Comparison of organic matter dynamics in soil between Japanese cedar (Cryptomeria japonica) forest and adjacent Japanese red pine (Pinus densiflora) forest established on flatland

In order to clarify the effects of tree species on organic matter dynamics in soil, we investigated the amount of forest floor material, leaf litter decomposition rate, soil chemical characteristics, soil respiration rate and cellulose decomposition rate in a Japanese cedar forest (cedar plot) and an adjacent Japanese red pine forest (pine plot) established on a flatland. The amount of forest floor material in the cedar plot was 34.5 Mg ha⁻¹ which was greater than that in the pine plot. Because the leaf litter decomposition rate was higher in the pine plot than in the cedar plot, it is likely that the difference in the amount of forest floor material between the plots is caused by the difference in the leaf litter decomposition rate. The C concentrations of soil in the cedar plot were 1.2–2.1 times higher than those in the pine plot. Soil pH(H₂O)s in the cedar plot were significantly higher than those in the pine plot. The soil respiration rates and the rates of mineralized C in the cedar plot byin vitro incubation were higher than those in the pine plot. From this result, it is assumed that soil organic matter in the cedar plot was decomposed relatively faster compared with the pine plot. Furthermore, microbial activities, which were reflected as cellulose decomposition rates in the cedar plot, were higher than those in the pine plot. A part of this paper was presented at the 109th Annual Meeting of the Japanese Forestry Society (1998).     

Genotypic effects on the variation of wood quality and growth traits in plantation forest made by cutting cultivars of Japanese cedar

We studied the effect of genotypes of planting stocks regarding the variation of the modulus of elasticity of tree trunks on standing trees (trunk-MOE), tree height (TH), and diameter at breast height (DBH) in a 19-year-old Japanese cedar plantation made with root cuttings. Trunk-MOE was assessed nondestructively using a tree-bending method. Genotypes of individual trees were detected using the random amplified polymorphic DNA (RAPD) technique. RAPD analysis revealed that the sampled plantation consisted of 14 genotypes. Genotypic effects on DBH and TH were unclear, and there was no significant difference among genotypes. This result indicated that an acquired variation should have more influence than an inherited variation on DBH and TH. For trunk-MOE, there were significant differences among the four largest genotypes at the 5% level. However the coefficient of variation in trunk-MOE of each genotype ranged from 7.5% to 26.8%. It seems reasonable to assume that the wide variation in trunk-MOE in a sampled plantation may depend on the environmental effect within a clone as well as on the genetic origin of clones. We therefore conclude that the use of multiple planting stocks from different cuttings for which the wood quality is unknown contributed strongly to the wide variation in trunk-MOE in the plantation of Japanese cedar.     

Effects of high temperature kiln drying on the practical performances of Japanese cedar wood (Cryptomeria japonica) I: changes in hygroscopicity due to heating

The effect of heating on the hygroscopicity of Japanese cedar wood was investigated as a simple evaluation of thermal degradation in large-dimension timber being kiln-dried at high temperatures (>100°C). Small wood pieces were heated at 120°C in the absence of moisture (dry heating) and steamed at 60°, 90°, and 120°C with saturated water vapor over 2 weeks, and their equilibrium moisture contents (M) at 20°C and 60% relative humidity (RH) were compared with those of unheated samples. No significant change was induced by steaming at 60°C, while heating above 90°C caused loss in weight (WL) and reduction in M of wood. The effects of steaming were greater than those of dry heating at the same heating temperature. After extraction in water, the steamed wood showed additional WL and slight increase in M because of the loss of water-soluble decomposition residue. The M of heated wood decreased with increasing WL, and such a correlation became clearer after the extraction in water. On the basis of experimental correlation, the WL of local parts in large-dimension kiln-dried timber was evaluated from their M values. The results indicated that the thermal degradation of inner parts was greater than that of outer parts.     

Effects of high temperature kiln drying on the practical performances of Japanese cedar wood (Cryptomeria japonica) II: Changes in mechanical properties due to heating

Japanese cedar wood specimens were steamed at 80°, 100°, and 120°C over 14 days, and their equilibrium moisture content (M) at 20°C and 60% relative humidity, longitudinal dynamic Young’s modulus (E), bending strength (σ _max), and breaking strain (ε _max) were compared with those of unheated specimens. Steaming for a longer duration at a higher temperature resulted in a greater reduction in M, σ _max, and ε _max. The E of wood was slightly enhanced by steaming at 100°C for 1–4 days and 120°C for 1–2 days, and thereafter it decreased. The slight increase in the E of sapwood was attributable to the reduction in hygroscopicity, while sufficient explanation was not given for a greater increase in the heartwood stiffness. Irrespective of the steaming temperature, the correlations between M and the mechanical properties of steamed wood were expressed in terms of simple curves. M values above 8% indicated a slight reduction in E and s max, whereas M values below 8% indicated a marked decrease in the mechanical performances. In addition, the e max decreased almost linearly with a decrease in the value of M. These results suggest that hygroscopicity measurement enables the evaluation of degradation in the mechanical performances of wood caused by steaming at high temperatures.     

