Mass Per Area Research Articles

Paleoclimate and paleoecology of the latest Eocene Florissant flora of central Colorado, U.S.A.

The uppermost Eocene Florissant Formation of central Colorado, U.S.A. contains a diverse flora and fauna preserved in lacustrine facies and represents a key episode in Earth history immediately preceding the Eocene-Oligocene boundary. Laminated shales contain impressions of non-monocot angiosperm leaves that were used to estimate paleoecological and paleoclimatic parameters using leaf physiognomic methods including: leaf mass per area (MA), digital leaf physiognomy (DiLP), leaf margin analysis (LMA), and leaf area analysis (LAA). The majority (58%) of the morphotypes analyzed for MA suggested a semi-evergreen leaf lifespan, whereas another 27% indicated a deciduous habit and 15% an evergreen habit. There was no significant relationship between MA and insect damage based on a small subset of Florissant's leaves. Higher MA values (~73% of leaves ≥ one-year lifespan), coupled with a tendency toward long and narrow leaf shapes and small leaf areas, indicate the existence of sclerophyllous vegetation. Using the global regression for mean annual temperature (MAT), the DiLP estimate of MAT was anomalously cold: 5.5 ± 4 °C. However, using a Northern Hemisphere regression the DiLP MAT estimate of 11.6 ± 3.3 °C was more plausible. Using DiLP, mean annual precipitation (MAP) was estimated at 740 + 608/−334 mm∙yr−1, which supports dry conditions. Estimates for MAT and MAP using the univariate LMA and LAA methods overlapped within uncertainty of the DiLP results. In addition, those taxa classified as growing in wet areas (riparian) had significantly more teeth than non-riparian taxa. These paleoclimatic and paleoecological results suggest that outside the riparian forest, the Florissant flora sampled a seasonally dry temperate sclerophyllous shrubland to woodland, perhaps similar to modern chaparral forests, in the western interior of the U.S.A. just before the transition into the cooler Oligocene.

Plant community ecology and climate on an upland volcanic landscape during the Early Eocene Climatic Optimum: McAbee Fossil Beds, British Columbia, Canada

The McAbee Fossil Beds, in south-central British Columbia, Canada, provide a record of forest ecosystems within a volcanically-active, upland landscape during the Early Eocene Climatic Optimum (EECO). To assess plant community ecology and climate within this environment, palynology and census-style macrofossil collections were investigated from two shale horizons separated in time by likely 103–104 years. An ensemble of leaf physiognomic estimates indicates a persistent warm (mean annual temperature [MAT] ≈ 10–12 °C) and mesic (mean annual precipitation ≈ 1000 mm∙yr−1) climate between the horizons. The plant community was similar in both horizons, comprising angiosperms (e.g., Ulmus, Fagus, Alnus, Betula, and Carya) and gymnosperms (e.g., Metasequoia, Pinus, Picea, and Larix). Plant diversity and the distribution of dicot leaf mass per area (MA) values were consistent between the two horizons, despite intervals of varying tuff thickness and frequency between the horizons. Differences in macrofossil abundances of Ulmus, Fagus, and Pinus, and a lack of such differences in their respective pollen abundances might be explained by local patch dynamics, influenced by spatial heterogeneity resulting from topographic diversity and disturbance. MA estimates suggest dicots were predominately deciduous, and the distribution of MA is similar to a modern forest in Panama influenced by seasonal precipitation. The diversity of dicots at McAbee, despite relatively lower mean annual temperatures, is comparable to fossil plant quarries of similar volume from early Eocene sites in Patagonia (e.g., Laguna del Hunco) and the Denver Basin with relatively warmer MATs (17–25 °C). This is best explained by a combination of predominately frost-free winters, high productivity, and an abiotic environment characterized by spatial heterogeneity and high rates of change. The sampled paleofloras of this study showcase an EECO plant community, likely representing an ecological solution to volcanic disturbance over millennial time scales.

INSECT FOLIVORY IN AN ANGIOSPERM-DOMINATED FLORA FROM THE MID-CRETACEOUS OF UTAH, U.S.A.

The Soap Wash flora contains 152 angiosperm leaf fossils from the Albian–Cenomanian boundary of central Utah. The flora exhibits many well-preserved examples of insect folivory for which the extent and type of damage on each leaf was recorded. Fewer than half of the specimens in the collection exhibit insect damage and most of the leaf damage affects less than five percent of the leaf area. Damage was distributed unevenly across the 18 leaf morphotypes described in the flora. Nineteen damage types were recognized. Most of the damage was of a generalized type, dominated by indiscriminate removal of leaf tissues (whole leaf feeding). We observed no correlation between leaf mass per area (MA) and the degree of damage by herbivores, which contrasts with Cenozoic and modern patterns. The low rate, modest area, and low diversity of damage type is similar to patterns reported through the Late Cretaceous and is consistent with a plateau in insect folivore diversity that persisted through the end of the Mesozoic. The preponderance of generalized damage types dominated by whole leaf feeding may reflect (1) the early stage in angiosperm radiation represented by this flora, and (2) the associated lag in folivore diversification and specialization.

