Interaction of nutrient limitation and elevated CO2 concentration on carbon assimilation of a tropical tree seedling (Cedrela odorata).

Carbon assimilation by Cedrela odorata L. (Meliaceae) seedlings was investigated in ambient and elevated CO2 concentrations ([CO2]) for 119 days, using small fumigation chambers. A solution containing macro- and micronutrients was supplied at two rates. The 5% rate (high rate) was designed to avoid nutrient limitation and allow a maximum rate of growth. The 1% rate (low rate) allowed examination of the effect of the nutrient limitation-elevated CO2 interaction on carbon assimilation. Root growth was stimulated by 23% in elevated [CO2] at a high rate of nutrient supply, but this did not lead to a change in the root:shoot ratio. Total biomass did not change at either rate of nutrient supply, despite an increase in relative growth rate at the low nutrient supply rate. Net assimilation rates and relative growth rates were stimulated by the high rate of nutrient addition, irrespective of [CO2]. We used a biochemical model of photosynthesis to investigate assimilation at the leaf level. Maximum rate of electron transport (Jmax) and maximum velocity of carboxylation (Vcmax) did not differ significantly with CO2 treatment, but showed a substantial reduction at the low rate of nutrient supply. Across both CO2 treatments, mean Jmax for seedlings grown at a high rate of nutrient supply was 75 micromol m(-2) s(-1) and mean Vcmax was 27 micromol m(-2) s(-1). The corresponding mean values for seedlings grown at a low rate of nutrient supply were 36 micromol m(-2) s(-1) and 15 micromol m(-2) s(-1), respectively. Concentrations of leaf nitrogen, on a mass basis, were significantly decreased by the low nutrient supply rate, in proportion to the observed decrease in photosynthetic parameters. Chlorophyll and carbohydrate concentrations of leaves were unaffected by growth [CO2]. Because there was no net increase in growth in response to elevated [CO2], despite increased assimilation of carbon at the leaf level, we hypothesize that the rate of respiration of non-photosynthetic organs was increased.

Photosynthetic capacity in a central Amazonian rain forest.

The vertical profile in leaf photosynthetic capacity was investigated in a terra firme rain forest in central Amazonia. Measurements of photosynthesis were made on leaves at five levels in the canopy, and a model was fitted to describe photosynthetic capacity for each level. In addition, vertical profiles of photosynthetic photon flux density, leaf nitrogen concentration and specific leaf area were measured. The derived parameters for maximum rate of electron transport (J(max)) and maximum rate of carboxylation by Rubisco (V(cmax)) increased significantly with canopy height (P < 0.05). The highest J(max) for a single canopy level was measured at the penultimate canopy level (20 m) and was 103.9 &mgr;mol m(-2) s(-1) +/- 24.2 (SE). The highest V(cmax) per canopy height was recorded at the top canopy level (24 m) and was 42.8 +/- 5.9 &mgr;mol m(-2) s(-1). Values of J(max) and V(cmax) at ground level were 35.8 +/- 3.3 and 20.5 +/- 1.3 &mgr;mol m(-2) s(-1), espectively. The increase in photosynthetic capacity with increasing canopy height was strongly correlated with leaf nitrogen concentration when examined on a leaf area basis, but was only weakly correlated on a mass basis. The correlation on an area basis can be largely explained by the concomitant decrease in specific leaf area with increasing height. Apparent daytime leaf respiration, on an area basis, also increased significantly with canopy height (P < 0.05). We conclude that canopy photosynthetic capacity can be represented as an average vertical profile, perturbations of which may be explained by variations in the environmental variables driving photosynthesis.

Do mite avoidance measures affect mite and cat airborne allergens?

