The Green Plant as an Intelligent Organism - Communication in Plants: Neuronal Aspects of Plant Life - page 9

1.4.1
Decisions and Choice in Plant Development
Plants actively forage for food resources by changing their architecture,
physiology and phenotype (De Kroon and Hutchings 1995; Drew et al.
1975; Evans and Cain 1995; Grime et al. 1986; Grime 1994; Hutchings
and De Kroon 1994; Slade and Hutchings 1987). When patches of rich
resource are located either by roots or by shoots and occupation of resource
receptorsreachescriticallevels,decisionsaremadetoinitiateenormous
proliferation, thus greatly increasing the surface area of absorption of both
energy minerals and water. Decisions are thus made continuously as plants
grow, placing roots, shoots and leaves in optimal positions according to the
abundance of perceived resources. Perhaps most crucial is that individual
plants compete vigorously with each other for resources and the decisions
are designed to improve fitness at the expense of others.
When given the choice between soil occupied by other plants and unoc-
cupied soil the roots of those plants examined move their new proliferation
into unoccupied soil and away from competitors (Gersani et al. 1998, 2001).
When roots are made to touch roots of alien individuals (but not their own),
the decision is made to cease growth (Callaway et al. 2003). Individual plants
grown with the same level of resources but in a bigger soil volume grow
much larger (McConnaghy and Bazzaz 1991, 1992; Schenk et al. 1999). This
suggests that plants have mechanisms that sense their own root distribu-
tion and optimize the phenotype. Plants are territorial (Schenk et al. 1999);
they minimize competition from their own roots and prefer unoccupied
soil (Callaway et al. 2003; Huber-Sannwald et al. 1997; Mahall and Callaway
1992).
If individuals are forced to grow in the same soil volume, the root sys-
tem proliferates in order to competitively sequester available root resources
from other individuals but with a trade off in seed production (Gersani et al.
2001; Maina et al. 2002). Further convincing studies indicate that root sys-
tems are self-sensing (Falik et al. 2003; Gruntmann and Novoplansky 2004;
Holzapfel and Alpert 2003), an important aspect of intelligent behaviour.
When clones of the same plant are separated, within several weeks the root
systems recognize each other as alien and proliferate accordingly. Plants
assess and respond to local opportunities that will in the future benefit the
whole plant (Falik et al. 2003).
Similar events take place in the shoot. Petioles and pulvini of many leaves
orient the plane of leaf growth to that of the primary plane of incident sun-
light and can move leaves out of this plane if light is too damagingly intense
(De Kroon and Hutchings 1995; Muth and Bazzaz 2002a, b, 2003; Paladin
1918). Leaves of shoots are often placed to minimize self-shading (Honda
and Fisher 1978; Yamada et al. 2000) just as roots are placed to minimize