两步法改善杉木表面的疏水性1）

采用两步法在杉木表面修饰疏水涂层，来改善其疏水性能。通过浸渍—提拉法在杉木表面涂上一层二氧化硅（ SiO2）涂层，分别采用氨处理和六甲基二硅氮烷（ HMDS）处理对杉木表面涂层进行固化和疏水修饰。采用动态接触角测量仪对修饰前后杉木的疏水性能进行表征。结果表明：修饰前杉木的吸水性强，其对水的接触角随观测时间不断减小，最后水被完全吸收，接触角为0°；两步法修饰后杉木的疏水性变好，其对水的接触角随观测时间几乎不变，最高达142．2°。红外结果表明：HMDS处理后，SiO2粉末在848 cm－1处出现新的吸收峰，归属于—Si—CH3吸收峰。     

Attachment and adhesion of conidia of Stagonospora nodorum to natural and artificial surfaces

Attachment and adhesion of conidia of a wheat-isolate of Stagonospora nodorum to leaf and artificial surfaces was studied. Attachment of conidia was a non-viable process, separate from adhesion, that occurred rapidly and irreversibly. Attachment involved conidial-surface carbohydrates and was partially influenced by surface hydrophobicity. The subsequent adhesion, via the secretion of extracellular matrix from conidia, was a viable process that induced the complete cover of conidia in response to wheat leaf surface components containing epi-cuticular wax and to a lesser extent to barley but inducing only partial covering on glass. Results suggest that specific surface components from the compatible host promote rapid attachment and adhesion of S. nodorum conidia.     

Synthesis and application of alkyl-substituted high chroma yellow dyes for unmodified polypropylene fiber

A series of new monoazo yellow dyes having different alkyl substituents was synthesized to dye unmodified polypropylene fiber. Color hue of the dyes exhibited light yellow with very high chroma enough to use as yellow primary color dyes. The affinity of the dyes onto unmodified polypropylene was increased with the increase of the length of alkyl substituents. Therefore, the hexyl-substituted dye having the longest alkyl group in this experiment showed very high color strength of dyeings with K/S value of over 26 at maximum absorption wavelength. The color fastnesses to washing, rubbing and light were also improved significantly for the longer alkyl substituted dyes, so that the hexyl-substituted dye exhibited a rating higher than 4∼5 for all kinds of fastnesses.     

Biocomposites based on flax short fibres and linseed oil

Insulating materials based on flax short fibres were prepared and their functional properties enhanced using linseed oil. In order to improve biocomposites hydrophobicity, the linseed oil was added to the initial formulation, mixed with the fibres and finally dried after the moulding process. Thus, the average water absorption of 10-40/140 g/g oil/fibres samples was reduced up to 10 times during the first hour of immersion, compared to the reference oil-free materials. Moreover, the linseed oil polymerization inside the lignocellulosic matrix, which occurred after 20 days of drying at 50 °C, also improved mechanical and thermal behaviour of biocomposites. Spontaneous combustion phenomena related to the exothermic oxidation-polymerization of linseed oil were described as well. Therefore, the process parameters such as oil/fibres ratio, drying time and temperature, were optimized to ensure the safety of the process and to avoid self ignition of the lignocellulosic fraction at temperatures below 200 °C.     

覆膜开孔条件下斥水性层状土壤蒸发实验

覆膜开孔影响田间非均质土壤的水分运动过程,尤其当斥水程度不同时,其运动过程更趋于复杂.在控制土表不同覆膜开孔率条件下,进行了不同斥水程度的塿夹砂和砂夹塿的土柱蒸发实验,测定和分析了不同条件下土壤水分蒸发量变化过程和含水率剖面.结果表明,全覆膜的累积蒸发量-时间曲线明显较低,相应的蒸发10d后土壤水分剖面也与初始水分剖面接近,对于塿夹砂尤其明显.覆膜开孔率增加时,同条件下两种层状土的累积蒸发量与全覆膜相比均有明显增加,表明一旦覆膜开孔,覆膜保墒效应便明显降低.斥水程度增加时,累积蒸发量有所减小,说明斥水性的存在降低了水分运移速率.当土壤为严重斥水时,斥水性对水分运动过程的影响比覆膜开孔率的影响更明显.对于不同斥水程度的塿夹砂,采用对数函数表达累积蒸发量和时间的定量关系较好,而对于不同斥水程度下的砂夹塿分别采用幂函数和对数函数表达.     

How air-drying and rewetting modify soil organic matter characteristics: An assessment to improve data interpretation and inference

Air-drying and wetting of air-dried soil samples with water (i.e., rewetting) are widely used sample treatments in soil analyses. It is recognized that both air-drying and rewetting of soil samples affect the characteristics of organic matter (OM), but systematic evaluations are scarce. In this review, we synthesize what is known in the scientific literature concerning the types and magnitudes of effects resulting from air-drying and rewetting with respect to i) characteristics of aggregate-associated and water-extractable OM, ii) soil microbiota, and iii) decomposition of OM. Air-drying of soil samples results in the formation of new and/or stronger OM-mineral interactions as well as increased hydrophobicity and mineral surface acidity. The formation of new and enhancement of existing OM-mineral interactions may lead to an increase in perceived aggregate stability, potentially affecting estimates of amount and persistence of OM associated with soil aggregates. Compared to field moist samples, air-dried samples had 8–41% higher relative dry mass proportions in the 2–0.25 mm aggregate size fraction. Pronounced changes in the amount and composition of the water-extractable OM and soil microbiota are also detected during the course of air-drying and rewetting with the potential to affect the conclusions derived from OM decomposition experiments. Air-dried soil samples were found to have 2–10 times higher amounts of water extractable organic carbon and a decrease between 3% and 69% in the microbial biomass carbon (using the substrate-induced respiration technique) compared to field moist samples. The magnitude of air-drying and rewetting derived effects on sample characteristics appears to be site and soil type specific.     

