Sowing density and harvest time affect fibre content in hemp (Cannabis sativa) through their effects on stem weight

Sowing density and harvest time are considered important crop management factors influencing fibre quantity and quality in hemp (Cannabis sativa). We investigated whether the effects of these factors are essentially different or that both factors affect stem weight and thereby total and long‐fibre content. The effects of all combinations of three sowing densities and three harvest times were studied for six different stem parts. Almost 500 samples consisting of stem parts from 50 plants and with a length of 50 cm were tested. Fibres were extracted by a controlled warm‐water retting procedure, followed by breaking and scutching. The initial sample weight was fractionated into retting losses, wood, tow and long fibre. In both Italy and the Netherlands, crops were successfully established with different stem densities (99–283 m^?2), plant heights (146–211 cm) and stem diameters (4.5–8.4 mm) at harvest. Stem dry matter yields (6.8–11.7 Mg ha^?1) increased with a delay in harvest time but were not affected by sowing density. Retting loss percentages were lower in lower stem parts and decreased with later harvest because maturation was associated with increasing amounts of fibre and wood. Within a certain stem part, however, the absolute retting losses were constant with harvest time. Multiple linear regression analyses showed that the amount of fibre in a hemp stem is almost completely determined by the weight and the position of that stem part. When the plant grows, the increase in dry matter is split up into fibres and wood in a fixed way. This total fibre/wood ratio was highest in the middle part of the stem and lower towards both bottom and top. Sowing density and harvest time effects were indirect through stem weight. The long‐fibre weight per stem increased with the total fibre weight and hence with stem weight. Stem weight increased with harvest time; as harvest time did not affect plant density, the highest long‐fibre yields were obtained at the last harvest time. The long fibre/total fibre ratio was lowest in the bottom 5 cm of the stems but similar for all other parts. Sowing density and harvest time effects again were indirect. Fibre percentages in retted hemp decreased with increasing stem weights towards a level that is presumably a variety characteristic. The dry matter increase between harvests, however, is much more important with respect to total and long‐fibre yield.     

Effects of selected pectinolytic bacterial strains on water-retting of hemp and fibre properties

Aims:  To study the effect of selected bacterial strains on hemp water-retting and properties of retted fibre.
Methods and Results:  The trials were performed in laboratory tanks. The traditional water-retting process, without inoculum addition, was compared to a process modified by inoculating water tanks with two selected pectinolytic bacteria: the anaerobic strain Clostridium sp. L1/6 and the aerobic strain Bacillus sp. ROO40B. Six different incubation times were compared. Half the fibre obtained from each tank was combed. Micromorphological analyses were performed by scanning electron microscopy on uncombed and combed fibres. Moreover, organoleptic and chemical analyses of uncombed fibres were performed.
Conclusions:  The inoculum , besides speeding up the process, significantly improved the fibre quality. The fibre was not damaged by mechanical hackling, thanks to the good retting level obtained by the addition of selected strains, differently to what happened with the traditionally retted fibre. The best fibre quality was obtained after 3–4 days of retting with the addition of the bacterial inoculum .
Significance and Impact of the Study:  Retting is the major limitation to an efficient production of high-quality hemp fibres. The water-retting process and fibre quality were substantially improved by simultaneously inoculating water tanks with two selected pectinolytic strains.     

The potential of hemp (Cannabis sativa L.) for sustainable fibre production: a crop physiological appraisal

