| Rice is an important source of food and nutrition for human population and cultivated on an area about 29.9 million ha in the world.Rice yield and quality were significantly enhanced with the cultivar improvement and the development of cultivation techniques in the past decades.However,rice production will have to face challenges from global warming in the future.IPCC(Intergovernmental Panel on Climate Change)2013 reported that global mean surface temperature has increased by 0.85? from 1880 to 2012,and it will continue to rise 0.3-4.8? by 2100 if no emission reduction model was undertaken.Grain filling,as the key period for the formation of rice yield and quality,is quite sensitive to temperature change.The effects of elevated temperature during grain filling on rice yield and quality were always the hot issue in the area of rice science.However,previous experiments were mostly carried out under closed or part-closed warming facility with rice being cultivated in pots.Moreover,these studies generally concerned the influence of high temperature stress.Results gained from these studies were difficult to reflect the actual response of rice to temperature increasing in this century.Otherwise,whether the negative effects from climate warming on rice production can be mitigated using nitrogen fertilizer management was still lacked of knowledge.Whether there are differences for results gained from open-field warming experiment and pot-greenhouse warming experiments remains unclear.Aim at the questions above,a 4-year open-field warming experiment was undertaken to derermine the influence of low-amplitude warming on rice yield,quality and grain filling based on FATE(Free-air Temperature enhancement)facility,the role of nitrogen spikelet fertilizer in reducing the negative effects of elevated temperature on rice quality was also explored in this study.Furthermore,we compared the the differences between open-field warming experiment and pot-greenhouse warming experiment.Main results are as follow:(1)low-amplitude warming during grain-filling stage did not cause obvious stress on rice yield and its components.Though elevated temperature accelerated the translocation of dry matter from stem and leaf to panicle during early grain-filling,there were no clear differences for dry matter distribution in rice organs at maturity stage.Superior spikelets and inferior spikelets presented different response to elevated temperature.For superior spikelets,grain filling rate and grain weight were enhanced by elevated temperature during early grain filling stage,and after reaching the maximum value,the grain filling rate decreased faster,finally induced a shorter grain filling period and grain weight loss.For inferior spikelets,elevated temperature improved its grain filling during middle and late grain filling stage,and finally enhanced its grain weight.The positive influence of elevated temperature on inferior spikelets filling during middle and late grain filling was associated with the improvement of IAA content and the activity of SuSase,SBE and ATPase.(2)A 4-year field experiment was conducted to investigate the response of rice quality to elevated temperature during grain filling stage.Results showed that elevated temperature decreased milled rice rate,head rice rate,amylose content,setback,consistency,and proportion of shorter chain in amylopectin,while increased chalky rate,chalkiness,amylopectin content,peak viscosity,hot viscosity,breakdown,proportion of longer chain in amylopectin,pasting temperature,gelatinisation enthalpy,mean granule diameter and relative crystallinity.The contents of most kinds of amino acids including 6 kinds of essential amino acids were increased under elevated temperature compared with natural temperature,but the relative proportions of most amino acids were not significantly changed by elevated temperature.Chalkiness rate was positively related to the temperature of 1-10 days after heading,while starch components and pasting temperature was closely related to the temperature of 11-20 days after heading.Generally,slight temperature increase during grain filling stage resulted in the deterioration of rice appearance quality,milling quality and cooking quality,and made rice soft,but improved rice nutritional quality.(3)This research found that the application of nitrogen spikelet fertilizer significantly reduced chalkiness area,setback and consistency,and increased head rice rate,contents of amino acids under 4? warming regime,and had no significant effects other quality parameters and grain weights.The above phenomenon indicated that the application of nitrogen fertilizer at heading stage is efficient to mitigate the deterioration of rice quality especially for appearance quality under higher temperature.The improvement of chalk characteristics was linked to the alleviation of grain filling rate and amyloplast development.(4)This research compared the results of open-field warming experiment and pot-greenhouse warming experiment from the aspects including warming performance,microclimate factor,rice yield and quality.Results showed that warming performance of open-field warming experiment well reflected the increasing amplitude and the asymmetry of global warming,and exhibited no obvious influence on other enivoemental factors including light intensity,relative humidity and CO2 concentration;glass greenhouse exhibited higher warming amplitude during daytime than nighttime.Meanwhile,it reduced light intensity,and increased relative humidity and CO2 concentration at daytime.The effects of elevated temperature on rice yield and its components in the open-field warming experiment presented smaller than those in the pot-greenhouse warming experiment.Lower pollen fertility,difficulty of dry matter translocation and weaker performance for grain filling of inferior spikelets were the main reasons for rice yield loss under elevated temperature in the pot-greenhouse warming experiment.Elevated temperature in the two warming experiments both significantly deteriorated rice appearance quality and milling quality. |
PDF Full Text Request