Impact of successive drought and re-watering cycles on growth and specific leaf area of two Populus x canadensis (Moench) clones, 'Dorskamp' and 'Luisa_Avanzo'

Responses to successive drought and re-watering cycles (1-3 cycles) were compared in greenhouse-grown cuttings of Populus x canadensis (Moench) clones, 'Luisa_ Avanzo' and 'Dorskamp.' Total leaf number increment rate, duration of leaf expansion, total and individual leaf area expansion rates and stomatal conductance were recorded periodically during the experiment. Soil water content (SWC) and predawn leaf water potential (Psi(WP)) were measured four times during each drought cycle. In parallel, relative leaf water content (RWC) and specific leaf area (SLA) were estimated on leaves collected from the top to bottom of each cutting. Under well-watered conditions, 'Luisa_Avanzo' and 'Dorskamp' differed in their patterns of leaf area expansion. Although duration of leaf expansion was similar between clones, 'Luisa_ Avanzo' exhibited higher total leaf number increment rates and individual leaf area increases than 'Dorskamp.' As a result, 'Luisa_Avanzo' cuttings reached larger individual and total leaf areas than 'Dorskamp.' 'Dorskamp' leaves had lower SLA than 'Luisa_Avanzo' leaves. In response to successive drought cycles, both clones underwent decreases in total leaf number increment rates and in total leaf area expansion rates, but both whole-plant and individual leaf areas were drastically reduced only in 'Luisa_Avanzo.' 'Dorskamp' maintained a constant leaf area as a result of an increase in the duration of leaf expansion during drought and a significant stimulation of individual leaf area expansion rate and total leaf number increment rate in response to re-watering. Drought caused a greater decrease in SLA in 'Luisa_Avanzo' than in 'Dorskamp.' Expanded leaves of 'Dorskamp' were constitutively dense or thick, or both, whereas leaves of 'Luisa_Avanzo' became dense or thick, or both, only in response to drought. In both clones, re-watering caused partial recovery of SLA to control values. Our data confirm previous field and greenhouse observations that 'Dorskamp' is more tolerant to successive drought and re-watering cycles than 'Luisa_Avanzo.' We conclude that this difference is mainly attributable to the plasticity of 'Dorskamp' after re-watering, rather than to clonal differences in drought responses.     

Differential responses of Bolivian timber species to prescribed fire and other gap treatments

We followed the establishment and growth response of 13 commercial tree species to canopy opening, above-ground biomass removal, and experimental burns of low and high intensities in a lowland dry forest in Bolivia. Three patterns of response to treatments were observed among the most abundant commercial tree species. (1) Shade-intolerant species regenerated mostly from seed and had the highest survival and growth rates following high-intensity burns. (2) Shade-tolerant species were abundant in gap control and plant removal treatments. Treatments had little effect on the height growth of these species. (3) Individuals of root sprouting species were most abundant following plant removal and low-intensity burn treatments. Treatments had little effect on the height growth of these species. The wide variation in species responses to gap treatments found in this study not only reinforces the concept that species are distributed along a continuum of shade-tolerance levels, but that other aspects of species biology, such as seed dispersal type or sprouting behavior, further differentiate regeneration strategies. The variety of regeneration strategies found among the species at this forest site will require a flexible management scheme that mixes more intensive silvicultural treatments such as prescribed burning with less intensive treatments.     

Cost minimization through the use of taungya system in pulpwood plantation establishment

The costs and benefits of the use of three labour alternatives: direct permanent, direct casual and taungya labour in Gmelina arborea pulpwood plantation establishment in Nigeria were investigated. Results show that cost per hectare is lowest with taungya labour and highest with permanent labour with savings in cost of as much as 30% and 47% by taungya labour over casual and permanent labour respectively. The net present value per hectare of investment is highest when taungya labour is used and lowest and negative with permanent labour. Also, the internal rate of return of investment is highest with taungya labour and lowest with permanent labour. The net present values and internal rates of return for Gmelina plantations calculated for the three pulp and paper mills in Nigeria show the same trend in favour of taungya labour.     

Do different densities of tree cover affect pasture biomass and soil microbial communities?

