Scaling of respiration to nitrogen in leaves, stems and roots of higher land plants.

Using a database of 2510 measurements from 287 species, we assessed whether general relationships exist between mass-based dark respiration rate and nitrogen concentration for stems and roots, and if they do, whether they are similar to those for leaves. The results demonstrate strong respiration-nitrogen scaling relationships for all observations and for data averaged by species; for roots, stems and leaves examined separately; and for life-forms (woody, herbaceous plants) and phylogenetic groups (angiosperms, gymnosperms) considered separately. No consistent differences in the slopes of these log-log scaling relations were observed among organs or among plant groups, but respiration rates at any common nitrogen concentration were consistently lower on average in leaves than in stems or roots, indicating that organ-specific relationships should be used in models that simulate respiration based on tissue nitrogen concentrations. The results demonstrate both common and divergent aspects of tissue-level respiration-nitrogen scaling for leaves, stems and roots across higher land plants, which are important in their own right and for their utility in modelling carbon fluxes at local to global scales.

Dark respiration rate increases with plant size in saplings of three temperate tree species despite decreasing tissue nitrogen and nonstructural carbohydrates.

In shaded environments, minimizing dark respiration during growth could be an important aspect of maintaining a positive whole-plant net carbon balance. Changes with plant size in both biomass distribution to different tissue types and mass-specific respiration rates (R(d)) of those tissues would have an impact on whole-plant respiration. In this paper, we evaluated size-related variation in R(d), biomass distribution, and nitrogen (N) and total nonstructural carbohydrate (TNC) concentrations of leaves, stems and roots of three cold-temperate tree species (Abies balsamea (L.) Mill, Acer rubrum L. and Pinus strobus L.) in a forest understory. We sampled individuals varying in age (6 to 24 years old) and in size (from 2 to 500 g dry mass), and growing across a range of irradiances (from 1 to 13% of full sun) in northern Minnesota, USA. Within each species, we found small changes in R(d), N and TNC when comparing plants growing across this range of light availability. Consistent with our hypotheses, as plants grew larger, whole-plant N and TNC concentrations in all species declined as a result of a combination of changes in tissue N and shifts in biomass distribution patterns. However, contrary to our hypotheses, whole-plant and tissue R(d) increased with plant size in the three species.

Universal scaling of respiratory metabolism, size and nitrogen in plants.

The scaling of respiratory metabolism to body size in animals is considered to be a fundamental law of nature, and there is substantial evidence for an approximate (3/4)-power relation. Studies suggest that plant respiratory metabolism also scales as the (3/4)-power of mass, and that higher plant and animal scaling follow similar rules owing to the predominance of fractal-like transport networks and associated allometric scaling. Here, however, using data obtained from about 500 laboratory and field-grown plants from 43 species and four experiments, we show that whole-plant respiration rate scales approximately isometrically (scaling exponent approximately 1) with total plant mass in individual experiments and has no common relation across all data. Moreover, consistent with theories about biochemically based physiological scaling, isometric scaling of whole-plant respiration rate to total nitrogen content is observed within and across all data sets, with a single relation common to all data. This isometric scaling is unaffected by growth conditions including variation in light, nitrogen availability, temperature and atmospheric CO2 concentration, and is similar within or among species or functional groups. These findings suggest that plants and animals follow different metabolic scaling relations, driven by distinct mechanisms.

Avaliação da influência de técnicas fisioterapêuticas manuais sobre as pressões inspiratória e expiratória em atletas de natação / Rvaluation of the influence of manual therapies on inspiratories and expiratories pressures in swimmers

Introdução: Músculos inspiratórios são considerados tônicos e, por isso, tendem à retração. A falta de flexibilidade destes leva à limitação na ventilação pulmonar. Sugere-se que técnicas de terapia manual possam modificar estruturalmente os tecidos, e, na cadeia respiratória, possam melhorar a dinâmica ventilatória. Objetivo: Avaliar a influência de técnicas fisioterapêuticas manuais, direcionadas aos músculos respiratórios, sobre as pressões inspiratórias e expiratórias. Método: Foram selecionados 16 atletas de natação de ambos os sexos, que foram randomicamente e igualmente divididos em grupo-controle (GC) e grupo tratado (GT). Inicialmente mensurou-se as pressões inspiratória e expiratória por mano-vacuometria. Em seguida, o GT foi submetido a um protocolo de técnicas manuais direcionadas aos músculos respiratórios por 10 sessões. Terminada a intervenção, os dois grupos foram novamente avaliados por manovacuometria. Os dados coletados foram submetidos ao teste de normalidade (Shapiro-Wilk). Se os dados se apresentarem normais, estes eram submetidos ao teste “t” de Student. Caso contrário, eram submetidos ao teste não-paramétrico, do tipo índice de base móvel. Resultados: Um atleta não realizou todas as avaliações e foi excluso da amostra, ficando esta com 15 atletas (GC=7 e GT=8). Os valores de PE Max e de PI Max do grupo controle não se apresentaram normais ao teste “t” de Student e, por isso, todos os dados foram tratados pelo índice de base móvel. Tanto a PE Max quanto a PI Max foram significativamente maiores no GT. Conclusão: As técnicas empregadas foram eficazes em aumentar as pressões pulmonares inspiratória e expiratória no GT.

Drought acclimation among tropical forest shrubs (Psychotria, Rubiaceae).

Mechanisms of dry-season drought resistance were evaluated for five evergreen shrubs (Psychotria, Rubiaceae) which occur syntopically in tropical moist forest in central Panama. Rooting depths, leaf conductance, tissue osmotic potentials and elasticity, and the timing of leaf production were evaluated. From wet to dry season, tissue osmotic potentials declined and moduli of elasticity increased in four and five species, respectively. Irrigation only affected osmotic adjustment by P. furcata. The other seasonal changes in leaf tissue properties represented ontogenetic change. Nevertheless, they made an important contribution to dry-season turgor maintenance. Small between-year differences in dry season rainfall had large effects on plant water status. In 1986, 51 mm of rain fell between 1 January and 31 March, and pre-dawn turgor potentials averaged <0.1 MPa for all five Psychotria species in March (Wright 1991). In 1989, 111 mm of rain fell in the same period, pre-dawn turgor potentials averaged from 0.75 to 1.0 MPa for three of the species in April, and only P. chagrensis lost turgor. The relation between leaf production and drought differed among species. P. limonensis was buffered against drought by the lowest dry-season conductances and the deepest roots (averaging 244% deeper than its congeners) and was the only species to produce large numbers of leaves in the dry season. P. chagrensis was most susceptible to drought, and leaf production ceased as turgor loss developed. For the other species, water stress during severe dry seasons may select against dry-season leaf production.