, the mechanical alterations of Chamaedorea and A. negundo petioles were significantly less than those observed for Spathiphyllum and A. saccharum petioles. The increase in E of Spathiphyllum and A. saccharum petioles attending dehydration was linearly correlated with an increase in the relative volume fraction of tissues with lignified, thick cell walls (“support tissues”). The decrease in I of Spathiphyllum and A. saccharum petioles was linearly correlated with a decrease in the relative volume fraction of tissues with nonlignified, thin cell walls (“ground tissues”). Similar trends were observed for the petioles of C. erumpens and A. negundo but were found not to be statistically significant. Anatomical differences in the relative volume fraction and spatial locations of support tissues in the petioles of these four taxa appear to account for the differences observed in the mechanical consequences of petiole dehydration.     

Testing 'Economy in Design' in Plants: are the Petioles and Rachises of Leaves 'Designed' According to the Principle of Uniform Strength?

Fifteen petioles and rachises from three dicotyledon species(Acer saccharum, A. negundo, and Aesculus hippocastanum), apalm (Chamaedorea erumpens), and a fern (Cyrtomium falcatum)were used to test the hypothesis of 'economy in design' in termsof the design principle of uniform strength, i.e. a beam inwhich the section modulus (Z) varies along beam-length (L) inthe same proportion as the bending moment (M). Such a beam is'economical' regarding the amount of material used in its 'construction'because each of its cross section has the minimum transversearea required to satisfy the conditions of strength. The extentto which the morphology of a petiole or rachis conformed withthis design principle was initially evaluated by normalizingZ (measured at a distance, x, from the tip of a petiole or rachis)with respect to the magnitude of Z measured at the base of thepetiole. The normalized values were plotted against normalizedpetiole-rachis length (x/L). The design principle was judgedto be demonstrated when such a plot was found to be isometric,i.e. when the plot had a slope of unity. This procedure wastested further by plotting M/Z vs. x/L for representative leavesof C. erumpens and A. saccharum, and judged adequate. The allometriesof all six simple/palmate leaves were found not agree with thedesign principle. The taperings of nine petioles and rachisesfrom pinnate leaves were consistent with the design principle.This was interpreted to provide circumstantial evidence for'economy in design' in the petioles of some pinnate leaves andevidence that the mechanical 'design' of the petioles of somesimple/palmate leaves differs substantially from that of pinnateleaves.Copyright 1993, 1999 Academic Press Leaf biomechanics, plant adaptation, petioles, rachises     

GRAVITY-INDUCED EFFECTS ON MATERIAL PROPERTIES AND SIZE OF LEAVES ON HORIZONTAL SHOOTS OF ACER SACCHARUM (ACERACEAE)

The influence of gravity on the size and mechanical properties of mature leaves on horizontal shoots and etiolated seedlings of Acer saccharum Marsh. (Aceraceae) was examined. Leaves were grouped into three categories regarding their location on shoots (dorsal or “top” T, lateral or “left/right” L/R, and ventral or “bottom” B). Young's modulus E, petiole length L, lamina surface area A and weight P, and the cross-sectional areas of different tissues within petioles were measured for each leaf and were found to be correlated with leaf location (T, L/R, and B): T leaves were smaller and had lower E than their B counterparts; the size and material properties of L/R leaves were intermediate between those of T and B leaves. In general, A, P, and E decreased from the base to the tip of shoots. In addition to anisophylly, the influence of gravity induced petiole bending and torsion and resulted in the horizontal planation of laminae. This was observed for field-grown mature plants and etiolated seedlings. Petiole bending and torsion were interpreted as gravimorphogenetic phenomena. Anatomically, L, E, and petiole deflection angle Fv measured from the vertical were highly correlated with the combined cross-sectional areas of phloem fibers and xylem in petioles of B leaves and when data from all leaves were pooled. It is tentatively advanced that the correlation of E with the transverse areas of phloem fibers and xylem is evidence that either the pattern or the extent of lignification of petiole tissues is influenced by petiole position with respect to gravity.     

