Solute diffusion into cell walls in solution-impregnated wood under conditioning process I: effect of relative humidity on solute diffusivity

Author

• Soichi TanakaEmail author
• Masako Seki
• Tsunehisa Miki
• Ichinori Shigematsu
• Kozo Kanayama

Abstract

This study focused on solute diffusing into cell walls in solution-impregnated wood under conditioning. The purpose of this paper was to clarify the effect of relative humidity (RH) of the conditioning on solute diffusivity in the impregnated wood. Water evaporation, swelling, and shrinkage of wood samples impregnated with an aqueous solution of polyethylene glycol (PEG) polymer were examined under conditioning at an RH of 11, 32, 55, or 80 % followed by drying under vacuum. Dried samples were observed using a micro-focus X-ray computed tomography instrument. The total amount of PEG polymer diffusing into cell walls during conditioning increased with RH. Theoretical interpretation indicated that this was caused by an increase in polymer (solute) diffusivity as the amount of water (solvent) in samples increased. Temporal variability of the evaporation rate of water and of the swelling rate of the sample also were examined. Solute diffusivity, which was similar at each RH at the beginning of conditioning, decreased during conditioning; this decrease was greater at lower RH values due to a higher evaporation rate.

Acknowledgements

Observations of the samples using micro-focus X-ray CT system were conducted in the Graduate School of Agriculture, Kyoto University. The authors would like to express their gratitude to Mr. Yosuke Matsuda, Dr. Yoshiyuki Yanase, and Dr. Yoshihisa Fujii in the University for their help.

Appendix

The relation of the amount of solute diffusing during Δt, Δn W1, to RH, H, was shown to be a concave-downward curve as follows.

According to the assumption in theory, K 1 and x C1 − x W1 were formulated as follows:

K1=aH,$$K_1=aH,$$

(12)

xC1−xW1=−bH+c,$$x_{\text{C}1}-x_{\text{W}1}=-bH+c,$$

(13)

where a and b represent constant of proportionality and c is intercept (a > 0, b > 0, c > 0). The reason for the absence of the intercept in Eq. (12) is that the polymer completely loses its diffusivity at H = 0, which is supported by the fact that the PEG polymer with molecular weight higher than 400 do not swell dried wood [10]. The relation of Δn W1 to H can be deduced by Eqs. (4), (12), and (13) as follows:

ΔnW1=(−abH2+acH)Δt.$$\mathrm{\Delta }{n}_{\text{W}1}=(-ab{H}^2+acH)\mathrm{\Delta }t.$$

(14)

The slope of the curve, Δn W1(H), can be deduced by taking the derivative of Δn W1 with respect to H as follows:

ddH(ΔnW1)=(−2abH+ac)Δt.$$\frac{\text{d}}{\text{d}H}(\mathrm{\Delta }{n}_{\text{W1}})=(-2abH+ac)\mathrm{\Delta }t.$$

(15)

In the RH range of H < c/2b, d(Δn W1)/dH > 0 consists, and thereby Δn W1 increases with H. In the range of H > c/2b, d(Δn W1)/dH < 0 consists, and thereby Δn W1 decreases with the increase in H. Thus, the relation of Δn W1 to H has concave-downward shape.

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Effect of human activities on forest ecosystems: N cycle and soil fertility

Nutrient Cycling in Agroecosystems

May 2000, Volume 57, Issue 1, pp 47–54| Cite as

Author

• G.X. ChenEmail author
• K.W. Yu
• L.P. Liao
• G.S. Xu

Abstract

Forests are important terrestrial ecosystems, with particular nutrient cycling mechanisms to maintain structure and functions. Nitrogen is essential for forest growth and development, and commonly limited for the forest productivity. N cycles in forest ecosystems are frequently disturbed by intensive human activities. Based on a variety of research results, some potentially important human disturbances are discussed and their effects on forest ecosystems are reviewed. Precipitation is a considerable N input to forest ecosystems. However acid precipitation is detrimental to the ecosystems in the long run. Acidification causes remarkable reduction in forest productivity in the world, due to the harmful effect of acid on plant physiology and more importantly to the reduction in soil fertility by lowering mineralization and increasing N loss by runoff and leaching. The most important nutrient cycling mechanism in forest ecosystems is litterfall. Removal of trunks only for commercial use will not affect N cycle in forest ecosystems significantly, but attention on the intensity and rotation times of harvest should be paid. Clear-cutting should be prevented in forest harvesting. It deserves more attention that the change of environment after clear-cutting will affect the N cycling processes in forest ecosystems, which substantially influence soil fertility and forest productivity. Ammonification and nitrification processes are stimulated after harvesting, by which N is becoming more moveable. Unfortunately in the situation of no assimilation after clear-cutting, much of N will be lost out of the ecosystems and soil fertility will be diminished. The N pool in forest floor and underlying mineral soil is big, but forest productivity is generally low in natural conditions. Forest management is needed to meet the increasing demand for forest products. Optimization of stands structure is the most economic way to increase soil fertility and forest productivity. Mixed coniferous-broad leaved forest is recommended for plantation practice. Addition of fertilizer N effectively promotes forest productivity and may compensate for the N loss from the systems by harvesting.

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