Kaneyuki Nakane

Seasonal changes in the contribution of root respiration to total soil respiration in a cool-temperate deciduous forest

A trenching method was used to determine the contribution of root respiration to soil respiration. Soil respiration rates in a trenched plot (Rtrench) and in a control plot (Rcontrol) were measured from May 2000 to September 2001 by using an open-flow gas exchange system with an infrared gas analyser. The decomposition rate of dead roots (RD) was estimated by using a root-bag method to correct the soil respiration measured from the trenched plots for the additional decaying root biomass. The soil respiration rates in the control plot increased from May (240–320 mg CO2 m−2 h−1) to August (840–1150 mg CO2 m−2 h−1) and then decreased during autumn (200–650 mg CO2 m−2 h−1). The soil respiration rates in the trenched plot showed a similar pattern of seasonal change, but the rates were lower than in the control plot except during the 2 months following the trenching. Root respiration rate (Rr) and heterotrophic respiration rate (Rh) were estimated from Rcontrol, Rtrench, and RD. We estimated that the contribution of Rr to total soil respiration in the growing season ranged from 27 to 71%. There was a significant relationship between Rh and soil temperature, whereas Rr had no significant correlation with soil temperature. The results suggest that the factors controlling the seasonal change of respiration differ between the two components of soil respiration, Rr and Rh.

Effects of rainfall events on soil CO2 flux in a cool temperate deciduous broad-leaved forest

The effects of rainfall events on soil CO2 fluxes were examined in a cool temperate Quercus/Betula forest in Japan. The soil CO2 fluxes were measured using an open-flow gas exchange system with an infrared gas analyzer in the snow-free season from August 1999 to November 2000. Soil CO2 flux showed no significant diurnal trend on days without rain. In contrast, rainfall events caused a significant increase in soil CO2 flux. To determine the effect of rainfall events and to evaluate more precisely the daily and annual soil carbon flux, we constructed a multiple polynomial regression model that included two variables, soil temperature and soil water content, using the soil CO2 flux data recorded on sunny days. Daily soil carbon fluxes on sunny days calculated by the model were almost the same as those determined by the field measurements. On the contrary, the fluxes measured on rainy days were significantly higher than those calculated daily from the soil carbon fluxes by the model. Annual soil carbon fluxes in 1999 and 2000 were estimated using models that both do and do not take rainfall effects into consideration. The result indicates that post-rainfall increases in soil CO2 flux represent approximately 16–21% of the annual soil carbon flux in this cool temperate deciduous forest.

Root respiration rate before and just after clear-felling in a mature, deciduous, broad-leaved forest

Soil respiration was measured throughout the year (June 1992 to May 1993) in a mature, deciduous, broad-leaved forest and an adjacent, clear-felled stand which was made in November 1991, in Hiroshima Prefecture, west Japan. The same soil temperature and soil moisture content as those in the forest stand were maintained in two frame boxes covered with sheets of white netting in the clear-felled stand to observe soil respiration. A herbicide was applied to the cut end of all stumps in one of the two frame boxes in order to kill the root system. There was no significant difference in the aboveground biomass and soil environmental conditions between the forest and the frame boxes in the clear-felled stands. The difference in soil respiration rate between the forest and the frame box, in which the root system was killed by the herbicide, was considered to be due largely to the contribution of root respiration. Taking into consideration CO2 evolution due to the decomposition of roots killed and the change in A0 layer respiration rate after clear-felling, the proportion of root respiration to the total soil respiration before clear-felling was estimated to be 51% annually, which coincides closely with those values estimated previously in mature forests by other methods. The difference in the soil respiration rate between the two frame boxes (one with killed roots and the other with undisturbed roots) suggested that the annual root respiration rate just after clear-felling dropped to about two-thirds (70%) of that before clear-felling.

