Carbon dioxide exchange at four intensively managed grassland sites across different climate zones of Japan and the influence of manure application on ecosystem carbon and greenhouse gas budgets

著者

Hirata R., Miyata A., Mano M., Shimizu M., Arita T., Kouda Y., Matsuura S., Niimi M., Saigusa T., Mori A., Hojito M., Kawamura O., Hatano R.

雑誌名

Agr. Forest. Meteorol., 177, 57-68

DOI

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概要

To investigate the influence of different fertilization regimes on carbon dioxide (CO₂) exchange and the effect of manure application on the carbon balance, we established two experimental plots, one with chemical fertilizers only and one with manure and supplementary chemical fertilizers, at each of four intensively managed grassland sites across the range of climate zones in Japan. By using eddy covariance CO₂ flux and biometric measurements, we evaluated gross primary production (GPP), ecosystem respiration (RE), net ecosystem production (NEP), and the net ecosystem carbon balance (NECB), which accounts for carbon input through manure application and carbon loss through harvest. The sites in warmer zones showed larger annual GPP and RE, but annual NEP did not display any clear temperature dependence. The annual NEP was positive at all study sites and plots. The annual GPP and autotrophic respiration differed only slightly between the two plots despite the different fertilization regimes, but the decomposition of applied manure increased the annual heterotrophic respiration, thus causing a reduction in the annual NEP. At all the study sites, NECB of the plots with application of chemical fertilizers only was negative, indicating the loss of carbon. Manure application increased NECB, and its effect was larger at the cool temperate sites than at the temperate and warm temperate sites because of the greater amount of applied manure and larger sequestration rate at the cool temperate sites. Thus, manure application increased the accumulation of carbon in grassland, which is favorable from the viewpoint of ecosystem carbon management. Even when the enhanced nitrous oxide emission from the plots with manure application was taken into account, our findings suggest that manure application is a favorable option for mitigating greenhouse gas emission from Japanese grasslands and effectively managing livestock waste.

施肥形態の違いが日本の草地の炭素収支ならびに温室効果ガス収支に与える影響の違いを調べた。化学肥料のみを施肥した場合、草地は炭素の放出源となったが、堆肥と補助的に化学肥料を施肥した場合は炭素の吸収源となった。堆肥の施肥は炭素吸収量を増加させる一方で、亜酸化窒素の放出量を増加させた。しかし、地球温暖化係数を考慮して温室効果ガス収支を評価したところ、亜酸化窒素放出量の増加を考慮しても堆肥の施肥は温室効果ガスの放出を緩和する働きがあることがわかった。日本の草地を炭素吸収源および温室効果ガスの吸収源とするには目安としてそれぞれ最低2.5tCha⁻¹、3.5tCha⁻¹の堆肥投入が必要であることがわかった。