9:45 AM - 10:15 AM
[ACG22-04] Effects of elevated CO2 levels and N fertilization on biomass and C and N contents of rice: Insights from Tsukuba FACE
Keywords:FACE, Rice, Rice yield, Biomass, Carbon cycle, Nitrogen cycle
A free-air CO2 enrichment (FACE) experiment in an open field enables to elucidate responses of actual ecosystems to eCO2. The National Institute for Agro-Environmental Sciences, Japan, had operated a FACE facility (Tsukuba FACE) in Tsukubamirai City, Ibaraki Prefecture since 2010. Single cropping of paddy rice is conducted with the following agricultural practices; submersion in late April; fertilization and puddling in middle May; transplanting of rice seedlings in late May; continuous submergence until the drainage in middle to late August; harvesting in middle to late September; a fallow season with bare soil and rice residues until the next spring; and several tillage events with a mixing depth of approximately 15 cm during the fallow season. Four rectangular bays are used for experiments. A FACE plot is set in each bay, accompanied by an ambient plot. Each FACE plot is equipped with an octagonal ring with a diameter of 17 m for pure CO2 release. The FACE equipment automatically regulates CO2 release to achieve the average target CO2 levels, 200 ppm above the ambient level. Treatments other than CO2 are N fertilization (0N, no application; SN, 8 g N m–2; HN, 12 g N m–2), temperature (ambient, +2°C for floodwater), and rice cultivars.
Five-year data (2010–2014) of Koshihikari, a staple cultivar in this region, showed that the aboveground biomass of rice was increased by eCO2 for all the N treatments (0N, +8%; SN, +10%, HN, +11%). The brown rice yield at SN and HN were also increased by eCO2 (SN, +12%; HN, +11%), whereas that at 0N did not respond to eCO2. Thus, the harvest index (the ratio of yield to aboveground biomass) of SN and HN were unchanged by eCO2, but that of 0N was decreased by 5% under eCO2. This result implies that the CO2 fertilization effect does not reach to grains under low N availability. The seasonal methane emissions were increased by 5% (SN) under eCO2. In the presentation, study results on the carbon and nitrogen contents and the allocation of biomass between shoot and root under eCO2 and different N availability will be shown. It is expected that such the knowledge gives good insights to research on responses of C and N cycles in terrestrial ecosystems to eCO2.
This study was supported by Grant-in-Aid for Scientific Research, Nos. 22248026, 24114711, and 2625206, provided by the Japan Society for the Promotion of Science. Tsukuba FACE was established and maintained by ‘‘Development of technologies for mitigation and adaptation to climate change in Agriculture, Forestry and Fisheries’’, a project provided by the Ministry of Agriculture, Forestry and Fisheries, Japan.