Grasses and cereals, such as wheat, are highly plastic in the number of tillers (lateral branches) they produce. When grown in isolation, a wheat plant grows numerous tillers of which many reach full maturity. However, when grown at high population densities, the same wheat plant can produce as few as 1 tiller or even no tillers at all. In such cases the plant invests more biomass in height growth, rather than in lateral growth, to prevent being completely shaded by neighbouring plants. This phenomenon is part of the so-called shade-avoidance syndrome, which enables plants to cope with future competition for light.
A key environmental determinant of this plastic property of plants is light quality, notably the red / far-red ratio. Neighbouring vegetation absorbs most of the red part of the light spectrum, whereas most of the far-red light is reflected. This changes the ratio between red and far-red light intensities, which can be perceived by a plant as a signal for competing plants in the vicinity.
Sub-project 1: the relationship between tiller production and the red / far-red ratio
The effects of the red / far-red ratio on tillering in wheat have been analysed using a functional-structural plant model of spring wheat, in combination with several field and growth-chamber experiments. An FSPM of spring wheat was created, calibrated and evaluated using several datasets, and simulations were performed as to analyse mode performance.
This PhD project started in October 2001 and ended in March 2006.
Sub-project 2: tiller production in relation to carbon acquisition and distribution
When wheat plants do shade each other, leaf photosynthesis rate is reduced, and less assimilates are available for growth and development of the plant, compared to unshaded conditions. This affects all aspects of plant development, among which tillering. The FSPM of spring wheat was modified to be able to simulate to absorbtion of photosynthetically active radiation, assimilation of CO2, production of new biomass and its subsequent distribution over all growing plant organs. Concepts of source and sink strength were implemented and used to simulate tiller production.This Postdoc project started in December 2005 and ended in April 2008.