Differences In Productivity And CH₄Emissions Among The Leading Rice Varieties Released During1950-2010in Shenyang

Rice is the most important staple food crops in China，and there are more than60percent of thepopulation fed on rice in the country. Meanwhile, paddy field is one of the major sources of CH₄, whichaccounts for about1/4of the total anthropogenic emissions. Continuously improving crop yield andmitigating cropland greenhouse gases （GHGs） emissions have become the important scientific issue andthe key agronomic technology. Genetic improvement plays an essential role in the continuously increaseof rice yield. However, it remains unclear how the GHGs emissions change during the geneticimprovement. Thus, clarifying the GHGs emission trends with the genetic improvement progress canprovide an essential theoretical basis for rice breeding for high yield with low carbon. Recently, it hasbecome the main area which contributes for the rice yield increase in northeast of China. Shenyang isthe center of rice genetic improvement and agronomic innovation in northeast of China. However, lessresearch were reported on GHGs emission. An experiment was conducted at Shenyang, Liaoningprovince, China, with12leading Japonica rice varieties released during1950-2010period to study thechanges of plant morphology, production and GHGs emissions with years during the geneticimprovement. Our results can provide an idea from both theoretical basis and technology approach forrice breeding and agronomic innovation for high yield with low GHGs emissions. The main results areas follows:（1） During the process of varieties evolution in Shenyang, the plant type was improved by decreasingthe plant height and invalid tiller number. The plant height, leaf area index, tiller number and effectivepanicle number per hill decreased among the six decades, while root weight per hill and ratio of root tocanopy at heading stage and grain number per panicle increased. The rice plant type was tall, strongtillering ability and with more effective panicle during1950-70s, and semi-dwarf, with fine tilleringability, optimum between the grains number and panicle during2000-2010.（2） Grain yield of modern varieties were mainly improved by increasing aboveground biomass while theharvest index kept stable with the years. The harvest index increased during1950-1980s, and thenremained stable. There were no consistent trends in the changes of1000-grain weight, but abovegroundbiomass of varieties released during1990-2010was significantly greater than the varieties releasedduring1950-1980s. Grain yield increased with the years by9.5%10yr-1from1950-60s to2010.（3） CH₄and nitrous oxide emissions of all the rice varieties showed one peak in rice entire growthperiod. CH₄emission peak was at tillering stage, while the N₂O peak occurred at the mature period.During the entire growth period, the average fluxes （in equivalent CO2） were lowest in the varietiesreleased in2010for CH₄with the value61.1m^-2h^-2, and were lowest in the varieties released in2000sfor N₂O with the value10.6mg m^-2h^-2. Cumulative emissions of CH₄in different period varietiesshowed the tillering stage> full heading stage> ripening, and N₂O emissions accumulation showedripening> full heading stage> tillering stage. （4）The CH₄emission intensifies were lower for the modern varieties than the older ones. Area-scaled,biomass-scaled and yield-scaled emissions of CH₄increased firstly and then decreased with years. Thevalues of the three intensity indicators existing in the varieties released in2010were reduced by4.9%,19.9%and39.2%, respectively, compared to the varieties released in1950-60s. Area-scaled,biomass-scaled and yield-scaled emissions of N₂O exhibited a declining trend with years. All of threenitrous oxide emissions intensity values referred to in the varieties released in2010s reduced by18.4%,43.2%and51.1%, respectively, compared to the varieties released in1950-60s.（5） Yield-scaled CH₄emission was significantly negatively correlated with the ratio of root to shoot atfull heading stage （P<0.01）, and with biomass per hill at heading stage and with aboveground biomassat maturity stage （P<0.05）. Area-scaled emission of N₂O was significantly positively correlated with thetiller number （P<0.05）. Biomass-scaled emission of N₂O was significantly negatively correlated withgrain yield （P<0.05）; and yield-scaled emissions was significantly negatively correlated with root dryweight at heading stage and the aboveground biomass at mature stage （P<0.05）, and with grain yield...