The role of functional leaf traits in pathogenic transmission in agroforestry systems

Variation of plant functional traits may predict ecosystem function1 , yet there is little work linking functional traits of crops and service trees, their interactions, and processes in agrofo­restry systems2, specifically the transmission of pathogens. Focusing on coffee as a model, we explore how multi-species functional traits adjust abiotic processes that affect the dispersal and persistence of coffee leaf rust (CLR)3. We hypothesize that shade tree canopy and leaf traits will mediate CLR transmission via abiotic modifications and that key coffee functional leaf traits will suppress CLR under different agroforestry systems. This study was conducted in CATIE's coffee agroforestry research trial in Costa Rica. Throughfall kinetic energy under diverse shade tree canopies was modified by shade tree composition, canopy characteristics (e.g. crown base height; CBH) and functional leaf traits (e.g. specific leaf area; SLA). Certain shade tree traits such as canopy depth, CBH and SLA also related to trends in plant-level CLR incidence (Figure 1 ). CLR tended to favour certain coffee leaf functional traits, where coffee plants with low mean leaf nitrogen concentration and high mean SLA had higher plant­level CLR incidence. These results suggest that managing the functional leaf trait variation of shade trees and targeting key coffee functional leaf traits can change the persistence of CLR, thus improving our understanding of alternative resistance measures available in agroforestry