A New Hammer to Crack an Old Nut: Interspecific Competitive Resource Capture by Plants Is Regulated by Nutrient Supply, Not Climate

Abstract

Although rarely acknowledged, our understanding of how competition is modulated by environmental drivers is severely hampered by our dependence on indirect measurements of outcomes, rather than the process of competition. To overcome this, we made direct measurements of plant competition for soil nitrogen (N). Using isotope pool-dilution, we examined the interactive effects of soil resource limitation and climatic severity between two common grassland species. Pool-dilution estimates the uptake of total N over a defined time period, rather than simply the uptake of 15N label, as used in most other tracer experiments. Competitive uptake of N was determined by its available form (NO3 − or NH4 +). Soil N availability had a greater effect than the climatic conditions (location) under which plants grew. The results did not entirely support either of the main current theories relating the role of competition to environmental conditions. We found no evidence for Tilman's theory that competition for soil nutrients is stronger at low, compared with high nutrient levels and partial support for Grime's theory that competition for soil nutrients is greater under potentially more productive conditions. These results provide novel insights by demonstrating the dynamic nature of plant resource competition.

Dynamic trajectories of growth and nitrogen capture by competing plants

“…N capture would also, ideally, be measured as gross rather than net N fluxes from soil to plant. This can be done using 15 N‐pool‐dilution approaches which we report elsewhere for a limited temporal window of competition between D. glomerata and P. lanceolata (Trinder et al , 2012). The logistical demands required to use 15 N‐pool dilution frequently enough to show detailed temporal trajectories of gross N capture by competing plants render that technique unsuitable for this purpose.…”

Species mixing effects on forest productivity in the Netherlands

“…Rich soils allow for a denser forest canopy with possibilities for complementary light use, particularly when species differ in shade tolerance or leaf phenology. Our results were consistent with studies that found stronger competition for light at rich soils ( Baribault and Kobe, 2011;Forrester, 2014;Jucker et al, 2014a), but weaker competition for light on high fertility soils was also reported in the literature (Trinder et al, 2012;Coates et al, 2013). In the end, this complementary light use at tree level might improve individual tree growth and drive higher stand productivity in mixed forests stands, i.e.…”

“…Other studies show that inter-specific competition had a positive effect on tree growth at dryer sites relative to intra-specific competition . One study found that competition for soil resources increased in one experiment on poor soils ( Baribault and Kobe, 2011), while another found that it decreased (Trinder et al, 2012). Our study shows stronger competition for soil resources on low fertile soils (chapter 3).…”

Light intensity alters the allelopathic effects of an exotic invader

“…Understanding this conditionality is important for a broader understanding of the relative importance of different ecological factors affecting the distributions and abundances of species. Conditionality has been demonstrated repeatedly for interspecific competition in the context of abiotic stress (Gurevitch 1986;Pennings and Callaway 1992;Brooker et al 2005), variation in resource supply (Besaw et al 2011;Trinder et al 2012), and other biotic interactions (Callaway and Pennings 1998;Alberti et al 2008). Mutualistic and facilitative interactions also show similar conditional responses to the same factors (Bronstein 2003;Baumeister and Callaway 2006;Cavieres and Badano 2009).…”