紫花苜蓿对轮作水稻产量和蔗糖代谢的影响

Effect of alfalfa on the yield and sucrose metabolism of rice in an alfalfa-rice rotation system

紫花苜蓿与水稻轮作具有改善稻田质量和增加水稻产量的作用,但苜蓿促进水稻增产的生理机制尚不清晰。试验设置种植黑麦草土+NPK基肥+尿素追肥(PRS)、种植苜蓿土+NPK基肥+尿素追肥(PAS)和苜蓿土+苜蓿绿肥+NPK基肥+尿素追肥(紫花苜蓿处理)3个处理。结果显示,与2个对照处理相比,紫花苜蓿处理显著提高了轮作水稻的分蘖数、生物量、籽实产量以及抽穗期叶片N、P、K含量;紫花苜蓿处理分蘖期、抽穗期和收获期的水稻净光合速率依次比PRS增加了16.99%、27.22%和40.99%,比PAS增加了16.88%、37.99%和33.51%;参与蔗糖代谢的关键基因OsAGPS1、OsAGPL1、OsMEX1、OsSPS1和OsSUS5的相对表达量在叶片(白天和夜间)和根系中明显变化,与PRS相比,5个基因在分蘖期夜间的表达量分别上调2.45、2.96、1.29、1.66和6.04倍,而白天仅OsMEX1和OsSPS1的表达量明显上调,同时,OsMEX1在抽穗期夜间和收获期明显下调;在根系中,OsAGPL1、OsMEX1和OsAGPS1在分蘖期或抽穗期明显上调表达;与此相应,分蘖期叶片的蔗糖磷酸合成酶和可溶性淀粉合成酶活性,以及新叶和叶鞘的淀粉、蔗糖和可溶性糖含量显著增加,而老叶中蔗糖和可溶性糖含量显著下降。研究结果表明紫花苜蓿通过影响轮作水稻分蘖期叶片N、P、K含量和蔗糖代谢通路关键基因的昼夜表达格局而改变淀粉、蔗糖和可溶性糖在水稻叶片和叶鞘的分配,从而促进水稻增产。

The alfalfa-rice crop rotation system can improve soil quality,increase rice yield,and reduce nitrogen fertilizer input.The aim of this study was to investigate the physiological and molecular mechanisms underlying the effect of alfalfa to promote the yield of rice in this type of crop rotation.We conducted an experiment in which rice plants were grown with soil from a ryegrass crop(control 1),soil from an alfalfa crop(control 2),and soil and green manure from an alfalfa crop(alfalfa treatment).Compared with the two controls,the alfalfa treatment significantly increased the number of tillers,biomass,seed yield,and nitrogen,phosphorus,and potassium contents in leaves of rice plants at the heading stage.The net photosynthetic rate of rice plants at the tillering stage,heading stage,and harvest stage was 16.99%,27.22%,and 40.99%higher,respectively,in the alfalfa treatment than in control 1;and 16.88%,37.99%,and 33.51%higher,respectively,in the alfalfa treatment than in control 2.The transcript levels of five key genes involved in sucrose metabolism(OsAGPS1,OsAGPL1,OsMEX1,OsSPS1,and OsSUS5)in the leaves(day and night)and roots differed significantly between the treatment and the controls.Compared with control 1,the alfalfa treatment resulted in up-regulation of OsAGPS1,OsAGPL1,OsMEX1,OsSPS1,and OsSUS5(by factors of 2.45,2.96,1.29,1.66,and 6.04,respectively)at night in leaves at the tillering stage,while only OsMEX1 and OsSPS1 were up-regulated in leaves during the daytime.OsMEX1 was significantly down-regulated during nighttime in leaves at the heading stage and harvesting stage in the alfalfa treatment.In roots,OsAGPL1,OsMEX1,and OsAGPS1 were significantly up-regulated at the tillering or heading stage in the alfalfa treatment.Correspondingly,the activity of sucrose phosphate synthase and soluble starch synthase in leaves at tillering stage,as well as the contents of starch,sucrose,and soluble sugars in new leaves and leaf sheaths were significantly increased,while sucrose and soluble sugar contents in old leaves were significantly decreased in the alfalfa treatment compared with the two controls.These results indicate that alfalfa green manure and soil can change the distribution of starch,sucrose,and soluble sugars in leaves and sheaths of rice plants grown in a rotation system by affecting the contents of N,P,K in leaves and the circadian expression pattern of key genes in the sucrose metabolic pathway at the tillering stage,thereby increasing rice yield.