Hemp (Cannabis sativa L.) fibre can be used as a raw material for paper and textile production. A comprehensive research programme in the Netherlands has concluded that fibre hemp is a potentially profitable crop, having the right profile to fit into sustainable farming systems. This paper presents an appraisal of the crop physiological characteristics and the agronomic potential of hemp. Parameter values of basic crop physiological characteristics such as light interception potential, radiation use efficiency and dry matter partitioning coefficients are given. The effect of crop management decisions such as cultivar choice, sowing date, plant density, and harvest date on the value of these parameters is discussed. A simple crop growth model was used to assess the yield potential of hemp for the climate of the Netherlands. Calculations made for a non-stressed late-flowering hemp crop sown on 15 April and harvested on 15 September give a stem dry matter yield of 17.1 t ha^-1. The effects of advancing or delaying sowing or harvest date on stem yield were calculated. Crop physiological characteristics of hemp are compared to those of kenaf (Hibiscus cannabinus L.). Radiation use efficiency and dry matter partitioning coefficients of the two crops are similar. Base temperatures for development and growth are lower in hemp than in kenaf. In a temperate climate with cool springs, canopy establishment will be more rapid in hemp than in kenaf. Hemp seems an excellent candidate to fill the niche for an annual fibre crop in a temperate climate.     

Determining the physical properties of flax fibre for industrial applications: the influence of agronomic practice

Field trials of fibre flax were sown in 2002 and 2003 comprising 29 and 26 flax varieties, respectively. In 2002, two nitrogen treatments of 40 and 80 kg ha^?1 were imposed. The trials were sprayed with a desiccating herbicide prior to retting at 35 and 15 days after midpoint of flowering in 2002 and 2003, respectively, and were harvested once retting had completed. Fibre was extracted from the flax stems using a laboratory‐scale scutcher and hackling pins, and long and total fibre yields were determined. The breaking load of flax technical fibres was assessed using a novel technique employing ‘zero twist’ yarns. Fineness was assessed using the Wool Industries Research Association airflow method. The tenacity of a single technical fibre was then derived from the average breaking load of the yarn and knowledge of its fineness. Both flax variety and season were found to contribute to variations in fibre fineness and strength, with the dry season in 2003 leading to less variation across the varieties and much finer fibres. Few of the varieties were found to be stable across seasons, and environmental variation accounted for 96% of the variation in fibre fineness between years, and 69% of the variation in tensile strength and breaking load. Fibre yield was found to be related to fibre fineness, with the coarser fibres corresponding to higher yields. The new yarn test presented herein has been shown to be a valid and useful method for determining the tensile properties of technical flax. The varieties and the sample sizes required to adequately measure variation in fibre properties are discussed.     

Assessment of flax and hemp fibres in terms of their impact on the growth performance and health status of weaned piglets

Weaning is a critical phase in intensive piglet production marked by the frequent occurrence of digestive disorders posing health and economic burden. To stave off such weaning-related problems, antibiotics and supplements containing high levels of ZnO are often used. In this study, we investigated whether natural fibres obtained from two plants known for their dietary fibre profile and antioxidant properties: flax (Linum usitatissimum L.) and hemp (Cannabis sativa L.), can serve as a health-promoting diet supplement. The study was conducted on a total of 191 Polish Large White piglets from 18 L, from their birth to 56 days of age. Piglets were divided by litters into six groups: W1.5, F1.5, H1.5, W2.0, F2.0, and H2.0. Groups W1.5, F1.5, and H1.5 received feed supplemented with 1.5% fibre from wood cellulose (W), flax (F), and hemp (H), respectively, while groups W2.0, F2.0, and H2.0 received feed with a higher 2.0% content of the same fibres. Flax and hemp fibres were characterised by a complex composition, antioxidant properties due to the presence of phenolic acids, and low risk of mycotoxin contamination. Flax fibre resulted in best weight gains and feed conversion ratio (P ≤ 0.05) of piglets, while hemp fibre had higher positive effect on antioxidant status (P ≤ 0.05) compared to the other two fibre additives. Neither flax nor hemp fibres had any adverse effect on the haematological and biochemical blood parameters. Piglets receiving a diet with 1.5% added fibre showed better growth performance, while diet supplementation with 2% fibre had a beneficial effect on the content of butyric acid in the small intestinal chyme (P ≤ 0.05). The results suggested that both flax and hemp fibres can be innovative feed additives for weaned piglets. However, further studies should be conducted in commercial farms, as the effects of dietary fibre could vary in more challenging environmental conditions.     

