Dimensions of Mechanical Fibres in Paulownia elongata S. Y. Hu Wood from Different Habitats

Paulownia elongata S. Y. Hu, has exceptionally fast growth in juvenile stage (more than 3 m in the second year). Due to its characteristic of easy generative and vegetative propagation (tissue culture) and renewal, it currently presents the most suitable plant for biomass production in our region, with short rotation time. Poplar clones provide raw material for paper and pulp industry at the moment, and this industry is the biggest softwood consumer in Serbia. Anatomical properties of wood mechanical fi bres in Paulownia elongata S. Y. Hu juvenile wood have not been researched in Serbia, since this species has been recently introduced from China (1993). The aim of this paper is to explore the impact of habitats (soil) and fertilisation on wood fi bre dimensions in juvenile wood of Paulownia elongata S. Y. Hu. Samples for research of wood fi bres originate from experimental plantations of Paulownia elongata S. Y. Hu, 2 years of age, from two different sites: Obrenovac-Veliko polje and Ub-Pambukovica. Based on research of wood anatomy, it has been concluded that there are signifi cant statistical differences in wood fi bre dimensions in Paulownia elongata S. Y. Hu from different habitats. Research of wood fi bre dimensions in Paulownia elongata S. Y. Hu juvenile wood from two different sites contributes to determine its use for the pulp industry, which supports cultivation of this fast growing species (Table 3, 4 i 5).


INTRODUCTION 1. UVOD
Paulownia elongata S. Y. Hu is characterised by its excessively fast growth in the juvenile phase (vertical growth is up to 4 m during the second year and within the same period the growth in diameter is about 5 -7 cm), as well as by its easy generative and vegetative propagation (tissue culture) and plantation renewal (Šoškić et al., 2003).Paulownia elongata characteristics show that the species is recommended for biomass production.(Vilotić et al., 2011).
There are many factors, such as soil and climate, that affect the anatomical properties of wood (Zhang, 1992;Vilotić and Knežević, 1994;Vilotić, 2000;Hacke and Sperry, 2001).Esteban et al. (2010) and Vilotić and Knežević (1994) state that ecological environmental circumstances have affected signifi cantly not only the properties of the tree, but also the dimensions of its conductive cells.Venugopal and Liangkuwang (2007) state that there is an obvious correlation between climatic parameters, activities of vascular cambium and xylem formation.Research has shown that the physical and chemical characteristics of soil have a great infl uence on macroscopic characteristics, microscopic structure, density, and physical, mechanical and technological properties of wood (Vilotić, 1992;Vilotić et al., 2005;Šoškić et al., 2003).
Paulownia elongata S. Y. Hu was introduced from China to Serbia in 1993.Anatomical characteristics of its wood fi bres in juvenile wood have not been researched so far.The goal of this paper was to examine: a) the infl uence of habitat (soil) on juvenile wood fi bre dimensions in Paulownia elongata S. Y. Hu; and b) the infl uence of fertilisation on juvenile wood fi bre dimensions of Paulownia elongata in different habitats.

MATERIJAL I METODE
Samples used for research of the infl uence of habitat and feeding on the dimensions of wood fi bres were taken from experimental 2-year-old plantations of Paulownia elongata S. Y. Hu, at two different sites: Obrenovac-Veliko polje and Ub-Pambukovica.

Klima
Obrenovac is located almost in the middle of a northern, moderate continental strip, with the climate milder than the typical Pannonian continental one.The climate in Pambukovica is a moderately continental one, with certain distinctive characteristics.The basic climate factors for the areas of Obrenovac and Pambukovica are given as the average monthly temperatures (Figure 1) and the average monthly precipitations (Figure 2), for the period from 1948 to 2012.The climate data for Obrenovac and Pambukovica areas were taken from the monitoring stations in Belgrade and Valjevo, respectively.Both monitoring stations are supervised by the Republic Hydrometeorological Service of Serbia.
Figures 1 and 2 show similar climate for the areas of Obrenovac and Pambukovica, in terms of the average monthly temperatures and the average monthly precipitations.The annual distribution of precipitations is very favourable for the agricultural production (the precipitation increases throughout the whole spring) (Pavlović et al., 2011).Table 1 shows physical and chemical soil characteristics in Obrenovac and Pambukovica.The low level of humus content in soils suggests that the total nitrogen content is also low.In addition, the lack of the organic substances and phosphorous is also notable, although potassium is present in satisfactory amounts.

