Testing and evaluation of natural durability of wood in above ground conditions in Europe – an overview

Natural durability of wood is determined by the European standard EN 252 for specimens in ground contact and EN 113 for basidiomycetes in the laboratory, but no test exists for above ground conditions. For above ground conditions, the European prestandard ENV 12037 and EN 330 are used to determine the durability of treated wood. The most important factors for fungal establishment on the surface and within wood are the moisture content, the surrounding temperature, and the relative humidity. Strength tests are the most sensitive for decay detection, but neither strength tests nor identification of fungi responsible for the decay are included in the standards of above ground durability in field tests. To detect decay, visual examination, pick or splinter tests, and mass loss determination are used. Identifying fungi with traditional methods, e.g., growth on solid medium, is time consuming and complicated. Molecular methods like polymerase chain reaction and sequencing do not require mycological skill for identification to species level, and furthermore the methods do not depend on the subjective judgement like most traditional methods, but are based on the objective information of the target organism (e.g., nucleotide sequences). The next generation of standard field tests will probably consider the drawbacks of standard tests today and be rapid and include both quality tests like molecular identification and nondestructive quantitative tests, e.g., acoustic tests. Laboratory tests can be improved by using fungi identified from field trials and by combining different fungi in the same test and thus simulate degradation in practice.     

杉木人工林树上宿存枯死枝、叶在冠层与在枯枝落叶层分解的比较研究

杉木枯死枝、叶有在树上宿存多年的特性。江西分宜大岗山地区一立地指数 14 ,林龄 13a ,保留密度 2 60 0株·hm- 2 的 1代林 ,树上宿存枯死枝、叶总量达 4 10 8 0kg·hm- 2 ,相当枯枝落叶层生物量的 3 5 4 %。树上宿存枯死枝、叶在冠层的分解速度 ,与置于枯枝落叶层的分解速度的测定结果表明 ,后者比前者快得多。说明在杉木林生长急需养分的速生期和杆材期 ,将树上宿存枯死枝、叶适时地打落于地表 ,使其在枯枝落叶层分解 ,与挂在冠层上的分解相比 ,对林木营养作用不同 ,前者比后者能及时、更多地提供养分。树上宿存枯死枝、叶在林冠下部由低到高呈 4层分布。鉴于各层死亡时间不同 ,经受的分解时间和雨水淋溶的强度也相异 ,其在树冠上的分解速度是分层测定的 ,上下层差异较大。在枯枝落叶层的分解速度也分层测定 ,上下层的差异较小。在枯枝落叶层分解时 ,本实验 1年间枝的各层分解量之和是树冠上分解时的近 2 3倍 ,叶为 5 4倍。在枯枝落叶层分解时 ,1年间各层枝、叶 ,营养元素归还量之和是树冠上分解时的 3 5倍。速生、杆材期 ,适时地将树上宿存枯死枝、叶打落于地表 ,对连栽杉木林长期生产力的保持更是有积极作用     

Comparative effectiveness of two alkylammonium compounds as wood preservatives

This study describes a laboratory evaluation of the efficacy of two alkylammonium compounds [didecyldimethylammonium tetrafluoroborate (DBF) and didecyldimethylammonium chloride (DDAC)] when applied via vacuum impregnation or superficial treatment. Treated wood specimens were tested for their termite and microbial resistance under controlled laboratory conditions. The higher chemical retentions were needed to suppress the feeding by Coptotermes formosanus ≦3% mass loss in the multichoice test than in the no-choice test. The DBF and DDAC retention levels necessary to meet the performance requirement ≦3% mass loss after 12-week fungal exposure varied with wood species. The retention level of 3 kg/m³ for DBF and DDAC was generally high to keep the nondurable wood species free of decay. Although there was no difference between DBF and DDAC in the efficacy against decay and termite attack, the former slightly outperformed the latter as an antimold and antisapstain agent.     

