From tropics to tundra: global convergence in plant functioning.

Despite striking differences in climate, soils, and evolutionary history among diverse biomes ranging from tropical and temperate forests to alpine tundra and desert, we found similar interspecific relationships among leaf structure and function and plant growth in all biomes. Our results thus demonstrate convergent evolution and global generality in plant functioning, despite the enormous diversity of plant species and biomes. For 280 plant species from two global data sets, we found that potential carbon gain (photosynthesis) and carbon loss (respiration) increase in similar proportion with decreasing leaf life-span, increasing leaf nitrogen concentration, and increasing leaf surface area-to-mass ratio. Productivity of individual plants and of leaves in vegetation canopies also changes in constant proportion to leaf life-span and surface area-to-mass ratio. These global plant functional relationships have significant implications for global scale modeling of vegetation-atmosphere CO2 exchange.

Different photosynthesis-nitrogen relations in deciduous hardwood and evergreen coniferous tree species.

The relationship between photosynthetic capacity (A max) and leaf nitrogen concentration (N) among all C3 species can be described roughly with one general equation, yet within that overall pattern species groups or individual species may have markedly different A max-N relationships. To determine whether one or several predictive, fundamental A max-N relationships exist for temperate trees we measured A max, specific leaf area (SLA) and N in 22 broad-leaved deciduous and 9 needle-leaved evergreen tree species in Wisconsin, United States. For broad-leaved deciduous trees, mass-based A max was highly correlated with leaf N (r 2=0.75, P<0.001). For evergreen conifers, mass-based A max was also correlated with leaf N (r 2=0.59, P<0.001) and the slope of the regression (rate of increase of A max per unit increase in N) was lower (P<0.001) by two-thirds than in the broad-leaved species (1.9 vs. 6.4 µmol CO2 g-1 N s-1), consistent with predictions based on tropical rain forest trees of short vs. long leaf life-span. On an area basis, there was a strong A max-N correlation among deciduous species (r 2=0.78, P<0.001) and no correlation (r 2=0.03, P>0.25) in the evergreen conifers. Compared to deciduous trees at a common leaf N (mass or area basis), evergreen trees had lower A max and SLA. For all data pooled, both leaf N and A max on a mass basis were correlated (r 2=0.6) with SLA; in contrast, area-based leaf N scaled tightly with SLA (r 2=0.81), but area-based A max did not (r 2=0.06) because of low A max per unit N in the evergreen conifers. Multiple regression analysis of all data pooled showed that both N (mass or area basis) and SLA were significantly (P<0.001) related to A max on mass (r 2=0.80) and area (r 2=0.55) bases, respectively. These results provide further evidence that A max-N relationships are fundamentally different for ecologically distinct species groups with differing suites of foliage characteristics: species with long leaf life-spans and low SLA, whether broad-leaved or needle-leaved, tend to have lower A max per unit leaf N and a lower slope and higher intercept of the A max-N relation than do species with shorter leaf life-span and higher SLA. A single global A max-N equation overestimates and underestimates A max for temperate trees at the upper and lower end of their leaf N range, respectively. Users of A max-N relationships in modeling photosynthesis in different ecosystems should appreciate the strengths and limitations of regression equations based on different species groupings.

Photosynthesis-nitrogen relations in Amazonian tree species : I. Patterns among species and communities.

