Masayoshi Mano

Inter-annual carbon dioxide uptake of a wet sedge tundra ecosystem in the Arctic

The CO2 flux of a wet sedge tundra ecosystem in the Arctic, at Barrow, Alaska, has been measured by the eddy correlation method since spring 1999, and the CO2 uptake by the vegetation during the spring and growing periods was examined between 1999 and 2000. CO2 flux changed to a sink immediately after the spring thaw in 1999 and the photosynthetic activity was high in the first half of the growing period. At this time the air temperature was low and solar radiation was high. In the 2000 season, the temperature was approximately 5°C lower during the snow-covered period, and increased up to 5 oC higher right after the spring thaw but the solar radiation decreased to two thirds of that in 1999. Thus, we found different CO2 accumulation during the snowmelt and the following two weeks between both years. The difference in the climate at beginning shoulder period of the growing season resulted in the difference of CO2 accumulation through the growing period. The maximum level of photosynthetic potential (Pmax) in late July was analyzed as being almost the same at 20 gCO2 m−2 d−1 for both years. However, the weekly average peak CO2 uptake was 16.4 and 11.9 gCO2 m−2 d−1 in 1999 and 2000, respectively, with the lower number in 2000 caused by the low radiation with high air temperatures. The CO2 accumulation during the spring and through the growing periods was a net sink of 593 gCO2 m−2 in 1999 and a sink of 384 gCO2 m−2 in 2000. High CO2 accumulation in 1999 was caused by earlier development of the vegetation, and the lower CO2 uptake in mid summer in 2000 was caused by unseasonable weather.

Influences of various calculation options on heat, water and carbon fluxes determined by open- and closed-path eddy covariance methods

ABSTRACT Synthesis studies using multiple-site datasets for eddy covariance potentially contain uncertainties originating from the use of different flux calculation options, because the choice of the process for calculating half-hourly fluxes from raw time series data is left to individual researchers. In this study, we quantified the uncertainties associated with different flux calculation methods at seven sites. The differences in the half-hourly fluxes were small, generally of the order less than a few percentiles, but they were substantial for the annual fluxes. After the standardisation under current recommendations in the FLUXNET communities, we estimated the uncertainties in the annual fluxes associated with the flux calculations to be 2.6±2.7 W m−2 (the mean 90% ± confidence interval) for the sensible heat flux, 72±37 g C m−2 yr−1 for net ecosystem exchange (NEE), 12±6% for evapotranspiration, 12±6% for gross primary productivity and 16±10% for ecosystem respiration. The self-heating correction strongly influenced the annual carbon balance (143±93 g C m−2 yr−1), not only for cold sites but also for warm sites, but did not fully account for differences between the open- and closed-path systems (413±189 g C m−2 yr−1).

Canopy-scale relationships between stomatal conductance and photosynthesis in irrigated rice

Modeling stomatal behavior is critical in research on land-atmosphere interactions and climate change. The most common model uses an existing relationship between photosynthesis and stomatal conductance. However, its parameters have been determined using infrequent and leaf-scale gas-exchange measurements and may not be representative of the whole canopy in time and space. In this study, we used a top-down approach based on a double-source canopy model and eddy flux measurements throughout the growing season. Using this approach, we quantified the canopy-scale relationship between gross photosynthesis and stomatal conductance for 3 years and their relationships with leaf nitrogen content throughout each growing season above a paddy rice canopy in Japan. The canopy-averaged stomatal conductance (gsc ) increased with increasing gross photosynthesis per unit green leaf area (Ag ), as was the case with leaf-scale measurements, and 41-90% of its variation was explained by variations in Ag adjusted to account for the leaf-to-air vapor-pressure deficit and CO2 concentration using the Leuning model. The slope (m) in this model (gsc versus the adjusted Ag ) was almost constant within a 15-day period, but changed seasonally. The m values determined using an ensemble dataset for two mid-growing-season 15-day periods were 30.8 (SE = 0.5), 29.9 (SE = 0.7), and 29.9 (SE = 0.6) in 2004, 2005, and 2006, respectively; the overall mid-season value was 30.3 and did not greatly differ among the 3 years. However, m appeared to be higher during the early and late growing seasons. The ontogenic changes in leaf nitrogen content strongly affected Ag and thus gsc . In addition, we have discussed the agronomic impacts of the interactions between leaf nitrogen content and gsc . Despite limitations in the observations and modeling, our canopy-scale results emphasize the importance of continuous, season-long estimates of stomatal model parameters for crops using top-down approaches.