The effect of temperature on leaf appearance and canopy establishment in fibre hemp (Cannabis sativa L.)

The effects of temperature on the development and growth of hemp (Cannabis sativa L.) have never been quantified. Therefore, to establish the effect of temperature on leaf appearance and canopy establishment of fibre hemp under controlled and field conditions, plants were grown in growth chambers at 11 regimes with average temperatures between 10°C and 28°C, and three cultivars were sown in the field in March, April and May in 1990, 1991 and 1992. In the field, thermal time (base 0°C) between sowing and emergence ranged from 68°Cd to 109.5°Cd (average 88.3°Cd). Rates of leaf appearance and stem elongation increased linearly with temperature between 10°C and 28°C. The base temperature for leaf appearance was 5.7°C from the growth chamber experiments and 1°C from the field experiments. In the field, the base temperature for the relationship between light interception by the canopy and thermal time was 2.5°C, and thermal time, calculated at the appropriate base temperature, accounted for about 98% of the variance in the number of leaves and for 98.6% of the variance in the proportion of light intercepted by the canopy. Days from emergence accounted for less of the variance in both parameters than thermal time. Interception of 90% of light was attained on average at 465°Cd (base 0°C) after emergence. It is concluded that thermal time is a simple and accurate tool to describe leaf appearance and light interception in fibre hemp.     

Easily available enzymes as natural retting agents

Easily available commercial enzymes currently have great potential in bast fibre processing and can be modified for different end uses. There are several new technologies using enzymes that are able to modify fibre parameters, achieve requested properties, improve processing results and are more beneficial to the ecology in the area of bast fibre processing and fabrics finishing. Enzymatic methods for retting of flax, "cottonisation" of bast fibres, hemp separation, and processing of flax rovings before wet spinning, etc., fall into this group of new technologies. Such enzymatic biotechnologies can provide benefits in textile, composite, reinforced plastic and other technical applications. Laboratory, pilot and industrial scale results and experiences have demonstrated the ability of selected enzymes to decompose interfibre-bonding layers based on pectin, lignin and hemicelluloses. Texazym SER spray is able to increase flax long fibre yields by more than 40%. Other enzymes in combination with mild mechanical treatment can replace aggressive and energy-intensive processing like Laroche "cottonisation". Texazym SCW and DLG pretreatments of flax rovings are presented.     

Muscle fibre growth dynamics in diploid and triploid rainbow trout

The effect of triploidy on muscle fibre growth was determined by comparing hyperplasia and hypertrophy of white muscle fibres in all-female, diploid and triploid rainbow trout Oncorhynchus mykiss (100–400 mm total length). Conventional morphometry and protein and DNA concentrations were used to assess muscle fibre hyperplasia and hypertrophy in white muscle samples derived from an anterio-dorsal location. Muscle fibre distributions were significantly different between triploids and diploids in trout <300 mm. The proportion of fibres <20 μm was higher in diploids than in triploids and the proportion of fibres in the 20–40 μm category was higher in triploids than in diploids. This indicates that the hyperplastic fibres of triploids are larger than those of diploids. Larger hyperplastic fibres in triploids are probably due to the combined effect of increased nuclear size in triploids and the relatively high nucleus: cell ratio observed in small muscle fibres. These larger fibres may be less favourable to cellular metabolic exchange because of their smaller surface area to volume ratios, and perhaps account for reduced viability and growth observed in triploids during early life stages. On the other hand, the lack of difference in the distribution of fibres <20 μm between diploids and triploids at larger body size ranges (301–400 mm) imply that triploid trout may have higher rates of new fibre recruitment and growth capacity at these sizes. There was no difference between diploid and triploid trout in the mean size of muscle fibres; however, the number of fibres per unit area was reduced by 10% in triploids. No differences were observed in protein or DNA concentrations in muscle tissues between the two genetic groups. Since triploid nuclei have 1·5 times more DNA than diploid nuclei, this deviation from the expected muscle DNA concentration (1·3–1·4 times more DNA in triploids when the 10% reduction in fibre density is considered) suggests that the number of nuclei per muscle fibre is reduced. In both diploids and triploids, mean fibre size increased with body length while fibre density decreased. Similarly, protein concentration in the muscle tissue increased and DNA concentration declined with increasing body length. Protein/DNA ratio was strongly and positively correlated with fibre size. These results demonstrate that changes in DNA and protein concentrations can be used to assess hyperplasia and hypertrophy in muscle tissues. However, the morphometric procedure provides better insight into muscle fibre growth as it enables the direct visualization and analysis of muscle fibre distribution patterns.     