Among species, photosynthetic capacity (Amax) is usually related to leaf nitrogen content (N), but variation in the species-specific relationship is not well understood. To address this issue, we studied Amax-N relationships in 23 species in adjacent Amazonian communities differentially limited by nitrogen (N), phosphorus (P), and/or other mineral nutrients. Five species were studied in each of three late successional forest types (Tierra Firme, Caatinga and Bana) and eight species were studied on disturbed sites (cultivated and early secondary successional Tierra Firme plots). Amax expressed on a mass basis (Amass) was correlated (p<0.05) with Nmass in 17 of 23 species, and Amax on an area basis (Aarea) was correlated (p<0.05) with Narea in 21 of 23 species. The slopes of Amax-N relationships were greater and intercepts lower for disturbance adapted early successional species than for late successional species. On a mass basis, the Amax-N slope averaged ≈15 µmol CO2 [g N]-1 s-1 for 7 early secondary successional species and ≈4 µmol CO2 [g N]-1 s-1 for 15 late successional species, respectively. Species from disturbed sites had shorter leaf life-span and greater specific leaf area (SLA) than late successional species. Across all 23 species, the slope of the Amass-Nmass relationship was related (p<0.001) positively to SLA (r2=0.70) and negatively to leaf life-span (r2=0.78) and temporal niche during secondary succession (years since cutting-and-burning, r2=0.90). Thus, disturbance adapted early successional species display a set of traits (short leaf life-span, high SLA and Amax and a steep slope of Amax-N) conducive to resource acquisition and rapid growth in their high resource regeneration niches. The significance and form of the Amax-N relationship were associated with the relative nutrient limitations in the three late successional communities. At species and community levels, Amax was more highly dependent on N in the N-limited Caatinga than in the P-and N-limited Bana and least in the P-and Ca-limited Tierra Firme on oxisol-and differences among these three communities in their massbased Amax-N slope reflects this pattern (6.0, 2.4, and 0.7 µmol CO2 [g N]-1 s-1, respectively). Among all 23 species, the estimated leaf Nmass needed to reach compensation (net photosynthesis ≈ zero) was positively related to the Amass-Nmass slope and to dark respiration rates and negatively related to leaf life-span. Variation among species in the Amax-N slope was well correlated with potential photosynthetic N use efficiency, Amax per unit leaf N. The dependence of Amax on N and the form of the relationship vary among Amazonian species and communities, consistent with both relative availabilities of N, P, and other mineral nutrients, and with intrinsic ecophysiological characteristics of species adapted to habitats of varying resource availability.

Photosynthesis-nitrogen relations in Amazonian tree species : II. Variation in nitrogen vis-a-vis specific leaf area influences mass- and area-based expressions.

The relationships between leaf nitrogen (N), specific leaf area (SLA) (an inverse index of leaf "thickness" or "density"), and photosynthetic capacity (Amax) were studied in 23 Amazonian tree species to characterize scaling in these properties among natural populations of leaves of different ages and light microenvironments, and to examine how variation within species in N and SLA can influence the expression of the Amax-to-N relationship on mass versus area bases. The slope of the Amax-N relationship, change in A per change in N (µmol CO2 gN-1 s-1), was consistently greater, by as much as 300%, when both measures were expressed on mass rather than area bases. The x-intercept of this relationship (N-compensation point) was generally positive on a mass but not an area basis. In this paper we address the causes and implications of such differences. Significant linear relationships (p<0.05) between mass-based leaf N (Nmass) and SLA were observed in 12 species and all 23 regressions had positive slopes. In 13 species, mass-based Amax (Amass) was positively related (p<0.05) with SLA. These patterns reflect the concurrent decline in Nmass and SLA with increasing leaf age. Significant (p<0.05) relationships between area-based leaf N (Narea) and SLA were observed in 18 species. In this case, all relationships had negative slopes. Taken collectively, and consistent in all species, as SLA decreased (leaves become "thicker") across increasing leaf age and light gradients, Nmass also decreased, but proportionally more slowly, such that Narea increased. Due to the linear dependence of Amass on Nmass and a negative 4-intercept, "thicker" leaves (low SLA) therefore tend, on average, to have lower Nmass and Amass but higher Narea than "thinner" leaves. This tendency towards decreasing Amass with increasing Narea, resulting in a lower slope of the Amax-N relationship on an area than mass basis in 16 of 17 species where both were significant. For the sole species exception (higher area than mass-based slope) variation in Narea was related to variation in Nmass and not in SLA, and thus, these data are also consistent with this explanation. The relations between N, SLA and Amax explain how the rate of change in Amax per change in N can vary three-fold depending on whether a mass or area mode of expression is used.

Relative growth rate in relation to physiological and morphological traits for northern hardwood tree seedlings: species, light environment and ontogenetic considerations.

