Summary Several factors which influence the treatment of timber products with vapour phase preservatives such as borate esters are considered. Gas flow rate through the substrate was found to be a significant factor limiting both preservative penetration and its rate of deposition. A theoretical model of the treatment process was developed and tested experimentally to determine the influence of several factors on the retention and distribution of boric acid. Gas flow into the timber product was influenced by permeability, pressure gradient and substrate moisture content. The implications of the findings are considered with regard to the treatment of wood and wood products with gaseous reagents.The authors wish to thank the following for their financial support and interest in this research programme — Rentokil Ltd, Rhone-Poulenc/Manchem Ltd, Forestry Commission, UK and Ireland Particleboard Association (now Panel Products Association), Norbord Highland plc (formerly Highland Forest Products plc), IMPEL 相似文献
Two old (Huangsedadou and Longxixiaohuangpi (LX)) and two new (Jindou 19 (JD) and Zhonghuang 30 (ZH)) soya bean (Glycine max (L.) Merr.) cultivars were used to investigate the influence of soil drying on the abscisic acid (ABA) accumulation in leaves, stomatal conductance (gs), leaf water relations, osmotic adjustment (OA), leaf desiccation tolerance, yield and yield components. The greater ABA accumulation was induced by soil drying, which also inducing gs decreased at higher soil water contents (SWC) and leaf relative water content (RWC) significantly decreased at lower SWC in the new soya bean cultivars than in the old soya bean cultivars. The soil water threshold between the value at which stomata began to close and the RWC began to decrease was significantly broader in the new cultivars than in the old cultivars. The new cultivars had significantly higher OA and lower lethal leaf water potential than old cultivars when the soil dried. The old cultivars had greater biomass, but lower grain yield than the new cultivars in well‐watered, moderate stress and severe stress conditions. Thus with soil drying, the new soya bean cultivars demonstrated greater adaptation to drought by inducing greater ABA accumulation, stomatal closure at higher SWC, enhanced OA and better water relations, associated with increased leaf desiccation tolerance, greater water use efficiency and higher yield. 相似文献
A previously developed mathematical model, which uses a comprehensive two-dimensional heat and mass transport code coupled
with a three-dimensional code for resolving Maxwell's equations in the time domain, will be used to investigate numerous aspects
of the microwave enhanced convective drying of softwood in an over-sized waveguide. At first, in order to highlight the predictive
capabilities of the developed model, comparisons will be made between theory and experiment for spruce heartwood. It will
be shown that the model is able to identify most of the important heat and mass transfer phenomena that arise throughout the
drying process. After validation of the numerical simulation results, the work focuses on using the model as a cognitive tool
for investigating important issues for closed microwave systems which include the effect of varying the sample dimensions
and changing the location of the material within the applicator. Finally, a study will be presented that compares the overall
drying kinetics generated within two different types of applicator designs. The first design uses a wave-trap located at the
end of the waveguide to prevent reflected energy from back-propagating into the over-sized section of the guide, while the
second design uses a short-circuit plane to ensure that this reflected energy is back – propagated towards the material. The
advantages and disadvantages of these two designs will be deliberated.
