Exposure to nuclear magnetic resonance imaging procedure attenuates morphine-induced analgesia in mice

Adult male mice exposed to a Nuclear Magnetic Resonance Imaging (NMRI) procedure during the mid-dark period and injected with morphine (10 mg/kg) failed to exhibit the normal nocturnally enhanced morphine analgesia response to a thermal stimulus that was displayed by mice exposed to a sham imaging procedure and treated with morphine (p less than .01). When tested during the mid-light period, animals exposed to the NMRI procedure and given morphine displayed attenuated analgesia levels relative to sham exposed mice (p less than .01) treated with morphine. However, the morphine induced analgesia was not totally abolished since the imaged mice still exhibited analgesia relative to saline treated mice (p less than .01). These results suggest that the magnetic and/or radio-frequency fields associated with the NMRI procedure alter both day- and night-time responses to morphine. These results may reflect magnetic field induced alterations in neuronal calcium binding and/or alterations in nocturnal pineal gland activity.     

Reduction of molecular gas diffusion through gaskets in leaf gas exchange cuvettes by leaf‐mediated pores

There is an ongoing debate on how to correct leaf gas exchange measurements for the unavoidable diffusion leakage that occurs when measurements are done in non‐ambient CO₂ concentrations. In this study, we present a theory on how the CO₂ diffusion gradient over the gasket is affected by leaf‐mediated pores (LMP) and how LMP reduce diffusive exchange across the gaskets. Recent discussions have so far neglected the processes in the quasi‐laminar boundary layer around the gasket. Counter intuitively, LMP reduce the leakage through gaskets, which can be explained by assuming that the boundary layer at the exterior of the cuvette is enriched with air from the inside of the cuvette. The effect can thus be reduced by reducing the boundary layer thickness. The theory clarifies conflicting results from earlier studies. We developed leaf adaptor frames that eliminate LMP during measurements on delicate plant material such as grass leaves with circular cross section, and the effectiveness is shown with respiration measurements on a harp of Deschampsia flexuosa leaves. We conclude that the best solution for measurements with portable photosynthesis systems is to avoid LMP rather than trying to correct for the effects.     

Stem respiration and carbon dioxide efflux of young <Emphasis Type="Italic">Populus deltoides</Emphasis> trees in relation to temperature and xylem carbon dioxide concentration

Oxidative respiration is strongly temperature driven. However, in woody stems, efflux of CO₂ to the atmosphere (E _A), commonly used to estimate the rate of respiration (R _S), and stem temperature (T _st) have often been poorly correlated, which we hypothesized was due to transport of respired CO₂ in xylem sap, especially under high rates of sap flow (f _s). To test this, we measured E _A, T _st, f _s and xylem sap CO₂ concentrations ([CO₂*]) in 3-year-old Populus deltoides trees under different weather conditions (sunny and rainy days) in autumn. We also calculated R _S by mass balance as the sum of both outward and internal CO₂ fluxes and hypothesized that R _S would correlate better with T _st than E _A. We found that E _A sometimes correlated well with T _st, but not on sunny mornings and afternoons or on rainy days. When the temperature effect on E _A was accounted for, a clear positive relationship between E _A and xylem [CO₂*] was found. [CO₂*] varied diurnally and increased substantially at night and during periods of rain. Changes in [CO₂*] were related to changes in f _s but not T _st. We conclude that changes in both respiration and internal CO₂ transport altered E _A. The dominant component flux of R _S was E _A. However, on a 24-h basis, the internal transport flux represented 9–18% and 3–7% of R _S on sunny and rainy days, respectively, indicating that the contribution of stem respiration to forest C balance may be larger than previously estimated based on E _A measurements. Unexpectedly, the relationship between R _S and T _st was sometimes weak in two of the three trees. We conclude that in addition to temperature, other factors such as water deficits or substrate availability exert control on the rate of stem respiration so that simple temperature functions are not sufficient to predict stem respiration.     

