Greater Relative Growth Rate Research Articles

Incorporation of topsoil and burn-pile debris substantially increases early growth of lodgepole pine on landings

Rehabilitation of skid trails, temporary roads, and log landings is required for many harvested sites in British Columbia; however, more information is needed regarding practical methods to return these access areas to productive forest. Lodgepole pine ( Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) seedlings (1 + 0) were planted into (i) fully rehabilitated landings (burn-pile debris and topsoil incorporated), (ii) tilled landings, and (iii) unprepared portions of the adjacent cutblock. After two seasons of growth in the field, seedlings planted on fully rehabilitated landings were 38% larger, more robust, and exhibited 44% greater absolute growth and 22% greater relative growth rates, than seedlings planted in the adjacent cutblock. Seedlings planted on tilled landings were 33% smaller, and exhibited absolute growth rates 38% less, and relative growth rates 18% less, than seedlings planted in the adjacent cutblock. Seedlings planted in the cutblock exhibited higher ectomycorrhizal colonization rates. Our results indicate that tillage alone was not sufficient to fully rehabilitate these landings, but that incorporation of recovered topsoil and burn-pile debris produced an excellent growth substrate. This method, using materials found on site, can prevent a significant loss of land regenerating to productive second-growth forest.

Seedling growth responses to water and nutrient augmentation in the understorey of a lowland moist forest, Panama

Abstract:We irrigated and fertilized (with nutrients) seedlings of Doliocarpus olivaceus (Dilleniaceae, a shade-tolerant liana), Faramea occidentalis (Rubiaceae, a shade-tolerant understorey tree) and Tetragastris panamensis (Burseraceae, a shade-tolerant canopy tree) growing in the understorey of an old-growth tropical moist forest in Panama to assess the impact of seasonal water availability and nutrient-poor soils on seedling growth rates. In control plots, height growth rates were greater in the dry season than in the wet season for Doliocarpus (21%) and for Faramea (89%), whereas Tetragastris had similar seasonal rates. For numbers of leaves, Faramea had 3.5-fold greater relative growth rates in the dry season than in the wet season, while Doliocarpus and Tetragastris lost leaves (semi-deciduous) during the same period. Irrigation and nutrient augmentation increased height growth rates for all three species (45% to 272%). For Doliocarpus, irrigation and nutrient augmentation prevented leaf fall during the dry season. For Faramea in the dry season, irrigation and nutrient augmentation when applied independently reduced the growth of new leaves by 65% to 87%, but relative growth rates for number of leaves were the same as the control rates in the combined irrigation and nutrient augmentation treatment. The growth of new leaves for Tetragastris responded to dry-season irrigation but not nutrient augmentation. Although all measurements occurred beneath the forest canopy, during the dry season, Tetragastris had a negative relationship between canopy openness and relative growth rate for number of leaves, whereas the other two species had a positive relationship. Our results show that soil resources influence growth rates even in the deep shade of the forest understorey, and demonstrate different responses to soil resources among species that might contribute to niche differentiation and species coexistence.

Photosynthesis, Growth, Carbon Allocation, and Fruit Load ofFrangula carolinianaandRhamnus cathartica

