Evolution of growth rates in Pooideae (Poaceae)

Abstract

The temperate grasses in the subfamily Pooideae (Poaceae) has a limited distribution range The species are mainly distributed to the Northern Temperate regions and are known to be adapted to the strong seasonality this region possess. To be able to grow in such conditions, the plants have to edapt to the shift between the mild but short growing seasons and the harsh, long winters. In this study, I ask if the distribution of the subfamily is linked to the species growth rate traits. To be able to reproduce before winter returns in Northern temperate regions, it is an advantage to grow fast. The fundamental process of plant growth can be quantified using various growth rate traits, such as Relative Growth Rate (RGR), Standardised Growth Rate (SGR) and Allometric Slope. In order to analyse the evolutionary history of growth rates within Pooideae, a growth experiment were done. Here, traits related to growth were measured. Chloroplast sequences were retrieved from all the 64 populations of 55 species included in the experiment. The acquired datasets consisting of values of growth rate traits connected to chloroplast sequences were used in joint phylogenetic analyses with Ancestral State Reconstruction (ASR). Pooideae species in the Northern temperate lineages allocate more biomass to the shoots than to the roots. The results suggests that the most recent common ancestor (MRCA) of the monophyletic group core Pooideae made a switch in growth rate and Allometric Slope around 34 Ma, during a global cooling event.