Acclimation of isoprene emission and photosynthesis to growth temperature in hybrid aspen: resolving structural and physiological controls.

Acclimation of foliage to growth temperature involves both structural and physiological modifications, but the relative importance of these two mechanisms of acclimation is poorly known, especially for isoprene emission responses. We grew hybrid aspen (Populus tremula x P. tremuloides) under control (day/night temperature of 25/20 °C) and high temperature conditions (35/27 °C) to gain insight into the structural and physiological acclimation controls. Growth at high temperature resulted in larger and thinner leaves with smaller and more densely packed chloroplasts and with lower leaf dry mass per area (MA). High growth temperature also led to lower photosynthetic and respiration rates, isoprene emission rate and leaf pigment content and isoprene substrate dimethylallyl diphosphate pool size per unit area, but to greater stomatal conductance. However, all physiological characteristics were similar when expressed per unit dry mass, indicating that the area-based differences were primarily driven by MA. Acclimation to high temperature further increased heat stability of photosynthesis and increased activation energies for isoprene emission and isoprene synthase rate constant. This study demonstrates that temperature acclimation of photosynthetic and isoprene emission characteristics per unit leaf area were primarily driven by structural modifications, and we argue that future studies investigating acclimation to growth temperature must consider structural modifications.

Biomechanical and leaf–climate relationships: A comparison of ferns and seed plants

Relationships of leaf size and shape (physiognomy) with climate have been well characterized for woody non-monocotyledonous angiosperms (dicots), allowing the development of models for estimating paleoclimate from fossil leaves. More recently, petiole width of seed plants has been shown to scale closely with leaf mass. By measuring petiole width and leaf area in fossils, leaf mass per area (MA) can be estimated and an approximate leaf life span inferred. However, little is known about these relationships in ferns, a clade with a deep fossil record and with the potential to greatly expand the applicability of these proxies. We measured the petiole width, MA, and leaf physiognomic characters of 179 fern species from 188 locations across six continents. We applied biomechanical models and assessed the relationship between leaf physiognomy and climate using correlational approaches. The scaling relationship between area-normalized petiole width and MA differs between fern fronds and pinnae. The scaling relationship is best modeled as an end-loaded cantilevered beam, which is different from the best-fit biomechanical model for seed plants. Fern leaf physiognomy is not influenced by climatic conditions. The cantilever beam model can be applied to fossil ferns. The lack of sensitivity of leaf physiognomy to climate in ferns argues against their use to reconstruct paleoclimate. Differences in climate sensitivity and biomechanical relationships between ferns and seed plants may be driven by differences in their hydraulic conductivity and/or their differing evolutionary histories of vein architecture and leaf morphology.

Deriving Plant Functional Types for Amazonian forests for use in vegetation dynamics models

a b s t r a c t Recent advances in our understanding of the linkages between plant physiological and morphological traits suggest a new means by which to define Plant Functional Types (˚) for use in conceptual and mathematical models of vegetation dynamics. In this study we used data from the RAINFOR-network database, aiming to numerically derivefor tropical forest trees by jointly analysing an Amazon-wide dataset of (409) species abundance, species functional traits (10) and site edaphic and climatic conditions across 53 plots. We followed a stepwise procedure of numericaldefinition with increasing complexity, starting from a simple PCA on species functional traits. We subsequently applied a three-table (RLQ) multivariate ordination method in two ways: with and without spatial autocorrelation between plots being taken into account. In all cases the environmental contribution to trait variation had been partialled out. Thus our results link species-specific inherent trait values with associated species abundances along environmental gradients. Our final classification of Amazonian tree species based on foliar dry leaf mass per area (MA), leaf concentrations of C, N, P, Ca, K, Mg, carbon isotopic discrimination (� ), branch xylem density (� X) and maximum tree height (Hmax) yielded four discrete ˚. Thesewere found to represent distinct life-history strategies and can be aligned with previous empirical definitions of tropical tree guilds. In particular, two ecological dimensions are identified: (1) a leaf deployment dimension which co-varies with soil fertility and (2) a stem deployment dimension which co-varies with soil texture. By analysing diameter growth rates of the same trees used to define the fourwe found eachto have a different overall growth pattern. Furthermore, from a Basin-wide forest survey, differences in the relative abundance of the fourwere related to stand level basal area growth and/or turnover rate variations. These new derivedshould enhance our ability to better understand and model the dynamics of the Amazon forest, with the general procedure for plant functional trait definition described here potentially applicable to many other ecosystems.

