Fumiaki Takakai

Rice cultivar responses to elevated CO2 at two free-air CO2 enrichment (FACE) sites in Japan

There is some evidence that rice cultivars respond differently to elevated CO2 concentrations ([CO2]), but [CO2]×cultivar interaction has never been tested under open-field conditions across different sites. Here, we report on trials conducted at free-air CO2 enrichment (FACE) facilities at two sites in Japan, Shizukuishi (2007 and 2008) and Tsukuba (2010). The average growing-season air temperature was more than 5°C warmer at Tsukuba than at Shizukuishi. For four cultivars tested at both sites, the [CO2]×cultivar interaction was significant for brown rice yield, but there was no significant interaction with site-year. Higher-yielding cultivars with a large sink size showed a greater [CO2] response. The Tsukuba FACE experiment, which included eight cultivars, revealed a wider range of yield enhancement (3-36%) than the multi-site experiment. All of the tested yield components contributed to this enhancement, but there was a highly significant [CO2]×cultivar interaction for percentage of ripened spikelets. These results suggest that a large sink is a prerequisite for higher productivity under elevated [CO2], but that improving carbon allocation by increasing grain setting may also be a practical way of increasing the yield response to elevated [CO2].

Effects of agricultural land-use change and forest fire on N2O emission from tropical peatlands, Central Kalimantan, Indonesia

Abstract Nitrous oxide (N2O) fluxes from tropical peatland soils were measured at a grassland, three croplands, a natural forest, a burned forest and a regenerated forest in Central Kalimantan, Indonesia. Only croplands received fertilization (665–1278 kg N ha−1 year−1). Mean annual N2O emissions from croplands were 21–131 kg N ha−1 year−1 in 2002–2003 and 52–259 kg N ha−1 year−1 in 2003–2004, and were significantly higher than the emissions from other comparable sites. Cropland N2O emissions were among the highest values reported from cultivated tropical, temperate and boreal organic soils. Mean annual N2O emissions were 7.1 (2002–2003) and 23 (2003–2004) kg N ha−1 year−1 from grassland, and were significantly higher than in natural, regenerated and burned forests (0.62, 0.40 and 0.97 kg N ha−1 year−1 in 2002–2003 and 4.4, 4.0 and 1.5 kg N ha−1 year−1 in 2003–2004, respectively). Annual N2O emissions did not differ significantly between forests in 2002–2003, but were significantly lower in burned forest in 2003–2004. Annual N2O emission was significantly correlated between years. Regression analysis revealed that annual N2O emissions in 2003–2004 were 1.9-fold the corresponding 2002–2003 value (annual precipitation of 2339 and 1994 mm, respectively). N2O fluxes were higher during the rainy season than during the dry season at all sites except the regenerated forest. N2O fluxes in cropland and grassland were significantly lower when the water-filled pore space (WFPS) was less than 60–70%, and increased with an increase in soil NO3–N concentration when WFPS exceeded this threshold. Thus, changes in soil moisture were important in controlling seasonal changes in N2O emission. Our results suggest that changing land use from forestry to agriculture will increase N2O production. The effect of forest fires on N2O emission from these soils was not clear.

Fungal N2O production in an arable peat soil in Central Kalimantan, Indonesia

Abstract To clarify the microbiological factors that explain high N2O emission in an arable peat soil in Central Kalimantan, Indonesia, a substrate-induced respiration-inhibition experiment was conducted for N2O production. The N2O emission rate decreased by 31% with the addition of streptomycin, whereas it decreased by 81% with the addition of cycloheximide, compared with a non-antibiotic-added control. This result revealed a greater contribution of the fungal community than bacterial community to the production of N2O in the soil. The population density of fungi in the soil, determined using the dilution plate method, was 5.5 log c.f.u. g−1 soil and 4.9 log c.f.u. g−1 soil in the non-selective medium (rose bengal) and the selective medium for Fusarium, respectively. The N2O-producing potential was randomly examined in each of these isolates by inoculation onto Czapek agar medium (pH 4.3) and incubation at 28°C for 14 days. Significant N2O-producing potential was found in six out of 19 strains and in five out of seven strains isolated from the non-selective and selective media, respectively. Twenty-three out of 26 strains produced more than 20% CO2 during the 14-day incubation period, suggesting the presence of facultative fungi in the soil. These strains were identified to be Fusarium oxysporum and Neocosmospora vasinfecta based on the sequence of 18S rDNA, irrespective of the N2O-producing potential and the growth potential in conditions of low O2 concentration.