Received 25 May 1997 相似文献
Elevated landslide rates in forested landscapes can adversely impact aquatic habitat and water quality and remove and/or degrade soil resources required for forest regeneration. As a result, understanding the associations between management actions, natural factors, and landslide rates is important information needed for land managers. An unusual and powerful storm in early December, 2007, caused record flooding and thousands of landslides across southwest Washington and northwest Oregon, USA, and provided a rare opportunity to examine the effects of both natural factors and forest management practices on landslide density. Landslide inventory data were collected from both aerial photos and systematic field surveys to provide a broad survey database that was used to develop estimates of landslide density and to examine associations between landslide density, precipitation, topography, and forest stand age across a 152,000 ha forested landscape in the Willapa Hills, Washington. We estimated the probability of detecting landslides on aerial photos for six strata defined by forest stand age and a broad range of rainfall intensity, expressed as percent of the 100-year, 24-h, maximum rainfall. Key findings are that landslide detection probability decreased with increasing stand age, but was similar across rainfall intensities. The overall fraction of field-detected landslides that were not detected on 1:12,000-scale aerial photos was 39%. Very few landslides occurred in the 0–100% of 100-year rainfall category, regardless of stand age or slope gradient class. At higher rainfall intensities, significantly higher landslide densities occurred on steep slopes (>70% gradient) compared to lower gradient slopes, as expected. Above ∼150% of 100-year rainfall, the density of landslides was ∼2–3 times larger in the 0–5 and 6–10 year stand age categories than in the 11–20, 21–30, 31–40, and 41+ categories. The effect of stand age was strongest at the highest rainfall intensities. Our results demonstrate that ground-based landslide inventory data are required in order to correct for detection bias from aerial photos, develop reasonable estimates of landslide density across environmental gradients such as rainfall magnitude and topography, and make unbiased interpretations of relationships between forest management associations and landslide occurrence. 相似文献
Abstract. Degradation of isoproturon in a heavy clay soil followed first-order reaction kinetics with half-lives at 15 °C of 27 and 208 days in the topsoil and subsoil, respectively. Adsorption when shaken with 3 mm sieved samples of the soil fitted the empirical Freundlich relationship with k values of 3.25 in the topsoil and 1.06 in the subsoil. Adsorption in a static system with different sized aggregates of soil did not reach equilibrium, even after 24 hours contact, and the rate of adsorption was slower with larger aggregates. Following an adsorption period of 24 hours, desorption equilibrium was reached more rapidly with larger (6–10 mm) than with smaller (<3 mm) aggregates. Adsorption isotherms measured in a static system with a soil:water ratio typical of field conditions in winter also indicated less adsorption than that measured in shaken, laboratory systems with low soil:water ratios. The rate of change in water extractable residues of the herbicide was more rapid than that of total extract-able residues following application of isoproturon to the heavy clay soil in the field. The implications of the results for isoproturon leaching under field conditions are discussed. 相似文献
Competition for water generates a classic aspect of the tragedy of the commons, the ‘race for fish’, where crops must allocate more resource to acquisition of the limiting resource than is optimal for crop yield allocation. A pot experiment using a simple additive (target–neighbour) design was conducted to examine the above‐ground and below‐ground growth of three spring wheat (Triticum aestivum L.) cultivars when grown alone and in mixtures at three levels of water availability. The effects of competition and water availability were compared by observing patterns of growth, biomass allocation and below‐ground outcomes. Competitive interactions were investigated among cultivars ‘HST’, ‘GY602’ and ‘LC8275’, target plant of each cultivar grown without neighbouring plants are referred to herein as control plant and one target plant of each cultivar sown surrounded either by same or another cultivar as intra‐ or inter‐cultivar competition. Competitive ability was assessed as the response ratio (lnRR) between the target plant surrounded by six other plants and the target plant in isolation. Our results showed that the cultivar ‘HST’, released over a century ago, produced a higher biomass and grain yield than the more recently released cultivars ‘LC8275’ and ‘GY602’ when grown as isolated plants with sufficient water supply. However, competition for resources from neighbours led to target plant biomass and grain yield being significantly reduced relative to controls in all three cultivars, particularly in ‘HST’. When subjected to intra‐cultivar competition, the two recently released cultivars ‘LC8275’ and ‘GY602’ had higher grain yields and water use efficiency for grain than ‘HST’ in all three water regimes. The landrace ‘HST’ had better and significantly linear relationships between biomass and biomass allocation, root length and specific root length, whereas the recent and modern cultivars had much more water‐related species‐specific changes in root morphology and allocation patterns. These results suggest that crop traits that influence competitive ability, such as biomass allocation to roots and root plasticity in response to drought have changed in modern wheat cultivars because of breeding and selection. 相似文献
