Foliar Surface Area Research Articles

Williamson Drive: Herbivory from a north-central Texas flora of latest Pennsylvanian age shows discrete component community structure, expansion of piercing and sucking, and plant counterdefenses

Insect herbivory during the Pennsylvanian–Permian transition interval (late Gzhelian) was estimated from the Williamson Drive locality of north-central Texas, USA. We investigated vegetational composition and the response of host plants to herbivores by characterization of insect-damage patterns. The bulk flora consists of four major plant groups: lycophytes, sphenophytes, pteridophytes, and pteridosperms, as well as unaffiliated morphotypes. Forty-six distinctive damage types (DTs) were recognized from 17 herbivorized plant-host taxa that were categorized into the five functional feeding groups (FFGs) of external foliage feeding (20 DTs), oviposition (11 DTs), piercing and sucking (9 DTs), galling (5 DTs), and wood boring (1 DT). The distributional patterns of FFGs and DTs on the most herbivorized plant hosts indicate several generalized and specialized patterns and organization into distinctive component communities. The overall herbivory level in the flora is elevated compared to other Cisuralian floras of north-central Texas, based on separate analyses of foliar surface area removed (0.86%) and frequency of herbivorized leaves (19.83%). One ubiquitous plant host, Macroneuropteris scheuchzeri (Hoffmann) Cleal, Shute and Zodrow, is disproportionately consumed, representing 35.75% of all specimens, but contributing 84.38% of the total herbivorized surface area, 60.87% of DT richness, and 55.44% of the DT abundance from all plant species. A notable feature is the abundance of nine piercing-and-sucking DTs on several hosts, representing three of the four new DTs described in this flora and indicating the ecological expansion of this FFG by Paleodictyopteroidea and earliest Hemipteroidea. There is evidence for physical and chemical antiherbivore defense afforded by trichomes and resin ducts of two major host plants, but the absence of seed predation is curious. Analyses of herbivory at Williamson Drive and four younger Cisuralian floras of the region support Feeny's apparency hypothesis. The overwhelming dominance of M. scheuchzeri herbivory at Williamson Drive, absent in earlier, peat-substrated Pennsylvanian floras, is typical of Cisuralian mineral-substrated plants.

Top canopy nitrogen allocation linked to increased grassland carbon uptake in stands of varying species richness

Models predict that vertical gradients of foliar nitrogen (N) allocation, increasing from bottom to top of plant canopies, emerge as a plastic response to optimise N utilisation for carbon assimilation. While this mechanism has been well documented in monocultures, its relevance for mixed stands of varying species richness remains poorly understood. We used 21 naturally assembled grassland communities to analyse the gradients of N in the canopy using N allocation coefficients (KN) estimated from the distribution of N per foliar surface area (KN-F) and ground surface area (KN-G). We tested whether: 1) increasing plant species richness leads to more pronounced N gradients as indicated by higher KN-values, 2) KN is a good predictor of instantaneous net ecosystem CO2 exchange and 3) functional diversity of leaf N concentration as estimated by Rao’s Q quadratic diversity metric is a good proxy of KN. Our results show a negative (for KN-G) or no relationship (for KN-F) between species richness and canopy N distribution, but emphasize a link (positive relationship) between more foliar N per ground surface area in the upper layers of the canopy (i.e. under higher KN-G) and ecosystem CO2 uptake. Rao’s Q was not a good proxy for either KN.

Fire form and function: evidence for exaptive flammability in the New Zealand flora

This study tests whether or not foliar flammability is related to resource-use and anti-herbivore defence strategies of plant species. We measured the flammability (at 400 °C) of 1640 dry and fresh leaves across 115 common native New Zealand woody and herbaceous species collected from sites throughout New Zealand. We used three indicators of foliar flammability—leaf temperature at smoke production and on ignition and the rate of increase in leaf temperature during the combustion process. We tested for relationships between these flammability measures, foliar morphological and chemical traits and growth form. All significant correlations showed increased foliar flammability with increasing foliar surface area:volume ratio (SAV) and nutrient content and decreasing tissue density, lignin and secondary metabolite concentrations. Coniferous trees were the growth form with the least flammable leaves due to leaf morphology associated low leaf SAV and high tissue density. This suggests there may be a general relationship between resource-use strategies and foliar flammability, via the influence of leaf morphology on both these aspects of plant function.

