Yasumi Fujinuma

CO2 and water vapor exchange of a larch forest in northern Japan

In the northern part of East Asia, forests dominated by larch are extensively distributed and probably play an important role in the global carbon cycle. However, a knowledge of the CO2 balance of larch forests based on long-term flux measurements is very restricted in East Asia. Thus, a long-term flux measurement has been started in 2000 at a larch plantation on a flat terrain in Hokkaido, Japan to obtain more information on the CO2 and energy balances of larch forests. From September 2000 to August 2001 the net ecosystem CO2 exchange (NEE) changed seasonally in accordance with the annual cycles of phenology and climate. NEE was negative for six months of the growing season, May—September; the larch ecosystem was a carbon sink with a peak intensity of –0.38 mol m−2 d−1 for this period. In the leafless season from November to April the forest ecosystem was a carbon source with an intensity ranging between 0 and 0.05 mol m−2 d−1. Annual NEE from September 2000 to August 2001 was −24.4 to −32.4 mol m−2 yr−1 (=−293 to −389 gC m−2 yr−1); this value is compatible with those reported from other temperate forests. Annual evapotranspiration for the same period was 367 mm, which was only 29% of annual precipitation.

Seasonal changes in the relationship between photochemical reflectance index and photosynthetic light use efficiency of Japanese larch needles

We investigated seasonal changes in the photochemical reflectance index (PRI) and its relation to the diurnal profile of photosynthetic light use efficiency (LUE) in mature Japanese larch (Larix kaempferi Sarg.) forest throughout the growing season from June to October 2003. The daily mean value of needle PRI showed seasonal variation, strongly correlated with the chlorophyll concentration and carotenoid/chlorophyll ratio of the needles. During the green period from early June to late September, the hourly values of both PRI and LUE showed significant midday depression, and were positively correlated. In late October, however, because the PRI of yellowing needles tended to increase slightly at midday in contrast to the LUE, this correlation became negative. Even before autumn senescence, the sensitivity of PRI to LUE changed with the season. Correlation analysis indicated that the slope and intercept of the regression line of the PRI–LUE relationship increased during summer, with peaks in July and August, respectively. The seasonal change in slope was strongly correlated with the foliar photosynthetic pigment concentration, nitrogen concentration, air temperature and the daily mean value of the normalized difference vegetation index (NDVI). The value of the intercept was positively correlated with the daily mean PRI. These results suggest that although diurnal change in LUE cannot be estimated quantitatively from PRI on its own throughout the growing season, the combined use of PRI and other variables such as foliar pigments or NDVI could improve the remote evaluation of seasonal changes in LUE of deciduous tree leaves.

Atmospheric methyl iodide: High correlation with surface seawater temperature and its implications on the sea-to-air flux

Intensive measurements of atmospheric methyl iodide taken at high, middle, and low latitudes over a period of 3 years have provided evidence for its photochemical production in seawater and given new information that sea-to-air transport of CH3I is mainly controlled by surface seawater temperature (SST). These findings suggest a highly localized production and distribution of CH3I in the surface microlayer. As a result, the oceanic emission of CH3I is likely to be larger than previous estimates based on the classical two-layer model. Owing to the SST dependence of atmospheric CH3I concentration, its impact on tropospheric or stratospheric ozone depletion would be increased by El Nino or future global warming.

Latitudinal distribution of atmospheric methyl bromide: Measurements and modeling

The global distribution of atmospheric methyl bromide (CH 3 Br) obtained from extensive new measurements of atmospheric CH 3 Br from latitude 82.5°N to 69.1°S, showed a small decrease from mid- to high-latitudes, a gradient between the northern and southern hemispheres with a ratio of 1.2 to 1.3, and occasional high concentrations in the tropics. The observed data and modeled distributions of industrial CH 3 Br were used to apportion CH 3 Br between natural and industrial components for both hemisphere. We obtained an estimated man-made contribution of 4.3 pptv and 2.3 pptv in the northern and southern hemispheres, respectively and a natural (non-industrial) background concentration in both hemispheres of 6 pptv with a slight increase in the tropics.