Pinus taeda forest growth predictions in the 21st century vary with site mean annual temperature and site quality

Climate projections from 20 downscaled global climate models (GCMs) were used with the 3‐PG model to predict the future productivity and water use of planted loblolly pine (Pinus taeda) growing across the southeastern United States. Predictions were made using Representative Concentration Pathways (RCP) 4.5 and 8.5. These represent scenarios in which total radiative forcing stabilizes before 2100 (RCP 4.5) or continues increasing throughout the century (RCP 8.5). Thirty‐six sites evenly distributed across the native range of the species were used in the analysis. These sites represent a range in current mean annual temperature (14.9–21.6°C) and precipitation (1,120–1,680 mm/year). The site index of each site, which is a measure of growth potential, was varied to represent different levels of management. The 3‐PG model predicted that aboveground biomass growth and net primary productivity will increase by 10%–40% in many parts of the region in the future. At cooler sites, the relative growth increase was greater than at warmer sites. By running the model with the baseline [CO₂] or the anticipated elevated [CO₂], the effect of CO₂ on growth was separated from that of other climate factors. The growth increase at warmer sites was due almost entirely to elevated [CO₂]. The growth increase at cooler sites was due to a combination of elevated [CO₂] and increased air temperature. Low site index stands had a greater relative increase in growth under the climate change scenarios than those with a high site index. Water use increased in proportion to increases in leaf area and productivity but precipitation was still adequate, based on the downscaled GCM climate projections. We conclude that an increase in productivity can be expected for a large majority of the planted loblolly pine stands in the southeastern United States during this century.     

Physiological attributes of three- and four-needle fascicles of loblolly pine (<Emphasis Type="Italic">Pinus taeda</Emphasis> L.)

Key message

Fascicle types differed morphologically but had similar photosynthetic capacity on a surface area basis.

Abstract

In Pinus species, fascicles can develop with a different number of needles than what is typical. For example, Pinus taeda fascicles typically have three needles, but sometimes have two or four. Although differing fascicle morphology could be a response to changes in the environment designed to optimize carbon gain or minimize water loss, we are unaware of any work comparing physiological differences between fascicles with different numbers of needles. We compared the physiological and morphological characteristics of three- and four-needle fascicles of a loblolly pine clone with an abnormally high abundance of four-needle fascicles to better understand whether differences in needle morphology affected photosynthetic capacity or transpiration. Three- and four-needle fascicles had equal length, diameter, and volume, but four-needle fascicles had significantly greater surface area, mass, and tissue density. Equal fascicle total volume resulted in smaller per-needle volume in four-needle fascicles compared to three-needle fascicles. On a unit surface area basis, light-saturated net assimilation, stomatal conductance and transpiration were similar between the three- and four-needle fascicles although the maximum rate of carboxylation was significantly greater in four-needle fascicles. On a per-fascicle basis, four-needle fascicles had greater transpiration, stomatal conductance, and maximum rate of light-saturated net assimilation. Our results suggest that several factors, including increased tissue density and stomatal density, offset the reduction in needle volume in four-needle fascicles, resulting in similar levels of gas exchange per unit surface area in three- and four-needle fascicles.

     

A simple calibration improved the accuracy of the thermal dissipation technique for sap flow measurements in juvenile trees of six species