Contribution of micro-organisms to the carbon dynamics in black spruce (Picea mariana) forest soil in Canada

In order to clarify the role of micro-organisms in the carbon cycle of the boreal forest ecosystem, the vertical distribution of soil carbon, soil microbial biomass and respiratory activity was studied in a black spruce forest near Candle Lake in Saskatchewan, Canada. The total amount of carbon contained in moss and soil layers (to the depth of 50 cm beneath the mineral soil surface) was 7.2 kg m−2, about 47% of which was in the L and FH horizons of the soil. Soil microbial biomass per dry weight of soil was largest in the L horizon, while the biomass per ground area was largest in the FH horizon. Soil respiration rate, measured using a portable infrared gas analyzer, was highest in the FH horizon, exceeding 50% of the total soil respiration. Low but significant CO2 emission was detected even in deeper soil horizon (E horizon). We also examined the respiration rate of cut roots and the effect of root excision on respiration. The contribution of root respiration to total soil respiration, calculated from root biomass and respiration rate of cut roots, was about 54%. The amount of carbon evolved through microbial respiration during the snow-free season (June–October) was estimated as 221 g C m−2. Micro-organisms in the L horizon showed high respiratory activity as compared with those in deeper soil horizons.

Assessing the Impacts of Four Land Use Types on the Water Quality of Wetlands in Japan

This study examined how changes in the composition of land use can affect wetland water quality. Twenty-four wetlands located in Hiroshima prefecture in the western part of Japan were selected for this purpose. The water quality parameters that were explored include: pH, electrical conductivity, turbidity, dissolved oxygen, total dissolved solid, temperature and different forms of nitrogen. These important indicators of the water quality in the study area were measured from December 2005 to December 2006. The composition of land uses was determined for the catchments of the wetlands. They were then categorized into three classes, including non-disturbed, moderately-disturbed and highly-disturbed wetlands, based on the extent of urban area (as the most disruptive land use type within the catchment of the wetlands). The relationship between land use types and water quality parameters for the wetlands was statistically examined. The findings indicated that there were significant positive relationships between the proportion (%) of urban areas within catchments of the wetlands and EC (r = 0.67, p < 0.01), TDS (r = 0.69, p < 0.01), TN (r = 0.92, p < 0.01), DON (r = 0.6, p < 0.01), NH4+(r = 0.47, p < 0.05), NO2− (r = 0.50, p < 0.05), while negative relationships were observed between the proportion (%) of forest area in these wetlands and EC (r = −0.62, p < 0.01), TDS (r = −0.68, p < 0.01), TN (r = −0.68, p < 0.01), DON (r = -0.43, p < 0.05), and NH4+ (r = −0.55, p < 0.01). Analysis of the variance also revealed significant differences within the wetland groups in terms of the annual mean of electrical conductivity, total dissolved solids, total nitrogen, nitrite, dissolved inorganic nitrogen and dissolved organic nitrogen in the study area. Moreover, the study also indicated that the forest area plays a significant role in withholding nutrient loads from the wetlands, and hence, it can act as a sink for surface/subsurface nutrient inputs flowing into such water bodies from the watersheds.

Soil carbon cycling in a Japanese cedar (Cryptomeria japonica) plantation

Abstract Soil carbon cycling was measured synthetically and quantitatively throughout a year in a Japanese ceder plantation, Mt. Amida, Hiroshima Prefecture, west Japan, and analyzed by a compartment model. The results observed and analyzed were compared with those obtained by the same methods in natural secondary (Japanese red pine) and climax (evergreen oak) forests developed in the same warm-temperate zone, west Japan. There was no clear seasonal trend in litterfall rate and accumulation of A 0 layer, but soil respiration increased in summer and decreased in winter with the change in soil surface temperature. The relative decomposition rate of the A 0 layer (0.187 year −1 ) observed in the cedar plantation was one-third of that in an evergreen oak forest and rather less than in a Japanese red pine forest. Transfer of humus from the A 0 layer to mineral soil was faster than in the pine forest, and thus the loss rate of the A 0 layer (0.262 year −1 ) was somewhat larger than that in the pine forest. However, the relative decomposition rate of humus in mineral soil (0.0063 year −1 ) was only one-third of those in the pine and evergreen oak forests. This suggests that soil carbon cycling was extremely slow in the cedar plantation. This is probably due to the great resistance of cedar litter to decomposition and to less broadleaf litterfall than in the pine forest, because the soil environmental conditions were no worse than in other two forests. Based on these results, a discussion is presented on the management of cedar plantations, how to maintain their productivity under conditions with slow material cycling and how to enhance this cycling.