消化道环境胁迫对青春双歧杆菌KLDS2.0003粘附能力影响

确定消化道环境胁迫对青春双歧杆菌KLDS2.0003粘附能力、菌体表面性质及菌体细胞膜脂肪酸组成影响.采用体外方法模拟消化道环境,以Caco-2细胞作为粘附模型,青春双歧杆菌KLDS2.0003相继经过模拟唾液、模拟胃液以及模拟肠液处理后,测定经历模拟消化道环境前后存活率、粘附能力、自动聚集能力和表面疏水性,同时采用扫描电镜和透射电镜观察菌体形态以及采用GS-MS法测定菌体处理前后细胞膜脂肪酸组成变化.结果表明,青春双歧杆菌KLDS2.0003经模拟消化道环境胁迫后,粘附能力下降,菌体表面疏水性、自动聚集能力菌下降、菌体细胞形态发生改变,膜不饱和脂肪酸与饱和脂肪酸比例增加,而且有一种新长链不饱和脂肪酸C18:2n6c产生.结果显示,消化道环境胁迫会降低青春双歧杆菌KLDS2.0003粘附能力,同时菌体自动聚集能力和表面疏水性均降低,三者之间呈现一定相关性,此外,在消化道环境胁迫条件下,膜脂肪酸组成发生改变,诱导产生一种新长链不饱和脂肪酸C18:2n6,c推测该菌通过调节膜脂肪酸组成变化以抵抗消化道环境中不利因素.     

Immediate effects of wildfires on water repellency and aggregate stability in Mediterranean calcareous soils

Alkaline soils are considered much less prone to developing water repellency induced by fire than acidic soils. Here we report on the persistence of water repellency present in calcareous soils immediately after wildfires in 10 burned areas in SE Spain, its distribution in different aggregate size fractions (< 2, 2–1, 1–0.5, 0.5–0.25 and < 0.25 mm) and on results from aggregate stability tests. We also distinguished between soil samples taken beneath pine (Pinus halepensis) and beneath understory vegetation.     

Soil water repellency and infiltration in coarse-textured soils of burned and unburned sagebrush ecosystems

Millions of dollars are spent each year in the United States to mitigate the effects of wildfires and reduce the risk of flash floods and debris flows. Research from forested, chaparral, and rangeland communities indicate that severe wildfires can cause significant increases in soil water repellency resulting in increased runoff and erosion. Few data are available to document the effects of fire on the spatial and temporal variability in soil water repellency and potential impacts on infiltration and runoff on sagebrush-dominated landscapes. Soil water repellency, infiltration and runoff were assessed after two wildfires and one prescribed fire in three steep, sagebrush-dominated watersheds with coarse-textured soils. Water repellency was generally greater on unburned hillslopes and annual variability in water repellency had a greater impact on infiltration capacity than fire effects. The most significant impact of fire was canopy and ground cover removal on coppice microsites. Infiltration rates decreased on coppice microsites after fire even though soil water repellency was reduced. Fire-induced reduction in infiltration resulted from the combined effect of canopy and ground cover removal and the presence of naturally strong water repellent soils. Removal of ground cover likely increased the spatial connectivity of runoff areas from strongly water repellent soils. The results indicate that for coarse-textured sagebrush landscapes with high pre-fire soil water repellency, post-fire increases in runoff are more influenced by fire removal of ground and canopy cover than fire effects on soil water repellency and that the degree of these impacts may be significantly influenced by short-term fluctuations in water repellent soil conditions.     

Effects of compaction on soil surface water repellency

Water repellency can reduce the infiltration capacity of soils over timescales similar to those of precipitation events. Compaction can also reduce infiltration capacity by decreasing soil hydraulic conductivity, but the effect of compaction on soil water repellency is unknown. This study explores the effect of compaction on the wettability of water repellent soil. Three air‐dry (water content ～4 g 100 g^?1) silt loam samples of contrasting wettability (non‐repellent, strongly and severely water repellent) were homogenized and subjected to various pressures in the range 0–1570 kPa in an odeometer for 24 h. Following removal, sample surface water repellency was reassessed using the water drop penetration time method and surface roughness using white light interferometry. An increase in compaction pressure caused a significant reduction in soil surface water repellency, which in turn increases the soil's initial infiltration capacity. The difference in surface roughness of soils compacted at the lowest and highest pressures was significant (at P > 0.2) suggesting an increase in the contact area between sessile water drops and soil surfaces was providing increased opportunities for surface wetting mechanisms to proceed. This suggests that compaction of a water repellent soil may lead to an increased rate of surface wetting, which is a precursor to successful infiltration of water into bulk soil. Although there may be a reduction in soil conductivity upon compaction, the more rapid initiation of infiltration may, in some circumstances, lead to an overall increase in the proportion of rain or irrigation water infiltrating water repellent soil, rather than contributing to surface run‐off or evaporation.