The thermal dissipation technique is widely used to estimate transpiration of individual trees and forest stands, but there are conflicting reports regarding its accuracy. We compared the rate of water uptake by stems of six tree species in potometers with sap flow (F _S) estimates derived from thermal dissipation sensors to evaluate the accuracy of the technique. To include the full range of xylem anatomies (i.e., diffuse-porous, ring-porous, and tracheid), we used saplings of sweetgum (Liquidambar styraciflua), eastern cottonwood (Populus deltoides), white oak (Quercus alba), American elm (Ulmus americana), shortleaf pine (Pinus echinata), and loblolly pine (Pinus taeda). In almost all instances, estimated F _S deviated substantially from actual F _S, with the discrepancy in cumulative F _S ranging from 9 to 55%. The thermal dissipation technique generally underestimated F _S. There were a number of potential causes of these errors, including species characteristics and probe construction and installation. Species with the same xylem anatomy generally did not show similar relationships between estimated and actual F _S, and the largest errors were in species with diffuse-porous (Populus deltoides, 34%) and tracheid (Pinus taeda, 55%) xylem anatomies, rather than ring-porous species Quercus alba (9%) and Ulmus americana (15%) as we had predicted. New species-specific α and β parameter values only modestly improved the accuracy of F _S estimates. However, the relationship between the estimated and actual F _S was linear in all cases and a simple calibration based on the slope of this relationship reduced the error to 1–4% in five of the species, and to 8% in Liquidambar styraciflua. Our calibration approach compensated simultaneously for variation in species characteristics and sensor construction and use. We conclude that species-specific calibrations can substantially increase the accuracy of the thermal dissipation technique.     

Stem CO2 efflux of ten species in temperate forests in Northeastern China

Stem CO₂ efflux (E _S) is an important component of forest ecosystem carbon budgets and net ecosystem CO₂ exchange, but little is known about E _S in temperate forests in Northeastern China, an area with a large extent of forest. We measured E _S along with stem temperature at 1?cm depth (Ts) over a 9?month period in 2007 on ten dominant tree species of secondary forests of the region. Other measurements included the autotrophic component of soil CO₂ efflux (E _A) and stem diameter at breast height (DBH). Our objectives were to (1) examine the seasonal patterns and species differences in E _S, and (2) determine the correlations between E _S and Ts, DBH and E _A. Mean E _S for the measurement period ranged from 1.09 to 1.74?μmol?CO₂?m^?2?s^?1 among the ten species. The sensitivity of E _S to Ts (Q ₁₀ ) ranged from 1.87 to 2.61. Across the ten species 57–89% of variation in E _S was explained by T _S and DBH. There was also a linear relationship between mean E _S and E _A. E _S was better predicted by Ts in the dormant season than the growing season, indicating that additional factors such as growth respiration and internal transport of CO₂ in the xylem became more important contributors to E _S during the growing season. Stem CO₂ efflux increased, and Q ₁₀ decreased, with increasing DBH in all species. Although temperature exerts strong control on the rate of cellular respiration, we conclude that in tree stems in situ, T _S, DBH and many other factors affect the relationship between CO₂ evolution by respiring cells and the diffusion of CO₂ to the stem surface.     

Differences in growth and water relations among Phaseolus vulgaris cultivars in response to induced drought stress

Relatively little ecophysiological research has been conducted to determine the responses to drought of Phaseolus vulgaris. Four bean cultivars (cvs.) from Brazil, A320, Carioca, Ouro Negro and Xodó were submitted to an imposed water deficit in order to evaluate the importance of some adaptive mechanisms of drought resistance through the analysis of growth parameters, water status, gas exchange and indicators of tolerance mechanisms at the cellular level. During the drought treatment, relative growth rates were more reduced for A320 and Xodó than Carioca and Ouro Negro. A320 closed its stomata very rapidly and complete stomatal closure was obtained at Psi(w)=-0.6 MPa, in contrast to the other cvs. where stomata were fully closed only at Psi(w)=-0.9 MPa. Net assimilation rates were closely related to stomatal conductances. Mechanisms at the cellular level appeared to be mostly important for higher tolerance. Carioca and Ouro Negro, when compared to A320 and Xodó, were characterized by having better drought tolerance mechanisms and higher tissue water retention capacity leading to a better growth under water deficits. The leaf dehydration rates of those cvs. were slow whereas those of the drought sensitive cvs. were rapid. The results were confirmed by the electrolyte leakage test and leaf osmotic potential measurements, which indicated higher membrane resistance and osmotic adjustment in the two tolerant cvs. Carioca and Ouro Negro. It appears from this study that despite being cultivated in the same geographical region, the four cvs. of P. vulgaris displayed somewhat different drought adaptive capacities for prolonged drought during the vegetative phase.