Rhamnus cathartica is an invasive shrub capable of high fecundity in North America. The physiology of R. cathartica has received little attention, but more is needed to understand traits that enhance its success in disturbed environments. Such data may help to predict invasiveness of closely related species such as Frangula caroliniana. We hypothesized that R. cathartica would have greater relative growth rate and specific leaf area over time than would F. caroliniana and that fecundity would be higher for R. cathartica than for F. caroliniana. Photosynthesis, growth, and carbon allocation patterns of both species were studied over time from July 3 to October 2, 2003. Carbon allocation to leaves (i.e., leaf mass fraction) of F. caroliniana was greater than that of R. cathartica after 28 d. The partitioning of carbon to stems (i.e., stem mass fraction) of R. cathartica, however, was greater after 28 d than that of F. caroliniana. The allocation of carbon to roots (i.e., root mass fraction) of R. cathartica was greater than that of F. caroliniana after 70 d. Relative growth rate of R. cathartica was greater than that of F. caroliniana after 14 d but not thereafter. Specific leaf area of R. cathartica was greater than that of F. caroliniana after 98 d, but specific leaf area and relative growth rate were poorly correlated. There was a stronger relationship, however, between relative growth rate and net assimilation rate for both species. Photosynthesis of R. cathartica was higher than that of F. caroliniana after 42 d, but there were no differences in plant dry mass after 28 d. Length, leaf surface area, and fruit count of 2‐yr‐old branches of both species were measured to determine their fecundity. Fruit count of F. caroliniana was 41% of that of R. cathartica. We conclude that under favorable field conditions, both species establish similarly and that growth and photosynthesis of R. cathartica exceed those of F. caroliniana over time. Rhamnus cathartica also has greater fecundity than F. caroliniana.

RELATEDNESS AND ENVIRONMENT AFFECT TRAITS ASSOCIATED WITH INVASIVE AND NONINVASIVE INTRODUCED COMMELINACEAE

Understanding the traits of invasive species may improve the ability to predict, prevent, and manage invasions. I compared morphological and performance traits of five congeneric pairs of invasive and noninvasive Commelinaceae across a factorial experiment using a range of water and nutrient availabilities. Invasive species had greater fecundity and vegetative reproduction than their noninvasive relatives. The invasive species also had higher relative growth rates, greater specific leaf area, and more plastic root-to-shoot ratios than noninvasive species. However, whether a trait was associated with invasiveness often depended on both environment and relatedness. Invasives had greater sexual and vegetative reproduction, higher specific leaf area, and greater relative growth rates than noninvasive congeners, but only in some environments. Differences between invasive and noninvasive taxa were greatest at high nutrient availabilities. These results suggest that studies of invasive species' traits must incorporate information on conditions under which the trait was measured. In addition, incorporating information on relatedness improved our ability to detect associations between species traits, such as specific leaf area and relative growth rate, and invasiveness, suggesting that such information may be required for a complete understanding of what makes a species invasive.

Growth, Water Relations, and Nutritive Value of Pasture Species Mixtures under Moisture Stress

Pasture productivity under harsh environments can be increased by planting more drought‐resistant species or by increasing species diversity. This research was conducted under two large (10.2 × 26.8 m) rainout shelters combined with a drip irrigation system to provide deficit, normal, and excessive moisture conditions. A two‐species mixture containing the relatively drought‐tolerant species, orchardgrass (Dactylis glomerata L.) and red clover (Trifolium pretense L.) and two five‐species mixtures were compared with a mixture containing the drought‐sensitive species, white clover (Trifolium repens L.) and Kentucky bluegrass (Poa pratensis L.), which are the predominant species in northeastern USA pastures. Plots were clipped from mid‐May to early October in 2000 and 2001 on a schedule that mimicked management‐intensive grazing practices. The five‐species mixture containing chicory (Cichorium intybus L.), orchardgrass, Kentucky bluegrass, perennial ryegrass (Lolium perenne L.), and white clover had the greatest dry matter yield at all moisture levels. Yield in that mixture increased 89% in the dry, 61% in the normal, and 43% (by weight) in the wet treatments compared with the white clover/Kentucky bluegrass mixture. Increased yield was primarily due to the robust growth of chicory which dominated the mixture, accounting for 71% of harvested biomass by the fall of 2001. In addition, white clover growing in the mixture with chicory had improved leaf water relations and greater relative growth rates than white clover growing in the two‐species mixture. Including the functional attribute of a deep‐rooted forb appeared to be more important than species richness, per se, in improving forage yield.

