The carbon–nutrient balance hypothesis: its rise and fall

Abstract

The idea that the concentration of secondary metabolites in plant tissues is controlled by the availability of carbon and nitrogen in the environment has been termed the carbon–nutrient balance hypothesis (CNB). This hypothesis has been invoked both for prediction and for post hoc explanation of the results of hundreds of studies. Although it successfully predicts outcomes in some cases, it fails to such an extent that it cannot any longer be considered useful as a predictive tool. As information from studies has accumulated, many attempts have been made to save CNB, but these have been largely unsuccessful and have managed only to limit its utility. The failure of CNB is rooted in assumptions that are now known to be incorrect and it is time to abandon CNB because continued use of the hypothesis is now hindering understanding of plant–consumer interactions. In its place we propose development of theory with a firm evolutionary basis that is mechanistically sophisticated in terms of plant and herbivore physiology and genetics.

Phenolic content and growth of wetland macrophytes: Is the allocation to secondary compounds driven by nutrient availability?

“…Contrasting results have been reported on how successful these hypotheses are in predicting the concentration of carbon based secondary compounds in different plant species/types (Koricheva et al 1998;Hamilton et al 2001). Mixed results are most likely due to large variation in compounds and environmental conditions.…”

Chemical mediation of interactions among marine organisms

“…In a manipulative experiment conducted in outdoor aquaria, only F. vesiculosus responded to changes in light intensity 113 The CNBH does not appear to have predictive value for other types of seaweed compounds such as terpenes. 91 ' 107 A recent review 114 shows that the CNBH fails to predict outcomes of nutrient interactions with terrestrial plant chemical defenses so often that it can no longer be considered a useful predictive tool. The authors argue that many of the fundamental assumptions of the CNBH are not true based on what we now know about plant physiology and the production of secondary metabolites.…”

“…They propose that ODT, which is based on evolution and adaptation, is a more robust model. 114 Environmental Stress Theory (EST) suggests that environmental stresses, which may either reduce growth due to inadequate nutrient supply or cause damage due to adverse conditions such as desiccation or UV exposure, will affect predator-prey interactions. Environmental stress often results in increased palatability to consumers, which may be due to either increases in nutritive value or decreases in defenses in the affected plants.…”

Higher Allocation to Low Cost Chemical Defenses in Invasive Species of Hawaii

“…They range from theories based on plant capacity to allocate resources in excess of growth demands into defenses, such as a "carbon excess" hypothesis (Bryant et al, 1983;Peñuelas and Estiarte, 1998), to theories with more evolutionary bases (Hamilton et al, 2001) that bypass theories on enhanced terpenoid production as a result of enhanced nutrient availability (Harley et al, 1994;Litvak et al, 1996;Peñuelas and Staudt, 2010). Some of these theories, mainly those based on "carbon excess", have been highly criticized and mostly dismissed (Hamilton et al, 2001;Koricheva, 2002;Nitao et al, 2002). Alien success could bring new clues to this topic.…”