Assessment of allometric algorithms for estimating leaf biomass, leaf area index and litter fall in different-aged Sitka spruce forests

The relationship between leaf area and diameter at breast height(d.b.h.) or sapwood area (AS) has been used to estimate standleaf area or biomass of forest canopies. It has been suggestedthat intra-specific variations in the relationship between standleaf area and d.b.h. or AS can introduce a systematic errorin these estimates for younger and older stands unless additionalparameters relating to canopy structure are included in allometricfunctions. We collected data from a Sitka spruce chronosequenceto parametrize and test different algorithms for the estimationof foliar biomass (FB) and litter inputs over a range of forestages. FB estimates were significantly improved when additionalbiometric information relating to crown structure (canopy opennessand height of live crown) was included in the models. Althoughthe use of the relationship between leaf area and AS for theestimation of leaf area is justified by theoretical considerations(pipe model theory), we show that d.b.h. and other canopy parametersprovided the most robust estimation of leaf area across different-agedstands. Our results also suggest that the accuracy of litterinput estimates depends on needle retention time and annualturnover rate, particularly immediately before and after canopyclosure.     

Effect of Chronic Administration of Phenobarbital,or Bromide,on Pharmacokinetics of Levetiracetam in Dogs with Epilepsy

Background

Levetiracetam (LEV) is a common add‐on antiepileptic drug (AED) in dogs with refractory seizures. Concurrent phenobarbital administration alters the disposition of LEV in healthy dogs.

Hypothesis/Objectives

To evaluate the pharmacokinetics of LEV in dogs with epilepsy when administered concurrently with conventional AEDs.

Animals

Eighteen client‐owned dogs on maintenance treatment with LEV and phenobarbital (PB group, n = 6), LEV and bromide (BR group, n = 6) or LEV, phenobarbital and bromide (PB–BR group, n = 6).

Methods

Prospective pharmacokinetic study. Blood samples were collected at 0, 1, 2, 4, and 6 hours after LEV administration. Plasma LEV concentrations were determined by high‐pressure liquid chromatography. To account for dose differences among dogs, LEV concentrations were normalized to the mean study dose (26.4 mg/kg). Pharmacokinetic analysis was performed on adjusted concentrations, using a noncompartmental method, and area‐under‐the‐curve (AUC) calculated to the last measured time point.

Results

Compared to the PB and PB–BR groups, the BR group had significantly higher peak concentration (C _max) (73.4 ± 24.0 versus 37.5 ± 13.7 and 26.5 ± 8.96 μg/mL, respectively, P < .001) and AUC (329 ± 114 versus 140 ± 64.7 and 98.7 ± 42.2 h*μg/mL, respectively, P < .001), and significantly lower clearance (CL/F) (71.8 ± 22.1 versus 187 ± 81.9 and 269 ± 127 mL/h/kg, respectively, P = .028).

Conclusions and Clinical Importance

Concurrent administration of PB alone or in combination with bromide increases LEV clearance in epileptic dogs compared to concurrent administration of bromide alone. Dosage increases might be indicated when utilizing LEV as add‐on treatment with phenobarbital in dogs.     

Medical dissolution and prevention of canine and feline uroliths: diagnostic and therapeutic caveats

Medical protocols designed to promote the dissolution of canine and feline struvite uroliths, the dissolution of canine ammonium urate and cystine uroliths and the prevention of all major types of canine and feline uroliths have been developed. However, because the causes of different types of uroliths vary, the medical protocols for their dissolution and prevention also vary. When the diagnosis of the underlying causes of uroliths becomes the rule rather than the exception, therapeutic failures should become the exception rather than the rule.     

Canola genotypes differ in potassium efficiency during vegetative growth

There is no knowledge about the differential capacity of canola genotypes to take up potassium (K) and produce dry matter under conditions of low soil K availability. Hence, 84 canola genotypes were screened for K efficiency in the glasshouse. Plants were grown in sealed pots containing K-responsive, sandy soil without or with K added. Twelve genotypes were selected for advanced screening in the glasshouse in a different K-responsive soil. Genotypes with a mean K efficiency ratio (the ratio of shoot dry weight at deficient and adequate K supply) greater than one standard error above or below the median genotype value were classified as K-efficient or K-inefficient, respectively. There were significant differences between genotypes in the K efficiency ratio in both screening experiments, indicating that genotypes responded differently to K availability. In the initial screening experiment, 19 genotypes were rated as K-efficient and nine genotypes rated as K-inefficient based on the K efficiency ratio. In the advanced screening experiment with 12 genotypes, three genotypes were rated as K-efficient and two as K-inefficient. Genotypes Wesbarker and Rainbow were K-efficient and Genkai K-inefficient in both experiments. Correlation of the K efficiency ratio with (i) shoot K content in the initial and advanced screening and (ii) shoot K concentration in the advanced screening, indicates that the observed differences in K efficiency were due to genotypic differences in both the uptake and the utilization of K. K-efficient genotypes have a potential to improve canola yields on soils with low K availability.     

Mercury in soils of British Columbia,a mercuriferous region

Mercury concentrations in various horizons of British Columbia soils were determined to estimate natural background levels in soils from various geographical areas of the province. Highly enriched concentrations near the Pinchi Lake cinnibar deposit declined to background levels ranging from 10 to 310 ppb Hg in the district. In six other regions, concentrations in surface mineral horizons averaged 85 ppb and ranged to 490 ppb but surface horizons of peaty muck soils and those predominated by vegetative litter contained 164 ppb Hg on the average and as much as 741 ppb. Concentrations in subsurface horizons were lower than at the surface. A significant relationship between Hg concentration and organic matter content was observed. Comparison with soils from outside British Columbia indicated its location within a generalized mercuriferous belt accounted for the relatively high concentrations observed.