Genetic modification of photosynthesis with E. coli genes for trehalose synthesis

Improvement in photosynthesis per unit leaf area has been difficult to alter by breeding or genetic modification. We report large changes in photosynthesis in Nicotiana tabacum transformed with E. coli genes for the trehalose pathway. Significantly, photosynthetic capacity (CO2 assimilation at varying light and CO2, and quantum yield of PSII electron transport) per unit leaf area and per leaf dry weight were increased in lines of N. tabacum transformed with the E. coli gene otsA, which encodes trehalose phosphate synthase. In contrast, transformation with otsB, which encodes trehalose phosphate phosphatase or Trec, encoding trehalose phosphate hydrolase, produced the opposite effect. Changes in CO2 assimilation per unit leaf area were closely related to the amount and activity of Rubisco, but not to the maximum activities of other Calvin cycle enzymes. Alterations in photosynthesis were associated with trehalose 6-phosphate content rather than trehalose. When growth parameters were determined, a greater photosynthetic capacity did not translate into greater relative growth rate or biomass. This was because photosynthetic capacity was negatively related to leaf area and leaf area ratio. In contrast, relative growth rate and biomass were positively related to leaf area. These results demonstrate a novel means of modifying Rubisco content and photosynthesis, and the complexities of regulation of photosynthesis at the whole plant level, with potential benefits to biomass production through improved leaf area.

Response of five dry tropical tree seedlings to elevated CO 2 : impact of seed size and successional status

2 area, Stomatal conductance, Transpiration, Water use efficiency Abstract. The impact of seed size and successional status on seedling growth under elevated CO was 2 studied for five dry tropical tree species viz. Albizia procera, Acacia nilotica, Phyllanthus emblica, Terminalia arjuna and Terminalia chebula. Seedlings from large (LS) and small seeds (SS) were grown at two CO levels (ambient and elevated, 700-750 ppm). CO assimilation rate, stomatal conductance, 2 2 water use efficiency and foliar N were determined after 30 d exposure to elevated CO . Seedlings were 2 harvested after 30 d and 60 d exposure periods. Height, diameter, leaf area, biomass and other growth traits (RGR, NAR, SLA, R:S) were determined. Seedling biomass across species was positively related with seed mass. Within species, LS seedlings exhibited greater biomass than SS seedlings. Elevated CO2 enhanced plant biomass for all the species. The relative growth rate (RGR), net assimilation rate (NAR), CO assimilation rate, R:S ratio and water use efficiency increased under elevated CO . However, the 2 2 positive impact of elevated CO was down regulated beyond 30 d exposure. Specific leaf area (SLA), 2 transpiration rate, stomatal conductance declined due to exposure to elevated CO . Fast growing, early 2 successional species exhibited greater RGR, NAR and CO assimilation rate. Per cent enhancement in 2 such traits was greater for slow growing species. The responses of individual species did not follow functional types (viz. legumes, non-legumes). The enhancement in biomass and RGR was greater for large-seeded species and LS seedlings within species. This study revealed that elevated CO could cause 2 large seeded, slow growing and late successional species to grow more vigorously.

Velvetleaf Interference Effects on Yield and Growth of Grain Sorghum

Weed competition studies with grain sorghum [Sorghum bicolor (L.) Moench] are limited. Improved knowledge of growth in response to weed competition could contribute to development of sorghum hybrids that compete better with weeds. Velvetleaf (Abutilon theophrasti Medic.) competition with sorghum hybrids was evaluated in field experiments on a Sharpsburg silty clay loam soil (fine smectitic, mesic Typic Arguidoll) in 1996 and 1997 at Lincoln, NE. The objective was to determine the effects of velvetleaf competition on interception of photosynthetically active radiation (PAR), growth, and yield of sorghum hybrids with different heights. Sorghum hybrids used were ‘FS2’ (1.8 to 2.4 m tall) and ‘DK54’ and ‘X260’ (1.2 to 1.5 m tall). Weed treatments included sorghum in monoculture and grown in mixture with velvetleaf. Medium‐height hybrids had 0.4 greater midseason leaf area indices (LAIs) than the tall hybrid in 1996, and in 1997, DK54 had 0.4 to 0.6 greater LAI than the other hybrids after 500 growing degree days. Interception of PAR was similar among hybrids except for 2 to 10% less for X260 in mixture in 1996. In 1996, when weed pressure was greater, the tall hybrid had greater relative growth rate and net assimilation rate but lower leaf area ratio than for the medium‐height hybrids. Sorghum intercepted more radiation and produced more biomass in monoculture than in mixture, but the reduction in growth and yield in presence of velvetleaf was less for the tall hybrid. Development of tall sorghum hybrids with high LAI would be useful for integrated weed management.