Treatments 2.3. Tretmani
In order to improve the nutritive values of these soils, the organic fertilizer was used at both sites.Three sample groups were taken from each site.Two sample groups (from each site) were treated with the combination of fertor (chicken fertilizer) and polimer (the quantities of the components are given in Table 2).In addition, the sand and the Sunoko calcifi cation agent were used at the Pambukovica site.The sand was added to improve the physical properties of the soil, while the Sunoko calcifi cation agent was added to decrease the soil acidity.The effects of the treatments on both sites were evaluated in regard to the control sample group (from each site), which has not been treated.
Fertor is an organic fertiliser, composed of 100 % of chicken fertiliser, improved by other organic substances of plant origin, increasing and enhancing the fertiliser nutritive value.In addition to main elements (N, P, K, Ca and Mg), it also contains microelements (Fe, Mn, B, Zn, Cu).Part of the macro and micro elements is easily accessible and readily available for the plant, while the remainder is gradually released (Web Source 1).
Sunoko calcifi cation agent is an inorganic improving agent for the soil, suitable for all plant culture as a fertiliser and agent for the enhancement of soil properties.It is recommended for all types of soil, whose pH value is lower than 5.5, as is the case with Pambukovica soil.With a content of minimum 70 % of CaCO 3 and MgCO 3 , but also P, K, Fe, as well as Mn, Zn, Cu, Co and pH value of 8.22, it improves the structure and pH value of acidic soils, and returns microelements into the soil, thus improving soil fertility (Web Source 2).

Sampling and preparation of samples 2.4. Uzorkovanje i priprema uzoraka
The samples were taken from root collars, as rolls 1 cm thick.These were chopped into match-size pieces and macerated in order to obtain individual cells of wood tissue suitable for measuring mechanical fi bre dimensions.
Wood tissue maceration of Paulownia elongata samples was carried out using Franklin's reagent (Franklin, 1945), a mixture of 30 % of hydrogen peroxide and glacial acetic acid in the ratio 1:1.

Measuring wood fi bre dimensions 2.5. Mjerenje dimenzija drvnih vlakanaca
Measurement of length and width of mechanical fi bres of Paulownia elongata was carried out at the Institute for Forestry in Belgrade, using an optical microscope, augmenting the sample magnifi ed 40 times, using the "Image Tool" programme.
The mean fi bre length and the mean fi bre width were obtained from 30 measurements (30 fi bres) on each of the three samples that made one sample group.The results were statistically analyzed by the single factor ANOVA test.3 RESULTS AND DISCUSSION 3. REZULTATI I DISKUSIJA Wood fi bres are the mechanical elements present in the Paulownia elongata tree.These are prosenchima elements, very sharp at the ends.
Statistical analysis of measured lengths and widths of mechanical fi bre samples from juvenile sprouts enabled an overview of the infl uences of feeding and habitat on the dimensions of Paulownia elongata wood fi bre.By the analysis of measured values within each of the sampling groups, minimum and maximum measured and mean values were obtained for lengths and widths of fi bres.From the mass of 90 measurements per sample, minimum and maximum values were selected for each group.Mean values for fi bre lengths and widths were obtained as arithmetic mean values of those measured in each sampling group.This procedure was applied to all sampling groups and both habitats.
Minimum, maximum and mean values, as well as standard deviations of fi bre length in Paulownia elongata control and treated samples taken from these two habitats are shown in Table 3.The results of the multiple range tests for both fi bre length and fi bre width of the Paulownia elongata are given in Table 4.

Infl uence of habitats on the length of wood fi bre 3.1. Utjecaj staništa na duljinu drvnih vlakanaca
The infl uence of habitat on the dimensions of wood fi bres can be seen through the comparison of values of fi bre length of Paulownia elongata control samples (those without fertilising) and the researched habitats.
Tables 3 and 4 show signifi cant statistical differences in the fi bre length of the control samples (OB.3 and P.3) from these two sites.Fibre length of samples of Paulownia elongata cultivated in Obrenovac have a mean value of 0.459 mm, while the mean value of samples of the same age taken from the site of Pambukovica is 0.371 mm.
In addition, it is interesting to compare maximum measured lengths of fi bres from these two sites.It can be seen that the maximum measured fi bre length of 1.25 mm recorded for a plant cultivated in Obrenovac is twice as long as the maximum measured fi bre length of 0.57 mm measured in a plant cultivated in Pambukovica.
This discrepancy in mean and maximum values of fi bre length in control samples from these sites indicates that the habitats and their properties greatly infl uenced the fi bre length.
Research conducted by Popović and Radošević (2011) showed that mean mass and mean numerical length of fi bres measured on a 12-year old Paulownia elongata cultivated in an experimental plantation in Bela Crkva, ranged between 0.985 and 1.022 mm, while values measured on Paulownia fortunei (the same age, from the same location) in terms of mass and numerical length of fi bres were somewhat smaller and ranged between 0.783 and 0.818 mm (Popović and Radošević, 2008).Similar values for Paulownia elongata fi bre length of 0.96-1.19mm were stated by Cheng (1983).Having in mind that the 2-year old Paulownia elongata (Table 3), cultivated in the Republic of Serbia, has the average fi bre length in the range between 0.371 and 0.459 mm, it could be assumed that there is an increasing trend in fi bre length with the increasing age, for this wood species.

