Growth of hybrid poplar as affected by dandelion and quackgrass competition

Abstract

A pot experiment was conducted in a growth chamber to investigate the effects of dandelion (Taraxacum officinale) and quackgrass (Elymus repens) on the growth of hybrid poplar (Populus deltoides×Populus×petrowskyana var. Walker). Single hybrid poplar seedlings were grown in pots either alone (SHP) or with four or eight dandelion plants per pot or with one or three quackgrass plants per pot in two soils collected from sites previously managed for alfalfa and pasture near Meadow Lake, Saskatchewan, Canada. Hybrid poplar and weed species were harvested approximately 7 and 14 weeks after planting. Approximately 14 weeks after planting, hybrid poplar shoot biomass in the SHP treatment was 28 g for the pasture soil and 22 g for the alfalfa soil. Corresponding shoot biomass for hybrid poplar grown with the dandelion and quackgrass treatments varied from 0.54 to 0.81 g and 0.3 to 3.66 g, respectively. Other hybrid poplar growth parameters including stem height, root collar diameter and fresh root biomass were similarly reduced by competition with the weed species. During the growing period, soil solution N and K concentrations decreased several-fold in both soils; however, the magnitude of decrease was comparatively higher in the weed treatments. Nitrogen, P and K uptake by hybrid poplar was greater in the SHP treatment in both the soils (337-425, 38-49 and 396-463 mg pot −1 , respectively) compared to the weed treatments (4-28, 0.4-6.2 and 0.6-54.0 mg pot −1 , respectively) by the end of the experiment. The presence of quackgrass and dandelion severely affects the growth of hybrid poplar by causing intense below-ground competition for nutrients.

Nutrient uptake of hybrid poplar in competition with weeds using the soil supply and nutrient demand (SSAND) model

“…It was observed that the supply of NO 3 -N was exhausted within the simulation time, in particular for the second harvest simulations in both soils. This observation is contradictory to the measured soil solution values for the control treatment pots where significant amounts of NO 3 -N were still present in the soil solution at the end of the second harvest (Kabba et al 2007). The presence of NO 3 suggests that the availability of N to the plant is through some other pools such as N mineralization (Stevenson 1986).…”

“…Details of the pot study are reported in Kabba et al (2007) and are briefly described here. Hybrid poplar seedlings were grown in pots from 7.5-cm long stem cuttings that were soaked overnight in water.…”

Relationships between understory vegetation and hybrid poplar growth and size in an operational plantation

“…Predominant non-leguminous forbs in our study area included Taraxacum officinale, which is known to be a competitive species detrimental to poplar growth (Kabba et al 2007). Henkel-Johnson et al (2016) also found that forbs consistently suppressed tree diameter growth during the first three years and speculated that this was due to the tallstatured and broadleaved growth habit of forbs reducing light availability to young tree saplings.…”

“…The negative influence of PG on hybrid poplar size and annual growth was expected and agrees with findings in other studies; these effects are particularly important given that they occurred despite the intensive understory control measures implemented as part of the ongoing silviculture management of these plantations (Landhäusser andLieffers 1998, Henkel-Johnson et al 2016). Grasses have been recognized to be a limiting agent for tree growth in potted experiments due to belowground competition for root space (Messier et al 2009) and nutrient uptake (Kabba et al 2007). Field studies examining the effect of the native marsh reed grass (Calamagrostis canadensis (Michx.)…”

“…Competition effects also vary depending on the identity and abundance of competitors, and generally results in a loss of tree biomass and altered crown morphology (Marino andGross 1998, Kabba et al 2007). Of particular interest is the highly damaging effects that neighbouring grasses, especially aggressive perennials, have on poplar growth due to competition for root space, nutrients, light, and soil moisture (Powell and Bork 2004, Kabba et al 2007, Messier et al 2009, Henkel-Johnson et al 2016. On the other hand there are the uncertain but potentially facilitative effects of understory legumes that contribute to soil nitrogen availability (Jose et al 2004, Powell andBork 2004).…”