Influence of forest disturbance on CO2, CH4 and N2O fluxes from larch forest soil in the permafrost taiga region of eastern Siberia

Abstract To evaluate the effect of increasing forest disturbances on greenhouse gas budgets in a taiga forest in eastern Siberia, CO2, CH4 and N2O fluxes from the soils were measured during the growing season in intact, burnt and clear-felled larch forests (4–5 years after the disturbance). Soil temperature and moisture were higher at the two disturbed sites than at the forest site. A 64–72% decrease in the Q 10 value of soil CO2 flux from the disturbed sites compared with the forest site (5.92) suggested a reduction in root respiration and a dominance of organic matter decomposition at the disturbed sites. However, the cumulative CO2 emissions (May–August) were not significantly different among the sites (2.81–2.90 Mg C ha−1 per 3 months). This might be because decreased larch root respiration was compensated for by increased organic matter decomposition resulting from an increase in the temperature and root respiration of invading vegetation at the disturbed sites. The CH4 uptake (kg C ha−1 per 4 months [May–September]) at the burnt site was significantly higher (–0.15) than the uptake at the forest (–0.045) and clear-felled sites (0.0027). Although there were no significant differences among the sites, N2O emission (kg N ha−1 per 4 months) was slightly lower at the burnt site (0.013) and higher at the clear-felled site (0.068) than at the forest site (0.038). This different influence of burning and tree felling on CH4 and N2O fluxes might result from changes in the physical and chemical properties of the soil with respect to forest fire.

Nitrous oxide emission derived from soil organic matter decomposition from tropical agricultural peat soil in central Kalimantan, Indonesia

Our previous research showed large amounts of nitrous oxide (N2O) emission (>200 kg N ha−1 year−1) from agricultural peat soil. In this study, we investigated the factors influencing relatively large N2O fluxes and the source of nitrogen (N) substrate for N2O in a tropical peatland in central Kalimantan, Indonesia. Using a static chamber method, N2O and carbon dioxide (CO2) fluxes were measured in three conventionally cultivated croplands (conventional), an unplanted and unfertilized bare treatment (bare) in each cropland, and unfertilized grassland over a three-year period. Based on the difference in N2O emission from two treatments, contribution of the N source for N2O was calculated. Nitrous oxide concentrations at five depths (5–80 cm) were also measured for calculating net N2O production in soil. Annual N fertilizer application rates in the croplands ranged from 472 to 1607 kg N ha−1 year−1. There were no significant differences in between N2O fluxes in the two treatments at each site. Annual N2O emission in conventional and bare treatments varied from 10.9 to 698 and 6.55 to 858 kg N ha−1 year−1, respectively. However, there was also no significant difference between annual N2O emissions in the two treatments at each site. This suggests most of the emitted N2O was derived from the decomposition of peat. There were significant positive correlations between N2O and CO2 fluxes in bare treatment in two croplands where N2O flux was higher than at another cropland. Nitrous oxide concentration distribution in soil measured in the conventional treatment showed that N2O was mainly produced in the surface soil down to 15 cm in the soil. The logarithmic value of the ratio of N2O flux and nitrate concentration was positively correlated with water filled pore space (WEPS). These results suggest that large N2O emission in agricultural tropical peatland was caused by denitrification with high decomposition of peat. In addition, N2O was mainly produced by denitrification at high range of WFPS in surface soil.

