Communication Between Undamaged Plants by Volatiles: the Role of Allelobiosis - Communication in Plants: Neuronal Aspects of Plant Life - page 426

Fig. 28.3. Change in pattern of biomass allocation in barley after exposure of a plant of one
cultivar to volatiles from a plant of a different cultivar. The exposed plant allocated greater
biomass to roots compared with the unexposed plant, but total biomass was unchanged
Even though plants exposed to volatiles from a different cultivar allo-
cated more biomass to roots than to shoots and leaves, their relative growth
rate (RGR, increase in biomass per unit biomass per unit time) and unit
leaf rate (ULR, increase in biomass per unit time and leaf area, a physio-
logical component of the RGR) were not significantly different from that
of either type of control plant. However, specific leaf area (SLA, leaf area
per leaf dry weight), one of the two morphological components of RGR,
was significantly increased in plants exposed to volatiles from the other
cultivar.Thisisinlinewithpreviousstudiesshowingthatreducedbiomass
allocation to leaves can be compensated for by higher SLA (Aerst et al.
1991). It has been speculated that fast-growing plants benefit from a high
SLA only if leaves increase their photosynthetic activity to the maximum
(Van der Werf 1996).
Gersani et al. (2001) showed that individual plants sharing rhizosphere
space with another plant produce more root mass than when one plant
'owns' that space. However, it seems that root growth can be stimulated
merely by volatiles from a neighbouring plant, even though the plants do
not share rhizosphere space (Ninkovic 2003). This indicates that allelobiotic
responses affect the whole plant, not only specific parts such as roots or
leaves.