The Effect of Nutrients and Enriched CO₂Environments on Production of Carbon-Based Allelochemicals in Plantago: A Test of the Carbon/Nutrient Balance Hypothesis

Abstract

In a test of the carbon/nutrient (C/N) balance hypothesis, we grew the perennial herb Plantago lanceolata in different CO2 and nutrient environments and then (1) measured the total allocation to shoots, roots, and reproductive parts and (2) quantified aucubin, catalpol, and verbascoside contents of replicate plants of six genotypes. Plants grown under low-nutrient conditions do have higher concentrations of carbon-based allelochemicals than plants grown under high-nutrient conditions. However, in contrast to the C/N balance hypothesis, plants grown in elevated (700 microL.L(-1)) CO2 conditions had similar, or lower, concentrations of carbon-based allelochemicals than plants grown in ambient (350 microL.L(-1) CO2 conditions. We suggest that augmented substrate concentrations (i.e., excess carbohydrates) are a necessary but insufficient trigger for increased secondary metabolism; instead, hormonal and/or direct physical cues (such as light) may be essential to synthesize or activate the appropriate enzyme systems. Moreover, although plant genotype significantly affected plant growth, reproduction, and chemistry, we never observed significant genotype-by-CO2 interactions for these factors, which suggests that changing CO2 environments may not improve the fitness of certain genotypes over others

Tissue chemistry and carbon allocation in seedlings of Pinus palustris subjected to elevated atmospheric CO2 and water stress

“…Changes in tissue chemistry may also affect plant susceptibility to insect or pathogen attack, or both (Lincoln and Couvet 1989, Waterman and Mole 1989, Entry et al 1991, Fajer et al 1992, Kinney et al 1997. Changes in C chemistry in response to elevated CO2 could alter nutrient leaching and turnover, tissue decomposition, as well as host-herbivore and host-pathogen interactions (O'Neill and Norby 1996, Prior et al 1997a, Pritchard et al 1997, Bezemer and Jones 1998.…”

“…The CO2-induced changes in the quality of plant tissues influence insect herbivory (Lincoln and Couvet 1989, Fajer et al 1992, Kinney et al 1997) and the incidence and severity of plant diseases (Thompson et al 1993, Thompson andDrake 1994). These changes also have the potential to alter decomposition processes (Melillo 1983, CoOteaux et al 1991, Cotrufo and Ineson 1996, O'Neill and Norby 1996, which could impact C turnover and storage in soils (Prior et al 1997c, Torbert et al 1997.…”

Plantas medicinais: fatores de influência no conteúdo de metabólitos secundários

“…A grande maioria dos estudos sobre influência de nutrientes no solo está correlacionada com intensidade de luz incidente e voltada para discussões sobre alocação de recursos (hipóteses de balanço carbono/nutrientes), as quais visam estabelecer uma relação entre as disponibilidades de nitrogênio, carbono e luz 128,131 . Nestes estudos, de modo geral, a produção de metabólitos secundários (exceto os nitrogenados) mostra uma correlação positiva com a proporção carbono/nutrientes (C/N), isto é, em solos pobres em nutrientes, paralelamente à menor taxa de crescimento, geralmente se verifica maior produção de metabólitos secundários, particularmente derivados fenólicos 79,94,129,130 .…”

“…Nestes estudos, de modo geral, a produção de metabólitos secundários (exceto os nitrogenados) mostra uma correlação positiva com a proporção carbono/nutrientes (C/N), isto é, em solos pobres em nutrientes, paralelamente à menor taxa de crescimento, geralmente se verifica maior produção de metabólitos secundários, particularmente derivados fenólicos 79,94,129,130 . Contudo, estas hipóteses não foram totalmente comprovadas, existindo resultados controversos e tentativas de refinamento das hipóteses de balanço C/N 34,128,[130][131][132][133][134] .…”

“…Por outro lado, Plantago lanceolata quando cultivada em atmosfera com elevada concentração de CO 2 (700 μL L -1 ) apresenta concentrações similares ou menores de iridóides que a cultivada em condição ambiente (CO 2 = 350 μL L -1 ) 131 .…”