Effects of Prescribed Fire on Physiology and Growth of Acer rubrum and Quercus spp. Seedlings in an Oak-Pine Forest on the Cumberland Plateau, KY

GILBERT, N. L. (Department of Biology, University of Kentucky, Lexington, KY, 40546), S. L. JOHNSON (Department of Biology, Middle Tennessee State University, Mufreesboro, TN, 37132) S. K. GLEESON (Department of Biology, University of Kentucky, Lexington, KY, 40546), B. A. BLANKENSHIP AND M. A. ARTHUR (Department of Forestry, University of Kentucky, Lexington, KY, 40546). Effects of prescribed fire on physiology and growth of Acer rubrum and Quercus spp. seedlings in an oak-pine forest on the Cumberland Plateau, KY. J. Torrey Bot. Soc. 130: 253-264. 2003.-Poor survival of oak regeneration has been attributed to fire suppression and the physiological limitations imposed by the increasing dominance of competitors, especially red maple (Acer rubrum L.). We examined the physiological responses of red maple, chestnut oak (Quercus prinus L.) and scarlet oak (Q. coccinea Muenchh.) seedlings following a prescribed fire in an upland oak-pine forest in eastern Kentucky. Immediately following fire, seedlings on burned sites had significantly greater foliar concentrations of N, P, K, and Mg than seedlings on unburned sites; this effect of treatment diminished over the first growing season. Seedlings on burned sites also demonstrated significantly higher photosynthetic potential and had greater relative growth rates of diameter and height through the second and third growing seasons postfire. Among species, chestnut oak consistently had the greatest foliar concentrations of all nutrients, with red maple being intermediate and scarlet oak the lowest. Both oaks had significantly greater maximum photosynthesis than red maple, but there were no significant differences among species for diameter or height relative growth rates. Treatment by species interactions indicated that red maple seedlings were significantly taller than oaks on the burned site, while there were no differences in height among species on the unburned site. Although a single fire improved the performance of all species, our results suggest no improvement in the status of oak regeneration based on post-fire seedling physiology and growth.

A Laboratory Exercise for Teaching Plant Interference and Relative Growth Rate Concepts1

Interference between weeds and crops is a key topic in undergraduate weed science courses. A laboratory exercise was developed at Iowa State University to actively demonstrate how small-seeded weeds can compete with large-seeded crops despite the initial seedling size disadvantage. Spring wheat and wild mustard were grown in pots in monoculture and in competition with each other. One set of plants was harvested at 1 wk after planting and another at 6 wk after planting. Relative growth rates (RGR) were calculated for the 5-wk period using the classical approach of plant growth analysis. The results from four semesters were analyzed to determine whether the experiment was meeting its intended outcomes. It was successful in this regard. In each of the four semesters, wild mustard had a lower initial dry weight and a greater RGR than did wheat. Students were required to write a scientific paper using the experimental results after completing a series of active-learning exercises. Assessment by students suggested that the experiment, active-learning exercises, and writing assignment were valuable activities.Nomenclature: Spring wheat, Triticum aestivum L. ‘Sharp’; wild mustard, Brassica kaber (DC.) L. C. Wheeler #3 SINAR.Additional index words: Education, weed biology, weed ecology.Abbreviations: RGR, relative growth rate.

