Division of Applied Life Science (BK 21+ Program), Gyeongsang National University, Jinju, Republic of Korea.
Soil & Fertilizer Management Division, National Institute of Agricultural Science, Wanju, Republic of Korea.
PLoS One. 2021 Sep 20;16(9):e0256796. doi: 10.1371/journal.pone.0256796. eCollection 2021.
In rice paddy, the closed chamber method is broadly used to estimate methane (CH4) emission rate. Since rice plants can significantly affect CH4 production, oxidation and emission, rice plantation inside the chamber is standardized in IPCC guidelines. Methane emission rate is calculated using the increased concentration inside the headspace. Biomass growth might decrease the headspace volume, and thus CH4 emission rates might be overestimated. To evaluate the influence of chamber headspace decreased by rice plant development on CH4 emission rates, five Korean rice cultivars were cultivated in a typical rice paddy, and physical volume changes in rice biomass were assayed using water displacement method. The recommended acrylic closed chambers (H. 1.2 m x W. 0.6 m x L. 0.6 m) were installed, and eight rice plants were transplanted inside the chamber with the same space interval with the outside. Biomass growth significantly decreased the headspace volume of the chamber. However, this volume covered only 0.48-0.55% of the closed chamber volume at the maximum growth stage. During the whole cropping period, mean 0.24-0.28% of chamber headspace was allocated by plant biomass, and thus this level of total CH4 emissions was overestimated. However, this overestimation was much smaller than the errors coming from other investigation processes (i.e., chamber closing hour, temperature recording, inconstant flooding level, different soil environments, etc.) and rice physiological changes. In conclusion, the influence of physical biomass volume inside the closed chamber was negligible to make the error in total CH4 emission assessment in rice paddies.
在稻田中，广泛采用密闭室法来估算甲烷（CH4）排放速率。由于水稻植株会显著影响 CH4 的产生、氧化和排放，因此在 IPCC 指南中对密闭室内的水稻种植进行了标准化。CH4 排放速率是通过增加的顶部空间浓度来计算的。生物量的生长可能会减少顶部空间的体积，从而可能高估 CH4 排放速率。为了评估由于水稻植株发育导致的密闭室顶部空间减少对 CH4 排放速率的影响，选用了五个韩国水稻品种在典型稻田中进行栽培，并采用排水法测定水稻生物量的物理体积变化。安装了推荐的丙烯酸密闭室（高 1.2 米 x 宽 0.6 米 x 长 0.6 米），并在密闭室内以与室外相同的空间间隔移植了 8 株水稻。生物量的生长显著降低了密闭室的顶部空间体积。然而，在最大生长阶段，这一空间体积仅占密闭室体积的 0.48-0.55%。在整个种植期内，平均有 0.24-0.28%的密闭室顶部空间被植物生物量占据，因此会高估总 CH4 排放量。然而，这种高估程度远小于来自其他调查过程（例如，密闭室关闭时间、温度记录、不稳定的淹水水平、不同的土壤环境等）和水稻生理变化带来的误差。总之，密闭室内物理生物量体积的影响可以忽略不计，不会对稻田中总 CH4 排放评估的误差产生影响。
