Variations in leaf growth parameters within the tree structure of adult Coffea arabica

The phyllochron is the time between the emergence of one leaf on the main stem of a plant and the next. Effectively it’s the time for a plant to grow one phytomer. This, with other factors like the duration of leaf expansion, leaf lifespan and bud mortality, determines tree architecture and canopy foliage distribution. In a new study Rakocevic and Matsunaga aimed to estimate leaf growth parameters in adult Arabica coffee plants based on leaf supporter axis order and position along the vertical profile, considering their modifications related to seasonal growth, air [CO₂] and water availability.

The authors followed growth and mortality of leaves and terminal buds of adult Arabica coffee trees in two sub-tropical climate regions of Brazil, Londrina-PR (Cfa) and Jaguariúna-SP (Cwa). In the Cwa climate, coffee trees were grown under a FACE (free air CO₂ enrichment) facility, where half of those had been irrigated. They observed the plants between every 15 to 30 days over a year.

Rakocevic and Matsunaga found the phyllochron and duration of leaf expansion increased with axis order, from the second to the fourth. The phyllochron and life span during the reduced vegetative seasonal growth were greater than during active growth. It took more thermal time for leaves from the first- to fourth-order axes to expand their blades under irrigation compared with rainfed conditions. The authors found compensation effects of high [CO₂] for low water availability on leaf retention on the second and third axes orders, and duration of leaf expansion on the first- and fourth-order axes. The second-degree polynomials modelled leaf growth parameter distribution in the vertical tree profile, and linear regressions modelled the proportion of terminal bud mortality.

The authors say: “The novelty of this work is that the phyllochron, leaf expansion and leaf life span in Arabica coffee plants vary within the tree structure and axes orders and that they were seasonally modified by the environment. This work could raise the question of the impact of branching order in other species. The seasonal environmental impacts on leaf growth parameters distinguished among regions of coffee production could be attributed to differences in minimum daily autumn/winter temperatures and water availability… [The findings] help to paint a more complete picture of possible morphophysiological responses in Arabica coffee under global climate changes.”