The Mechanisms Of Intra And Interspecific Interaction On Regulating Growth And N/P Acquisition By Intercropped Wheat And Fababean

Intercropping is an important approach to improve the biodiversity in agro-ecosystem.However,we are not clear about the absolute yield gain of intercrops and the contribution of complementarity effect and selection effect to the yield gain.Cereal/legume intercrops are prevalent in previous intercrop studies.Wheat/faba bean intercropping is popular in Southwest and Northwest of China.However,the intraspecific interaction in intercropping was less studied.Therefore,we conducted a meta-analysis by collecting data from previous studies,and quantified the net effect,complementarity effect and selection effect and the related factors of intercrops in China.Pot experiments focusing on wheat/faba bean intercrops were carried out to study the dynamics of plant interactions between crop species when they were with no plant interaction,with intraspecific plant interactions and with both intra and interspecific interactions combined with different soil nitrogen(N)and phosphorus(P)levels.The main results and conclusions were summarized as follows:1.The net yield gain of Chinese grain intercrops was mainly contributed by complementarity effect.Intercrops with short co-growth period can reduce the competition to increase the complementarity effect and y:ield gain.C3/C4 intercrops had 1.5 ton ha-1 higher net effect than C3/C3 intercrops.Soil N supply decreased the net effect of cereal/legume intercrops but improved the complementarity effect and yield gain of cereal/cereal intercrops.Cereal/legume intercrops had the highest net effect and complementarity effect under moderate soil P supply.2.In the experiment about the response of wheat/faba bean to N levels,intraspecific competition dominated in wheat/faba bean intercrop.Under low soil N level,intraspecific competition decreased the biomass and N content of wheat by 76%,85%,and decreased the biomass and N content of faba bean by 45%,30%.Intercropping of wheat and faba bean decreased the intraspecific competition among wheat monocrops,which happened 28-31 days after sowing;under high soil N level,the interspecific competition was decreased,and intercropping also decreased the intraspecific competition among wheat monocrops,which happened at 20-12 days after sowing.Intercropping strengthened interspecific competition since wheat dominated in intercropping.Intercropping and N addition did not make up the decrease in biomass and N content of single species,there could be other resources competed by species.3.In the experiment about the response of wheat/faba bean intercropping to soil P levels,the effect of plant interaction on P uptake was mainly due to intraspecific competition,but the interspecific competition was not obvious.Under both low and high soil P levels,biomass and P content of wheat was decreased by 72-76%and 83-85%due to intraspecific competition.Under high soil P level,intraspecific competition in monocropped wheat was strengthened due to increased soil P availability.Under low soil P level,wheat and faba bean was in P deficiency at later growth stage,wheat and faba bean had higher amount of malate and citrate in rhizosphere at later growth stage.4.Under low supply of soil N and P,wheat/faba bean intercropping had significant interspecific competition when there were only interspecific interactions in intercrop.Interspecific competition decreased biomass of wheat and faba bean by 35%,32%,and decreased P content by 24%,42%.Therefore,intraspecific competition reduced the growth potential of wheat/faba bean intercropping.Low soil N and P stimulated interspecific competition between wheat and faba bean.There was no significant competition at early growth period.With depletion of soil nutrients,the competitive intensity of N uptake increased,while the competitive intensity of P uptake was maximum at 60 days after sowing,then it decreased in the later growth stage.In response to the deletion of soil nutrients,the acid phosphatase activity and carboxylates of faba bean increased,which can moderate the interspecific competition between intercropped wheat and faba bean.In summary,the yield gain of intercrops was mainly from complementarity effect.Both intraspecific and interspecific plant interaction can affect plant growth and nutrient uptake by intercrop.Intercropping can reduce intraspecific competition.Intraspecific competition reduces the potential of overyielding of intercrops,moderating intraspecific competition is one of the ways to improve overyielding of intercrops.