Chemical retting of flax using chelating compounds

A wide range of concentrations of ethylenediaminetetra acetic acid (EDTA) was tested as a retting agent at a range of temperatures, pHs and stem: liquor ratios. Treatment of stems at 2 and 3 g/litre at 40 °C in a liquor ratio of 1:10 at pH 11 produced the finest and strongest fibre. Dried-green stem retted slightly better than the glyphosate-desiccated stem and after multiple retting with EDTA, Trilon TB and diethyltriaminepenta acetic acid (DTPA), the dried-green stem produced the finest fibre. Trilon TB and DTPA retted better than EDTA and produced a high yield of fibres. The fluidity of fibres scutched from the dried-green stem was lower than the fluidity of the fibres from glyphosate-desiccated stem.     

亚麻脱胶菌种的选育及脱胶过程的初步研究

从沤麻主生物期的水中分离产果胶酶的菌株经初筛、复筛获得了三株专性厌氧细菌,初步鉴定为费氏芽孢杆菌,对其亚麻脱胶性能进行了初步研究,确定人工加菌沤麻的最适工艺条件为：加菌量2％,加菌时间：沤麻进入主生物期零时,菌株A优于其它菌株．结果表明：采用上述工艺进行沤麻实验,可缩短沤麻时间30％,并可提高麻纤维质量。     

Steam explosion of woody hemp chènevotte

This paper concerns the morphology of hemp woody core cells, investigated by optical and scanning electron microscopy, and the chemical analysis of the hemp cells. Steam explosion was investigated as a pre-treatment step for woody hemp ‘chènevotte’, with the aim of optimizing the separation and delignification of woody fibres.

In this study, we report the results of five experiments performed on ‘chènevotte’ samples impregnated in acid solution (0.1% w/w H₂SO₄) and steamed at 200, 210, 220, 230 and 240°C for 180 s. The effect of process temperatures on the woody hemp core after acidic impregnation was followed by optical and scanning electron microscopy, by assessment of the chemical composition, and by evolution of the average degree of polymerization (DPv) values of the purified wood fibres.

We found that treatment at 200 and 210°C led to samples that were difficult to delignify because the destructuring and disintegration of lignocellulosic materials were insufficient. A temperature of the order of 220–230°C is required to obtain well-separated fibres. However, at a temperature of 240°C, degradation and fibre damage were noted.     

A mechanical investigation of the retting process in dew-retted hemp (Cannabis sativa)