Effects of thinning and site productivity on culmination of stand growth: results from long-term monitoring experiments in Japanese cedar (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis> D. Don) forests in northeastern Japan

We analyzed data from 28 long-term experimental monitoring plots installed in Japanese cedar (Cryptomeria japonica D. Don) plantations in northeastern Japan to examine how site productivity and thinning practices relate to culmination in stand growth. Site productivity and thinning practices in the plots were evaluated by site index (dominant tree height at 40-years old) and by cumulative thinning rate (cumulative thinning volume divided by cumulative gross production during the entire period of measurement). Culmination of stand growth was evaluated by culmination age of the mean annual increment (MAI) and its maximum value (Max MAI). Max MAI for the mean annual gross increment (MAIgross) and mean annual net increment (MAInet) increased with increasing site index, but did not change with cumulative thinning rate. Culmination age for MAIgross decreased with increasing site index, but did not change with cumulative thinning rate. Culmination age for MAInet decreased with increasing site index. Additionally, culmination age for MAInet increased with increasing cumulative thinning rate in sites with a high site index (>19.3 m) but not in those with a low site index (<19.3 m). These results indicate that thinning extends the culmination age without changing Max MAInet under high site productivity. Therefore, thinning increases total net yield in sites with high productivity based on a long-term perspective.     

Effects of flow rate and chamber position on measurement of stem respiration rate with an open flow system in a Japanese red pine

The effects of air flow rate and chamber position on measuring stem respiration rate (R_stem) were examined using an open flow system on six Japanese red pine (Pinus densiflora Sieb. and Zucc) trees. R_stem was more closely correlated with stem temperature observed 2–6 h earlier than with current stem temperature. R_stem was not affected by the air flow rate passing through the stem chamber. Although there were no differences in stem temperatures between azimuth angles, there were significant differences in R_stem between azimuth angles (except for only one case) of each sample stem. The distance from below the bark to the stem centre varied at each azimuth in the samples, and was significantly positively correlated with R₀ (p < 0.01). The chamber type did not affect the measurement of stem respiration, because the mean R_stem of four azimuth angles measured with in a rectangular chamber was almost the same as R_stem measured with in a circular chamber. From these results, we suggest that a whole circumference estimate made by either:

(1) measuring stem respiration at each azimuth separately with a rectangular chamber, or

(2) measuring the total CO₂ efflux from the whole radial circumference with a circular chamber,

must be conducted for scaling-up chamber measurements to individual or stand level.

Effects of biochar and litter on carbon and nitrogen mineralization and soil microbial community structure in a China fir plantation

To investigate the effects of biochar addition(1 or 3%)to the soil of a China fir plantation with or without litter,we conducted a 90-day incubation experiment.We also studied the C and N dynamics and the microbial community structure of the soil.In soil without litter,the application of biochar at a rate of 3%significantly decreased CO2 emissions,while addition of 1%biochar had no effect.Biochar application did not affect the net N mineralization rate but significantly reduced the NH4?concentration after 90 days.In litter-enriched soil,biochar application had no significant effect on total CO2 emissions;however,application of 3%biochar significantly reduced the net N mineralization rate.Biochar application to soil with or without litter immediately reduced the dissolved organic carbon(DOC)concentration independent of the application rate,which was primarily due to sorption of DOC by the biochar.Phospholipid fatty acid analysis demonstrated that both concentrations of added biochar to soil(with or without litter)altered the soil microbial community structure at the end of incubation,although the effect of biochar was not as strong as the effect of time or litter application.The effect of biochar addition alone on microbial community structure was inconsistent over time.Litter added to soil significantly increased fungi and reduced Gram-positive bacteria.In the presence of litter,biochar applied at both 1%and 3%significantly increased(p<0.05)the proportion of actinomycete only at day 90.Our results indicate biochar as a potentially effective measure for C sequestration in the test soil of a China fir plantation,even in the presence of litter.     

Effects of genetically modified Burkholderia pyrrocinia JK‐SH007E1 on soil microbial community in poplar rhizosphere

It is important to assess the biosafety of genetically engineered bacteria before release into the environment. In a previous study, the genetically engineered bacterium Burkholderia pyrrocinia JK‐SH007E1 was developed, showing biological control activity against a poplar canker disease. In the present work, the potential effects of B. pyrrocinia JK‐SH007E1 on soil microbial diversity and population structure in the poplar rhizosphere were assessed. The micro‐ecological effects of JK‐SH007E1 on soil microbial communities were investigated using substrate utilization assays (Biolog EcoPlate), enzyme activity assays and 16S rRNA sequencing to research species diversity and population structure of soil microbial communities. The genetically engineered isolate JK‐SH007E1 improved the functional diversity, soil enzyme activities and alpha diversity of soil microbial communities. However, the positive effects after inoculation attenuated with time, except for soil enzyme activities. Treatments with JK‐SH007 or JK‐SH007E1 were not different in impacts on soil enzyme activity and functional diversity of soil microbial communities. The results demonstrated that inoculation of JK‐SH007E1 into the poplar rhizosphere posed little or no threat to soil microbial communities in the long term. This work provides an additional insight into the effects of genetically engineered JK‐SH007E1 on the environment during long‐term use as biological control against poplar canker diseases.