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Container-grown walnut seedlings (Juglans regia L.) were subjected to competition with rye grass (Lolium perenne L.) and to a 2-week soil drying cycle. One and 2 weeks after the beginning of the drought treatment, H2 18O (delta approximately equals +100%) was added to the bottom layer of soil in the plant containers to create a vertical H2 18O gradient. Rye grass competition reduced aboveground and belowground biomass of the walnut seedlings by 60%, whereas drought had no effect. The presence of rye grass reduced the dry weight of walnut roots in the upper soil layer and caused a 50% reduction in lateral root length. Rye grass competition combined with the drought treatment reduced walnut leaf CO2 assimilation rate (A) and leaf conductance (gw) by 20 and 39%, respectively. Transpiration rates in rye grass, both at the leaf level and at the plant or tiller level, were higher than in walnut seedlings. Leaf intrinsic water-use efficiency (A/gw) of walnut seedlings increased in response to drought and no differences were observed between the single-species and mixed-species treatments, as confirmed by leaf carbon isotope discrimination measurements. Measurement of delta18O in soil and in plant xylem sap indicated that the presence of rye grass did not affect the vertical profile of soil water uptake by walnut seedlings. Walnut seedlings and rye grass withdrew water from the top and middle soil layers in well-watered conditions, whereas during the drought treatment, walnut seedlings obtained water from all soil layers, but rye grass took up water from the bottom soil layer only. 相似文献
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In a naturally regenerated beech (Fagus sylvatica L.) standin northeastern France, five regeneration patches were selectedwith different degrees of canopy closure; the percentage ofabove-canopy light (PACL) ranged between 5 and 45 per cent.The canopy was removed by a storm 2 years later. In order toanalyse the immediate and delayed effects of PACL on seedlingdiameter and height growth, the effects of the light conditionsprevailing before canopy opening on seedling growth measuredbefore and after canopy opening were tested. The effects oflocal density were examined using neighbourhood analysis. Fourdifferent competition indices (CIs) and neighbourhood radiiranging from 10 to 200 cm were tested. Models including PACLand CI accounted for between 56 and 64 per cent of the variationin individual seedling annual diameter or height growth. Localdensity had a strong negative influence on diameter growth anda much smaller influence on height growth. PACL was positivelycorrelated with diameter and height growth before canopy opening.Delayed effects of PACL on height growth were observed justafter canopy opening, but disappeared after 2 years. No delayedeffects of PACL on diameter growth after canopy opening wereobserved. 相似文献
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Growth and mortality in underplanted tree seedlings in response to variations in canopy closure of Norway spruce stands 总被引：2，自引：0，他引：2
Lof Magnus; Karlsson Matts; Sonesson Kerstin; Welander Torkel N.; Collet Catherine 《Forestry》2007,80(4):371-383
Six broadleaved tree species and Picea abies (L.) Karst. wereplanted under spruce plantations of varying densities, in Sweden.Treatments included control (994 stems ha–1), dense (538stems ha–1), sparse (294 stems ha–1) and gap (0stems ha–1) overstory treatments. There was an increasein height and diameter growth from control to sparse overstorytreatment of all underplanted tree species except for ash (Fraxinusexcelsior L.) and Norway maple (Acer platanoides L.). Site conditionsmay have hampered the growth of these species, as well as wildcherry (Prunus avium L.). Both oak (Quercus robur L.) and sprucehad greater growth in the gap treatment, relative to the othertreatments. Insecticide application did not influence seedlinggrowth or survival. The performance of beech (Fagus sylvaticaL.), lime (Tilia cordata Mill.), spruce and oak was consistentwith shade tolerance ranking. Beech and lime had a very highsurvival rate, even under the densest canopy. The growth andmortality of ash, maple and wild cherry differed significantlyfrom what was expected. This experiment demonstrated significantvariation in interspecific growth and mortality between sevenplanted tree species in relation to canopy density. Correctsite and species selection is crucial when underplanting inshelterwood systems. 相似文献
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G. V. Kozloski L. Oliveira C. H. E. C. Poli E. B. Azevedo D. B. David H. M. N. Ribeiro Filho S. G. Collet 《Journal of animal physiology and animal nutrition》2014,98(4):659-666
Data from twenty‐two digestibility trials were compiled to examine the relationship between faecal N concentration and organic matter (OM) digestibility (OMD), and between faecal N excretion and OM intake (OMI) by wethers fed tropical or temperate forages alone or with supplements. Data set was grouped by diet type as follows: only tropical grass (n = 204), only temperate grass (n = 160), tropical grass plus supplement (n = 216), temperate grass plus supplement (n = 48), tropical grass plus tropical legume (n = 60) and temperate grass with ruminal infusion of tannins (n = 16). Positive correlation between OMD and either total faecal N concentration (Nfc, % of OM) or metabolic faecal N concentration (Nmetfc, % of OM) was significant for most diet types. Exceptions were the diet that included a tropical legume, where both relationships were negative, and the diet that included tannin extract, where the correlation between OMD and Nfc was not significant. Pearson correlation and linear regressions between OM intake (OMI, g/day) and faecal N excretion (Nf, g/day) were