Above-ground plant interactions: consequences for growth and volatile emission

The environment that plants grow in can be highly dynamic through a plant’s lifetime. In many cases, plants have to compete with other plants in their direct surroundings for a limited pool of resources. Competitive interactions among plants shape vegetation composition and control biodiversity, making it one of the most important processes for the development of local vegetation patterns. To compete successfully, plants exploit a range of phenotypic responses that enhance resource capture and thus increase their fitness during competition. These responses depend on detection of proximate neighbours and adequate responses to the environment. This thesis describes the earliest cues that are involved in the detection of neighbouring plants. Further, the effect of competition for light on the emission and functionality of volatile organic compounds (VOCs) is investigated. In chapter 2, the touch of leaftips of neighbouring plants is introduced as a cue to detect these neighbours. In Arabidopsis thaliana, this touch functions as the earliest signal to detect neighbours. Duet o this touch, leafs are more vertically orientated (which is called hyponasty). This leads to an environment in which the red to farred ratio decrease, which is the next cue for plants to detect neighbours. In chapter 3, the interaction between the volatile plant hormone ethylene and a reduction in R:FR was further investigated. Here, it is described that perception of ethylene is required for low R:FR induced petiole elongation, when the R:FR ratio is mildly reduced. At a more severely reduced R:FR ratio, perception of ethylene enhances the rate of hyponastic leaf movement. Chapter 4 describes effects of neighbour-induced alterations in the light environment on VOC emissions in Arabidopsis. Light signals that represent different degrees of competition for light led to similar reductions in the emission of VOCs. The emission of methyl-jasmonate-induced VOCs, was found to be reduced in low R:FR conditions and this affected plant preference of the specialist herbivore Pieris brassicae. In the last experimental chapter, the effect of low R:FR conditions on volatile effects between plants is demonstrated in barley (Hordeum vulgare). When volatile-emitting plants were exposed to low R:FR, VOC emissions were reduced. As a consequence, effects on carbon allocation by VOCs from emitter plants of one cultivar (Alva) on receivers plant from another (Kara) depend highly on the R:FR conditions of the emitter. These data indicate the importance of the light environment on chemical interactions between plants