Phyllochron, leaf expansion and life span in adult Coffea Arabica L. plants: Impact of axis order, growth intensity period and emitted leaf position

Phyllochron is a morphogenetic characteristic defined as a time interval between the appearance of two successive leaves. In adult Arabica coffee plants (Coffea Arabica L.), the greatest part of the annual vegetative growth occurs in the warm, rainy season, while the smaller part of annual growth happens during the cool, dry season. We aimed to estimate the phyllochron, leaf expansion duration and life span in adult Arabica coffee plants depending on growth intensity periods, axis order and position of emitted leaves. Four-year-old plants were codified following the VPlants methodology in dynamic multiscale-tree-graphs. The leaf growth parameters were estimated on five axis orders. To integrate the effect of temperature on leaf growth parameters, they were expressed as functions of accumulated thermal time (growing degree-days — GDD). The demands in GDD for phyllochron were roughly 30 to 40% higher during the reduced compared to the active growth period. The lowest GDD of phyllochron was observed on the 2^nd order axes, and the highest on the 5^th order ones. The similar requirement in GDD for leaf expansion and life span was noted in leaves on 1^st and 2^nd order axes, while leaves born on 3^rd to 5^th axis orders showed higher GDD requirements. Leaves born on 2^nd order axes finished their expansion more rapidly during the reduced than during the active growth period, indicating the occurrence of acclimation to temperatures over the same tree. The leaf emission duration and life span over the axes ranks followed binomial distributions. The results suggest that the phyllochron changed within the branching hierarchy and is seasonally modified by the environment. In future studies, longer period and apex mortality rate will be considered to improve the understanding of complex orchestration in structural development of Arabica coffee plants in 3D architectural dynamics modeling.