The influence of grazing on the evolution, morphology and physiology of plants as modular organisms

Abstract

Plants are modular organisms, i.e. they consist of repetitive multicellular units. The integrity of the plant is arranged by active meristems that hormonally suppress activity of other meristems. This basic design makes it possible for plants to have semi-independent, or totally independent, parts even within one structural individual. Accordingly, plant parts like ramets or branches may be qualitatively different because of developmental, environmental or genetical influences. They may respond to herbivory separately from other parts in the same structural individual. The modular structure allows easy recovery after damage by herbivores. Simultaneously it may constrain possible functions and lead to seemingly non-optimal responses. Effects of herbivory on the very basic modular design must be limited. Instead, herbivory may function as an evolutionary force modifying regulation of plant structure and function, like location of meristems, and rules determining outcomes of interactions among meristems. Indirectly, herbivory may prevent evolution of more unitary plant individuals.

Impact of leaf damage on growth of mountain birch shoots

“…No one module is vital to the organism (White, 1979). The distribution of resources between modules is via vascular connections, and seems to depend on among-module concentration gradients of relevant resources (Haukioja, 1991 ;Sprugel et al, 1991 ;Sachs et al, 1993). The carbon economy of leafbearing shoots is regarded as relatively autonomous (Watson & Casper, 1984), but that of shoot modules is dynamic, depending on the status of the shoot as a sink or a source, and whether the source-stage leaves in a shoot provision sinks within the shoot module itself or ones located outside the module (Ruohoma$ ki et al, 1997).…”

Whole-Plant Physiology: Synergistic Emergence Rather Than Modularity

“…The extreme view is that performance of whole plants is a by-product of responses of modules (de Kroon et al 2005). This view culminated with the caricature that "a tree is not a tightly integrated organism but a by-product of its parts" (Haukioja 1991).…”

“…This has a strong touch of thinking in terms of modularity where blocks of omics data are taken as modules. Plants are considered as modular organisms having semi-independent and totally independent parts (Haukioja 1991). The extreme view is that performance of whole plants is a by-product of responses of modules (de Kroon et al 2005).…”

Effects of artificial damage on the branching pattern of Nothofagus dombeyi (Nothofagaceae)

“…The existence of plant responses compensating or overcompensating in terms of biomass production after biomass losses caused by herbivory has been repeatedly demonstrated, mainly for herbaceous plants [24,33]. On the contrary, little is known about the extent to which traumatic factors affect the branching pattern of woody plants and the capacity of these plants to restore this pattern after a trauma [4,5,8,23,31,33]. Two major reasons for this information deficiency are the high architectural complexity and slow short-term response to damage of woody plants as compared to those of herbaceous species [24].…”