Modelling Carbon Fluxes as an Aid to Understanding Perennial Ryegrass (Lolium perenne) Root Dynamics

Abstract

Despite the importance of roots in determining plant performance, the factors controlling their development and longevity remain poorly understood. Grass morphology is based on repeating units called phytomers, with each capable of producing one leaf, one daughter tiller, and one or more roots. We developed a phytomer-based understanding of root birth, growth and senescence in Lolium perenne, using a modeling approach to explore seasonal effects on root turnover dynamics, and to explore cultivar differences in these processes. Similar to leaves, roots exhibit a clear progression from initiation, growing for approximately seven phyllochrons, with growth rates strongly influenced by environmental conditions. In spring, the phyllochron decreased over the experiment, while it increased in autumn. In spring, C availability exceeding maintenance respiratory requirements allowed root growth at each phytomer position, with a 70/30 split between maintenance and growth. Under C-deficient conditions in autumn, this split was approximately 80/20, with growth limited to younger phytomer positions, while older roots were more susceptible to starvation-induced senescence due to their high C requirements for maintenance respiration.