In perennial grasses, the reproductive development consists of major phenological stages which highly determine the seasonal variations of grassland biomass production in terms of quantity and quality. The reproductive development is regulated by climatic conditions through complex interactions subjected to high genetic diversity. Understanding these interactions and their impact on plant development and growth is essential to optimize grassland management and identify the potential consequences of climate change. Here, we review the main stages of reproductive development, from floral induction to heading, i.e., spike emergence, considering the effect of the environmental conditions and the genetic diversity observed in perennial grasses. We first describe the determinants and consequences of reproductive development at individual tiller scale before examining the interactions between plant tillers and their impact on grassland perenniality. Then, we review the available grassland models through their ability to account for the complexity of reproductive development and genetic × environmental interactions. This review shows that (1) The reproductive development of perennial grasses is characterized by a large intraspecific diversity which has the same order of magnitude as the diversity observed between species or environmental conditions. (2) The reproductive development is determined by complex interactions between the processes of floral induction and morphogenesis of the tiller. (3) The perenniality of a plant is dependent on the reproductive behavior of each tiller. (4) Published models only partly explain the complex interactions between morphogenesis and climate on reproductive development. (5) Introducing more explicitly the underlying processes involved in reproductive development in models would improve our ability to anticipate grassland behavior in future growth conditions.

In the context of climate change and agrosystem complexification, process-based models of the reproductive phenology of perennial grasses are essential to optimize the agronomic and ecologic services provided by grasslands. We present a functional–structural model called L-GrassF, which integrates the vegetative and reproductive development of individual Lolium perenne plants. The vegetative development in L-GrassF was adapted from a previous model of perennial ryegrass where leaf elongation and tillering dynamics partially result from self-regulated processes. Significant improvements have been made to this vegetative module in order to deal with the whole growing cycle during which plants are exposed to contrasting temperatures. The reproductive module is a new functionality describing the floral induction of the individual tiller from daily temperature and photoperiod as well as its phenological state. From the interactions between the vegetative and reproductive developments, L-GrassF simulates the dynamics of plant architecture, the floral transition and heading date (HD) at tiller level. A sensitivity analysis was performed on L-GrassF and showed that parameters controlling the kinetics of leaf elongation and leaf appearance rate have a significant impact on HD. After calibration, L-GrassF was able to simulate the HD on seven L. perenne cultivars grown in a broad range of environmental conditions, as provided by an independent data set. We conclude that L-GrassF is a significant step towards better prediction of grassland phenology in contrasted conditions.