BACKGROUND: Effective mite allergen avoidance measures are presumed to reduce airborne allergens yet the quantity in the air is rarely measured. OBJECTIVE: To monitor airborne allergen during a placebo-controlled mite allergen avoidance study. METHODS: Bedrooms of 56 atopic asthmatic children were randomly allocated to hot washing and encasing covers + acaricide (active regime) or placebo treatment. Dust was collected from the mattress, bedding and carpets; airborne allergen was measured using Casella samplers and dust settling in open Petri dishes. Der p 1, Der p 2 and Fel d 1 were measured. RESULTS: After 24 weeks of mite allergen avoidance the Casella air-samplers collected Der p 1 less frequently in active than placebo-treated bedrooms (0 vs. 29%, P<0.05) and Petri dishes in the active group collected less than baseline (0.2 vs. 0.6 ng/day P<0.05). Homes without cats had less cat allergen than cat-owning homes and when actively treated for 24 weeks showed a greater reduction (P = 0.03) in mattress cat allergen than the placebo group. CONCLUSION: Encasing covers and hot washing of bed linen reduced mite aeroallergen (and mattress cat allergen in the absence of cats). This could mean dual benefits to a patient sensitive to both mite and cat.

The respiratory effects of reduction of mite allergen in the bedrooms of asthmatic children--a double-blind controlled trial.

BACKGROUND: Inhalation of house dust mite (HDM) allergen may provoke attacks of asthma. OBJECTIVE: We investigated whether a double-blind placebo-controlled community-based study aimed at reducing the HDM allergens in the bedrooms of HDM sensitive asthmatic children using the best methods available would prove beneficial to the children's health. METHODS: The children (mean age 9.9 years, 34 boys) were recruited by a questionnaire submitted to 7386 families in a geographically-defined area of the UK. Subjects were chosen to take part in the double-blind placebo-controlled trial if they were asthmatic, skin sensitive to mites, and had mite allergen in their mattresses. Seventy children were randomly allocated to groups. In the active group, the children's bedrooms were treated with an acaricide (Acarosan) and the mattresses, pillows and duvets were encased in exclusion covers. The control group received placebo treatments. RESULTS: Forty-nine complete data sets were obtained. Applying bedding covers and Acarosan led to a median reduction of 480 ng (100%) in mite allergen on the mattress vs 215 ng (53%) reduction in placebo-treated group by 6 weeks. No evidence was found that the acaricide reduced mite allergen level. A change in bronchial reactivity to histamine was observed in the children after 6 weeks. This was not associated with any change in thrice-daily records of peak expiratory flow rate. By 24 weeks, the actively-treated children had improved forced expiratory volume in 1s (FEV1) and fewer required bronchodilator therapy or reported asthmatic symptoms than did the controls. CONCLUSIONS: The results suggest that mite removal procedures may modestly improve mite-sensitive asthmatics and could perhaps be of value in exceptionally mite-sensitive and/or highly mite-exposed individuals whose response to the attempted removal should be measured.

Early focal abnormalities on chest radiographs and respiratory prognosis in children with cystic fibrosis.

The variable rate of progression of respiratory disease in cystic fibrosis demands reliable prognostic markers for rational treatment. This study aims to determine whether or not focal abnormalities on chest radiographs during the early clinical course of cystic fibrosis could be used as such a marker. A retrospective review of patient records was carried out. Demographic details, genotype, presentation, and course of respiratory disease over the first 6 years were recorded for all patients, together with spirometry and chest radiograph scores at 7 and 13 years for surviving patients. Comparison was made between those with and those without documented focal opacification on chest radiography during the first 6 years of life. 30 patients satisfied the study entry criteria and had complete records available. Of these, 17 had focal consolidation documented during the first 6 years, and 13 did not. Survival was significantly worse in those with previous consolidation (p < 0.01), as was peak expiratory flow at 7 years (p = 0.02). There were no other statistically significant differences between the groups, although those with previous consolidation apparently had worse lung function and more advanced disease on chest radiography at both 7 and 13 years. This study suggests that early focal chest radiographic abnormalities may predict a poorer outcome in cystic fibrosis.

