Co2 exchange and biomass development of the herbaceous vegetation in the portuguese montado ecosystem during spring

Montado are spatially heterogeneous ecosystems that are economically important for the production of cork and herbaceous biomass that provide fodder for animals. Understanding of how trees and the herbaceous layer interact to determine pasture yield and the overall CO2 exchange of the herbaceous layer is crucial. Portable chamberswere used to study CO2 exchange by the herbaceous layer component of the montado ecosystem in southern Portugal. Biomass, Net herbaceous layer CO2 exchange (NEE) and respiration (Reco) were measured in the open and understory locations between March and May, during the active growing period. Parameter fits on the NEE data were performed using empirical hyperbolic light response model, while ecosystem respiration (Reco) data were fitted with a two-parameter exponential model. Annual green biomass productions were 405.8 9.0 and 250.6 6.3 g m 2 in the open and the understory, respectively. The respective maximum NEE during the day were 24.0 2.9 and 9.6 2.2 mmol m 2 s 1 while maximum Reco were 20.6 2.2 and 10.0 1.6 mmol m 2 s 1, occurring in April. Photosynthetic photon flux density (PPFD) explained more that 70% of variations in daytime NEE while soil temperature at 10 cm depth (Tsoil) explained >50% of the variations in Reco under non-limiting soil moisture conditions. Both the herbaceous layer communities shared similar plant functional types and no significant difference in nutrient nitrogen (N) occurred between them. The two herbaceous layer components shared similar physiological characteristics and differences that arose in their CO2 uptake capacities and green biomass production were the result of microclimatic differences created by tree shadin

The rate of nitrite reduction in leaves as indicated by O2 and CO2 exchange during photosynthesis

Light response (at 300 ppm CO2 and 10–50 ppm O2 in N2) and CO2 response curves [at absorbed photon fluence rate (PAD) of 550 μmol m−2 s−1] of O2 evolution and CO2 uptake were measured in tobacco (Nicotiana tabacum L.) leaves grown on either NO3− or NH4+ as N source and in potato (Solanum tuberosum L.), sorghum (Sorghum bicolor L. Moench), and amaranth (Amaranthus cruentus L.) leaves grown on NH4NO3. Photosynthetic O2 evolution in excess of CO2 uptake was measured with a stabilized zirconia O2 electrode and an infrared CO2 analyser, respectively, and the difference assumed to represent the rate of electron flow to acceptors alternative to CO2, mainly NO2−, SO42−, and oxaloacetate. In NO3−-grown tobacco, as well as in sorghum, amaranth, and young potato, the photosynthetic O2–CO2 flux difference rapidly increased to about 1 μmol m−2 s−1 at very low PADs and the process was saturated at 50 μmol quanta m−2 s−1. At higher PADs the O2–CO2 flux difference continued to increase proportionally with the photosynthetic rate to a maximum of about 2 μmol m−2 s−1. In NH4+-grown tobacco, as well as in potato during tuber filling, the low-PAD component of surplus O2 evolution was virtually absent. The low-PAD phase was ascribed to photoreduction of NO2− which successfully competes with CO2 reduction and saturates at a rate of about 1 μmol O2 m−2 s−1 (9% of the maximum O2 evolution rate). The high-PAD component of about 1 μmol O2 m−2 s−1, superimposed on NO2− reduction, may represent oxaloacetate reduction. The roles of NO2−, oxaloacetate, and O2 reduction in the regulation of ATP/NADPH balance are discussed

Cognitive behavioral therapy of socially phobic children focusing on cognition: a randomised wait-list control study

BACKGROUND: Although literature provides support for cognitive behavioral therapy (CBT) as an efficacious intervention for social phobia, more research is needed to improve treatments for children. METHODS: Forty four Caucasian children (ages 8-14) meeting diagnostic criteria of social phobia according to the Diagnostic and Statistical Manual of Mental Disorders (4th ed.; APA, 1994) were randomly allocated to either a newly developed CBT program focusing on cognition according to the model of Clark and Wells (n = 21) or a wait-list control group (n = 23). The primary outcome measure was clinical improvement. Secondary outcomes included improvements in anxiety coping, dysfunctional cognitions, interaction frequency and comorbid symptoms. Outcome measures included child report and clinican completed measures as well as a diagnostic interview. RESULTS: Significant differences between treatment participants (4 dropouts) and controls (2 dropouts) were observed at post test on the German version of the Social Phobia and Anxiety Inventory for Children. Furthermore, in the treatment group, significantly more children were free of diagnosis than in wait-list group at post-test. Additional child completed and clinician completed measures support the results. DISCUSSION: The study is a first step towards investigating whether CBT focusing on cognition is efficacious in treating children with social phobia. Future research will need to compare this treatment to an active treatment group. There remain the questions of whether the effect of the treatment is specific to the disorder and whether the underlying theoretical model is adequate. CONCLUSION: Preliminary support is provided for the efficacy of the cognitive behavioral treatment focusing on cognition in socially phobic children. Active comparators should be established with other evidence-based CBT programs for anxiety disorders, which differ significantly in their dosage and type of cognitive interventions from those of the manual under evaluation (e.g. Coping Cat)

Metabolic control of photosynthetic electron transport in crassulacean acid metabolism-induced Mesembryanthemum crystallinum

We investigated photosynthetic electron transport in leaves of the facultative crassulacean acid metabolism (CAM) plant Mesembryanthemum crystallinum L. After CAM induction, electron transport exhibited variable redox kinetics during the diurnal CAM cycle. In CAM Phase IV, most of PSI (P-700) and chlorophyll a fluorescence relaxed with a halftime of 20 ms after a saturating light pulse. This time-constant may reflect the overall linear electron flux from PSII to PSI in saturating light. Comparable relaxation kinetics were also determined for C-3 plants. At the end of CAM Phase I and during Phase II, slow components (> 50% of signal amplitude) appeared in both P-700 reduction and fluorescence relaxation. They displayed halftimes > 250 ms and > 1 s, suggesting a strong restriction of the linear electron flux from H2O to NADP. The appearance of the slow redox components was accompanied by a decrease in the F-v/F-m ratio of chlorophyll a fluorescence, suggesting a reversible detachment of light-harvesting complex (LHC) II from PSII. The slow redox fractions and the depression of F-v/F-m disappeared again in parallel to malate decarboxylation during CAM Phase III. We discuss a reversible downregulation of linear electron flux during CAM Phases II and III, due to a reversible deprivation of cytochrome-b(6)f complexes (cyt-bfs) and PSI from the linear system. In parallel, a redistribution of some LHCIIs could also occur. This could be an adaptive response to a reduced metabolic demand for NADPH due to a limited carbon flux through the Calvin cycle, resulting from low Rubisco activation. Furthermore, the cyt-bfs and PSIs deprived of linear electron transport could support cyclic electron flux to cover an increased ATP demand during gluconeogenesis in CAM Phase III