Effect of Neotyphodium endophyte infection on growth and leaf gas exchange of Arizona fescue under contrasting water availability regimes

We assessed how Neotyphodium infection influenced the biomass production and growth of Arizona fescue ( Festuca arizonica Vasey), a dominant understory grass in Ponderosa pine ( Pinus ponderosa) forests of the southwest USA, by growing potted infected (E+) and uninfected (E−) plants under a high and a low water availability regime for 87 days. We measured growth analysis parameters, leaf net photosynthesis ( P n), chlorophyll fluorescence parameters, conductance to water vapor ( g l) and water potential ( Ψ), to provide explanations for differences in biomass production under these treatments. Under high water availability, E− plants produced more biomass and had greater relative growth rates (RGR; rate of biomass gain per biomass); higher RGR of E− plants was correlated with higher P n as well as production of less dense, presumably thinner leaves, which provided more leaf area per leaf biomass, and greater LAR (leaf area ratio; leaf area per total plant biomass). Under low water availability, E+ plants produced more aboveground biomass and had greater RGR; higher RGR of E+ plants was correlated with higher net assimilation rates, as well as production of less dense leaves and greater LAR. Infected plants tended to have lower midday P n and g l in both water availability regimes. Lower P n in E+ plants appeared primarily due to stomatal, rather than biochemical, limitations to photosynthesis. When a more severe water stress was imposed in the low water availability treatment over the last 61 days of the experiment, E+ plants tended to have higher midday P n and g l. Infected plants also tended to have less negative leaf Ψ regardless of water availability regime. Lower g l and transpirational losses of E+ plants probably conserved soil moisture, such that when a more severe water stress was subsequently imposed, higher soil moisture availability allowed E+ plants to maintain higher P n and g l. Neotyphodium infection appears beneficial to Arizona fescue performance under low water availability and detrimental under ample water availability.

The advantage of early flowering in the spring ephemeral annual plant Floerkea proserpinacoides.

• Internal conflicts in the allocation of resources lead to trade-offs or compromises that can influence fitness and the evolution of specific life-history traits. • Here, the reproductive schedule of Floerkea proserpinacoides plants, a spring ephemeral annual of the deciduous forests of eastern North America, was manipulated to determine the presence of potential conflicts between growth and reproduction, and the advantage of early reproduction. • Plants on which flowering was delayed had a greater relative growth rate (RGR) and vegetative biomass than control plants after 8wks (when control plants started to senesce). Delayed-flowering plants took 1week longer to senesce, which allowed them to mature almost as many seeds as did control plants in 8wks. • However, late flowering in F. proserpinacoides may be maladaptive. With reduced light availability through canopy closure, early flowering plants can rapidly divert most of the resources accumulated in the stem and leaves to seed maturation. Thus, the advantage of maintaining a higher RGR by delaying flowering is associated with the greater disadvantage of necessitating more time to mature seeds.

N2 fixation by Acacia species increases under elevated atmospheric CO2

AbstractIn the present study the effect of elevated CO2 on growth and nitrogen fixation of seven Australian Acacia species was investigated. Two species from semi‐arid environments in central Australia (Acacia aneura and A. tetragonophylla) and five species from temperate south‐eastern Australia (Acacia irrorata, A. mearnsii, A. dealbata, A. implexa and A. melanoxylon) were grown for up to 148 d in controlled greenhouse conditions at either ambient (350 µmol mol−1) or elevated (700 µmol mol−1) CO2 concentrations. After establishment of nodules, the plants were completely dependent on symbiotic nitrogen fixation. Six out of seven species had greater relative growth rates and lower whole plant nitrogen concentrations under elevated versus normal CO2. Enhanced growth resulted in an increase in the amount of nitrogen fixed symbiotically for five of the species. In general, this was the consequence of lower whole‐plant nitrogen concentrations, which equate to a larger plant and greater nodule mass for a given amount of nitrogen. Since the average amount of nitrogen fixed per unit nodule mass was unaltered by atmospheric CO2, more nitrogen could be fixed for a given amount of plant nitrogen. For three of the species, elevated CO2 increased the rate of nitrogen fixation per unit nodule mass and time, but this was completely offset by a reduction in nodule mass per unit plant mass.