Experimental evaluation of water vapour cross-sensitivity for accurate eddy covariance measurement of CO 2 flux using open-path CO 2 /H 2 O gas analysers

Non-dispersive infrared CO2/H2O gas analysers produce erroneous CO2 outputs when CO2 is measured in humid air, unless a correction for water vapour cross-sensitivity is applied. Spectroscopic cross-sensitivities arising from direct absorption interference and from the pressure broadening effect are significant in CO2 flux measurements by the eddy covariance technique using open-path gas analysers over the ocean, as opposed to land-surface measurements, where CO2 fluxes are orders of magnitude larger. In this study, a widely used analyser with manufacturer-determined correction coefficients for both cross-sensitivities was tested by laboratory experiments. Our results showed that the correction coefficient for direct absorption interference was not optimised to calculate CO2 flux accurately, and that the correction coefficient for the pressure broadening caused overestimation of the CO2 mixing ratio flux in the same direction as the water vapour flux. Overestimations of open-path eddy covariance measurements of upward CO2 fluxes in previous ocean observations probably resulted from inaccuracies in both of these correction coefficients. We also found that slight changes in spectroscopic cross-sensitivities due to contamination of the analysers optical windows by sea salt caused a low bias in CO2 outputs with increasing H2O; however, this contamination effect was not always observed in repeated tests under different contamination conditions. We suggest that previously proposed methods for correcting the effect of optical window contamination is of limited value and that measurement of small CO2 fluxes by the open-path eddy covariance technique over the ocean should be performed after confirming the spectroscopic cross-sensitivity and ensuring that the optical windows are as clean as possible.

Manure application has an effect on the carbon budget of a managed grassland in southern Hokkaido, Japan

Abstract The carbon (C) budget of managed grassland in a cool-temperate region of Japan was estimated using a combination of eddy covariance and the biometric method for five years, to evaluate the effect of manure application. Chemical fertilizer was applied to the fertilizer (F) plot at a rate of 79 ± 20 kg N ha−1 yr−1. In the manure (M) plot, dairy cattle manure was applied at a rate of 10 Mg fresh matter ha−1 yr−1 (1923 ± 407 kg C ha−1 yr−1, 159 ± 68 kg N ha−1 yr−1). There was no significant difference in seasonal gross primary production (GPP) and harvest between the treatment plots, indicating that both fertilizer and manure can increase the biomass production. Annual net ecosystem production (NEP) and ecosystem respiration (RE) was significantly different between the treatment plots. The difference in RE, and between M and F plots approximates heterotrophic respiration of manure (RHm), which ranged from 0.9 to 1.3 Mg C ha−1 yr−1. Average annual RHm was 1.1 ± 0.4 Mg C ha−1 yr−1, and accounted for 56% of the total amount of applied manure C. The annual net biome production (NBP) in the M plot (from 0.0 to 1.5 Mg C ha−1 yr−1) was significantly higher than in the F plot (−1.4 to 0.5 Mg C ha−1 yr−1). The long-term effect of manure application combined with chemical fertilizer did not reduce grass production compared with chemical fertilizer only; however, manure application decreased the NEP throughout manure decomposition, and long-term manure application enhanced the NBP.