The influence of ontogeny, light environment and species on relationships of relative growth rate (RGR) to physiological and morphological traits were examined for first-year northern hardwood tree seedlings. Three Betulaceae species (Betula papyrifera, Betula alleghaniensis and Ostrya virginiana) were grown in high and low light and Quercus rubra and Acer saccharum were grown only in high light. Plant traits were determined at four ages: 41, 62, 83 and 104 days after germination. In high light (610 µmol m-2 s-1 PPFD), across species and ages, RGR was positively related to the proportion of the plant in leaves (leaf weight ratio, LWR; leaf area ratio, LAR), in situ rates of average canopy net photosynthesis (A) per unit mass (Amass) and per unit area (Aarea), and rates of leaf, stem and root respiration. In low light (127 µmol m-2 s-1 PPFD), RGR was not correlated with Amass and Aarea whereas RGR was positively correlated with LAR, LWR, and rates of root and stem respiration. RGR was negatively correlated with leaf mass per area in both high and low light. Across light levels, relationships of CO2 exchange and morphological characteristics with RGR were generally weaker than within light environments. Moreover, relationships were weaker for plant parameters containing a leaf area component (leaf mass per area, LAR and Aarea), than those that were solely mass-based (respiration rates, LWR and Amass). Across light environments, parameters incorporating the proportion of the plant in leaves and rates of photosynthesis explained a greater amount of variation in RGR (e.g. LWR*Amass, R2=0.64) than did any single parameter related to whole-plant carbon gain. RGR generally declined with age and mass, which were used as scalars of ontogeny. LWR (and LAR) also declined for seven of the eight species-light treatments and A declined in four of the five species in high light. Decreasing LWR and A with ontogeny may have been partially responsible for decreasing RGR. Declines in RGR were not due to increased respiration resulting from an increase in the proportion of solely respiring tissue (roots and stems). In general, although LWR declined with ontogeny, specific rates of leaf, stem, and root respiration also decreased. The net result was that whole-plant respiration rates per unit leaf mass decreased for all eight treatments. Identifying the major determinants of variation in growth (e.g. LWR*Amass) across light environments, species and ontogeny contributes to the establishment of a framework for exploring limits to productivity and the nature of ecological success as measured by growth. The generality of these relationships both across the sources of variation we explored here and across other sources of variation in RGR needs further study.

Growth, biomass distribution and CO2 exchange of northern hardwood seedlings in high and low light: relationships with successional status and shade tolerance.

The physiology, morphology and growth of first-year Betula papyrifera Marsh., Betula alleghaniensis Britton, Ostrya virginiana (Mill.) K. Koch, Acer saccharum Marsh., and Quercus rubra L. seedlings, which differ widely in reported successional affinity and shade tolerance, were compared in a controlled high-resource environment. Relative to late-successional, shade-tolerant Acer and Ostrya species, early-successional, shade-intolerant Betula species had high relative growth rates (RGR) and high rates of photosynthesis, nitrogen uptake and respiration when grown in high light. Fire-adapted Quercus rubra had intermediate photosynthetic rates, but had the lowest RGR and leaf area ratio and the highest root weight ratio of any species. Interspecific variation in RGR in high light was positively correlated with allocation to leaves and rates of photosynthesis and respiration, and negatively related to seed mass and leaf mass per unit area. Despite higher respiration rates, early-successional Betula papyrifera lost a lower percentage of daily photosynthetic CO2 gain to respiration than other species in high light. A subset comprised of the three Betulaceae family members was also grown in low light. As in high light, low-light grown Betula species had higher growth rates than tolerant Ostrya virainiana. The rapid growth habit of sarly-successional species in low light was associated with a higher proportion of biomass distributed to leaves, lower leaf mass per unit area, a lower proportion of biomass in roots, and a greater height per unit stem mass. Variation in these traits is discussed in terms of reported species ecologies in a resource availability context.

Pulmonary function variation in ventilator dependent critically ill infants on peritoneal dialysis.

Four ventilator dependent infants on PD for acute renal failure underwent pulmonary function (PFT) evaluation at varying times in the PD cycle. Mid dwell peak intraperitoneal pressure (IPP) correlated with a significant decrease in pulmonary compliance and increase in air way resistance. This further correlated with a decrease in PO2 and an increase in PCO2 on arterial blood gas analysis. Etiology of the PFT changes appear to correlate most closely with IPP yet other factors including pulmonary artery shunting as well as hypercapnea secondary to a 4.25% dialysate are being evaluated as additional causative factors.

Leaf lifespan as a determinant of leaf structure and function among 23 amazonian tree species.