Screening of Chickpeas for Adaptation to Autumn Sowing

Dry matter accumulation was determined in 27 chickpea (Cicer arietinum) lines in time‐of‐sowing field trials and in controlled‐environment chambers at day/night temperatures of 13/5, 18/8 and 23/13 °C to assess tolerance to growth‐inhibiting temperatures. Field trials were based at Narrabri, NSW, Australia, in a region of summer‐dominant rainfall where winter crops are grown on stored soil moisture. Percentage emergence was lower than expected in some field trials and in the coolest controlled environment. Subsequent dry matter accumulation showed the effects of poor crop establishment until the onset of flowering. Kabuli types were more susceptible to poor emergence than desi types. Different lines yielded the greatest dry matter production at different stages of growth. In the seedling phase, to 30 days after emergence, kabuli accessions SP1.563 and Garnet showed significantly greater dry matter accumulation than all other accessions in all controlled environments, suggesting broad adaptation. One desi accession, Gully, was almost as productive as these two kabuli accessions in the intermediate environment but was much poorer in the other environments, indicating very narrow adaptation. In the vegetative phase, the greatest relative growth rates were found in the desi accessions. Line 940‐26 was identified as highly productive in both field and controlled‐environment experiments. Dry matter accumulation was not significantly affected by temperature, although it was slightly greater in the coolest controlled environment than in the other two. The accession by temperature interaction was not significant, showing that the breadth of adaptation was similar in all accessions during this growth phase. The optimum time of sowing for dry matter accumulation was late May, 4–6 weeks before the winter solstice. The results showed that chickpeas are well adapted to germination and seedling establishment in moderate conditions, followed by vegetative growth in cooler conditions. These conditions are typical following autumn sowing in a Mediterranean or temperate environment. Kabuli types appear to have stronger growth during the seedling phase and desi types during the vegetative phase. Recombination of these traits could lead to more productive cultivars.

A greater relative growth rate of Brassica rapa L. at low temperatures increases biomass at anthesis

0t, n.s.). These relationships suggested that it might be possible to develop early flowering cultivars with increased seed yield by selecting for higher RGR before anthesis. RGR of BC 2 F 3:4 lines in the field during winter was correlated with RGR at low temperatures (13/4°C) in a controlled environment, suggesting that genotypes producing more dry weight at anthesis grew more at the low temperatures normally experienced in the field. This was supported by a significant (P < 0.05 0.05) negative correlation (r = –0.69**) between growth in the field and potassium leakage from leaf tissue at 4

Photosynthetic and respiratory acclimation and growth response of Antarctic vascular plants to contrasting temperature regimes