Comparison of chitosans with different molecular weights as possible wood preservatives

Fungi cause serious problems in wood utilization, and environmentally benign wood protection is required as an alternative to traditional chemicals. Chitosan has shown promising antimicrobial properties against several microorganisms. In this study, we present the characterization of and antifungal properties of a commercial chitosan formulation developed for impregnation of wood. A broad range of chemical and mycological methods were used to evaluate the uptake, fixation, and antifungal properties of chitosan for wood preservation. The results show that the higher the uptake of chitosan the lower the relative recovery of chitosan in wood after leaching, and the higher the molecular weight of chitosan the higher the recovery. Chitosan with high molecular weight proved to be more efficient against decay fungi than chitosan with low molecular weight. The fungi tested on chitosan-amended nutrient agar medium were totally inhibited at 1% (w/v) concentration. In decay studies using small wood blocks, 4.8% (w/v) chitosan concentration gave the best protection against brown rot fungi.     

Long-term changes in forest floor processes in southern Appalachian forests

Soil nutrient concentrations decreased in an aggrading southern Appalachian forest over a 20-year period. Construction of nutrient budgets showed significant nutrient sequestration aboveground including increased forest floor mass. We hypothesized that the changes in forest floor mass resulted from decreased litter decomposition rates because of decreased litter quality. In 1992 and 1993, we repeated a litter decomposition experiment conducted in 1969 and 1970 to test this hypothesis. In addition, we examined microarthropod populations and functional groups as litter decomposed. For four of the five species tested, first-year decomposition rates were about the same in both experiments. Initial litter nutrient concentrations of P were lower in all tree species in the most recent sampling. N, Ca, and Mg concentrations also declined in some species. These declines often resulted in decreased nutrient release rates during decomposition. Microarthropod populations differed significantly among litter species, as well as between years (probably resulting from differences in growing-season rainfall). For some litter species we found significant relationships between microarthropod populations and nutrient concentration (primarily C and N); however, most r²-values were low. Data suggest that changes in forest floor mass probably resulted from decreased litter quality and that those changes may have an effect on microarthropod populations.     

How well does a log decay-class system capture the ecology of decomposition? - A case-study from Tasmanian Eucalyptus obliqua forest

The use of decay-class systems in characterising the state of decomposition of a forest’s complement of rotting logs is widespread. While most systems are based on an assessment of logs’ external characteristics, there is an implicit assumption that doing so captures important information on the underlying processes of internal decomposition. However, the validity of this remains largely untested. We explored the relationship between decay-class and internal state of decomposition in logs of Eucalyptus obliqua in the lowland wet eucalypt forests of Southern Tasmania, Australia. We examined rotten-wood samples from a large population of logs across a wide range of diameters. From this we determined that smaller-diameter (<60 cm: regrowth-sized) logs differ from larger-diameter (>60 cm: mature-sized) logs in their pathways of internal decomposition. Decomposition in regrowth-sized logs is characterised by greater activity of surface rots, with white rot-types predominating. Decomposition in mature-sized logs is more concentrated in the interior of the log, with brown rot-types tending to dominate. These differences probably both reflect and help shape the communities of organisms inhabiting logs of different origins. Despite these differences, regrowth and mature-sized logs show the same general progression of internal decomposition across the five decay-classes, to the extent that each class represents logs that have lost a predictable proportion of their original mass. We conclude that a decay-class system that is restricted to a single dimension, such as the five-class system used for E. obliqua, will be quite able to capture the main trajectory of biomass loss, but will not be able to characterise the complexity of the ecological processes giving rise to this loss. Studies that employ single-dimension decay classes, and which aggregate decay-class data across logs, can be given added ecological meaning by first partitioning logs into diameter-classes that reflect the underlying differences in the maturity of the trees giving rise to the logs. For E. obliqua logs, a cut-off diameter of 60 cm offers an appropriate distinction between regrowth-aged and mature-aged trees.     

