Age-related changes in Miscanthus × giganteus phenology and the effect of nitrogen fertilization
Perennial plants go through noticeable morphological, developmental, and physiological changes as they age. Whether these age-related changes are driven by ontogenetic differences, are the result of different environmental conditions, or an artifact of plant size remains unknown. In this research we used the warm-season grass Miscanthus × giganteus as model herbaceous perennial species to study age-related changes on phenology. Age-related experiments are usually based on field experimental design that confound growing season and age effects and ignore variability generated during the establishment of the stand. Here, we used a staggered-start experimental design where stands are repeatedly planted over subsequent years providing the ability to separate plant age effects from environmental effects. We hypothesized (i) M. × giganteus would produce more plant structures and reach more advanced developmental stages in a given growing season as it aged. (ii) Juvenile stands would have faster developmental rates and start development sooner and (iii) Mature stands would start senescence sooner in the growing season. Finally, we studied nitrogen (N) fertilization effects on M. × giganteus phenology as to assess whether age-related changes could be an artifact of size and N dilution in mature bigger individuals. We hypothesized that (iv) fertilized juvenile stands would have similar dynamics as mature unfertilized stands. Data were collected bi-weekly on all established stands during 2016 and 2017. Ten stems were harvested from each plot and staged at the lab according to M. × giganteus morphological scale developed by Tejera & Heaton (2017). Time series progression were then analyzed using non-linear models and parameters were compared across stand ages, N treatments and growing seasons. R scripts used to analyze the data are available upon request.