Air temperatures have risen over the past 50 yr along the Antarctic Peninsula, and it is unclear what impact this is having on Antarctic plants. We examined the growth response of the Antarctic vascular plants Colobanthus quitensis (Caryophyllaceae) and Deschampsia antarctica (Poaceae) to temperature and also assessed their ability for thermal acclimation, in terms of whole-canopy net photosynthesis (P(n)) and dark respiration (R(d)), by growing plants for 90 d under three contrasting temperature regimes: 7°C day/7°C night, 12°C day/7°C night, and 20°C day/7°C night (18 h/6 h). These daytime temperatures represent suboptimal (7°C), near-optimal (12°C), and supraoptimal (20°C) temperatures for P(n) based on field measurements at the collection site near Palmer Station along the west coast of the Antarctic Peninsula. Plants of both species grown at a daytime temperature of 20°C had greater RGR (relative growth rate) and produced 2.2-3.3 times as much total biomass as plants grown at daytime temperatures of 12° or 7°C. Plants grown at 20°C also produced 2.0-4.1 times as many leaves, 3.4-5.5 times as much total leaf area, and had 1.5-1.6 times the LAR (leaf area ratio; leaf area:total biomass) and 1.1-1.4 times the LMR (leaf mass ratio; leaf mass:total biomass) of plants grown at 12° or 7°C. Greater RGR and biomass production at 20°C appeared primarily due to greater biomass allocation to leaf production in these plants. Rates of P(n) (leaf-area basis), when measured at their respective daytime growth temperatures, were highest in plants grown at 12°C, and rates of plants grown at 20°C were only 58 (C. quitensis) or 64% (D. antarctica) of the rates in plants grown at 12°C. Thus, lower P(n) per leaf area in plants grown at 20°C was more than offset by much greater leaf-area production. Rates of whole-canopy P(n) (per plant), when measured at their respective daytime growth temperatures, were highest in plants grown at 20°C, and appeared well correlated with differences in RGR and total biomass among treatments. Colobanthus quitensis exhibited only a slight ability for relative acclimation of P(n) (leaf-area basis) as the optimal temperature for P(n) increased from 8.4° to 10.3° to 11.5°C as daytime growth temperatures increased from 7° to 12° to 20°C. There was no evidence for relative acclimation of P(n) in D. antarctica, as plants grown at all three temperature regimes had a similar optimal temperature (10°C) for P(n). There was no evidence for absolute acclimation of P(n) in either species, as rates of P(n) in plants grown at a daytime temperature of 12°C were higher than those of plants grown at daytime temperatures of 7° or 20°C, when measured at their respective growth temperatures. The poor ability for photosynthetic acclimation in these species may be associated with the relatively stable maritime temperature regime during the growing season along the Peninsula. In contrast to P(n), both species exhibited full acclimation of R(d), and rates of R(d) on a leaf-area basis were similar among treatments when measured at their respective daytime growth temperature. Our results suggest that in the absence of interspecific competition, continued warming along the Peninsula will lead to improved vegetative growth of these species due to (1) greater biomass allocation to leaf-area production (as opposed to improved rates of P(n) per leaf area) and (2) their ability to acclimate R(d), such that respiratory losses per leaf area do not increase under higher temperature regimes.

Fat transfer and energetics during lactation in the hooded seal: the roles of tissue lipoprotein lipase in milk fat secretion and pup blubber deposition.

Hooded seals (Cystophora cristata) lactate for 3.6 days during which females simultaneously fast and transfer large amounts of energy to their pups through fat-rich milk. Pups grow rapidly, principally due to blubber deposition. Lipoprotein lipase (LPL), the primary enzyme responsible for tissue uptake of triglyceride fatty acids, may strongly influence both maternal milk fat secretion and pup blubber deposition. We measured the energetic costs of lactation (using hydrogen isotope dilution, 3H2O), milk composition, prolactin, and LPL activity (post-heparin plasma LPL [PH LPL], blubber, mammary gland and milk; U) in six females. PH LPL and blubber LPL were measured in their pups. Females depleted 216.3 MJ.day-1 of body energy and fat accounted for 59% of maternal mass loss and 90% of postpartum body energy loss, but maternal body composition changed little. Maternal blubber LPL was negligible (0.0-0.2 U), while mammary LPL was elevated (1.8-2.5 U) and was paralleled by changes in prolactin. Estimated total mammary LPL activity was high (up to 20,000 U.animal-1) effectively favoring the mammary gland for lipid uptake. Levels of total blubber LPL in pups increased seven-fold over lactation. Pups with higher PH LPL at birth had greater relative growth rates (P = 0.025). Pups with greater blubber stores and total blubber LPL activity had elevated rates of fat deposition (P = 0.035).