Hemp (Cannabis sativa) produces phloem fibres, which are formed in bundles towards the periphery of the stem. This study investigated one aspect of the retting process, the dissociation of these fibres from the core of the stem, which is influenced by the action of micro-organisms. Peel tests were used to investigate the work required to remove a tissue peel, rich in fibres, from the core of the stem. Two separate experiments studied (1) the effects of tissue dehydration as stems were dried out in the oven; and (2) the progress of retting in stems that were dew-retted in the field. A comparison between two different types of peel tests, where the stems were clamped either vertically or horizontally in the jaws of a tensile testing machine and the load applied vertically, showed that the work required to peel stems in the vertical position was over 20% greater than that for the horizontal position. Freshly harvested stems were dehydrated in an oven at 40°C over a period of 42 h and as the moisture content decreased there was a significant increase in the work to peel. In contrast, stems that had been dew-retted in the field showed a significant decrease in work to peel. When the moisture content of stems dried in the oven decreased below 12%, the work to peel rapidly decreased. As the plant tissues dehydrated their fracture characteristics changed and this was reflected in the increase in the work to peel seen in the oven-dried samples. This, however, was not evident in the field-retted samples, in which there was a decrease in work to peel. The field-retted samples were exposed to the activity of micro-organisms for a prolonged period of time compared with the oven-dried samples; this increased the potential degradation caused by microbial enzymes. Thus, the reduced work to peel in dew-retted stems is thought to be due to the colonisation of the stem by micro-organisms and the subsequent retting process. The dramatic decrease in work to peel at low moisture content in the oven-dried stems is thought to result from mechanical changes leading to brittle fracture characteristics. This study indicates that peel tests can be used to objectively monitor the reduction in work to peel for dew-retted stems and relate this reduction to the progress of retting. Thus, peel tests may be used to monitor the effects of different factors on the process of retting in hemp.     

Down-regulation of GhADF1 gene expression affects cotton fibre properties

Cotton fibre is the most important natural fibres for textile industry. To date, the mechanism that governs the development of fibre traits is largely unknown. In this study, we have characterized the function of a member of the actin depolymerizing factor (ADF) family in Gossypium hirsutum by down-regulation of the gene (designated as GhADF1 ) expression in the transgenic cotton plants. We observed that both the fibre length and strength of the GhADF1 -underexpressing plants increased as compared to the wild-type fibre, and transgenic fibres contained more abundant F-actin filaments in the cortical region of the cells. Moreover, the secondary cell wall of the transgenic fibre appeared thicker and the cellulose content was higher than that of the control fibre. Our results suggest that organization of actin cytoskeleton regulated by actin-associated proteins such as GhADF1 plays a critical role in the processes of elongation and secondary cell wall formation during fibre development. Additionally, our study provided a candidate intrinsic gene for the improvement of fibre traits via genetic engineering.     

Comparison of subjective and objective methods to assess flax straw cultivars and fibre quality after dew-retting

Subjective and objective methods were compared for the assessment of the quality of unretted and retted straw, and the fibres obtained after dew-retting of four flax cultivars, Ariane, Evelin, Laura and Viola. Maturity of straw, degree of retting, ease of decortication after retting, divisibility, handle, cleanliness and colour were assessed as subjective factors and of these, degree of retting and handle appear to be useful for assessing quality. The samples were also analysed for physical and chemical differences using a range of objective methods. Straw quality could not be graded using height and maturity, although stem diameter and technical length could indicate quality. Changes in N, lipid and ash content, as a result of retting, were observed. The increase in the proportions of fibre fractions present in retted compared with unretted straw, due to microbial degradation of pectin, could be identified by thermal analysis. Analyses of the fibre samples to determine fineness, strength, cellulose, hemicellulose, lignin and minerals were carried out and significant differences in some of the parameters were identified. Cultivar Laura produced the best fibre. Fibre fineness, ash, lipid, caustic weight loss and fibre fractions as determined by thermal analysis were found to be important objective parameters for quality assessment. The assessment of fibre samples performed subjectively by an expert grader and by selected objective methods gave similar quality rankings.     

