Effect Of Elevated UV-B Radiation And CRNF Sypply On Growth And CH₄Emission In Herbicide Resistant Transgenic Rice From A Paddy Soil

Rice is one of the predominant staple foods in the world, which feeds over50%of the worldwide population for about80%of their food requirements. So far, the effect of elevated UV-B radiation on rice production has received more attentions. Population explosion and limited arable soils are threatening food supply security. Field and pot experiment with rice cultivars were conducted to investigate the effects of elevated UV-B radiation and controlled-release nitrogen fertilizer (CRNF) on the growth characteristics, photo synthetic characteristics, CH4emission, CH4production potentials and so on. This study will be helpful in further improving ecological risk assessment on transgenic rice.Main results are as follows:(1) Rice growth characteristics:Elevated UV-B radiation inhibited rice single leaf area, till numbers, plant height, above and underground biomass, finally decreased rice production and component factors (i.e. main panicle length, effective panicles, filled grains, productive panicle rate,1000-grain weight and so on).Single leaf area and plant height were higher under urea treatment than CRNF treatment until booting stage, and then the difference between two fertilizer treatments gradually diminished. Tiller numbers between before and after late-tillering stage came to the similar conclusion. Application of CRNF finally increased above and underground biomass, rice production and component factors (i.e. effective panicles, filled grains,1000-grain weight and so on).(2) Rice photosynthetic characteristics:Elevated UV-B radiation decreased the net photosynthetic rate (Pn), transpiration rate (Tr), water use efficiency (WUE) of two cultivars at tillering, blooming and mature stage, stomata conductance (Gs) at blooming stage under saturation light. In addition, elevated UV-B radiation decreased the diurnal variation of Pn, Tr, Gs and WUE at above three stages and Pn, Tr, Gs and WUE to photosynthetic active radiation at tillering stage. Farquhar models showed that maximum apparent photosynthesis rate (Pnmax)、dark respiration rate (Rd)、light compensation point (LCP) and light saturation point (LSP) of two culivars were inhibited by elevated UV-B radiation at tillering stage.CRNF increased Pn, Tr, WUE of two rice cultivars at tillering, blooming and mature stage, Gs at blooming stage under saturation light. In addition, diurnal variation of Pn, Tr, Gs and WUE at above three stages and Pn, Tr, Gs and WUE to photosynthetic active radiation at tillering and mature stage were improved by CRNF application. Farquhar models showed that CRNF increased Pnmax、Rd and LCP of transgenic rice, Rd and LCP of parent rice at tillering stage and Pnmax、Rd、LCP and LSP of two cultivars at mature stage.(3) CH4emission in rice:Elevated UV-B radiation had no effect on seasonal dynamics of CH4flux in paddy field. Compared with control, elevated UV-B radiation increased CH4flux and total amount of CH4emission (p<0.05) and CH4diurnal variation (p>0.05).Compared with control (urea), one-time basal application of CRNF decreased CH4emission (p<0.05) and CH4diurnal variation (p<0.05) in the paddy soil.Regardless of UV-B radiation and fertilizer treatments, CH4flux and total amount of CH4emission were higher in parent rice than transgenic rice.(4) Methane production potentials in rhizosphere and non-rhizosphere paddy soil:Elevated UV-B radiation increased methane production potentials in rhizosphere and non-rhizosphere soils(p>0.05), while CRNF decreased them(p>0.05)at blooming and mature stage. Regardless of UV-B radiation and fertilizer treatments, methane production potentials in rhizosphere and non-rhizosphere from parent rice paddy soils were higher than from transgenic rice. Methane production potentials in rhizosphere soil were larger than non-rhizosphere soil.(5) Rice root residues decomposition:The fluxes of CH4and CO2were higher in the soil amended with transgenic rice root residues than those with conventional parental root residues. Compared with the control, the fluxes of CH4and CO2were obviously increased by amending rice root residues. The CH4fluxes were lower in the aerobic treatments than in the flooding treatments, but opposite for CO2fluxes. A significant correlation was found between CH4fluxes and soil temperatures, negatively under aerobic conditions at the later stage and positively under flooding condition. The CH4fluxes were significantly correlated with the amounts of microbial biomass C under flooding condition, regardless of the type of rice root residues amended.