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     

Shade adaptation and shade tolerance in saplings of three Acer species from eastern North America

Summary Saplings of three, co-occurring maple species in a mature maple-beech forest differed in a suite of structural and physiological characters that separated the canopy species, Acer, saccharum, from the two subcanopy species, A. pensylvanicum and A. spicatum. Acer saccharum had both more dense wood and tougher and heavier but thinner leaves than the subcanopy species. Acer pensylvanicum had the largest, lightest leaves with high stomatal density and its canopy architecture was the most effective in terms of leaf display for light interception. Acer spicatum had weaker wood similar to that of A. pensylvanicum but also small, soft and relatively poorly displayed leaves. Both subcanopy species maintained marginally higher average rates of photosynthesis over the growing season in the understory environment. We consider juvenile A. saccharum only shade-tolerant, capable of persisting through long periods in the closed canopy until a gap occurs but not specifically adapted to the understory environment. Juvenile A. sacchrum appears to be constrained functionally by the requirements set by the canopy environment that adults will occupy. Characters such as high wood density are already expressed in the understory sapling; this investment in denser wood slows the growth of saplings, but is necessary for structural reasons in the adult. Juvenile A. saccaharum have morphological and photosynthetic characters better suited to gas exchange and extension growth under the increased photon flux densities in large forest gaps, characteristics that will also be advantageous in the sunlit canopy environment of adults.Both subcanopy maples appear to be more truly shade-adapted, although in somewhat different ways. Acer pensylvanicum has characteristics that enhance the potential for capture and utilization of sunflecks and is able to sustain higher growth rates than A. saccharum in the shaded subcanopy environment. Acer spicatum shares some shade-adapted features with A. pensylvanicum, and its habit of lateral spread through stem layering may confer an additional advantage in foraging for small light gaps.     

TEMPORAL AND SPATIAL PATTERNS OF SPECIFIC LEAF WEIGHT IN SUCCESSIONAL NORTHERN HARDWOOD TREE SPECIES

Temporal and spatial patterns of specific leaf weight (SLW, g/m²) were determined for deciduous hardwood tree species in natural habitats in northern lower Michigan to evaluate the utility of SLW as an index of leaf photosynthetic capacity. No significant diurnal changes in SLW were found. Specific leaf weight decreased and then increased during leaf expansion in the spring. Most species, especially those located in the understory, then had relatively constant SLW for most of the growing season, followed by a decline in SLW during autumn. Specific leaf weight decreased exponentially down through the canopy with increasing cumulative leaf area index. Red oak (Quercus rubra), paper birch (Betula papyrifera), bigtooth aspen (Populus grandidentata), red maple (Acer rubrum), sugar maple (A. saccharum), and beech (Fagus grandifolia) generally had successively lower SLW, for leaves at any one level in the canopy. On a given site, comparisons between years and comparisons of leaves growing within 35 cm of each other showed that differences in SLW among species were not due solely to microenvironmental effects on SLW. Bigtooth aspen, red oak, and red maple on lower-fertility sites had lower SLW than the same species on higher-fertility sites. Maximum CO₂ exchange rate, measured at light-saturation in ambient CO₂ and leaf temperatures of 20 to 25 C, increased with SLW. Photosynthetic capacities of species ranked by SLW in a shaded habitat suggest that red oak, red maple, sugar maple, and beech are successively better adapted to shady conditions.     

Association of red coloration with senescence of sugar maple leaves in autumn

We evaluated the association of red coloration with senescence in sugar maple (Acer saccharum Marsh.) leaves by assessing differences in leaf retention strength and the progression of the abscission layer through the vascular bundle of green, yellow, and red leaves of 14 mature open-grown trees in October 2002. Computer image analysis confirmed visual categorization of leaves as predominantly green, yellow or red, and chemical quantification of leaf pigment concentrations verified that leaf color reflected underlying differences in leaf biochemistry. Significantly lower chlorophyll concentrations within red and yellow leaves indicated that senescence was more advanced in leaves from these color categories relative to green leaves. Among leaf types, only red leaves contained high concentrations of anthocyanins. There were significant differences in leaf retention capacity among color categories, with the petioles of green leaves being the most firmly attached to twigs, followed by red and then yellow leaves. Microscopic analysis indicated that yellow leaves had the most advanced extension of the abscission layer through the vasculature, with green and red leaves having significantly less abscission layer progression than yellow. A more limited progression of the abscission layer through vascular bundles may be evidence of delayed leaf senescence that could extend resorption of mobile leaf constituents. Together, results from this study suggest an association between leaf anthocyanin content and functional delays in senescence.     

