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'     

Marron N  Dreyer E  Boudouresque E  Delay D  Petit JM  Delmotte FM  Brignolas F 《Tree physiology》2003,23(18):1225-1235

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.  相似文献   

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

Deborah K.?KennardEmail author  Francis E.?Putz 《New Forests》2005,30(1):1-20

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.  相似文献   

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

Francis O. C. Nwonwu 《Agroforestry Systems》1987,5(4):455-462

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.  相似文献   

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

Neira  Pablo  Henríquez-Castillo  Carlos  Ortiz  Juan  Stolpe  Neal  Dube  Francis 《Agroforestry Systems》2021,95(8):1465-1478

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...  相似文献   

Vertical variations in wood basic density for two softwood species     

Billard  Antoine  Bauer  Rodolphe  Mothe  Frédéric  Colin  Francis  Christine  Deleuze  Longuetaud  Fleur 《European Journal of Forest Research》2021,140(6):1401-1416

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...  相似文献   

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

Mermer  Serhan  Pfab  Ferdinand  Tait  Gabriella  Isaacs  Rufus  Fanning  Philip D.  Van Timmeren  Steven  Loeb  Gregory M.  Hesler  Stephen P.  Sial  Ashfaq A.  Hunter  Jamal H.  Bal  Harit Kaur  Drummond  Francis  Ballman  Elissa  Collins  Judith  Xue  Lan  Jiang  Duo  Walton  Vaughn M. 《Journal of pest science》2021,94(3):743-755

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.

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Loss of genetic diversity due to fishing pressure   总被引：1，自引：0，他引：1  

P. J. Smith  R. I. C. C. Francis  M. McVeagh 《Fisheries Research》1991,10(3-4):309-316

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.  相似文献   

Vaccination of dogs with multi-component vaccines     

DH DAVIES  S. PIDFORD 《Australian veterinary journal》1991,68(5):183-184

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Performance of draught cattle in communal farming areas in Zimbabwe after dry season supplementation     

L. R. Ndlovu  J. Francis  E. Hove 《Tropical animal health and production》1996,28(4):298-306

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

D H Francis 《Veterinary microbiology》1986,11(1-2):117-123

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.  相似文献