A combined approach to reduce mite allergen in the bedroom.

BACKGROUND: Asthma is a common chronic disease of childhood. House dust mite (HDM) are known to be a major source of allergen affecting atopic asthmatics. No single control method has been demonstrated to consistently reduce asthma. OBJECTIVE: We investigated the effect of a combination of two methods of HDM allergen control on HDM allergen content in the bedding and carpets of asthmatic children. METHODS: This was a double-blind placebo-controlled trial treating the bedrooms of 56 mite-sensitive asthmatic children. The carpet and the mattress, duvet and pillows (bedding) in the bedroom of children of the active group were treated with the acaricide Acarosan (benzyl benzoate). The bedding was then encased in vapour permeable waterproof fabric (Intervent--cotton coated with polyurethane) for 24 weeks. The carpet and bedding of the control group were treated with placebo and the bedding encased in cotton covers for 24 weeks. Dust samples were collected from all these items in a standard manner at regular intervals and Der p I content analysed. RESULTS: The group with active treatment had a median reduction of 480 ng (100%) in mite allergen from the mattress vs 215 ng (53%) reduction in placebo-treated group by 6 weeks. The Der p I content of the active group's bedding was always less than the placebo group after treatment (P < 0.01). The acaricide applied to the carpets or inside the mattress covers was ineffective in reducing allergen content. CONCLUSION: This study confirms the effectiveness of encasing covers in reducing the mite allergen exposure but indicates there is no further advantage in applying acaricide simultaneously.

The quantitative distribution of nebulized antibiotic in the lung in cystic fibrosis.

Nebulized antibiotic therapy in cystic fibrosis is an established procedure. The present study was designed to quantitate deposition, and assess its relation to the disease state. Twenty seven children and young adults with cystic fibrosis (mean 11.6 years, range 4-23 years, 12 females) were studied to establish the quantity and pattern of deposition of nebulized tobramycin in the respiratory tract. A single (120 mg) dose of nebulized 99 m technetium-labelled tobramycin was administered, and imaged with a gamma-camera. The mean penetration index (which compares the distribution of 81 m-Krypton gas with Tc-radioaerosol) was also used to measure peripheral deposition efficiency. The aerosol mass median diameter (MMAD) for the compressor-nebulizer system used was 5.3 u, measured with the Malvern Mastersizer. Serial sputum samples were fluroimmunoassayed for tobramycin in nine patients. A mean of 8.0 (SEM 1.0) mg tobramycin reached the lungs. There was no relationship between the total pulmonary deposition and indices of pulmonary damage in cystic fibrosis. Sixteen percent of the lung tobramycin reached the periphery. The greater the lung damage as indicated by FEV1 and Chrispin-Norman scores, the smaller the proportion of pulmonary tobramycin that reached the periphery. The mean penetration index increased with increase in the FRC, but bore no relation to other respiratory function tests or to chest X-ray scores. Sputum tobramycin concentrations reached levels bactericidal for Pseudomonas aeruginosa. Airway obstruction and damage affected the proportion of pulmonary tobramycin reaching the periphery. The proportion of tobramycin reaching the lungs was small and variable.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of potential ototoxicity following high-dose nebulized tobramycin in patients with cystic fibrosis.

A deterioration in pulmonary function is a common problem in patients with cystic fibrosis. One strategy which might help to arrest this process is the administration of aminoglycosides by nebulizer in dosages which greatly exceed those which are normally given parenterally. Ten patients (4-19 years of age) with cystic fibrosis underwent evoked response audiometry at regular intervals following a 400 mg dose of nebulized tobramycin; the concentrations of tobramycin in samples of blood taken at the same time intervals were also determined. No significant abnormalities in the audiometric investigations were detected. The relationship between shifts in vestibulocochlear potentials and long-term ototoxic sequelae in patients receiving aminoglycosides via a nebulizer requires further evaluation.