Greenhouse gas emissions after a prescribed fire in white birch-dwarf bamboo stands in northern Japan, focusing on the role of charcoal

Forest fires affect both carbon (C) and nitrogen (N) cycling in forest ecosystems, and thereby influence the soil–atmosphere exchange of major greenhouse gases (GHGs): carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). To determine changes in the soil GHG fluxes following a forest fire, we arranged a low-intensity surface fire in a white birch forest in northern Japan. We established three treatments, having four replications each: a control plot (CON), a burned plot (BURN), and a plot burned with removal of the resulting charcoal (BURN-CHA). Soil GHG fluxes and various properties of the soil were determined on four or five occasions during a period that spanned two growing seasons. We observed increased concentrations of ammonium-N (NH4-N) in BURN and BURN-CHA after the fire, while nitrate–N (NO3-N) concentration was only increased in BURN-CHA after the fire. The soil CO2 flux was significantly higher in CON than in BURN or BURN-CHA, but there was no difference in soil CH4 uptake between the three treatments. Moreover, the N2O flux from BURN-CHA soil was slightly greater than in CON or BURN. In BURN-CHA, the soil N2O flux peaked in August, but there was no peak in BURN. We found temporal correlations between soil GHG fluxes and soil variables, e.g. soil temperature or NO3-N. Our results suggest that environmental changes following fire, including the increased availability of N and the disappearance of the litter layer, have the potential to change soil GHG fluxes. Fire-produced charcoal could be significant in reducing soil N2O flux in temperate forests.

Effects of preceding compost application on the nitrogen budget in an upland soybean field converted from a rice paddy field on gray lowland soil in Akita, Japan

Abstract The annual nitrogen (N) budget was measured in a soybean-cultivated upland field during the first year after conversion from a paddy field on gray lowland soil, which is typically found on the Sea of Japan side of northern Japan. Forage rice was cultivated on lysimeter fields for 4 consecutive years with applications of chemical fertilizer, immature compost, or mature compost (the control, immature compost, and mature compost plots, respectively), and then the fields were converted to upland fields for soybean (Glycine max [L.] Merrill cultivar Ryuho) cultivation. Input (seed, bulk N deposition, and symbiotic dinitrogen [N2] fixation) and output (harvested grain, leached N via drainage water, and nitrous oxide emission) N flows were measured, and the field N budget was estimated from the difference between the input and output. The soybean plants in the immature and mature compost plots grew well and had higher yields (498–511 g m)−2) compared to the control plot (410 g m)−2). Total N accumulation in the soybean plants derived from N2 fixation (g N m)−2) in the mature compost plot (27.7) was higher than those in the control (18.1) and immature compost plots (19.9). Percentages of soybean N accumulation derived from N2 fixation ranged from 53% to 74%. N derived from symbiotic N2 fixation accounted for more than 90% of the total N input, whereas harvested grain accounted for approximately 85% of the total N output. N leaching mainly occurred during the fallow period, accounting for 13–15% of the total N output. The annual N budgets were negative (−10.0,−14.2, and −6.4 g N m)−2 year)−1 for the control, immature compost, andmature compost plots, respectively). The Nloss from the immature compost plot was higher than that of the control plot, because the N output in harvested grain was higher, and the N input by N2 fixation was similar between plots. While the N loss from the mature compost plot was lower than that of the control plot because the N output in harvested grain was higher, as was the case in the immature compost plot, the N input by N2 fixation was also higher. Preceding compost application—whether immature or mature compost—to paddy fields increased the subsequent soybean yield during the first year after conversion. This result suggests that N loss and the following decrease in soil N availability in the field could be mitigated by increased N2 fixation resulting from mature compost application with an appropriate application practice.

Effect of groundwater level fluctuation on soil respiration rate of tropical peatland in Central Kalimantan, Indonesia

