Intraspecific leaf trait variation in tropical agroforestry systems: a case study of shade-grown coffee

Understanding plant functional traits is critical for a mechanistic understanding of agroecological processes, with increasing attention on understanding specifically the extent, causes, and consequences of within-species trait variation of cultivated crops. However, to date there are few studies that evaluate how traits vary simultaneously within any crop, across multiple interacting environmental and management-related conditions, and throughout plant development. Using coffee (Coffea arabica var. Caturra), one of the world's most important commodity crops, in Central American agroforestry systems as a case study, we present findings from multiple comparative studies that quantify patterns of intraspecific leaf trait variation across: 1) shade tree diversity gradients, 2) multiple soil fertility levels, 3) different climatic conditions, and 4) plant ontogeny. We demonstrate considerable intraspecific variation in key coffee physiological and morphological leaf traits, that! occurs across different environmental gradients and throughout plant development. Generally, patterns of bivariate and multivariate intraspecific trait variation in coffee are consistent with, but weaker than, well-documented interspecific patterns. Our research shows overwhelmingly that mean trait values (even when measured at the site or management-level) are unlikely to accurately represent the breadth of functional variation within crop species (or even cultivars). Understanding how traits covary across integrated scales of environmental variation or biological organization is critical for comprehensively quantifying intraspecific trait variation in crops and plants. In turn, research in this field is critical for i) developing new diagnostics for appropriate management of shade and other agricultural management practices, and ii) understanding how agroecological function responds to both natural and anthropogenic environmental change. (Texte intégral)