Competitive advantage of Rumex obtusifolius L. might increase in intensively managed temperate grasslands under drier climate

Abstract

Climate models predict decreasing amounts of precipitation for future summers in Switzerland. Since grasslands cover about one quarter of the area, severe consequences might be expected for Swiss agriculture, ranging from loss of grassland productivity to changes in vegetation composition. Since stressed ecosystems are also more susceptible to invasion, future drier conditions might favour the emergence of weeds. However, the response of temperate grasslands to drought has not been investigated in great detail so far. Using transparent rain shelters, we simulated extreme summer drought conditions in intensively managed temperate grassland in the Swiss lowlands at 400 m (Chamau, located near the city of Lucerne) and studied the drought response of Rumex obtusifolius, one of the most troublesome weeds for forage production. We quantified above-ground biomass and assessed the resource use in terms of carbon, nitrogen and water. R. obtusifolius increased its above-ground biomass production in response to drought, comprising up to 80% of the total community biomass in 2006. Within the drought plots, highest pre-dawn leaf water potentials, high values for midday leaf water potentials, stomatal conductance and assimilation clearly indicated that R. obtusifolius was much less affected by drought than other plant species. In general, no significant differences were found for these variables between drought and control R. obtusifolius plants, in contrast to the other plant species. Higher water use efficiency together with a change in N acquisition patterns resulted in a competitive advantage of R. obtusifolius over other species, favouring the spread of this weed. Thus, our results suggest a potential increase of weed pressure by R. obtusifolius under future climatic conditions, demanding additional management measures to limit its success.3

Effects of an extended drought period on physiological properties of grassland species in the field

“…Therefore this species may access water from deeper soil layers which is not available to other plant species with smaller root systems like grasses, under drought (Zaller 2007). Results from the physiological analyses reported here were consistent with previously published findings indicating that R. obtusifolius was able to increase its above-ground biomass production under drought conditions in 2006, as a consequence of a competitive advantage of this species over the others (Gilgen et al 2010). In 2006, the higher leaf water potentials (W p and W m ) of R. obtusifolius compared to the grass species support this hypothesis.…”

Response of temperate grasslands at different altitudes to simulated summer drought differed but scaled with annual precipitation

“…During the three years of the experiment, no fertiliser was applied to the plots and no grazing was allowed on the plots. In autumn 2006, the weed species Rumex obtusifolius L. had to be removed manually from the experimental plots at Chamau due to Swiss regulations (Gilgen et al, 2010), overseeding took place in early March 2007 to re-establish a closed vegetation cover. In addition, we assessed soil moisture by taking additional measurements of gravimetric soil water content in 2007.…”

“…No treatment effect was found at Früebüel in any of the three years, while annual community above-ground productivity at Alp Weissenstein was significantly decreased by drought in both years (Table 3). However, above-ground productivities at Chamau were strongly influenced by one weed species, Rumex obtusifolius, which gained competitive advantage over the other species in 2006 (Gilgen et al, 2010). We therefore excluded R. obtusifolius biomass at Chamau from all further above-ground productivity analyses.…”

Shifts in microbial communities do not explain the response of grassland ecosystem function to plant functional composition and rainfall change

“…Changing rainfall patterns are 59 likely to alter microbial community structure, which can have implications for many 60 ecosystem functions, including those relating to nutrient cycling and carbon (C) sequestration 61 (Morecroft et al 2004;Gilgen et al 2010). Changes to rainfall patterns will also be 62 accompanied by changes to the diversity and functional composition of plant communities, 63 which can be driven by a number of global change drivers including nitrogen (N) deposition 64 and land use intensification (Manning 2012, Southon et al, 2013, Allan et al 2015.…”