Coordination of morphological and physiological traits in naturally recruited Abies alba Mill. saplings: insights from a structural equation modeling approach

Abstract

Apical dominance ratio (ADR), reported as a suitable indicator for the growth and development of Abies alba , is concurrently determined by morphological and functional plant traits. Structural equation modeling (SEM) proved here to be an effective multivariate technique to represent the contribution of different variables in explaining ADR variability. During the natural recruitment of understory tree saplings, the light environment and competition among individuals may change drastically as well as their growth patterns. To cope with this, saplings have a remarkable ability to accordingly modify their physiology and morphology. Therefore, understanding the ecological significance of plant structural patterns requires an integrated view of morphological, architectural, and physiological attributes of plants. Here, we applied a SEM approach to understand the mechanisms influencing the ADR, recently reported as suitable indicator of the growth conditions favoring silver fir (Abies alba Mill.) natural regeneration in Mediterranean areas. A series of plant traits (e.g., root-collar diameter, leaf mass per area, and isotope composition) were combined into two main latent variables, namely Morphology and Physiology, to account for their relative contribution in explaining the ADR variability. Our results underline the importance of variables accounting for the photosynthetic capacity and leaf economics in determining ADR; among them, leaf mass per area (LMA) emerged as an important driving variable. SEM proved to be an effective multivariate technique to represent the coordination of different morphological and functional variables in explaining ADR variability in silver fir.