Modelling assimilation and intercellular CO2 from measured conductance: a synthesis of approaches

A spectrum of models that estimate assimilation rate A from intercellular carbon dioxide concentration (C_i) and measured stomatal conductance to CO₂ (g_c) were investigated using leaf‐level gas exchange measurements. The gas exchange measurements were performed in a uniform loblolly pine stand (Pinus taeda L.) using the Free Air CO₂ Enrichment (FACE) facility under ambient and elevated atmospheric CO₂ for 3 years. These measurements were also used to test a newly proposed framework that combines basic properties of the A–C_i curve with a Fickian diffusion transport model to predict the relationship between C_i/C_a and g_c, where C_a is atmospheric carbon dioxide concentration. The widely used Ball–Berry model and five other models as well as the biochemical model proposed by Farquhar et al. (1980) were also reformulated to express variations in C_i/C_a as a function of their corresponding driving mechanisms. To assess the predictive capabilities of these approaches, their respective parameters were estimated from independent measurements of long‐term stable carbon isotope determinations (δ¹³C), meteorological variables, and ensemble A–C_i curves. All eight approaches reproduced the measured A reasonably well, in an ensemble sense, from measured water vapour conductance and modeled C_i/C_a. However, the scatter in the instantaneous A estimates was sufficiently large for both ambient and elevated C_a to suggest that other transient processes were not explicitly resolved by all eight parameterizations. An important finding from our analysis is that added physiological complexity in modeling C_i/C_a (when g_c is known) need not always translate to increased accuracy in predicting A. Finally, the broader utility of these approaches to estimate assimilation and net ecosystem exchange is discussed in relation to elevated atmospheric CO₂.     

Canopy leaf area of a mature evergreen Eucalyptus woodland does not respond to elevated atmospheric [CO2] but tracks water availability

Canopy leaf area, quantified by the leaf area index (L), is a crucial driver of forest productivity, water use and energy balance. Because L responds to environmental drivers, it can represent an important feedback to climate change, but its responses to rising atmospheric [CO₂] and water availability of forests have been poorly quantified. We studied canopy leaf area dynamics for 28 months in a native evergreen Eucalyptus woodland exposed to free‐air CO₂ enrichment (the EucFACE experiment), in a subtropical climate where water limitation is common. We hypothesized that, because of expected stimulation of productivity and water‐use efficiency, L should increase with elevated [CO₂]. We estimated L from diffuse canopy transmittance, and measured monthly leaf litter production. Contrary to expectation, L did not respond to elevated [CO₂]. We found that L varied between 1.10 and 2.20 across the study period. The dynamics of L showed a quick increase after heavy rainfall and a steady decrease during periods of low rainfall. Leaf litter production was correlated to changes in L, both during periods of decreasing L (when no leaf growth occurred) and during periods of increasing L (active shedding of old foliage when new leaf growth occurred). Leaf lifespan, estimated from mean L and total annual litter production, was up to 2 months longer under elevated [CO₂] (1.18 vs. 1.01 years; P = 0.05). Our main finding that L was not responsive to elevated CO₂ is consistent with other forest FACE studies, but contrasts with the positive response of L commonly predicted by many ecosystem models.     

Interaction with Shelter Dogs Reduces Negative Affect of Adolescents in Substance Use Disorder Treatment

We investigated the effectiveness of a human–animal interaction program, involving dogs from an animal shelter, in improving affect of adolescent males in inpatient treatment for substance use disorder (SUD). We hypothesized that adolescents would experience improvements in affect and attitudes toward activities when participating in human–dog interaction activities (dog-interaction condition) compared with “treatment-as-is” recreational activities (control condition). Participants were assigned to weekly 1-h-long condition activities for 8 weeks (4 weeks per condition). Due to attrition, only the participants’ first and second exposures to each condition were evaluated. Using a withinand between-subjects, repeated measures crossover design, we assessed effects of the two conditions on affective states as indexed by Positive and Negative Affect Scale-Expanded Form (PANAS-X) subscales (mixed linear model, n = 12). Attitudes toward doginteraction and control activities were assessed using a researcher-generated survey (ordered logistic regression, n = 14, mean age = 16.2 years). Condition impacted Hostility (F_(1,31) = 6.55, p < 0.05) and Sadness (F_(1,41) = 4.62, p < 0.05) subscale scores; scores were higher following the control condition and lower following the dog-interaction condition. There was a carryover effect of condition in the previous activity session on Sadness scores during the current activity session (F_(1,41) = 4.32, p < 0.05), suggesting that the prior session experience affected current expectations. In the attitudes survey, the dog-interaction condition elicited more positive responses than the control condition (X² ≥ 4.10, df = 1, p < 0.05). From this exploratory study, we conclude that the dog-interaction activities induced an improvement in affect, specifically within dimensions of negative affect, and participants had a more favorable attitude toward the dog activities than the treatment-as-is activities. Offering activities involving interaction with shelter dogs thus shows promise as a useful method for restoring responsiveness to naturally reinforcing (non-substance-related) affective stimuli in adolescents with SUD.     