ABSTRACT Soil respiration (SR) rate was measured at the burned land (BL), the cropland (CL), the forest land (FL) and the grassland (GL) of a tropical peatland in Central Kalimantan, Indonesia from 2002 to 2011 for the purpose of analysis with a relation to the drying and rewetting. The SR rate was fitted with groundwater level (GWL) to the equation of log(SR) = α – β × GWL using hierarchical Bayesian analysis where α and β were regression coefficients classified by GWL changing directions (drying, rewetting and fluctuating), water-filled pore space (WFPS) ranges in topsoil (low 0–0.54, intermediate 0.54–0.75 and high 0.75–1 m3 m−3), and land uses (BL, CL, FL and GL). SR rate (Mean ± SD, mg C m−2 h−1) was the significantly largest in the CL (333 ± 178) followed by GL (259 ± 151), FL (127 ± 69) and lastly BL (100 ± 90). In the CL, the significantly larger SR rate was found in the rewetting period than in the drying period in the high WFPS range. Also, the significantly steeper slope (β) in the rewetting period was obtained in the high WFPS range than in the drying period. These results suggested that the rewetting of peatland enhanced the SR rate rapidly in the CL, and that the further rise of GWL decreased the SR rate. In contrast, the SR rate in the rewetting period was significantly smaller than in the drying period in the BL in the high WFPS range, because the BL in the high WFPS range was flooded in most cases. The SR rate in the rewetting period was not significantly different from the drying period in the FL and GL. All of β were significant in the high WFPS range in all land uses, but not in the low–intermediate WFPS ranges, suggesting that GWL was not controlling factor of the SR rate when the GWL was deep due to the disconnection of capillary force under dry conditions. According to the results of correlation analysis of the α and β, the α was significantly correlated with relative humidity, soil temperature and soil pH, suggesting that the α was enhanced by dry condition, high soil temperature and neutralization of soil acidity, respectively. The β was significantly correlated with exchangeable Na+ and Mg2+ in the soil, but the reason was not clear. In conclusion, SR rate was enhanced by rising GWL with rewetting in the CL in the high WFPS ranges as well as by deepening GWL.

Flood effect on CH4 emission from the alas in Central Yakutia, East Siberia

Abstract During four years (2006–2009), methane (CH4) emission was measured at different biomes (dry, wet grasslands, lake and lake vegetation) of mature thermokarst depression located at the most typical thermokarst terrain on the east bank of the Lena River, Central Yakutia, Russia (62°08′N, 130°30′E). To estimate total CH4 emission from the whole thermokarst depression ecosystem, CH4 emissions via plant bodies and ebullition were measured in addition to diffusive CH4 flux measurement. The lake area increased twice from 20.4 ha in 2006 to 43.3 ha in 2007 and then did not change significantly in 2008 and 2009 (46.5 and 44.4 ha, respectively). Ebullition was considered to be a minor source for CH4 emission from the lake in the studied thermokarst depression. CH4 emissions from the lake water surface and via the plant body of lake vegetation (hygrophyte and hydrophyte vegetation) were the main sources of CH4 and these increased by flooding both CH4 emission rate and area. Using spatial changes of these biomes, the annual emission of CH4 was calculated taking into account different sources of CH4. Total CH4 emission from the studied alas (63.7 ha) was 5.7, 5.2, 20.1 and 50.1 Mg carbon (C) in 2006–2009, respectively, and its difference during this period reached about 10 times. An extreme increase in CH4 emission from the lake occurred in the second year of continuous flooding (2008), which might have been caused by the decomposition of flooded organic C. So, the lake water ecosystem is the main source of CH4 in thermokarst depression controlled by the duration of flooding. Under future global climate change, thermokarst depressions in Central Yakutia have potential for lake expansion, causing significant increase in CH4 emission in the studied region.

Effects of hairy vetch foliage application on nodulation and nitrogen fixation in soybean cultivated in three soil types

We investigated the effects of applying hairy vetch foliage on nodulation and atmospheric nitrogen (N2) fixation in soybean cultivated in three soil types in pot experiments. Soybean plants were grown in Gley Lowland soil (GLS), Non-allophanic Andosol (NAS), and Sand-dune Regosol (SDR) with hairy vetch foliage application in a greenhouse for 45 days. In GLS, the nodule number was not influenced by the application, however, nodule dry weight and N2 fixation activity tended to increase. In NAS and SDR, nodule formation was depressed by foliage application. Soybean plant growth was promoted in GLS and SDR but not in NAS. These promotive effects of hairy vetch foliage application on soybean plant growth in GLS were considered to be mainly caused by the increase in N2 fixation activity of the nodules, whereas it was considered to be mainly caused by the increase in nitrogen uptake activity of the roots in SDR. The varying effects of hairy vetch foliage application on soybean nodulation may be due to soil chemical properties such as pH and cation exchange capacity, which are related to soil texture. Therefore, we conclude that it is important to use hairy vetch for soybean cultivation based on the different effects of hairy vetch on soybean plant growth in different soil types.