Growth Analysis and Reproductive Allocation of Japanese Forbs and Grasses in Relation to Organ Toughness under Trampling

Abstract: The growth and reproduction of Japanese forbs (Artemisia princeps and Piantago asiatica) and grasses (Digitaria ad‐scendens and Eleusine indica) treated to 25 tramplings (3 g m‐2) per week were investigated in relation to the toughness (tensile strength) of organs. The perennial erect forb, A. princeps, was the most sensitive to trampling in terms of a remarkable depression of plant size and relative growth rate (RGR). RGR and net assimilation rate (NAR) of trampled A. princeps were negative. This was promoted by a loss of organs due to a reduced toughness of organs following trampling. In contrast to this species which did not flower after trampling, the perennial rosette forb, P. asiatica, maintained its plant biomass, NAR, RGR and reproduction under trampling because of tougher organs. However, NAR without trampling was lower in P. asiatica due to a larger leaf dry mass per leaf area (LMA), which could contribute to leaf toughness under trampling. The annual tussock grass, D. adscendens, which has a greater RGR than that of another grass, E. indica, without trampling was intolerant to trampling in terms of decreased biomass and RGR under trampling due to more sensitive organs, although it maintained an ability to reproduce. On the other hand, E. indica showed a marked trampling tolerance, with hardly reduced plant biomass and RGR. This species showed increased toughness of organs when trampled and frequently formed inflorescences in the growing period and produced similar biomass allocation to reproductive organs to untrarnpled plants. Between the grasses, RGR without trampling was slower in E. indica, partly because of its larger LMA. These results suggest that plants face a dilemma between trampling tolerance and efficient assimilative capacity and/or growth rate.

Partitioning of Nitrate Assimilation between Shoots and Roots of Kentucky Bluegrass

Turfgrass roots play an important role in the overall metabolism of NO−3 partly because leaves of turfgrasses are partially lost during mowing. Nitrate transported to shoots stimulates shoot growth and decreases N use efficiency through clipping removal. This study was conducted to quantify NO−3 reduction by shoots and roots of Kentucky bluegrass (Poa pratensis L.). Two cultivars, Livingston, which performed better under high N fertility, and Merit, which performed better under low N fertility, were grown in aerated nutrient solution containing 0.1 to 5.2 mM NO−3. These grasses were analyzed for relative growth rate (RGR), shoothoot ratio (S/R),in situ NO−3 uptake rate (NUR), in vivo NO−3 reductase activity (NRA), metabolic NO−3 pool (MNP), and storage NO−3 pool (SNP) in shoots and roots. Under low NO−3 levels, Merit exhibited a higher NUR, a larger root SNP, a smaller shoot SNP and a greater RGR than Livingston. Under high NO−3 levels, Livingston exhibited a greater shoot growth rate and reduced a greater proportion of NO−3 in its shoots than did Merit. In both cultivars, root contribution to the plant total NO−3 reduction (PTNR), estimated from NRA, was <5%. When dissolved O2 was decreased and root carbohydrate content increased, root contribution to PTNR increased to 40 and 15%, respectively. Our results suggest that root carbohydrate status and root-zone O2 levels strongly influence root contribution to PTNR and N use efficiency of Kentucky bluegrass in response to N fertility. This in turn is a function of the partitioning of NO−3 assimilation between shoots and roots.

Functional growth analysis of red pine trees under variable intensities of competition

A functional approach is proposed for comparing the development of individual red pine (Pinus resinosa Ait.) trees which had been growing under different intensities of competition from ages 13 to 43. Growth rate measures, based on absolute growth rate, relative growth rate and the ratio of absolute growth rate to crown width, were obtained from the differentiation of a cumulative growth function. Individual tree data were obtained from stands of the same age, but with different initial spacings: 1.5 × 1.5 m, 2.4 × 2.4 m, and 4.3 × 4.3 m. The Chapman-Richards function represented adequately the growth trends of individual trees. While cumulative growth indicated a fairly consistent pattern, that is, the bigger the tree initially, the bigger it remained, absolute growth rate was not related to tree size. Some of the smallest trees had the greatest absolute growth rate. Relative growth rate was more informative on the effect of competition. Before competition became severe, small trees had greater relative growth rates than large trees, and the effect of competition was to reverse this trend. The ratio of absolute growth rate to crown width indicated that the ability of trees to occupy the aerial growing space was not related to tree size. Key words: red pine (Pinus resinosa Ait.), growth functions, absolute growth rate, relative growth rate, functional approach