Improving retting of fibre through genetic modification of flax to express pectinases

Flax (Linum usitatissimum L.) is a raw material used for important industrial products. Linen has very high quality textile properties, such as its strength, water absorption, comfort and feel. However, it occupies less than 1% of the total textile market. The major reason for this is the long and difficult retting process by which linen fibres are obtained. In retting, bast fibre bundles are separated from the core, the epidermis and the cuticle. This is accomplished by the cleavage of pectins and hemicellulose in the flax cell wall, a process mainly carried out by plant pathogens like filamentous fungi. The remaining bast fibres are mainly composed of cellulose and lignin. The aim of this study was to generate plants that could be retted more efficiently. To accomplish this, we employed the novel approach of transgenic flax plant generation with increased polygalacturonase (PGI ) and rhamnogalacturonase (RHA) activities. The constitutive expression of Aspergillus aculeatus genes resulted in a significant reduction in the pectin content in tissue-cultured and field-grown plants. This pectin content reduction was accompanied by a significantly higher (more than 2-fold) retting efficiency of the transgenic plant fibres as measured by a modified Fried’s test. No alteration in the lignin or cellulose content was observed in the transgenic plants relative to the control. This indicates that the over-expression of the two enzymes does not affect flax fibre composition. The growth rate and soluble sugar and starch contents were in the range of the control levels. It is interesting to note that the RHA and PGI plants showed higher resistance to Fusarium culmorum and F. oxysporum attack, which correlates with the increased phenolic acid level. In this report, we demonstrate for the first time that over-expression of the A. aculeatus genes results in flax plants more readily usable for fibre production. The biochemical parameters of the cell wall components indicated that the fibre quality remains similar to that of wild-type plants, which is an important pre-requisite for industrial applications. Magdalena Musialak and Magdalena Wróbel-Kwiatkowska participated equally in the preparation of this paper     

Secondary cell-wall assembly in flax phloem fibres: role of galactans

Non-lignified fibre cells (named gelatinous fibres) are present in tension wood and the stems of fibre crops (such as flax and hemp). These cells develop a very thick S2 layer within the secondary cell wall, which is characterised by (1) cellulose microfibrils largely parallel to the longitudinal axis of the cell, and (2) a high proportion of galactose-containing polymers among the non-cellulosic polysaccharides. In this review, we focus on the role of these polymers in the assembly of gelatinous fibres of flax. At the different stages of fibre development, we analyse in detail data based on sugar composition, linkages of pectic polymers, and immunolocalisation of the β-(1→4)-galactans. These data indicate that high molecular-mass gelatinous galactans accumulate in specialised Golgi-derived vesicles during fibre cell-wall thickening. They consist of RG-I-like polymers with side chains of β-(1→4)-linked galactose. Most of them are short, but there are also long chains containing up to 28 galactosyl residues. At fibre maturity, two types of cross-linked galactans are identified, a C–L structure that resembles the part of soluble galactan with long side chains and a C–S structure with short chains. Different possibilities for soluble galactan to give rise to C–L and C–S are analysed. In addition, we discuss the prospect for the soluble galactan in preventing the newly formed cellulose chains from completing immediate crystallisation. This leads to a hypothesis that firstly the secretion of soluble galactans plays a role in the axial orientation of cellulose microfibrils, and secondly the remodelling and cross-linking of pectic galactans are linked to the dehydration and the assembly of S2 layer.     

Three muscle fibre types in the axial muscle of axolotl (Ambystoma mexicanum Shaw) A quantitative lightand electron microscopic study

Morphometric analysis by light microscopy of p-phenylene-diamine stained semithin sections of axolotl tail muscle revealed differences in the cross-sectional area of the fibres and in the number of mitochondria and of lipid inclusions per fibre, and indicated the presence of three distinct types of fibres. The tripartition was found to be statistically highly significant. Representative fibres from each group established by light microscopic morphometry were subjected to an ultrastructural morphometric analysis. The volume content of mitochondria amounted to 9.8% of the fibre volume for red, 4.0% for intermediate and 0.8% for white fibres. The myofibrils composed 60%, 70% and 83% in the same fibres. The volume of the sarcotubular system (t-tubuli and sarcoplasmic reticulum) was 2.5% in red, 4.5% in intermediate and 11.7% in white fibres. The three fibre types also demonstrated differences in myofibrillar cross-striation pattern and number of triads. The reliability of the light microscopic morphometry was tested by correlation with EM montages of the representative fibres.     