Physical properties of compressive knits compound with different matters impregnated by microcapsules moisturizing

The compressive knits include a very varied group of different device functions, from the more merely (protection) to the more developed (scars improvement, skin hydration?). We combined two therapy forms the pressure and the hydration of burned skin. We essayed to reunite the advantages of two techniques pressure and hydration in only one and the same instrument in the form of compressive knit with microencapsulated surface. The compressive knits are elaborated with different textile matters such us Cotton/Spandex, Polyester/Spandex, Polyamide/Spandex, Viscose/Spandex and Cotton/Polyester/Spandex. The hydration product chosen in this application is the Jojoba Oil. The microcapsules were prepared according to the Phase Separation Method. The physical properties such us the Pressure, the Mass per Area, the Thickness, the Air Permeability and the Adiathermic Power are tested. According to the results, we conclude that the knits are compressive, comfort, smooth, no allergen, thinness and washable. The raw materials selected for the samples studied are biocompatible with human skin.

Fossil leaf economics quantified: calibration, Eocene case study, and implications

Leaf mass per area (MA) is a central ecological trait that is intercorrelated with leaf life span, photosynthetic rate, nutrient concentration, and palatability to herbivores. These coordinated variables form a globally convergent leaf economics spectrum, which represents a general continuum running from rapid resource acquisition to maximized resource retention. Leaf economics are little studied in ancient ecosystems because they cannot be directly measured from leaf fossils. Here we use a large extant data set (65 sites; 667 species-site pairs) to develop a new, easily measured scaling relationship between petiole width and leaf mass, normalized for leaf area; this enables MA estimation for fossil leaves from petiole width and leaf area, two variables that are commonly measurable in leaf compression floras. The calibration data are restricted to woody angiosperms exclusive of monocots, but a preliminary data set (25 species) suggests that broad-leaved gymnosperms exhibit a similar scaling. Application to two well-studied, classic Eocene floras demonstrates that MA can be quantified in fossil assemblages. First, our results are consistent with predictions from paleobotanical and pa- leoclimatic studies of these floras. We found exclusively low-MA species from Republic (Washington, U.S.A., 49 Ma), a humid, warm-temperate flora with a strong deciduous component among the an- giosperms, and a wide MA range in a seasonally dry, warm-temperate flora from the Green River Formation at Bonanza (Utah, U.S.A, 47 Ma), presumed to comprise a mix of short and long leaf life spans. Second, reconstructed MA in the fossil species is negatively correlated with levels of insect herbivory, whether measured as the proportion of leaves with insect damage, the proportion of leaf area removed by herbivores, or the diversity of insect-damage morphotypes. These correlations are consistent with herbivory observations in extant floras and they reflect fundamental trade-offs in plant-herbivore associations. Our results indicate that several key aspects of plant and plant-animal ecology can now be quantified in the fossil record and demonstrate that herbivory has helped shape the evolution of leaf structure for millions of years.

Light capture efficiency decreases with increasing tree age and size in the southern hemisphere gymnosperm Agathis australis

We investigated leaf and shoot architecture in relation to growth irradiance (Qint) in young and mature trees of a New Zealand native gymnosperm Agathis australis (D. Don) Lindl. to determine tree size-dependent and age-dependent controls on light interception efficiency. A binomial 3-D turbid medium model was constructed to distinguish between differences in shoot light interception efficiency due to variations in leaf area density, angular distribution and leaf aggregation. Because of the positive effect of light on leaf dry mass per area (MA), nitrogen content per area (NA) increased with increasing irradiance in both young and mature trees. At a common irradiance, NA, MA and the components of MA, density and thickness, were larger in mature trees, indicating a greater accumulation of photosynthetic biomass per unit area, but also a larger fraction of support biomass in older trees. In both young and mature trees, shoot inclination angle relative to horizontal, and leaf number per unit stem length decreased, and silhouette to total leaf area ratio (SS) increased with decreasing irradiance, demonstrating more efficient light harvesting in low light. The shoots of young trees were more horizontal and less densely leafed with a larger SS than those of mature trees, signifying greater light interception efficiency in young plants. Superior light harvesting in young trees resulted from more planar leaf arrangement and less clumped foliage. These results suggest that the age-dependent and/or size-dependent decreases in stand productivity may partly result from reduced light interception efficiency in larger mature relative to smaller and younger plants.