Cogongrass (Imperata cylindrica), an Alien Invasive Grass, Reduces Survival and Productivity of an Establishing Pine Forest

Abstract A 27-month-long study was conducted to compare the impacts of Imperata cylindrica (L.) (Beauv.) and native vegetation competition on the productivity of Pinus taeda (L.) seedlings. In March 2003, 1-year-old pine seedlings were planted in the following treatments: vegetation free (VF), native competition (NC), and I. cylindrica (IC) competition. At the end of the study, only 26% of the IC seedlings survived, half of what was observed in the NC treatment. The IC seedlings had significantly smaller root collar diameter than the NC seedlings (P < 0.0001) after the first growing season and by the end of the third growing season the height and stem volume index were significantly less as well (P < 0.0001). After one full growing season, the NC and IC pine seedlings had 21 and 11.5% of the total biomass of the VF seedlings, respectively. After three growing seasons, the IC pine seedling total biomass was 2.4% of that of the VF seedlings and 18% of that of the NC seedlings (P < 0.0001). The greatest difference was in the pine needle biomass with the IC pine needle biomass being only 11% of that of the NC. During the first growing season, the IC pine seedlings maintained the lowest levels of light-saturated net photosynthesis and stomatal conductance. These results may be explained by reduced amounts of foliar nitrogen and water stress that result from I. cylindrica competition. The pines in the IC treatment had the lowest total foliar surface area and the lowest specific leaf area, which may explain the reduced productivity. Evidence from this study suggests that I. cylindrica competition significantly reduces the productivity and growth of P. taeda seedlings compared with that from native vegetation.

"Diminishing returns" in the scaling of functional leaf traits across and within species groups.

More than 5,000 measurements from 1,943 plant species were used to explore the scaling relationships among the foliar surface area and the dry, water, and nitrogen/phosphorus mass of mature individual leaves. Although they differed statistically, the exponents for the relationships among these variables were numerically similar among six species groups (ferns, graminoids, forbs, shrubs, trees, and vines) and within 19 individual species. In general, at least one among the many scaling exponents was <1.0, such that increases in one or more features influencing foliar function (e.g., surface area or living leaf mass) failed to keep pace with increases in mature leaf size. Thus, a general set of scaling relationships exists that negatively affects increases in leaf size. We argue that this set reflects a fundamental property of all plants and helps to explain why annual growth fails to keep pace with increases in total body mass across species.

Plant morphology and root hydraulics are altered by nutrient deficiency in Pistacia lentiscus (L.)

The plants in arid and semiarid areas are often limited by water and nutrients. Morpho-functional adjustments to improve nutrient capture may have important implications on plant water balance, and on plant capacity to withstand drought. Several studies have shown that N and P deficiencies may decrease plant hydraulic conductance. Surprisingly, studies on the implications of nutrient limitations on water use in xerophytes are scarce. We have evaluated the effects of strong reductions in nitrogen and phosphorus availability on morphological traits and hydraulic conductance in seedlings of a common Mediterranean shrub, Pistacia lentiscus L.. Nitrogen deficiency resulted in a decrease in aboveground biomass accumulation, but it did not affect belowground biomass accumulation or root morphology. Phosphorus-deficient plants showed a decrease in leaf area, but no changes in aboveground biomass. Root length, root surface area, and specific root length were higher in phosphorus-deficient plants than in control plants. Nitrogen and phosphorus deficiency reduced both root hydraulic conductance and root hydraulic conductance scaled by total root surface area. On the other hand, nutrient limitations did not significantly affect root conductance per unit of foliar surface area. Thus, adaptation to low nutrient availability did not affect seedling capacity for maintaining water supply to leaves. The implications for drought resistance and survival during seedling establishment in semi-arid environments are discussed.