The relationships between resource availability, plant succession, and species' life history traits are often considered key to understanding variation among species and communities. Leaf lifespan is one trait important in this regard. We observed that leaf lifespan varies 30-fold among 23 species from natural and disturbed communities within a 1-km radius in the northern Amazon basin, near San Carlos de Rio Negro, Venezuela. Moreover, leaf lifespan was highly correlated with a number of important leaf structural and functional characterisues. Stomatal conductance to water vapor (g) and both mass and area-based net photosynthesis decreased with increasing leaf lifespan (r2=0.74, 0.91 and 0.75, respectively). Specific leaf area (SLA) also decreased with increasing leaf lifespan (r2=0.78), while leaf toughness increased (r2=0.62). Correlations between leaf lifespan and leaf nitrogen and phosphorus concentrations were moderate on a weight basis and not significant on an area basis. On an absolute basis, changes in SLA, net photosynthesis and leaf chemistry were large as leaf lifespan varied from 1.5 to 12 months, but such changes were small as leaf lifespan increased from 1 to 5 years. Mass-based net photosynthesis (A/mass) was highly correlated with SLA (r2=0.90) and mass-based leaf nitrogen (N/mass) (r2=0.85), but area-based net photosynthesis (A/area) was not well correlated with any index of leaf structure or chemistry including N/area. Overall, these results indicate that species allocate resources towards a high photosynthetic assimilation rate for a brief time, or provide resistant physical structure that results in a lower rate of carbon assimilation over a longer time, but not both.

Response of Ulmus americana seedlings to varying nitrogen and water status. 1 Photosynthesis and growth.

Well-watered American elm (Ulmus americana L.) seedlings responded to increased nitrate availability with increased leaf nitrogen (N) concentration and photosynthetic rate, larger and more numerous leaves, greater total growth and greater proportional allocation of carbon to shoot than root. Plasticity of growth and carbon allocation were greater than plasticity of N concentration and photosynthetic capacity. For a given N availability, allocation of N per unit leaf area was positively correlated with dry mass per unit leaf area (specific leaf mass), but these relationships differed with N availability. Rates of net photosynthesis and leaf conductance declined logarithmically with decreasing predawn water status. Increased water stress resulted in a greater relative decline in net photosynthesis and leaf conductance for high-N than low-N plants.

Response of Ulmus americana seedlings to varying nitrogen and water status. 2 Water and nitrogen use efficiency in photosynthesis.

Photosynthetic utilization of water and nitrogen in Ulmus americana L. seedlings was tightly linked with the relative availability of each resource. During periodic drying cycles, water use efficiency increased as predawn water potential fell from -0.5 to -2.0 MPa. During the later stages of such drying cycles, the relative contribution of stomatal limitations to the total net photosynthetic limitation appeared to be at its greatest, whereas biochemical limitations were predominant in well-watered plants grown under low nitrogen (N) availability. For any level of leaf water status, water use efficiency of photosynthesis (WUE) was always greater in plants with high leaf N content than in plants with low leaf N content. Photosynthetic nitrogen use efficiency (PNUE) was always greater in plants with low leaf N content than in plants with high leaf N content, for any level of water status. In combined N treatments and predawn water status classes, there was a significant inverse relationship between PNUE and WUE.

Ventilatory threshold and training heart rate in exercising cardiac patients.

The purpose of this study was to determine the relationship between previously prescribed training heart rates (THR) for patients training for six months or more in a cardiac rehabilitation program (CRP), calculated Karvonen percentage heart rate reserve (THRk), and the ventilatory threshold (VT). In twenty male patients (ages 41-63) with documented coronary heart disease (CAD) [non-medicated] mean training heart rate (THR, 75% HRmax) was determined by a telemetry during training sessions. Incremental treadmill testing for determinations of the gas-exchange VT VOE vs. (VO2, Excess CO2) was performed, and the HR at the VT (VTHR) was determined. VO2max was 35.57 +/- 5.57 mL.kg-1.min-1; the VT, expressed as a percentage of VO2max, was 54.45%. The mean THR (133.8 +/- 13.4 bpm) and calculated THRk (141.1 +/- 9.74 bpm) were significantly greater (p less than .05) than the VTHR (124.8 +/- 15.5 bpm), indicating that VT occurs below intensities determined by other methods.

Photosynthetic light acclimation in two rainforest Piper species with different ecological amplitudes.

Piper auritum (H.B. & K.), a pioneer tree restricted to open sites and Piper hispidum (Swartz), a shrub common in sites ranging from recent clearings to shaded understory, both adjust photosynthetic characteristics in response to light availability during growth. The sensitivity of photosynthetic capacity to light availability during growth was indistinguishable for the two species growing in their natural habitat. Photosynthetic capacity was strongly correlated with leaf nitrogen in both species, and the relationship was similar between species. Dark respiration and leaf specific mass were more sensitive to light during growth in P. hispidum, the species with the broad habitat ange, than in P. auritum. In general, similarities between the species were more striking than differences between them. The differences in dark respiration could have important implications for carbon balance. The difference in the responsiveness of leaf specific mass to light indicates that the broad-ranging species maintains access to modes of response little utilized by the open-site specialist. We did not and, in the gas exchange characteristics, any evidence that the open site specialist is better suited than the generalist to high-light sites.

