How flowering relates to biomass accumulation in forage grasses ?
The basic idea of crop science is to mazimize the capture of solar radiation by plant canopy and to convert it efficiently to chemical energy. In forage grasses yield components that determine the extent of biomass accumulation are the number of tillers per area and the weight of an individual tiller. The maximum light interception and net assimilation is achieved when the canopy consists of tall, stem forming tillers. Those tillers are also heavy, contributing significantly to the accumulating biomass.
Our studies have shown that at a rapid stage of biomass accumulation in spring, the development of tillers is synchronized by vernalization and the proportion of flowering stems in the yield is high. Similarly to winter cereals, VRN1 has a key role in a transition of apices from vegetative leaf forming stage to generative stage producing flowering structures.
It is thought that flowering causes a rapid decrease in digestibility and nutritive value of harvested forage biomass due to lignification of the stem. We followed the development of apices and stem elongation in field conditions and studied it's relationship to development of lignified schlerenchyma ring. Our studies showed that transition to generative stage is not necessary for the initiation of extensive stem lignification but rather the height of the stem was important. Together with our colleques in Luke Maaninka we identified a third tiller type in timothy so called elongating tiller, where stem elongation had initiated without flowering stimulus. These elongating tillers contribute significantly to summer and autumn yields and their digestibility decreases as the stem elongation proceeds.
Seppänen, M.M., Pakarinen, K., Jokela, V., Andersen, J., Pedersen, A., Virkajärvi, P. 2010. Vernalization response of Phleum pratense L. and its relationship to canopy architecture, stem morphology and expression of VRN1 and VRN2 genes. Annals of Botany 106:697-707.
Jokela, V. 2015. Regulation of flowering and canopy structure in timothy (Phleum pratense L.). Article based doctoral dissertation. pp. 101. Faculty of Agriculture and Forestry, University of Helsinki, Finland. Dissertationes Schola Doctoralis Scientiae Circumiectalis, Alimentariae, Biologicae: 28/2015.