Effects of simulated nitrogen deposition on weeds growth and nitrogen uptake

In this paper,a greenhouse experiment was conducted to study the responses of different functional groups of weeds to simulated nitrogen deposition (4.0 g N· m -2·yr -1).Native weed species Poa annua,Lolium perenne,Avena fatua,Medicago lupulina,Trifolium repens,Plantago virginica,Veronica didyma,Echinochloa crusgalli var.mitis,Eleusine indica and Amaranthus spinosus in orchard ecosystem were used as test materials,and their above-and underground biomass and nitrogen uptake were measured.The results showed that under simulated N deposition,the total biomass,shoot biomass and root biomass of all weed species tended to increase,while the total biomass was differed for different functional groups of weeds.The biomass of C 4 grass,C 3 legumes and C 3 grass was significantly increased under N deposition,while that of C 3 and C 4 forbs was not significantly impacted.The root/shoot biomass ratio of Avena fatua and Plantago virginica was enhanced by N deposition,but that of Poa annu,Lolium perenne,Medicago lupulina,Trifolium repens and Amarathus spinosus was not impacted significantly.N deposition had no significant effect on plant N concentration,but significantly enhanced the N uptake of all test weed species except Amarathus spinosus,Poa annua and Veronica didyma.It was suggested that the further increase of N deposition might speed up the changes of the community structure of weed species due to their different responses to N deposition.