UV-B增强下施硅对稻田CH4和N2O排放及其增温潜势的影响

大气平流层臭氧损耗导致的地表紫外辐射增强作为全球变化重要问题之一,受到广泛关注。硅是水稻生长有益元素,但施硅是否影响稻田CH_4和 N_2O排放,迄今相关报道尚不多见。通过大田试验,研究UV-B增强下施硅对水稻生长、稻田甲烷(CH_4)和氧化亚氮( N_2O)排放及其增温潜势的影响。UV-B辐照设2水平,即对照(A,自然光)和增强20%(E);施硅量设2水平,即对照(Si0,0 kg SiO_2/hm2)和施硅(Si1,200 kg SiO_2/hm2)。结果表明,UV-B增强降低了成熟期水稻地上部和地下部生物量,而施硅能缓解UV-B增强对水稻生长的抑制作用,使水稻地上部和地下部生物量增加。UV-B增强可显著提高稻田CH_4和 N_2O排放通量和累积排放量,增加稻田CH_4和 N_2O排放的综合增温潜势。施硅能明显降低稻田CH_4排放,促进 N_2O排放,降低稻田CH_4和 N_2O排放的综合增温潜势。研究表明,施硅显著降低稻田CH_4和 N_2O的全球增温潜势,缓解UV-B增强对稻田CH_4和 N_2O的全球增温潜势的促进作用。

Effect of silicate supply on CH4 and N2O emissions and their global warming potentials in a Chinese paddy soil under enhanced UV-B radiation

Enhanced ultraviolet-B (UV-B) radiation, one of the most important problems caused by global climate change, is induced by the depletion of the stratospheric ozone layer and has received considerable attention worldwide. It has resulted in damage to various plant processes, including growth inhibition, photosynthetic depression, lipid peroxidation, and ultra-structural change, and this has led to crop yield reductions. Methane (CH₄) and nitrous oxide (N₂O) are two potent greenhouse gases, and have 21 and 310 times higher global warming potentials (GWP), respectively, than CO₂ on a 100-year time scale. N₂O is the most important ozone-depleting substance in the 21st century, and paddy fields are regarded as one of the most important biological sources of N₂O and CH₄. Silicate is beneficial to rice growth, but so far there have been few reports on whether silicate application can reduce CH₄ and N₂O emissions from paddy soils. A field experiment was conducted to investigate the effects of silicate application on CH₄ and N₂O emissions and their GWPs in a Chinese paddy soil under enhanced UV-B radiation. The experiment had two UV-B radiation levels, i.e. ambient UV-B (A, ambient) and enhanced UV-B radiation (E, enhanced by 20%); and two silicate application levels, i.e. a control (Si0, 0 kg SiO₂/hm²) and added silicate (Si1, 200 kg SiO₂/hm²). The experiment was undertaken at the Station of Agricultural Meteorology, Nanjing University of Information Science and Technology, Nanjing, China. The emission fluxes for CH₄ and N₂O were determined by the closed chamber method at one-week intervals during the rice growing period. The results showed that, compared to ambient UV-B radiation, enhanced UV-B radiation decreased the shoot, root, and whole rice plant dry matter weights at the maturity stage by 13.12%, 53.31%, and 25.85%, respectively, in the no silicate treatment; and by 1.47%, 34.49%, and 11.12%, respectively, in the added silicate treatments. Therefore, enhanced UV-B radiation clearly depressed rice growth, but supplying silicate could significantly alleviate the depressive effect of enhanced UV-B radiation on rice growth. Enhanced UV-B radiation significantly increased CH₄ flux and its accumulated emissions, whereas supplying silicate significantly reduced CH₄ flux and its accumulated emissions. In the treatments without adding silicate, enhanced UV-B radiation significantly increased CH₄ accumulated emissions at the tillering stage, jointing-booting stage, heading-flowering stage, grain filling-maturity stage, and over the whole growth period by 101.65%, 63.12%, 13.96%, 3.94%, and 89.43%, respectively, over that under the ambient UV-B radiation. Under enhanced UV-B radiation, adding silicate significantly decreased CH₄ accumulated emissions by 35.83%, 45.96%, 39.84%, 10.29%, and 38.41%, respectively. Enhanced UV-B radiation also significantly increased N₂O flux and its accumulated emission levels. In the treatments with no additional silicate, enhanced UV-B radiation significantly increased N₂O accumulated emission levels at the tillering stage, jointing-booting stage, heading-flowering stage, grain filling-maturity stage and over the whole growth period by 69.89%, 41.62%, 134.57%, 84.46%, and 73.69%, respectively, over those under the ambient UV-B radiation. The effects of silicate supply on N₂O emissions from the paddy soil changed depending on the rice growth stage. Under enhanced UV-B radiation, supplying silicate significantly reduced N₂O accumulated emissions at the tillering stage and heading-flowering stage by 16.57% and 32.97%, respectively, but increased N₂O accumulated emissions at the jointing-booting stage, grain filling-maturity stage, and over the whole growth period by 68.06%, 23.09%, and 29.53%, respectively. It also significantly increased the global warming potentials (GWPs) of CH₄ and N₂O by 51.92% to 83.31%, respectively. Supplying silicate significantly reduced the GWPs of CH₄ and N₂O by 1.19% to 18.10%, respectively. In conclusion, enhanced UV-B radiation significantly increased N₂O flux and its accumulated emissions, and stimulated the GWPs of CH₄ and N₂O. Silicate application significantly reduced CH₄ flux and its accumulated emissions, promoted N₂O flux and accumulated emissions, and reduced the GWPs of CH₄ and N₂O. This study suggests that silicate application can reduce CH₄ and N₂O emissions and subsequent GWPs, and reduce the contribution of enhanced UV-B radiation to global warming potentials.