Below‐ground competition favors character convergence but not character displacement in root traits

Abstract

Summary Character displacement can play a major role in species ecology and evolution; however, research testing whether character displacement can influence the evolution of root traits in plant systems remains scarce in the literature. Here we investigated the potential that character displacement may influence the evolution of root traits using two closely related morning glory species, Ipomoea purpurea and Ipomoea hederacea. We performed a field experiment where we grew the common morning glory, I. purpurea, in the presence and absence of competition from I. hederacea and examined the potential that the process of character displacement could influence the evolution of root traits. We found maternal line variation in root phenotypes and evidence that below‐ground competition acts as an agent of selection on these traits. Our test of character displacement, however, showed evidence of character convergence on our measure of root architecture rather than displacement. These results suggest that plants may be constrained by their local environments to express a phenotype that enhances fitness. Therefore, the conditions of the competitive environment experienced by a plant may influence the potential for character convergence or displacement to influence the evolution of root traits.

Coordination of root growth with root morphology, physiology and defense functions in response to root pruning in Platycladus orientalis

“…After six hours following root pruning, root IAA content declined and recovered to the unpruned level at 504 h. This could be an evolutionarily reasonable result because if the IAA content is still high at 504 h following pruning, the new lateral root apices can be stimulated and hence produce much denser roots. The dense root system could cause strong within-root competition in the limited soil space [56] , [57] , which hinders root resource foraging and could be eliminated by natural selection.…”

“…Plants are generally confronted with a tradeoff between growth and defense functioning [22] , [58] , [59] . This tradeoff can be more significant under stress or disturbance conditions as plants need to invest more resources into defense, hence reducing the investment in growth [57] . In the present study on P. orientalis , root growth remained constant in the early time (e.g., 6 and 72 h) after the pruning treatment but increased significantly in the late time (504 h) ( Fig.…”

Rapid transgenerational adaptation in response to intercropping increases facilitation and reduces competition

“…However, it might be that this short common community history has favoured a specific species or a specific trait that was particularly plastic or beneficial for fitness 23,24 .…”

“…7 & Table 15). While surprising, this result is not unheard of 23 , and suggests that our plants might have adapted to express the phenotype that would maximise their fitness [34][35][36] . This ideal phenotype is, in our mixture communities, characterized by taller plants with lower leaf dry matter content, the latter indicating soft leaves associated with rapid biomass production 37 , and consequently less resource-conservative strategies 38 .…”

“…This is unexpected, as selection effects have not, to our knowledge, been shown to increase over time 22 . However, it might be that this short common community history has favoured a specific species or a specific trait that was particularly plastic or beneficial for fitness 23,24 .…”