Effects of cover crops and limiting resources on biomass allocation in Elymus repens (L.) Gould

Abstract: Weed control has always been a major challenge in arable lands. Elymus repens (couch grass), a rhizomatous perennial grass, is a particularly problematic weed in both annual and perennial crops in temperate climates. E. repens is dominant particularly in farming systems with no or limited use of herbicides. Ecological farming is in the rise due to the environmental and health awareness of consumers. Cover crops have been successfully used to reduce many weed species, but the effect on E. repens has been inconsistent and seemingly highly dependent on cover crop density. The aim of this study was to investigate the effect that limiting resources and cover crops have on biomass allocation and acquisition of E. repens. To test these, two greenhouse experiments were conducted in 2014. In the first experiment, E. repens was grown under a combination of three light and three nutrient supply levels. Under decreasing light levels, E. repens shifted the allocation towards the above ground biomass and reduced the number of shoots, tillers and spikes; explained by the elongation of the stems seeking light. A decrease in nutrient availability increased the below ground (roots and rhizomes) fraction and decreased the number of tillers. Both treatments decreased total biomass compared to the control. In the second experiment,E. repens was grown under three seeding densities of red clover or perennial ryegrass. The use of both cover crops reduced the total biomass, number of aerial shoots and spikes of E. repens. Red clover did not change the allocation pattern while ryegrass increased the belowground mass fraction of E. repens, indicating that it competed strongly for nutrients. In conclusion, biomass allocation and acquisition in E. repens was altered by abiotic and biotic factors.