Cardiovascular effects of epinephrine and dipivalyl epinephrine applied topically to the eye in patients with glaucoma.

The cardiovascular effects of topical ophthalmological preparations of 2% epinephrine (EPI), 0.1% dipivalyl epinephrine (DPE), and placebo were studied in double-blind fashion in 20 patients with glaucoma. Both drugs and placebo produced a decrease in heart rate (2 +/- 3 beats/min) which, although small, was highly significant (p less than 0.001). Neither drug not placebo produced a significant effect on mean or systolic blood pressure (BP) over the group as a whole (p greater than 0.1). However, 5 of 20 patients responded to EPI with a significant rise in mean or systolic BP (defined as a change greater than mean change +/- 2 SD), whereas there were no such responses to DPE or placebo. One patient developed marked ventricular ectopy after EPI. We conclude that EPI may cause cardiovascular side effects in a high percentage of patients (25% in this study) through individual susceptibility rather than a predictable effect. DPE, a new epinephrine analogue, appears to be devoid of these effects.

Refractory heart failure.

WHEN A PATIENT WITH CONGESTIVE HEART FAILURE IS NOT RESPONDING OR DETERIORATING WITH TREATMENT, THE FOLLOWING QUESTIONS MUST BE ASKED: 1. Are the symptoms due to heart failure or an associated condition? 2. Has maximum therapy been administered? 3. What is the cause of the heart failure and is there a condition which is amenable to specific therapy? 4. Are there associated conditions which may be responsible for the poor response to treatment? 5. Is the patient a candidate for vasodilator therapy? In spite of all efforts there are some patients who will remain with intractable heart failure, but many with so called refractory failure can be improved when the above points are carefully considered.

Calcific stenosis of a glutaraldehyde-treated porcine bioprosthesis in the aortic position.

The porcine xenograft bioprosthesis is used widely at the present time, although its long-term durability is still being evaluated. Calcification resulting in stenosis of the glutaraldehyde-treated bioprosthesis has been reported infrequently. In the patient described herein, severe calcific stenosis of a porcine xenograft in the aortic position occurred 45 months after implantation. This report emphasizes the life-threatening and rapidly progressive nature of this complication in the long-term survivor after valve replacement.

Graft patency in coronary bypass surgery.

A total of 514 vein bypass grafts and 49 internal mammary (IMA) grafts in 328 patients were studied after operation. Forty-two vein bypass grafts were performed without the use of a pump oxygenator, with a patency rate of 52%. When a pump oxygenator was used, the patency rate for vein bypass grafts was 78%. Patency rates for IMA grafts were 70% and 86%, respectively. In a small group of patients, endarterectomy with vein bypass grafts resulted in a patency rate of 59% in the right coronary artery, 88% in the left anterior descending coronary artery, and 74% in the circumflex artery. Except for the right coronary artery, these results compare favorably with those from vein bypass graft patency without endarterectomy. On the basis of these findings, insertion of bypass grafts into the coronary arteries without the use of a pump oxygenator cannot be recommended, unless the technique employed can be shown to produce graft patency rates comparable to those resulting from grafts done with the use of a pump oxygenator. Endarterectomy to the left anterior descending and circumflex arteries would not appear to affect vein bypass graft patency.

Ventricular aneurysm following myocardial infarction.

Cineradiographic examination appears to be the best method for the study of cardiac pulsations. Fifty consecutive patients, who had sustained transmural myocardial infarction at least six months previously, were studied by this technique. Thirty-six had some abnormality of pulsation and eight had dynamic ventricular aneurysm. Six of the eight had suffered severe infarct. Functional recovery in those with aneurysm was not as complete as in the rest of the group. Two made a poor functional recovery, two a fair recovery, and four a moderately good recovery. Clinically, there were no systemic emboli in the patients with dynamic aneurysms. Five of the 50 had persistent ST-segment elevation and "coving" of the T waves; three of these patients had aneurysms. There was no good correlation between the electrocardiographic site of the infarct and the site of the abnormal pulsation.