Variability in Leaf Morphology and Chemical Composition as a Function of Canopy Light Environment in Coexisting Deciduous Trees.

Morphology, chemical composition, and photosynthetic capacity of leaf laminas were investigated in Populus tremula L. and Tilia cordata Mill. along a canopy light gradient. Variables determining the thickness of boundary layer for heat and water exchange at a given wind speed-effective leaf width (Ww) and length (Wd)-scaled positively with daily integrated quantum flux density averaged over the season (Qint, mol m-2 d-1) in T. cordata, but Wd decreased and Ww was constant with increasing Qint in P. tremula, bringing about a moderately improved capacity for convective cooling at greater irradiances in the latter species. Foliar stable carbon isotope discrimination (Delta) decreased with increasing Qint, demonstrating that, possibly because of more severe foliar water stress, leaves operated at a lower intercellular CO2 concentration in the upper canopy. Further analysis of foliar characteristics provided additional evidence of the interaction between water stress and Qint. Leaf dry matter content and both components of lamina dry mass per area (MA)-lamina thickness and density (dry mass per unit volume, rhoB)-increased with increasing Qint in both species. The rhoB and lamina dry matter content were also positively related to lamina carbon concentration, variability in which along the canopy was related to changes in carbon-rich lignin concentration. Since both increases in lamina density and lignin concentration improve leaf tolerance of low-water potentials, these foliar modifications were interpreted as indicative of acclimation to enhanced water limitations in high light. For the whole material, foliar nitrogen concentrations decreased with increasing rhoB, suggesting that an improvement of foliar mechanical strength may result in declining foliar assimilative potential. However, foliar photosynthetic electron transport capacity per unit area increased with increasing rhoB, possibly because increases in rhoB with light are not only attributable to greater cell wall lignification but also to denser packing of leaf cells, in particular, in fractional increases in palisade tissues with Qint. Because of a positive scaling of leaf thickness and density with total tree height, MA was greater in taller trees of T. cordata, foliage of which also had lower Delta and was likely to function with less open stomata. In summary, we conclude that leaf water stress, which scales with both Qint and total tree height, is a major factor altering foliage structure and assimilative capacity.

Acclimation to high irradiance in temperate deciduous trees in the field: changes in xanthophyll cycle pool size and in photosynthetic capacity along a canopy light gradient

To test the hypothesis that in temperate deciduous trees acclimation to potentially damaging high irradiances occurs via long‐term adjustments in foliar photosynthetic capacity, and short‐term changes in xanthophyll cycle pool size in response to weather fluctuations, nitrogen concentration and pigment composition were examined along a canopy light gradient in three species –Betula pendula, Populus tremula and Tilia cordata (from most shade intolerant to tolerant), and foliage photosynthetic potentials in P. tremula and T. cordata. Integrated quantum flux density (Qi) incident on leaves was estimated with a method combining hemispherical photography and light measurements with quantum sensors made over the growing season. Long‐ and short‐term light indices – average total seasonal daily integrated quantum flux density (Ts, mol m–2 d–1) and that of the 3 d preceding foliage sampling (T3d) – were calculated for each sampled leaf. In addition to total integrated quantum flux density, the part of Qi attributable to direct flux was also computed. Strong linear relationships between the capacity for photosynthetic electron transport per area (Jamax), estimated from in situ measurements of effective quantum yield of photosystem II (PS II), and Qi averaged over the season and over the preceding 3 d were found for all studied species. However, the major determinant of Jamax, the product of electron transport capacity per leaf dry mass (Jmmax) and leaf dry mass per area (MA), was MA rather than Jmmax, which was relatively constant along the light gradient. There was evidence that Jamax is more tightly related to Ts, which characterizes the light climate during foliar development, than to short‐term integrated light, possibly because there is little flexibility in adjustments in MA after the completion of foliar growth. Leaf chlorophyll concentrations and the investment of leaf nitrogen in chlorophyll (Chl/N) were negatively related to Qi– an investment pattern which improves light harvesting in low light. Xanthophyll cycle pool size (VAZ, violaxanthin + antheraxanthin + zeaxanthin) either expressed per unit chlorophyll (VAZ/Chl) or as a fraction of total carotenoids (VAZ/Car) increased with increasing Qi in all species. However, contrary to Jamax, it tended to correlate more strongly with short‐term than with long‐term average integrated light. There were few interspecific differences in Jamax, Chl/N, VAZ/Chl and VAZ/Car when the variability in light level incident to the leaves was accounted for, indicating that the foliage of both shade‐intolerant and ‐tolerant temperate tree species possesses considerable phenotypic flexibility. Collectively these results support the view that rapid adjustment of the xanthophyll cycle pool size provides an important means for acclimation to light fluctuations in a time scale of days, during which the potential for photosynthetic quenching of excitation energy is not likely to change appreciably.