Agroforestry Systems - Soil biota is considered a crucial component of soil health. Currently, the soil microbiota and its genomic material (microbiome) have received increasing attention due to...     

Vertical variations in wood basic density for two softwood species

European Journal of Forest Research - Studies on wood basic density (BD) vertical variations become essential to predict more accurately the within-stem distributions of biomass and wood quality in...     

Timing and order of different insecticide classes drive control of Drosophila suzukii; a modeling approach

The spotted-wing drosophila, Drosophila suzukii Matsumura, is an invasive pest causing significant damage to soft skinned fruits. Control of D. suzukii is critical since there is no tolerance for infested fruit in the market. While most insecticides control one or more D. suzukii life-stages (e.g., egg, larvae, and adult), the impact of insecticides that are toxic to immature stages  is unclear on the subsequent generation of a field population. Insecticides were applied at field recommended rates on cherries and blueberries in the laboratory to determine immature D. suzukii mortality. Spinetoram, cyantraniliprole, malathion, methomyl, spinosad, and phosmet resulted in relatively high mortality of all immature life stages. Zeta-cypermethrin, cyclaniliprole, and fenpropathrin resulted in lower mortality of egg and all larval instars. Malathion was also applied to lowbush blueberries with different fruit sizes (small, medium, and large) in the laboratory and there was no statistical difference in mortality rates depending on fruit sizes. Mortality data from the laboratory experiments were used to parameterize a refined D. suzukii population model. The model revealed that the timing and order of different insecticide classes are important to control D. suzukii population. Model runs that included early applications of more effective insecticides resulted in high immature mortality and greater reduction of D. suzukii populations compared to treatments applied later.

     

Loss of genetic diversity due to fishing pressure

Loss of genetic diversity in the orange roughy, Hoplostethus atlanticus, caught off New Zealand, was measured by gel electrophoresis of nine polymorphic enzyme loci. There has been a significant reduction in genetic diversity on three spawning sites over the past 6 years, during which time the virgin biomass has been reduced by 70%. It is suggested that fishing activities which concentrate on spawning populations differentially remove the older and more heterozygous individuals from the virgin stock. Commercial fishing activities may have had significant genetic effects on fish stocks without reducing them to near-extinction levels.     

Effect of amino acids on expression of K99 adherence pili by Escherichia coli

Various common L-amino acids differed in their ability to suppress K99 production in E. coli. Strains of E. coli also varied in their sensitivity to amino acid-mediated suppression of K99. Alanine, methionine, leucine, and valine were the most suppressive amino acids. However, when compared to single amino acids, mixtures of these amino acids were frequently either less suppressive, non-suppressive, or even stimulatory for K99 expression.     

Salinomycin toxicosis in horses

CASE DESCRIPTION: A 4-month-old American Paint filly was evaluated because of sudden onset of ataxia that progressed to recumbency. Five additional horses from the same and neighboring premises developed signs of poor performance, generalized weakness, ataxia, and recumbency; 2 of those horses were also evaluated. A new batch of a commercial feed supplement had been introduced to the horses' diet on each farm within the preceding 3 days. CLINICAL FINDINGS: Other than recumbency, findings of physical and neurologic examinations of the foal were unremarkable. The other 2 horses had generalized weakness and mild ataxia, and 1 horse also had persistent tachycardia. The foal had mild leukocytosis with neutrophilia, hyperglycemia, and mildly high serum creatine kinase activity. Results of cervical radiography, CSF analysis, and assessments of heavy metals and selenium concentrations in blood and vitamin E concentration in serum were within reference limits. Feed analysis revealed high concentrations of the ionophore antimicrobial salinomycin. TREATMENT AND OUTCOME: The 5 affected horses survived, but the foal was euthanized. At necropsy, a major histopathologic finding was severe vacuolation within neurons of the dorsal root ganglia, which was compatible with ionophore toxicosis. The surviving horses developed muscle atrophy, persistent weakness, and ataxia. CLINICAL RELEVANCE: In horses, ionophore toxicosis should be considered as a differential diagnosis for acute weakness, ataxia, recumbency, or sudden death. Furthermore, ionophore toxicosis should be considered as a cause of poor performance, weakness, muscle wasting, and cardiac arrhythmias in horses. Surviving horses may have impaired athletic performance.