Recent studies has shown that acquisition roots function in a more complex set of functional tradeoffs than those reported for foliar tissues. Additionally, root syndromes seem invariant across phylogenetic groups, suggesting that the type of strategy acquired by lineages over evolutionary time is highly conserved. However, some of these conclusions are biased to studies in temperate areas, even when most of the diversity in plant species in concentrated in tropical rain-forests. Tree diversity in the tropics is largely concentrated in mega-diverse groups, with some particular genera ranging in the hundreds of species, many of them coexisting in close proximity. This diversification may indicate strong niche segregation in functional traits among close relatives. We hypothesized that, since soil nutrient competition can be a strong force for niche differentiation, we will find significant variation in root traits among con-generic species. However, due to strong evolutionary constraints, root syndromes will remain significant among families.
To test our hypothesis we investigate root functional traits for >300 species of trees distributed in nine hyperdiverse tree lineages: Burseraceae (Protium), Chrysobalanaceae (Licania s.l.), Fabaceae (Inga), Lauraceae, Lecythidaceae (Eschweilera), Malvaceae, Moraceae, Myrtaceae, Rubiaceae and Sapotaceae (Micropholis) in three localities across the Amazon Basin (French Guyana, Manaus region in Brazil, and Loreto region in Peru). In each area, we sampled in three different habitats: well-drained upland ridges, periodically inundated riparian areas and white sand banks. In each of the 78 plots installed me measure five root morphological and architectural variables in ten seedlings belonging to each lineage.
Results/Conclusions
We found little effect of habitat on the distribution of functional traits among communities, although there was a trend to more acquisitive syndromes toward the Peruvian forests, suggesting an overall effect of soil fertility on root functional traits at the community level. Among families, there was important contrast in root morphology. Myrtaceae and Lauraceae reported similar trait syndromes to those already reported in literature. Protium, Eschweilera, Licania and Malvaceae were also highly consistent across habitats and regions. However, Micropholis, Moraceae and Rubiaceae showed high variability in traits across species overlapping with other families. Our results support partially the hypothesis of highly conserved root traits across phylogenetic groups in tropical trees, and suggest that switches in acquisition strategies may account for the diversification of some hyper-diverse families in tropical forests.