The use of multiple measurement techniques to refine estimates of conifer needle geometry

Knowledge of foliar surface area is important in many fields, but estimating the area of nonflat conifer needles is difficult. The primary goal of this study was to use optical scanning and immersion methods to test and refine the standard cross-sectional geometries assumed for black spruce (Picea mariana (Mill.) BSP) and jack pine (Pinus banksiana Lamb.) needles. Projected leaf area (PLA, measured using a flatbed scanner), and hemisurface leaf area (HSLA, estimated from water immersion) were compared for conifer samples from a 37-year-old even-aged stand in northern Manitoba, Canada. The HSLA–PLA relationship was used to infer information about needle cross-sectional geometry after assuming a basic form (rhombus for black spruce and hemiellipse for jack pine). The cross section of black spruce needles was best approximated as a rhombus with a major/minor diagonal ratio of 1.35. Jack pine needles were best described by a hemiellipse with major/minor axis ratio of 1.30. Minor but incorrect assumptions of needle cross-sectional geometry resulted in foliar area errors of 6–8% using scanning methods and 1–2% using immersion methods. Simple equations are presented to calculate hemisurface needle area from volume or projected needle area based on these refined parameters.

Early Permian insect folivory on a gigantopterid-dominated riparian flora from north-central Texas

Quantitative analysis of 11,562 cm 2 of foliar surface area from an Early Permian flora from north-central Texas reveals that 2.6% was removed by insect folivores. Of the 1346 foliar items analyzed, 31.8% were attacked by insect folivores. This Permian insect herbivory approximated one-third the level in modern tropical to temperate forests. Three taxa of Gigantopteridaceae exhibited disproportionately high insect consumption levels, ranging from 3.1 to 4.4% of leaf area, and attack frequencies of 39.6 to 82.8% —levels comparable to taxon-specific values for modern woody dicotyledonous angiosperms. Qualitative analysis of folivory type also indicates that five of the eight categories of herbivore damage occurring on this flora were confined to or overwhelmingly represented on Gigantopteridaceae, suggesting preferential host specificity for Gigantopteridaceae by insect folivores. By contrast, other pteridophylls, conifers, cycadophytes, and two taxa of uncertain affinity, showed low levels of leaf area removal and attack frequencies. The Gigantopteridaceae, an enigmatic group of Permian plants with large, megaphyllous foliage, foreshadowed physiognomic attributes occurring in later angiosperms. Both groups had similar consumption patterns and intensities by insect folivores. In this moderately diverse Early Permian flora, insect folivory was significant, at least in one riparian environment outside the Euramerican coal-swamp ecosystem, indicating that modern modes and magnitudes of insect consumption of vascular plant tissue were in place during the Late Paleozoic.

Growth of Young Trees of Acer platanoides and Quercus robur Along a Gap- Understory Continuum: Interrelationships between Allometry, Biomass Partitioning, Nitrogen, and Shade Tolerance