Impacts of a spring heat wave on canopy processes in a northern hardwood forest

Heat wave frequency, duration, and intensity are predicted to increase with global warming, but the potential impacts of short‐term high temperature events on forest functioning remain virtually unstudied. We examined canopy processes in a forest in Central Ontario following 3 days of record‐setting high temperatures (31–33 °C) that coincided with the peak in leaf expansion of dominant trees in late May 2010. Leaf area dynamics, leaf morphology, and leaf‐level gas‐exchange were compared to data from prior years of sampling (2002–2008) at the same site, focusing on Acer saccharum Marsh., the dominant tree in the region. Extensive shedding of partially expanded leaves was observed immediately following high temperature days, with A. saccharum losing ca. 25% of total leaf production but subsequently producing an unusual second flush of neoformed leaves. Both leaf losses and subsequent reflushing were highest in the upper canopy; however, retained preformed leaves and neoformed leaves showed reduced size, resulting in an overall decline in end‐of‐season leaf area index of 64% in A. saccharum, and 16% in the entire forest. Saplings showed lower leaf losses, but also a lower capacity to reflush relative to mature trees. Both surviving preformed and neoformed leaves had severely depressed photosynthetic capacity early in the summer of 2010, but largely regained photosynthetic competence by the end of the growing season. These results indicate that even short‐term heat waves can have severe impacts in northern forests, and suggest a particular vulnerability to high temperatures during the spring period of leaf expansion in temperate deciduous forests.     

The Comparative Biology of Closely Related Species: VI. ANALYSIS OF THE GROWTH OF TRIFOLIUM REPENS AND T. FRAGIFERUM IN PURE AND MIXED POPULATIONS

An analysis was made of the first season's growth of pure andmixed stands of Trifolium repens and T. fragiferum. T. repens,although having smaller seeds and cotyledon area, achieved afaster early rate of leaf production than T. fragiferum andquickly developed a larger area of leaf both in pure standsand in mixtures. By the 18th and 21st weeks from sowing, T.fragiferum had more elongated petioles than T. repens, leaveswere borne higher in the canopy and contributed an increasingpart to the Leaf Area Index of mixtures. The increase in leaf area of swards with time was largely associatedwith increased area of individual leaves. The differences betweenspecies were largely due to differences in number of leaves. These results are discussed in relation to the conditions underwhich stable associations of species may be formed.     

Positive and Negative Messages from Roots Induce Foliar Desiccation and Stomatal Closure in Flooded Pea Plants

Flooding the soil for 5–7 d caused partial desiccationin leaves of pea plants (Pisum sativum. L. cv. ‘Sprite’).The injury was associated with anaerobiosis in the soil, a largeincrease in the permeability of leaf tissue to electrolytesand other substances, a low leaf water content and an increasedwater saturation deficit (WSD). Desiccating leaves also lackedthe capacity to rehydrate in humid atmospheres, a disabilityexpressed as a water resaturation deficit (WRSD). This irreversibleinjury was preceded during the first 4–5 d of floodingby closure of stomata within 24 h, decreased transpiration,an unusually large leaf water content and small WSD. Leaf waterpotentials were higher than those in well-drained controls.Also, there was no appreciable WRSD. Leaflets detached fromflooded plants during this early phase retained their watermore effectively than those from controls when left exposedto the atmosphere for 5 min. Stomatal closure and the associated increase in leaf hydrationcould be simulated by excising leaves and incubating them withtheir petioles in open vials of water. Thus, such changes inflooded plants possibly represented a response to a deficiencyin the supply of substances that would usually be transportedfrom roots to leaves in healthy plants (negative message). Ionleakage and the associated loss of leaf hydration that occurswhen flooding is extended for more than 5 d could not be simulatedby isolating the leaves from the roots. Appearance of this symptomdepended on leaves remaining attached to flooded root systems,implying that the damage is caused by injurious substances passingupwards (positive message). Both ethylene and ethanol have beeneliminated as likely causes, but flooding increased phosphorusin the leaves to concentrations that may be toxic. Key words: Pisum sativum, Flooding, Foliar desiccation, Stomata, Ethylene     

Interactions between aquatic bacteria and an aquatic hyphomycete on decomposing maple leaves

Processing of leaf litter is an important function in many environments and is influenced strongly by microorganisms. We investigated interactions between an aquatic hyphomycete, Tetrachaetum elegans, and two bacteria from the Cytophaga-Flavobacterium-Bacteroides group, that were isolated from decaying leaves in a stream. Laboratory experiments were used to examine interactions, as indicated by growth, between bacteria and fungi on sugar maple (Acer saccharum) leaves. Responses to amendments with labile dissolved organic carbon (DOC) were also examined. Fungal biomass was not affected by glucose amendment or bacterial presence. Likewise, bacterial biomass did not respond consistently to the glucose amendment, nor did the fungus affect bacterial biomass. In general, we found little evidence of resource competition or facilitation, in contrast to other studies. Our experiments suggest that fungal–bacterial interactions are not always significant and may depend on environmental conditions and the types of microorganisms examined.     