Hybrid poplar stomata unresponsive to changes in environmental conditions

SummaryThe factors affecting stomatal conductance (gs) of I-214 (Populus euramericana) and a hybrid poplar, Peace (P. koreana x P. trichocarpa), were examined in the field and under controlled environment conditions. Unusual opening of the stomata was observed with Peace leaves at all positions. Ontogenetic changes in gs were similar between these two poplar species in the light. However, the dark/light ratio of gs in Peace poplar varied from 0.58 to 1.23 with the insertion level while that of I-214 poplar was zero except for the third leaf from the top. The gs of I-214 poplar changed with time of the day, varying from 0.74 mol m-2s-1 in the morning to zero at night, while the gs of Peace poplar changed only from the minimum value of 0.23 mol m-2s-1 at night to the maximum of 0.48 mol m-2s-1 in the morning. Under severe water stress, below -1.5 MPa, which decreased the gs of I-214 poplar to almost zero, the gs of Peace poplar remained about onethird of that observed with well-watered leaves. Exposure to a relatively high concentration of O3 caused the gs of I-214 poplar to decrease nearly to zero but had no effect on the gs of Peace. Stomata of Peace poplar were not affected by ABA and the gs did not change even with 10-4M ABA, while the gs of I-214 decreased to almost zero on the application of this concentration of ABA.

Ground-based millimeter-wave observations of ozone in the upper stratosphere and mesosphere over Tsukuba

We present ground-based millimeter-wave observations of the upper stratospheric and mesospheric ozone, conducted at the National Institute for Environmental Studies (NIES) in Tsukuba, Japan (36°N, 140°E). The measurements were started in October 1995. The millimeter-wave radiometer used for the present study is equipped with the superconductor-insulator-superconductor (SIS) mixer receiver and the acousto-optical spectrometer (AOS). Vertical profiles of ozone mixing ratio from 20 to 80 km were retrieved from the observed ozone spectra for 23 months from October 1996 to August 1998 by using the weighted-damped least squares algorithm adopted for differential emission. Vertical resolution is estimated to be 14 km from the averaging kernels. The total random error on the retrieval is estimated to range from 3 to 13% in summer, and from 2 to 9% in winter, respectively, between 38 and 76 km in altitude. The ozone number density at 38 km with the radiometer which was convolved with the vertical resolution of the lidar agrees well with that of the lidar within a systematic difference of 1%, indicating that the millimeter-wave data at 38 km are validated by the lidar measurements. Annual and semi-annual variations are clearly seen at 50 and 76 km, respectively, in the time series of the ozone mixing ratio observed during 23 months. The annual variation at 50 km is consistent with that in the climatological models. The semi-annual variation at 76 km observed in this work is similar to that of the Solar Mesospheric Explorer (SME) data, except that the ozone mixing ratio in spring measured with SME is about 1.7 times larger than that in autumn while those with the radiometer are almost same.

Diurnal variations and vertical gradients of biogenic volatile and semi-volatile organic compounds at the Tomakomai larch forest station in Japan

Volatile and semi-volatile organic compounds (VOCs and SVOCs) in the atmosphere control oxidative capacity of the air and formation of organic aerosols. To investigate sources, variations and fluxes of VOCs and SVOCs in the forest atmosphere, samples were collected in a larch forest at different heights in Tomakomai, Japan, from 3 to 5 September 2003 and were analyzed for VOCs (isoprene and α-pinene) and SVOCs (n-nonanal, n-decanal, glycolaldehyde, hydroxyacetone, glyoxal and methylglyoxal) using GC-FID and GC-MS. Isoprene (8–851 pptv) showed a diurnal variation with a maximum in daytime, whereas diurnal pattern was indistinct for α-pinene (6–145 pptv). SVOCs showed diurnal variations similar to isoprene, suggesting their origin to be biogenic. Denuder samplings of SVOCs demonstrated that up to 60% of SVOCs were present in aerosol particles. n-Nonanal and n-decanal were more abundant at lower altitude, suggesting their primary emissions from vegetations. In contrast, other four SVOCs showed an opposite or no trend and are considered as oxidation products of biogenic precursors such as isoprene. The averaged upward fluxes of isoprene and α-pinene were obtained to be 34.8 and 9.8 ng m-2 s-1, respectively. Magnitudes of SVOC fluxes were comparable to those of α-pinene, indicating that SVOCs affect budgets of organic gases/aerosols over the forest.

