Effect Of Alopecurus Japonicus On Wheat Photosynthetic Physiology Under Different Growth Densities

Due to the effects of lifestyles changes,farming system adjustments,herbicide selection pressure and other factors,the weed of wheat field and the dominant weed in community composition were constantly evolving.Alopecurus japonicus has strong tillering ability,high growth rate and spike rate,and it is one of the most troublesome and common weeds infesting wheat fields in china currently.In recent years,the harm of Alopecurus japonicus on the wheat fields of china was getting greater,so,the study of Alopecurus japonicus on wheat fields was attracting more and more attention,Alopecurus japonicus compete with wheat for environmental resource in limited supply,i.e.light.space and nutrients,which would affect the photosynthesis of wheat,and then resulted in yield loss.The competitive ability of Alopecurus japonicus and wheat may be changed because of their seeding density.Currently,the studys about Alopecurus japonicus mainly focus on weed resistance and yield loss,but there is little research on the physiological mechanism of yield loss which resulted from wheat competition.Therefore,in this experiment,we measured the photosynthetic gas exchange,the content of chlorophyll,the activity of Rubisco and other indicators of wheat,and then analyzed the effects of Alopecurus japonicus on photosynthetic physiology of different wheat varieties,and the effects of Alopecurus japonicus on wheat photosynthetic physiology under different planting density.This study investigated the effect of Alopecurus japonicus with different density on photosynthetic characteristics and yields of wheat(Yangmai 16 and Ningmai 13).Results showed that the competitive relationship between wheat and Alopecurus japonicus was not only effected by cultivated varieties but also cultivation methods.Under pot Gsition,leaf area,net photosynthetic rate and transpiration rate of wheat decreased with increasing densities of Alopecurus japonicus,but there is no significant change on fluorescence parameter at grain-filling stage.Correlation analysis revealed that the yield of wheat was positively correlated with net photosynthetic rate and the maximum photochemical efficiency of PSII at grain-filling stage.The correlations reached significant or extremely significant level.Under field condition,plant height,panicle length,Net photosynthetic rate,Rubisco activity,and grain yield of wheat decreased with increasing densities of Alopecurus japonicus.The reduction in panicle length,Net photosynthetic rate,maximum photochemical efficiency of PSII,and Rubisco activity of Ningmai 13 were less than that of Yangmai 16.Correlation analysis revealed that the net photosynthetic rate was positively correlated with Rubisco activity significantly.The yield was positively correlated with the net photosynthetic rate significantly.A comprehensive analysis indicates that interference of Alopecurus japonicus decreased Rubisco activity,leaf photosynthetic capacity,and energy conversion efficiency,thereby caused wheat yield reduction.Compared with Ningmai 13,Yangmai 16 was more sensitive to the weed interference.Further research of different planting density on the effects of Alopecurus japonicus on wheat photosynthetic physiology showed that,interference of Alopecurus japonicas affected the photosynthetic rate,chlorophyll fluorescence parameters,chloroplast Hill reaction,Rubisco activity and other photosynthetic physiological indexes.Compared with the conventional seeding rate,the effect of Alopecurus japonicas interference on photosynthesis of wheat was lower under high seeding rate.Interference of Alopecurus japonicus inhibited photochemical reaction of wheat,reduced chloroplast Hill reaction activity,decreased PSII electron transfer efficiency,and inhibited Rubisco activity simultaneously,thereby caused wheat yield reduction.At the high seeding density,wheat could alleviate weed stress by increase specific leaf weight,maintain Rubisco activity and reduce photoinhibition of leaves.