Growth and biomass partitioning across a natural light gradient were examined in saplings (0.3-2.6 m in height) of relatively shade-tolerant Acer platanoides L. and relatively intolerant Quercus robur L. for dependence on relative irradiance, calculated from hemispherical photographs (RI), and on total tree height (H). H and RI were independent. All allometric relationships between H and the parameters of plant biomass and dimensions were positively affected by RI, signifying that at a common H, saplings increased horizontal growth relative to vertical growth in environments with greater irradiance. Root mass ratio (coarse plus fine roots per total plant biomass) increased with increasing irradiance in both species and was not different between the species. However, Q. robur had a larger stem mass ratio, while A. platanoides had a greater leaf mass ratio (LMR). At a common irradiance, leaf mass per area (LMA) was lower in A. platanoides. As a result of these interspecific differences in fractional allocation of sapling biomass in foliage and biomass requirement for construction of foliar surface area, leaf area ratio (LAR = LMR/LMA) was larger in A. platanoides. Relative growth rate of standing biomass (RGR) was significantly correlated with RI in both species and was not different between the species. In contrast, net assimilation rate per unit leaf area (NAR) was larger in Q. robur. Thus, in these species a similar RGR (NAR x LAR) was achieved in a completely different way: A platanoides increased the intercepting foliar area, while Q. robur increased the productivity per unit area. Growth analysis repeated on a nitrogen basis demonstrated that nitrogen use efficiency (biomass increment per unit nitrogen) was similar between the species, and that the species differences in NAR resulted from different foliar N concentrations; fractional nitrogen investment in foliage was independent of species, but lower nitrogen cost of leaves allowed A. platanoides to construct a more extensive foliar display with the same nitrogen investment in foliage. Biomass allocation between different compartments was also dependent on sapling size. With increasing H, A. platanoides maintained a constant proportion of biomass in foliage, but the relative amount of foliage decreased in Q. robur. Therefore, due to a decreasing investment of resources in foliage construction with advancing sapling ontogeny, saplings of similar height require more light to survive in Q. robur than in A. platanoides. Greater investment of biomass in leaves vs. standing biomass may result in lower volume gain and reduced competitive ability in more open habitats in A. platanoides. These results indicate that interspecific differences in allometry and nitrogen allocation patterns significantly alter species competitive relations during sapling development across the gap-understory continuum.

Summer throughfall and winter deposition in the San Bernardino Mountains in Southern California

Summer throughfall and year-round precipitation chemistry were studied for three years at Barton Flats (BF), a low to moderate pollution site in the San Bernardino Mountains (SBM) in southern California. Winter fog plus dry deposition, and bulk deposition were also measured during one season at three sites traversing an atmospheric deposition gradient in the SBM. Throughfall N (NO 3 − + NH 4 +) inputs during the growing season in 1993 were 4.0 kg ha −1 compared to 0.4 kg ha −1 for S. Deposition of N and S in summer 1994 was 50% of that in 1993, and precipitation in summer 1994 was 31 % as high as in 1993. Summer throughfall concentrations were highest in 1994, the summer with the lowest precipitation. Ionic concentrations in rain and throughfall at BF during the summer, particularly NO 3 −, were generally as high or higher than values reported for forests in Europe and eastern North America with much higher atmospheric deposition inputs. The high throughfall concentrations at BF were apparently due to the washoff of accumulated dry pollutants from mature trees with large surface areas during infrequent low-volume rain events. White fir, the species with the greatest foliar surface area, had the highest throughfall concentrations and the lowest throughfall volumes. Canopy effects of ponderosa and Jeffrey pine on precipitation chemistry and volume were intermediate, while California black oak throughfall was less modified chemically than the throughfall of the conifer species. Ionic deposition (mg m −2 land area) was highest under fir and pine, intermediate under oak, and lowest in rainfall. During the winter, peaks in wet deposition inputs at BF were associated with high monthly rain volumes (11–44 cm), while similar wet deposition peaks in August occurred with only a few light rains (1.4–3.4 cm). Winter (13 December 1993 to 11 April 1994) bulk deposition of N and S at Camp Paivika, a western high-deposition site, was 7.7 and 1.7 kg ha −1, respectively, compared to 0.9 and 0.3 kg ha −1 of N and S at BF. Winter deposition of NO 3 −, NH 4 + and SO 4 2− to passive nylon line collectors (fog plus dry deposition) was 15-,18- and 6-times greater at Camp Paivika than at BF. Winter deposition in both wet and dry forms in the SBM was greater than previously estimated from precipitation data for other forest sites in southern California.

Plant growth-form alters the relationship between foliar morphology and species shade-tolerance ranking in temperate woody taxa

