Fine-root morphological trait variation in tropical forest ecosystems: an evidence synthesis

Abstract

Key functions of fine roots are often related to their morphological traits, yet little is known about the patterns and controls on fine-root morphological traits in the tropical forest biome. In this study, we consolidated data on key root morphological traits to describe patterns of root trait variation among different tropical regions and examined the relationships among root traits and climate and soil properties. We synthesized root traits (root diameter, specific root length (SRL), specific root area (SRA) and root tissue density (RTD)) from 59 site observations from nine countries in Africa, Asia, and Central and South America to determine the patterns and variation in root traits among different tropical regions. We also examined relationships among fine-root morphological traits, climate (mean annual precipitation, MAP; mean annual temperature, MAT) and soil properties (including available phosphorus (P), base saturation and clay content) using linear mixed-effects modelling. Plant fine-root morphological traits showed systematic variation among tropical regions—Africa, Asia and the Neotropics. Across the tropical biome, SRL was positively related to MAT, suggesting that in warmer tropical sites, plants tended to produce thinner roots with high SRL. Specific root length and SRA were positively related to base saturation, while soil available P explained some of the variation in SRL. This study demonstrates that soil properties, and to a lesser extent MAT, partially explain variation in key fine-root morphological traits across tropical forests. Importantly, we also identified wide variation in fine-root morphological trait values in the tropical biome that encompasses much of the variation seen worldwide. Consequently, attempts to predict tropical forest ecosystem functioning could improve significantly if regional differences in root traits are incorporated into process-based models.