The water-filled versus air-filled status of vessels cut open in air: the 'Scholander assumption' revisited

When petioles of transpiring leaves are cut in the air, according to the ‘Scholander assumption’, the vessels cut open should fill with air as the water is drained away by continued transpiration. The distribution of air‐filled vessels versus distance from the cut surface should match the distribution of lengths of ‘open vessels’, i.e. vessels cut open when the leaf is excised. Three different methods were used to estimate the length distribution of open vessels and compared it to the observed distribution of embolisms by the cryo‐scanning electron microscope (SEM) method. In the cryo‐SEM method, petioles are frozen in liquid nitrogen soon after the petiole is cut. The petioles are then cut at different distances from the original cut surface while frozen and examined in a cryo‐SEM facility, where it is easy to distinguish vessels filled with air from those filled with ice. In petioles of Acer platanoides and Juglans regia, the distribution of embolized vessels agrees with expectations. This is in contrast to a previous study on sunflower where cryo‐SEM results did not agree with expectations. The reason for this disagreement requires further study for a full elucidation.     

HETEROPHYLLY AND NEOFORMATION OF LEAVES IN SUGAR MAPLE (ACER SACCHARUM)

Variation in leaf form and timing of leaf initiation were investigated in vigorous leader shoots of open-grown saplings and larger forest trees of sugar maple (Acer saccharum Marsh.). Winter buds of leader shoots usually contained 6 or 8 leaf primordia and embryonic leaves, whereas 12 to 18 leaves typically expanded along the shoots each year. Preformed (early) leaves differ in form from neoformed (late) leaves. As in some other Acer species, the first-formed late leaves have large angles of secondary lobe divergence and deeply indented sinuses. This pattern of heterophylly contributes to the multilayered nature of open-grown saplings and leader shoots of forest trees of sugar maple.     

The spatial pattern of air seeding thresholds in mature sugar maple trees

Air seeding threshold (P_a) of xylem vessels from current year growth rings were measured along the vertical axis of mature sugar maple trees (Acer saccharum Marsh.), with sampling points in primary leaf veins, petioles, 1-, 3-, and 7-year-old branches, large branches, the trunk and roots. The air seeding threshold was taken as the pressure required to force nitrogen gas through intervessel pit membranes. Although all measurements were made on wood produced in the same year, P_a varied between different regions of A. saccharum, with distal organs such as leaves and petioles having lower P_a than basal regions. Mean (SE) P_a ranged from 1.0 (± 0.1) MPa in primary leaf veins to 4.8 (± 0.1) MPa in the main trunk. Roots exhibited a P_a of 2.8 (± 0.2) MPa, lower than all other regions of the tree except leaf veins and petioles. Mean xylem vessel diameter increased basipetally, with the widest vessels occurring in the trunk and roots. Within the shoot, wider vessels had greater air seeding thresholds, contrasting with trends previously reported. However, further experimentation revealed that differences in P_a between regions of the stem were driven by the presence of primary xylem conduits, rather than differences in vessel diameter. In 1-year-old branches, P_a was significantly lower in primary xylem vessels than in adjacent secondary xylem vessels. This explained the lower values of P_a measured in petioles and leaf veins, which possessed a greater ratio of primary xylem to secondary xylem than other regions. The difference in P_a between primary and secondary xylem was attributed to the greater area of primary cell wall (pit membrane) exposed in primary xylem conduits with helical or annular thickening.     

Stomatal Responses to Water Deficits and Abscisic Acid in Leaves of Sunflower Plants (Helianthus annuus L.) Grown under Different Conditions

The decrease in diffusive conductance of a leaf exposed to waterstress or to exogenous abscisic acid (ABA) was smaller in leavesof sunflower plants (Helianthus annuus L. cv. NK285) that hadbeen grown in a phytotron in humid air than in leaves of sunflowersgrown outdoors. Stomata of the phytotron-grown plants were slowerto close after detachment of a leaf than those of the outdoorplants. When stomata closed rapidly, as they did in detachedleaves and after treatment with ABA, the extent of closure wasvaried over the leaf's surface, in particular in the case ofphytotron-grown plants, and the extent of the heterogeneitywas greater in the phytotrongrown plants than in the outdoorplants. When stomata closed gradually, for example, under conditionsof limited moisture in the soil, closure occurred uniformlyover leaves of plants of both types. The smaller decrease indiffusive conductance of leaves from phytotron-grown plantsafter treatment with ABA resulted from the presence of patcheson the surface in which stomata remained open. The smaller decreaseof diffusive conductance in the phytotron-grown plants underconditions of limited moisture in the soil resulted from theuniformly lower responsiveness of stomata on a leaf to the decreasein water potential. When estimates are made of the intercellularconcentration of CO₂ (Ci) from gas-exchange measurements, heterogeneityin stomatal closure should be monitored when stomata close rapidly,in particular in plants grown in humid air, because heterogeneousstomatal closure can lead to overestimates of Ci. (Received April 18, 1994; Accepted May 25, 1995)     