Brassica rapa L. is a genetically diverse parent species of the allotetraploid species, oilseed rape (B. napus) and a potential source of drought tolerance for B. napus. We examined the effect of a 13‐day drought stress period during the early reproductive phase, relative to a well‐watered (WW) control, on subsequent growth and development in nine accessions of B. rapa and one accession of Brassica juncea selected for their wide morphological and genetic diversity. We measured leaf water potential, stomatal conductance, water use, and leaf and bud temperatures during the stress period and aboveground dry weight of total biomass at maturity. Dry weight of seeds and reproductive tissue were not useful measures of drought tolerance due to self‐incompatibility in B. rapa. The relative total biomass (used as the measure of drought tolerance in this study) of the 10 accessions exposed to drought stress ranged from 47 % to 117 % of the WW treatment and was negatively correlated with leaf‐to‐air and bud‐to‐air temperature difference when averaged across the 13‐day stress period. Two wild‐type (B. rapa ssp. sylvestris) accessions had higher relative total and non‐reproductive biomass at maturity and cooler leaves and buds than other types. We conclude that considerable genotypic variation for drought tolerance exists in B. rapa and cooler leaves and buds during a transient drought stress in the early reproductive phase may be a useful screening tool for drought tolerance. 相似文献
Forests growing on former agricultural land often have reduced frequencies of many native forest herbs compared with forests that were never cleared for agriculture. A leading explanation for this pattern is that many forest herbs are dispersal limited, but environmental conditions may also hinder colonization. We examined the response of six forest herb taxa (Arisaema triphyllum, Cimicifuga racemosa, Disporum lanuginosum, Osmorhiza spp., Polygonatum spp., and Prenanthes altissima) to nitrogen (N) fertilization in forests with and without an agricultural history to investigate how N availability affects plant performance. The study was conducted in the southern Appalachian Mountains in western North Carolina, USA. There was a significant interaction between land-use history and N treatment for several species. In A. triphyllum and Osmorhiza spp., N fertilization increased aboveground biomass or leaf area more in the post-agriculture site than in the reference site. However, in the reference site, N fertilization depressed aboveground biomass or leaf area in the same taxa, as well as in C. racemosa. The foliar N concentration of these three taxa was elevated in fertilized plots regardless of land-use history, and there was no indication that the light environment differed among plots. These results suggest that some plants growing in post-agricultural stands may be N limited, whereas undisturbed stands in this region appear to be approaching N saturation. Thus, environmental conditions, and particularly N availability, may be an obstacle to the restoration of forest herb communities. 相似文献
We examine the relationship between the number of bird species and environment within 500 000 ha of eucalypt forests in south-eastern New South Wales, Australia. Birds were surveyed at 39 sites within 31 eucalypt communities, which were, in turn, scored by altitude, temperature, rainfall, basal areas of trees and levels of the nutrients nitrogen, phosphorus, potassium and magnesium in the eucalypt foliage.
Ninety bird species were recorded. Numbers per site, averaged over the whole sample period, ranged between 20 and 38 over all surveys, 24 and 42 in ‘summer’ (October to March) when migrant species were present, and 13 and 38 in ‘winter’ (April to September). A forward stepwise Poisson regression model was used to fit bird species richness to the environmental variables. Over all surveys and in ‘summer’, foliar magnesium and tree basal area (including the basal area of dead trees) were significantly (positive) correlated with the number of bird species. In ‘winter’ the correlations were with altitude and temperature (both negative), presumably the result of emigration of species that avoid cold weather, and tree basal area (positive).
The positive association of number of species over all surveys and in ‘summer’ with tree basal area, including dead trees, and foliar magnesium may index the level of forest maturity and productivity.
Forest management directed solely to timber production reduces the basal area and the number of dead trees and may thereby reduce bird species richness permanently.
A methodology is offered, based on the relationship between the physical environment and the more productive eucalypt communities, for determining forest areas containing the most species of birds. 相似文献
Brans of specialty sorghum varieties (high tannin, black, and black with tannin) were used to investigate the effects of sorghum phenolic compounds on starch digestibility of soft and hard sorghum endosperm porridges. Endosperms of varieties with the highest and lowest grain hardness index were mixed with brans of specialty sorghum varieties in the ratio of 85:15 and cooked into porridges with distilled water using a Rapid Visco Analyzer. Brans of condensed tannin containing sorghum varieties (high‐tannin and black with tannin sorghums) significantly (P < 0.05) decreased starch digestibility and estimated glycemic index (EGI) and increased resistant starch (RS) content of endosperm porridges. However, the addition of phenolic‐rich tannin‐free (mostly anthocyanins) black sorghum bran significantly (P < 0.05) increased starch digestibility and EGI but did not affect RS content of endosperm porridges. The disparate effects with black bran may, in part, result from its larger particle size and different bran structure compared with other sorghum varieties evaluated. Thus, our study showed that not only presence of phenolic compounds in the brans but also structural differences of specialty sorghum brans can have significant effects on starch digestibility. 相似文献