Measurements of Surface Seawater fCO2 from Volunteer Commercial Ships: Techniques and Experiences from Skaugran

Abstract Chemical measurements made in the northern North Pacific from a commercial volunteer observing ship (VOS) program during March 1995–March 1998 are presented. Quasi-continuous measurements of the fugacity of CO2 (fCO2, which takes into account the nonideal nature of the gas; the values are within 0.5–1.5 μatm of the partial pressure in surface water) in seawater were made from two independent systems with different designs, and those results are emphasized here. One system used a fast response bubbling equilibrator with measurements each minute; the other system used a showerhead equilibrator with hourly measurements. Comparison of the results from these side-by-side systems provides useful information about the requirements for making high quality measurements of surface seawater and atmospheric fCO2. From this comparison, the fast response system is deemed to be more stable and potentially more accurate. The utility of this system in waters with high spatial variability is also demonstrated. Fac...

Variations in atmospheric nitrous oxide observed at Hateruma monitoring station

Abstract In situ measurement of atmospheric nitrous oxide (N 2 O) has been carried out at Hateruma monitoring station (lat 24°03 ′ N, long 123°48 ′ E) since March 1996 by the National Institute for Environmental Studies (NIES). A fully automated gas chromatograph equipped with an electron capture detector (ECD) measures the N 2 O concentrations at a frequency of 3 air samples per hour. Details of the experimental methods and procedures are presented in this paper. The N 2 O concentrations observed from March 1996 to February 1999 increased at an average rate of 0.64 ppb/yr. The observed data also suggest that there is a weak annual cycle of N 2 O concentration, increasing in autumn and winter and decreasing in spring and summer, with a peak-to-peak amplitude of at most 0.3 ppb. The N 2 O mixing ratios, smoothed with the 24-h running average, clearly showed short-term variability with synoptic timescales and had peak-to-peak amplitudes of about 1 ppb or less. These short-term variations correlated positively with the short-term variations of CO 2 during the period from winter to early spring when the air masses arriving at Hateruma are dominantly transported from the Asian continent. The ΔN 2 O/ΔCO 2 ratios could be used to constrain the relative strengths of these fluxes on a regional scale.

Effect of spatial variation of soil respiration rates following disturbance by timber harvesting in a larch plantation in northern Japan

Harvesting of trees or the loss of trees due to strong winds may lead to large variations at the ground surface that, in turn, causes spatial and temporal variability of soil respiration. We performed thinning (partial harvest) on a mature larch plantation (ca. 50 yr‐old) in Tomakomai National Forest (Japan) with the purpose of studying the effects of thinning on soil respiration (Rs). We conducted field measurements to determine how soil temperature (Ts), mineral soil water content (MSWC), litter water content (LWC), fine root density, litter density, and carbon to nitrogen ratio (C/N) individually influence soil respiration. Soil respiration values did not differ significantly at the disturbed site. Soil temperature was significantly greater at the disturbed site than at the control site (t‐test= ‐12.7, P<0.05), and the MSWC and LWC did not differ between sites. Despite these observations we found no proof that Ts or MSWC influences Rs. At the disturbed site, LWC appeared to be a primary microclimatic factor driving spatial variations in Rs (r= ‐0.41, P<0.05). Thinning led to large variations in Rs, Ts, fine root density, and litter density. Root and litter densities were 18% (insignificant value) and 15% (t‐test=2.86, P<0.05) lower in the disturbed site, respectively. In fact, variations in soil respiration can be explained on the basis of litter density and C/N.