significant for all diet types. When OMI was estimated from the OM faecal excretion and Nfc‐based OMD values, the linear comparison between observed and estimated OMI values showed intercept different from 0 and slope different from 1. When OMI was estimated using the Nf‐based linear regressions, the linear comparison between observed and estimated OMI values showed neither intercept different from 0 nor slope different from 1. Both linear comparisons showed similar R2 values (i.e. 0.78 vs. 0.79). In conclusion, linear equations are suitable for directly estimating OM intake by wethers, fed only forage or forage plus supplements, from the amount of N excreted in faeces. The use of this approach in experiments with grazing wethers has the advantage of accounting for individual variations in diet selection and digestion processes and precludes the use of techniques to estimate forage digestibility. 相似文献
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Collet E Lemée-Cailleau MH Buron-Le Cointe M Cailleau H Wulff M Luty T Koshihara SY Meyer M Toupet L Rabiller P Techert S 《Science (New York, N.Y.)》2003,300(5619):612-615
We report the direct observation by x-ray diffraction of a photoinduced paraelectric-to-ferroelectric structural phase transition using monochromatic 100-picosecond synchrotron pulses. It occurs in tetrathiafulvalene-p-chloranil, a charge-transfer molecular material in which electronic and structural changes are strongly coupled. An optical 300-femtosecond laser pulse switches the material from a neutral to an ionic state on a 500-picosecond time scale and, by virtue of intrinsic cooperativity, generates self-organized long-range structural order. The x-ray data indicate a macroscopic ferroelectric reorganization after the laser irradiation. Refinement of the structures before and after laser irradiation indicates structural changes at the molecular level. 相似文献
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Marine Dodet Catherine Collet Henri Frochot L��on Wehrlen 《European Journal of Forest Research》2011,130(1):41-53
By increasing resource availability, canopy opening enhances tree recruitment as well as the development of neighbouring vegetation. The proliferation of early successional and highly competitive vegetation may have dramatic consequences on seedling establishment. However, differences in competitive abilities have been shown among the plant growth forms commonly encountered in forests. We may thus expect that vegetation management leading to control of different plant growth forms would have different consequences on tree seedling growth and development. To test this hypothesis, we analysed the effects of an intensity gradient of four vegetation control treatments (untreated, coppice control, coppice and non-tree plant control, and coppice, non-tree and pioneer (tree) plant control) on plant species richness and natural tree regeneration in three post-storm sites. Higher plant species richness and a better natural tree regeneration were observed in the more intensive treatments that significantly improved the balance of the relative abundance of tree species. Suppressing the more competitive vegetation, mainly Rubus fruticosus and graminoids, led to the recruitment and growth of tree species sensitive to competition and good tree species diversity. Practical recommendations in terms of vegetation control relative to tree regeneration and plant species richness are given. 相似文献
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Carrington AC Collet B Holland JW Secombes CJ 《Veterinary immunology and immunopathology》2004,101(3-4):211-222
Bacterial DNA and CpG ODN have both been shown to have immunostimulatory effects in mammals, activating APCs and inducing a potent Th1 type immune response. They have also been shown to have a strong adjuvant effect and up-regulate MHC class 2 expression in murine cells, augment human and murine NK cell lytic activity, activate human B cells and induce murine B cell proliferation. However, little work has been carried out with regard to their effects on the piscine immune system. Here it is shown that various CpG ODN induce proliferation of peripheral blood leucocytes, spleen and head kidney cells from rainbow trout although, at the range of concentrations tested CpG ODN 2133 lacked the ability to induce specific antibody production to a protein antigen. 相似文献
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Effect of repeated exposure to AQUI‐S® on the viability and growth of Neoparamoeba perurans 
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下载免费PDF全文 There have been recent efforts amongst immunologists to develop approaches for following individual fish during challenges with viral and bacterial pathogens. This study contributes to assessing the feasibility of using such approaches to study amoebic gill disease (AGD). Neoparamoeba perurans, agent of AGD, has been responsible for widespread economic and fish loss in salmonid aquaculture. With the emergence of AGD in Europe, research into infection dynamics and host response has increased. This study investigated the effect of repeat exposure to anaesthesia, a necessary requirement when following disease progression in individual fish, on N. perurans. In vitro cultures of N. perurans were exposed every 4 days over a 28‐day period to AQUI‐S® (isoeugenol), a popular anaesthetic choice for AGD challenges, at a concentration and duration required to sedate post‐smolt salmonids. Population growth was measured by sequential counts of amoeba over the period, while viability of non‐attached amoeba in the culture was assessed with a vital stain. AQUI‐S® was found to be a suitable choice for in vivo ectoparasitic challenges with N. perurans during which repetitive anaesthesia is required for analysis of disease progression. 相似文献