Gibberellin signaling

A study of stem anatomy and the sclerenchyma fibre cells associated with the phloem tissues of hemp (Cannabis sativa L.) plants is of interest for both understanding the formation of secondary cell walls and for the enhancement of fibre utility as industrial fibres and textiles. Using a range of molecular probes for cell wall polysaccharides we have surveyed the presence of cell wall components in stems of hemp in conjunction with an anatomical survey of stem and phloem fibre development. The only polysaccharide detected to occur abundantly throughout the secondary cell walls of phloem fibres was cellulose. Pectic homogalacturonan epitopes were detected in the primary cell walls/intercellular matrices between the phloem fibres although these epitopes were present at a lower level than in the surrounding parenchyma cell walls. Arabinogalactan-protein glycan epitopes displayed a diversity of occurrence in relation to fibre development and the JIM14 epitope was specific to fibre cells, binding to the inner surface of secondary cell walls, throughout development. Xylan epitopes were found to be present in the fibre cells (and xylem secondary cell walls) and absent from adjacent parenchyma cell walls. Analysis of xylan occurrence in the phloem fibre cells of hemp and flax indicated that xylan epitopes were restricted to the primary cell walls of fibre cells and were not present in the secondary cell walls of these cells.     

The number of satellite cells in slow and fast fibres from human vastus lateralis muscle

The aim of this investigation was to study the distribution of satellite cells in slow (type I fibres) and fast (type II fibres) fibres from human vastus lateralis muscle. This muscle is characterised by a mixed fibre type composition and is considered as the site of choice for biopsies in research work and for clinical diagnosis. Biopsy samples were obtained from five healthy young volunteers and a total of 1,747 type I fibres and 1,760 type II fibres were assessed. Satellite cells and fibre type composition were studied on serial muscle cross-sections stained with specific monoclonal antibodies. From a total of 218 satellite cells, 116 satellite cells were found in contact with type I fibres (53.6±8% of the satellite cells associated to type I fibres) and 102 satellite cells in contact with type II fibres (46.4±8% of the satellite cells associated to type II fibres). There was no significant difference (P=0.4) between the percentages of satellite cells in contact with type I and with type II fibres. Additionally, there was no relationship between the mean number of satellite cells per fibre and the mean cross-sectional area of muscle fibres. In conclusion, our results show that there is no fibre type-specific distribution of satellite cells in a human skeletal muscle with mixed fibre type composition.     

Short-term effects of nitrogen availability on wood formation and fibre properties in hybrid poplar

The application of nitrogen-containing fertilisers is one approach used to increase growth rates and productivity of forest tree plantations. However, the effects of nitrogen fertilisation on wood properties have not been systematically assessed. The aim of this work was to document the impacts of nitrogen fertilisation on wood formation and secondary xylem fibre properties. We used three fertilisation treatments in which the level of ammonium nitrate was adjusted to 0, 1 and 10 mM in a complete nutrient solution applied daily over a period of 28 days in standardised greenhouse experiments with clonal material of Populus trichocarpa (Torr and Gray) × deltoides (Bartr. ex Marsh). We showed that there was a short-term and repeatable response in which xylem fibre morphology and secondary cell wall structure adapt to a shift in N availability. Under high-nitrogen exposure, xylem fibres were 17% wider and 18% shorter compared to the adequate nitrogen treatment. A very significant thickening of the fibre cell walls was also observed throughout the stem of trees receiving the high-N treatment. It appeared that cell wall structure was greatly affected by the high-N treatment as fibres developed a modified inner cell wall layer. Histological observations indicated that the internal cell wall layer was enriched in cellulose and chemical determinations showed that wood contained more holocellulose. Together, these results indicate that the response of poplar to nitrogen availability may involve marked effects on secondary xylem formation.