Effects of understory vegetation on the ecophysiological characteristics of an overstory pine, Pinus densiflora

Abstract The ecophysiological effects of understory vegetation on an overstory tree Pinus densiflora were examined in secondary pine forest stands, west Japan. Three pairs of pine forests were compared. Each pair contained an unmanaged stand and a managed stand in which the understory vegetation was clear cut. The two stands in each pair were adjacent to each other and had similar light conditions, ground matrix, precipitation and aerial conditions. Total fine root biomass in the soil surface layer was significantly larger in the unmanaged stands than in the managed stands because of the invasion of other understory trees. In the unmanaged stands, the maximum net photosynthesis (Pmax) and stomatal conductance (glmax) were smaller and δ 13 C values of needles were larger than those in the managed stands. These results suggested that water for pine needles was more restricted and water use efficiency (WUE) was higher in the unmanaged stand than in the managed stands. Nitrogen contents in the needles and photosynthetic nitrogen use efficiency (NUE) in the unmanaged stands were lower than those in the managed stands. There was no significant difference between the managed and the unmanaged stands in the emission of stress ethylene from needles. Our results showed that the understory vegetation which invaded during the process of secondary succession had negative physiological effects on the overstory pine needles through the competition of roots for water and nutrients. The traditional style of forest floor management in Japan had significant positive effects on the health condition of P. densiflora plantations.

Cycling of soil carbon in a Japanese red pine forest I. Before a clear-felling

Cycling of soil carbon was measured synthetically and quantitatively throughout a year in two Japanese red pine forest stands on mid- and foot-slopes at Mt. Takao, Hiroshima Prefecture, west Japan. There was no distinct difference of soil temperature along the slopes, but the soil water content was higher on the foot-slope than on the midslope. The carbon flow (litterfall, soil respiration, etc.) rates were larger on the foot-slope than on the mid-slope, but there was no significant difference of the accumulation of soil carbon (A0 layer or human in mineral soil) between the areas. The results of the analysis of soil carbon cycling based on a compartment model show that the relative decomposition rate of A0 layer and humaus in mineral soil increased 1.4–1.5 fold from the mid- to the foot-slopes, corresponding to the soil moisture condition. The relative decomposition rate of A0 layer was, however, about one-third of that in a evergreen oak forest. This fact suggests that the great resistance of needle litter to decomposition is one of the main limiting factors of the cycling of soil carbon and prevents the fertilization of mineral soil in the pine forest, which was also proven by the simulation of dynamics of soil carbon cycling.

Seasonal patterns of fine root demography in a cool-temperate deciduous forest in central Japan

In forest ecosystems, fine roots have a considerable role in carbon cycling. To investigate the seasonal pattern of fine root demography, we observed the fine root production and decomposition processes using a minirhizotron system in a Betula-dominated forest with understory evergreen dwarf bamboo. The length density of fine roots decreased with increasing soil depth. The seasonal patterns of each fine root demographic parameter (length density of visible roots, rates of stand-total fine root production and decomposition) were almost the same at different soil depths. The peak seasons of the fine root demographic parameters were observed in the order: stand-total fine root production rate (late summer) > length density of the visible roots (early autumn) > stand-total fine root decomposition rate (autumn, and a second small peak in spring). The fine root production rate was high in the latter part of the plant growing season. Fine root production peaked in late summer and remained high until the end of the tree defoliation season. The higher stand-total fine root production rate in autumn suggests the effect of understory evergreen bamboo on the stand-total fine root demography. The stand-total fine root decomposition rate was high in late autumn. In the snow-cover period, the rates of both fine root production and decomposition were low. The fine root demographic parameters appeared to show seasonal patterns. The fine root production rate had a clearer seasonality than the fine root decomposition rate. The seasonal pattern of stand-total fine root production rate could be explained by both overstory and understory above-ground productivities.

Cycling of soil carbon in a Japanese red pine forest. II: Changes occurring in the first year after a clear-felling

Cycling of soil carbon in the first year after a clear-felling was compared with that before the felling in a Japanese red pine forest in Hiroshima Prefecture, west Japan. The daily mean temperature at the soil surface in summer was increased after the felling in comparison to that before felling, and the water content of both the A0 layer and the surface mineral soil was decreased due to the loss of the forest canopy. The rate of weight loss of the A0 layer was reduced after felling. However, accumulation of the A0 layer rapidly decreased because of the lack of litter supply to the forest floor. Low soil respiration after felling was mainly caused by the cessation of root respiration. Analysis of annual soil carbon cycling was then conducted using a compartment model. The relative decomposition rate of the A0 layer decreased whereas that of humus and dead roots in mineral soil increased to some extent after felling. The accumulation of carbon in mineral soil, however, increased slightly due to the supply of humus from roots killed by the felling.