The Response of Transpiration Resistance to Leaf Temperature as a Desiccation Resistance Mechanism in Tree Seedlings

Transpiration rate and leaf transfer resistance to water vapor loss were determined under a range of leaf temperatures for Quercus macrocarpa, Q. velutina, Q. alba, Q. rubra, and Acer saccharum. Transfer resistance increased with rising leaf temperatures between 20 and 40°C in all species, but the rate of increase in resistance was greatest in species which normally occupy xeric sites. Increased transfer resistance with rising leaf temperature may be significant in preventing rapid desiccation of leaves under the large evaporative stress imposed by high leaf temperature.     

Flexible Leaf Orientations ofArisaema heterophyllumMaximize Light Capture in a Forest Understorey and Avoid Excess Irradiance at a Deforested Site

Effects of flexible leaflet orientations on light capture andphotosynthesis were investigated forArisaema heterophyllumBlume,a perennial herb with a single palmately compound leaf, in twocontrasting light environments: a riparian forest understoreyand an adjacent deforested open site. Leaf orientations aredetermined by inclination of leaflet midvein and folding ofleaflet blade. Leaves were flatter and had smaller angles ofinclination at the forest site than at the deforested site.Directions (angular altitude and azimuth) of leaf surfaces ofthe forest site plants were close to those predicted to maximizediffuse light capture at each microsite, as determined by theanalysis of a hemispherical canopy photograph. Mean light captureefficiency (the ratio of actual diffuse light capture by a leafto maximal receivable light) reached 98%. In contrast, markedleaflet folding occurred only at the deforested site. The degreeof folding varied diurnally with the maximum around noon. Computersimulations showed that PPFDs (photosynthetically active photonflux density) over the photosynthetic saturation level ofA.heterophyllumcan be effectively reduced by increasing the slopeof leaflet surfaces. The importance of decreasing excess irradianceto avoid photoinhibition and to maintain high rates of photosynthesiswas confirmed by artificially constraining leaves horizontally.Copyright1998 Annals of Botany Company Arisaema heterophyllumBlume, forest understorey, hemispherical canopy photograph, high light stress, leaf orientation, light capture efficiency, microsite light availability, midday depression, photoinhibition, photosynthesis.     

The Effect of Root Formation on Photosynthesis of Detached Leaves

The CO₂ exchange of fully expanded detached primary leaves ofdwarf bean (Phaseolus vulgaris) with roots on the petioles hasbeen measured. Rates of apparent photosynthesis and respirationincreased as roots grew, decreased when roots were removed,and increased again as root regenerated. Rates of photosynthesisof different leaves were highly correlated with the dry weightof root on their petioles. Photosynthesis and respiration weredecreased when root growth was restricted by kinetin, and wereincreased when root growth was stimulated by IAA. Photosynthesisof an attached leaf declined with time while that of a comparabledetached leaf increased. The results suggest that photosynthesisis correlated with the size of the roots that are a sink forphotosynthates.     

Biomechanical Responses of Chamaedorea and Spathiphyllum Petioles to Tissue Dehydration

Data are presented for the mechanical responses to dehydrationof petioles from two monocotyledons (Chamaedorea erumpens andSpathiphyllum Clevelandii). These data were used to test thehypothesis that the mechanical properties (elastic modulus Eand flexural stiffness EI) of petioles from C. erumpens arealtered significantly less by dehydration than those of petiolesfrom Spathiphyllum. Dehydration, resulting from either dryingat room temperature or from submergence in various concentrationsof mannitol solutions, produced significant increases in E anddecreases in EI (due to geometric distortions) in both youngand mature Spathiphyllum petioles. Similar trends were observedfor young petioles of C. erumpens, but significantly less sofor mature petioles of this species. Regardless of petiolarage, E increased allometrically as a linear function of tissuedensity, which in turn correlated with the volume fraction oflignified tissues in petioles; however, the proportional increaseof E as a function of tissue density was significantly greaterfor C. erumpens petioles than for Spathiphyllum. Anatomicalanalyses of petiolar transections indicated that Chamaedoreapetioles had larger volume fractions of lignified tissues thanthose of Spathiphyllum and that these tissues were located tomaximize stiffness. These data (and previously reported allometricrelationships between EI and petiolar length) shed light onthe difficulties in evaluating the ‘costs’ of committingtissues to mechanical support. Petioles, biomechanics, leaf anatomy, monocotyledons