Fine root dynamics and morphological traits in tropical forest ecosystems

A major challenge in tropical belowground carbon allocation ecology is to understand how fine root dynamics and traits change across different ecosystems and environmental gradients. This study examines the spatial variation of fine root carbon stock, productivity, fractional carbon allocation of total productivity to the fine roots, and residence time across pantropical forest types. At a regional scale, this thesis investigates the vertical distribution and seasonal variation of fine root carbon stock, productivity, mortality, and residence time in lowland Amazon rainforests and Andean montane forests. In addition, this thesis examines how fine root morphological traits are related to soil properties and climatic variables from lowland to montane forests. My first study was the largest fine root carbon stock and dynamics study across tropical forests in South America, Africa, and Southeast Asia. The analysis was carried out separately in lowland and montane forests to understand the spatial variation and the effect of soil properties and climate variables. Root dynamics were better predicted by soil properties, such as soil sand content, soil pH, and soil phosphorus content than by climatic variables, and a different set of predictors were identified for lowland and montane forests. Lower values of mean annual productivity of fine roots were observed in upper montane forests and Southeast Asian lowland forests. My second study examined the vertical and seasonal variation in fine root dynamics in the Amazon-Andes region. The vertical distribution of fine root carbon stock and productivity in the soil profile showed proportionally more stock and productivity in the surface soil in montane forests, particularly in lower montane forests, than in lowland forests, which was related to the thickness of the organic layer. Root mortality increased in the dry season in both lowland and montane forests. I concluded my thesis by analyzing fine root morphological traits and the root-environment relationships. These features were strongly related to soil properties and some root dynamics traits. Root tissue density emerged as the principal trait in determining the variation in root morphological traits and the rate of root foraging for resources. This is one of the first pan-tropical studies to explore fine root dynamics along environmental gradients in neotropical and paleotropical regions. I worked with the Global Ecosystems Monitoring network teams across old-growth tropical forests ecosystems. Ultimately, my thesis provides a common analytical framework for estimating below-ground dynamics in different environmental gradients across the tropics, and the results may be used for improving global vegetation models.