Infl uence of fertilising on the length of wood fi bres 3.2. Utjecaj gnojidbe na duljinu drvnih vlakanaca
Statistical analysis of the length and width of the mechanical fi bres of Paulownia elongata samples provide the possibility to determine the infl uence of various treatments on the fi bre dimensions.For that purpose, the results of the treated samples were compared with the results obtained from the control sample group at the related site (Table 4).
Based on the analysis of fi bre length mean values for the Obrenovac site, presented in Table 3, it can be concluded that the fi bre length mean value of 0.459 mm in the control sample is higher than the fi bre length of samples treated by fertiliser (0.441 and 0.409 mm), which indicates that fertilising did not positively affect the length of wood fi bres in this habitat.
Table 3 also shows mean values for Paulownia elongata fi bre lengths from the Pambukovica site.In addition, it can be noticed that fi bre length mean value of 0.371 mm in a control sample (P.3 sample) has the lowest value, while mean values of fi bres taken from fertilised samples (P.1 and P.2) of 0.457 mm and 0.478 mm, respectively, are signifi cantly higher (Table 4).Based on that, it can be concluded that fertilising had a positive infl uence on fi bre length in the Pambukovica site.
Table 5 shows mean values and standard deviation, as well as maximum and minimum values measured for fi bre width in control and fertilised samples of Paulownia elongata from these two habitats.

Infl uence of habitat on width of wood fi bres 3.3. Utjecaj staništa na širinu drvnih vlakanaca
It can be observed that mean values of fi bre width measured in control samples of Paulownia elongata cultivated in Obrenovac and Pambukovica, shown in Table 5, do not show statistically signifi cant differences (Table 4).The maximum measured value of fi bre width in control samples cultivated in Obrenovac of 50 μm is somewhat higher than fi bre width in control samples cultivated in Pambukovica of 30 μm, while the minimum measured values of fi bre width in control samples cultivated in these two habitats are identical.These results suggest that the site itself had no infl uence on the fi bre width.

Infl uence of fertilising on width of wood fi bres 3.4. Utjecaj gnojidbe na širinu drvnih vlakanaca
Treated sample group OB.1 (Obrenovac site) showed 1 μm higher values of mean fi bre width in comparison to non-treated samples (OB.3), which is not a statistically signifi cant difference.Mean fi bre with of the treated sample group OB.2 was signifi cantly higher in regard to the control samples (Table 5 and Table 4).
The differences of the mean fi bre values between the treated and the control samples are higher at the Pambukovica site (in regard to Obrenovac site), and they are statistically signifi cant when comparing the P.1 sample group with the other two.
Minimum values of fi bre width measured in fertilised and untreated samples taken from both habitats are the same.As for maximum values of measured fibre width, control samples taken from the Obrenovac site are a little bit higher than fertilised ones, while maximum measured values of fi bre width in control samples taken from the Pambukovica site are a little bit lower than in fertilised samples.However, the statistical analysis of the results does not provide the confi rmation that the observed differences occurred as the consequence of the treatments.

ZAKLJUČAK
Based on the conducted research, it can be concluded that there are differences in fi bre lengths measured in control samples of Paulownia elongata from different habitats, indicating that habitat with its properties (climate, soils, and so on) affects the fi bre length.
Taking into account that fi bre length measured in control samples from Pambukovica shows signifi cantly lower values compared to the ones from Obrenovac, it can be concluded that habitat in Pambukovica is not suitable for this plant species.
Differences in fi bre width measured in control samples of Paulownia elongata from different habitats are not signifi cant, which leads to the conclusion that habitat did not affect the fi bre width.
The treatments performed at the Obrenovac site did not have a positive infl uence on the fi bre length, according to the statistical analysis of the fi bre length values for the control and the treated samples.