A gas chromatographic-mass spectrometric analysis of the esterifying alcohols of pumpkin seed protochlorophylls

The esterifying alcohols of protochlorophyll a and 4-vinyl-(4-desethyl)-protochlorophyll a (purified as the respective pheophytins) from pumpkin seeds were examined by gas chromatography-mass spectrometry. The results of the analysis suggested that pumpkin seed protochlorophyll a is esterified with all possible C₂₀ isoprenoid alcohols between and including geranylgeraniol and phytol, phytol comprising 90% or more of the mixture of esterifying alcohols, and that the 4-vinyl-(4-desethyl)-protochlorophyll a is esterified with farnesol and all possible C₂₀ isoprenoid alcohols between and including geranylgeranoid and phytanol, phytol comprising 50% or more of the mixture of esterifying alcohols. The 4-vinyl-(4-desethyl)-protochlorophyll a from a sample of older mature pumpkin seeds was found to be richer in esterifying alcohols corresponding to isoprenoid precursors of phytol then was the 4-vinyl-(4-desethyl)-protochlorophyll a from a sample of younger mature seeds. Other isoprenoid alcohols may have been present in very minor quantities in the mixtures of esterifying alcohols from the pumpkin seed protochlorophylls but were not looked for in this study. These results are discussed in terms of a biosynthetic accumulation of 4-vinyl-(4-desethyl)-protochlorophyll a in pumpkin inner seed-coat tissue.     

Pulmonary prostacyclin production with increased flow and sympathetic stimulation

We evaluated the effects of an abrupt increase in flow and of a subsequent sympathetic nerve stimulation on the pulmonary production of prostacyclin (PGI2) and thromboxane A2 (TXA2) in canine isolated left lower lobes perfused in situ with pulsatile flow. When flow was abruptly increased from 50 +/- 3 to 288 +/- 2 ml/min, mean pulmonary arterial pressure (Ppa) increased by 15 +/- 2 Torr and then declined by 2.4 Torr over the next 5 min. This secondary decrease in Ppa was associated with a significant 0.26 +/- 0.11 ng/ml increase in the pulmonary venous concentration of the stable PGI2 hydrolysis product 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) as determined by radioimmunoassay. Stimulation of the left stellate ganglion usually resulted in an increase in Ppa which peaked at 1.1 +/- 0.6 Torr above its prestimulus level and then declined over the next 5 min. Associated with this decline was a 0.24 +/- 0.11 ng/ml increase in 6-keto-PGF1 alpha at 1 min. We suggest that the decline in Ppa is due to the synthesis and release of PGI2 by the endothelial cells in response to an increase in perfusion pressure.     

INCORPORATION OF TRITIATED THYMIDINE IN THE CELLS OF CAENORHABDITIS BRIGGSAE (NEMATODA) REARED IN AXENIC CULTURE

In the rhabditid nematode Caenorhabditis briggsae the incorporation of thymidine-H³ has been studied by autoradiography after Feulgen staining, with animals maintained under axenic conditions in a medium of only partly defined composition. Labeling has been followed in adults left in the presence of thymidine-H³ for periods of from ½ to 24 hours, as well as in adults reared from larvae in the presence of the tritiated nucleoside. A massive incorporation is found in the nuclei of the gonads and intestine; also a less intense particulate cytoplasmic incorporation is clear in certain cells, especially those of the intestine. In general, all labeling has proved to be sensitive to DNase, but resistant to RNase. The label's stability has been tested by the transfer of adults into a medium containing "cold" thymidine. They remain there for up to 48 hours. A transfer for 24 hours results in a considerable decrease in the intensity of nuclear and cytoplasmic labeling; a stay of 48 hours leads to its complete disappearance from non-dividing (intestinal) as well as dividing (gonadal) nuclei. A phenomenon of DNA turnover is envisaged and discussed as a possible physiological attribute of C. briggsae.