Vascular architecture and patchy nutrient availability generate within‐plant heterogeneity in plant traits important to herbivores

Abstract

Within-plant heterogeneity in growth, morphology, and chemistry is ubiquitous, and is commonly attributed to differences in tissue age, light availability, or previous damage by herbivores. Although these factors are important, we argue that plant vascular architecture is an underappreciated determinant of heterogeneity. Vascular architecture can restrict the transport of resources (nutrients, photosynthate, hormones, etc.) to within specific sectors of the plant: this is referred to as sectoriality. Although studies have documented sectoriality in the transport of isotopes and dyes from roots to shoots, the ecological consequences of this sectoriality remain poorly understood. We tested the hypothesis that spatial variation in belowground nutrient availability combined with sectorial transport results in localized "fertilization" of aboveground plant parts and generates heterogeneity in traits important to herbivores. Our split-root experiments with tomato (Lycopersicon esculentum Mill) clearly demonstrate that fertilization to isolated lateral roots generates heterogeneity in leaf morphology, phenolic chemistry, and side-shoot growth. Specifically, leaflets with direct connections to these lateral roots were larger and had lower levels of rutin and chlorogenic acid than did leaflets in other sectors lacking direct vascular connections. Moreover, side-shoot production was greater in the connected sectors. We discuss the implications of this heterogeneity for plant-herbivore interactions.

Is polyphenol induction simply a result of altered carbon and nitrogen accumulation?

“…Our evidence leads us to suggest that branch-level "induction" of CHO-based compounds in response to insects or other elicitors arises from an increased CHO/N ratio driven by enhanced sink strength. This is consistent with evidence that induced "defense" is a local phenomenon, constrained by vascular architecture [27][28] and that local nutrient status can influence both constitutive and inducible defenses. 22,27,29,30 Substrates for many putative CHObased defenses, e.g., flavonoids and tannins, arise from the shikimic acid and phenylpropanoid pathways.…”

Perennial Roots to Immortality ,

“…Specifically, leaflets with direct connections to these lateral roots were larger than leaflets in other sectors lacking direct vascular connections. Moreover, side-shoot production was greater in the connected sectors (Orians et al, 2002). This is only one example of how different modules compete for resources and how modularity and sectoriality affect the physiology of perennial plants and their interaction with other organisms and the environment.…”

In Defense of Roots: A Research Agenda for Studying Plant Resistance to Belowground Herbivory

“…Vascular constraints in shoots result in unequal systemic induction of plant secondary metabolites in different aboveground plant parts after elicitation at one site of attack (Frost et al, 2007). Similar vascular constrains are well known in the relationship between belowground and aboveground allocation of nutrients and secondary metabolites (Orians et al, 2002). The well-documented examples of signal molecules traveling from one damaged leaf to others via direct vascular connections begs the question of similar constraints in aboveground induction after root herbivory in particular zones of the rhizosphere.…”