Variation in leaf size (area per leaf) and leaf dry weight per area (LWA) in relation to species shade- and drought-tolerance, characterised by Ellenberg's light (ELD) and water demand (EWD) values, respectively, were examined in 60 temperate woody taxa at constant relative irradiance. LWA was independent of plant size, but leaf size increased with total plant height at constant ELD. Canopy position also affected leaf morphology: leaves from the upper crown third had higher LWA and were larger than leaves from the lower third. Leaf size and LWA were negatively correlated, and leaf size decreased and LWA increased with decreasing species shade-tolerance. Mean LWA was similar for trees and shrubs, but trees had larger leaves than shrubs. Furthermore, all relationships were altered by plant growth-form: none of the qualitative tendencies was significant for trees. This implies the considerably lower plasticity of foliar parameters in trees than those in shrubs. Accordingly, shade-tolerance of trees, having relatively constant leaf structure, may be most affected by the variability in biomass partitioning and crown geometry which influence foliage distribution and spacing and finally determine canopy light absorptance. Alteration of leaf form and investment pattern for construction of unit foliar surface area which change the efficiency of light interception per unit biomass investment in leaves, is a competitive strategy inherent to shrubs. EWD as well as wood anatomy did not control LWA and leaf size, though there was a trend of ring-porous tree species to be more shade-tolerant than diffuse-porous trees. Since ring-porous species are more vulnerable to cavitation than diffuse-porous species, they may be constrained to environments where irradiances and consequently evaporative demand is lower.

The influence of CO2 enrichment, phosphorus deficiency and water stress on the growth, conductance and water use of Pinus radiata D. Don

Abstract. Seedlings of Pinus radiata D. Don were grown in growth chambers for 22 weeks with two levels of phosphorus, under either well‐watered or water‐stressed conditions at CO2 concentrations of either 330 or 660mm3 dm−3. Plant growth, water use efficiency and conductance were measured and the relationship between these and needle photosynthetic capacity, water use efficiency and conductance was determined by gas exchange at week 22. Phosphorus deficiency decreased growth and foliar surface area at both CO2concentrations; however, it only reduced the maximum photosynthetic rates of the needles at 660 mm3 CO2 dm−3 (plants grown and measured at the same CO2 concentration). Water stress reduced growth and foliar surface area at both CO2 concentrations. Increases in needle photosynthetic rates appeared to be partly responsible for the increased growth at high CO2 where phosphorus was adequate. This effect was amplified by accompanying increases in needle production. Phosphorus deficiency inhibited these responses because it severely impaired needle photosynthetic function. The relative increase in growth in response to high CO2 was higher in the periodically water‐stressed plants. This was not due to the maintenance of cell volume during drought. Plant water use efficiency was increased by CO2 enrichment due to an increase in dry weight rather than a decrease in shoot conductance and, therefore, transpirational water loss. Changes in needle conductance and water use efficiency in response to high CO2 were generally in the same direction as those at the whole plant level. If the atmospheric CO2 level reaches the predicted concentration of 660 mm3 dm−3 by the end of next Century, then the growth of P. radiata will only be increased in areas where phosphorus nutrition is adequate. Growth will be increased in drought‐affected regions but total water use is unlikely to be reduced.

Phase change in loblolly pine:Shoot development as a function of age

The growth behavior of grafted scions from 1‐, 4‐, 8‐ and 12‐year‐old ortets representing five half‐sib loblolly pine families was observed over a two‐year period (three for strobilus production) following grafting. Significant, persistent decreases in total number of cycles produced, height and diameter increment, number of branches produced, foliar surface area and total scion biomass were observed with increasing age. Needle length, diameter, and ability to form male and female strobili increased with increasing scion age. The persistence of these differences is not a function of size since the scions were the same length at grafting. The significance of these results to the establishment of breeding orchards, early genetic evaluation, and the nature of phase change is discussed.

Growth and water relations of black locust and pine seedlings exposed to controlled water stress

Some responses of very young jack pine (Pinusbanksiana Lamb.), red pine (Pinusresinosa Ait.), and black locust (Robiniapseudoacacia L.) seedlings grown under constant water stress conditions induced by polyethylene glycol 4000 culture solutions were investigated. Seedlings grown under stressful conditions had lower leaf conductance, produced less foliar surface area, and accumulated less dry weight than nonstressed seedlings. Seedlings grown under nonstressed conditions were found to undergo considerable transpiration at night. When compared with the pines, black locust seedlings grew more rapidly, had lower (more negative) xylem pressure potentials, and showed poorer survival under the more stressful growth conditions.