Differential Responses To Temperature And Light Change In Seeds And Seedling Of Rape And Companion Weeds

Weed community in rape field is changing with occurrence of extreme weather eventsand global warming. The objective of this study was to investigate the effects of temperatureand light intensity changes on rape seed (Brassica napus L.,‘Qinyou-10’) and8companionweeds, i.e. Descurainia sophia (L.) Schur., Euphorbia helioscopia L., Avena fatua L.,Polypogon fugax N., Veronica didyma L., Alopecurus aequalis L., Chenopodium glaucum L.and Amaranthus retroflexus L.. Temperature and light intensity were controlled byclimate-control growth chambers, and single factor experiment was conducted. Results of thisstudy can help with predicting the succession of companion weed communities underchanging climate. Conclusions are as follows:1. There were significant differences in adaptation to temperature and light intensitychanges among weed species and rapeUnder the extreme high temperature, the ranking order of seed germination rate fromhigh to low was Brassica napus L., Amaranthus retroflexus L, Veronica didyma L., Polypogonfugax N., Alopecurus aequalis Sobol., Chenopodium glaucum L., Euphorbia helioscopia L.,Descurainia sophia (L.) Schur. and Avena fatua L.. And the ranking order changes whenunder the extreme strong light intensity, that is Brassica napus L., Amaranthus retroflexus L.,Polypogon fugax N., Veronica didyma L., Chenopodium glaucum L., Euphorbia helioscopiaL., Descurainia sophia (L.) Schur., Alopecurus aequalis Sobol. and Avena fatua L..2. Amaranthus retroflexus L. have good adaptabilities to high temperature and stronglight intensityUnder high temperarature and strong light intensity, Amaranthus retroflexus L. showedhigh seed germination rate and powerful viability. The germination rate reached to the highestpoint (91%) at temperature of40/35℃, seedlings grew vigorously, their malondialdehyde(MDA) content reduced, the concentrations of soluble sugar and soluble protein and theactivities of SOD and POD in seedlings all increased with temperature raised. When lightintensity was9000lx, germination rate of Amaranthus retroflexus L. was significantly higherthan that of weak and normal light treatments, which reached100%, and seedlings grew well, demonstrating that strong light intensity promotes germination and enlongation ofAmaranthus retroflexus. That is the reason why Amaranthus retroflexus L. is becoming aweed in rape field that is different to control. Therefore, this weed should be paid moreattention in the Yangtze river basin, especially in extreme high temperature years.3. Chenopodium glaucum L. can adapt to high temperature and strong light intensitySeed germination rate of Chenopodium glaucum L. were generally low, but reached26%and30%at high temperature and strong light intensity, respectively, which were significantlyhigher than those at low temperature and weak light intensity treatments. Chenopodiumglaucum L. emerges more and more frequently in arid area in northern China, and itsgermination rate and growth under high temperature and strong light intensity were secondonly to Amaranthus retroflexus L.. With the boundary of rape moving northward, this weed,which has been proved possesses drought-resistant ability, will expand, and thus preventionsshould be made in advance.4. Avena fatua L. and Descurainia Sophia (L.) Schur. can resist low temperatureAt the temperature of10/5℃, seed germination of Avena fatua L. reached100%, and theseedlings exhibited high soluble sugar and soluble protein concentrations as well as high SODand POD activities, indicating the strong ability of this weed species in adapting to lowtemperature stress. Descurainia sophia had similar responses with Avena fatua in seedgermination and physiological metabolism. Therefore, these two weed species should be paidmore attention in the Huang-Huai river basin, during extreme cold spells.5. Qinyou-10tested in this study had good adaptability to temperature and light intensitychanges. This may be one of the reasons why this cultivar has been planted in large area.