Ethanol vapor and saprophytic yeast treatments reduce decay and maintain quality of intact and fresh-cut sweet cherries

The objective of this study was to evaluate the use of an ethanol vapor release pad and a saprophytic yeast Cryptococcus infirmo-miniatum (CIM) to reduce decay and maintain postharvest quality of intact or fresh-cut sweet cherries (Prunus avium) cv. Lapins and Bing. Intact or fresh-cut fruit were packed in perforated clamshells (capacity 454 g) and stored at 1, 10 or 20 °C for up to 21, 14 and 8 d, respectively. For ethanol treatment, a pad made with silica gel powder containing 10 g ethanol and covered with perforated film, which allows ethanol vapor to diffuse gradually, was attached to the upper lid of the clamshells. Ethanol treatment caused accumulation of ethanol in the packaging headspace, about 10 μL L⁻¹ with little change within 14 d at 1 °C, 23 μL L⁻¹ at d 1 and decreased to 15 μL L⁻¹ at d 10 at 10 °C, and 26 μL L⁻¹ at d 1 and decreased to 13 μL L⁻¹ at d 3 at 20 °C. Ethanol content in fruit was less than 9 mg kg⁻¹ in all the control fruit, and increased to 16, 34 and 43 mg kg⁻¹ in ethanol-treated fruit at 1, 10 and 20 °C, respectively. Nonetheless, a sensory taste panel did not perceive any flavor difference from the ethanol treatment. The ethanol treatment retarded softening, darkening, and acid decrease in fruit as well as discoloration of the stems, and extended shelf-life of intact cherries. Ethanol reduced brown rot (Monilinia fructicola) in fresh-cut cherries stored at 20 °C, but not at 1 and 10 °C. A pre-packaging dip in CIM completely controlled brown rot in inoculated fresh-cut cherries stored at 1 °C, and in naturally infected cherries at 20 °C.     

牛烂蹄坏尾病致病弯角镰刀菌代谢产物分离鉴定

取金寨县耕牛烂蹄坏尾病致病弯角镰刀菌的玉米培养物，用丙酮提取，硅胶净化，制备型硅胶大板分离，得到无色针状结晶体，经质谱和红外光谱分析，并经相关谱图数据库联机检索、甄别，按其分子量、化学式及结构式确定为麦角甾醇，从而证实了致牛烂蹄坏尾病的弯角镰刀菌可产生麦角甾醇。     

Steam treatment to prevent carrot decay during storage

Organically grown carrots (Daucus carota L.) have a relatively short storage and shelf life, mainly because chemical measures cannot be implemented to control plant pathogens. Laboratory experiments demonstrated that steam treatments substantially reduced decay of stored organically grown carrots. Prior to being packaged, winter carrots were exposed to 3 s of steam. After 60 days of storage at 0.5°C plus an additional week at shelf conditions (20°C), 2% of the carrots were decayed, as opposed to 23% in the nontreated control. When carrot was inoculated with the fungi Alternaria alternata, [(Fr. : Fr.) Keissler] A. radicina (Meier) and Sclerotinia sclerotiorum [(Lib.) De Bary], percentages of decay, after similar periods of storage and shelf life, were 5% for steam-treated carrot and 65% for the nontreated control. In semi-commercial experiments carrots were treated with steam during the sorting process, and similar results were obtained. Higher decay was found in spring-grown carrots because of the presence of the bacterium Erwinia carotovora.sub. sp. carotovora     

茶树油对香蕉果实的保鲜效果

研究茶树油（TTO）处理对香蕉果实采后病害控制和贮藏期果实品质的影响。结果表明：利用1.25 g/L TTO熏蒸处理能够有效控制香蕉果实的发病,推迟了果实果皮的褪绿变黄,延缓了果肉硬度和淀粉含量的下降,维持了较高的可溶性糖含量,有利于保持果实的外观和品质;同时随着果皮表面残留TTO的迅速挥发,果实保持了自身较好的风味。TTO作为一种天然的防腐剂,在果蔬采后防腐保鲜方面具有应用前景。