A model separating leaf structural and physiological effects on carbon gain along light gradients for the shade‐tolerant species Acer saccharum

ABSTRACTA process‐based leaf gas exchange model for C3 plants was developed which specifically describes the effects observed along light gradients of shifting nitrogen investment in carboxylation and bioenergetics and modified leaf thickness due to altered stacking of photosynthetic units. The model was parametrized for the late‐successional, shade‐tolerant deciduous species Acer saccharum Marsh. The specific activity of ribulose‐1,5‐bisphosphate carboxylase (Rubisco) and the maximum photosynthetic electron transport rate per unit cytochrome f (cyt f) were used as indices that vary proportionally with nitrogen investment in the capacities for carboxylation and electron transport. Rubisco and cyt f per unit leaf area are related in the model to leaf dry mass per area (MA), leaf nitrogen content per unit leaf dry mass (Nm), and partitioning coefficients for leaf nitrogen in Rubisco (PR) and in bioenergetics (PB). These partitioning coefficients are estimated from characteristic response curves of photosynthesis along with information on lear structure and composition. While PR and PB determine the light‐saturated value of photosynthesis, the fraction of leaf nitrogen in thylakoid light‐harvesting components (PL) and the ratio of leaf chlorophyll to leaf nitrogen invested in light harvesting (CB), which is dependent on thylakoid stoichiometry, determine the initial photosynthetic light utilization efficiency in the model. Carbon loss due to mitochondrial respiration, which also changes along light gradients, was considered to vary in proportion with carboxylation capacity. Key model parameters ‐ Nm, PR, PB, PLCB and stomatal sensitivity with respect to changes in net photosynthesis (Gr) – were examined as a function of MA, which is linearly related to irradiance during growth of the leaves. The results of the analysis applied to A. saccharum indicate that PB and PR increase, and Gf, PL and CB decrease with increasing MA. As a result of these effects of irradiaiice on nitrogen partitioning, the slope of the light‐saturated net photosynthesis rate per unit leaf dry mass (Ammax) versus Nm relationship increased with increasing growth irradiance in mid‐season. Furthermore, the nitrogen partitioning coefficients as well as the slopes of Ammax versus Nm were independent of season, except during development of the leaf photosynthetic apparatus. Simulations revealed that the acclimation to high light increased Ammax by 40% with respect to the low light regime. However, light‐saturated photosynthesis per leaf area (Aamax) varied 3‐fold between these habitats, suggesting that the acclimation to high light was dominated by adjustments in leaf anatomy (Aamax=AmmaxMA) rather than in foliar biochemistry. This differed from adaptation to low light, where the alterations in foliar biochemistry were predicted to be at least as important as anatomical modifications. Due to the light‐related accumulation of photosynthetic mass per unit area, Aamax depended on MA and leaf nitrogen per unit area (Na). However, Na conceals the variation in both MA and Nm (Na=NmMA), and prevents clear separation of anatomical adjustments in foliage structure and biochemical modifications in foliar composition. Given the large seasonal and site nutrient availability‐related variation in Nm, and the influences of growth irradiance on nitrogen partitioning, the relationship between Aamax and Na is universal neither in time nor in space and in natural canopies at mid‐season is mostly driven by variability in MA. Thus, we conclude that analyses of the effects of nitrogen investments on potential carbon acquisition should use mass‐based rather than area‐based expressions.

Structural analysis of the S-Layer of Lampropedia hyalina

The two-dimensional (2D) structure of the regularly structured surface layer (S-layer) of the gram-negative eubacterium Lampropedia hyalina has been determined at the molecular level to a nominal resolution of 2.1 nm by transmission electron microscopy and digital image processing. The inner, or “perforate,” layer consists of dimeric block-shaped units located at two-fold symmetry axes. These morphological dimers associate around three-fold symmetry axes to form a continuous layer with p6 symmetry and a lattice constant of 14.6 ± 0.4 nm. Scanning transmission electron microscopy (STEM) yields a mass-per-area (MPA) value for the perforate layer of 3.5 kDa/nm 2. The outer, or “punctate,” layer is composed of long, roughly cylindrical units centered on six-fold symmetry axes, which are connected by six fine linking arms joining at the three-fold symmetry axes to create a hexagonal layer with a lattice constant of 25.6 ± 0.5 nm. The MPA of the “composite”-i.e., perforate plus punctate—layer is 10.2 kDa/nm 2.