Directly quantifying multiple interacting influences on plant competition

Abstract

When plants compete what influences that interaction? To answer this we measured belowground competition directly, as the simultaneous capture of soil ammonium and nitrate by co‐existing herbaceous perennials, Dactylis glomerata and Plantago lanceolata, under the influence of: species identity; N uptake and biomass of focal and neighbour plants; location (benign lowland versus harsher upland site); N availability (low or high N fertilizer); N ion, ammonium or nitrate production (mineralisation) rate, and competition type (intra‐ or interspecific), as direct effects or pairwise interactions in linear models. We also measured biomass as an indirect proxy for competition. Only three factors influenced both competitive N uptake and biomass production: focal species identity, N ion and the interaction between N ion and neighbour N uptake. Location had little effect on N uptake but a strong influence on biomass production. N uptake increased linearly with biomass only in isolated plants. Our results support the view that measuring resource capture or biomass production tells you different things about how competitors interact with one another and their environment, and that biomass is a longer‐term integrative proxy for the outcomes of multiple separate interactions—such as competition for N—occurring between plants.

Nutrient‐use strategy and not competition determines native and invasive species response to changes in soil nutrient availability

“…Rii quantifies the relative change in biomass of a target species as a result of growing with a neighbor and indicates the magnitude and direction (i.e. (Trinder et al 2020).…”

Growth and Physiological Performance of a Coastal Species Trifolium fragiferum as Affected by a Coexistence with Trifolium repens, NaCl Treatment and Inoculation with Rhizobia

“…Species interactions have been assessed in field conditions through some experimental manipulation leading to changes in resource availability, and usually comparing responses in respect to the natural gradient of certain environmental factors [ 33 , 34 ] as well as through studies in controlled conditions [ 35 , 36 ]. Recently, more information has become available on the role of soil microorganisms in predicting the outcome of plant species coexistence through multifaceted interactions [ 37 , 38 ] and this also gained a broader theoretical perspective [ 39 ].…”

Plant–plant interactions

“…The final paper in this special issue comes from Trinder, Brooker, Davidson, and Robinson (2020), addressing the question (as the authors put it), “when plants compete, what influences that interaction?” I have chosen this paper as a capstone for the Special Issue because I think it illustrates many of the ongoing challenges in investigating plant–plant interactions, and acts as a salutary warning to the field. This paper clearly demonstrates the difficulties in drawing inferences from physiological and growth data, and the care needed to ensure that conclusions are robust and reproducible.…”