Mitigation Effect of Farmyard Manure Application on Greenhouse Gas Emissions from Managed Grasslands in Japan

Applying manure can lead to decrease of chemical nitrogen (N) fertilizer use and increase of soil carbon (C) sequestration. The effect of manure application on net ecosystem C balance (NECB), methane (CH4) and nitrous oxide (N2O) emissions and global warming potential (GWP) was examined at four managed grasslands on Andosols in different climatic regions in Japan for 3 years. At adjoining manure and fertilizer plots in each site, net ecosystem exchange (NEE) and CH4 and N2O fluxes were measured by the eddy covariance method and dark chamber methods, respectively. Manure application decreased fertilizer N application rate in manure plot to 65–88 % in fertilizer plot. NECB (= NEE−C applied in manure + harvested C) was higher in fertilizer plot (1.9 ± 0.9 MgC ha−1 year−1) than in manure plot (−1.8 ± 1.8 MgC ha−1 year−1), indicating that the soils in fertilizer plots lost C. There was no significant difference in harvested C between fertilizer and manure plots (4.3 ± 0.8 and 4.1 ± 0.6 MgC ha−1 year−1, respectively). NEE showed more CO2 uptake in fertilizer plots (−2.4 ± 1.1 MgC ha−1 year−1) than in manure plots (−1.6 ± 0.7 MgC ha−1 year−1), but manure application could compensate for the shortage in NEE. CH4 emission was close to zero, while the N2O emission was greater in manure plots (6.2 ± 3.7 kgN ha−1 year−1) than in fertilizer plots (3.6 ± 3.2 kgN ha−1 year−1). The difference of GWP between manure and fertilizer plots showed a negative relationship with manure C application rate (y = −4.45 ln(x) + 2.84; R 2 = 0.85; p < 0.01), indicating that manure application rate more than 2 MgC ha−1 year−1 can mitigate global warming in the Japanese grasslands.

Natural cadmium loading and balance in a non-polluted rice paddy field in Japan

We determined the natural Cd balance in a cultivated rice paddy field in Japan. The main sources of Cd in the non-polluted paddy field were phosphorus fertilizer and precipitation (annual input of Cd, 2,000 mg ha(-1) and 1,020 mg ha(-1), respectively). These sources account for 95% of the total input of Cd (3,192 mg ha(-1)). The actual increase of Cd in the soil was 0.0016 mg kg(-1), we thus consider Cd in soil increases only slightly as a result of rice culture. This study indicates that it is difficult to reduce Cd loading by irrigation water treatment in a non-polluted paddy field. This further indicates that once a field is polluted by Cd it is difficult to decrease the accumulated Cd by the ordinary cultivation of rice plants.

Function of the methanogenic community in mangrove soils as influenced by the chemical properties of the hydrosphere

ABSTRACT Coastal ecosystems represent a potential additional source of the greenhouse gas methane (CH4) that has been insufficiently quantified. Thus, to understand the mechanisms controlling greenhouse gas emissions in these ecosystems, this study investigated CH4 emissions from and the related microbial properties of mangrove soils. Soil and gas samples were collected from several plots at different distances from the seashore in Soc Trang and Ca Mau in Vietnam, and the Sundarbans in India. Soil samples were incubated under different conditions, i.e., anaerobic or aerobic, and the microbial properties of each soil sample with the addition of different amounts of seawater were analyzed. Relatively high CH4 fluxes and production were detected during the aerobic incubation of samples from the seashore plots in Soc Trang and Ca Mau. However, CH4 production was reduced under anaerobic conditions [soil electrical conductivity (EC): 179–289 mS m−1, pH (H2O): 7.45–8.10] compared with aerobic conditions [water content: 38.9–109.2%, EC: 187–299 mS m−1, pH (H2O): 6.86–7.72], but it increased with increasing sulfate concentration, soil EC and cellulase activity and lowering soil pH under anaerobic conditions. Furthermore, mangrove soil with a relatively high level of total organic carbon (C) exhibited relatively high CH4 production when diluted 4-fold with seawater under anaerobic conditions [water content: 38.9–109.2%, EC: 533 mS m−1, pH (H2O): 6.67]. Nearly all of the DNA bands excised from polymerase chain reaction-denaturing gradient gel electrophoresis contained identical sequences related to archaea from the class Halobacteria. The high potential of the seashore plot for CH4 emissions could be due to the enhancement of cellulase activity under the intermittent oxygen supply, which promotes polysaccharide depolymerization and subsequently increases anaerobic methanogenic activities during tidal flooding. This study also indicates that the major archaea responsible for CH4 production require a particular hydrospheric salt concentration and soil pH.